osdl.org!shemminger | aba5acd | 2004-04-15 20:56:59 +0000 | [diff] [blame] | 1 | \documentstyle[12pt,twoside]{article} |
| 2 | \def\TITLE{IP Command Reference} |
| 3 | \input preamble |
| 4 | \begin{center} |
| 5 | \Large\bf IP Command Reference. |
| 6 | \end{center} |
| 7 | |
| 8 | |
| 9 | \begin{center} |
| 10 | { \large Alexey~N.~Kuznetsov } \\ |
| 11 | \em Institute for Nuclear Research, Moscow \\ |
| 12 | \verb|kuznet@ms2.inr.ac.ru| \\ |
| 13 | \rm April 14, 1999 |
| 14 | \end{center} |
| 15 | |
| 16 | \vspace{5mm} |
| 17 | |
| 18 | \tableofcontents |
| 19 | |
| 20 | \newpage |
| 21 | |
| 22 | \section{About this document} |
| 23 | |
| 24 | This document presents a comprehensive description of the \verb|ip| utility |
| 25 | from the \verb|iproute2| package. It is not a tutorial or user's guide. |
| 26 | It is a {\em dictionary\/}, not explaining terms, |
| 27 | but translating them into other terms, which may also be unknown to the reader. |
| 28 | However, the document is self-contained and the reader, provided they have a |
| 29 | basic networking background, will find enough information |
| 30 | and examples to understand and configure Linux-2.2 IP and IPv6 |
| 31 | networking. |
| 32 | |
| 33 | This document is split into sections explaining \verb|ip| commands |
| 34 | and options, decrypting \verb|ip| output and containing a few examples. |
| 35 | More voluminous examples and some topics, which require more elaborate |
| 36 | discussion, are in the appendix. |
| 37 | |
| 38 | The paragraphs beginning with NB contain side notes, warnings about |
| 39 | bugs and design drawbacks. They may be skipped at the first reading. |
| 40 | |
| 41 | \section{{\tt ip} --- command syntax} |
| 42 | |
| 43 | The generic form of an \verb|ip| command is: |
| 44 | \begin{verbatim} |
| 45 | ip [ OPTIONS ] OBJECT [ COMMAND [ ARGUMENTS ]] |
| 46 | \end{verbatim} |
| 47 | where \verb|OPTIONS| is a set of optional modifiers affecting the |
| 48 | general behaviour of the \verb|ip| utility or changing its output. All options |
| 49 | begin with the character \verb|'-'| and may be used in either long or abbreviated |
| 50 | forms. Currently, the following options are available: |
| 51 | |
| 52 | \begin{itemize} |
| 53 | \item \verb|-V|, \verb|-Version| |
| 54 | |
| 55 | --- print the version of the \verb|ip| utility and exit. |
| 56 | |
| 57 | |
| 58 | \item \verb|-s|, \verb|-stats|, \verb|-statistics| |
| 59 | |
| 60 | --- output more information. If the option |
| 61 | appears twice or more, the amount of information increases. |
| 62 | As a rule, the information is statistics or some time values. |
| 63 | |
| 64 | |
| 65 | \item \verb|-f|, \verb|-family| followed by a protocol family |
| 66 | identifier: \verb|inet|, \verb|inet6| or \verb|link|. |
| 67 | |
| 68 | --- enforce the protocol family to use. If the option is not present, |
| 69 | the protocol family is guessed from other arguments. If the rest of the command |
| 70 | line does not give enough information to guess the family, \verb|ip| falls back to the default |
| 71 | one, usually \verb|inet| or \verb|any|. \verb|link| is a special family |
| 72 | identifier meaning that no networking protocol is involved. |
| 73 | |
| 74 | \item \verb|-4| |
| 75 | |
| 76 | --- shortcut for \verb|-family inet|. |
| 77 | |
| 78 | \item \verb|-6| |
| 79 | |
| 80 | --- shortcut for \verb|-family inet6|. |
| 81 | |
| 82 | \item \verb|-0| |
| 83 | |
| 84 | --- shortcut for \verb|-family link|. |
| 85 | |
| 86 | |
| 87 | \item \verb|-o|, \verb|-oneline| |
| 88 | |
| 89 | --- output each record on a single line, replacing line feeds |
| 90 | with the \verb|'\'| character. This is convenient when you want to |
| 91 | count records with \verb|wc| or to \verb|grep| the output. The trivial |
| 92 | script \verb|rtpr| converts the output back into readable form. |
| 93 | |
| 94 | \item \verb|-r|, \verb|-resolve| |
| 95 | |
| 96 | --- use the system's name resolver to print DNS names instead of |
| 97 | host addresses. |
| 98 | |
| 99 | \begin{NB} |
| 100 | Do not use this option when reporting bugs or asking for advice. |
| 101 | \end{NB} |
| 102 | \begin{NB} |
| 103 | \verb|ip| never uses DNS to resolve names to addresses. |
| 104 | \end{NB} |
| 105 | |
| 106 | \end{itemize} |
| 107 | |
| 108 | \verb|OBJECT| is the object to manage or to get information about. |
| 109 | The object types currently understood by \verb|ip| are: |
| 110 | |
| 111 | \begin{itemize} |
| 112 | \item \verb|link| --- network device |
| 113 | \item \verb|address| --- protocol (IP or IPv6) address on a device |
| 114 | \item \verb|neighbour| --- ARP or NDISC cache entry |
| 115 | \item \verb|route| --- routing table entry |
| 116 | \item \verb|rule| --- rule in routing policy database |
| 117 | \item \verb|maddress| --- multicast address |
| 118 | \item \verb|mroute| --- multicast routing cache entry |
| 119 | \item \verb|tunnel| --- tunnel over IP |
| 120 | \end{itemize} |
| 121 | |
| 122 | Again, the names of all objects may be written in full or |
| 123 | abbreviated form, f.e.\ \verb|address| is abbreviated as \verb|addr| |
| 124 | or just \verb|a|. |
| 125 | |
| 126 | \verb|COMMAND| specifies the action to perform on the object. |
| 127 | The set of possible actions depends on the object type. |
| 128 | As a rule, it is possible to \verb|add|, \verb|delete| and |
| 129 | \verb|show| (or \verb|list|) objects, but some objects |
| 130 | do not allow all of these operations or have some additional commands. |
| 131 | The \verb|help| command is available for all objects. It prints |
| 132 | out a list of available commands and argument syntax conventions. |
| 133 | |
| 134 | If no command is given, some default command is assumed. |
| 135 | Usually it is \verb|list| or, if the objects of this class |
| 136 | cannot be listed, \verb|help|. |
| 137 | |
| 138 | \verb|ARGUMENTS| is a list of arguments to the command. |
| 139 | The arguments depend on the command and object. There are two types of arguments: |
| 140 | {\em flags\/}, consisting of a single keyword, and {\em parameters\/}, |
| 141 | consisting of a keyword followed by a value. For convenience, |
| 142 | each command has some {\em default parameter\/} |
| 143 | which may be omitted. F.e.\ parameter \verb|dev| is the default |
| 144 | for the {\tt ip link} command, so {\tt ip link ls eth0} is equivalent |
| 145 | to {\tt ip link ls dev eth0}. |
| 146 | In the command descriptions below such parameters |
| 147 | are distinguished with the marker: ``(default)''. |
| 148 | |
| 149 | Almost all keywords may be abbreviated with several first (or even single) |
| 150 | letters. The shortcuts are convenient when \verb|ip| is used interactively, |
| 151 | but they are not recommended in scripts or when reporting bugs |
| 152 | or asking for advice. ``Officially'' allowed abbreviations are listed |
| 153 | in the document body. |
| 154 | |
| 155 | |
| 156 | |
| 157 | \section{{\tt ip} --- error messages} |
| 158 | |
| 159 | \verb|ip| may fail for one of the following reasons: |
| 160 | |
| 161 | \begin{itemize} |
| 162 | \item |
| 163 | A syntax error on the command line: an unknown keyword, incorrectly formatted |
| 164 | IP address {\em et al\/}. In this case \verb|ip| prints an error message |
| 165 | and exits. As a rule, the error message will contain information |
| 166 | about the reason for the failure. Sometimes it also prints a help page. |
| 167 | |
| 168 | \item |
| 169 | The arguments did not pass verification for self-consistency. |
| 170 | |
| 171 | \item |
| 172 | \verb|ip| failed to compile a kernel request from the arguments |
| 173 | because the user didn't give enough information. |
| 174 | |
| 175 | \item |
| 176 | The kernel returned an error to some syscall. In this case \verb|ip| |
| 177 | prints the error message, as it is output with \verb|perror(3)|, |
| 178 | prefixed with a comment and a syscall identifier. |
| 179 | |
| 180 | \item |
| 181 | The kernel returned an error to some RTNETLINK request. |
| 182 | In this case \verb|ip| prints the error message, as it is output |
| 183 | with \verb|perror(3)| prefixed with ``RTNETLINK answers:''. |
| 184 | |
| 185 | \end{itemize} |
| 186 | |
| 187 | All the operations are atomic, i.e.\ |
| 188 | if the \verb|ip| utility fails, it does not change anything |
| 189 | in the system. One harmful exception is \verb|ip link| command |
| 190 | (Sec.\ref{IP-LINK}, p.\pageref{IP-LINK}), |
| 191 | which may change only some of the device parameters given |
| 192 | on command line. |
| 193 | |
| 194 | It is difficult to list all the error messages (especially |
| 195 | syntax errors). However, as a rule, their meaning is clear |
| 196 | from the context of the command. |
| 197 | |
| 198 | The most common mistakes are: |
| 199 | |
| 200 | \begin{enumerate} |
| 201 | \item Netlink is not configured in the kernel. The message is: |
| 202 | \begin{verbatim} |
| 203 | Cannot open netlink socket: Invalid value |
| 204 | \end{verbatim} |
| 205 | |
| 206 | \item RTNETLINK is not configured in the kernel. In this case |
| 207 | one of the following messages may be printed, depending on the command: |
| 208 | \begin{verbatim} |
| 209 | Cannot talk to rtnetlink: Connection refused |
| 210 | Cannot send dump request: Connection refused |
| 211 | \end{verbatim} |
| 212 | |
| 213 | \item The \verb|CONFIG_IP_MULTIPLE_TABLES| option was not selected |
| 214 | when configuring the kernel. In this case any attempt to use the |
| 215 | \verb|ip| \verb|rule| command will fail, f.e. |
| 216 | \begin{verbatim} |
| 217 | kuznet@kaiser $ ip rule list |
| 218 | RTNETLINK error: Invalid argument |
| 219 | dump terminated |
| 220 | \end{verbatim} |
| 221 | |
| 222 | \end{enumerate} |
| 223 | |
| 224 | |
| 225 | \section{{\tt ip link} --- network device configuration} |
| 226 | \label{IP-LINK} |
| 227 | |
| 228 | \paragraph{Object:} A \verb|link| is a network device and the corresponding |
| 229 | commands display and change the state of devices. |
| 230 | |
| 231 | \paragraph{Commands:} \verb|set| and \verb|show| (or \verb|list|). |
| 232 | |
| 233 | \subsection{{\tt ip link set} --- change device attributes} |
| 234 | |
| 235 | \paragraph{Abbreviations:} \verb|set|, \verb|s|. |
| 236 | |
| 237 | \paragraph{Arguments:} |
| 238 | |
| 239 | \begin{itemize} |
| 240 | \item \verb|dev NAME| (default) |
| 241 | |
| 242 | --- \verb|NAME| specifies the network device on which to operate. |
| 243 | |
| 244 | \item \verb|up| and \verb|down| |
| 245 | |
| 246 | --- change the state of the device to \verb|UP| or \verb|DOWN|. |
| 247 | |
| 248 | \item \verb|arp on| or \verb|arp off| |
| 249 | |
| 250 | --- change the \verb|NOARP| flag on the device. |
| 251 | |
| 252 | \begin{NB} |
| 253 | This operation is {\em not allowed\/} if the device is in state \verb|UP|. |
| 254 | Though neither the \verb|ip| utility nor the kernel check for this condition. |
| 255 | You can get unpredictable results changing this flag while the |
| 256 | device is running. |
| 257 | \end{NB} |
| 258 | |
| 259 | \item \verb|multicast on| or \verb|multicast off| |
| 260 | |
| 261 | --- change the \verb|MULTICAST| flag on the device. |
| 262 | |
| 263 | \item \verb|dynamic on| or \verb|dynamic off| |
| 264 | |
| 265 | --- change the \verb|DYNAMIC| flag on the device. |
| 266 | |
| 267 | \item \verb|name NAME| |
| 268 | |
| 269 | --- change the name of the device. This operation is not |
| 270 | recommended if the device is running or has some addresses |
| 271 | already configured. |
| 272 | |
| 273 | \item \verb|txqueuelen NUMBER| or \verb|txqlen NUMBER| |
| 274 | |
| 275 | --- change the transmit queue length of the device. |
| 276 | |
| 277 | \item \verb|mtu NUMBER| |
| 278 | |
| 279 | --- change the MTU of the device. |
| 280 | |
| 281 | \item \verb|address LLADDRESS| |
| 282 | |
| 283 | --- change the station address of the interface. |
| 284 | |
| 285 | \item \verb|broadcast LLADDRESS|, \verb|brd LLADDRESS| or \verb|peer LLADDRESS| |
| 286 | |
| 287 | --- change the link layer broadcast address or the peer address when |
| 288 | the interface is \verb|POINTOPOINT|. |
| 289 | |
| 290 | \vskip 1mm |
| 291 | \begin{NB} |
| 292 | For most devices (f.e.\ for Ethernet) changing the link layer |
| 293 | broadcast address will break networking. |
| 294 | Do not use it, if you do not understand what this operation really does. |
| 295 | \end{NB} |
| 296 | |
Benjamin Thery | e2613dc | 2008-06-20 11:07:35 +0200 | [diff] [blame] | 297 | \item \verb|netns PID| |
| 298 | |
| 299 | --- move the device to the network namespace associated with the process PID. |
| 300 | |
osdl.org!shemminger | aba5acd | 2004-04-15 20:56:59 +0000 | [diff] [blame] | 301 | \end{itemize} |
| 302 | |
| 303 | \vskip 1mm |
| 304 | \begin{NB} |
Tomas Janousek | e17b733 | 2007-11-20 15:38:21 +0100 | [diff] [blame] | 305 | The \verb|PROMISC| and \verb|ALLMULTI| flags are considered |
| 306 | obsolete and should not be changed administratively, though |
| 307 | the {\tt ip} utility will allow that. |
osdl.org!shemminger | aba5acd | 2004-04-15 20:56:59 +0000 | [diff] [blame] | 308 | \end{NB} |
| 309 | |
| 310 | \paragraph{Warning:} If multiple parameter changes are requested, |
| 311 | \verb|ip| aborts immediately after any of the changes have failed. |
| 312 | This is the only case when \verb|ip| can move the system to |
| 313 | an unpredictable state. The solution is to avoid changing |
| 314 | several parameters with one {\tt ip link set} call. |
| 315 | |
| 316 | \paragraph{Examples:} |
| 317 | \begin{itemize} |
| 318 | \item \verb|ip link set dummy address 00:00:00:00:00:01| |
| 319 | |
| 320 | --- change the station address of the interface \verb|dummy|. |
| 321 | |
| 322 | \item \verb|ip link set dummy up| |
| 323 | |
| 324 | --- start the interface \verb|dummy|. |
| 325 | |
| 326 | \end{itemize} |
| 327 | |
| 328 | |
| 329 | \subsection{{\tt ip link show} --- display device attributes} |
| 330 | \label{IP-LINK-SHOW} |
| 331 | |
| 332 | \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|lst|, \verb|sh|, \verb|ls|, |
| 333 | \verb|l|. |
| 334 | |
| 335 | \paragraph{Arguments:} |
| 336 | \begin{itemize} |
| 337 | \item \verb|dev NAME| (default) |
| 338 | |
| 339 | --- \verb|NAME| specifies the network device to show. |
| 340 | If this argument is omitted all devices are listed. |
| 341 | |
| 342 | \item \verb|up| |
| 343 | |
| 344 | --- only display running interfaces. |
| 345 | |
| 346 | \end{itemize} |
| 347 | |
| 348 | |
| 349 | \paragraph{Output format:} |
| 350 | |
| 351 | \begin{verbatim} |
| 352 | kuznet@alisa:~ $ ip link ls eth0 |
| 353 | 3: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc cbq qlen 100 |
| 354 | link/ether 00:a0:cc:66:18:78 brd ff:ff:ff:ff:ff:ff |
| 355 | kuznet@alisa:~ $ ip link ls sit0 |
| 356 | 5: sit0@NONE: <NOARP,UP> mtu 1480 qdisc noqueue |
| 357 | link/sit 0.0.0.0 brd 0.0.0.0 |
| 358 | kuznet@alisa:~ $ ip link ls dummy |
| 359 | 2: dummy: <BROADCAST,NOARP> mtu 1500 qdisc noop |
| 360 | link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff |
| 361 | kuznet@alisa:~ $ |
| 362 | \end{verbatim} |
| 363 | |
| 364 | |
| 365 | The number before each colon is an {\em interface index\/} or {\em ifindex\/}. |
| 366 | This number uniquely identifies the interface. This is followed by the {\em interface name\/} |
| 367 | (\verb|eth0|, \verb|sit0| etc.). The interface name is also |
| 368 | unique at every given moment. However, the interface may disappear from the |
| 369 | list (f.e.\ when the corresponding driver module is unloaded) and another |
| 370 | one with the same name may be created later. Besides that, |
| 371 | the administrator may change the name of any device with |
| 372 | \verb|ip| \verb|link| \verb|set| \verb|name| |
| 373 | to make it more intelligible. |
| 374 | |
| 375 | The interface name may have another name or \verb|NONE| appended |
| 376 | after the \verb|@| sign. This means that this device is bound to some other |
| 377 | device, |
| 378 | i.e.\ packets send through it are encapsulated and sent via the ``master'' |
| 379 | device. If the name is \verb|NONE|, the master is unknown. |
| 380 | |
| 381 | Then we see the interface {\em mtu\/} (``maximal transfer unit''). This determines |
| 382 | the maximal size of data which can be sent as a single packet over this interface. |
| 383 | |
| 384 | {\em qdisc\/} (``queuing discipline'') shows the queuing algorithm used |
| 385 | on the interface. Particularly, \verb|noqueue| means that this interface |
| 386 | does not queue anything and \verb|noop| means that the interface is in blackhole |
| 387 | mode i.e.\ all packets sent to it are immediately discarded. |
| 388 | {\em qlen\/} is the default transmit queue length of the device measured |
| 389 | in packets. |
| 390 | |
| 391 | The interface flags are summarized in the angle brackets. |
| 392 | |
| 393 | \begin{itemize} |
| 394 | \item \verb|UP| --- the device is turned on. It is ready to accept |
| 395 | packets for transmission and it may inject into the kernel packets received |
| 396 | from other nodes on the network. |
| 397 | |
| 398 | \item \verb|LOOPBACK| --- the interface does not communicate with other |
| 399 | hosts. All packets sent through it will be returned |
| 400 | and nothing but bounced packets can be received. |
| 401 | |
| 402 | \item \verb|BROADCAST| --- the device has the facility to send packets |
| 403 | to all hosts sharing the same link. A typical example is an Ethernet link. |
| 404 | |
| 405 | \item \verb|POINTOPOINT| --- the link has only two ends with one node |
| 406 | attached to each end. All packets sent to this link will reach the peer |
| 407 | and all packets received by us came from this single peer. |
| 408 | |
| 409 | If neither \verb|LOOPBACK| nor \verb|BROADCAST| nor \verb|POINTOPOINT| |
| 410 | are set, the interface is assumed to be NMBA (Non-Broadcast Multi-Access). |
| 411 | This is the most generic type of device and the most complicated one, because |
| 412 | the host attached to a NBMA link has no means to send to anyone |
| 413 | without additionally configured information. |
| 414 | |
| 415 | \item \verb|MULTICAST| --- is an advisory flag indicating that the interface |
| 416 | is aware of multicasting i.e.\ sending packets to some subset of neighbouring |
| 417 | nodes. Broadcasting is a particular case of multicasting, where the multicast |
| 418 | group consists of all nodes on the link. It is important to emphasize |
| 419 | that software {\em must not\/} interpret the absence of this flag as the inability |
| 420 | to use multicasting on this interface. Any \verb|POINTOPOINT| and |
| 421 | \verb|BROADCAST| link is multicasting by definition, because we have |
| 422 | direct access to all the neighbours and, hence, to any part of them. |
| 423 | Certainly, the use of high bandwidth multicast transfers is not recommended |
| 424 | on broadcast-only links because of high expense, but it is not strictly |
| 425 | prohibited. |
| 426 | |
