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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/proc/sys/net/ipv4/* Variables:
2
3ip_forward - BOOLEAN
4 0 - disabled (default)
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00005 not 0 - enabled
Linus Torvalds1da177e2005-04-16 15:20:36 -07006
7 Forward Packets between interfaces.
8
9 This variable is special, its change resets all configuration
10 parameters to their default state (RFC1122 for hosts, RFC1812
11 for routers)
12
13ip_default_ttl - INTEGER
Eric Dumazetcc6f02d2010-12-13 12:50:49 -080014 Default value of TTL field (Time To Live) for outgoing (but not
15 forwarded) IP packets. Should be between 1 and 255 inclusive.
16 Default: 64 (as recommended by RFC1700)
Linus Torvalds1da177e2005-04-16 15:20:36 -070017
Hannes Frederic Sowacd174e62013-12-14 05:13:45 +010018ip_no_pmtu_disc - INTEGER
19 Disable Path MTU Discovery. If enabled in mode 1 and a
Hannes Frederic Sowa188b04d2013-12-14 04:42:13 +010020 fragmentation-required ICMP is received, the PMTU to this
21 destination will be set to min_pmtu (see below). You will need
22 to raise min_pmtu to the smallest interface MTU on your system
23 manually if you want to avoid locally generated fragments.
Hannes Frederic Sowacd174e62013-12-14 05:13:45 +010024
25 In mode 2 incoming Path MTU Discovery messages will be
26 discarded. Outgoing frames are handled the same as in mode 1,
27 implicitly setting IP_PMTUDISC_DONT on every created socket.
28
Hannes Frederic Sowa8ed1dc42014-01-09 10:01:17 +010029 Mode 3 is a hardend pmtu discover mode. The kernel will only
30 accept fragmentation-needed errors if the underlying protocol
31 can verify them besides a plain socket lookup. Current
32 protocols for which pmtu events will be honored are TCP, SCTP
33 and DCCP as they verify e.g. the sequence number or the
34 association. This mode should not be enabled globally but is
35 only intended to secure e.g. name servers in namespaces where
36 TCP path mtu must still work but path MTU information of other
37 protocols should be discarded. If enabled globally this mode
38 could break other protocols.
39
40 Possible values: 0-3
Hannes Frederic Sowa188b04d2013-12-14 04:42:13 +010041 Default: FALSE
Linus Torvalds1da177e2005-04-16 15:20:36 -070042
43min_pmtu - INTEGER
Eric Dumazet20db93c2011-11-08 14:21:44 -050044 default 552 - minimum discovered Path MTU
Linus Torvalds1da177e2005-04-16 15:20:36 -070045
Hannes Frederic Sowaf87c10a2014-01-09 10:01:15 +010046ip_forward_use_pmtu - BOOLEAN
47 By default we don't trust protocol path MTUs while forwarding
48 because they could be easily forged and can lead to unwanted
49 fragmentation by the router.
50 You only need to enable this if you have user-space software
51 which tries to discover path mtus by itself and depends on the
52 kernel honoring this information. This is normally not the
53 case.
54 Default: 0 (disabled)
55 Possible values:
56 0 - disabled
57 1 - enabled
58
Ben Greearcbaf0872010-11-08 09:13:48 +000059route/max_size - INTEGER
60 Maximum number of routes allowed in the kernel. Increase
61 this when using large numbers of interfaces and/or routes.
62
YOSHIFUJI Hideaki / 吉藤英明27246802013-01-22 05:20:05 +000063neigh/default/gc_thresh1 - INTEGER
64 Minimum number of entries to keep. Garbage collector will not
65 purge entries if there are fewer than this number.
Li RongQingb66c66d2013-03-14 22:49:47 +000066 Default: 128
YOSHIFUJI Hideaki / 吉藤英明27246802013-01-22 05:20:05 +000067
Ben Greearcbaf0872010-11-08 09:13:48 +000068neigh/default/gc_thresh3 - INTEGER
69 Maximum number of neighbor entries allowed. Increase this
70 when using large numbers of interfaces and when communicating
71 with large numbers of directly-connected peers.
Shan Weicc868022012-12-04 18:50:35 +000072 Default: 1024
Ben Greearcbaf0872010-11-08 09:13:48 +000073
Eric Dumazet8b5c1712011-11-09 12:07:14 +000074neigh/default/unres_qlen_bytes - INTEGER
75 The maximum number of bytes which may be used by packets
76 queued for each unresolved address by other network layers.
77 (added in linux 3.3)
stephen hemminger3b09adc2013-01-03 07:50:29 +000078 Setting negative value is meaningless and will return error.
Shan Weicc868022012-12-04 18:50:35 +000079 Default: 65536 Bytes(64KB)
Eric Dumazet8b5c1712011-11-09 12:07:14 +000080
81neigh/default/unres_qlen - INTEGER
82 The maximum number of packets which may be queued for each
83 unresolved address by other network layers.
84 (deprecated in linux 3.3) : use unres_qlen_bytes instead.
Shan Weicc868022012-12-04 18:50:35 +000085 Prior to linux 3.3, the default value is 3 which may cause
Shan Wei5d248c42012-12-06 16:27:51 +000086 unexpected packet loss. The current default value is calculated
Shan Weicc868022012-12-04 18:50:35 +000087 according to default value of unres_qlen_bytes and true size of
88 packet.
89 Default: 31
Eric Dumazet8b5c1712011-11-09 12:07:14 +000090
Linus Torvalds1da177e2005-04-16 15:20:36 -070091mtu_expires - INTEGER
92 Time, in seconds, that cached PMTU information is kept.
93
94min_adv_mss - INTEGER
95 The advertised MSS depends on the first hop route MTU, but will
96 never be lower than this setting.
97
98IP Fragmentation:
99
100ipfrag_high_thresh - INTEGER
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000101 Maximum memory used to reassemble IP fragments. When
Linus Torvalds1da177e2005-04-16 15:20:36 -0700102 ipfrag_high_thresh bytes of memory is allocated for this purpose,
103 the fragment handler will toss packets until ipfrag_low_thresh
104 is reached.
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000105
Linus Torvalds1da177e2005-04-16 15:20:36 -0700106ipfrag_low_thresh - INTEGER
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000107 See ipfrag_high_thresh
Linus Torvalds1da177e2005-04-16 15:20:36 -0700108
109ipfrag_time - INTEGER
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000110 Time in seconds to keep an IP fragment in memory.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700111
112ipfrag_secret_interval - INTEGER
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000113 Regeneration interval (in seconds) of the hash secret (or lifetime
Linus Torvalds1da177e2005-04-16 15:20:36 -0700114 for the hash secret) for IP fragments.
115 Default: 600
116
Herbert Xu89cee8b2005-12-13 23:14:27 -0800117ipfrag_max_dist - INTEGER
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000118 ipfrag_max_dist is a non-negative integer value which defines the
119 maximum "disorder" which is allowed among fragments which share a
120 common IP source address. Note that reordering of packets is
121 not unusual, but if a large number of fragments arrive from a source
122 IP address while a particular fragment queue remains incomplete, it
123 probably indicates that one or more fragments belonging to that queue
124 have been lost. When ipfrag_max_dist is positive, an additional check
125 is done on fragments before they are added to a reassembly queue - if
126 ipfrag_max_dist (or more) fragments have arrived from a particular IP
127 address between additions to any IP fragment queue using that source
128 address, it's presumed that one or more fragments in the queue are
129 lost. The existing fragment queue will be dropped, and a new one
Herbert Xu89cee8b2005-12-13 23:14:27 -0800130 started. An ipfrag_max_dist value of zero disables this check.
