| /proc/sys/net/ipv4/* Variables: |
| |
| ip_forward - BOOLEAN |
| 0 - disabled (default) |
| not 0 - enabled |
| |
| Forward Packets between interfaces. |
| |
| This variable is special, its change resets all configuration |
| parameters to their default state (RFC1122 for hosts, RFC1812 |
| for routers) |
| |
| ip_default_ttl - INTEGER |
| Default value of TTL field (Time To Live) for outgoing (but not |
| forwarded) IP packets. Should be between 1 and 255 inclusive. |
| Default: 64 (as recommended by RFC1700) |
| |
| ip_no_pmtu_disc - INTEGER |
| Disable Path MTU Discovery. If enabled in mode 1 and a |
| fragmentation-required ICMP is received, the PMTU to this |
| destination will be set to min_pmtu (see below). You will need |
| to raise min_pmtu to the smallest interface MTU on your system |
| manually if you want to avoid locally generated fragments. |
| |
| In mode 2 incoming Path MTU Discovery messages will be |
| discarded. Outgoing frames are handled the same as in mode 1, |
| implicitly setting IP_PMTUDISC_DONT on every created socket. |
| |
| Mode 3 is a hardend pmtu discover mode. The kernel will only |
| accept fragmentation-needed errors if the underlying protocol |
| can verify them besides a plain socket lookup. Current |
| protocols for which pmtu events will be honored are TCP, SCTP |
| and DCCP as they verify e.g. the sequence number or the |
| association. This mode should not be enabled globally but is |
| only intended to secure e.g. name servers in namespaces where |
| TCP path mtu must still work but path MTU information of other |
| protocols should be discarded. If enabled globally this mode |
| could break other protocols. |
| |
| Possible values: 0-3 |
| Default: FALSE |
| |
| min_pmtu - INTEGER |
| default 552 - minimum discovered Path MTU |
| |
| ip_forward_use_pmtu - BOOLEAN |
| By default we don't trust protocol path MTUs while forwarding |
| because they could be easily forged and can lead to unwanted |
| fragmentation by the router. |
| You only need to enable this if you have user-space software |
| which tries to discover path mtus by itself and depends on the |
| kernel honoring this information. This is normally not the |
| case. |
| Default: 0 (disabled) |
| Possible values: |
| 0 - disabled |
| 1 - enabled |
| |
| fwmark_reflect - BOOLEAN |
| Controls the fwmark of kernel-generated IPv4 reply packets that are not |
| associated with a socket for example, TCP RSTs or ICMP echo replies). |
| If unset, these packets have a fwmark of zero. If set, they have the |
| fwmark of the packet they are replying to. |
| Default: 0 |
| |
| route/max_size - INTEGER |
| Maximum number of routes allowed in the kernel. Increase |
| this when using large numbers of interfaces and/or routes. |
| From linux kernel 3.6 onwards, this is deprecated for ipv4 |
| as route cache is no longer used. |
| |
| neigh/default/gc_thresh1 - INTEGER |
| Minimum number of entries to keep. Garbage collector will not |
| purge entries if there are fewer than this number. |
| Default: 128 |
| |
| neigh/default/gc_thresh2 - INTEGER |
| Threshold when garbage collector becomes more aggressive about |
| purging entries. Entries older than 5 seconds will be cleared |
| when over this number. |
| Default: 512 |
| |
| neigh/default/gc_thresh3 - INTEGER |
| Maximum number of neighbor entries allowed. Increase this |
| when using large numbers of interfaces and when communicating |
| with large numbers of directly-connected peers. |
| Default: 1024 |
| |
| neigh/default/unres_qlen_bytes - INTEGER |
| The maximum number of bytes which may be used by packets |
| queued for each unresolved address by other network layers. |
| (added in linux 3.3) |
| Setting negative value is meaningless and will return error. |
| Default: 65536 Bytes(64KB) |
| |
| neigh/default/unres_qlen - INTEGER |
| The maximum number of packets which may be queued for each |
| unresolved address by other network layers. |
| (deprecated in linux 3.3) : use unres_qlen_bytes instead. |
| Prior to linux 3.3, the default value is 3 which may cause |
| unexpected packet loss. The current default value is calculated |
| according to default value of unres_qlen_bytes and true size of |
| packet. |
| Default: 31 |
| |
| mtu_expires - INTEGER |
| Time, in seconds, that cached PMTU information is kept. |
| |
| min_adv_mss - INTEGER |
| The advertised MSS depends on the first hop route MTU, but will |
| never be lower than this setting. |
| |
| IP Fragmentation: |
| |
| ipfrag_high_thresh - INTEGER |
| Maximum memory used to reassemble IP fragments. When |
| ipfrag_high_thresh bytes of memory is allocated for this purpose, |
| the fragment handler will toss packets until ipfrag_low_thresh |
| is reached. This also serves as a maximum limit to namespaces |
| different from the initial one. |
| |
| ipfrag_low_thresh - INTEGER |
| Maximum memory used to reassemble IP fragments before the kernel |
| begins to remove incomplete fragment queues to free up resources. |
| The kernel still accepts new fragments for defragmentation. |
| |
| ipfrag_time - INTEGER |
| Time in seconds to keep an IP fragment in memory. |
| |
| ipfrag_max_dist - INTEGER |
| ipfrag_max_dist is a non-negative integer value which defines the |
| maximum "disorder" which is allowed among fragments which share a |
| common IP source address. Note that reordering of packets is |
| not unusual, but if a large number of fragments arrive from a source |
| IP address while a particular fragment queue remains incomplete, it |
| probably indicates that one or more fragments belonging to that queue |
| have been lost. When ipfrag_max_dist is positive, an additional check |
| is done on fragments before they are added to a reassembly queue - if |
| ipfrag_max_dist (or more) fragments have arrived from a particular IP |
| address between additions to any IP fragment queue using that source |
| address, it's presumed that one or more fragments in the queue are |
| lost. The existing fragment queue will be dropped, and a new one |
| started. An ipfrag_max_dist value of zero disables this check. |
| |
| Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can |
| result in unnecessarily dropping fragment queues when normal |
| reordering of packets occurs, which could lead to poor application |
| performance. Using a very large value, e.g. 50000, increases the |
| likelihood of incorrectly reassembling IP fragments that originate |
| from different IP datagrams, which could result in data corruption. |
| Default: 64 |
| |
| INET peer storage: |
| |
| inet_peer_threshold - INTEGER |
| The approximate size of the storage. Starting from this threshold |
| entries will be thrown aggressively. This threshold also determines |
| entries' time-to-live and time intervals between garbage collection |
| passes. More entries, less time-to-live, less GC interval. |
| |
| inet_peer_minttl - INTEGER |
| Minimum time-to-live of entries. Should be enough to cover fragment |
| time-to-live on the reassembling side. This minimum time-to-live is |
| guaranteed if the pool size is less than inet_peer_threshold. |
| Measured in seconds. |
| |
| inet_peer_maxttl - INTEGER |
| Maximum time-to-live of entries. Unused entries will expire after |
| this period of time if there is no memory pressure on the pool (i.e. |
| when the number of entries in the pool is very small). |
| Measured in seconds. |
| |
| TCP variables: |
| |
| somaxconn - INTEGER |
| Limit of socket listen() backlog, known in userspace as SOMAXCONN. |
| Defaults to 128. See also tcp_max_syn_backlog for additional tuning |
| for TCP sockets. |
| |
| tcp_abort_on_overflow - BOOLEAN |
| If listening service is too slow to accept new connections, |
| reset them. Default state is FALSE. It means that if overflow |
| occurred due to a burst, connection will recover. Enable this |
| option _only_ if you are really sure that listening daemon |
| cannot be tuned to accept connections faster. Enabling this |
| option can harm clients of your server. |
| |
| tcp_adv_win_scale - INTEGER |
| Count buffering overhead as bytes/2^tcp_adv_win_scale |
| (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale), |
| if it is <= 0. |
| Possible values are [-31, 31], inclusive. |
| Default: 1 |
| |
| tcp_allowed_congestion_control - STRING |
| Show/set the congestion control choices available to non-privileged |
| processes. The list is a subset of those listed in |
| tcp_available_congestion_control. |
| Default is "reno" and the default setting (tcp_congestion_control). |
| |
| tcp_app_win - INTEGER |
| Reserve max(window/2^tcp_app_win, mss) of window for application |
| buffer. Value 0 is special, it means that nothing is reserved. |
| Default: 31 |
| |
| tcp_autocorking - BOOLEAN |
| Enable TCP auto corking : |
| When applications do consecutive small write()/sendmsg() system calls, |
| we try to coalesce these small writes as much as possible, to lower |
| total amount of sent packets. This is done if at least one prior |
| packet for the flow is waiting in Qdisc queues or device transmit |
| queue. Applications can still use TCP_CORK for optimal behavior |
| when they know how/when to uncork their sockets. |
| Default : 1 |
| |
| tcp_available_congestion_control - STRING |
| Shows the available congestion control choices that are registered. |