| 427 | \item \verb|PROMISC| --- the device listens to and feeds to the kernel all |
| 428 | traffic on the link even if it is not destined for us, not broadcasted |
| 429 | and not destined for a multicast group of which we are member. Usually |
| 430 | this mode exists only on broadcast links and is used by bridges and for network |
| 431 | monitoring. |
| 432 | |
| 433 | \item \verb|ALLMULTI| --- the device receives all multicast packets |
| 434 | wandering on the link. This mode is used by multicast routers. |
| 435 | |
| 436 | \item \verb|NOARP| --- this flag is different from the other ones. It has |
| 437 | no invariant value and its interpretation depends on the network protocols |
| 438 | involved. As a rule, it indicates that the device needs no address |
| 439 | resolution and that the software or hardware knows how to deliver packets |
| 440 | without any help from the protocol stacks. |
| 441 | |
| 442 | \item \verb|DYNAMIC| --- is an advisory flag indicating that the interface is |
| 443 | dynamically created and destroyed. |
| 444 | |
| 445 | \item \verb|SLAVE| --- this interface is bonded to some other interfaces |
| 446 | to share link capacities. |
| 447 | |
| 448 | \end{itemize} |
| 449 | |
| 450 | \vskip 1mm |
| 451 | \begin{NB} |
| 452 | There are other flags but they are either obsolete (\verb|NOTRAILERS|) |
| 453 | or not implemented (\verb|DEBUG|) or specific to some devices |
| 454 | (\verb|MASTER|, \verb|AUTOMEDIA| and \verb|PORTSEL|). We do not discuss |
| 455 | them here. |
| 456 | \end{NB} |
osdl.org!shemminger | aba5acd | 2004-04-15 20:56:59 +0000 | [diff] [blame] | 457 | |
| 458 | |
| 459 | The second line contains information on the link layer addresses |
| 460 | associated with the device. The first word (\verb|ether|, \verb|sit|) |
| 461 | defines the interface hardware type. This type determines the format and semantics |
| 462 | of the addresses and is logically part of the address. |
| 463 | The default format of the station address and the broadcast address |
| 464 | (or the peer address for pointopoint links) is a |
| 465 | sequence of hexadecimal bytes separated by colons, but some link |
| 466 | types may have their natural address format, f.e.\ addresses |
| 467 | of tunnels over IP are printed as dotted-quad IP addresses. |
| 468 | |
| 469 | \vskip 1mm |
| 470 | \begin{NB} |
| 471 | NBMA links have no well-defined broadcast or peer address, |
| 472 | however this field may contain useful information, f.e.\ |
| 473 | about the address of broadcast relay or about the address of the ARP server. |
| 474 | \end{NB} |
| 475 | \begin{NB} |
| 476 | Multicast addresses are not shown by this command, see |
| 477 | \verb|ip maddr ls| in~Sec.\ref{IP-MADDR} (p.\pageref{IP-MADDR} of this |
| 478 | document). |
| 479 | \end{NB} |
| 480 | |
| 481 | |
| 482 | \paragraph{Statistics:} With the \verb|-statistics| option, \verb|ip| also |
| 483 | prints interface statistics: |
| 484 | |
| 485 | \begin{verbatim} |
| 486 | kuznet@alisa:~ $ ip -s link ls eth0 |
| 487 | 3: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc cbq qlen 100 |
| 488 | link/ether 00:a0:cc:66:18:78 brd ff:ff:ff:ff:ff:ff |
| 489 | RX: bytes packets errors dropped overrun mcast |
| 490 | 2449949362 2786187 0 0 0 0 |
| 491 | TX: bytes packets errors dropped carrier collsns |
| 492 | 178558497 1783945 332 0 332 35172 |
| 493 | kuznet@alisa:~ $ |
| 494 | \end{verbatim} |
| 495 | \verb|RX:| and \verb|TX:| lines summarize receiver and transmitter |
| 496 | statistics. They contain: |
| 497 | \begin{itemize} |
| 498 | \item \verb|bytes| --- the total number of bytes received or transmitted |
| 499 | on the interface. This number wraps when the maximal length of the data type |
| 500 | natural for the architecture is exceeded, so continuous monitoring requires |
| 501 | a user level daemon snapping it periodically. |
| 502 | \item \verb|packets| --- the total number of packets received or transmitted |
| 503 | on the interface. |
| 504 | \item \verb|errors| --- the total number of receiver or transmitter errors. |
| 505 | \item \verb|dropped| --- the total number of packets dropped due to lack |
| 506 | of resources. |
| 507 | \item \verb|overrun| --- the total number of receiver overruns resulting |
| 508 | in dropped packets. As a rule, if the interface is overrun, it means |
| 509 | serious problems in the kernel or that your machine is too slow |
| 510 | for this interface. |
| 511 | \item \verb|mcast| --- the total number of received multicast packets. This option |
| 512 | is only supported by a few devices. |
| 513 | \item \verb|carrier| --- total number of link media failures f.e.\ because |
| 514 | of lost carrier. |
| 515 | \item \verb|collsns| --- the total number of collision events |
| 516 | on Ethernet-like media. This number may have a different sense on other |
| 517 | link types. |
| 518 | \item \verb|compressed| --- the total number of compressed packets. This is |
| 519 | available only for links using VJ header compression. |
| 520 | \end{itemize} |
| 521 | |
| 522 | |
| 523 | If the \verb|-s| option is entered twice or more, |
| 524 | \verb|ip| prints more detailed statistics on receiver |
| 525 | and transmitter errors. |
| 526 | |
| 527 | \begin{verbatim} |
| 528 | kuznet@alisa:~ $ ip -s -s link ls eth0 |
| 529 | 3: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc cbq qlen 100 |
| 530 | link/ether 00:a0:cc:66:18:78 brd ff:ff:ff:ff:ff:ff |
| 531 | RX: bytes packets errors dropped overrun mcast |
| 532 | 2449949362 2786187 0 0 0 0 |
| 533 | RX errors: length crc frame fifo missed |
| 534 | 0 0 0 0 0 |
| 535 | TX: bytes packets errors dropped carrier collsns |
| 536 | 178558497 1783945 332 0 332 35172 |
| 537 | TX errors: aborted fifo window heartbeat |
| 538 | 0 0 0 332 |
| 539 | kuznet@alisa:~ $ |
| 540 | \end{verbatim} |
| 541 | These error names are pure Ethernetisms. Other devices |
| 542 | may have non zero values in these fields but they may be |
| 543 | interpreted differently. |
| 544 | |
| 545 | |
| 546 | \section{{\tt ip address} --- protocol address management} |
| 547 | |
| 548 | \paragraph{Abbreviations:} \verb|address|, \verb|addr|, \verb|a|. |
| 549 | |
| 550 | \paragraph{Object:} The \verb|address| is a protocol (IP or IPv6) address attached |
| 551 | to a network device. Each device must have at least one address |
| 552 | to use the corresponding protocol. It is possible to have several |
| 553 | different addresses attached to one device. These addresses are not |
| 554 | discriminated, so that the term {\em alias\/} is not quite appropriate |
| 555 | for them and we do not use it in this document. |
| 556 | |
| 557 | The \verb|ip addr| command displays addresses and their properties, |
| 558 | adds new addresses and deletes old ones. |
| 559 | |
| 560 | \paragraph{Commands:} \verb|add|, \verb|delete|, \verb|flush| and \verb|show| |
| 561 | (or \verb|list|). |
| 562 | |
| 563 | |
| 564 | \subsection{{\tt ip address add} --- add a new protocol address} |
| 565 | \label{IP-ADDR-ADD} |
| 566 | |
| 567 | \paragraph{Abbreviations:} \verb|add|, \verb|a|. |
| 568 | |
| 569 | \paragraph{Arguments:} |
| 570 | |
| 571 | \begin{itemize} |
| 572 | \item \verb|dev NAME| |
| 573 | |
| 574 | \noindent--- the name of the device to add the address to. |
| 575 | |
| 576 | \item \verb|local ADDRESS| (default) |
| 577 | |
| 578 | --- the address of the interface. The format of the address depends |
| 579 | on the protocol. It is a dotted quad for IP and a sequence of hexadecimal halfwords |
| 580 | separated by colons for IPv6. The \verb|ADDRESS| may be followed by |
| 581 | a slash and a decimal number which encodes the network prefix length. |
| 582 | |
| 583 | |
| 584 | \item \verb|peer ADDRESS| |
| 585 | |
| 586 | --- the address of the remote endpoint for pointopoint interfaces. |
| 587 | Again, the \verb|ADDRESS| may be followed by a slash and a decimal number, |
| 588 | encoding the network prefix length. If a peer address is specified, |
| 589 | the local address {\em cannot\/} have a prefix length. The network prefix is associated |
| 590 | with the peer rather than with the local address. |
| 591 | |
| 592 | |
| 593 | \item \verb|broadcast ADDRESS| |
| 594 | |
| 595 | --- the broadcast address on the interface. |
| 596 | |
| 597 | It is possible to use the special symbols \verb|'+'| and \verb|'-'| |
| 598 | instead of the broadcast address. In this case, the broadcast address |
| 599 | is derived by setting/resetting the host bits of the interface prefix. |
| 600 | |
| 601 | \vskip 1mm |
| 602 | \begin{NB} |
| 603 | Unlike \verb|ifconfig|, the \verb|ip| utility {\em does not\/} set any broadcast |
| 604 | address unless explicitly requested. |
| 605 | \end{NB} |
| 606 | |
| 607 | |
| 608 | \item \verb|label NAME| |
| 609 | |
| 610 | --- Each address may be tagged with a label string. |
| 611 | In order to preserve compatibility with Linux-2.0 net aliases, |
| 612 | this string must coincide with the name of the device or must be prefixed |
| 613 | with the device name followed by colon. |
| 614 | |
| 615 | |
| 616 | \item \verb|scope SCOPE_VALUE| |
| 617 | |
| 618 | --- the scope of the area where this address is valid. |
| 619 | The available scopes are listed in file \verb|/etc/iproute2/rt_scopes|. |
| 620 | Predefined scope values are: |
| 621 | |
| 622 | \begin{itemize} |
| 623 | \item \verb|global| --- the address is globally valid. |
| 624 | \item \verb|site| --- (IPv6 only) the address is site local, |
| 625 | i.e.\ it is valid inside this site. |
| 626 | \item \verb|link| --- the address is link local, i.e.\ |
| 627 | it is valid only on this device. |
| 628 | \item \verb|host| --- the address is valid only inside this host. |
| 629 | \end{itemize} |
| 630 | |
| 631 | Appendix~\ref{ADDR-SEL} (p.\pageref{ADDR-SEL} of this document) |
| 632 | contains more details on address scopes. |
| 633 | |
| 634 | \end{itemize} |
| 635 | |
| 636 | \paragraph{Examples:} |
| 637 | \begin{itemize} |
| 638 | \item \verb|ip addr add 127.0.0.1/8 dev lo brd + scope host| |
| 639 | |
| 640 | --- add the usual loopback address to the loopback device. |
| 641 | |
| 642 | \item \verb|ip addr add 10.0.0.1/24 brd + dev eth0 label eth0:Alias| |
| 643 | |
| 644 | --- add the address 10.0.0.1 with prefix length 24 (i.e.\ netmask |
| 645 | \verb|255.255.255.0|), standard broadcast and label \verb|eth0:Alias| |
| 646 | to the interface \verb|eth0|. |
| 647 | \end{itemize} |
| 648 | |
| 649 | |
| 650 | \subsection{{\tt ip address delete} --- delete a protocol address} |
| 651 | |
| 652 | \paragraph{Abbreviations:} \verb|delete|, \verb|del|, \verb|d|. |
| 653 | |
| 654 | \paragraph{Arguments:} coincide with the arguments of \verb|ip addr add|. |
| 655 | The device name is a required argument. The rest are optional. |
| 656 | If no arguments are given, the first address is deleted. |
| 657 | |
| 658 | \paragraph{Examples:} |
| 659 | \begin{itemize} |
| 660 | \item \verb|ip addr del 127.0.0.1/8 dev lo| |
| 661 | |
| 662 | --- deletes the loopback address from the loopback device. |
| 663 | It would be best not to repeat this experiment. |
| 664 | |
| 665 | \item Disable IP on the interface \verb|eth0|: |
| 666 | \begin{verbatim} |
| 667 | while ip -f inet addr del dev eth0; do |
| 668 | : nothing |
| 669 | done |
| 670 | \end{verbatim} |
| 671 | Another method to disable IP on an interface using {\tt ip addr flush} |
| 672 | may be found in sec.\ref{IP-ADDR-FLUSH}, p.\pageref{IP-ADDR-FLUSH}. |
| 673 | |
| 674 | \end{itemize} |
| 675 | |
| 676 | |
| 677 | \subsection{{\tt ip address show} --- display protocol addresses} |
| 678 | |
| 679 | \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|lst|, \verb|sh|, \verb|ls|, |
| 680 | \verb|l|. |
| 681 | |
| 682 | \paragraph{Arguments:} |
| 683 | |
| 684 | \begin{itemize} |
| 685 | \item \verb|dev NAME| (default) |
| 686 | |
| 687 | --- the name of the device. |
| 688 | |
| 689 | \item \verb|scope SCOPE_VAL| |
| 690 | |
| 691 | --- only list addresses with this scope. |
| 692 | |
| 693 | \item \verb|to PREFIX| |
| 694 | |
| 695 | --- only list addresses matching this prefix. |
| 696 | |
| 697 | \item \verb|label PATTERN| |
| 698 | |
| 699 | --- only list addresses with labels matching the \verb|PATTERN|. |
| 700 | \verb|PATTERN| is a usual shell style pattern. |
| 701 | |
| 702 | |
| 703 | \item \verb|dynamic| and \verb|permanent| |
| 704 | |
| 705 | --- (IPv6 only) only list addresses installed due to stateless |
| 706 | address configuration or only list permanent (not dynamic) addresses. |
| 707 | |
| 708 | \item \verb|tentative| |
| 709 | |
| 710 | --- (IPv6 only) only list addresses which did not pass duplicate |
| 711 | address detection. |
| 712 | |
| 713 | \item \verb|deprecated| |
| 714 | |
| 715 | --- (IPv6 only) only list deprecated addresses. |
| 716 | |
| 717 | |
| 718 | \item \verb|primary| and \verb|secondary| |
| 719 | |
| 720 | --- only list primary (or secondary) addresses. |
| 721 | |
| 722 | \end{itemize} |
| 723 | |
| 724 | |
| 725 | \paragraph{Output format:} |
| 726 | |
| 727 | \begin{verbatim} |
| 728 | kuznet@alisa:~ $ ip addr ls eth0 |
| 729 | 3: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc cbq qlen 100 |
| 730 | link/ether 00:a0:cc:66:18:78 brd ff:ff:ff:ff:ff:ff |
| 731 | inet 193.233.7.90/24 brd 193.233.7.255 scope global eth0 |
| 732 | inet6 3ffe:2400:0:1:2a0:ccff:fe66:1878/64 scope global dynamic |
| 733 | valid_lft forever preferred_lft 604746sec |
| 734 | inet6 fe80::2a0:ccff:fe66:1878/10 scope link |
| 735 | kuznet@alisa:~ $ |
| 736 | \end{verbatim} |
| 737 | |
| 738 | The first two lines coincide with the output of \verb|ip link ls|. |
| 739 | It is natural to interpret link layer addresses |
| 740 | as addresses of the protocol family \verb|AF_PACKET|. |
| 741 | |
| 742 | Then the list of IP and IPv6 addresses follows, accompanied by |
| 743 | additional address attributes: scope value (see Sec.\ref{IP-ADDR-ADD}, |
| 744 | p.\pageref{IP-ADDR-ADD} above), flags and the address label. |
| 745 | |
| 746 | Address flags are set by the kernel and cannot be changed |
| 747 | administratively. Currently, the following flags are defined: |
| 748 | |
| 749 | \begin{enumerate} |
| 750 | \item \verb|secondary| |
| 751 | |
| 752 | --- the address is not used when selecting the default source address |
| 753 | of outgoing packets (Cf.\ Appendix~\ref{ADDR-SEL}, p.\pageref{ADDR-SEL}.). |
| 754 | An IP address becomes secondary if another address with the same |
| 755 | prefix bits already exists. The first address is primary. |
| 756 | It is the leader of the group of all secondary addresses. When the leader |
| 757 | is deleted, all secondaries are purged too. |
Andreas Henriksson | 3a9e482 | 2008-01-12 17:17:02 +0100 | [diff] [blame] | 758 | There is a tweak in \verb|/proc/sys/net/ipv4/conf/<dev>/promote_secondaries| |
| 759 | which activate secondaries promotion when a primary is deleted. |
| 760 | To permanently enable this feature on all devices add |
| 761 | \verb|net.ipv4.conf.all.promote_secondaries=1| to \verb|/etc/sysctl.conf|. |
| 762 | This tweak is available in linux 2.6.15 and later. |
osdl.org!shemminger | aba5acd | 2004-04-15 20:56:59 +0000 | [diff] [blame] | 763 | |
| 764 | |
| 765 | \item \verb|dynamic| |
| 766 | |
| 767 | --- the address was created due to stateless autoconfiguration~\cite{RFC-ADDRCONF}. |
| 768 | In this case the output also contains information on times, when |
| 769 | the address is still valid. After \verb|preferred_lft| expires the address is |
| 770 | moved to the deprecated state. After \verb|valid_lft| expires the address |
| 771 | is finally invalidated. |
| 772 | |
| 773 | \item \verb|deprecated| |
| 774 | |
| 775 | --- the address is deprecated, i.e.\ it is still valid, but cannot |
| 776 | be used by newly created connections. |
| 777 | |
| 778 | \item \verb|tentative| |
| 779 | |
| 780 | --- the address is not used because duplicate address detection~\cite{RFC-ADDRCONF} |
| 781 | is still not complete or failed. |
| 782 | |
| 783 | \end{enumerate} |
| 784 | |
| 785 | |
| 786 | \subsection{{\tt ip address flush} --- flush protocol addresses} |
| 787 | \label{IP-ADDR-FLUSH} |
| 788 | |
| 789 | \paragraph{Abbreviations:} \verb|flush|, \verb|f|. |
| 790 | |
| 791 | \paragraph{Description:}This command flushes the protocol addresses |
| 792 | selected by some criteria. |
| 793 | |
| 794 | \paragraph{Arguments:} This command has the same arguments as \verb|show|. |
| 795 | The difference is that it does not run when no arguments are given. |
| 796 | |
| 797 | \paragraph{Warning:} This command (and other \verb|flush| commands |
| 798 | described below) is pretty dangerous. If you make a mistake, it will |
| 799 | not forgive it, but will cruelly purge all the addresses. |
| 800 | |
| 801 | \paragraph{Statistics:} With the \verb|-statistics| option, the command |
| 802 | becomes verbose. It prints out the number of deleted addresses and the number |
| 803 | of rounds made to flush the address list. If this option is given |
| 804 | twice, \verb|ip addr flush| also dumps all the deleted addresses |
| 805 | in the format described in the previous subsection. |
| 806 | |
| 807 | \paragraph{Example:} Delete all the addresses from the private network |
| 808 | 10.0.0.0/8: |
| 809 | \begin{verbatim} |
| 810 | netadm@amber:~ # ip -s -s a f to 10/8 |
| 811 | 2: dummy inet 10.7.7.7/16 brd 10.7.255.255 scope global dummy |
| 812 | 3: eth0 inet 10.10.7.7/16 brd 10.10.255.255 scope global eth0 |
| 813 | 4: eth1 inet 10.8.7.7/16 brd 10.8.255.255 scope global eth1 |
| 814 | |
| 815 | *** Round 1, deleting 3 addresses *** |
| 816 | *** Flush is complete after 1 round *** |
| 817 | netadm@amber:~ # |
| 818 | \end{verbatim} |
| 819 | Another instructive example is disabling IP on all the Ethernets: |
| 820 | \begin{verbatim} |
| 821 | netadm@amber:~ # ip -4 addr flush label "eth*" |
| 822 | \end{verbatim} |
| 823 | And the last example shows how to flush all the IPv6 addresses |
| 824 | acquired by the host from stateless address autoconfiguration |
| 825 | after you enabled forwarding or disabled autoconfiguration. |
| 826 | \begin{verbatim} |
| 827 | netadm@amber:~ # ip -6 addr flush dynamic |
| 828 | \end{verbatim} |
| 829 | |
| 830 | |
| 831 | |
| 832 | \section{{\tt ip neighbour} --- neighbour/arp tables management} |
| 833 | |
| 834 | \paragraph{Abbreviations:} \verb|neighbour|, \verb|neighbor|, \verb|neigh|, |
| 835 | \verb|n|. |
| 836 | |
| 837 | \paragraph{Object:} \verb|neighbour| objects establish bindings between protocol |
| 838 | addresses and link layer addresses for hosts sharing the same link. |
| 839 | Neighbour entries are organized into tables. The IPv4 neighbour table |
| 840 | is known by another name --- the ARP table. |
| 841 | |
| 842 | The corresponding commands display neighbour bindings |
| 843 | and their properties, add new neighbour entries and delete old ones. |
| 844 | |
| 845 | \paragraph{Commands:} \verb|add|, \verb|change|, \verb|replace|, |