131
132 Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
133 result in unnecessarily dropping fragment queues when normal
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000134 reordering of packets occurs, which could lead to poor application
135 performance. Using a very large value, e.g. 50000, increases the
136 likelihood of incorrectly reassembling IP fragments that originate
Herbert Xu89cee8b2005-12-13 23:14:27 -0800137 from different IP datagrams, which could result in data corruption.
138 Default: 64
139
Linus Torvalds1da177e2005-04-16 15:20:36 -0700140INET peer storage:
141
142inet_peer_threshold - INTEGER
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000143 The approximate size of the storage. Starting from this threshold
Linus Torvalds1da177e2005-04-16 15:20:36 -0700144 entries will be thrown aggressively. This threshold also determines
145 entries' time-to-live and time intervals between garbage collection
146 passes. More entries, less time-to-live, less GC interval.
147
148inet_peer_minttl - INTEGER
149 Minimum time-to-live of entries. Should be enough to cover fragment
150 time-to-live on the reassembling side. This minimum time-to-live is
151 guaranteed if the pool size is less than inet_peer_threshold.
Stephen Hemminger77a538d2008-07-01 17:22:48 -0700152 Measured in seconds.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700153
154inet_peer_maxttl - INTEGER
155 Maximum time-to-live of entries. Unused entries will expire after
156 this period of time if there is no memory pressure on the pool (i.e.
157 when the number of entries in the pool is very small).
Stephen Hemminger77a538d2008-07-01 17:22:48 -0700158 Measured in seconds.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700159
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000160TCP variables:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700161
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800162somaxconn - INTEGER
163 Limit of socket listen() backlog, known in userspace as SOMAXCONN.
164 Defaults to 128. See also tcp_max_syn_backlog for additional tuning
165 for TCP sockets.
166
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800167tcp_abort_on_overflow - BOOLEAN
168 If listening service is too slow to accept new connections,
169 reset them. Default state is FALSE. It means that if overflow
170 occurred due to a burst, connection will recover. Enable this
171 option _only_ if you are really sure that listening daemon
172 cannot be tuned to accept connections faster. Enabling this
173 option can harm clients of your server.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700174
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800175tcp_adv_win_scale - INTEGER
176 Count buffering overhead as bytes/2^tcp_adv_win_scale
177 (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
178 if it is <= 0.
Alexey Dobriyan0147fc02010-11-22 12:54:21 +0000179 Possible values are [-31, 31], inclusive.
Eric Dumazetb49960a2012-05-02 02:28:41 +0000180 Default: 1
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800181
182tcp_allowed_congestion_control - STRING
183 Show/set the congestion control choices available to non-privileged
184 processes. The list is a subset of those listed in
185 tcp_available_congestion_control.
186 Default is "reno" and the default setting (tcp_congestion_control).
187
188tcp_app_win - INTEGER
189 Reserve max(window/2^tcp_app_win, mss) of window for application
190 buffer. Value 0 is special, it means that nothing is reserved.
191 Default: 31
192
Eric Dumazetf54b3112013-12-05 22:36:05 -0800193tcp_autocorking - BOOLEAN
194 Enable TCP auto corking :
195 When applications do consecutive small write()/sendmsg() system calls,
196 we try to coalesce these small writes as much as possible, to lower
197 total amount of sent packets. This is done if at least one prior
198 packet for the flow is waiting in Qdisc queues or device transmit
199 queue. Applications can still use TCP_CORK for optimal behavior
200 when they know how/when to uncork their sockets.
201 Default : 1
202
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800203tcp_available_congestion_control - STRING
204 Shows the available congestion control choices that are registered.
205 More congestion control algorithms may be available as modules,
206 but not loaded.
207
John Heffner71599cd2007-02-27 10:03:56 -0800208tcp_base_mss - INTEGER
Stephen Hemminger4edc2f32008-07-10 16:50:26 -0700209 The initial value of search_low to be used by the packetization layer
210 Path MTU discovery (MTU probing). If MTU probing is enabled,
211 this is the initial MSS used by the connection.
John Heffner71599cd2007-02-27 10:03:56 -0800212
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800213tcp_congestion_control - STRING
214 Set the congestion control algorithm to be used for new
215 connections. The algorithm "reno" is always available, but
216 additional choices may be available based on kernel configuration.
217 Default is set as part of kernel configuration.
Eric Dumazetd8a6e652011-11-30 01:02:41 +0000218 For passive connections, the listener congestion control choice
219 is inherited.
220 [see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ]
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800221
222tcp_dsack - BOOLEAN
223 Allows TCP to send "duplicate" SACKs.
224
Yuchung Chengeed530b2012-05-02 13:30:03 +0000225tcp_early_retrans - INTEGER
226 Enable Early Retransmit (ER), per RFC 5827. ER lowers the threshold
227 for triggering fast retransmit when the amount of outstanding data is
228 small and when no previously unsent data can be transmitted (such
Nandita Dukkipati6ba8a3b2013-03-11 10:00:43 +0000229 that limited transmit could be used). Also controls the use of
Masanari Iida3dd17ed2013-05-24 07:05:59 +0000230 Tail loss probe (TLP) that converts RTOs occurring due to tail
Nandita Dukkipati6ba8a3b2013-03-11 10:00:43 +0000231 losses into fast recovery (draft-dukkipati-tcpm-tcp-loss-probe-01).
Yuchung Chengeed530b2012-05-02 13:30:03 +0000232 Possible values:
233 0 disables ER
234 1 enables ER
235 2 enables ER but delays fast recovery and fast retransmit
236 by a fourth of RTT. This mitigates connection falsely
237 recovers when network has a small degree of reordering
238 (less than 3 packets).
Nandita Dukkipati6ba8a3b2013-03-11 10:00:43 +0000239 3 enables delayed ER and TLP.
240 4 enables TLP only.
241 Default: 3
Yuchung Chengeed530b2012-05-02 13:30:03 +0000242
Peter Chubb34a6ef32011-02-02 15:39:58 -0800243tcp_ecn - INTEGER
Rick Jones7e3a2dc2012-11-28 09:53:10 +0000244 Control use of Explicit Congestion Notification (ECN) by TCP.
245 ECN is used only when both ends of the TCP connection indicate
246 support for it. This feature is useful in avoiding losses due
247 to congestion by allowing supporting routers to signal
248 congestion before having to drop packets.
Ilpo Järvinen255cac92009-05-04 11:07:36 -0700249 Possible values are:
Rick Jones7e3a2dc2012-11-28 09:53:10 +0000250 0 Disable ECN. Neither initiate nor accept ECN.
Vijay Subramanian3d55b322013-01-09 12:21:30 +0000251 1 Enable ECN when requested by incoming connections and
252 also request ECN on outgoing connection attempts.
253 2 Enable ECN when requested by incoming connections
Rick Jones7e3a2dc2012-11-28 09:53:10 +0000254 but do not request ECN on outgoing connections.
Ilpo Järvinen255cac92009-05-04 11:07:36 -0700255 Default: 2
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800256
257tcp_fack - BOOLEAN
258 Enable FACK congestion avoidance and fast retransmission.
259 The value is not used, if tcp_sack is not enabled.
260
261tcp_fin_timeout - INTEGER
Rick Jonesd825da22012-12-10 11:33:00 +0000262 The length of time an orphaned (no longer referenced by any
263 application) connection will remain in the FIN_WAIT_2 state
264 before it is aborted at the local end. While a perfectly
265 valid "receive only" state for an un-orphaned connection, an
266 orphaned connection in FIN_WAIT_2 state could otherwise wait
267 forever for the remote to close its end of the connection.