| More congestion control algorithms may be available as modules, |
| but not loaded. |
| |
| tcp_base_mss - INTEGER |
| The initial value of search_low to be used by the packetization layer |
| Path MTU discovery (MTU probing). If MTU probing is enabled, |
| this is the initial MSS used by the connection. |
| |
| tcp_congestion_control - STRING |
| Set the congestion control algorithm to be used for new |
| connections. The algorithm "reno" is always available, but |
| additional choices may be available based on kernel configuration. |
| Default is set as part of kernel configuration. |
| For passive connections, the listener congestion control choice |
| is inherited. |
| [see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ] |
| |
| tcp_dsack - BOOLEAN |
| Allows TCP to send "duplicate" SACKs. |
| |
| tcp_early_retrans - INTEGER |
| Enable Early Retransmit (ER), per RFC 5827. ER lowers the threshold |
| for triggering fast retransmit when the amount of outstanding data is |
| small and when no previously unsent data can be transmitted (such |
| that limited transmit could be used). Also controls the use of |
| Tail loss probe (TLP) that converts RTOs occurring due to tail |
| losses into fast recovery (draft-dukkipati-tcpm-tcp-loss-probe-01). |
| Possible values: |
| 0 disables ER |
| 1 enables ER |
| 2 enables ER but delays fast recovery and fast retransmit |
| by a fourth of RTT. This mitigates connection falsely |
| recovers when network has a small degree of reordering |
| (less than 3 packets). |
| 3 enables delayed ER and TLP. |
| 4 enables TLP only. |
| Default: 3 |
| |
| tcp_ecn - INTEGER |
| Control use of Explicit Congestion Notification (ECN) by TCP. |
| ECN is used only when both ends of the TCP connection indicate |
| support for it. This feature is useful in avoiding losses due |
| to congestion by allowing supporting routers to signal |
| congestion before having to drop packets. |
| Possible values are: |
| 0 Disable ECN. Neither initiate nor accept ECN. |
| 1 Enable ECN when requested by incoming connections and |
| also request ECN on outgoing connection attempts. |
| 2 Enable ECN when requested by incoming connections |
| but do not request ECN on outgoing connections. |
| Default: 2 |
| |
| tcp_ecn_fallback - BOOLEAN |
| If the kernel detects that ECN connection misbehaves, enable fall |
| back to non-ECN. Currently, this knob implements the fallback |
| from RFC3168, section 6.1.1.1., but we reserve that in future, |
| additional detection mechanisms could be implemented under this |
| knob. The value is not used, if tcp_ecn or per route (or congestion |
| control) ECN settings are disabled. |
| Default: 1 (fallback enabled) |
| |
| tcp_fack - BOOLEAN |
| Enable FACK congestion avoidance and fast retransmission. |
| The value is not used, if tcp_sack is not enabled. |
| |
| tcp_fin_timeout - INTEGER |
| The length of time an orphaned (no longer referenced by any |
| application) connection will remain in the FIN_WAIT_2 state |
| before it is aborted at the local end. While a perfectly |
| valid "receive only" state for an un-orphaned connection, an |
| orphaned connection in FIN_WAIT_2 state could otherwise wait |
| forever for the remote to close its end of the connection. |
| Cf. tcp_max_orphans |
| Default: 60 seconds |
| |
| tcp_frto - INTEGER |
| Enables Forward RTO-Recovery (F-RTO) defined in RFC5682. |
| F-RTO is an enhanced recovery algorithm for TCP retransmission |
| timeouts. It is particularly beneficial in networks where the |
| RTT fluctuates (e.g., wireless). F-RTO is sender-side only |
| modification. It does not require any support from the peer. |
| |
| By default it's enabled with a non-zero value. 0 disables F-RTO. |
| |
| tcp_invalid_ratelimit - INTEGER |
| Limit the maximal rate for sending duplicate acknowledgments |
| in response to incoming TCP packets that are for an existing |
| connection but that are invalid due to any of these reasons: |
| |
| (a) out-of-window sequence number, |
| (b) out-of-window acknowledgment number, or |
| (c) PAWS (Protection Against Wrapped Sequence numbers) check failure |
| |
| This can help mitigate simple "ack loop" DoS attacks, wherein |
| a buggy or malicious middlebox or man-in-the-middle can |
| rewrite TCP header fields in manner that causes each endpoint |
| to think that the other is sending invalid TCP segments, thus |
| causing each side to send an unterminating stream of duplicate |
| acknowledgments for invalid segments. |
| |
| Using 0 disables rate-limiting of dupacks in response to |
| invalid segments; otherwise this value specifies the minimal |
| space between sending such dupacks, in milliseconds. |
| |
| Default: 500 (milliseconds). |
| |
| tcp_keepalive_time - INTEGER |
| How often TCP sends out keepalive messages when keepalive is enabled. |
| Default: 2hours. |
| |
| tcp_keepalive_probes - INTEGER |
| How many keepalive probes TCP sends out, until it decides that the |
| connection is broken. Default value: 9. |
| |
| tcp_keepalive_intvl - INTEGER |
| How frequently the probes are send out. Multiplied by |
| tcp_keepalive_probes it is time to kill not responding connection, |
| after probes started. Default value: 75sec i.e. connection |
| will be aborted after ~11 minutes of retries. |
| |
| tcp_low_latency - BOOLEAN |
| If set, the TCP stack makes decisions that prefer lower |
| latency as opposed to higher throughput. By default, this |
| option is not set meaning that higher throughput is preferred. |
| An example of an application where this default should be |
| changed would be a Beowulf compute cluster. |
| Default: 0 |
| |
| tcp_max_orphans - INTEGER |
| Maximal number of TCP sockets not attached to any user file handle, |
| held by system. If this number is exceeded orphaned connections are |
| reset immediately and warning is printed. This limit exists |
| only to prevent simple DoS attacks, you _must_ not rely on this |
| or lower the limit artificially, but rather increase it |
| (probably, after increasing installed memory), |
| if network conditions require more than default value, |
| and tune network services to linger and kill such states |
| more aggressively. Let me to remind again: each orphan eats |
| up to ~64K of unswappable memory. |
| |
| tcp_max_syn_backlog - INTEGER |
| Maximal number of remembered connection requests, which have not |
| received an acknowledgment from connecting client. |
| The minimal value is 128 for low memory machines, and it will |
| increase in proportion to the memory of machine. |
| If server suffers from overload, try increasing this number. |
| |
| tcp_max_tw_buckets - INTEGER |
| Maximal number of timewait sockets held by system simultaneously. |
| If this number is exceeded time-wait socket is immediately destroyed |
| and warning is printed. This limit exists only to prevent |
| simple DoS attacks, you _must_ not lower the limit artificially, |
| but rather increase it (probably, after increasing installed memory), |
| if network conditions require more than default value. |
| |
| tcp_mem - vector of 3 INTEGERs: min, pressure, max |
| min: below this number of pages TCP is not bothered about its |
| memory appetite. |
| |
| pressure: when amount of memory allocated by TCP exceeds this number |
| of pages, TCP moderates its memory consumption and enters memory |
| pressure mode, which is exited when memory consumption falls |
| under "min". |
| |
| max: number of pages allowed for queueing by all TCP sockets. |
| |
| Defaults are calculated at boot time from amount of available |
| memory. |
| |
| tcp_moderate_rcvbuf - BOOLEAN |
| If set, TCP performs receive buffer auto-tuning, attempting to |
| automatically size the buffer (no greater than tcp_rmem[2]) to |
| match the size required by the path for full throughput. Enabled by |
| default. |
| |
| tcp_mtu_probing - INTEGER |
| Controls TCP Packetization-Layer Path MTU Discovery. Takes three |
| values: |
| 0 - Disabled |
| 1 - Disabled by default, enabled when an ICMP black hole detected |
| 2 - Always enabled, use initial MSS of tcp_base_mss. |
| |
| tcp_probe_interval - INTEGER |
| Controls how often to start TCP Packetization-Layer Path MTU |
| Discovery reprobe. The default is reprobing every 10 minutes as |
| per RFC4821. |
| |
| tcp_probe_threshold - INTEGER |
| Controls when TCP Packetization-Layer Path MTU Discovery probing |
| will stop in respect to the width of search range in bytes. Default |
| is 8 bytes. |
| |
| tcp_no_metrics_save - BOOLEAN |
| By default, TCP saves various connection metrics in the route cache |
| when the connection closes, so that connections established in the |
| near future can use these to set initial conditions. Usually, this |
| increases overall performance, but may sometimes cause performance |
| degradation. If set, TCP will not cache metrics on closing |
| connections. |
| |
| tcp_orphan_retries - INTEGER |
| This value influences the timeout of a locally closed TCP connection, |
| when RTO retransmissions remain unacknowledged. |
| See tcp_retries2 for more details. |
| |
| The default value is 8. |
| If your machine is a loaded WEB server, |
| you should think about lowering this value, such sockets |
| may consume significant resources. Cf. tcp_max_orphans. |
| |
| tcp_reordering - INTEGER |
| Initial reordering level of packets in a TCP stream. |