| 846 | \verb|delete|, \verb|flush| and \verb|show| (or \verb|list|). |
| 847 | |
| 848 | \paragraph{See also:} Appendix~\ref{PROXY-NEIGH}, p.\pageref{PROXY-NEIGH} |
| 849 | describes how to manage proxy ARP/NDISC with the \verb|ip| utility. |
| 850 | |
| 851 | |
| 852 | \subsection{{\tt ip neighbour add} --- add a new neighbour entry\\ |
| 853 | {\tt ip neighbour change} --- change an existing entry\\ |
| 854 | {\tt ip neighbour replace} --- add a new entry or change an existing one} |
| 855 | |
| 856 | \paragraph{Abbreviations:} \verb|add|, \verb|a|; \verb|change|, \verb|chg|; |
| 857 | \verb|replace|, \verb|repl|. |
| 858 | |
| 859 | \paragraph{Description:} These commands create new neighbour records |
| 860 | or update existing ones. |
| 861 | |
| 862 | \paragraph{Arguments:} |
| 863 | |
| 864 | \begin{itemize} |
| 865 | \item \verb|to ADDRESS| (default) |
| 866 | |
| 867 | --- the protocol address of the neighbour. It is either an IPv4 or IPv6 address. |
| 868 | |
| 869 | \item \verb|dev NAME| |
| 870 | |
| 871 | --- the interface to which this neighbour is attached. |
| 872 | |
| 873 | |
| 874 | \item \verb|lladdr LLADDRESS| |
| 875 | |
| 876 | --- the link layer address of the neighbour. \verb|LLADDRESS| can also be |
| 877 | \verb|null|. |
| 878 | |
| 879 | \item \verb|nud NUD_STATE| |
| 880 | |
| 881 | --- the state of the neighbour entry. \verb|nud| is an abbreviation for ``Neighbour |
| 882 | Unreachability Detection''. The state can take one of the following values: |
| 883 | |
| 884 | \begin{enumerate} |
| 885 | \item \verb|permanent| --- the neighbour entry is valid forever and can be only be removed |
| 886 | administratively. |
| 887 | \item \verb|noarp| --- the neighbour entry is valid. No attempts to validate |
| 888 | this entry will be made but it can be removed when its lifetime expires. |
| 889 | \item \verb|reachable| --- the neighbour entry is valid until the reachability |
| 890 | timeout expires. |
| 891 | \item \verb|stale| --- the neighbour entry is valid but suspicious. |
| 892 | This option to \verb|ip neigh| does not change the neighbour state if |
| 893 | it was valid and the address is not changed by this command. |
| 894 | \end{enumerate} |
| 895 | |
| 896 | \end{itemize} |
| 897 | |
| 898 | \paragraph{Examples:} |
| 899 | \begin{itemize} |
| 900 | \item \verb|ip neigh add 10.0.0.3 lladdr 0:0:0:0:0:1 dev eth0 nud perm| |
| 901 | |
| 902 | --- add a permanent ARP entry for the neighbour 10.0.0.3 on the device \verb|eth0|. |
| 903 | |
| 904 | \item \verb|ip neigh chg 10.0.0.3 dev eth0 nud reachable| |
| 905 | |
| 906 | --- change its state to \verb|reachable|. |
| 907 | \end{itemize} |
| 908 | |
| 909 | |
| 910 | \subsection{{\tt ip neighbour delete} --- delete a neighbour entry} |
| 911 | |
| 912 | \paragraph{Abbreviations:} \verb|delete|, \verb|del|, \verb|d|. |
| 913 | |
| 914 | \paragraph{Description:} This command invalidates a neighbour entry. |
| 915 | |
| 916 | \paragraph{Arguments:} The arguments are the same as with \verb|ip neigh add|, |
| 917 | except that \verb|lladdr| and \verb|nud| are ignored. |
| 918 | |
| 919 | |
| 920 | \paragraph{Example:} |
| 921 | \begin{itemize} |
| 922 | \item \verb|ip neigh del 10.0.0.3 dev eth0| |
| 923 | |
| 924 | --- invalidate an ARP entry for the neighbour 10.0.0.3 on the device \verb|eth0|. |
| 925 | |
| 926 | \end{itemize} |
| 927 | |
| 928 | \begin{NB} |
| 929 | The deleted neighbour entry will not disappear from the tables |
| 930 | immediately. If it is in use it cannot be deleted until the last |
| 931 | client releases it. Otherwise it will be destroyed during |
| 932 | the next garbage collection. |
| 933 | \end{NB} |
| 934 | |
| 935 | |
| 936 | \paragraph{Warning:} Attempts to delete or manually change |
| 937 | a \verb|noarp| entry created by the kernel may result in unpredictable behaviour. |
| 938 | Particularly, the kernel may try to resolve this address even |
| 939 | on a \verb|NOARP| interface or if the address is multicast or broadcast. |
| 940 | |
| 941 | |
| 942 | \subsection{{\tt ip neighbour show} --- list neighbour entries} |
| 943 | |
| 944 | \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|sh|, \verb|ls|. |
| 945 | |
| 946 | \paragraph{Description:}This commands displays neighbour tables. |
| 947 | |
| 948 | \paragraph{Arguments:} |
| 949 | |
| 950 | \begin{itemize} |
| 951 | |
| 952 | \item \verb|to ADDRESS| (default) |
| 953 | |
| 954 | --- the prefix selecting the neighbours to list. |
| 955 | |
| 956 | \item \verb|dev NAME| |
| 957 | |
| 958 | --- only list the neighbours attached to this device. |
| 959 | |
| 960 | \item \verb|unused| |
| 961 | |
| 962 | --- only list neighbours which are not currently in use. |
| 963 | |
| 964 | \item \verb|nud NUD_STATE| |
| 965 | |
| 966 | --- only list neighbour entries in this state. \verb|NUD_STATE| takes |
| 967 | values listed below or the special value \verb|all| which means all states. |
| 968 | This option may occur more than once. If this option is absent, \verb|ip| |
| 969 | lists all entries except for \verb|none| and \verb|noarp|. |
| 970 | |
| 971 | \end{itemize} |
| 972 | |
| 973 | |
| 974 | \paragraph{Output format:} |
| 975 | |
| 976 | \begin{verbatim} |
| 977 | kuznet@alisa:~ $ ip neigh ls |
| 978 | :: dev lo lladdr 00:00:00:00:00:00 nud noarp |
| 979 | fe80::200:cff:fe76:3f85 dev eth0 lladdr 00:00:0c:76:3f:85 router \ |
| 980 | nud stale |
| 981 | 0.0.0.0 dev lo lladdr 00:00:00:00:00:00 nud noarp |
| 982 | 193.233.7.254 dev eth0 lladdr 00:00:0c:76:3f:85 nud reachable |
| 983 | 193.233.7.85 dev eth0 lladdr 00:e0:1e:63:39:00 nud stale |
| 984 | kuznet@alisa:~ $ |
| 985 | \end{verbatim} |
| 986 | |
| 987 | The first word of each line is the protocol address of the neighbour. |
| 988 | Then the device name follows. The rest of the line describes the contents of |
| 989 | the neighbour entry identified by the pair (device, address). |
| 990 | |
| 991 | \verb|lladdr| is the link layer address of the neighbour. |
| 992 | |
| 993 | \verb|nud| is the state of the ``neighbour unreachability detection'' machine |
| 994 | for this entry. The detailed description of the neighbour |
| 995 | state machine can be found in~\cite{RFC-NDISC}. Here is the full list |
| 996 | of the states with short descriptions: |
| 997 | |
| 998 | \begin{enumerate} |
| 999 | \item\verb|none| --- the state of the neighbour is void. |
| 1000 | \item\verb|incomplete| --- the neighbour is in the process of resolution. |
| 1001 | \item\verb|reachable| --- the neighbour is valid and apparently reachable. |
| 1002 | \item\verb|stale| --- the neighbour is valid, but is probably already |
| 1003 | unreachable, so the kernel will try to check it at the first transmission. |
| 1004 | \item\verb|delay| --- a packet has been sent to the stale neighbour and the kernel is waiting |
| 1005 | for confirmation. |
| 1006 | \item\verb|probe| --- the delay timer expired but no confirmation was received. |
| 1007 | The kernel has started to probe the neighbour with ARP/NDISC messages. |
| 1008 | \item\verb|failed| --- resolution has failed. |
| 1009 | \item\verb|noarp| --- the neighbour is valid. No attempts to check the entry |
| 1010 | will be made. |
| 1011 | \item\verb|permanent| --- it is a \verb|noarp| entry, but only the administrator |
| 1012 | may remove the entry from the neighbour table. |
| 1013 | \end{enumerate} |
| 1014 | |
| 1015 | The link layer address is valid in all states except for \verb|none|, |
| 1016 | \verb|failed| and \verb|incomplete|. |
| 1017 | |
| 1018 | IPv6 neighbours can be marked with the additional flag \verb|router| |
| 1019 | which means that the neighbour introduced itself as an IPv6 router~\cite{RFC-NDISC}. |
| 1020 | |
| 1021 | \paragraph{Statistics:} The \verb|-statistics| option displays some usage |
| 1022 | statistics, f.e.\ |
| 1023 | |
| 1024 | \begin{verbatim} |
| 1025 | kuznet@alisa:~ $ ip -s n ls 193.233.7.254 |
| 1026 | 193.233.7.254 dev eth0 lladdr 00:00:0c:76:3f:85 ref 5 used 12/13/20 \ |
| 1027 | nud reachable |
| 1028 | kuznet@alisa:~ $ |
| 1029 | \end{verbatim} |
| 1030 | |
| 1031 | Here \verb|ref| is the number of users of this entry |
| 1032 | and \verb|used| is a triplet of time intervals in seconds |
| 1033 | separated by slashes. In this case they show that: |
| 1034 | |
| 1035 | \begin{enumerate} |
| 1036 | \item the entry was used 12 seconds ago. |
| 1037 | \item the entry was confirmed 13 seconds ago. |
| 1038 | \item the entry was updated 20 seconds ago. |
| 1039 | \end{enumerate} |
| 1040 | |
| 1041 | \subsection{{\tt ip neighbour flush} --- flush neighbour entries} |
| 1042 | |
| 1043 | \paragraph{Abbreviations:} \verb|flush|, \verb|f|. |
| 1044 | |
| 1045 | \paragraph{Description:}This command flushes neighbour tables, selecting |
| 1046 | entries to flush by some criteria. |
| 1047 | |
| 1048 | \paragraph{Arguments:} This command has the same arguments as \verb|show|. |
| 1049 | The differences are that it does not run when no arguments are given, |
| 1050 | and that the default neighbour states to be flushed do not include |
| 1051 | \verb|permanent| and \verb|noarp|. |
| 1052 | |
| 1053 | |
| 1054 | \paragraph{Statistics:} With the \verb|-statistics| option, the command |
| 1055 | becomes verbose. It prints out the number of deleted neighbours and the number |
| 1056 | of rounds made to flush the neighbour table. If the option is given |
| 1057 | twice, \verb|ip neigh flush| also dumps all the deleted neighbours |
| 1058 | in the format described in the previous subsection. |
| 1059 | |
| 1060 | \paragraph{Example:} |
| 1061 | \begin{verbatim} |
| 1062 | netadm@alisa:~ # ip -s -s n f 193.233.7.254 |
| 1063 | 193.233.7.254 dev eth0 lladdr 00:00:0c:76:3f:85 ref 5 used 12/13/20 \ |
| 1064 | nud reachable |
| 1065 | |
| 1066 | *** Round 1, deleting 1 entries *** |
| 1067 | *** Flush is complete after 1 round *** |
| 1068 | netadm@alisa:~ # |
| 1069 | \end{verbatim} |
| 1070 | |
| 1071 | |
| 1072 | \section{{\tt ip route} --- routing table management} |
| 1073 | \label{IP-ROUTE} |
| 1074 | |
| 1075 | \paragraph{Abbreviations:} \verb|route|, \verb|ro|, \verb|r|. |
| 1076 | |
| 1077 | \paragraph{Object:} \verb|route| entries in the kernel routing tables keep |
| 1078 | information about paths to other networked nodes. |
| 1079 | |
| 1080 | Each route entry has a {\em key\/} consisting of a {\em prefix\/} |
| 1081 | (i.e.\ a pair containing a network address and the length of its mask) and, |
| 1082 | optionally, the TOS value. An IP packet matches the route if the highest |
| 1083 | bits of its destination address are equal to the route prefix at least |
| 1084 | up to the prefix length and if the TOS of the route is zero or equal to |
| 1085 | the TOS of the packet. |
| 1086 | |
| 1087 | If several routes match the packet, the following pruning rules |
| 1088 | are used to select the best one (see~\cite{RFC1812}): |
| 1089 | \begin{enumerate} |
| 1090 | \item The longest matching prefix is selected. All shorter ones |
| 1091 | are dropped. |
| 1092 | |
| 1093 | \item If the TOS of some route with the longest prefix is equal to the TOS |
| 1094 | of the packet, the routes with different TOS are dropped. |
| 1095 | |
| 1096 | If no exact TOS match was found and routes with TOS=0 exist, |
| 1097 | the rest of routes are pruned. |
| 1098 | |
| 1099 | Otherwise, the route lookup fails. |
| 1100 | |
| 1101 | \item If several routes remain after the previous steps, then |
| 1102 | the routes with the best preference values are selected. |
| 1103 | |
| 1104 | \item If we still have several routes, then the {\em first\/} of them |
| 1105 | is selected. |
| 1106 | |
| 1107 | \begin{NB} |
| 1108 | Note the ambiguity of the last step. Unfortunately, Linux |
| 1109 | historically allows such a bizarre situation. The sense of the |
| 1110 | word ``first'' depends on the order of route additions and it is practically |
| 1111 | impossible to maintain a bundle of such routes in this order. |
| 1112 | \end{NB} |
| 1113 | |
| 1114 | For simplicity we will limit ourselves to the case where such a situation |
| 1115 | is impossible and routes are uniquely identified by the triplet |
| 1116 | \{prefix, tos, preference\}. Actually, it is impossible to create |
| 1117 | non-unique routes with \verb|ip| commands described in this section. |
| 1118 | |
| 1119 | One useful exception to this rule is the default route on non-forwarding |
| 1120 | hosts. It is ``officially'' allowed to have several fallback routes |
| 1121 | when several routers are present on directly connected networks. |
| 1122 | In this case, Linux-2.2 makes ``dead gateway detection''~\cite{RFC1122} |
| 1123 | controlled by neighbour unreachability detection and by advice |
| 1124 | from transport protocols to select a working router, so the order |
| 1125 | of the routes is not essential. However, in this case, |
| 1126 | fiddling with default routes manually is not recommended. Use the Router Discovery |
| 1127 | protocol (see Appendix~\ref{EXAMPLE-SETUP}, p.\pageref{EXAMPLE-SETUP}) |
| 1128 | instead. Actually, Linux-2.2 IPv6 does not give user level applications |
| 1129 | any access to default routes. |
| 1130 | \end{enumerate} |
| 1131 | |
| 1132 | Certainly, the steps above are not performed exactly |
| 1133 | in this sequence. Instead, the routing table in the kernel is kept |
| 1134 | in some data structure to achieve the final result |
| 1135 | with minimal cost. However, not depending on a particular |
| 1136 | routing algorithm implemented in the kernel, we can summarize |
| 1137 | the statements above as: a route is identified by the triplet |
| 1138 | \{prefix, tos, preference\}. This {\em key\/} lets us locate |
| 1139 | the route in the routing table. |
| 1140 | |
| 1141 | \paragraph{Route attributes:} Each route key refers to a routing |
| 1142 | information record containing |
| 1143 | the data required to deliver IP packets (f.e.\ output device and |
| 1144 | next hop router) and some optional attributes (f.e. the path MTU or |
| 1145 | the preferred source address when communicating with this destination). |
| 1146 | These attributes are described in the following subsection. |
| 1147 | |
| 1148 | \paragraph{Route types:} \label{IP-ROUTE-TYPES} |
| 1149 | It is important that the set |
| 1150 | of required and optional attributes depend on the route {\em type\/}. |
| 1151 | The most important route type |
| 1152 | is \verb|unicast|. It describes real paths to other hosts. |
| 1153 | As a rule, common routing tables contain only such routes. However, |
| 1154 | there are other types of routes with different semantics. The |
| 1155 | full list of types understood by Linux-2.2 is: |
| 1156 | \begin{itemize} |
| 1157 | \item \verb|unicast| --- the route entry describes real paths to the |
| 1158 | destinations covered by the route prefix. |
| 1159 | \item \verb|unreachable| --- these destinations are unreachable. Packets |
| 1160 | are discarded and the ICMP message {\em host unreachable\/} is generated. |
| 1161 | The local senders get an \verb|EHOSTUNREACH| error. |
| 1162 | \item \verb|blackhole| --- these destinations are unreachable. Packets |
| 1163 | are discarded silently. The local senders get an \verb|EINVAL| error. |
| 1164 | \item \verb|prohibit| --- these destinations are unreachable. Packets |
| 1165 | are discarded and the ICMP message {\em communication administratively |
| 1166 | prohibited\/} is generated. The local senders get an \verb|EACCES| error. |
| 1167 | \item \verb|local| --- the destinations are assigned to this |
| 1168 | host. The packets are looped back and delivered locally. |
| 1169 | \item \verb|broadcast| --- the destinations are broadcast addresses. |
| 1170 | The packets are sent as link broadcasts. |
| 1171 | \item \verb|throw| --- a special control route used together with policy |
| 1172 | rules (see sec.\ref{IP-RULE}, p.\pageref{IP-RULE}). If such a route is selected, lookup |
| 1173 | in this table is terminated pretending that no route was found. |
| 1174 | Without policy routing it is equivalent to the absence of the route in the routing |
| 1175 | table. The packets are dropped and the ICMP message {\em net unreachable\/} |
| 1176 | is generated. The local senders get an \verb|ENETUNREACH| error. |
| 1177 | \item \verb|nat| --- a special NAT route. Destinations covered by the prefix |
| 1178 | are considered to be dummy (or external) addresses which require translation |
| 1179 | to real (or internal) ones before forwarding. The addresses to translate to |
| 1180 | are selected with the attribute \verb|via|. More about NAT is |
| 1181 | in Appendix~\ref{ROUTE-NAT}, p.\pageref{ROUTE-NAT}. |
| 1182 | \item \verb|anycast| --- ({\em not implemented\/}) the destinations are |
| 1183 | {\em anycast\/} addresses assigned to this host. They are mainly equivalent |
| 1184 | to \verb|local| with one difference: such addresses are invalid when used |
| 1185 | as the source address of any packet. |
| 1186 | \item \verb|multicast| --- a special type used for multicast routing. |
| 1187 | It is not present in normal routing tables. |
| 1188 | \end{itemize} |
| 1189 | |
| 1190 | \paragraph{Route tables:} Linux-2.2 can pack routes into several routing |
| 1191 | tables identified by a number in the range from 1 to 255 or by |
| 1192 | name from the file \verb|/etc/iproute2/rt_tables|. By default all normal |
| 1193 | routes are inserted into the \verb|main| table (ID 254) and the kernel only uses |
| 1194 | this table when calculating routes. |
| 1195 | |
| 1196 | Actually, one other table always exists, which is invisible but |
| 1197 | even more important. It is the \verb|local| table (ID 255). This table |
| 1198 | consists of routes for local and broadcast addresses. The kernel maintains |
| 1199 | this table automatically and the administrator usually need not modify it |
| 1200 | or even look at it. |
| 1201 | |
| 1202 | The multiple routing tables enter the game when {\em policy routing\/} |
| 1203 | is used. See sec.\ref{IP-RULE}, p.\pageref{IP-RULE}. |
| 1204 | In this case, the table identifier effectively becomes |
| 1205 | one more parameter, which should be added to the triplet |
| 1206 | \{prefix, tos, preference\} to uniquely identify the route. |
| 1207 | |
| 1208 | |
| 1209 | \subsection{{\tt ip route add} --- add a new route\\ |
| 1210 | {\tt ip route change} --- change a route\\ |
| 1211 | {\tt ip route replace} --- change a route or add a new one} |
| 1212 | \label{IP-ROUTE-ADD} |
| 1213 | |
| 1214 | \paragraph{Abbreviations:} \verb|add|, \verb|a|; \verb|change|, \verb|chg|; |
| 1215 | \verb|replace|, \verb|repl|. |
| 1216 | |
| 1217 | |
| 1218 | \paragraph{Arguments:} |
| 1219 | \begin{itemize} |
| 1220 | \item \verb|to PREFIX| or \verb|to TYPE PREFIX| (default) |
| 1221 | |
| 1222 | --- the destination prefix of the route. If \verb|TYPE| is omitted, |
| 1223 | \verb|ip| assumes type \verb|unicast|. Other values of \verb|TYPE| |
| 1224 | are listed above. \verb|PREFIX| is an IP or IPv6 address optionally followed |