268 Cf. tcp_max_orphans
269 Default: 60 seconds
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800270
Ilpo Järvinen89808062007-02-27 10:10:55 -0800271tcp_frto - INTEGER
Yuchung Chenge33099f2013-03-20 13:33:00 +0000272 Enables Forward RTO-Recovery (F-RTO) defined in RFC5682.
Ilpo Järvinencd998892007-09-20 11:35:26 -0700273 F-RTO is an enhanced recovery algorithm for TCP retransmission
Yuchung Chenge33099f2013-03-20 13:33:00 +0000274 timeouts. It is particularly beneficial in networks where the
275 RTT fluctuates (e.g., wireless). F-RTO is sender-side only
276 modification. It does not require any support from the peer.
Stephen Hemminger4edc2f32008-07-10 16:50:26 -0700277
Yuchung Chenge33099f2013-03-20 13:33:00 +0000278 By default it's enabled with a non-zero value. 0 disables F-RTO.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700279
280tcp_keepalive_time - INTEGER
281 How often TCP sends out keepalive messages when keepalive is enabled.
282 Default: 2hours.
283
284tcp_keepalive_probes - INTEGER
285 How many keepalive probes TCP sends out, until it decides that the
286 connection is broken. Default value: 9.
287
288tcp_keepalive_intvl - INTEGER
289 How frequently the probes are send out. Multiplied by
290 tcp_keepalive_probes it is time to kill not responding connection,
291 after probes started. Default value: 75sec i.e. connection
292 will be aborted after ~11 minutes of retries.
293
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800294tcp_low_latency - BOOLEAN
295 If set, the TCP stack makes decisions that prefer lower
296 latency as opposed to higher throughput. By default, this
297 option is not set meaning that higher throughput is preferred.
298 An example of an application where this default should be
299 changed would be a Beowulf compute cluster.
300 Default: 0
Linus Torvalds1da177e2005-04-16 15:20:36 -0700301
302tcp_max_orphans - INTEGER
303 Maximal number of TCP sockets not attached to any user file handle,
304 held by system. If this number is exceeded orphaned connections are
305 reset immediately and warning is printed. This limit exists
306 only to prevent simple DoS attacks, you _must_ not rely on this
307 or lower the limit artificially, but rather increase it
308 (probably, after increasing installed memory),
309 if network conditions require more than default value,
310 and tune network services to linger and kill such states
311 more aggressively. Let me to remind again: each orphan eats
312 up to ~64K of unswappable memory.
313
Linus Torvalds1da177e2005-04-16 15:20:36 -0700314tcp_max_syn_backlog - INTEGER
Peter Pan(潘卫平)99b53bd2011-12-05 21:39:41 +0000315 Maximal number of remembered connection requests, which have not
316 received an acknowledgment from connecting client.
317 The minimal value is 128 for low memory machines, and it will
318 increase in proportion to the memory of machine.
319 If server suffers from overload, try increasing this number.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700320
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800321tcp_max_tw_buckets - INTEGER
322 Maximal number of timewait sockets held by system simultaneously.
323 If this number is exceeded time-wait socket is immediately destroyed
324 and warning is printed. This limit exists only to prevent
325 simple DoS attacks, you _must_ not lower the limit artificially,
326 but rather increase it (probably, after increasing installed memory),
327 if network conditions require more than default value.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700328
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800329tcp_mem - vector of 3 INTEGERs: min, pressure, max
330 min: below this number of pages TCP is not bothered about its
331 memory appetite.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700332
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800333 pressure: when amount of memory allocated by TCP exceeds this number
334 of pages, TCP moderates its memory consumption and enters memory
335 pressure mode, which is exited when memory consumption falls
336 under "min".
Linus Torvalds1da177e2005-04-16 15:20:36 -0700337
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800338 max: number of pages allowed for queueing by all TCP sockets.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700339
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800340 Defaults are calculated at boot time from amount of available
341 memory.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700342
John Heffner71599cd2007-02-27 10:03:56 -0800343tcp_moderate_rcvbuf - BOOLEAN
Stephen Hemminger4edc2f32008-07-10 16:50:26 -0700344 If set, TCP performs receive buffer auto-tuning, attempting to
John Heffner71599cd2007-02-27 10:03:56 -0800345 automatically size the buffer (no greater than tcp_rmem[2]) to
346 match the size required by the path for full throughput. Enabled by
347 default.
348
349tcp_mtu_probing - INTEGER
350 Controls TCP Packetization-Layer Path MTU Discovery. Takes three
351 values:
352 0 - Disabled
353 1 - Disabled by default, enabled when an ICMP black hole detected
354 2 - Always enabled, use initial MSS of tcp_base_mss.
355
356tcp_no_metrics_save - BOOLEAN
357 By default, TCP saves various connection metrics in the route cache
358 when the connection closes, so that connections established in the
359 near future can use these to set initial conditions. Usually, this
360 increases overall performance, but may sometimes cause performance
Simon Arlott0f035b82007-10-20 01:30:25 +0200361 degradation. If set, TCP will not cache metrics on closing
John Heffner71599cd2007-02-27 10:03:56 -0800362 connections.
363
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800364tcp_orphan_retries - INTEGER
Damian Lukowski5d789222009-09-01 10:24:04 +0000365 This value influences the timeout of a locally closed TCP connection,
366 when RTO retransmissions remain unacknowledged.
367 See tcp_retries2 for more details.
368
David S. Miller06b8fc52011-07-08 09:31:31 -0700369 The default value is 8.
Damian Lukowski5d789222009-09-01 10:24:04 +0000370 If your machine is a loaded WEB server,
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800371 you should think about lowering this value, such sockets
372 may consume significant resources. Cf. tcp_max_orphans.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700373
374tcp_reordering - INTEGER
375 Maximal reordering of packets in a TCP stream.
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000376 Default: 3
Linus Torvalds1da177e2005-04-16 15:20:36 -0700377
378tcp_retrans_collapse - BOOLEAN
379 Bug-to-bug compatibility with some broken printers.
380 On retransmit try to send bigger packets to work around bugs in
381 certain TCP stacks.
382
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800383tcp_retries1 - INTEGER
Damian Lukowski5d789222009-09-01 10:24:04 +0000384 This value influences the time, after which TCP decides, that
385 something is wrong due to unacknowledged RTO retransmissions,
386 and reports this suspicion to the network layer.
387 See tcp_retries2 for more details.
388
389 RFC 1122 recommends at least 3 retransmissions, which is the
390 default.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700391
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800392tcp_retries2 - INTEGER
Damian Lukowski5d789222009-09-01 10:24:04 +0000393 This value influences the timeout of an alive TCP connection,
394 when RTO retransmissions remain unacknowledged.
395 Given a value of N, a hypothetical TCP connection following
396 exponential backoff with an initial RTO of TCP_RTO_MIN would
397 retransmit N times before killing the connection at the (N+1)th RTO.
398
399 The default value of 15 yields a hypothetical timeout of 924.6
400 seconds and is a lower bound for the effective timeout.
401 TCP will effectively time out at the first RTO which exceeds the
402 hypothetical timeout.
403
404 RFC 1122 recommends at least 100 seconds for the timeout,
405 which corresponds to a value of at least 8.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700406
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800407tcp_rfc1337 - BOOLEAN
408 If set, the TCP stack behaves conforming to RFC1337. If unset,
409 we are not conforming to RFC, but prevent TCP TIME_WAIT
410 assassination.