| TCP stack can then dynamically adjust flow reordering level |
| between this initial value and tcp_max_reordering |
| Default: 3 |
| |
| tcp_max_reordering - INTEGER |
| Maximal reordering level of packets in a TCP stream. |
| 300 is a fairly conservative value, but you might increase it |
| if paths are using per packet load balancing (like bonding rr mode) |
| Default: 300 |
| |
| tcp_retrans_collapse - BOOLEAN |
| Bug-to-bug compatibility with some broken printers. |
| On retransmit try to send bigger packets to work around bugs in |
| certain TCP stacks. |
| |
| tcp_retries1 - INTEGER |
| This value influences the time, after which TCP decides, that |
| something is wrong due to unacknowledged RTO retransmissions, |
| and reports this suspicion to the network layer. |
| See tcp_retries2 for more details. |
| |
| RFC 1122 recommends at least 3 retransmissions, which is the |
| default. |
| |
| tcp_retries2 - INTEGER |
| This value influences the timeout of an alive TCP connection, |
| when RTO retransmissions remain unacknowledged. |
| Given a value of N, a hypothetical TCP connection following |
| exponential backoff with an initial RTO of TCP_RTO_MIN would |
| retransmit N times before killing the connection at the (N+1)th RTO. |
| |
| The default value of 15 yields a hypothetical timeout of 924.6 |
| seconds and is a lower bound for the effective timeout. |
| TCP will effectively time out at the first RTO which exceeds the |
| hypothetical timeout. |
| |
| RFC 1122 recommends at least 100 seconds for the timeout, |
| which corresponds to a value of at least 8. |
| |
| tcp_rfc1337 - BOOLEAN |
| If set, the TCP stack behaves conforming to RFC1337. If unset, |
| we are not conforming to RFC, but prevent TCP TIME_WAIT |
| assassination. |
| Default: 0 |
| |
| tcp_rmem - vector of 3 INTEGERs: min, default, max |
| min: Minimal size of receive buffer used by TCP sockets. |
| It is guaranteed to each TCP socket, even under moderate memory |
| pressure. |
| Default: 1 page |
| |
| default: initial size of receive buffer used by TCP sockets. |
| This value overrides net.core.rmem_default used by other protocols. |
| Default: 87380 bytes. This value results in window of 65535 with |
| default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit |
| less for default tcp_app_win. See below about these variables. |
| |
| max: maximal size of receive buffer allowed for automatically |
| selected receiver buffers for TCP socket. This value does not override |
| net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables |
| automatic tuning of that socket's receive buffer size, in which |
| case this value is ignored. |
| Default: between 87380B and 6MB, depending on RAM size. |
| |
| tcp_sack - BOOLEAN |
| Enable select acknowledgments (SACKS). |
| |
| tcp_slow_start_after_idle - BOOLEAN |
| If set, provide RFC2861 behavior and time out the congestion |
| window after an idle period. An idle period is defined at |
| the current RTO. If unset, the congestion window will not |
| be timed out after an idle period. |
| Default: 1 |
| |
| tcp_stdurg - BOOLEAN |
| Use the Host requirements interpretation of the TCP urgent pointer field. |
| Most hosts use the older BSD interpretation, so if you turn this on |
| Linux might not communicate correctly with them. |
| Default: FALSE |
| |
| tcp_synack_retries - INTEGER |
| Number of times SYNACKs for a passive TCP connection attempt will |
| be retransmitted. Should not be higher than 255. Default value |
| is 5, which corresponds to 31seconds till the last retransmission |
| with the current initial RTO of 1second. With this the final timeout |
| for a passive TCP connection will happen after 63seconds. |
| |
| tcp_syncookies - BOOLEAN |
| Only valid when the kernel was compiled with CONFIG_SYN_COOKIES |
| Send out syncookies when the syn backlog queue of a socket |
| overflows. This is to prevent against the common 'SYN flood attack' |
| Default: 1 |
| |
| Note, that syncookies is fallback facility. |
| It MUST NOT be used to help highly loaded servers to stand |
| against legal connection rate. If you see SYN flood warnings |
| in your logs, but investigation shows that they occur |
| because of overload with legal connections, you should tune |
| another parameters until this warning disappear. |
| See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow. |
| |
| syncookies seriously violate TCP protocol, do not allow |
| to use TCP extensions, can result in serious degradation |
| of some services (f.e. SMTP relaying), visible not by you, |
| but your clients and relays, contacting you. While you see |
| SYN flood warnings in logs not being really flooded, your server |
| is seriously misconfigured. |
| |
| If you want to test which effects syncookies have to your |
| network connections you can set this knob to 2 to enable |
| unconditionally generation of syncookies. |
| |
| tcp_fastopen - INTEGER |
| Enable TCP Fast Open feature (draft-ietf-tcpm-fastopen) to send data |
| in the opening SYN packet. To use this feature, the client application |
| must use sendmsg() or sendto() with MSG_FASTOPEN flag rather than |
| connect() to perform a TCP handshake automatically. |
| |
| The values (bitmap) are |
| 1: Enables sending data in the opening SYN on the client w/ MSG_FASTOPEN. |
| 2: Enables TCP Fast Open on the server side, i.e., allowing data in |
| a SYN packet to be accepted and passed to the application before |
| 3-way hand shake finishes. |
| 4: Send data in the opening SYN regardless of cookie availability and |
| without a cookie option. |
| 0x100: Accept SYN data w/o validating the cookie. |
| 0x200: Accept data-in-SYN w/o any cookie option present. |
| 0x400/0x800: Enable Fast Open on all listeners regardless of the |
| TCP_FASTOPEN socket option. The two different flags designate two |
| different ways of setting max_qlen without the TCP_FASTOPEN socket |
| option. |
| |
| Default: 1 |
| |
| Note that the client & server side Fast Open flags (1 and 2 |
| respectively) must be also enabled before the rest of flags can take |
| effect. |
| |
| See include/net/tcp.h and the code for more details. |
| |
| tcp_syn_retries - INTEGER |
| Number of times initial SYNs for an active TCP connection attempt |
| will be retransmitted. Should not be higher than 255. Default value |
| is 6, which corresponds to 63seconds till the last retransmission |
| with the current initial RTO of 1second. With this the final timeout |
| for an active TCP connection attempt will happen after 127seconds. |
| |
| tcp_timestamps - BOOLEAN |
| Enable timestamps as defined in RFC1323. |
| |
| tcp_min_tso_segs - INTEGER |
| Minimal number of segments per TSO frame. |
| Since linux-3.12, TCP does an automatic sizing of TSO frames, |
| depending on flow rate, instead of filling 64Kbytes packets. |
| For specific usages, it's possible to force TCP to build big |
| TSO frames. Note that TCP stack might split too big TSO packets |
| if available window is too small. |
| Default: 2 |
| |
| tcp_tso_win_divisor - INTEGER |
| This allows control over what percentage of the congestion window |
| can be consumed by a single TSO frame. |
| The setting of this parameter is a choice between burstiness and |
| building larger TSO frames. |
| Default: 3 |
| |
| tcp_tw_recycle - BOOLEAN |
| Enable fast recycling TIME-WAIT sockets. Default value is 0. |
| It should not be changed without advice/request of technical |
| experts. |
| |
| tcp_tw_reuse - BOOLEAN |
| Allow to reuse TIME-WAIT sockets for new connections when it is |
| safe from protocol viewpoint. Default value is 0. |
| It should not be changed without advice/request of technical |
| experts. |
| |
| tcp_window_scaling - BOOLEAN |
| Enable window scaling as defined in RFC1323. |
| |
| tcp_wmem - vector of 3 INTEGERs: min, default, max |
| min: Amount of memory reserved for send buffers for TCP sockets. |
| Each TCP socket has rights to use it due to fact of its birth. |
| Default: 1 page |
| |
| default: initial size of send buffer used by TCP sockets. This |
| value overrides net.core.wmem_default used by other protocols. |
| It is usually lower than net.core.wmem_default. |
| Default: 16K |
| |
| max: Maximal amount of memory allowed for automatically tuned |
| send buffers for TCP sockets. This value does not override |
| net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables |
| automatic tuning of that socket's send buffer size, in which case |
| this value is ignored. |
| Default: between 64K and 4MB, depending on RAM size. |
| |
| tcp_notsent_lowat - UNSIGNED INTEGER |
| A TCP socket can control the amount of unsent bytes in its write queue, |
| thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll() |
| reports POLLOUT events if the amount of unsent bytes is below a per |
| socket value, and if the write queue is not full. sendmsg() will |
| also not add new buffers if the limit is hit. |
| |
| This global variable controls the amount of unsent data for |
| sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change |
| to the global variable has immediate effect. |
| |
| Default: UINT_MAX (0xFFFFFFFF) |
| |
| tcp_workaround_signed_windows - BOOLEAN |
| If set, assume no receipt of a window scaling option means the |
| remote TCP is broken and treats the window as a signed quantity. |
| If unset, assume the remote TCP is not broken even if we do |