| 1225 | by a slash and the prefix length. If the length of the prefix is missing, |
| 1226 | \verb|ip| assumes a full-length host route. There is also a special |
| 1227 | \verb|PREFIX| --- \verb|default| --- which is equivalent to IP \verb|0/0| or |
| 1228 | to IPv6 \verb|::/0|. |
| 1229 | |
| 1230 | \item \verb|tos TOS| or \verb|dsfield TOS| |
| 1231 | |
| 1232 | --- the Type Of Service (TOS) key. This key has no associated mask and |
| 1233 | the longest match is understood as: First, compare the TOS |
| 1234 | of the route and of the packet. If they are not equal, then the packet |
| 1235 | may still match a route with a zero TOS. \verb|TOS| is either an 8 bit hexadecimal |
| 1236 | number or an identifier from {\tt /etc/iproute2/rt\_dsfield}. |
| 1237 | |
| 1238 | |
| 1239 | \item \verb|metric NUMBER| or \verb|preference NUMBER| |
| 1240 | |
| 1241 | --- the preference value of the route. \verb|NUMBER| is an arbitrary 32bit number. |
| 1242 | |
| 1243 | \item \verb|table TABLEID| |
| 1244 | |
| 1245 | --- the table to add this route to. |
| 1246 | \verb|TABLEID| may be a number or a string from the file |
| 1247 | \verb|/etc/iproute2/rt_tables|. If this parameter is omitted, |
| 1248 | \verb|ip| assumes the \verb|main| table, with the exception of |
| 1249 | \verb|local|, \verb|broadcast| and \verb|nat| routes, which are |
| 1250 | put into the \verb|local| table by default. |
| 1251 | |
| 1252 | \item \verb|dev NAME| |
| 1253 | |
| 1254 | --- the output device name. |
| 1255 | |
| 1256 | \item \verb|via ADDRESS| |
| 1257 | |
| 1258 | --- the address of the nexthop router. Actually, the sense of this field depends |
| 1259 | on the route type. For normal \verb|unicast| routes it is either the true nexthop |
| 1260 | router or, if it is a direct route installed in BSD compatibility mode, |
| 1261 | it can be a local address of the interface. |
| 1262 | For NAT routes it is the first address of the block of translated IP destinations. |
| 1263 | |
| 1264 | \item \verb|src ADDRESS| |
| 1265 | |
| 1266 | --- the source address to prefer when sending to the destinations |
| 1267 | covered by the route prefix. |
| 1268 | |
| 1269 | \item \verb|realm REALMID| |
| 1270 | |
| 1271 | --- the realm to which this route is assigned. |
| 1272 | \verb|REALMID| may be a number or a string from the file |
| 1273 | \verb|/etc/iproute2/rt_realms|. Sec.\ref{RT-REALMS} (p.\pageref{RT-REALMS}) |
| 1274 | contains more information on realms. |
| 1275 | |
| 1276 | \item \verb|mtu MTU| or \verb|mtu lock MTU| |
| 1277 | |
| 1278 | --- the MTU along the path to the destination. If the modifier \verb|lock| is |
| 1279 | not used, the MTU may be updated by the kernel due to Path MTU Discovery. |
| 1280 | If the modifier \verb|lock| is used, no path MTU discovery will be tried, |
| 1281 | all packets will be sent without the DF bit in IPv4 case |
| 1282 | or fragmented to MTU for IPv6. |
| 1283 | |
| 1284 | \item \verb|window NUMBER| |
| 1285 | |
| 1286 | --- the maximal window for TCP to advertise to these destinations, |
| 1287 | measured in bytes. It limits maximal data bursts that our TCP |
| 1288 | peers are allowed to send to us. |
| 1289 | |
| 1290 | \item \verb|rtt NUMBER| |
| 1291 | |
| 1292 | --- the initial RTT (``Round Trip Time'') estimate. |
| 1293 | |
| 1294 | |
| 1295 | \item \verb|rttvar NUMBER| |
| 1296 | |
| 1297 | --- \threeonly the initial RTT variance estimate. |
| 1298 | |
| 1299 | |
| 1300 | \item \verb|ssthresh NUMBER| |
| 1301 | |
| 1302 | --- \threeonly an estimate for the initial slow start threshold. |
| 1303 | |
| 1304 | |
| 1305 | \item \verb|cwnd NUMBER| |
| 1306 | |
| 1307 | --- \threeonly the clamp for congestion window. It is ignored if the \verb|lock| |
| 1308 | flag is not used. |
| 1309 | |
| 1310 | |
| 1311 | \item \verb|advmss NUMBER| |
| 1312 | |
| 1313 | --- \threeonly the MSS (``Maximal Segment Size'') to advertise to these |
| 1314 | destinations when establishing TCP connections. If it is not given, |
| 1315 | Linux uses a default value calculated from the first hop device MTU. |
| 1316 | |
| 1317 | \begin{NB} |
| 1318 | If the path to these destination is asymmetric, this guess may be wrong. |
| 1319 | \end{NB} |
| 1320 | |
| 1321 | \item \verb|reordering NUMBER| |
| 1322 | |
| 1323 | --- \threeonly Maximal reordering on the path to this destination. |
| 1324 | If it is not given, Linux uses the value selected with \verb|sysctl| |
| 1325 | variable \verb|net/ipv4/tcp_reordering|. |
| 1326 | |
| 1327 | |
| 1328 | |
| 1329 | \item \verb|nexthop NEXTHOP| |
| 1330 | |
| 1331 | --- the nexthop of a multipath route. \verb|NEXTHOP| is a complex value |
| 1332 | with its own syntax similar to the top level argument lists: |
| 1333 | \begin{itemize} |
| 1334 | \item \verb|via ADDRESS| is the nexthop router. |
| 1335 | \item \verb|dev NAME| is the output device. |
| 1336 | \item \verb|weight NUMBER| is a weight for this element of a multipath |
| 1337 | route reflecting its relative bandwidth or quality. |
| 1338 | \end{itemize} |
| 1339 | |
| 1340 | \item \verb|scope SCOPE_VAL| |
| 1341 | |
| 1342 | --- the scope of the destinations covered by the route prefix. |
| 1343 | \verb|SCOPE_VAL| may be a number or a string from the file |
| 1344 | \verb|/etc/iproute2/rt_scopes|. |
| 1345 | If this parameter is omitted, |
| 1346 | \verb|ip| assumes scope \verb|global| for all gatewayed \verb|unicast| |
| 1347 | routes, scope \verb|link| for direct \verb|unicast| and \verb|broadcast| routes |
| 1348 | and scope \verb|host| for \verb|local| routes. |
| 1349 | |
| 1350 | \item \verb|protocol RTPROTO| |
| 1351 | |
| 1352 | --- the routing protocol identifier of this route. |
| 1353 | \verb|RTPROTO| may be a number or a string from the file |
| 1354 | \verb|/etc/iproute2/rt_protos|. If the routing protocol ID is |
| 1355 | not given, \verb|ip| assumes protocol \verb|boot| (i.e.\ |
| 1356 | it assumes the route was added by someone who doesn't |
| 1357 | understand what they are doing). Several protocol values have a fixed interpretation. |
| 1358 | Namely: |
| 1359 | \begin{itemize} |
| 1360 | \item \verb|redirect| --- the route was installed due to an ICMP redirect. |
| 1361 | \item \verb|kernel| --- the route was installed by the kernel during |
| 1362 | autoconfiguration. |
| 1363 | \item \verb|boot| --- the route was installed during the bootup sequence. |
| 1364 | If a routing daemon starts, it will purge all of them. |
| 1365 | \item \verb|static| --- the route was installed by the administrator |
| 1366 | to override dynamic routing. Routing daemon will respect them |
| 1367 | and, probably, even advertise them to its peers. |
| 1368 | \item \verb|ra| --- the route was installed by Router Discovery protocol. |
| 1369 | \end{itemize} |
| 1370 | The rest of the values are not reserved and the administrator is free |
| 1371 | to assign (or not to assign) protocol tags. At least, routing |
| 1372 | daemons should take care of setting some unique protocol values, |
| 1373 | f.e.\ as they are assigned in \verb|rtnetlink.h| or in \verb|rt_protos| |
| 1374 | database. |
| 1375 | |
| 1376 | |
| 1377 | \item \verb|onlink| |
| 1378 | |
| 1379 | --- pretend that the nexthop is directly attached to this link, |
| 1380 | even if it does not match any interface prefix. One application of this |
| 1381 | option may be found in~\cite{IP-TUNNELS}. |
| 1382 | |
| 1383 | \item \verb|equalize| |
| 1384 | |
| 1385 | --- allow packet by packet randomization on multipath routes. |
| 1386 | Without this modifier, the route will be frozen to one selected |
| 1387 | nexthop, so that load splitting will only occur on per-flow base. |
| 1388 | \verb|equalize| only works if the kernel is patched. |
| 1389 | |
| 1390 | |
| 1391 | \end{itemize} |
| 1392 | |
| 1393 | |
| 1394 | \begin{NB} |
| 1395 | Actually there are more commands: \verb|prepend| does the same |
| 1396 | thing as classic \verb|route add|, i.e.\ adds a route, even if another |
| 1397 | route to the same destination exists. Its opposite case is \verb|append|, |
| 1398 | which adds the route to the end of the list. Avoid these |
| 1399 | features. |
| 1400 | \end{NB} |
| 1401 | \begin{NB} |
| 1402 | More sad news, IPv6 only understands the \verb|append| command correctly. |
| 1403 | All the others are translated into \verb|append| commands. Certainly, |
| 1404 | this will change in the future. |
| 1405 | \end{NB} |
| 1406 | |
| 1407 | \paragraph{Examples:} |
| 1408 | \begin{itemize} |
| 1409 | \item add a plain route to network 10.0.0/24 via gateway 193.233.7.65 |
| 1410 | \begin{verbatim} |
| 1411 | ip route add 10.0.0/24 via 193.233.7.65 |
| 1412 | \end{verbatim} |
| 1413 | \item change it to a direct route via the \verb|dummy| device |
| 1414 | \begin{verbatim} |
| 1415 | ip ro chg 10.0.0/24 dev dummy |
| 1416 | \end{verbatim} |
| 1417 | \item add a default multipath route splitting the load between \verb|ppp0| |
| 1418 | and \verb|ppp1| |
| 1419 | \begin{verbatim} |
| 1420 | ip route add default scope global nexthop dev ppp0 \ |
| 1421 | nexthop dev ppp1 |
| 1422 | \end{verbatim} |
| 1423 | Note the scope value. It is not necessary but it informs the kernel |
| 1424 | that this route is gatewayed rather than direct. Actually, if you |
| 1425 | know the addresses of remote endpoints it would be better to use the |
| 1426 | \verb|via| parameter. |
| 1427 | \item announce that the address 192.203.80.144 is not a real one, but |
| 1428 | should be translated to 193.233.7.83 before forwarding |
| 1429 | \begin{verbatim} |
| 1430 | ip route add nat 192.203.80.144 via 193.233.7.83 |
| 1431 | \end{verbatim} |
| 1432 | Backward translation is setup with policy rules described |
| 1433 | in the following section (sec.\ref{IP-RULE}, p.\pageref{IP-RULE}). |
| 1434 | \end{itemize} |
| 1435 | |
| 1436 | \subsection{{\tt ip route delete} --- delete a route} |
| 1437 | |
| 1438 | \paragraph{Abbreviations:} \verb|delete|, \verb|del|, \verb|d|. |
| 1439 | |
| 1440 | \paragraph{Arguments:} \verb|ip route del| has the same arguments as |
| 1441 | \verb|ip route add|, but their semantics are a bit different. |
| 1442 | |
| 1443 | Key values (\verb|to|, \verb|tos|, \verb|preference| and \verb|table|) |
| 1444 | select the route to delete. If optional attributes are present, \verb|ip| |
| 1445 | verifies that they coincide with the attributes of the route to delete. |
| 1446 | If no route with the given key and attributes was found, \verb|ip route del| |
| 1447 | fails. |
| 1448 | \begin{NB} |
| 1449 | Linux-2.0 had the option to delete a route selected only by prefix address, |
| 1450 | ignoring its length (i.e.\ netmask). This option no longer exists |
| 1451 | because it was ambiguous. However, look at {\tt ip route flush} |
| 1452 | (sec.\ref{IP-ROUTE-FLUSH}, p.\pageref{IP-ROUTE-FLUSH}) which |
| 1453 | provides similar and even richer functionality. |
| 1454 | \end{NB} |
| 1455 | |
| 1456 | \paragraph{Example:} |
| 1457 | \begin{itemize} |
| 1458 | \item delete the multipath route created by the command in previous subsection |
| 1459 | \begin{verbatim} |
| 1460 | ip route del default scope global nexthop dev ppp0 \ |
| 1461 | nexthop dev ppp1 |
| 1462 | \end{verbatim} |
| 1463 | \end{itemize} |
| 1464 | |
| 1465 | |
| 1466 | |
| 1467 | \subsection{{\tt ip route show} --- list routes} |
| 1468 | |
| 1469 | \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|sh|, \verb|ls|, \verb|l|. |
| 1470 | |
| 1471 | \paragraph{Description:} the command displays the contents of the routing tables |
| 1472 | or the route(s) selected by some criteria. |
| 1473 | |
| 1474 | |
| 1475 | \paragraph{Arguments:} |
| 1476 | \begin{itemize} |
| 1477 | \item \verb|to SELECTOR| (default) |
| 1478 | |
| 1479 | --- only select routes from the given range of destinations. \verb|SELECTOR| |
| 1480 | consists of an optional modifier (\verb|root|, \verb|match| or \verb|exact|) |
| 1481 | and a prefix. \verb|root PREFIX| selects routes with prefixes not shorter |
| 1482 | than \verb|PREFIX|. F.e.\ \verb|root 0/0| selects the entire routing table. |
| 1483 | \verb|match PREFIX| selects routes with prefixes not longer than |
| 1484 | \verb|PREFIX|. F.e.\ \verb|match 10.0/16| selects \verb|10.0/16|, |
| 1485 | \verb|10/8| and \verb|0/0|, but it does not select \verb|10.1/16| and |
| 1486 | \verb|10.0.0/24|. And \verb|exact PREFIX| (or just \verb|PREFIX|) |
| 1487 | selects routes with this exact prefix. If neither of these options |
| 1488 | are present, \verb|ip| assumes \verb|root 0/0| i.e.\ it lists the entire table. |
| 1489 | |
| 1490 | |
| 1491 | \item \verb|tos TOS| or \verb|dsfield TOS| |
| 1492 | |
| 1493 | --- only select routes with the given TOS. |
| 1494 | |
| 1495 | |
| 1496 | \item \verb|table TABLEID| |
| 1497 | |
| 1498 | --- show the routes from this table(s). The default setting is to show |
| 1499 | \verb|table| \verb|main|. \verb|TABLEID| may either be the ID of a real table |
| 1500 | or one of the special values: |
| 1501 | \begin{itemize} |
| 1502 | \item \verb|all| --- list all of the tables. |
| 1503 | \item \verb|cache| --- dump the routing cache. |
| 1504 | \end{itemize} |
| 1505 | \begin{NB} |
| 1506 | IPv6 has a single table. However, splitting it into \verb|main|, \verb|local| |
| 1507 | and \verb|cache| is emulated by the \verb|ip| utility. |
| 1508 | \end{NB} |
| 1509 | |
| 1510 | \item \verb|cloned| or \verb|cached| |
| 1511 | |
| 1512 | --- list cloned routes i.e.\ routes which were dynamically forked from |
| 1513 | other routes because some route attribute (f.e.\ MTU) was updated. |
| 1514 | Actually, it is equivalent to \verb|table cache|. |
| 1515 | |
| 1516 | \item \verb|from SELECTOR| |
| 1517 | |
| 1518 | --- the same syntax as for \verb|to|, but it binds the source address range |
| 1519 | rather than destinations. Note that the \verb|from| option only works with |
| 1520 | cloned routes. |
| 1521 | |
| 1522 | \item \verb|protocol RTPROTO| |
| 1523 | |
| 1524 | --- only list routes of this protocol. |
| 1525 | |
| 1526 | |
| 1527 | \item \verb|scope SCOPE_VAL| |
| 1528 | |
| 1529 | --- only list routes with this scope. |
| 1530 | |
| 1531 | \item \verb|type TYPE| |
| 1532 | |
| 1533 | --- only list routes of this type. |
| 1534 | |
| 1535 | \item \verb|dev NAME| |
| 1536 | |
| 1537 | --- only list routes going via this device. |
| 1538 | |
| 1539 | \item \verb|via PREFIX| |
| 1540 | |
| 1541 | --- only list routes going via the nexthop routers selected by \verb|PREFIX|. |
| 1542 | |
| 1543 | \item \verb|src PREFIX| |
| 1544 | |
| 1545 | --- only list routes with preferred source addresses selected |
| 1546 | by \verb|PREFIX|. |
| 1547 | |
| 1548 | \item \verb|realm REALMID| or \verb|realms FROMREALM/TOREALM| |
| 1549 | |
| 1550 | --- only list routes with these realms. |
| 1551 | |
| 1552 | \end{itemize} |
| 1553 | |
| 1554 | \paragraph{Examples:} Let us count routes of protocol \verb|gated/bgp| |
| 1555 | on a router: |
| 1556 | \begin{verbatim} |
| 1557 | kuznet@amber:~ $ ip ro ls proto gated/bgp | wc |
| 1558 | 1413 9891 79010 |
| 1559 | kuznet@amber:~ $ |
| 1560 | \end{verbatim} |
| 1561 | To count the size of the routing cache, we have to use the \verb|-o| option |
| 1562 | because cached attributes can take more than one line of output: |
| 1563 | \begin{verbatim} |
| 1564 | kuznet@amber:~ $ ip -o ro ls cloned | wc |
| 1565 | 159 2543 18707 |
| 1566 | kuznet@amber:~ $ |
| 1567 | \end{verbatim} |
| 1568 | |
| 1569 | |
| 1570 | \paragraph{Output format:} The output of this command consists |
| 1571 | of per route records separated by line feeds. |
| 1572 | However, some records may consist |
| 1573 | of more than one line: particularly, this is the case when the route |
| 1574 | is cloned or you requested additional statistics. If the |
| 1575 | \verb|-o| option was given, then line feeds separating lines inside |
| 1576 | records are replaced with the backslash sign. |
| 1577 | |
| 1578 | The output has the same syntax as arguments given to {\tt ip route add}, |
| 1579 | so that it can be understood easily. F.e.\ |
| 1580 | \begin{verbatim} |
| 1581 | kuznet@amber:~ $ ip ro ls 193.233.7/24 |
| 1582 | 193.233.7.0/24 dev eth0 proto gated/conn scope link \ |
| 1583 | src 193.233.7.65 realms inr.ac |
| 1584 | kuznet@amber:~ $ |
| 1585 | \end{verbatim} |
| 1586 | |
| 1587 | If you list cloned entries, the output contains other attributes which |
| 1588 | are evaluated during route calculation and updated during route |
| 1589 | lifetime. An example of the output is: |
| 1590 | \begin{verbatim} |
| 1591 | kuznet@amber:~ $ ip ro ls 193.233.7.82 tab cache |
| 1592 | 193.233.7.82 from 193.233.7.82 dev eth0 src 193.233.7.65 \ |
| 1593 | realms inr.ac/inr.ac |
| 1594 | cache <src-direct,redirect> mtu 1500 rtt 300 iif eth0 |
| 1595 | 193.233.7.82 dev eth0 src 193.233.7.65 realms inr.ac |
| 1596 | cache mtu 1500 rtt 300 |
| 1597 | kuznet@amber:~ $ |
| 1598 | \end{verbatim} |
| 1599 | \begin{NB} |
| 1600 | \label{NB-strange-route} |
| 1601 | The route looks a bit strange, doesn't it? Did you notice that |
| 1602 | it is a path from 193.233.7.82 back to 193.233.82? Well, you will |
| 1603 | see in the section on \verb|ip route get| (p.\pageref{NB-nature-of-strangeness}) |
| 1604 | how it appeared. |
| 1605 | \end{NB} |
| 1606 | The second line, starting with the word \verb|cache|, shows |
| 1607 | additional attributes which normal routes do not possess. |
| 1608 | Cached flags are summarized in angle brackets: |
| 1609 | \begin{itemize} |
| 1610 | \item \verb|local| --- packets are delivered locally. |
| 1611 | It stands for loopback unicast routes, for broadcast routes |
| 1612 | and for multicast routes, if this host is a member of the corresponding |
| 1613 | group. |
| 1614 | |
| 1615 | \item \verb|reject| --- the path is bad. Any attempt to use it results |
| 1616 | in an error. See attribute \verb|error| below (p.\pageref{IP-ROUTE-GET-error}). |
| 1617 | |
| 1618 | \item \verb|mc| --- the destination is multicast. |
| 1619 | |
| 1620 | \item \verb|brd| --- the destination is broadcast. |
| 1621 | |
| 1622 | \item \verb|src-direct| --- the source is on a directly connected |
| 1623 | interface. |
| 1624 | |
| 1625 | \item \verb|redirected| --- the route was created by an ICMP Redirect. |
| 1626 | |
| 1627 | \item \verb|redirect| --- packets going via this route will |
| 1628 | trigger an ICMP redirect. |
| 1629 | |
| 1630 | \item \verb|fastroute| --- the route is eligible to be used for fastroute. |
| 1631 | |
| 1632 | \item \verb|equalize| --- make packet by packet randomization |
| 1633 | along this path. |
| 1634 | |
| 1635 | \item \verb|dst-nat| --- the destination address requires translation. |
| 1636 | |
| 1637 | \item \verb|src-nat| --- the source address requires translation. |
| 1638 | |
| 1639 | \item \verb|masq| --- the source address requires masquerading. |
| 1640 | This feature disappeared in linux-2.4. |
| 1641 | |
| 1642 | \item \verb|notify| --- ({\em not implemented}) change/deletion |