411 Default: 0
Linus Torvalds1da177e2005-04-16 15:20:36 -0700412
413tcp_rmem - vector of 3 INTEGERs: min, default, max
414 min: Minimal size of receive buffer used by TCP sockets.
415 It is guaranteed to each TCP socket, even under moderate memory
416 pressure.
Max Matveev6539fef2011-06-21 21:18:13 +0000417 Default: 1 page
Linus Torvalds1da177e2005-04-16 15:20:36 -0700418
J. Bruce Fields53025f52008-07-10 16:47:41 -0700419 default: initial size of receive buffer used by TCP sockets.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700420 This value overrides net.core.rmem_default used by other protocols.
421 Default: 87380 bytes. This value results in window of 65535 with
422 default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
423 less for default tcp_app_win. See below about these variables.
424
425 max: maximal size of receive buffer allowed for automatically
426 selected receiver buffers for TCP socket. This value does not override
J. Bruce Fields53025f52008-07-10 16:47:41 -0700427 net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables
428 automatic tuning of that socket's receive buffer size, in which
429 case this value is ignored.
Eric Dumazetb49960a2012-05-02 02:28:41 +0000430 Default: between 87380B and 6MB, depending on RAM size.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700431
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800432tcp_sack - BOOLEAN
433 Enable select acknowledgments (SACKS).
Rick Jones15d99e02006-03-20 22:40:29 -0800434
David S. Miller35089bb2006-06-13 22:33:04 -0700435tcp_slow_start_after_idle - BOOLEAN
436 If set, provide RFC2861 behavior and time out the congestion
437 window after an idle period. An idle period is defined at
438 the current RTO. If unset, the congestion window will not
439 be timed out after an idle period.
440 Default: 1
441
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800442tcp_stdurg - BOOLEAN
Stephen Hemminger4edc2f32008-07-10 16:50:26 -0700443 Use the Host requirements interpretation of the TCP urgent pointer field.
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800444 Most hosts use the older BSD interpretation, so if you turn this on
445 Linux might not communicate correctly with them.
446 Default: FALSE
447
448tcp_synack_retries - INTEGER
449 Number of times SYNACKs for a passive TCP connection attempt will
450 be retransmitted. Should not be higher than 255. Default value
Alex Bergmann6c9ff972012-08-31 02:48:31 +0000451 is 5, which corresponds to 31seconds till the last retransmission
452 with the current initial RTO of 1second. With this the final timeout
453 for a passive TCP connection will happen after 63seconds.
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800454
455tcp_syncookies - BOOLEAN
Shan Weia3c910d2013-06-21 15:18:32 +0800456 Only valid when the kernel was compiled with CONFIG_SYN_COOKIES
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800457 Send out syncookies when the syn backlog queue of a socket
Stephen Hemminger4edc2f32008-07-10 16:50:26 -0700458 overflows. This is to prevent against the common 'SYN flood attack'
Shan Weia3c910d2013-06-21 15:18:32 +0800459 Default: 1
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800460
461 Note, that syncookies is fallback facility.
462 It MUST NOT be used to help highly loaded servers to stand
Stephen Hemminger4edc2f32008-07-10 16:50:26 -0700463 against legal connection rate. If you see SYN flood warnings
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800464 in your logs, but investigation shows that they occur
465 because of overload with legal connections, you should tune
466 another parameters until this warning disappear.
467 See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
468
469 syncookies seriously violate TCP protocol, do not allow
470 to use TCP extensions, can result in serious degradation
471 of some services (f.e. SMTP relaying), visible not by you,
472 but your clients and relays, contacting you. While you see
Stephen Hemminger4edc2f32008-07-10 16:50:26 -0700473 SYN flood warnings in logs not being really flooded, your server
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800474 is seriously misconfigured.
475
Hannes Frederic Sowa5ad37d52013-07-26 17:43:23 +0200476 If you want to test which effects syncookies have to your
477 network connections you can set this knob to 2 to enable
478 unconditionally generation of syncookies.
479
Yuchung Chengcf60af02012-07-19 06:43:09 +0000480tcp_fastopen - INTEGER
481 Enable TCP Fast Open feature (draft-ietf-tcpm-fastopen) to send data
482 in the opening SYN packet. To use this feature, the client application
Jerry Chu10467162012-08-31 12:29:11 +0000483 must use sendmsg() or sendto() with MSG_FASTOPEN flag rather than
484 connect() to perform a TCP handshake automatically.
Yuchung Chengcf60af02012-07-19 06:43:09 +0000485
Jerry Chu10467162012-08-31 12:29:11 +0000486 The values (bitmap) are
Yuchung Cheng0d41cca2013-10-31 09:19:32 -0700487 1: Enables sending data in the opening SYN on the client w/ MSG_FASTOPEN.
Jerry Chu10467162012-08-31 12:29:11 +0000488 2: Enables TCP Fast Open on the server side, i.e., allowing data in
489 a SYN packet to be accepted and passed to the application before
490 3-way hand shake finishes.
491 4: Send data in the opening SYN regardless of cookie availability and
492 without a cookie option.
493 0x100: Accept SYN data w/o validating the cookie.
494 0x200: Accept data-in-SYN w/o any cookie option present.
495 0x400/0x800: Enable Fast Open on all listeners regardless of the
496 TCP_FASTOPEN socket option. The two different flags designate two
497 different ways of setting max_qlen without the TCP_FASTOPEN socket
498 option.
Yuchung Chengcf60af02012-07-19 06:43:09 +0000499
Yuchung Cheng0d41cca2013-10-31 09:19:32 -0700500 Default: 1
Yuchung Chengcf60af02012-07-19 06:43:09 +0000501
Jerry Chu10467162012-08-31 12:29:11 +0000502 Note that the client & server side Fast Open flags (1 and 2
503 respectively) must be also enabled before the rest of flags can take
504 effect.
505
506 See include/net/tcp.h and the code for more details.
507
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800508tcp_syn_retries - INTEGER
509 Number of times initial SYNs for an active TCP connection attempt
510 will be retransmitted. Should not be higher than 255. Default value
stephen hemminger3b09adc2013-01-03 07:50:29 +0000511 is 6, which corresponds to 63seconds till the last retransmission
Alex Bergmann6c9ff972012-08-31 02:48:31 +0000512 with the current initial RTO of 1second. With this the final timeout
513 for an active TCP connection attempt will happen after 127seconds.
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800514
515tcp_timestamps - BOOLEAN
516 Enable timestamps as defined in RFC1323.
517
Eric Dumazet95bd09e2013-08-27 05:46:32 -0700518tcp_min_tso_segs - INTEGER
519 Minimal number of segments per TSO frame.
520 Since linux-3.12, TCP does an automatic sizing of TSO frames,
521 depending on flow rate, instead of filling 64Kbytes packets.
522 For specific usages, it's possible to force TCP to build big
523 TSO frames. Note that TCP stack might split too big TSO packets
524 if available window is too small.
525 Default: 2
526
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800527tcp_tso_win_divisor - INTEGER
528 This allows control over what percentage of the congestion window
529 can be consumed by a single TSO frame.
530 The setting of this parameter is a choice between burstiness and
531 building larger TSO frames.
532 Default: 3
533
534tcp_tw_recycle - BOOLEAN
535 Enable fast recycling TIME-WAIT sockets. Default value is 0.
536 It should not be changed without advice/request of technical
537 experts.
538
539tcp_tw_reuse - BOOLEAN
540 Allow to reuse TIME-WAIT sockets for new connections when it is
541 safe from protocol viewpoint. Default value is 0.
542 It should not be changed without advice/request of technical
543 experts.