| not receive a window scaling option from them. |
| Default: 0 |
| |
| tcp_thin_linear_timeouts - BOOLEAN |
| Enable dynamic triggering of linear timeouts for thin streams. |
| If set, a check is performed upon retransmission by timeout to |
| determine if the stream is thin (less than 4 packets in flight). |
| As long as the stream is found to be thin, up to 6 linear |
| timeouts may be performed before exponential backoff mode is |
| initiated. This improves retransmission latency for |
| non-aggressive thin streams, often found to be time-dependent. |
| For more information on thin streams, see |
| Documentation/networking/tcp-thin.txt |
| Default: 0 |
| |
| tcp_thin_dupack - BOOLEAN |
| Enable dynamic triggering of retransmissions after one dupACK |
| for thin streams. If set, a check is performed upon reception |
| of a dupACK to determine if the stream is thin (less than 4 |
| packets in flight). As long as the stream is found to be thin, |
| data is retransmitted on the first received dupACK. This |
| improves retransmission latency for non-aggressive thin |
| streams, often found to be time-dependent. |
| For more information on thin streams, see |
| Documentation/networking/tcp-thin.txt |
| Default: 0 |
| |
| tcp_limit_output_bytes - INTEGER |
| Controls TCP Small Queue limit per tcp socket. |
| TCP bulk sender tends to increase packets in flight until it |
| gets losses notifications. With SNDBUF autotuning, this can |
| result in a large amount of packets queued in qdisc/device |
| on the local machine, hurting latency of other flows, for |
| typical pfifo_fast qdiscs. |
| tcp_limit_output_bytes limits the number of bytes on qdisc |
| or device to reduce artificial RTT/cwnd and reduce bufferbloat. |
| Default: 131072 |
| |
| tcp_challenge_ack_limit - INTEGER |
| Limits number of Challenge ACK sent per second, as recommended |
| in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks) |
| Default: 100 |
| |
| UDP variables: |
| |
| udp_mem - vector of 3 INTEGERs: min, pressure, max |
| Number of pages allowed for queueing by all UDP sockets. |
| |
| min: Below this number of pages UDP is not bothered about its |
| memory appetite. When amount of memory allocated by UDP exceeds |
| this number, UDP starts to moderate memory usage. |
| |
| pressure: This value was introduced to follow format of tcp_mem. |
| |
| max: Number of pages allowed for queueing by all UDP sockets. |
| |
| Default is calculated at boot time from amount of available memory. |
| |
| udp_rmem_min - INTEGER |
| Minimal size of receive buffer used by UDP sockets in moderation. |
| Each UDP socket is able to use the size for receiving data, even if |
| total pages of UDP sockets exceed udp_mem pressure. The unit is byte. |
| Default: 1 page |
| |
| udp_wmem_min - INTEGER |
| Minimal size of send buffer used by UDP sockets in moderation. |
| Each UDP socket is able to use the size for sending data, even if |
| total pages of UDP sockets exceed udp_mem pressure. The unit is byte. |
| Default: 1 page |
| |
| CIPSOv4 Variables: |
| |
| cipso_cache_enable - BOOLEAN |
| If set, enable additions to and lookups from the CIPSO label mapping |
| cache. If unset, additions are ignored and lookups always result in a |
| miss. However, regardless of the setting the cache is still |
| invalidated when required when means you can safely toggle this on and |
| off and the cache will always be "safe". |
| Default: 1 |
| |
| cipso_cache_bucket_size - INTEGER |
| The CIPSO label cache consists of a fixed size hash table with each |
| hash bucket containing a number of cache entries. This variable limits |
| the number of entries in each hash bucket; the larger the value the |
| more CIPSO label mappings that can be cached. When the number of |
| entries in a given hash bucket reaches this limit adding new entries |
| causes the oldest entry in the bucket to be removed to make room. |
| Default: 10 |
| |
| cipso_rbm_optfmt - BOOLEAN |
| Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of |
| the CIPSO draft specification (see Documentation/netlabel for details). |
| This means that when set the CIPSO tag will be padded with empty |
| categories in order to make the packet data 32-bit aligned. |
| Default: 0 |
| |
| cipso_rbm_structvalid - BOOLEAN |
| If set, do a very strict check of the CIPSO option when |
| ip_options_compile() is called. If unset, relax the checks done during |
| ip_options_compile(). Either way is "safe" as errors are caught else |
| where in the CIPSO processing code but setting this to 0 (False) should |
| result in less work (i.e. it should be faster) but could cause problems |
| with other implementations that require strict checking. |
| Default: 0 |
| |
| IP Variables: |
| |
| ip_local_port_range - 2 INTEGERS |
| Defines the local port range that is used by TCP and UDP to |
| choose the local port. The first number is the first, the |
| second the last local port number. |
| If possible, it is better these numbers have different parity. |
| (one even and one odd values) |
| The default values are 32768 and 60999 respectively. |
| |
| ip_local_reserved_ports - list of comma separated ranges |
| Specify the ports which are reserved for known third-party |
| applications. These ports will not be used by automatic port |
| assignments (e.g. when calling connect() or bind() with port |
| number 0). Explicit port allocation behavior is unchanged. |
| |
| The format used for both input and output is a comma separated |
| list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and |
| 10). Writing to the file will clear all previously reserved |
| ports and update the current list with the one given in the |
| input. |
| |
| Note that ip_local_port_range and ip_local_reserved_ports |
| settings are independent and both are considered by the kernel |
| when determining which ports are available for automatic port |
| assignments. |
| |
| You can reserve ports which are not in the current |
| ip_local_port_range, e.g.: |
| |
| $ cat /proc/sys/net/ipv4/ip_local_port_range |
| 32000 60999 |
| $ cat /proc/sys/net/ipv4/ip_local_reserved_ports |
| 8080,9148 |
| |
| although this is redundant. However such a setting is useful |
| if later the port range is changed to a value that will |
| include the reserved ports. |
| |
| Default: Empty |
| |
| ip_nonlocal_bind - BOOLEAN |
| If set, allows processes to bind() to non-local IP addresses, |
| which can be quite useful - but may break some applications. |
| Default: 0 |
| |
| ip_dynaddr - BOOLEAN |
| If set non-zero, enables support for dynamic addresses. |
| If set to a non-zero value larger than 1, a kernel log |
| message will be printed when dynamic address rewriting |
| occurs. |
| Default: 0 |
| |
| ip_early_demux - BOOLEAN |
| Optimize input packet processing down to one demux for |
| certain kinds of local sockets. Currently we only do this |
| for established TCP sockets. |
| |
| It may add an additional cost for pure routing workloads that |
| reduces overall throughput, in such case you should disable it. |
| Default: 1 |
| |
| icmp_echo_ignore_all - BOOLEAN |
| If set non-zero, then the kernel will ignore all ICMP ECHO |
| requests sent to it. |
| Default: 0 |
| |
| icmp_echo_ignore_broadcasts - BOOLEAN |
| If set non-zero, then the kernel will ignore all ICMP ECHO and |
| TIMESTAMP requests sent to it via broadcast/multicast. |
| Default: 1 |
| |
| icmp_ratelimit - INTEGER |
| Limit the maximal rates for sending ICMP packets whose type matches |
| icmp_ratemask (see below) to specific targets. |
| 0 to disable any limiting, |
| otherwise the minimal space between responses in milliseconds. |
| Note that another sysctl, icmp_msgs_per_sec limits the number |
| of ICMP packets sent on all targets. |
| Default: 1000 |
| |
| icmp_msgs_per_sec - INTEGER |
| Limit maximal number of ICMP packets sent per second from this host. |
| Only messages whose type matches icmp_ratemask (see below) are |
| controlled by this limit. |
| Default: 1000 |
| |
| icmp_msgs_burst - INTEGER |
| icmp_msgs_per_sec controls number of ICMP packets sent per second, |
| while icmp_msgs_burst controls the burst size of these packets. |
| Default: 50 |
| |
| icmp_ratemask - INTEGER |
| Mask made of ICMP types for which rates are being limited. |
| Significant bits: IHGFEDCBA9876543210 |
| Default mask: 0000001100000011000 (6168) |
| |
| Bit definitions (see include/linux/icmp.h): |
| 0 Echo Reply |
| 3 Destination Unreachable * |
| 4 Source Quench * |
| 5 Redirect |
| 8 Echo Request |
| B Time Exceeded * |
| C Parameter Problem * |
| D Timestamp Request |
| E Timestamp Reply |
| F Info Request |
| G Info Reply |
| H Address Mask Request |
| I Address Mask Reply |
| |
| * These are rate limited by default (see default mask above) |
| |
| icmp_ignore_bogus_error_responses - BOOLEAN |
| Some routers violate RFC1122 by sending bogus responses to broadcast |
| frames. Such violations are normally logged via a kernel warning. |
| If this is set to TRUE, the kernel will not give such warnings, which |
| will avoid log file clutter. |
| Default: 1 |
| |
| icmp_errors_use_inbound_ifaddr - BOOLEAN |
| |
| If zero, icmp error messages are sent with the primary address of |
| the exiting interface. |
| |
| If non-zero, the message will be sent with the primary address of |