| 1643 | of this route will trigger RTNETLINK notification. |
| 1644 | \end{itemize} |
| 1645 | |
| 1646 | Then some optional attributes follow: |
| 1647 | \begin{itemize} |
| 1648 | \item \verb|error| --- on \verb|reject| routes it is error code |
| 1649 | returned to local senders when they try to use this route. |
| 1650 | These error codes are translated into ICMP error codes, sent to remote |
| 1651 | senders, according to the rules described above in the subsection |
| 1652 | devoted to route types (p.\pageref{IP-ROUTE-TYPES}). |
| 1653 | \label{IP-ROUTE-GET-error} |
| 1654 | |
| 1655 | \item \verb|expires| --- this entry will expire after this timeout. |
| 1656 | |
| 1657 | \item \verb|iif| --- the packets for this path are expected to arrive |
| 1658 | on this interface. |
| 1659 | \end{itemize} |
| 1660 | |
| 1661 | \paragraph{Statistics:} With the \verb|-statistics| option, more |
| 1662 | information about this route is shown: |
| 1663 | \begin{itemize} |
| 1664 | \item \verb|users| --- the number of users of this entry. |
| 1665 | \item \verb|age| --- shows when this route was last used. |
| 1666 | \item \verb|used| --- the number of lookups of this route since its creation. |
| 1667 | \end{itemize} |
| 1668 | |
| 1669 | |
| 1670 | \subsection{{\tt ip route flush} --- flush routing tables} |
| 1671 | \label{IP-ROUTE-FLUSH} |
| 1672 | |
| 1673 | \paragraph{Abbreviations:} \verb|flush|, \verb|f|. |
| 1674 | |
| 1675 | \paragraph{Description:} this command flushes routes selected |
| 1676 | by some criteria. |
| 1677 | |
| 1678 | \paragraph{Arguments:} the arguments have the same syntax and semantics |
| 1679 | as the arguments of \verb|ip route show|, but routing tables are not |
| 1680 | listed but purged. The only difference is the default action: \verb|show| |
| 1681 | dumps all the IP main routing table but \verb|flush| prints the helper page. |
| 1682 | The reason for this difference does not require any explanation, does it? |
| 1683 | |
| 1684 | |
| 1685 | \paragraph{Statistics:} With the \verb|-statistics| option, the command |
| 1686 | becomes verbose. It prints out the number of deleted routes and the number |
| 1687 | of rounds made to flush the routing table. If the option is given |
| 1688 | twice, \verb|ip route flush| also dumps all the deleted routes |
| 1689 | in the format described in the previous subsection. |
| 1690 | |
| 1691 | \paragraph{Examples:} The first example flushes all the |
| 1692 | gatewayed routes from the main table (f.e.\ after a routing daemon crash). |
| 1693 | \begin{verbatim} |
| 1694 | netadm@amber:~ # ip -4 ro flush scope global type unicast |
| 1695 | \end{verbatim} |
| 1696 | This option deserves to be put into a scriptlet \verb|routef|. |
| 1697 | \begin{NB} |
| 1698 | This option was described in the \verb|route(8)| man page borrowed |
| 1699 | from BSD, but was never implemented in Linux. |
| 1700 | \end{NB} |
| 1701 | |
| 1702 | The second example flushes all IPv6 cloned routes: |
| 1703 | \begin{verbatim} |
| 1704 | netadm@amber:~ # ip -6 -s -s ro flush cache |
| 1705 | 3ffe:2400::220:afff:fef4:c5d1 via 3ffe:2400::220:afff:fef4:c5d1 \ |
| 1706 | dev eth0 metric 0 |
| 1707 | cache used 2 age 12sec mtu 1500 rtt 300 |
| 1708 | 3ffe:2400::280:adff:feb7:8034 via 3ffe:2400::280:adff:feb7:8034 \ |
| 1709 | dev eth0 metric 0 |
| 1710 | cache used 2 age 15sec mtu 1500 rtt 300 |
| 1711 | 3ffe:2400::280:c8ff:fe59:5bcc via 3ffe:2400::280:c8ff:fe59:5bcc \ |
| 1712 | dev eth0 metric 0 |
| 1713 | cache users 1 used 1 age 23sec mtu 1500 rtt 300 |
| 1714 | 3ffe:2400:0:1:2a0:ccff:fe66:1878 via 3ffe:2400:0:1:2a0:ccff:fe66:1878 \ |
| 1715 | dev eth1 metric 0 |
| 1716 | cache used 2 age 20sec mtu 1500 rtt 300 |
| 1717 | 3ffe:2400:0:1:a00:20ff:fe71:fb30 via 3ffe:2400:0:1:a00:20ff:fe71:fb30 \ |
| 1718 | dev eth1 metric 0 |
| 1719 | cache used 2 age 33sec mtu 1500 rtt 300 |
| 1720 | ff02::1 via ff02::1 dev eth1 metric 0 |
| 1721 | cache users 1 used 1 age 45sec mtu 1500 rtt 300 |
| 1722 | |
| 1723 | *** Round 1, deleting 6 entries *** |
| 1724 | *** Flush is complete after 1 round *** |
| 1725 | netadm@amber:~ # ip -6 -s -s ro flush cache |
| 1726 | Nothing to flush. |
| 1727 | netadm@amber:~ # |
| 1728 | \end{verbatim} |
| 1729 | |
| 1730 | The third example flushes BGP routing tables after a \verb|gated| |
| 1731 | death. |
| 1732 | \begin{verbatim} |
| 1733 | netadm@amber:~ # ip ro ls proto gated/bgp | wc |
| 1734 | 1408 9856 78730 |
| 1735 | netadm@amber:~ # ip -s ro f proto gated/bgp |
| 1736 | |
| 1737 | *** Round 1, deleting 1408 entries *** |
| 1738 | *** Flush is complete after 1 round *** |
| 1739 | netadm@amber:~ # ip ro f proto gated/bgp |
| 1740 | Nothing to flush. |
| 1741 | netadm@amber:~ # ip ro ls proto gated/bgp |
| 1742 | netadm@amber:~ # |
| 1743 | \end{verbatim} |
| 1744 | |
| 1745 | |
| 1746 | \subsection{{\tt ip route get} --- get a single route} |
| 1747 | \label{IP-ROUTE-GET} |
| 1748 | |
| 1749 | \paragraph{Abbreviations:} \verb|get|, \verb|g|. |
| 1750 | |
| 1751 | \paragraph{Description:} this command gets a single route to a destination |
| 1752 | and prints its contents exactly as the kernel sees it. |
| 1753 | |
| 1754 | \paragraph{Arguments:} |
| 1755 | \begin{itemize} |
| 1756 | \item \verb|to ADDRESS| (default) |
| 1757 | |
| 1758 | --- the destination address. |
| 1759 | |
| 1760 | \item \verb|from ADDRESS| |
| 1761 | |
| 1762 | --- the source address. |
| 1763 | |
| 1764 | \item \verb|tos TOS| or \verb|dsfield TOS| |
| 1765 | |
| 1766 | --- the Type Of Service. |
| 1767 | |
| 1768 | \item \verb|iif NAME| |
| 1769 | |
| 1770 | --- the device from which this packet is expected to arrive. |
| 1771 | |
| 1772 | \item \verb|oif NAME| |
| 1773 | |
| 1774 | --- force the output device on which this packet will be routed. |
| 1775 | |
| 1776 | \item \verb|connected| |
| 1777 | |
| 1778 | --- if no source address (option \verb|from|) was given, relookup |
| 1779 | the route with the source set to the preferred address received from the first lookup. |
| 1780 | If policy routing is used, it may be a different route. |
| 1781 | |
| 1782 | \end{itemize} |
| 1783 | |
| 1784 | Note that this operation is not equivalent to \verb|ip route show|. |
| 1785 | \verb|show| shows existing routes. \verb|get| resolves them and |
| 1786 | creates new clones if necessary. Essentially, \verb|get| |
| 1787 | is equivalent to sending a packet along this path. |
| 1788 | If the \verb|iif| argument is not given, the kernel creates a route |
| 1789 | to output packets towards the requested destination. |
| 1790 | This is equivalent to pinging the destination |
| 1791 | with a subsequent {\tt ip route ls cache}, however, no packets are |
| 1792 | actually sent. With the \verb|iif| argument, the kernel pretends |
| 1793 | that a packet arrived from this interface and searches for |
| 1794 | a path to forward the packet. |
| 1795 | |
| 1796 | \paragraph{Output format:} This command outputs routes in the same |
| 1797 | format as \verb|ip route ls|. |
| 1798 | |
| 1799 | \paragraph{Examples:} |
| 1800 | \begin{itemize} |
| 1801 | \item Find a route to output packets to 193.233.7.82: |
| 1802 | \begin{verbatim} |
| 1803 | kuznet@amber:~ $ ip route get 193.233.7.82 |
| 1804 | 193.233.7.82 dev eth0 src 193.233.7.65 realms inr.ac |
| 1805 | cache mtu 1500 rtt 300 |
| 1806 | kuznet@amber:~ $ |
| 1807 | \end{verbatim} |
| 1808 | |
| 1809 | \item Find a route to forward packets arriving on \verb|eth0| |
| 1810 | from 193.233.7.82 and destined for 193.233.7.82: |
| 1811 | \begin{verbatim} |
| 1812 | kuznet@amber:~ $ ip r g 193.233.7.82 from 193.233.7.82 iif eth0 |
| 1813 | 193.233.7.82 from 193.233.7.82 dev eth0 src 193.233.7.65 \ |
| 1814 | realms inr.ac/inr.ac |
| 1815 | cache <src-direct,redirect> mtu 1500 rtt 300 iif eth0 |
| 1816 | kuznet@amber:~ $ |
| 1817 | \end{verbatim} |
| 1818 | \begin{NB} |
| 1819 | \label{NB-nature-of-strangeness} |
| 1820 | This is the command that created the funny route from 193.233.7.82 |
| 1821 | looped back to 193.233.7.82 (cf.\ NB on~p.\pageref{NB-strange-route}). |
| 1822 | Note the \verb|redirect| flag on it. |
| 1823 | \end{NB} |
| 1824 | |
| 1825 | \item Find a multicast route for packets arriving on \verb|eth0| |
| 1826 | from host 193.233.7.82 and destined for multicast group 224.2.127.254 |
| 1827 | (it is assumed that a multicast routing daemon is running. |
| 1828 | In this case, it is \verb|pimd|) |
| 1829 | \begin{verbatim} |
| 1830 | kuznet@amber:~ $ ip r g 224.2.127.254 from 193.233.7.82 iif eth0 |
| 1831 | multicast 224.2.127.254 from 193.233.7.82 dev lo \ |
| 1832 | src 193.233.7.65 realms inr.ac/cosmos |
| 1833 | cache <mc> iif eth0 Oifs: eth1 pimreg |
| 1834 | kuznet@amber:~ $ |
| 1835 | \end{verbatim} |
| 1836 | This route differs from the ones seen before. It contains a ``normal'' part |
| 1837 | and a ``multicast'' part. The normal part is used to deliver (or not to |
| 1838 | deliver) the packet to local IP listeners. In this case the router |
| 1839 | is not a member |
| 1840 | of this group, so that route has no \verb|local| flag and only |
| 1841 | forwards packets. The output device for such entries is always loopback. |
| 1842 | The multicast part consists of an additional \verb|Oifs:| list showing |
| 1843 | the output interfaces. |
| 1844 | \end{itemize} |
| 1845 | |
| 1846 | |
| 1847 | It is time for a more complicated example. Let us add an invalid |
| 1848 | gatewayed route for a destination which is really directly connected: |
| 1849 | \begin{verbatim} |
| 1850 | netadm@alisa:~ # ip route add 193.233.7.98 via 193.233.7.254 |
| 1851 | netadm@alisa:~ # ip route get 193.233.7.98 |
| 1852 | 193.233.7.98 via 193.233.7.254 dev eth0 src 193.233.7.90 |
| 1853 | cache mtu 1500 rtt 3072 |
| 1854 | netadm@alisa:~ # |
| 1855 | \end{verbatim} |
| 1856 | and probe it with ping: |
| 1857 | \begin{verbatim} |
| 1858 | netadm@alisa:~ # ping -n 193.233.7.98 |
| 1859 | PING 193.233.7.98 (193.233.7.98) from 193.233.7.90 : 56 data bytes |
| 1860 | From 193.233.7.254: Redirect Host(New nexthop: 193.233.7.98) |
| 1861 | 64 bytes from 193.233.7.98: icmp_seq=0 ttl=255 time=3.5 ms |
| 1862 | From 193.233.7.254: Redirect Host(New nexthop: 193.233.7.98) |
| 1863 | 64 bytes from 193.233.7.98: icmp_seq=1 ttl=255 time=2.2 ms |
| 1864 | 64 bytes from 193.233.7.98: icmp_seq=2 ttl=255 time=0.4 ms |
| 1865 | 64 bytes from 193.233.7.98: icmp_seq=3 ttl=255 time=0.4 ms |
| 1866 | 64 bytes from 193.233.7.98: icmp_seq=4 ttl=255 time=0.4 ms |
| 1867 | ^C |
| 1868 | --- 193.233.7.98 ping statistics --- |
| 1869 | 5 packets transmitted, 5 packets received, 0% packet loss |
| 1870 | round-trip min/avg/max = 0.4/1.3/3.5 ms |
| 1871 | netadm@alisa:~ # |
| 1872 | \end{verbatim} |
| 1873 | What happened? Router 193.233.7.254 understood that we have a much |
| 1874 | better path to the destination and sent us an ICMP redirect message. |
| 1875 | We may retry \verb|ip route get| to see what we have in the routing |
| 1876 | tables now: |
| 1877 | \begin{verbatim} |
| 1878 | netadm@alisa:~ # ip route get 193.233.7.98 |
| 1879 | 193.233.7.98 dev eth0 src 193.233.7.90 |
| 1880 | cache <redirected> mtu 1500 rtt 3072 |
| 1881 | netadm@alisa:~ # |
| 1882 | \end{verbatim} |
| 1883 | |
| 1884 | |
| 1885 | |
| 1886 | \section{{\tt ip rule} --- routing policy database management} |
| 1887 | \label{IP-RULE} |
| 1888 | |
| 1889 | \paragraph{Abbreviations:} \verb|rule|, \verb|ru|. |
| 1890 | |
| 1891 | \paragraph{Object:} \verb|rule|s in the routing policy database control |
| 1892 | the route selection algorithm. |
| 1893 | |
| 1894 | Classic routing algorithms used in the Internet make routing decisions |
| 1895 | based only on the destination address of packets (and in theory, |
| 1896 | but not in practice, on the TOS field). The seminal review of classic |
| 1897 | routing algorithms and their modifications can be found in~\cite{RFC1812}. |
| 1898 | |
| 1899 | In some circumstances we want to route packets differently depending not only |
| 1900 | on destination addresses, but also on other packet fields: source address, |
| 1901 | IP protocol, transport protocol ports or even packet payload. |
| 1902 | This task is called ``policy routing''. |
| 1903 | |
| 1904 | \begin{NB} |
| 1905 | ``policy routing'' $\neq$ ``routing policy''. |
| 1906 | |
| 1907 | \noindent ``policy routing'' $=$ ``cunning routing''. |
| 1908 | |
| 1909 | \noindent ``routing policy'' $=$ ``routing tactics'' or ``routing plan''. |
| 1910 | \end{NB} |
| 1911 | |
| 1912 | To solve this task, the conventional destination based routing table, ordered |
| 1913 | according to the longest match rule, is replaced with a ``routing policy |
| 1914 | database'' (or RPDB), which selects routes |
| 1915 | by executing some set of rules. The rules may have lots of keys of different |
| 1916 | natures and therefore they have no natural ordering, but one imposed |
| 1917 | by the administrator. Linux-2.2 RPDB is a linear list of rules |
| 1918 | ordered by numeric priority value. |
| 1919 | RPDB explicitly allows matching a few packet fields: |
| 1920 | |
| 1921 | \begin{itemize} |
| 1922 | \item packet source address. |
| 1923 | \item packet destination address. |
| 1924 | \item TOS. |
| 1925 | \item incoming interface (which is packet metadata, rather than a packet field). |
| 1926 | \end{itemize} |
| 1927 | |
| 1928 | Matching IP protocols and transport ports is also possible, |
| 1929 | indirectly, via \verb|ipchains|, by exploiting their ability |
| 1930 | to mark some classes of packets with \verb|fwmark|. Therefore, |
| 1931 | \verb|fwmark| is also included in the set of keys checked by rules. |
| 1932 | |
| 1933 | Each policy routing rule consists of a {\em selector\/} and an {\em action\/} |
| 1934 | predicate. The RPDB is scanned in the order of increasing priority. The selector |
| 1935 | of each rule is applied to \{source address, destination address, incoming |
| 1936 | interface, tos, fwmark\} and, if the selector matches the packet, |
| 1937 | the action is performed. The action predicate may return with success. |
| 1938 | In this case, it will either give a route or failure indication |
| 1939 | and the RPDB lookup is terminated. Otherwise, the RPDB program |
| 1940 | continues on the next rule. |
| 1941 | |
| 1942 | What is the action, semantically? The natural action is to select the |
| 1943 | nexthop and the output device. This is what |
| 1944 | Cisco IOS~\cite{IOS} does. Let us call it ``match \& set''. |
| 1945 | The Linux-2.2 approach is more flexible. The action includes |
| 1946 | lookups in destination-based routing tables and selecting |
| 1947 | a route from these tables according to the classic longest match algorithm. |
| 1948 | The ``match \& set'' approach is the simplest case of the Linux one. It is realized |
| 1949 | when a second level routing table contains a single default route. |
| 1950 | Recall that Linux-2.2 supports multiple tables |
| 1951 | managed with the \verb|ip route| command, described in the previous section. |
| 1952 | |
| 1953 | At startup time the kernel configures the default RPDB consisting of three |
| 1954 | rules: |
| 1955 | |
| 1956 | \begin{enumerate} |
| 1957 | \item Priority: 0, Selector: match anything, Action: lookup routing |
| 1958 | table \verb|local| (ID 255). |
| 1959 | The \verb|local| table is a special routing table containing |
| 1960 | high priority control routes for local and broadcast addresses. |
| 1961 | |
| 1962 | Rule 0 is special. It cannot be deleted or overridden. |
| 1963 | |
| 1964 | |
| 1965 | \item Priority: 32766, Selector: match anything, Action: lookup routing |
| 1966 | table \verb|main| (ID 254). |
| 1967 | The \verb|main| table is the normal routing table containing all non-policy |
| 1968 | routes. This rule may be deleted and/or overridden with other |
| 1969 | ones by the administrator. |
| 1970 | |
| 1971 | \item Priority: 32767, Selector: match anything, Action: lookup routing |
| 1972 | table \verb|default| (ID 253). |
| 1973 | The \verb|default| table is empty. It is reserved for some |
| 1974 | post-processing if no previous default rules selected the packet. |
| 1975 | This rule may also be deleted. |
| 1976 | |
| 1977 | \end{enumerate} |
| 1978 | |
| 1979 | Do not confuse routing tables with rules: rules point to routing tables, |
| 1980 | several rules may refer to one routing table and some routing tables |
| 1981 | may have no rules pointing to them. If the administrator deletes all the rules |
| 1982 | referring to a table, the table is not used, but it still exists |
| 1983 | and will disappear only after all the routes contained in it are deleted. |
| 1984 | |
| 1985 | |
| 1986 | \paragraph{Rule attributes:} Each RPDB entry has additional |
| 1987 | attributes. F.e.\ each rule has a pointer to some routing |
| 1988 | table. NAT and masquerading rules have an attribute to select new IP |
| 1989 | address to translate/masquerade. Besides that, rules have some |
| 1990 | optional attributes, which routes have, namely \verb|realms|. |
| 1991 | These values do not override those contained in the routing tables. They |
| 1992 | are only used if the route did not select any attributes. |
| 1993 | |
| 1994 | |
| 1995 | \paragraph{Rule types:} The RPDB may contain rules of the following |
| 1996 | types: |
| 1997 | \begin{itemize} |
| 1998 | \item \verb|unicast| --- the rule prescribes to return the route found |
| 1999 | in the routing table referenced by the rule. |
| 2000 | \item \verb|blackhole| --- the rule prescribes to silently drop the packet. |
| 2001 | \item \verb|unreachable| --- the rule prescribes to generate a ``Network |
| 2002 | is unreachable'' error. |
| 2003 | \item \verb|prohibit| --- the rule prescribes to generate |
| 2004 | ``Communication is administratively prohibited'' error. |
| 2005 | \item \verb|nat| --- the rule prescribes to translate the source address |
| 2006 | of the IP packet into some other value. More about NAT is |
| 2007 | in Appendix~\ref{ROUTE-NAT}, p.\pageref{ROUTE-NAT}. |
| 2008 | \end{itemize} |
| 2009 | |
| 2010 | |
| 2011 | \paragraph{Commands:} \verb|add|, \verb|delete| and \verb|show| |
| 2012 | (or \verb|list|). |
| 2013 | |
| 2014 | \subsection{{\tt ip rule add} --- insert a new rule\\ |
| 2015 | {\tt ip rule delete} --- delete a rule} |
| 2016 | \label{IP-RULE-ADD} |
| 2017 | |
| 2018 | \paragraph{Abbreviations:} \verb|add|, \verb|a|; \verb|delete|, \verb|del|, |
| 2019 | \verb|d|. |
| 2020 | |
| 2021 | \paragraph{Arguments:} |
| 2022 | |
| 2023 | \begin{itemize} |
| 2024 | \item \verb|type TYPE| (default) |
| 2025 | |
| 2026 | --- the type of this rule. The list of valid types was given in the previous |
| 2027 | subsection. |
| 2028 | |
| 2029 | \item \verb|from PREFIX| |
| 2030 | |
| 2031 | --- select the source prefix to match. |
| 2032 | |
| 2033 | \item \verb|to PREFIX| |
| 2034 | |
| 2035 | --- select the destination prefix to match. |
| 2036 | |
| 2037 | \item \verb|iif NAME| |
| 2038 | |