544
545tcp_window_scaling - BOOLEAN
546 Enable window scaling as defined in RFC1323.
547
548tcp_wmem - vector of 3 INTEGERs: min, default, max
J. Bruce Fields53025f52008-07-10 16:47:41 -0700549 min: Amount of memory reserved for send buffers for TCP sockets.
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800550 Each TCP socket has rights to use it due to fact of its birth.
Max Matveev6539fef2011-06-21 21:18:13 +0000551 Default: 1 page
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800552
J. Bruce Fields53025f52008-07-10 16:47:41 -0700553 default: initial size of send buffer used by TCP sockets. This
554 value overrides net.core.wmem_default used by other protocols.
555 It is usually lower than net.core.wmem_default.
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800556 Default: 16K
557
J. Bruce Fields53025f52008-07-10 16:47:41 -0700558 max: Maximal amount of memory allowed for automatically tuned
559 send buffers for TCP sockets. This value does not override
560 net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables
561 automatic tuning of that socket's send buffer size, in which case
562 this value is ignored.
563 Default: between 64K and 4MB, depending on RAM size.
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800564
Eric Dumazetc9bee3b72013-07-22 20:27:07 -0700565tcp_notsent_lowat - UNSIGNED INTEGER
566 A TCP socket can control the amount of unsent bytes in its write queue,
567 thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll()
568 reports POLLOUT events if the amount of unsent bytes is below a per
569 socket value, and if the write queue is not full. sendmsg() will
570 also not add new buffers if the limit is hit.
571
572 This global variable controls the amount of unsent data for
573 sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change
574 to the global variable has immediate effect.
575
576 Default: UINT_MAX (0xFFFFFFFF)
577
Stephen Hemmingeref56e622006-11-09 16:37:26 -0800578tcp_workaround_signed_windows - BOOLEAN
579 If set, assume no receipt of a window scaling option means the
580 remote TCP is broken and treats the window as a signed quantity.
581 If unset, assume the remote TCP is not broken even if we do
582 not receive a window scaling option from them.
583 Default: 0
584
Chris Leech72d0b7a2007-03-08 09:57:35 -0800585tcp_dma_copybreak - INTEGER
586 Lower limit, in bytes, of the size of socket reads that will be
587 offloaded to a DMA copy engine, if one is present in the system
588 and CONFIG_NET_DMA is enabled.
589 Default: 4096
590
Andreas Petlund36e31b0a2010-02-18 02:47:01 +0000591tcp_thin_linear_timeouts - BOOLEAN
592 Enable dynamic triggering of linear timeouts for thin streams.
593 If set, a check is performed upon retransmission by timeout to
594 determine if the stream is thin (less than 4 packets in flight).
595 As long as the stream is found to be thin, up to 6 linear
596 timeouts may be performed before exponential backoff mode is
597 initiated. This improves retransmission latency for
598 non-aggressive thin streams, often found to be time-dependent.
599 For more information on thin streams, see
600 Documentation/networking/tcp-thin.txt
601 Default: 0
602
Andreas Petlund7e380172010-02-18 04:48:19 +0000603tcp_thin_dupack - BOOLEAN
604 Enable dynamic triggering of retransmissions after one dupACK
605 for thin streams. If set, a check is performed upon reception
606 of a dupACK to determine if the stream is thin (less than 4
607 packets in flight). As long as the stream is found to be thin,
608 data is retransmitted on the first received dupACK. This
609 improves retransmission latency for non-aggressive thin
610 streams, often found to be time-dependent.
611 For more information on thin streams, see
612 Documentation/networking/tcp-thin.txt
613 Default: 0
614
Eric Dumazet46d3cea2012-07-11 05:50:31 +0000615tcp_limit_output_bytes - INTEGER
616 Controls TCP Small Queue limit per tcp socket.
617 TCP bulk sender tends to increase packets in flight until it
618 gets losses notifications. With SNDBUF autotuning, this can
619 result in a large amount of packets queued in qdisc/device
620 on the local machine, hurting latency of other flows, for
621 typical pfifo_fast qdiscs.
622 tcp_limit_output_bytes limits the number of bytes on qdisc
623 or device to reduce artificial RTT/cwnd and reduce bufferbloat.
Eric Dumazet46d3cea2012-07-11 05:50:31 +0000624 Default: 131072
625
Eric Dumazet282f23c2012-07-17 10:13:05 +0200626tcp_challenge_ack_limit - INTEGER
627 Limits number of Challenge ACK sent per second, as recommended
628 in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
629 Default: 100
630
Hideo Aoki95766ff2007-12-31 00:29:24 -0800631UDP variables:
632
633udp_mem - vector of 3 INTEGERs: min, pressure, max
634 Number of pages allowed for queueing by all UDP sockets.
635
636 min: Below this number of pages UDP is not bothered about its
637 memory appetite. When amount of memory allocated by UDP exceeds
638 this number, UDP starts to moderate memory usage.
639
640 pressure: This value was introduced to follow format of tcp_mem.
641
642 max: Number of pages allowed for queueing by all UDP sockets.
643
644 Default is calculated at boot time from amount of available memory.
645
646udp_rmem_min - INTEGER
647 Minimal size of receive buffer used by UDP sockets in moderation.
648 Each UDP socket is able to use the size for receiving data, even if
649 total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
Max Matveev6539fef2011-06-21 21:18:13 +0000650 Default: 1 page
Hideo Aoki95766ff2007-12-31 00:29:24 -0800651
652udp_wmem_min - INTEGER
653 Minimal size of send buffer used by UDP sockets in moderation.
654 Each UDP socket is able to use the size for sending data, even if
655 total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
Max Matveev6539fef2011-06-21 21:18:13 +0000656 Default: 1 page
Hideo Aoki95766ff2007-12-31 00:29:24 -0800657
Paul Moore8802f612006-08-03 16:45:49 -0700658CIPSOv4 Variables:
659
660cipso_cache_enable - BOOLEAN
661 If set, enable additions to and lookups from the CIPSO label mapping
662 cache. If unset, additions are ignored and lookups always result in a
663 miss. However, regardless of the setting the cache is still
664 invalidated when required when means you can safely toggle this on and
665 off and the cache will always be "safe".
666 Default: 1
667
668cipso_cache_bucket_size - INTEGER
669 The CIPSO label cache consists of a fixed size hash table with each
670 hash bucket containing a number of cache entries. This variable limits
671 the number of entries in each hash bucket; the larger the value the
672 more CIPSO label mappings that can be cached. When the number of
673 entries in a given hash bucket reaches this limit adding new entries
674 causes the oldest entry in the bucket to be removed to make room.
675 Default: 10
676
677cipso_rbm_optfmt - BOOLEAN
678 Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
679 the CIPSO draft specification (see Documentation/netlabel for details).
680 This means that when set the CIPSO tag will be padded with empty
681 categories in order to make the packet data 32-bit aligned.
682 Default: 0
683
684cipso_rbm_structvalid - BOOLEAN
685 If set, do a very strict check of the CIPSO option when
686 ip_options_compile() is called. If unset, relax the checks done during
687 ip_options_compile(). Either way is "safe" as errors are caught else
688 where in the CIPSO processing code but setting this to 0 (False) should
689 result in less work (i.e. it should be faster) but could cause problems
690 with other implementations that require strict checking.