| the interface that received the packet that caused the icmp error. |
| This is the behaviour network many administrators will expect from |
| a router. And it can make debugging complicated network layouts |
| much easier. |
| |
| Note that if no primary address exists for the interface selected, |
| then the primary address of the first non-loopback interface that |
| has one will be used regardless of this setting. |
| |
| Default: 0 |
| |
| igmp_max_memberships - INTEGER |
| Change the maximum number of multicast groups we can subscribe to. |
| Default: 20 |
| |
| Theoretical maximum value is bounded by having to send a membership |
| report in a single datagram (i.e. the report can't span multiple |
| datagrams, or risk confusing the switch and leaving groups you don't |
| intend to). |
| |
| The number of supported groups 'M' is bounded by the number of group |
| report entries you can fit into a single datagram of 65535 bytes. |
| |
| M = 65536-sizeof (ip header)/(sizeof(Group record)) |
| |
| Group records are variable length, with a minimum of 12 bytes. |
| So net.ipv4.igmp_max_memberships should not be set higher than: |
| |
| (65536-24) / 12 = 5459 |
| |
| The value 5459 assumes no IP header options, so in practice |
| this number may be lower. |
| |
| conf/interface/* changes special settings per interface (where |
| "interface" is the name of your network interface) |
| |
| conf/all/* is special, changes the settings for all interfaces |
| |
| igmp_qrv - INTEGER |
| Controls the IGMP query robustness variable (see RFC2236 8.1). |
| Default: 2 (as specified by RFC2236 8.1) |
| Minimum: 1 (as specified by RFC6636 4.5) |
| |
| log_martians - BOOLEAN |
| Log packets with impossible addresses to kernel log. |
| log_martians for the interface will be enabled if at least one of |
| conf/{all,interface}/log_martians is set to TRUE, |
| it will be disabled otherwise |
| |
| accept_redirects - BOOLEAN |
| Accept ICMP redirect messages. |
| accept_redirects for the interface will be enabled if: |
| - both conf/{all,interface}/accept_redirects are TRUE in the case |
| forwarding for the interface is enabled |
| or |
| - at least one of conf/{all,interface}/accept_redirects is TRUE in the |
| case forwarding for the interface is disabled |
| accept_redirects for the interface will be disabled otherwise |
| default TRUE (host) |
| FALSE (router) |
| |
| forwarding - BOOLEAN |
| Enable IP forwarding on this interface. |
| |
| mc_forwarding - BOOLEAN |
| Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE |
| and a multicast routing daemon is required. |
| conf/all/mc_forwarding must also be set to TRUE to enable multicast |
| routing for the interface |
| |
| medium_id - INTEGER |
| Integer value used to differentiate the devices by the medium they |
| are attached to. Two devices can have different id values when |
| the broadcast packets are received only on one of them. |
| The default value 0 means that the device is the only interface |
| to its medium, value of -1 means that medium is not known. |
| |
| Currently, it is used to change the proxy_arp behavior: |
| the proxy_arp feature is enabled for packets forwarded between |
| two devices attached to different media. |
| |
| proxy_arp - BOOLEAN |
| Do proxy arp. |
| proxy_arp for the interface will be enabled if at least one of |
| conf/{all,interface}/proxy_arp is set to TRUE, |
| it will be disabled otherwise |
| |
| proxy_arp_pvlan - BOOLEAN |
| Private VLAN proxy arp. |
| Basically allow proxy arp replies back to the same interface |
| (from which the ARP request/solicitation was received). |
| |
| This is done to support (ethernet) switch features, like RFC |
| 3069, where the individual ports are NOT allowed to |
| communicate with each other, but they are allowed to talk to |
| the upstream router. As described in RFC 3069, it is possible |
| to allow these hosts to communicate through the upstream |
| router by proxy_arp'ing. Don't need to be used together with |
| proxy_arp. |
| |
| This technology is known by different names: |
| In RFC 3069 it is called VLAN Aggregation. |
| Cisco and Allied Telesyn call it Private VLAN. |
| Hewlett-Packard call it Source-Port filtering or port-isolation. |
| Ericsson call it MAC-Forced Forwarding (RFC Draft). |
| |
| shared_media - BOOLEAN |
| Send(router) or accept(host) RFC1620 shared media redirects. |
| Overrides ip_secure_redirects. |
| shared_media for the interface will be enabled if at least one of |
| conf/{all,interface}/shared_media is set to TRUE, |
| it will be disabled otherwise |
| default TRUE |
| |
| secure_redirects - BOOLEAN |
| Accept ICMP redirect messages only for gateways, |
| listed in default gateway list. |
| secure_redirects for the interface will be enabled if at least one of |
| conf/{all,interface}/secure_redirects is set to TRUE, |
| it will be disabled otherwise |
| default TRUE |
| |
| send_redirects - BOOLEAN |
| Send redirects, if router. |
| send_redirects for the interface will be enabled if at least one of |
| conf/{all,interface}/send_redirects is set to TRUE, |
| it will be disabled otherwise |
| Default: TRUE |
| |
| bootp_relay - BOOLEAN |
| Accept packets with source address 0.b.c.d destined |
| not to this host as local ones. It is supposed, that |
| BOOTP relay daemon will catch and forward such packets. |
| conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay |
| for the interface |
| default FALSE |
| Not Implemented Yet. |
| |
| accept_source_route - BOOLEAN |
| Accept packets with SRR option. |
| conf/all/accept_source_route must also be set to TRUE to accept packets |
| with SRR option on the interface |
| default TRUE (router) |
| FALSE (host) |
| |
| accept_local - BOOLEAN |
| Accept packets with local source addresses. In combination with |
| suitable routing, this can be used to direct packets between two |
| local interfaces over the wire and have them accepted properly. |
| default FALSE |
| |
| route_localnet - BOOLEAN |
| Do not consider loopback addresses as martian source or destination |
| while routing. This enables the use of 127/8 for local routing purposes. |
| default FALSE |
| |
| rp_filter - INTEGER |
| 0 - No source validation. |
| 1 - Strict mode as defined in RFC3704 Strict Reverse Path |
| Each incoming packet is tested against the FIB and if the interface |
| is not the best reverse path the packet check will fail. |
| By default failed packets are discarded. |
| 2 - Loose mode as defined in RFC3704 Loose Reverse Path |
| Each incoming packet's source address is also tested against the FIB |
| and if the source address is not reachable via any interface |
| the packet check will fail. |
| |
| Current recommended practice in RFC3704 is to enable strict mode |
| to prevent IP spoofing from DDos attacks. If using asymmetric routing |
| or other complicated routing, then loose mode is recommended. |
| |
| The max value from conf/{all,interface}/rp_filter is used |
| when doing source validation on the {interface}. |
| |
| Default value is 0. Note that some distributions enable it |
| in startup scripts. |
| |
| arp_filter - BOOLEAN |
| 1 - Allows you to have multiple network interfaces on the same |
| subnet, and have the ARPs for each interface be answered |
| based on whether or not the kernel would route a packet from |
| the ARP'd IP out that interface (therefore you must use source |
| based routing for this to work). In other words it allows control |
| of which cards (usually 1) will respond to an arp request. |
| |
| 0 - (default) The kernel can respond to arp requests with addresses |
| from other interfaces. This may seem wrong but it usually makes |
| sense, because it increases the chance of successful communication. |
| IP addresses are owned by the complete host on Linux, not by |
| particular interfaces. Only for more complex setups like load- |
| balancing, does this behaviour cause problems. |
| |
| arp_filter for the interface will be enabled if at least one of |
| conf/{all,interface}/arp_filter is set to TRUE, |
| it will be disabled otherwise |
| |
| arp_announce - INTEGER |
| Define different restriction levels for announcing the local |
| source IP address from IP packets in ARP requests sent on |
| interface: |
| 0 - (default) Use any local address, configured on any interface |
| 1 - Try to avoid local addresses that are not in the target's |
| subnet for this interface. This mode is useful when target |
| hosts reachable via this interface require the source IP |
| address in ARP requests to be part of their logical network |
| configured on the receiving interface. When we generate the |
| request we will check all our subnets that include the |
| target IP and will preserve the source address if it is from |
| such subnet. If there is no such subnet we select source |
| address according to the rules for level 2. |
| 2 - Always use the best local address for this target. |
| In this mode we ignore the source address in the IP packet |
| and try to select local address that we prefer for talks with |
| the target host. Such local address is selected by looking |
| for primary IP addresses on all our subnets on the outgoing |
| interface that include the target IP address. If no suitable |
| local address is found we select the first local address |
| we have on the outgoing interface or on all other interfaces, |