| 2039 | --- select the incoming device to match. If the interface is loopback, |
| 2040 | the rule only matches packets originating from this host. This means that you |
| 2041 | may create separate routing tables for forwarded and local packets and, |
| 2042 | hence, completely segregate them. |
| 2043 | |
| 2044 | \item \verb|tos TOS| or \verb|dsfield TOS| |
| 2045 | |
| 2046 | --- select the TOS value to match. |
| 2047 | |
| 2048 | \item \verb|fwmark MARK| |
| 2049 | |
| 2050 | --- select the \verb|fwmark| value to match. |
| 2051 | |
| 2052 | \item \verb|priority PREFERENCE| |
| 2053 | |
| 2054 | --- the priority of this rule. Each rule should have an explicitly |
| 2055 | set {\em unique\/} priority value. |
| 2056 | \begin{NB} |
| 2057 | Really, for historical reasons \verb|ip rule add| does not require a |
| 2058 | priority value and allows them to be non-unique. |
| 2059 | If the user does not supplied a priority, it is selected by the kernel. |
| 2060 | If the user creates a rule with a priority value that |
| 2061 | already exists, the kernel does not reject the request. It adds |
| 2062 | the new rule before all old rules of the same priority. |
| 2063 | |
| 2064 | It is mistake in design, no more. And it will be fixed one day, |
| 2065 | so do not rely on this feature. Use explicit priorities. |
| 2066 | \end{NB} |
| 2067 | |
| 2068 | |
| 2069 | \item \verb|table TABLEID| |
| 2070 | |
| 2071 | --- the routing table identifier to lookup if the rule selector matches. |
| 2072 | |
| 2073 | \item \verb|realms FROM/TO| |
| 2074 | |
| 2075 | --- Realms to select if the rule matched and the routing table lookup |
| 2076 | succeeded. Realm \verb|TO| is only used if the route did not select |
| 2077 | any realm. |
| 2078 | |
| 2079 | \item \verb|nat ADDRESS| |
| 2080 | |
| 2081 | --- The base of the IP address block to translate (for source addresses). |
| 2082 | The \verb|ADDRESS| may be either the start of the block of NAT addresses |
| 2083 | (selected by NAT routes) or in linux-2.2 a local host address (or even zero). |
| 2084 | In the last case the router does not translate the packets, |
| 2085 | but masquerades them to this address; this feature disappered in 2.4. |
| 2086 | More about NAT is in Appendix~\ref{ROUTE-NAT}, |
| 2087 | p.\pageref{ROUTE-NAT}. |
| 2088 | |
| 2089 | \end{itemize} |
| 2090 | |
| 2091 | \paragraph{Warning:} Changes to the RPDB made with these commands |
| 2092 | do not become active immediately. It is assumed that after |
| 2093 | a script finishes a batch of updates, it flushes the routing cache |
| 2094 | with \verb|ip route flush cache|. |
| 2095 | |
| 2096 | \paragraph{Examples:} |
| 2097 | \begin{itemize} |
| 2098 | \item Route packets with source addresses from 192.203.80/24 |
| 2099 | according to routing table \verb|inr.ruhep|: |
| 2100 | \begin{verbatim} |
| 2101 | ip ru add from 192.203.80.0/24 table inr.ruhep prio 220 |
| 2102 | \end{verbatim} |
| 2103 | |
| 2104 | \item Translate packet source address 193.233.7.83 into 192.203.80.144 |
| 2105 | and route it according to table \#1 (actually, it is \verb|inr.ruhep|): |
| 2106 | \begin{verbatim} |
| 2107 | ip ru add from 193.233.7.83 nat 192.203.80.144 table 1 prio 320 |
| 2108 | \end{verbatim} |
| 2109 | |
| 2110 | \item Delete the unused default rule: |
| 2111 | \begin{verbatim} |
| 2112 | ip ru del prio 32767 |
| 2113 | \end{verbatim} |
| 2114 | |
| 2115 | \end{itemize} |
| 2116 | |
| 2117 | |
| 2118 | |
| 2119 | \subsection{{\tt ip rule show} --- list rules} |
| 2120 | \label{IP-RULE-SHOW} |
| 2121 | |
| 2122 | \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|sh|, \verb|ls|, \verb|l|. |
| 2123 | |
| 2124 | |
| 2125 | \paragraph{Arguments:} Good news, this is one command that has no arguments. |
| 2126 | |
| 2127 | \paragraph{Output format:} |
| 2128 | |
| 2129 | \begin{verbatim} |
| 2130 | kuznet@amber:~ $ ip ru ls |
| 2131 | 0: from all lookup local |
| 2132 | 200: from 192.203.80.0/24 to 193.233.7.0/24 lookup main |
| 2133 | 210: from 192.203.80.0/24 to 192.203.80.0/24 lookup main |
| 2134 | 220: from 192.203.80.0/24 lookup inr.ruhep realms inr.ruhep/radio-msu |
| 2135 | 300: from 193.233.7.83 to 193.233.7.0/24 lookup main |
| 2136 | 310: from 193.233.7.83 to 192.203.80.0/24 lookup main |
| 2137 | 320: from 193.233.7.83 lookup inr.ruhep map-to 192.203.80.144 |
| 2138 | 32766: from all lookup main |
| 2139 | kuznet@amber:~ $ |
| 2140 | \end{verbatim} |
| 2141 | |
| 2142 | In the first column is the rule priority value followed |
| 2143 | by a colon. Then the selectors follow. Each key is prefixed |
| 2144 | with the same keyword that was used to create the rule. |
| 2145 | |
| 2146 | The keyword \verb|lookup| is followed by a routing table identifier, |
| 2147 | as it is recorded in the file \verb|/etc/iproute2/rt_tables|. |
| 2148 | |
| 2149 | If the rule does NAT (f.e.\ rule \#320), it is shown by the keyword |
| 2150 | \verb|map-to| followed by the start of the block of addresses to map. |
| 2151 | |
| 2152 | The sense of this example is pretty simple. The prefixes |
| 2153 | 192.203.80.0/24 and 193.233.7.0/24 form the internal network, but |
| 2154 | they are routed differently when the packets leave it. |
| 2155 | Besides that, the host 193.233.7.83 is translated into |
| 2156 | another prefix to look like 192.203.80.144 when talking |
| 2157 | to the outer world. |
| 2158 | |
| 2159 | |
| 2160 | |
| 2161 | \section{{\tt ip maddress} --- multicast addresses management} |
| 2162 | \label{IP-MADDR} |
| 2163 | |
| 2164 | \paragraph{Object:} \verb|maddress| objects are multicast addresses. |
| 2165 | |
| 2166 | \paragraph{Commands:} \verb|add|, \verb|delete|, \verb|show| (or \verb|list|). |
| 2167 | |
| 2168 | \subsection{{\tt ip maddress show} --- list multicast addresses} |
| 2169 | |
| 2170 | \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|sh|, \verb|ls|, \verb|l|. |
| 2171 | |
| 2172 | \paragraph{Arguments:} |
| 2173 | |
| 2174 | \begin{itemize} |
| 2175 | |
| 2176 | \item \verb|dev NAME| (default) |
| 2177 | |
| 2178 | --- the device name. |
| 2179 | |
| 2180 | \end{itemize} |
| 2181 | |
| 2182 | \paragraph{Output format:} |
| 2183 | |
| 2184 | \begin{verbatim} |
| 2185 | kuznet@alisa:~ $ ip maddr ls dummy |
| 2186 | 2: dummy |
| 2187 | link 33:33:00:00:00:01 |
| 2188 | link 01:00:5e:00:00:01 |
| 2189 | inet 224.0.0.1 users 2 |
| 2190 | inet6 ff02::1 |
| 2191 | kuznet@alisa:~ $ |
| 2192 | \end{verbatim} |
| 2193 | |
| 2194 | The first line of the output shows the interface index and its name. |
| 2195 | Then the multicast address list follows. Each line starts with the |
| 2196 | protocol identifier. The word \verb|link| denotes a link layer |
| 2197 | multicast addresses. |
| 2198 | |
| 2199 | If a multicast address has more than one user, the number |
| 2200 | of users is shown after the \verb|users| keyword. |
| 2201 | |
| 2202 | One additional feature not present in the example above |
| 2203 | is the \verb|static| flag, which indicates that the address was joined |
| 2204 | with \verb|ip maddr add|. See the following subsection. |
| 2205 | |
| 2206 | |
| 2207 | |
| 2208 | \subsection{{\tt ip maddress add} --- add a multicast address\\ |
| 2209 | {\tt ip maddress delete} --- delete a multicast address} |
| 2210 | |
| 2211 | \paragraph{Abbreviations:} \verb|add|, \verb|a|; \verb|delete|, \verb|del|, \verb|d|. |
| 2212 | |
| 2213 | \paragraph{Description:} these commands attach/detach |
| 2214 | a static link layer multicast address to listen on the interface. |
| 2215 | Note that it is impossible to join protocol multicast groups |
| 2216 | statically. This command only manages link layer addresses. |
| 2217 | |
| 2218 | |
| 2219 | \paragraph{Arguments:} |
| 2220 | |
| 2221 | \begin{itemize} |
| 2222 | \item \verb|address LLADDRESS| (default) |
| 2223 | |
| 2224 | --- the link layer multicast address. |
| 2225 | |
| 2226 | \item \verb|dev NAME| |
| 2227 | |
| 2228 | --- the device to join/leave this multicast address. |
| 2229 | |
| 2230 | \end{itemize} |
| 2231 | |
| 2232 | |
| 2233 | \paragraph{Example:} Let us continue with the example from the previous subsection. |
| 2234 | |
| 2235 | \begin{verbatim} |
| 2236 | netadm@alisa:~ # ip maddr add 33:33:00:00:00:01 dev dummy |
| 2237 | netadm@alisa:~ # ip -0 maddr ls dummy |
| 2238 | 2: dummy |
| 2239 | link 33:33:00:00:00:01 users 2 static |
| 2240 | link 01:00:5e:00:00:01 |
| 2241 | netadm@alisa:~ # ip maddr del 33:33:00:00:00:01 dev dummy |
| 2242 | \end{verbatim} |
| 2243 | |
| 2244 | \begin{NB} |
| 2245 | Neither \verb|ip| nor the kernel check for multicast address validity. |
| 2246 | Particularly, this means that you can try to load a unicast address |
| 2247 | instead of a multicast address. Most drivers will ignore such addresses, |
| 2248 | but several (f.e.\ Tulip) will intern it to their on-board filter. |
| 2249 | The effects may be strange. Namely, the addresses become additional |
| 2250 | local link addresses and, if you loaded the address of another host |
| 2251 | to the router, wait for duplicated packets on the wire. |
| 2252 | It is not a bug, but rather a hole in the API and intra-kernel interfaces. |
| 2253 | This feature is really more useful for traffic monitoring, but using it |
| 2254 | with Linux-2.2 you {\em have to\/} be sure that the host is not |
| 2255 | a router and, especially, that it is not a transparent proxy or masquerading |
| 2256 | agent. |
| 2257 | \end{NB} |
| 2258 | |
| 2259 | |
| 2260 | |
| 2261 | \section{{\tt ip mroute} --- multicast routing cache management} |
| 2262 | \label{IP-MROUTE} |
| 2263 | |
| 2264 | \paragraph{Abbreviations:} \verb|mroute|, \verb|mr|. |
| 2265 | |
| 2266 | \paragraph{Object:} \verb|mroute| objects are multicast routing cache |
| 2267 | entries created by a user level mrouting daemon |
| 2268 | (f.e.\ \verb|pimd| or \verb|mrouted|). |
| 2269 | |
| 2270 | Due to the limitations of the current interface to the multicast routing |
| 2271 | engine, it is impossible to change \verb|mroute| objects administratively, |
| 2272 | so we may only display them. This limitation will be removed |
| 2273 | in the future. |
| 2274 | |
| 2275 | \paragraph{Commands:} \verb|show| (or \verb|list|). |
| 2276 | |
| 2277 | |
| 2278 | \subsection{{\tt ip mroute show} --- list mroute cache entries} |
| 2279 | |
| 2280 | \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|sh|, \verb|ls|, \verb|l|. |
| 2281 | |
| 2282 | \paragraph{Arguments:} |
| 2283 | |
| 2284 | \begin{itemize} |
| 2285 | \item \verb|to PREFIX| (default) |
| 2286 | |
| 2287 | --- the prefix selecting the destination multicast addresses to list. |
| 2288 | |
| 2289 | |
| 2290 | \item \verb|iif NAME| |
| 2291 | |
| 2292 | --- the interface on which multicast packets are received. |
| 2293 | |
| 2294 | |
| 2295 | \item \verb|from PREFIX| |
| 2296 | |
| 2297 | --- the prefix selecting the IP source addresses of the multicast route. |
| 2298 | |
| 2299 | |
| 2300 | \end{itemize} |
| 2301 | |
| 2302 | \paragraph{Output format:} |
| 2303 | |
| 2304 | \begin{verbatim} |
| 2305 | kuznet@amber:~ $ ip mroute ls |
| 2306 | (193.232.127.6, 224.0.1.39) Iif: unresolved |
| 2307 | (193.232.244.34, 224.0.1.40) Iif: unresolved |
| 2308 | (193.233.7.65, 224.66.66.66) Iif: eth0 Oifs: pimreg |
| 2309 | kuznet@amber:~ $ |
| 2310 | \end{verbatim} |
| 2311 | |
| 2312 | Each line shows one (S,G) entry in the multicast routing cache, |
| 2313 | where S is the source address and G is the multicast group. \verb|Iif| is |
| 2314 | the interface on which multicast packets are expected to arrive. |
| 2315 | If the word \verb|unresolved| is there instead of the interface name, |
| 2316 | it means that the routing daemon still hasn't resolved this entry. |
| 2317 | The keyword \verb|oifs| is followed by a list of output interfaces, separated |
| 2318 | by spaces. If a multicast routing entry is created with non-trivial |
| 2319 | TTL scope, administrative distances are appended to the device names |
| 2320 | in the \verb|oifs| list. |
| 2321 | |
| 2322 | \paragraph{Statistics:} The \verb|-statistics| option also prints the |
| 2323 | number of packets and bytes forwarded along this route and |
| 2324 | the number of packets that arrived on the wrong interface, if this number is not zero. |
| 2325 | |
| 2326 | \begin{verbatim} |
| 2327 | kuznet@amber:~ $ ip -s mr ls 224.66/16 |
| 2328 | (193.233.7.65, 224.66.66.66) Iif: eth0 Oifs: pimreg |
| 2329 | 9383 packets, 300256 bytes |
| 2330 | kuznet@amber:~ $ |
| 2331 | \end{verbatim} |
| 2332 | |
| 2333 | |
| 2334 | \section{{\tt ip tunnel} --- tunnel configuration} |
| 2335 | \label{IP-TUNNEL} |
| 2336 | |
| 2337 | \paragraph{Abbreviations:} \verb|tunnel|, \verb|tunl|. |
| 2338 | |
| 2339 | \paragraph{Object:} \verb|tunnel| objects are tunnels, encapsulating |
| 2340 | packets in IPv4 packets and then sending them over the IP infrastructure. |
| 2341 | |
| 2342 | \paragraph{Commands:} \verb|add|, \verb|delete|, \verb|change|, \verb|show| |
| 2343 | (or \verb|list|). |
| 2344 | |
| 2345 | \paragraph{See also:} A more informal discussion of tunneling |
| 2346 | over IP and the \verb|ip tunnel| command can be found in~\cite{IP-TUNNELS}. |
| 2347 | |
| 2348 | \subsection{{\tt ip tunnel add} --- add a new tunnel\\ |
| 2349 | {\tt ip tunnel change} --- change an existing tunnel\\ |
| 2350 | {\tt ip tunnel delete} --- destroy a tunnel} |
| 2351 | |
| 2352 | \paragraph{Abbreviations:} \verb|add|, \verb|a|; \verb|change|, \verb|chg|; |
| 2353 | \verb|delete|, \verb|del|, \verb|d|. |
| 2354 | |
| 2355 | |
| 2356 | \paragraph{Arguments:} |
| 2357 | |
| 2358 | \begin{itemize} |
| 2359 | |
| 2360 | \item \verb|name NAME| (default) |
| 2361 | |
| 2362 | --- select the tunnel device name. |
| 2363 | |
| 2364 | \item \verb|mode MODE| |
| 2365 | |
| 2366 | --- set the tunnel mode. Three modes are currently available: |
| 2367 | \verb|ipip|, \verb|sit| and \verb|gre|. |
| 2368 | |
| 2369 | \item \verb|remote ADDRESS| |
| 2370 | |
| 2371 | --- set the remote endpoint of the tunnel. |
| 2372 | |
| 2373 | \item \verb|local ADDRESS| |
| 2374 | |
| 2375 | --- set the fixed local address for tunneled packets. |
| 2376 | It must be an address on another interface of this host. |
| 2377 | |
| 2378 | \item \verb|ttl N| |
| 2379 | |
| 2380 | --- set a fixed TTL \verb|N| on tunneled packets. |
| 2381 | \verb|N| is a number in the range 1--255. 0 is a special value |
| 2382 | meaning that packets inherit the TTL value. |
| 2383 | The default value is: \verb|inherit|. |
| 2384 | |
| 2385 | \item \verb|tos T| or \verb|dsfield T| |
| 2386 | |
| 2387 | --- set a fixed TOS \verb|T| on tunneled packets. |
| 2388 | The default value is: \verb|inherit|. |
| 2389 | |
| 2390 | |
| 2391 | |
| 2392 | \item \verb|dev NAME| |
| 2393 | |
| 2394 | --- bind the tunnel to the device \verb|NAME| so that |
| 2395 | tunneled packets will only be routed via this device and will |
| 2396 | not be able to escape to another device when the route to endpoint changes. |
| 2397 | |
| 2398 | \item \verb|nopmtudisc| |
| 2399 | |
| 2400 | --- disable Path MTU Discovery on this tunnel. |
| 2401 | It is enabled by default. Note that a fixed ttl is incompatible |
| 2402 | with this option: tunnelling with a fixed ttl always makes pmtu discovery. |
| 2403 | |
| 2404 | \item \verb|key K|, \verb|ikey K|, \verb|okey K| |
| 2405 | |
| 2406 | --- (only GRE tunnels) use keyed GRE with key \verb|K|. \verb|K| is |
| 2407 | either a number or an IP address-like dotted quad. |
| 2408 | The \verb|key| parameter sets the key to use in both directions. |
| 2409 | The \verb|ikey| and \verb|okey| parameters set different keys for input and output. |
| 2410 | |
| 2411 | |
| 2412 | \item \verb|csum|, \verb|icsum|, \verb|ocsum| |
| 2413 | |
| 2414 | --- (only GRE tunnels) generate/require checksums for tunneled packets. |
| 2415 | The \verb|ocsum| flag calculates checksums for outgoing packets. |
| 2416 | The \verb|icsum| flag requires that all input packets have the correct |
| 2417 | checksum. The \verb|csum| flag is equivalent to the combination |
| 2418 | ``\verb|icsum| \verb|ocsum|''. |
| 2419 | |
| 2420 | \item \verb|seq|, \verb|iseq|, \verb|oseq| |
| 2421 | |
| 2422 | --- (only GRE tunnels) serialize packets. |
| 2423 | The \verb|oseq| flag enables sequencing of outgoing packets. |
| 2424 | The \verb|iseq| flag requires that all input packets are serialized. |
| 2425 | The \verb|seq| flag is equivalent to the combination ``\verb|iseq| \verb|oseq|''. |
| 2426 | |
| 2427 | \begin{NB} |
| 2428 | I think this option does not |
| 2429 | work. At least, I did not test it, did not debug it and |
| 2430 | do not even understand how it is supposed to work or for what |
| 2431 | purpose Cisco planned to use it. Do not use it. |
| 2432 | \end{NB} |
| 2433 | |
| 2434 | |
| 2435 | \end{itemize} |
| 2436 | |
| 2437 | \paragraph{Example:} Create a pointopoint IPv6 tunnel with maximal TTL of 32. |
| 2438 | \begin{verbatim} |
| 2439 | netadm@amber:~ # ip tunl add Cisco mode sit remote 192.31.7.104 \ |
| 2440 | local 192.203.80.142 ttl 32 |
| 2441 | \end{verbatim} |
| 2442 | |
| 2443 | \subsection{{\tt ip tunnel show} --- list tunnels} |
| 2444 | |
| 2445 | \paragraph{Abbreviations:} \verb|show|, \verb|list|, \verb|sh|, \verb|ls|, \verb|l|. |
| 2446 | |
| 2447 | |
| 2448 | \paragraph{Arguments:} None. |
| 2449 | |
| 2450 | \paragraph{Output format:} |
| 2451 | \begin{verbatim} |
| 2452 | kuznet@amber:~ $ ip tunl ls Cisco |
| 2453 | Cisco: ipv6/ip remote 192.31.7.104 local 192.203.80.142 ttl 32 |
| 2454 | kuznet@amber:~ $ |
| 2455 | \end{verbatim} |
| 2456 | The line starts with the tunnel device name followed by a colon. |
| 2457 | Then the tunnel mode follows. The parameters of the tunnel are listed |
| 2458 | with the same keywords that were used when creating the tunnel. |
| 2459 | |
| 2460 | \paragraph{Statistics:} |
| 2461 | |
| 2462 | \begin{verbatim} |
| 2463 | kuznet@amber:~ $ ip -s tunl ls Cisco |
| 2464 | Cisco: ipv6/ip remote 192.31.7.104 local 192.203.80.142 ttl 32 |
| 2465 | RX: Packets Bytes Errors CsumErrs OutOfSeq Mcasts |
| 2466 | 12566 1707516 0 0 0 0 |
| 2467 | TX: Packets Bytes Errors DeadLoop NoRoute NoBufs |
| 2468 | 13445 1879677 0 0 0 0 |
| 2469 | kuznet@amber:~ $ |
| 2470 | \end{verbatim} |
| 2471 | Essentially, these numbers are the same as the numbers |
| 2472 | printed with {\tt ip -s link show} |
| 2473 | (sec.\ref{IP-LINK-SHOW}, p.\pageref{IP-LINK-SHOW}) but the tags are different |
| 2474 | to reflect that they are tunnel specific. |
| 2475 | \begin{itemize} |
| 2476 | \item \verb|CsumErrs| --- the total number of packets dropped |
| 2477 | because of checksum failures for a GRE tunnel with checksumming enabled. |
| 2478 | \item \verb|OutOfSeq| --- the total number of packets dropped |
| 2479 | because they arrived out of sequence for a GRE tunnel with |
| 2480 | serialization enabled. |
| 2481 | \item \verb|Mcasts| --- the total number of multicast packets |
| 2482 | received on a broadcast GRE tunnel. |
| 2483 | \item \verb|DeadLoop| --- the total number of packets which were not |