691 Default: 0
692
Linus Torvalds1da177e2005-04-16 15:20:36 -0700693IP Variables:
694
695ip_local_port_range - 2 INTEGERS
696 Defines the local port range that is used by TCP and UDP to
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000697 choose the local port. The first number is the first, the
Fernando Luis Vazquez Cao5d6bd862012-04-03 08:41:40 +0000698 second the last local port number. The default values are
699 32768 and 61000 respectively.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700700
Amerigo Wange3826f12010-05-05 00:27:06 +0000701ip_local_reserved_ports - list of comma separated ranges
702 Specify the ports which are reserved for known third-party
703 applications. These ports will not be used by automatic port
704 assignments (e.g. when calling connect() or bind() with port
705 number 0). Explicit port allocation behavior is unchanged.
706
707 The format used for both input and output is a comma separated
708 list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and
709 10). Writing to the file will clear all previously reserved
710 ports and update the current list with the one given in the
711 input.
712
713 Note that ip_local_port_range and ip_local_reserved_ports
714 settings are independent and both are considered by the kernel
715 when determining which ports are available for automatic port
716 assignments.
717
718 You can reserve ports which are not in the current
719 ip_local_port_range, e.g.:
720
721 $ cat /proc/sys/net/ipv4/ip_local_port_range
722 32000 61000
723 $ cat /proc/sys/net/ipv4/ip_local_reserved_ports
724 8080,9148
725
726 although this is redundant. However such a setting is useful
727 if later the port range is changed to a value that will
728 include the reserved ports.
729
730 Default: Empty
731
Linus Torvalds1da177e2005-04-16 15:20:36 -0700732ip_nonlocal_bind - BOOLEAN
733 If set, allows processes to bind() to non-local IP addresses,
734 which can be quite useful - but may break some applications.
735 Default: 0
736
737ip_dynaddr - BOOLEAN
738 If set non-zero, enables support for dynamic addresses.
739 If set to a non-zero value larger than 1, a kernel log
740 message will be printed when dynamic address rewriting
741 occurs.
742 Default: 0
743
Cong Wange3d73bc2013-06-11 18:54:39 +0800744ip_early_demux - BOOLEAN
745 Optimize input packet processing down to one demux for
746 certain kinds of local sockets. Currently we only do this
747 for established TCP sockets.
748
749 It may add an additional cost for pure routing workloads that
750 reduces overall throughput, in such case you should disable it.
751 Default: 1
752
Linus Torvalds1da177e2005-04-16 15:20:36 -0700753icmp_echo_ignore_all - BOOLEAN
David S. Miller7ce312462005-10-03 16:07:30 -0700754 If set non-zero, then the kernel will ignore all ICMP ECHO
755 requests sent to it.
756 Default: 0
757
Linus Torvalds1da177e2005-04-16 15:20:36 -0700758icmp_echo_ignore_broadcasts - BOOLEAN
David S. Miller7ce312462005-10-03 16:07:30 -0700759 If set non-zero, then the kernel will ignore all ICMP ECHO and
760 TIMESTAMP requests sent to it via broadcast/multicast.
761 Default: 1
Linus Torvalds1da177e2005-04-16 15:20:36 -0700762
763icmp_ratelimit - INTEGER
764 Limit the maximal rates for sending ICMP packets whose type matches
765 icmp_ratemask (see below) to specific targets.
Stephen Hemminger6dbf4bc2008-07-01 19:29:07 -0700766 0 to disable any limiting,
767 otherwise the minimal space between responses in milliseconds.
768 Default: 1000
Linus Torvalds1da177e2005-04-16 15:20:36 -0700769
770icmp_ratemask - INTEGER
771 Mask made of ICMP types for which rates are being limited.
772 Significant bits: IHGFEDCBA9876543210
773 Default mask: 0000001100000011000 (6168)
774
775 Bit definitions (see include/linux/icmp.h):
776 0 Echo Reply
777 3 Destination Unreachable *
778 4 Source Quench *
779 5 Redirect
780 8 Echo Request
781 B Time Exceeded *
782 C Parameter Problem *
783 D Timestamp Request
784 E Timestamp Reply
785 F Info Request
786 G Info Reply
787 H Address Mask Request
788 I Address Mask Reply
789
790 * These are rate limited by default (see default mask above)
791
792icmp_ignore_bogus_error_responses - BOOLEAN
793 Some routers violate RFC1122 by sending bogus responses to broadcast
794 frames. Such violations are normally logged via a kernel warning.
795 If this is set to TRUE, the kernel will not give such warnings, which
796 will avoid log file clutter.
Rami Rosene8b265e2013-06-07 20:16:19 +0000797 Default: 1
Linus Torvalds1da177e2005-04-16 15:20:36 -0700798
Horms95f7daf2006-02-02 17:02:25 -0800799icmp_errors_use_inbound_ifaddr - BOOLEAN
800
801 If zero, icmp error messages are sent with the primary address of
802 the exiting interface.
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000803
Horms95f7daf2006-02-02 17:02:25 -0800804 If non-zero, the message will be sent with the primary address of
805 the interface that received the packet that caused the icmp error.
806 This is the behaviour network many administrators will expect from
807 a router. And it can make debugging complicated network layouts
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000808 much easier.
Horms95f7daf2006-02-02 17:02:25 -0800809
810 Note that if no primary address exists for the interface selected,
811 then the primary address of the first non-loopback interface that
Matt LaPlanted6bc8ac2006-10-03 22:54:15 +0200812 has one will be used regardless of this setting.
Horms95f7daf2006-02-02 17:02:25 -0800813
814 Default: 0
815
Linus Torvalds1da177e2005-04-16 15:20:36 -0700816igmp_max_memberships - INTEGER
817 Change the maximum number of multicast groups we can subscribe to.
818 Default: 20
819
Jeremy Ederd67ef352010-11-15 05:41:31 +0000820 Theoretical maximum value is bounded by having to send a membership
821 report in a single datagram (i.e. the report can't span multiple
822 datagrams, or risk confusing the switch and leaving groups you don't
823 intend to).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700824
Jeremy Ederd67ef352010-11-15 05:41:31 +0000825 The number of supported groups 'M' is bounded by the number of group
826 report entries you can fit into a single datagram of 65535 bytes.
827
828 M = 65536-sizeof (ip header)/(sizeof(Group record))
829
830 Group records are variable length, with a minimum of 12 bytes.
831 So net.ipv4.igmp_max_memberships should not be set higher than:
832
833 (65536-24) / 12 = 5459
834
835 The value 5459 assumes no IP header options, so in practice
836 this number may be lower.
837
838 conf/interface/* changes special settings per interface (where
839 "interface" is the name of your network interface)
840
841 conf/all/* is special, changes the settings for all interfaces
Linus Torvalds1da177e2005-04-16 15:20:36 -0700842
843log_martians - BOOLEAN
844 Log packets with impossible addresses to kernel log.
845 log_martians for the interface will be enabled if at least one of
846 conf/{all,interface}/log_martians is set to TRUE,
847 it will be disabled otherwise
848
849accept_redirects - BOOLEAN
850 Accept ICMP redirect messages.
851 accept_redirects for the interface will be enabled if:
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000852 - both conf/{all,interface}/accept_redirects are TRUE in the case
853 forwarding for the interface is enabled
Linus Torvalds1da177e2005-04-16 15:20:36 -0700854 or
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000855 - at least one of conf/{all,interface}/accept_redirects is TRUE in the
856 case forwarding for the interface is disabled
Linus Torvalds1da177e2005-04-16 15:20:36 -0700857 accept_redirects for the interface will be disabled otherwise
858 default TRUE (host)
859 FALSE (router)
860
861forwarding - BOOLEAN
862 Enable IP forwarding on this interface.
863
864mc_forwarding - BOOLEAN
865 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
866 and a multicast routing daemon is required.