| with the hope we will receive reply for our request and |
| even sometimes no matter the source IP address we announce. |
| |
| The max value from conf/{all,interface}/arp_announce is used. |
| |
| Increasing the restriction level gives more chance for |
| receiving answer from the resolved target while decreasing |
| the level announces more valid sender's information. |
| |
| arp_ignore - INTEGER |
| Define different modes for sending replies in response to |
| received ARP requests that resolve local target IP addresses: |
| 0 - (default): reply for any local target IP address, configured |
| on any interface |
| 1 - reply only if the target IP address is local address |
| configured on the incoming interface |
| 2 - reply only if the target IP address is local address |
| configured on the incoming interface and both with the |
| sender's IP address are part from same subnet on this interface |
| 3 - do not reply for local addresses configured with scope host, |
| only resolutions for global and link addresses are replied |
| 4-7 - reserved |
| 8 - do not reply for all local addresses |
| |
| The max value from conf/{all,interface}/arp_ignore is used |
| when ARP request is received on the {interface} |
| |
| arp_notify - BOOLEAN |
| Define mode for notification of address and device changes. |
| 0 - (default): do nothing |
| 1 - Generate gratuitous arp requests when device is brought up |
| or hardware address changes. |
| |
| arp_accept - BOOLEAN |
| Define behavior for gratuitous ARP frames who's IP is not |
| already present in the ARP table: |
| 0 - don't create new entries in the ARP table |
| 1 - create new entries in the ARP table |
| |
| Both replies and requests type gratuitous arp will trigger the |
| ARP table to be updated, if this setting is on. |
| |
| If the ARP table already contains the IP address of the |
| gratuitous arp frame, the arp table will be updated regardless |
| if this setting is on or off. |
| |
| mcast_solicit - INTEGER |
| The maximum number of multicast probes in INCOMPLETE state, |
| when the associated hardware address is unknown. Defaults |
| to 3. |
| |
| ucast_solicit - INTEGER |
| The maximum number of unicast probes in PROBE state, when |
| the hardware address is being reconfirmed. Defaults to 3. |
| |
| app_solicit - INTEGER |
| The maximum number of probes to send to the user space ARP daemon |
| via netlink before dropping back to multicast probes (see |
| mcast_resolicit). Defaults to 0. |
| |
| mcast_resolicit - INTEGER |
| The maximum number of multicast probes after unicast and |
| app probes in PROBE state. Defaults to 0. |
| |
| disable_policy - BOOLEAN |
| Disable IPSEC policy (SPD) for this interface |
| |
| disable_xfrm - BOOLEAN |
| Disable IPSEC encryption on this interface, whatever the policy |
| |
| igmpv2_unsolicited_report_interval - INTEGER |
| The interval in milliseconds in which the next unsolicited |
| IGMPv1 or IGMPv2 report retransmit will take place. |
| Default: 10000 (10 seconds) |
| |
| igmpv3_unsolicited_report_interval - INTEGER |
| The interval in milliseconds in which the next unsolicited |
| IGMPv3 report retransmit will take place. |
| Default: 1000 (1 seconds) |
| |
| promote_secondaries - BOOLEAN |
| When a primary IP address is removed from this interface |
| promote a corresponding secondary IP address instead of |
| removing all the corresponding secondary IP addresses. |
| |
| |
| tag - INTEGER |
| Allows you to write a number, which can be used as required. |
| Default value is 0. |
| |
| Alexey Kuznetsov. |
| kuznet@ms2.inr.ac.ru |
| |
| Updated by: |
| Andi Kleen |
| ak@muc.de |
| Nicolas Delon |
| delon.nicolas@wanadoo.fr |
| |
| |
| |
| |
| /proc/sys/net/ipv6/* Variables: |
| |
| IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also |
| apply to IPv6 [XXX?]. |
| |
| bindv6only - BOOLEAN |
| Default value for IPV6_V6ONLY socket option, |
| which restricts use of the IPv6 socket to IPv6 communication |
| only. |
| TRUE: disable IPv4-mapped address feature |
| FALSE: enable IPv4-mapped address feature |
| |
| Default: FALSE (as specified in RFC3493) |
| |
| flowlabel_consistency - BOOLEAN |
| Protect the consistency (and unicity) of flow label. |
| You have to disable it to use IPV6_FL_F_REFLECT flag on the |
| flow label manager. |
| TRUE: enabled |
| FALSE: disabled |
| Default: TRUE |
| |
| auto_flowlabels - INTEGER |
| Automatically generate flow labels based on a flow hash of the |
| packet. This allows intermediate devices, such as routers, to |
| identify packet flows for mechanisms like Equal Cost Multipath |
| Routing (see RFC 6438). |
| 0: automatic flow labels are completely disabled |
| 1: automatic flow labels are enabled by default, they can be |
| disabled on a per socket basis using the IPV6_AUTOFLOWLABEL |
| socket option |
| 2: automatic flow labels are allowed, they may be enabled on a |
| per socket basis using the IPV6_AUTOFLOWLABEL socket option |
| 3: automatic flow labels are enabled and enforced, they cannot |
| be disabled by the socket option |
| Default: 0 |
| |
| flowlabel_state_ranges - BOOLEAN |
| Split the flow label number space into two ranges. 0-0x7FFFF is |
| reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF |
| is reserved for stateless flow labels as described in RFC6437. |
| TRUE: enabled |
| FALSE: disabled |
| Default: true |
| |
| anycast_src_echo_reply - BOOLEAN |
| Controls the use of anycast addresses as source addresses for ICMPv6 |
| echo reply |
| TRUE: enabled |
| FALSE: disabled |
| Default: FALSE |
| |
| idgen_delay - INTEGER |
| Controls the delay in seconds after which time to retry |
| privacy stable address generation if a DAD conflict is |
| detected. |
| Default: 1 (as specified in RFC7217) |
| |
| idgen_retries - INTEGER |
| Controls the number of retries to generate a stable privacy |
| address if a DAD conflict is detected. |
| Default: 3 (as specified in RFC7217) |
| |
| mld_qrv - INTEGER |
| Controls the MLD query robustness variable (see RFC3810 9.1). |
| Default: 2 (as specified by RFC3810 9.1) |
| Minimum: 1 (as specified by RFC6636 4.5) |
| |
| IPv6 Fragmentation: |
| |
| ip6frag_high_thresh - INTEGER |
| Maximum memory used to reassemble IPv6 fragments. When |
| ip6frag_high_thresh bytes of memory is allocated for this purpose, |
| the fragment handler will toss packets until ip6frag_low_thresh |
| is reached. |
| |
| ip6frag_low_thresh - INTEGER |
| See ip6frag_high_thresh |
| |
| ip6frag_time - INTEGER |
| Time in seconds to keep an IPv6 fragment in memory. |
| |
| conf/default/*: |
| Change the interface-specific default settings. |
| |
| |
| conf/all/*: |
| Change all the interface-specific settings. |
| |
| [XXX: Other special features than forwarding?] |
| |
| conf/all/forwarding - BOOLEAN |
| Enable global IPv6 forwarding between all interfaces. |
| |
| IPv4 and IPv6 work differently here; e.g. netfilter must be used |
| to control which interfaces may forward packets and which not. |
| |
| This also sets all interfaces' Host/Router setting |
| 'forwarding' to the specified value. See below for details. |
| |
| This referred to as global forwarding. |
| |
| proxy_ndp - BOOLEAN |
| Do proxy ndp. |
| |
| fwmark_reflect - BOOLEAN |
| Controls the fwmark of kernel-generated IPv6 reply packets that are not |
| associated with a socket for example, TCP RSTs or ICMPv6 echo replies). |
| If unset, these packets have a fwmark of zero. If set, they have the |
| fwmark of the packet they are replying to. |
| Default: 0 |
| |
| conf/interface/*: |
| Change special settings per interface. |
| |
| The functional behaviour for certain settings is different |
| depending on whether local forwarding is enabled or not. |
| |
| accept_ra - INTEGER |
| Accept Router Advertisements; autoconfigure using them. |
| |
| It also determines whether or not to transmit Router |
| Solicitations. If and only if the functional setting is to |
| accept Router Advertisements, Router Solicitations will be |
| transmitted. |
| |
| Possible values are: |
| 0 Do not accept Router Advertisements. |
| 1 Accept Router Advertisements if forwarding is disabled. |
| 2 Overrule forwarding behaviour. Accept Router Advertisements |
| even if forwarding is enabled. |
| |
| Functional default: enabled if local forwarding is disabled. |
| disabled if local forwarding is enabled. |
| |
| accept_ra_defrtr - BOOLEAN |
| Learn default router in Router Advertisement. |
| |
| Functional default: enabled if accept_ra is enabled. |
| disabled if accept_ra is disabled. |
| |
| accept_ra_from_local - BOOLEAN |
| Accept RA with source-address that is found on local machine |
| if the RA is otherwise proper and able to be accepted. |
| Default is to NOT accept these as it may be an un-intended |
| network loop. |
| |
| Functional default: |
| enabled if accept_ra_from_local is enabled |
| on a specific interface. |
| disabled if accept_ra_from_local is disabled |
| on a specific interface. |
| |
| accept_ra_min_hop_limit - INTEGER |
| Minimum hop limit Information in Router Advertisement. |
| |
| Hop limit Information in Router Advertisement less than this |
| variable shall be ignored. |
| |
| Default: 1 |
| |
| accept_ra_pinfo - BOOLEAN |
| Learn Prefix Information in Router Advertisement. |
| |
| Functional default: enabled if accept_ra is enabled. |
| disabled if accept_ra is disabled. |
| |