| 2484 | transmitted because the tunnel is looped back to itself. |
| 2485 | \item \verb|NoRoute| --- the total number of packets which were not |
| 2486 | transmitted because there is no IP route to the remote endpoint. |
| 2487 | \item \verb|NoBufs| --- the total number of packets which were not |
| 2488 | transmitted because the kernel failed to allocate a buffer. |
| 2489 | \end{itemize} |
| 2490 | |
| 2491 | |
| 2492 | \section{{\tt ip monitor} and {\tt rtmon} --- state monitoring} |
| 2493 | \label{IP-MONITOR} |
| 2494 | |
| 2495 | The \verb|ip| utility can monitor the state of devices, addresses |
| 2496 | and routes continuously. This option has a slightly different format. |
| 2497 | Namely, |
| 2498 | the \verb|monitor| command is the first in the command line and then |
| 2499 | the object list follows: |
| 2500 | \begin{verbatim} |
| 2501 | ip monitor [ file FILE ] [ all | OBJECT-LIST ] |
| 2502 | \end{verbatim} |
| 2503 | \verb|OBJECT-LIST| is the list of object types that we want to monitor. |
| 2504 | It may contain \verb|link|, \verb|address| and \verb|route|. |
| 2505 | If no \verb|file| argument is given, \verb|ip| opens RTNETLINK, |
| 2506 | listens on it and dumps state changes in the format described |
| 2507 | in previous sections. |
| 2508 | |
| 2509 | If a file name is given, it does not listen on RTNETLINK, |
| 2510 | but opens the file containing RTNETLINK messages saved in binary format |
| 2511 | and dumps them. Such a history file can be generated with the |
| 2512 | \verb|rtmon| utility. This utility has a command line syntax similar to |
| 2513 | \verb|ip monitor|. |
| 2514 | Ideally, \verb|rtmon| should be started before |
| 2515 | the first network configuration command is issued. F.e.\ if |
| 2516 | you insert: |
| 2517 | \begin{verbatim} |
| 2518 | rtmon file /var/log/rtmon.log |
| 2519 | \end{verbatim} |
| 2520 | in a startup script, you will be able to view the full history |
| 2521 | later. |
| 2522 | |
| 2523 | Certainly, it is possible to start \verb|rtmon| at any time. |
| 2524 | It prepends the history with the state snapshot dumped at the moment |
| 2525 | of starting. |
| 2526 | |
| 2527 | |
| 2528 | \section{Route realms and policy propagation, {\tt rtacct}} |
| 2529 | \label{RT-REALMS} |
| 2530 | |
| 2531 | On routers using OSPF ASE or, especially, the BGP protocol, routing |
| 2532 | tables may be huge. If we want to classify or to account for the packets |
| 2533 | per route, we will have to keep lots of information. Even worse, if we |
| 2534 | want to distinguish the packets not only by their destination, but |
| 2535 | also by their source, the task gets quadratic complexity and its solution |
| 2536 | is physically impossible. |
| 2537 | |
| 2538 | One approach to propagating the policy from routing protocols |
| 2539 | to the forwarding engine has been proposed in~\cite{IOS-BGP-PP}. |
| 2540 | Essentially, Cisco Policy Propagation via BGP is based on the fact |
| 2541 | that dedicated routers all have the RIB (Routing Information Base) |
| 2542 | close to the forwarding engine, so policy routing rules can |
| 2543 | check all the route attributes, including ASPATH information |
| 2544 | and community strings. |
| 2545 | |
| 2546 | The Linux architecture, splitting the RIB (maintained by a user level |
| 2547 | daemon) and the kernel based FIB (Forwarding Information Base), |
| 2548 | does not allow such a simple approach. |
| 2549 | |
| 2550 | It is to our fortune because there is another solution |
| 2551 | which allows even more flexible policy and richer semantics. |
| 2552 | |
| 2553 | Namely, routes can be clustered together in user space, based on their |
| 2554 | attributes. F.e.\ a BGP router knows route ASPATH, its community; |
| 2555 | an OSPF router knows the route tag or its area. The administrator, when adding |
| 2556 | routes manually, also knows their nature. Providing that the number of such |
| 2557 | aggregates (we call them {\em realms\/}) is low, the task of full |
| 2558 | classification both by source and destination becomes quite manageable. |
| 2559 | |
| 2560 | So each route may be assigned to a realm. It is assumed that |
| 2561 | this identification is made by a routing daemon, but static routes |
| 2562 | can also be handled manually with \verb|ip route| (see sec.\ref{IP-ROUTE}, |
| 2563 | p.\pageref{IP-ROUTE}). |
| 2564 | \begin{NB} |
| 2565 | There is a patch to \verb|gated|, allowing classification of routes |
| 2566 | to realms with all the set of policy rules implemented in \verb|gated|: |
| 2567 | by prefix, by ASPATH, by origin, by tag etc. |
| 2568 | \end{NB} |
| 2569 | |
| 2570 | To facilitate the construction (f.e.\ in case the routing |
| 2571 | daemon is not aware of realms), missing realms may be completed |
| 2572 | with routing policy rules, see sec.~\ref{IP-RULE}, p.\pageref{IP-RULE}. |
| 2573 | |
| 2574 | For each packet the kernel calculates a tuple of realms: source realm |
| 2575 | and destination realm, using the following algorithm: |
| 2576 | |
| 2577 | \begin{enumerate} |
| 2578 | \item If the route has a realm, the destination realm of the packet is set to it. |
| 2579 | \item If the rule has a source realm, the source realm of the packet is set to it. |
| 2580 | If the destination realm was not inherited from the route and the rule has a destination realm, |
| 2581 | it is also set. |
| 2582 | \item If at least one of the realms is still unknown, the kernel finds |
| 2583 | the reversed route to the source of the packet. |
| 2584 | \item If the source realm is still unknown, get it from the reversed route. |
| 2585 | \item If one of the realms is still unknown, swap the realms of reversed |
| 2586 | routes and apply step 2 again. |
| 2587 | \end{enumerate} |
| 2588 | |
| 2589 | After this procedure is completed we know what realm the packet |
| 2590 | arrived from and the realm where it is going to propagate to. |
| 2591 | If some of the realms are unknown, they are initialized to zero |
| 2592 | (or realm \verb|unknown|). |
| 2593 | |
| 2594 | The main application of realms is the TC \verb|route| classifier~\cite{TC-CREF}, |
| 2595 | where they are used to help assign packets to traffic classes, |
| 2596 | to account, police and schedule them according to this |
| 2597 | classification. |
| 2598 | |
| 2599 | A much simpler but still very useful application is incoming packet |
| 2600 | accounting by realms. The kernel gathers a packet statistics summary |
| 2601 | which can be viewed with the \verb|rtacct| utility. |
| 2602 | \begin{verbatim} |
| 2603 | kuznet@amber:~ $ rtacct russia |
| 2604 | Realm BytesTo PktsTo BytesFrom PktsFrom |
| 2605 | russia 20576778 169176 47080168 153805 |
| 2606 | kuznet@amber:~ $ |
| 2607 | \end{verbatim} |
| 2608 | This shows that this router received 153805 packets from |
| 2609 | the realm \verb|russia| and forwarded 169176 packets to \verb|russia|. |
| 2610 | The realm \verb|russia| consists of routes with ASPATHs not leaving |
| 2611 | Russia. |
| 2612 | |
| 2613 | Note that locally originating packets are not accounted here, |
| 2614 | \verb|rtacct| shows incoming packets only. Using the \verb|route| |
| 2615 | classifier (see~\cite{TC-CREF}) you can get even more detailed |
| 2616 | accounting information about outgoing packets, optionally |
| 2617 | summarizing traffic not only by source or destination, but |
| 2618 | by any pair of source and destination realms. |
| 2619 | |
| 2620 | |
| 2621 | \begin{thebibliography}{99} |
| 2622 | \addcontentsline{toc}{section}{References} |
| 2623 | \bibitem{RFC-NDISC} T.~Narten, E.~Nordmark, W.~Simpson. |
| 2624 | ``Neighbor Discovery for IP Version 6 (IPv6)'', RFC-2461. |
| 2625 | |
| 2626 | \bibitem{RFC-ADDRCONF} S.~Thomson, T.~Narten. |
| 2627 | ``IPv6 Stateless Address Autoconfiguration'', RFC-2462. |
| 2628 | |
| 2629 | \bibitem{RFC1812} F.~Baker. |
| 2630 | ``Requirements for IP Version 4 Routers'', RFC-1812. |
| 2631 | |
| 2632 | \bibitem{RFC1122} R.~T.~Braden. |
| 2633 | ``Requirements for Internet hosts --- communication layers'', RFC-1122. |
| 2634 | |
| 2635 | \bibitem{IOS} ``Cisco IOS Release 12.0 Network Protocols |
| 2636 | Command Reference, Part 1'' and |
| 2637 | ``Cisco IOS Release 12.0 Quality of Service Solutions |
| 2638 | Configuration Guide: Configuring Policy-Based Routing'',\\ |
| 2639 | http://www.cisco.com/univercd/cc/td/doc/product/software/ios120. |
| 2640 | |
| 2641 | \bibitem{IP-TUNNELS} A.~N.~Kuznetsov. |
| 2642 | ``Tunnels over IP in Linux-2.2'', \\ |
| 2643 | In: {\tt ftp://ftp.inr.ac.ru/ip-routing/iproute2-current.tar.gz}. |
| 2644 | |
| 2645 | \bibitem{TC-CREF} A.~N.~Kuznetsov. ``TC Command Reference'',\\ |
| 2646 | In: {\tt ftp://ftp.inr.ac.ru/ip-routing/iproute2-current.tar.gz}. |
| 2647 | |
| 2648 | \bibitem{IOS-BGP-PP} ``Cisco IOS Release 12.0 Quality of Service Solutions |
| 2649 | Configuration Guide: Configuring QoS Policy Propagation via |
| 2650 | Border Gateway Protocol'',\\ |
| 2651 | http://www.cisco.com/univercd/cc/td/doc/product/software/ios120. |
| 2652 | |
| 2653 | \bibitem{RFC-DHCP} R.~Droms. |
| 2654 | ``Dynamic Host Configuration Protocol.'', RFC-2131 |
| 2655 | |
| 2656 | \end{thebibliography} |
| 2657 | |
| 2658 | |
| 2659 | |
| 2660 | |
| 2661 | \appendix |
| 2662 | \addcontentsline{toc}{section}{Appendix} |
| 2663 | |
| 2664 | \section{Source address selection} |
| 2665 | \label{ADDR-SEL} |
| 2666 | |
| 2667 | When a host creates an IP packet, it must select some source |
| 2668 | address. Correct source address selection is a critical procedure, |
| 2669 | because it gives the receiver the information needed to deliver a |
| 2670 | reply. If the source is selected incorrectly, in the best case, |
| 2671 | the backward path may appear different to the forward one which |
| 2672 | is harmful for performance. In the worst case, when the addresses |
| 2673 | are administratively scoped, the reply may be lost entirely. |
| 2674 | |
| 2675 | Linux-2.2 selects source addresses using the following algorithm: |
| 2676 | |
| 2677 | \begin{itemize} |
| 2678 | \item |
| 2679 | The application may select a source address explicitly with \verb|bind(2)| |
| 2680 | syscall or supplying it to \verb|sendmsg(2)| via the ancillary data object |
| 2681 | \verb|IP_PKTINFO|. In this case the kernel only checks the validity |
| 2682 | of the address and never tries to ``improve'' an incorrect user choice, |
| 2683 | generating an error instead. |
| 2684 | \begin{NB} |
| 2685 | Never say ``Never''. The sysctl option \verb|ip_dynaddr| breaks |
| 2686 | this axiom. It has been made deliberately with the purpose |
| 2687 | of automatically reselecting the address on hosts with dynamic dial-out interfaces. |
| 2688 | However, this hack {\em must not\/} be used on multihomed hosts |
| 2689 | and especially on routers: it would break them. |
| 2690 | \end{NB} |
| 2691 | |
| 2692 | |
| 2693 | \item Otherwise, IP routing tables can contain an explicit source |
| 2694 | address hint for this destination. The hint is set with the \verb|src| parameter |
| 2695 | to the \verb|ip route| command, sec.\ref{IP-ROUTE}, p.\pageref{IP-ROUTE}. |
| 2696 | |
| 2697 | |
| 2698 | \item Otherwise, the kernel searches through the list of addresses |
| 2699 | attached to the interface through which the packets will be routed. |
| 2700 | The search strategies are different for IP and IPv6. Namely: |
| 2701 | |
| 2702 | \begin{itemize} |
| 2703 | \item IPv6 searches for the first valid, not deprecated address |
| 2704 | with the same scope as the destination. |
| 2705 | |
| 2706 | \item IP searches for the first valid address with a scope wider |
| 2707 | than the scope of the destination but it prefers addresses |
| 2708 | which fall to the same subnet as the nexthop of the route |
| 2709 | to the destination. Unlike IPv6, the scopes of IPv4 destinations |
| 2710 | are not encoded in their addresses but are supplied |
| 2711 | in routing tables instead (the \verb|scope| parameter to the \verb|ip route| command, |
| 2712 | sec.\ref{IP-ROUTE}, p.\pageref{IP-ROUTE}). |
| 2713 | |
| 2714 | \end{itemize} |
| 2715 | |
| 2716 | |
| 2717 | \item Otherwise, if the scope of the destination is \verb|link| or \verb|host|, |
| 2718 | the algorithm fails and returns a zero source address. |
| 2719 | |
| 2720 | \item Otherwise, all interfaces are scanned to search for an address |
| 2721 | with an appropriate scope. The loopback device \verb|lo| is always the first |
| 2722 | in the search list, so that if an address with global scope (not 127.0.0.1!) |
| 2723 | is configured on loopback, it is always preferred. |
| 2724 | |
| 2725 | \end{itemize} |
| 2726 | |
| 2727 | |
| 2728 | \section{Proxy ARP/NDISC} |
| 2729 | \label{PROXY-NEIGH} |
| 2730 | |
| 2731 | Routers may answer ARP/NDISC solicitations on behalf of other hosts. |
| 2732 | In Linux-2.2 proxy ARP on an interface may be enabled |
| 2733 | by setting the kernel \verb|sysctl| variable |
| 2734 | \verb|/proc/sys/net/ipv4/conf/<dev>/proxy_arp| to 1. After this, the router |
| 2735 | starts to answer ARP requests on the interface \verb|<dev>|, provided |
| 2736 | the route to the requested destination does {\em not\/} go back via the same |
| 2737 | device. |
| 2738 | |
| 2739 | The variable \verb|/proc/sys/net/ipv4/conf/all/proxy_arp| enables proxy |
| 2740 | ARP on all the IP devices. |
| 2741 | |
| 2742 | However, this approach fails in the case of IPv6 because the router |
| 2743 | must join the solicited node multicast address to listen for the corresponding |
| 2744 | NDISC queries. It means that proxy NDISC is possible only on a per destination |
| 2745 | basis. |
| 2746 | |
| 2747 | Logically, proxy ARP/NDISC is not a kernel task. It can easily be implemented |
| 2748 | in user space. However, similar functionality was present in BSD kernels |
| 2749 | and in Linux-2.0, so we have to preserve it at least to the extent that |
| 2750 | is standardized in BSD. |
| 2751 | \begin{NB} |
| 2752 | Linux-2.0 ARP had a feature called {\em subnet\/} proxy ARP. |
| 2753 | It is replaced with the sysctl flag in Linux-2.2. |
| 2754 | \end{NB} |
| 2755 | |
| 2756 | |
| 2757 | The \verb|ip| utility provides a way to manage proxy ARP/NDISC |
| 2758 | with the \verb|ip neigh| command, namely: |
| 2759 | \begin{verbatim} |
| 2760 | ip neigh add proxy ADDRESS [ dev NAME ] |
| 2761 | \end{verbatim} |
| 2762 | adds a new proxy ARP/NDISC record and |
| 2763 | \begin{verbatim} |
| 2764 | ip neigh del proxy ADDRESS [ dev NAME ] |
| 2765 | \end{verbatim} |
| 2766 | deletes it. |
| 2767 | |
| 2768 | If the name of the device is not given, the router will answer solicitations |
| 2769 | for address \verb|ADDRESS| on all devices, otherwise it will only serve |
| 2770 | the device \verb|NAME|. Even if the proxy entry is created with |
| 2771 | \verb|ip neigh|, the router {\em will not\/} answer a query if the route |
| 2772 | to the destination goes back via the interface from which the solicitation |
| 2773 | was received. |
| 2774 | |
| 2775 | It is important to emphasize that proxy entries have {\em no\/} |
| 2776 | parameters other than these (IP/IPv6 address and optional device). |
| 2777 | Particularly, the entry does not store any link layer address. |
| 2778 | It always advertises the station address of the interface |
| 2779 | on which it sends advertisements (i.e. it's own station address). |
| 2780 | |
| 2781 | \section{Route NAT status} |
| 2782 | \label{ROUTE-NAT} |
| 2783 | |
| 2784 | NAT (or ``Network Address Translation'') remaps some parts |
| 2785 | of the IP address space into other ones. Linux-2.2 route NAT is supposed |
| 2786 | to be used to facilitate policy routing by rewriting addresses |
| 2787 | to other routing domains or to help while renumbering sites |
| 2788 | to another prefix. |
| 2789 | |
| 2790 | \paragraph{What it is not:} |
| 2791 | It is necessary to emphasize that {\em it is not supposed\/} |
| 2792 | to be used to compress address space or to split load. |
| 2793 | This is not missing functionality but a design principle. |
| 2794 | Route NAT is {\em stateless\/}. It does not hold any state |
| 2795 | about translated sessions. This means that it handles any number |
| 2796 | of sessions flawlessly. But it also means that it is {\em static\/}. |
| 2797 | It cannot detect the moment when the last TCP client stops |
| 2798 | using an address. For the same reason, it will not help to split |
| 2799 | load between several servers. |
| 2800 | \begin{NB} |
| 2801 | It is a pretty commonly held belief that it is useful to split load between |
| 2802 | several servers with NAT. This is a mistake. All you get from this |
| 2803 | is the requirement that the router keep the state of all the TCP connections |
| 2804 | going via it. Well, if the router is so powerful, run apache on it. 8) |
| 2805 | \end{NB} |
| 2806 | |
| 2807 | The second feature: it does not touch packet payload, |
| 2808 | does not try to ``improve'' broken protocols by looking |
| 2809 | through its data and mangling it. It mangles IP addresses, |
| 2810 | only IP addresses and nothing but IP addresses. |
| 2811 | This also, is not missing any functionality. |
| 2812 | |
| 2813 | To resume: if you need to compress address space or keep |
| 2814 | active FTP clients happy, your choice is not route NAT but masquerading, |
| 2815 | port forwarding, NAPT etc. |
| 2816 | \begin{NB} |
| 2817 | By the way, you may also want to look at |
| 2818 | http://www.suse.com/\~mha/HyperNews/get/linux-ip-nat.html |
| 2819 | \end{NB} |
| 2820 | |
| 2821 | |
| 2822 | \paragraph{How it works.} |
| 2823 | Some part of the address space is reserved for dummy addresses |
| 2824 | which will look for all the world like some host addresses |
| 2825 | inside your network. No other hosts may use these addresses, |
| 2826 | however other routers may also be configured to translate them. |
| 2827 | \begin{NB} |
| 2828 | A great advantage of route NAT is that it may be used not |
| 2829 | only in stub networks but in environments with arbitrarily complicated |
| 2830 | structure. It does not firewall, it {\em forwards.} |
| 2831 | \end{NB} |
| 2832 | These addresses are selected by the \verb|ip route| command |
| 2833 | (sec.\ref{IP-ROUTE-ADD}, p.\pageref{IP-ROUTE-ADD}). F.e.\ |
| 2834 | \begin{verbatim} |
| 2835 | ip route add nat 192.203.80.144 via 193.233.7.83 |
| 2836 | \end{verbatim} |
| 2837 | states that the single address 192.203.80.144 is a dummy NAT address. |
| 2838 | For all the world it looks like a host address inside our network. |
| 2839 | For neighbouring hosts and routers it looks like the local address |
| 2840 | of the translating router. The router answers ARP for it, advertises |
| 2841 | this address as routed via it, {\em et al\/}. When the router |
| 2842 | receives a packet destined for 192.203.80.144, it replaces |
| 2843 | this address with 193.233.7.83 which is the address of some real |
| 2844 | host and forwards the packet. If you need to remap |