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000867 conf/all/mc_forwarding must also be set to TRUE to enable multicast
868 routing for the interface
Linus Torvalds1da177e2005-04-16 15:20:36 -0700869
870medium_id - INTEGER
871 Integer value used to differentiate the devices by the medium they
872 are attached to. Two devices can have different id values when
873 the broadcast packets are received only on one of them.
874 The default value 0 means that the device is the only interface
875 to its medium, value of -1 means that medium is not known.
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000876
Linus Torvalds1da177e2005-04-16 15:20:36 -0700877 Currently, it is used to change the proxy_arp behavior:
878 the proxy_arp feature is enabled for packets forwarded between
879 two devices attached to different media.
880
881proxy_arp - BOOLEAN
882 Do proxy arp.
883 proxy_arp for the interface will be enabled if at least one of
884 conf/{all,interface}/proxy_arp is set to TRUE,
885 it will be disabled otherwise
886
Jesper Dangaard Brouer65324142010-01-05 05:50:47 +0000887proxy_arp_pvlan - BOOLEAN
888 Private VLAN proxy arp.
889 Basically allow proxy arp replies back to the same interface
890 (from which the ARP request/solicitation was received).
891
892 This is done to support (ethernet) switch features, like RFC
893 3069, where the individual ports are NOT allowed to
894 communicate with each other, but they are allowed to talk to
895 the upstream router. As described in RFC 3069, it is possible
896 to allow these hosts to communicate through the upstream
897 router by proxy_arp'ing. Don't need to be used together with
898 proxy_arp.
899
900 This technology is known by different names:
901 In RFC 3069 it is called VLAN Aggregation.
902 Cisco and Allied Telesyn call it Private VLAN.
903 Hewlett-Packard call it Source-Port filtering or port-isolation.
904 Ericsson call it MAC-Forced Forwarding (RFC Draft).
905
Linus Torvalds1da177e2005-04-16 15:20:36 -0700906shared_media - BOOLEAN
907 Send(router) or accept(host) RFC1620 shared media redirects.
908 Overrides ip_secure_redirects.
909 shared_media for the interface will be enabled if at least one of
910 conf/{all,interface}/shared_media is set to TRUE,
911 it will be disabled otherwise
912 default TRUE
913
914secure_redirects - BOOLEAN
915 Accept ICMP redirect messages only for gateways,
916 listed in default gateway list.
917 secure_redirects for the interface will be enabled if at least one of
918 conf/{all,interface}/secure_redirects is set to TRUE,
919 it will be disabled otherwise
920 default TRUE
921
922send_redirects - BOOLEAN
923 Send redirects, if router.
924 send_redirects for the interface will be enabled if at least one of
925 conf/{all,interface}/send_redirects is set to TRUE,
926 it will be disabled otherwise
927 Default: TRUE
928
929bootp_relay - BOOLEAN
930 Accept packets with source address 0.b.c.d destined
931 not to this host as local ones. It is supposed, that
932 BOOTP relay daemon will catch and forward such packets.
933 conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
934 for the interface
935 default FALSE
936 Not Implemented Yet.
937
938accept_source_route - BOOLEAN
939 Accept packets with SRR option.
940 conf/all/accept_source_route must also be set to TRUE to accept packets
941 with SRR option on the interface
942 default TRUE (router)
943 FALSE (host)
944
Patrick McHardy8153a102009-12-03 01:25:58 +0000945accept_local - BOOLEAN
David S. Millerc801e3c2012-06-30 22:39:27 -0700946 Accept packets with local source addresses. In combination
947 with suitable routing, this can be used to direct packets
948 between two local interfaces over the wire and have them
949 accepted properly.
950
951 rp_filter must be set to a non-zero value in order for
952 accept_local to have an effect.
953
Patrick McHardy8153a102009-12-03 01:25:58 +0000954 default FALSE
955
Thomas Grafd0daebc32012-06-12 00:44:01 +0000956route_localnet - BOOLEAN
957 Do not consider loopback addresses as martian source or destination
958 while routing. This enables the use of 127/8 for local routing purposes.
959 default FALSE
960
Stephen Hemmingerc1cf8422009-02-20 08:25:36 +0000961rp_filter - INTEGER
Linus Torvalds1da177e2005-04-16 15:20:36 -0700962 0 - No source validation.
Stephen Hemmingerc1cf8422009-02-20 08:25:36 +0000963 1 - Strict mode as defined in RFC3704 Strict Reverse Path
964 Each incoming packet is tested against the FIB and if the interface
965 is not the best reverse path the packet check will fail.
966 By default failed packets are discarded.
967 2 - Loose mode as defined in RFC3704 Loose Reverse Path
968 Each incoming packet's source address is also tested against the FIB
969 and if the source address is not reachable via any interface
970 the packet check will fail.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700971
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000972 Current recommended practice in RFC3704 is to enable strict mode
Jesper Dangaard Brouerbf869c32009-02-23 04:37:55 +0000973 to prevent IP spoofing from DDos attacks. If using asymmetric routing
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +0000974 or other complicated routing, then loose mode is recommended.
Stephen Hemmingerc1cf8422009-02-20 08:25:36 +0000975
Shan Wei1f5865e2009-12-02 15:39:04 -0800976 The max value from conf/{all,interface}/rp_filter is used
977 when doing source validation on the {interface}.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700978
979 Default value is 0. Note that some distributions enable it
980 in startup scripts.
981
982arp_filter - BOOLEAN
983 1 - Allows you to have multiple network interfaces on the same
984 subnet, and have the ARPs for each interface be answered
985 based on whether or not the kernel would route a packet from
986 the ARP'd IP out that interface (therefore you must use source
987 based routing for this to work). In other words it allows control
988 of which cards (usually 1) will respond to an arp request.
989
990 0 - (default) The kernel can respond to arp requests with addresses
991 from other interfaces. This may seem wrong but it usually makes
992 sense, because it increases the chance of successful communication.
993 IP addresses are owned by the complete host on Linux, not by
994 particular interfaces. Only for more complex setups like load-
995 balancing, does this behaviour cause problems.
996
997 arp_filter for the interface will be enabled if at least one of
998 conf/{all,interface}/arp_filter is set to TRUE,
999 it will be disabled otherwise
1000
1001arp_announce - INTEGER
1002 Define different restriction levels for announcing the local
1003 source IP address from IP packets in ARP requests sent on
1004 interface:
1005 0 - (default) Use any local address, configured on any interface
1006 1 - Try to avoid local addresses that are not in the target's
1007 subnet for this interface. This mode is useful when target
1008 hosts reachable via this interface require the source IP
1009 address in ARP requests to be part of their logical network
1010 configured on the receiving interface. When we generate the
1011 request we will check all our subnets that include the
1012 target IP and will preserve the source address if it is from
1013 such subnet. If there is no such subnet we select source
1014 address according to the rules for level 2.
1015 2 - Always use the best local address for this target.
1016 In this mode we ignore the source address in the IP packet
1017 and try to select local address that we prefer for talks with
1018 the target host. Such local address is selected by looking
1019 for primary IP addresses on all our subnets on the outgoing
1020 interface that include the target IP address. If no suitable
1021 local address is found we select the first local address
1022 we have on the outgoing interface or on all other interfaces,
1023 with the hope we will receive reply for our request and
1024 even sometimes no matter the source IP address we announce.
1025
1026 The max value from conf/{all,interface}/arp_announce is used.
1027
1028 Increasing the restriction level gives more chance for
1029 receiving answer from the resolved target while decreasing
1030 the level announces more valid sender's information.