| accept_ra_rt_info_max_plen - INTEGER |
| Maximum prefix length of Route Information in RA. |
| |
| Route Information w/ prefix larger than or equal to this |
| variable shall be ignored. |
| |
| Functional default: 0 if accept_ra_rtr_pref is enabled. |
| -1 if accept_ra_rtr_pref is disabled. |
| |
| accept_ra_rtr_pref - BOOLEAN |
| Accept Router Preference in RA. |
| |
| Functional default: enabled if accept_ra is enabled. |
| disabled if accept_ra is disabled. |
| |
| accept_ra_mtu - BOOLEAN |
| Apply the MTU value specified in RA option 5 (RFC4861). If |
| disabled, the MTU specified in the RA will be ignored. |
| |
| Functional default: enabled if accept_ra is enabled. |
| disabled if accept_ra is disabled. |
| |
| accept_redirects - BOOLEAN |
| Accept Redirects. |
| |
| Functional default: enabled if local forwarding is disabled. |
| disabled if local forwarding is enabled. |
| |
| accept_source_route - INTEGER |
| Accept source routing (routing extension header). |
| |
| >= 0: Accept only routing header type 2. |
| < 0: Do not accept routing header. |
| |
| Default: 0 |
| |
| autoconf - BOOLEAN |
| Autoconfigure addresses using Prefix Information in Router |
| Advertisements. |
| |
| Functional default: enabled if accept_ra_pinfo is enabled. |
| disabled if accept_ra_pinfo is disabled. |
| |
| dad_transmits - INTEGER |
| The amount of Duplicate Address Detection probes to send. |
| Default: 1 |
| |
| forwarding - INTEGER |
| Configure interface-specific Host/Router behaviour. |
| |
| Note: It is recommended to have the same setting on all |
| interfaces; mixed router/host scenarios are rather uncommon. |
| |
| Possible values are: |
| 0 Forwarding disabled |
| 1 Forwarding enabled |
| |
| FALSE (0): |
| |
| By default, Host behaviour is assumed. This means: |
| |
| 1. IsRouter flag is not set in Neighbour Advertisements. |
| 2. If accept_ra is TRUE (default), transmit Router |
| Solicitations. |
| 3. If accept_ra is TRUE (default), accept Router |
| Advertisements (and do autoconfiguration). |
| 4. If accept_redirects is TRUE (default), accept Redirects. |
| |
| TRUE (1): |
| |
| If local forwarding is enabled, Router behaviour is assumed. |
| This means exactly the reverse from the above: |
| |
| 1. IsRouter flag is set in Neighbour Advertisements. |
| 2. Router Solicitations are not sent unless accept_ra is 2. |
| 3. Router Advertisements are ignored unless accept_ra is 2. |
| 4. Redirects are ignored. |
| |
| Default: 0 (disabled) if global forwarding is disabled (default), |
| otherwise 1 (enabled). |
| |
| hop_limit - INTEGER |
| Default Hop Limit to set. |
| Default: 64 |
| |
| mtu - INTEGER |
| Default Maximum Transfer Unit |
| Default: 1280 (IPv6 required minimum) |
| |
| ip_nonlocal_bind - BOOLEAN |
| If set, allows processes to bind() to non-local IPv6 addresses, |
| which can be quite useful - but may break some applications. |
| Default: 0 |
| |
| router_probe_interval - INTEGER |
| Minimum interval (in seconds) between Router Probing described |
| in RFC4191. |
| |
| Default: 60 |
| |
| router_solicitation_delay - INTEGER |
| Number of seconds to wait after interface is brought up |
| before sending Router Solicitations. |
| Default: 1 |
| |
| router_solicitation_interval - INTEGER |
| Number of seconds to wait between Router Solicitations. |
| Default: 4 |
| |
| router_solicitations - INTEGER |
| Number of Router Solicitations to send until assuming no |
| routers are present. |
| Default: 3 |
| |
| use_oif_addrs_only - BOOLEAN |
| When enabled, the candidate source addresses for destinations |
| routed via this interface are restricted to the set of addresses |
| configured on this interface (vis. RFC 6724, section 4). |
| |
| Default: false |
| |
| use_tempaddr - INTEGER |
| Preference for Privacy Extensions (RFC3041). |
| <= 0 : disable Privacy Extensions |
| == 1 : enable Privacy Extensions, but prefer public |
| addresses over temporary addresses. |
| > 1 : enable Privacy Extensions and prefer temporary |
| addresses over public addresses. |
| Default: 0 (for most devices) |
| -1 (for point-to-point devices and loopback devices) |
| |
| temp_valid_lft - INTEGER |
| valid lifetime (in seconds) for temporary addresses. |
| Default: 604800 (7 days) |
| |
| temp_prefered_lft - INTEGER |
| Preferred lifetime (in seconds) for temporary addresses. |
| Default: 86400 (1 day) |
| |
| max_desync_factor - INTEGER |
| Maximum value for DESYNC_FACTOR, which is a random value |
| that ensures that clients don't synchronize with each |
| other and generate new addresses at exactly the same time. |
| value is in seconds. |
| Default: 600 |
| |
| regen_max_retry - INTEGER |
| Number of attempts before give up attempting to generate |
| valid temporary addresses. |
| Default: 5 |
| |
| max_addresses - INTEGER |
| Maximum number of autoconfigured addresses per interface. Setting |
| to zero disables the limitation. It is not recommended to set this |
| value too large (or to zero) because it would be an easy way to |
| crash the kernel by allowing too many addresses to be created. |
| Default: 16 |
| |
| disable_ipv6 - BOOLEAN |
| Disable IPv6 operation. If accept_dad is set to 2, this value |
| will be dynamically set to TRUE if DAD fails for the link-local |
| address. |
| Default: FALSE (enable IPv6 operation) |
| |
| When this value is changed from 1 to 0 (IPv6 is being enabled), |
| it will dynamically create a link-local address on the given |
| interface and start Duplicate Address Detection, if necessary. |
| |
| When this value is changed from 0 to 1 (IPv6 is being disabled), |
| it will dynamically delete all address on the given interface. |
| |
| accept_dad - INTEGER |
| Whether to accept DAD (Duplicate Address Detection). |
| 0: Disable DAD |
| 1: Enable DAD (default) |
| 2: Enable DAD, and disable IPv6 operation if MAC-based duplicate |
| link-local address has been found. |
| |
| force_tllao - BOOLEAN |
| Enable sending the target link-layer address option even when |
| responding to a unicast neighbor solicitation. |
| Default: FALSE |
| |
| Quoting from RFC 2461, section 4.4, Target link-layer address: |
| |
| "The option MUST be included for multicast solicitations in order to |
| avoid infinite Neighbor Solicitation "recursion" when the peer node |
| does not have a cache entry to return a Neighbor Advertisements |
| message. When responding to unicast solicitations, the option can be |
| omitted since the sender of the solicitation has the correct link- |
| layer address; otherwise it would not have be able to send the unicast |
| solicitation in the first place. However, including the link-layer |
| address in this case adds little overhead and eliminates a potential |
| race condition where the sender deletes the cached link-layer address |
| prior to receiving a response to a previous solicitation." |
| |
| ndisc_notify - BOOLEAN |
| Define mode for notification of address and device changes. |
| 0 - (default): do nothing |
| 1 - Generate unsolicited neighbour advertisements when device is brought |
| up or hardware address changes. |
| |
| mldv1_unsolicited_report_interval - INTEGER |
| The interval in milliseconds in which the next unsolicited |
| MLDv1 report retransmit will take place. |
| Default: 10000 (10 seconds) |
| |
| mldv2_unsolicited_report_interval - INTEGER |
| The interval in milliseconds in which the next unsolicited |
| MLDv2 report retransmit will take place. |
| Default: 1000 (1 second) |
| |
| force_mld_version - INTEGER |
| 0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed |
| 1 - Enforce to use MLD version 1 |
| 2 - Enforce to use MLD version 2 |
| |
| suppress_frag_ndisc - INTEGER |
| Control RFC 6980 (Security Implications of IPv6 Fragmentation |
| with IPv6 Neighbor Discovery) behavior: |
| 1 - (default) discard fragmented neighbor discovery packets |
| 0 - allow fragmented neighbor discovery packets |
| |
| optimistic_dad - BOOLEAN |
| Whether to perform Optimistic Duplicate Address Detection (RFC 4429). |
| 0: disabled (default) |
| 1: enabled |
| |
| use_optimistic - BOOLEAN |
| If enabled, do not classify optimistic addresses as deprecated during |
| source address selection. Preferred addresses will still be chosen |
| before optimistic addresses, subject to other ranking in the source |
| address selection algorithm. |
| 0: disabled (default) |
| 1: enabled |
| |
| stable_secret - IPv6 address |
| This IPv6 address will be used as a secret to generate IPv6 |
| addresses for link-local addresses and autoconfigured |
| ones. All addresses generated after setting this secret will |
| be stable privacy ones by default. This can be changed via the |
| addrgenmode ip-link. conf/default/stable_secret is used as the |
| secret for the namespace, the interface specific ones can |
| overwrite that. Writes to conf/all/stable_secret are refused. |
| |
| It is recommended to generate this secret during installation |
| of a system and keep it stable after that. |
| |
| By default the stable secret is unset. |
| |
| icmp/*: |
| ratelimit - INTEGER |
| Limit the maximal rates for sending ICMPv6 packets. |
| 0 to disable any limiting, |
| otherwise the minimal space between responses in milliseconds. |
| Default: 1000 |
| |
| |
| IPv6 Update by: |
| Pekka Savola <pekkas@netcore.fi> |
| YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org> |
| |
| |