| 2845 | blocks of addresses, you may use a command like: |
| 2846 | \begin{verbatim} |
| 2847 | ip route add nat 192.203.80.192/26 via 193.233.7.64 |
| 2848 | \end{verbatim} |
| 2849 | This command will map a block of 63 addresses 192.203.80.192-255 to |
| 2850 | 193.233.7.64-127. |
| 2851 | |
| 2852 | When an internal host (193.233.7.83 in the example above) |
| 2853 | sends something to the outer world and these packets are forwarded |
| 2854 | by our router, it should translate the source address 193.233.7.83 |
| 2855 | into 192.203.80.144. This task is solved by setting a special |
| 2856 | policy rule (sec.\ref{IP-RULE-ADD}, p.\pageref{IP-RULE-ADD}): |
| 2857 | \begin{verbatim} |
| 2858 | ip rule add prio 320 from 193.233.7.83 nat 192.203.80.144 |
| 2859 | \end{verbatim} |
| 2860 | This rule says that the source address 193.233.7.83 |
| 2861 | should be translated into 192.203.80.144 before forwarding. |
| 2862 | It is important that the address after the \verb|nat| keyword |
| 2863 | is some NAT address, declared by {\tt ip route add nat}. |
| 2864 | If it is just a random address the router will not map to it. |
| 2865 | \begin{NB} |
| 2866 | The exception is when the address is a local address of this |
| 2867 | router (or 0.0.0.0) and masquerading is configured in the linux-2.2 |
| 2868 | kernel. In this case the router will masquerade the packets as this address. |
| 2869 | If 0.0.0.0 is selected, the result is equivalent to one |
| 2870 | obtained with firewalling rules. Otherwise, you have the way |
| 2871 | to order Linux to masquerade to this fixed address. |
| 2872 | NAT mechanism used in linux-2.4 is more flexible than |
| 2873 | masquerading, so that this feature has lost meaning and disabled. |
| 2874 | \end{NB} |
| 2875 | |
| 2876 | If the network has non-trivial internal structure, it is |
| 2877 | useful and even necessary to add rules disabling translation |
| 2878 | when a packet does not leave this network. Let us return to the |
| 2879 | example from sec.\ref{IP-RULE-SHOW} (p.\pageref{IP-RULE-SHOW}). |
| 2880 | \begin{verbatim} |
| 2881 | 300: from 193.233.7.83 to 193.233.7.0/24 lookup main |
| 2882 | 310: from 193.233.7.83 to 192.203.80.0/24 lookup main |
| 2883 | 320: from 193.233.7.83 lookup inr.ruhep map-to 192.203.80.144 |
| 2884 | \end{verbatim} |
| 2885 | This block of rules causes normal forwarding when |
| 2886 | packets from 193.233.7.83 do not leave networks 193.233.7/24 |
| 2887 | and 192.203.80/24. Also, if the \verb|inr.ruhep| table does not |
| 2888 | contain a route to the destination (which means that the routing |
| 2889 | domain owning addresses from 192.203.80/24 is dead), no translation |
| 2890 | will occur. Otherwise, the packets are translated. |
| 2891 | |
| 2892 | \paragraph{How to only translate selected ports:} |
| 2893 | If you only want to translate selected ports (f.e.\ http) |
| 2894 | and leave the rest intact, you may use \verb|ipchains| |
| 2895 | to \verb|fwmark| a class of packets. |
| 2896 | Suppose you did and all the packets from 193.233.7.83 |
| 2897 | destined for port 80 are marked with marker 0x1234 in input fwchain. |
| 2898 | In this case you may replace rule \#320 with: |
| 2899 | \begin{verbatim} |
| 2900 | 320: from 193.233.7.83 fwmark 1234 lookup main map-to 192.203.80.144 |
| 2901 | \end{verbatim} |
| 2902 | and translation will only be enabled for outgoing http requests. |
| 2903 | |
| 2904 | \section{Example: minimal host setup} |
| 2905 | \label{EXAMPLE-SETUP} |
| 2906 | |
| 2907 | The following script gives an example of a fault safe |
| 2908 | setup of IP (and IPv6, if it is compiled into the kernel) |
| 2909 | in the common case of a node attached to a single broadcast |
| 2910 | network. A more advanced script, which may be used both on multihomed |
| 2911 | hosts and on routers, is described in the following |
| 2912 | section. |
| 2913 | |
| 2914 | The utilities used in the script may be found in the |
| 2915 | directory ftp://ftp.inr.ac.ru/ip-routing/: |
| 2916 | \begin{enumerate} |
| 2917 | \item \verb|ip| --- package \verb|iproute2|. |
| 2918 | \item \verb|arping| --- package \verb|iputils|. |
| 2919 | \item \verb|rdisc| --- package \verb|iputils|. |
| 2920 | \end{enumerate} |
| 2921 | \begin{NB} |
| 2922 | It also refers to a DHCP client, \verb|dhcpcd|. I should refrain from |
| 2923 | recommending a good DHCP client to use. All that I can |
| 2924 | say is that ISC \verb|dhcp-2.0b1pl6| patched with the patch that |
| 2925 | can be found in the \verb|dhcp.bootp.rarp| subdirectory of |
| 2926 | the same ftp site {\em does\/} work, |
| 2927 | at least on Ethernet and Token Ring. |
| 2928 | \end{NB} |
| 2929 | |
| 2930 | \begin{verbatim} |
| 2931 | #! /bin/bash |
| 2932 | \end{verbatim} |
| 2933 | \begin{flushleft} |
| 2934 | \# {\bf Usage: \verb|ifone ADDRESS[/PREFIX-LENGTH] [DEVICE]|}\\ |
| 2935 | \# {\bf Parameters:}\\ |
| 2936 | \# \$1 --- Static IP address, optionally followed by prefix length.\\ |
| 2937 | \# \$2 --- Device name. If it is missing, \verb|eth0| is asssumed.\\ |
| 2938 | \# F.e. \verb|ifone 193.233.7.90| |
| 2939 | \end{flushleft} |
| 2940 | \begin{verbatim} |
| 2941 | dev=$2 |
| 2942 | : ${dev:=eth0} |
| 2943 | ipaddr= |
| 2944 | \end{verbatim} |
| 2945 | \# Parse IP address, splitting prefix length. |
| 2946 | \begin{verbatim} |
| 2947 | if [ "$1" != "" ]; then |
| 2948 | ipaddr=${1%/*} |
| 2949 | if [ "$1" != "$ipaddr" ]; then |
| 2950 | pfxlen=${1#*/} |
| 2951 | fi |
| 2952 | : ${pfxlen:=24} |
| 2953 | fi |
| 2954 | pfx="${ipaddr}/${pfxlen}" |
| 2955 | \end{verbatim} |
| 2956 | |
| 2957 | \begin{flushleft} |
| 2958 | \# {\bf Step 0} --- enable loopback.\\ |
| 2959 | \#\\ |
| 2960 | \# This step is necessary on any networked box before attempt\\ |
| 2961 | \# to configure any other device.\\ |
| 2962 | \end{flushleft} |
| 2963 | \begin{verbatim} |
| 2964 | ip link set up dev lo |
| 2965 | ip addr add 127.0.0.1/8 dev lo brd + scope host |
| 2966 | \end{verbatim} |
| 2967 | \begin{flushleft} |
| 2968 | \# IPv6 autoconfigure themself on loopback.\\ |
| 2969 | \#\\ |
| 2970 | \# If user gave loopback as device, we add the address as alias and exit. |
| 2971 | \end{flushleft} |
| 2972 | \begin{verbatim} |
| 2973 | if [ "$dev" = "lo" ]; then |
| 2974 | if [ "$ipaddr" != "" -a "$ipaddr" != "127.0.0.1" ]; then |
| 2975 | ip address add $ipaddr dev $dev |
| 2976 | exit $? |
| 2977 | fi |
| 2978 | exit 0 |
| 2979 | fi |
| 2980 | \end{verbatim} |
| 2981 | |
| 2982 | \noindent\# {\bf Step 1} --- enable device \verb|$dev| |
| 2983 | |
| 2984 | \begin{verbatim} |
| 2985 | if ! ip link set up dev $dev ; then |
| 2986 | echo "Cannot enable interface $dev. Aborting." 1>&2 |
| 2987 | exit 1 |
| 2988 | fi |
| 2989 | \end{verbatim} |
| 2990 | \begin{flushleft} |
| 2991 | \# The interface is \verb|UP|. IPv6 started stateless autoconfiguration itself,\\ |
| 2992 | \# and its configuration finishes here. However,\\ |
| 2993 | \# IP still needs some static preconfigured address. |
| 2994 | \end{flushleft} |
| 2995 | \begin{verbatim} |
| 2996 | if [ "$ipaddr" = "" ]; then |
| 2997 | echo "No address for $dev is configured, trying DHCP..." 1>&2 |
| 2998 | dhcpcd |
| 2999 | exit $? |
| 3000 | fi |
| 3001 | \end{verbatim} |
| 3002 | |
| 3003 | \begin{flushleft} |
| 3004 | \# {\bf Step 2} --- IP Duplicate Address Detection~\cite{RFC-DHCP}.\\ |
| 3005 | \# Send two probes and wait for result for 3 seconds.\\ |
| 3006 | \# If the interface opens slower f.e.\ due to long media detection,\\ |
| 3007 | \# you want to increase the timeout.\\ |
| 3008 | \end{flushleft} |
| 3009 | \begin{verbatim} |
| 3010 | if ! arping -q -c 2 -w 3 -D -I $dev $ipaddr ; then |
| 3011 | echo "Address $ipaddr is busy, trying DHCP..." 1>&2 |
| 3012 | dhcpcd |
| 3013 | exit $? |
| 3014 | fi |
| 3015 | \end{verbatim} |
| 3016 | \begin{flushleft} |
| 3017 | \# OK, the address is unique, we may add it on the interface.\\ |
| 3018 | \#\\ |
| 3019 | \# {\bf Step 3} --- Configure the address on the interface. |
| 3020 | \end{flushleft} |
| 3021 | |
| 3022 | \begin{verbatim} |
| 3023 | if ! ip address add $pfx brd + dev $dev; then |
| 3024 | echo "Failed to add $pfx on $dev, trying DHCP..." 1>&2 |
| 3025 | dhcpcd |
| 3026 | exit $? |
| 3027 | fi |
| 3028 | \end{verbatim} |
| 3029 | |
| 3030 | \noindent\# {\bf Step 4} --- Announce our presence on the link. |
| 3031 | \begin{verbatim} |
| 3032 | arping -A -c 1 -I $dev $ipaddr |
| 3033 | noarp=$? |
| 3034 | ( sleep 2; |
| 3035 | arping -U -c 1 -I $dev $ipaddr ) >& /dev/null </dev/null & |
| 3036 | \end{verbatim} |
| 3037 | |
| 3038 | \begin{flushleft} |
| 3039 | \# {\bf Step 5} (optional) --- Add some control routes.\\ |
| 3040 | \#\\ |
| 3041 | \# 1. Prohibit link local multicast addresses.\\ |
| 3042 | \# 2. Prohibit link local (alias, limited) broadcast.\\ |
| 3043 | \# 3. Add default multicast route. |
| 3044 | \end{flushleft} |
| 3045 | \begin{verbatim} |
| 3046 | ip route add unreachable 224.0.0.0/24 |
| 3047 | ip route add unreachable 255.255.255.255 |
| 3048 | if [ `ip link ls $dev | grep -c MULTICAST` -ge 1 ]; then |
| 3049 | ip route add 224.0.0.0/4 dev $dev scope global |
| 3050 | fi |
| 3051 | \end{verbatim} |
| 3052 | |
| 3053 | \begin{flushleft} |
| 3054 | \# {\bf Step 6} --- Add fallback default route with huge metric.\\ |
| 3055 | \# If a proxy ARP server is present on the interface, we will be\\ |
| 3056 | \# able to talk to all the Internet without further configuration.\\ |
| 3057 | \# It is not so cheap though and we still hope that this route\\ |
| 3058 | \# will be overridden by more correct one by rdisc.\\ |
| 3059 | \# Do not make this step if the device is not ARPable,\\ |
| 3060 | \# because dead nexthop detection does not work on them. |
| 3061 | \end{flushleft} |
| 3062 | \begin{verbatim} |
| 3063 | if [ "$noarp" = "0" ]; then |
| 3064 | ip ro add default dev $dev metric 30000 scope global |
| 3065 | fi |
| 3066 | \end{verbatim} |
| 3067 | |
| 3068 | \begin{flushleft} |
| 3069 | \# {\bf Step 7} --- Restart router discovery and exit. |
| 3070 | \end{flushleft} |
| 3071 | \begin{verbatim} |
| 3072 | killall -HUP rdisc || rdisc -fs |
| 3073 | exit 0 |
| 3074 | \end{verbatim} |
| 3075 | |
| 3076 | |
| 3077 | \section{Example: {\protect\tt ifcfg} --- interface address management} |
| 3078 | \label{EXAMPLE-IFCFG} |
| 3079 | |
| 3080 | This is a simplistic script replacing one option of \verb|ifconfig|, |
| 3081 | namely, IP address management. It not only adds |
| 3082 | addresses, but also carries out Duplicate Address Detection~\cite{RFC-DHCP}, |
| 3083 | sends unsolicited ARP to update the caches of other hosts sharing |
| 3084 | the interface, adds some control routes and restarts Router Discovery |
| 3085 | when it is necessary. |
| 3086 | |
| 3087 | I strongly recommend using it {\em instead\/} of \verb|ifconfig| both |
| 3088 | on hosts and on routers. |
| 3089 | |
| 3090 | \begin{verbatim} |
| 3091 | #! /bin/bash |
| 3092 | \end{verbatim} |
| 3093 | \begin{flushleft} |
| 3094 | \# {\bf Usage: \verb?ifcfg DEVICE[:ALIAS] [add|del] ADDRESS[/LENGTH] [PEER]?}\\ |
| 3095 | \# {\bf Parameters:}\\ |
| 3096 | \# ---Device name. It may have alias suffix, separated by colon.\\ |
| 3097 | \# ---Command: add, delete or stop.\\ |
| 3098 | \# ---IP address, optionally followed by prefix length.\\ |
| 3099 | \# ---Optional peer address for pointopoint interfaces.\\ |
| 3100 | \# F.e. \verb|ifcfg eth0 193.233.7.90/24| |
| 3101 | |
| 3102 | \noindent\# This function determines, whether it is router or host.\\ |
| 3103 | \# It returns 0, if the host is apparently not router. |
| 3104 | \end{flushleft} |
| 3105 | \begin{verbatim} |
| 3106 | CheckForwarding () { |
| 3107 | local sbase fwd |
| 3108 | sbase=/proc/sys/net/ipv4/conf |
| 3109 | fwd=0 |
| 3110 | if [ -d $sbase ]; then |
| 3111 | for dir in $sbase/*/forwarding; do |
| 3112 | fwd=$[$fwd + `cat $dir`] |
| 3113 | done |
| 3114 | else |
| 3115 | fwd=2 |
| 3116 | fi |
| 3117 | return $fwd |
| 3118 | } |
| 3119 | \end{verbatim} |
| 3120 | \begin{flushleft} |
| 3121 | \# This function restarts Router Discovery.\\ |
| 3122 | \end{flushleft} |
| 3123 | \begin{verbatim} |
| 3124 | RestartRDISC () { |
| 3125 | killall -HUP rdisc || rdisc -fs |
| 3126 | } |
| 3127 | \end{verbatim} |
| 3128 | \begin{flushleft} |
| 3129 | \# Calculate ABC "natural" mask length\\ |
| 3130 | \# Arg: \$1 = dotquad address |
| 3131 | \end{flushleft} |
| 3132 | \begin{verbatim} |
| 3133 | ABCMaskLen () { |
| 3134 | local class; |
| 3135 | class=${1%%.*} |
| 3136 | if [ $class -eq 0 -o $class -ge 224 ]; then return 0 |
| 3137 | elif [ $class -ge 192 ]; then return 24 |
| 3138 | elif [ $class -ge 128 ]; then return 16 |
| 3139 | else return 8 ; fi |
| 3140 | } |
| 3141 | \end{verbatim} |
| 3142 | |
| 3143 | |
| 3144 | \begin{flushleft} |
| 3145 | \# {\bf MAIN()}\\ |
| 3146 | \#\\ |
| 3147 | \# Strip alias suffix separated by colon. |
| 3148 | \end{flushleft} |
| 3149 | \begin{verbatim} |
| 3150 | label="label $1" |
| 3151 | ldev=$1 |
| 3152 | dev=${1%:*} |
| 3153 | if [ "$dev" = "" -o "$1" = "help" ]; then |
| 3154 | echo "Usage: ifcfg DEV [[add|del [ADDR[/LEN]] [PEER] | stop]" 1>&2 |
| 3155 | echo " add - add new address" 1>&2 |
| 3156 | echo " del - delete address" 1>&2 |
| 3157 | echo " stop - completely disable IP" 1>&2 |
| 3158 | exit 1 |
| 3159 | fi |
| 3160 | shift |
| 3161 | |
| 3162 | CheckForwarding |
| 3163 | fwd=$? |
| 3164 | \end{verbatim} |
| 3165 | \begin{flushleft} |
| 3166 | \# Parse command. If it is ``stop'', flush and exit. |
| 3167 | \end{flushleft} |
| 3168 | \begin{verbatim} |
| 3169 | deleting=0 |
| 3170 | case "$1" in |
| 3171 | add) shift ;; |
| 3172 | stop) |
| 3173 | if [ "$ldev" != "$dev" ]; then |
| 3174 | echo "Cannot stop alias $ldev" 1>&2 |
| 3175 | exit 1; |
| 3176 | fi |
| 3177 | ip -4 addr flush dev $dev $label || exit 1 |
| 3178 | if [ $fwd -eq 0 ]; then RestartRDISC; fi |
| 3179 | exit 0 ;; |
| 3180 | del*) |
| 3181 | deleting=1; shift ;; |
| 3182 | *) |
| 3183 | esac |
| 3184 | \end{verbatim} |
| 3185 | \begin{flushleft} |
| 3186 | \# Parse prefix, split prefix length, separated by slash. |
| 3187 | \end{flushleft} |
| 3188 | \begin{verbatim} |
| 3189 | ipaddr= |
| 3190 | pfxlen= |
| 3191 | if [ "$1" != "" ]; then |
| 3192 | ipaddr=${1%/*} |
| 3193 | if [ "$1" != "$ipaddr" ]; then |
| 3194 | pfxlen=${1#*/} |
| 3195 | fi |
| 3196 | if [ "$ipaddr" = "" ]; then |
| 3197 | echo "$1 is bad IP address." 1>&2 |
| 3198 | exit 1 |
| 3199 | fi |
| 3200 | fi |
| 3201 | shift |
| 3202 | \end{verbatim} |
| 3203 | \begin{flushleft} |
| 3204 | \# If peer address is present, prefix length is 32.\\ |
| 3205 | \# Otherwise, if prefix length was not given, guess it. |
| 3206 | \end{flushleft} |
| 3207 | \begin{verbatim} |
| 3208 | peer=$1 |
| 3209 | if [ "$peer" != "" ]; then |
| 3210 | if [ "$pfxlen" != "" -a "$pfxlen" != "32" ]; then |
| 3211 | echo "Peer address with non-trivial netmask." 1>&2 |
| 3212 | exit 1 |
| 3213 | fi |
| 3214 | pfx="$ipaddr peer $peer" |
| 3215 | else |
| 3216 | if [ "$pfxlen" = "" ]; then |
| 3217 | ABCMaskLen $ipaddr |
| 3218 | pfxlen=$? |
| 3219 | fi |
| 3220 | pfx="$ipaddr/$pfxlen" |
| 3221 | fi |
| 3222 | if [ "$ldev" = "$dev" -a "$ipaddr" != "" ]; then |
| 3223 | label= |
| 3224 | fi |
| 3225 | \end{verbatim} |
| 3226 | \begin{flushleft} |
| 3227 | \# If deletion was requested, delete the address and restart RDISC |
| 3228 | \end{flushleft} |
| 3229 | \begin{verbatim} |
| 3230 | if [ $deleting -ne 0 ]; then |
| 3231 | ip addr del $pfx dev $dev $label || exit 1 |
| 3232 | if [ $fwd -eq 0 ]; then RestartRDISC; fi |
| 3233 | exit 0 |
| 3234 | fi |
| 3235 | \end{verbatim} |
| 3236 | \begin{flushleft} |
| 3237 | \# Start interface initialization.\\ |
| 3238 | \#\\ |
| 3239 | \# {\bf Step 0} --- enable device \verb|$dev| |
| 3240 | \end{flushleft} |
| 3241 | \begin{verbatim} |
| 3242 | if ! ip link set up dev $dev ; then |
| 3243 | echo "Error: cannot enable interface $dev." 1>&2 |
| 3244 | exit 1 |
| 3245 | fi |
| 3246 | if [ "$ipaddr" = "" ]; then exit 0; fi |
| 3247 | \end{verbatim} |
| 3248 | \begin{flushleft} |
| 3249 | \# {\bf Step 1} --- IP Duplicate Address Detection~\cite{RFC-DHCP}.\\ |
| 3250 | \# Send two probes and wait for result for 3 seconds.\\ |
| 3251 | \# If the interface opens slower f.e.\ due to long media detection,\\ |
| 3252 | \# you want to increase the timeout.\\ |
| 3253 | \end{flushleft} |
| 3254 | \begin{verbatim} |
| 3255 | if ! arping -q -c 2 -w 3 -D -I $dev $ipaddr ; then |
| 3256 | echo "Error: some host already uses address $ipaddr on $dev." 1>&2 |
| 3257 | exit 1 |
| 3258 | fi |
| 3259 | \end{verbatim} |
| 3260 | \begin{flushleft} |
| 3261 | \# OK, the address is unique. We may add it to the interface.\\ |
| 3262 | \#\\ |
| 3263 | \# {\bf Step 2} --- Configure the address on the interface. |
| 3264 | \end{flushleft} |
| 3265 | \begin{verbatim} |
| 3266 | if ! ip address add $pfx brd + dev $dev $label; then |
| 3267 | echo "Error: failed to add $pfx on $dev." 1>&2 |
| 3268 | exit 1 |
| 3269 | fi |
| 3270 | \end{verbatim} |
| 3271 | \noindent\# {\bf Step 3} --- Announce our presence on the link |
| 3272 | \begin{verbatim} |
| 3273 | arping -q -A -c 1 -I $dev $ipaddr |
| 3274 | noarp=$? |
| 3275 | ( sleep 2 ; |
| 3276 | arping -q -U -c 1 -I $dev $ipaddr ) >& /dev/null </dev/null & |
| 3277 | \end{verbatim} |
| 3278 | \begin{flushleft} |
| 3279 | \# {\bf Step 4} (optional) --- Add some control routes.\\ |
| 3280 | \#\\ |
| 3281 | \# 1. Prohibit link local multicast addresses.\\ |
| 3282 | \# 2. Prohibit link local (alias, limited) broadcast.\\ |
| 3283 | \# 3. Add default multicast route. |
| 3284 | \end{flushleft} |
| 3285 | \begin{verbatim} |
| 3286 | ip route add unreachable 224.0.0.0/24 >& /dev/null |
| 3287 | ip route add unreachable 255.255.255.255 >& /dev/null |
| 3288 | if [ `ip link ls $dev | grep -c MULTICAST` -ge 1 ]; then |
| 3289 | ip route add 224.0.0.0/4 dev $dev scope global >& /dev/null |
| 3290 | fi |
| 3291 | \end{verbatim} |
| 3292 | \begin{flushleft} |
| 3293 | \# {\bf Step 5} --- Add fallback default route with huge metric.\\ |
| 3294 | \# If a proxy ARP server is present on the interface, we will be\\ |
| 3295 | \# able to talk to all the Internet without further configuration.\\ |
| 3296 | \# Do not make this step on router or if the device is not ARPable.\\ |
| 3297 | \# because dead nexthop detection does not work on them. |
| 3298 | \end{flushleft} |
| 3299 | \begin{verbatim} |
| 3300 | if [ $fwd -eq 0 ]; then |
| 3301 | if [ $noarp -eq 0 ]; then |
| 3302 | ip ro append default dev $dev metric 30000 scope global |
| 3303 | elif [ "$peer" != "" ]; then |
| 3304 | if ping -q -c 2 -w 4 $peer ; then |
| 3305 | ip ro append default via $peer dev $dev metric 30001 |
| 3306 | fi |
| 3307 | fi |
| 3308 | RestartRDISC |
| 3309 | fi |
| 3310 | |
| 3311 | exit 0 |
| 3312 | \end{verbatim} |
| 3313 | \begin{flushleft} |
| 3314 | \# End of {\bf MAIN()} |
| 3315 | \end{flushleft} |
| 3316 | |
| 3317 | |
| 3318 | \end{document} |