| /proc/sys/net/bridge/* Variables: |
| |
| bridge-nf-call-arptables - BOOLEAN |
| 1 : pass bridged ARP traffic to arptables' FORWARD chain. |
| 0 : disable this. |
| Default: 1 |
| |
| bridge-nf-call-iptables - BOOLEAN |
| 1 : pass bridged IPv4 traffic to iptables' chains. |
| 0 : disable this. |
| Default: 1 |
| |
| bridge-nf-call-ip6tables - BOOLEAN |
| 1 : pass bridged IPv6 traffic to ip6tables' chains. |
| 0 : disable this. |
| Default: 1 |
| |
| bridge-nf-filter-vlan-tagged - BOOLEAN |
| 1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables. |
| 0 : disable this. |
| Default: 0 |
| |
| bridge-nf-filter-pppoe-tagged - BOOLEAN |
| 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables. |
| 0 : disable this. |
| Default: 0 |
| |
| bridge-nf-pass-vlan-input-dev - BOOLEAN |
| 1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan |
| interface on the bridge and set the netfilter input device to the vlan. |
| This allows use of e.g. "iptables -i br0.1" and makes the REDIRECT |
| target work with vlan-on-top-of-bridge interfaces. When no matching |
| vlan interface is found, or this switch is off, the input device is |
| set to the bridge interface. |
| 0: disable bridge netfilter vlan interface lookup. |
| Default: 0 |
| |
| proc/sys/net/sctp/* Variables: |
| |
| addip_enable - BOOLEAN |
| Enable or disable extension of Dynamic Address Reconfiguration |
| (ADD-IP) functionality specified in RFC5061. This extension provides |
| the ability to dynamically add and remove new addresses for the SCTP |
| associations. |
| |
| 1: Enable extension. |
| |
| 0: Disable extension. |
| |
| Default: 0 |
| |
| addip_noauth_enable - BOOLEAN |
| Dynamic Address Reconfiguration (ADD-IP) requires the use of |
| authentication to protect the operations of adding or removing new |
| addresses. This requirement is mandated so that unauthorized hosts |
| would not be able to hijack associations. However, older |
| implementations may not have implemented this requirement while |
| allowing the ADD-IP extension. For reasons of interoperability, |
| we provide this variable to control the enforcement of the |
| authentication requirement. |
| |
| 1: Allow ADD-IP extension to be used without authentication. This |
| should only be set in a closed environment for interoperability |
| with older implementations. |
| |
| 0: Enforce the authentication requirement |
| |
| Default: 0 |
| |
| auth_enable - BOOLEAN |
| Enable or disable Authenticated Chunks extension. This extension |
| provides the ability to send and receive authenticated chunks and is |
| required for secure operation of Dynamic Address Reconfiguration |
| (ADD-IP) extension. |
| |
| 1: Enable this extension. |
| 0: Disable this extension. |
| |
| Default: 0 |
| |
| prsctp_enable - BOOLEAN |
| Enable or disable the Partial Reliability extension (RFC3758) which |
| is used to notify peers that a given DATA should no longer be expected. |
| |
| 1: Enable extension |
| 0: Disable |
| |
| Default: 1 |
| |
| max_burst - INTEGER |
| The limit of the number of new packets that can be initially sent. It |
| controls how bursty the generated traffic can be. |
| |
| Default: 4 |
| |
| association_max_retrans - INTEGER |
| Set the maximum number for retransmissions that an association can |
| attempt deciding that the remote end is unreachable. If this value |
| is exceeded, the association is terminated. |
| |
| Default: 10 |
| |
| max_init_retransmits - INTEGER |
| The maximum number of retransmissions of INIT and COOKIE-ECHO chunks |
| that an association will attempt before declaring the destination |
| unreachable and terminating. |
| |
| Default: 8 |
| |
| path_max_retrans - INTEGER |
| The maximum number of retransmissions that will be attempted on a given |
| path. Once this threshold is exceeded, the path is considered |
| unreachable, and new traffic will use a different path when the |
| association is multihomed. |
| |
| Default: 5 |
| |
| pf_retrans - INTEGER |
| The number of retransmissions that will be attempted on a given path |
| before traffic is redirected to an alternate transport (should one |
| exist). Note this is distinct from path_max_retrans, as a path that |
| passes the pf_retrans threshold can still be used. Its only |
| deprioritized when a transmission path is selected by the stack. This |
| setting is primarily used to enable fast failover mechanisms without |
| having to reduce path_max_retrans to a very low value. See: |
| http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt |
| for details. Note also that a value of pf_retrans > path_max_retrans |
| disables this feature |
| |
| Default: 0 |
| |
| rto_initial - INTEGER |
| The initial round trip timeout value in milliseconds that will be used |
| in calculating round trip times. This is the initial time interval |
| for retransmissions. |
| |
| Default: 3000 |
| |
| rto_max - INTEGER |
| The maximum value (in milliseconds) of the round trip timeout. This |
| is the largest time interval that can elapse between retransmissions. |
| |
| Default: 60000 |
| |
| rto_min - INTEGER |
| The minimum value (in milliseconds) of the round trip timeout. This |
| is the smallest time interval the can elapse between retransmissions. |
| |
| Default: 1000 |
| |
| hb_interval - INTEGER |
| The interval (in milliseconds) between HEARTBEAT chunks. These chunks |
| are sent at the specified interval on idle paths to probe the state of |
| a given path between 2 associations. |
| |
| Default: 30000 |
| |
| sack_timeout - INTEGER |
| The amount of time (in milliseconds) that the implementation will wait |
| to send a SACK. |
| |
| Default: 200 |
| |
| valid_cookie_life - INTEGER |
| The default lifetime of the SCTP cookie (in milliseconds). The cookie |
| is used during association establishment. |
| |
| Default: 60000 |
| |
| cookie_preserve_enable - BOOLEAN |
| Enable or disable the ability to extend the lifetime of the SCTP cookie |
| that is used during the establishment phase of SCTP association |
| |
| 1: Enable cookie lifetime extension. |
| 0: Disable |
| |
| Default: 1 |
| |
| cookie_hmac_alg - STRING |
| Select the hmac algorithm used when generating the cookie value sent by |
| a listening sctp socket to a connecting client in the INIT-ACK chunk. |
| Valid values are: |
| * md5 |
| * sha1 |
| * none |
| Ability to assign md5 or sha1 as the selected alg is predicated on the |
| configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and |
| CONFIG_CRYPTO_SHA1). |
| |
| Default: Dependent on configuration. MD5 if available, else SHA1 if |
| available, else none. |
| |
| rcvbuf_policy - INTEGER |
| Determines if the receive buffer is attributed to the socket or to |
| association. SCTP supports the capability to create multiple |
| associations on a single socket. When using this capability, it is |
| possible that a single stalled association that's buffering a lot |
| of data may block other associations from delivering their data by |
| consuming all of the receive buffer space. To work around this, |
| the rcvbuf_policy could be set to attribute the receiver buffer space |
| to each association instead of the socket. This prevents the described |
| blocking. |
| |
| 1: rcvbuf space is per association |
| 0: rcvbuf space is per socket |
| |
| Default: 0 |
| |
| sndbuf_policy - INTEGER |
| Similar to rcvbuf_policy above, this applies to send buffer space. |
| |
| 1: Send buffer is tracked per association |
| 0: Send buffer is tracked per socket. |
| |
| Default: 0 |
| |
| sctp_mem - vector of 3 INTEGERs: min, pressure, max |
| Number of pages allowed for queueing by all SCTP sockets. |
| |
| min: Below this number of pages SCTP is not bothered about its |
| memory appetite. When amount of memory allocated by SCTP exceeds |
| this number, SCTP starts to moderate memory usage. |
| |
| pressure: This value was introduced to follow format of tcp_mem. |
| |
| max: Number of pages allowed for queueing by all SCTP sockets. |
| |
| Default is calculated at boot time from amount of available memory. |
| |
| sctp_rmem - vector of 3 INTEGERs: min, default, max |
| Only the first value ("min") is used, "default" and "max" are |
| ignored. |
| |
| min: Minimal size of receive buffer used by SCTP socket. |
| It is guaranteed to each SCTP socket (but not association) even |
| under moderate memory pressure. |
| |
| Default: 1 page |
| |
| sctp_wmem - vector of 3 INTEGERs: min, default, max |
| Currently this tunable has no effect. |
| |
| addr_scope_policy - INTEGER |
| Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00 |
| |
| 0 - Disable IPv4 address scoping |
| 1 - Enable IPv4 address scoping |
| 2 - Follow draft but allow IPv4 private addresses |
| 3 - Follow draft but allow IPv4 link local addresses |
| |
| Default: 1 |
| |
| |
| /proc/sys/net/core/* |
| Please see: Documentation/sysctl/net.txt for descriptions of these entries. |
| |
| |
| /proc/sys/net/unix/* |
| max_dgram_qlen - INTEGER |
| The maximum length of dgram socket receive queue |
| |
| Default: 10 |
| |
| |
| UNDOCUMENTED: |
| |
| /proc/sys/net/irda/* |
| fast_poll_increase FIXME |
| warn_noreply_time FIXME |
| discovery_slots FIXME |
| slot_timeout FIXME |
| max_baud_rate FIXME |
| discovery_timeout FIXME |
| lap_keepalive_time FIXME |
| max_noreply_time FIXME |
| max_tx_data_size FIXME |
| max_tx_window FIXME |
| min_tx_turn_time FIXME |