1031
1032arp_ignore - INTEGER
1033 Define different modes for sending replies in response to
1034 received ARP requests that resolve local target IP addresses:
1035 0 - (default): reply for any local target IP address, configured
1036 on any interface
1037 1 - reply only if the target IP address is local address
1038 configured on the incoming interface
1039 2 - reply only if the target IP address is local address
1040 configured on the incoming interface and both with the
1041 sender's IP address are part from same subnet on this interface
1042 3 - do not reply for local addresses configured with scope host,
1043 only resolutions for global and link addresses are replied
1044 4-7 - reserved
1045 8 - do not reply for all local addresses
1046
1047 The max value from conf/{all,interface}/arp_ignore is used
1048 when ARP request is received on the {interface}
1049
Stephen Hemmingereefef1c2009-02-01 01:04:33 -08001050arp_notify - BOOLEAN
1051 Define mode for notification of address and device changes.
1052 0 - (default): do nothing
Ian Campbell3f8dc232010-05-26 00:09:41 +00001053 1 - Generate gratuitous arp requests when device is brought up
Stephen Hemmingereefef1c2009-02-01 01:04:33 -08001054 or hardware address changes.
1055
Neil Hormanc1b1bce2006-03-20 22:40:03 -08001056arp_accept - BOOLEAN
Octavian Purdila6d955182010-01-18 12:58:44 +00001057 Define behavior for gratuitous ARP frames who's IP is not
1058 already present in the ARP table:
1059 0 - don't create new entries in the ARP table
1060 1 - create new entries in the ARP table
1061
1062 Both replies and requests type gratuitous arp will trigger the
1063 ARP table to be updated, if this setting is on.
1064
1065 If the ARP table already contains the IP address of the
1066 gratuitous arp frame, the arp table will be updated regardless
1067 if this setting is on or off.
1068
Neil Hormanc1b1bce2006-03-20 22:40:03 -08001069
Linus Torvalds1da177e2005-04-16 15:20:36 -07001070app_solicit - INTEGER
1071 The maximum number of probes to send to the user space ARP daemon
1072 via netlink before dropping back to multicast probes (see
1073 mcast_solicit). Defaults to 0.
1074
1075disable_policy - BOOLEAN
1076 Disable IPSEC policy (SPD) for this interface
1077
1078disable_xfrm - BOOLEAN
1079 Disable IPSEC encryption on this interface, whatever the policy
1080
Hannes Frederic Sowafc4eba52013-08-14 01:03:46 +02001081igmpv2_unsolicited_report_interval - INTEGER
1082 The interval in milliseconds in which the next unsolicited
1083 IGMPv1 or IGMPv2 report retransmit will take place.
1084 Default: 10000 (10 seconds)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001085
Hannes Frederic Sowafc4eba52013-08-14 01:03:46 +02001086igmpv3_unsolicited_report_interval - INTEGER
1087 The interval in milliseconds in which the next unsolicited
1088 IGMPv3 report retransmit will take place.
1089 Default: 1000 (1 seconds)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001090
Martin Schwenked922e1c2014-01-28 15:26:42 +11001091promote_secondaries - BOOLEAN
1092 When a primary IP address is removed from this interface
1093 promote a corresponding secondary IP address instead of
1094 removing all the corresponding secondary IP addresses.
1095
1096
Linus Torvalds1da177e2005-04-16 15:20:36 -07001097tag - INTEGER
1098 Allows you to write a number, which can be used as required.
1099 Default value is 0.
1100
Linus Torvalds1da177e2005-04-16 15:20:36 -07001101Alexey Kuznetsov.
1102kuznet@ms2.inr.ac.ru
1103
1104Updated by:
1105Andi Kleen
1106ak@muc.de
1107Nicolas Delon
1108delon.nicolas@wanadoo.fr
1109
1110
1111
1112
1113/proc/sys/net/ipv6/* Variables:
1114
1115IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also
1116apply to IPv6 [XXX?].
1117
1118bindv6only - BOOLEAN
1119 Default value for IPV6_V6ONLY socket option,
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001120 which restricts use of the IPv6 socket to IPv6 communication
Linus Torvalds1da177e2005-04-16 15:20:36 -07001121 only.
1122 TRUE: disable IPv4-mapped address feature
1123 FALSE: enable IPv4-mapped address feature
1124
Geoffrey Thomasd5c073ca2011-08-22 11:28:57 -07001125 Default: FALSE (as specified in RFC3493)
Linus Torvalds1da177e2005-04-16 15:20:36 -07001126
Florent Fourcot6444f722014-01-17 17:15:05 +01001127flowlabel_consistency - BOOLEAN
1128 Protect the consistency (and unicity) of flow label.
1129 You have to disable it to use IPV6_FL_F_REFLECT flag on the
1130 flow label manager.
1131 TRUE: enabled
1132 FALSE: disabled
1133 Default: TRUE
1134
FX Le Bail509aba32014-01-07 14:57:27 +01001135anycast_src_echo_reply - BOOLEAN
1136 Controls the use of anycast addresses as source addresses for ICMPv6
1137 echo reply
1138 TRUE: enabled
1139 FALSE: disabled
1140 Default: FALSE
1141
Linus Torvalds1da177e2005-04-16 15:20:36 -07001142IPv6 Fragmentation:
1143
1144ip6frag_high_thresh - INTEGER
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001145 Maximum memory used to reassemble IPv6 fragments. When
Linus Torvalds1da177e2005-04-16 15:20:36 -07001146 ip6frag_high_thresh bytes of memory is allocated for this purpose,
1147 the fragment handler will toss packets until ip6frag_low_thresh
1148 is reached.
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001149
Linus Torvalds1da177e2005-04-16 15:20:36 -07001150ip6frag_low_thresh - INTEGER
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001151 See ip6frag_high_thresh
Linus Torvalds1da177e2005-04-16 15:20:36 -07001152
1153ip6frag_time - INTEGER
1154 Time in seconds to keep an IPv6 fragment in memory.
1155
1156ip6frag_secret_interval - INTEGER
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001157 Regeneration interval (in seconds) of the hash secret (or lifetime
Linus Torvalds1da177e2005-04-16 15:20:36 -07001158 for the hash secret) for IPv6 fragments.
1159 Default: 600
1160
1161conf/default/*:
1162 Change the interface-specific default settings.
1163
1164
1165conf/all/*:
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001166 Change all the interface-specific settings.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001167
1168 [XXX: Other special features than forwarding?]
1169
1170conf/all/forwarding - BOOLEAN
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001171 Enable global IPv6 forwarding between all interfaces.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001172
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001173 IPv4 and IPv6 work differently here; e.g. netfilter must be used
Linus Torvalds1da177e2005-04-16 15:20:36 -07001174 to control which interfaces may forward packets and which not.
1175
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001176 This also sets all interfaces' Host/Router setting
Linus Torvalds1da177e2005-04-16 15:20:36 -07001177 'forwarding' to the specified value. See below for details.
1178
1179 This referred to as global forwarding.
1180
YOSHIFUJI Hideakifbea49e2006-09-22 14:43:49 -07001181proxy_ndp - BOOLEAN
1182 Do proxy ndp.
1183
Linus Torvalds1da177e2005-04-16 15:20:36 -07001184conf/interface/*:
1185 Change special settings per interface.
1186
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001187 The functional behaviour for certain settings is different
Linus Torvalds1da177e2005-04-16 15:20:36 -07001188 depending on whether local forwarding is enabled or not.
1189
Roy.Li605b91c2011-09-28 19:51:54 +00001190accept_ra - INTEGER
Linus Torvalds1da177e2005-04-16 15:20:36 -07001191 Accept Router Advertisements; autoconfigure using them.
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001192
Tore Anderson026359b2011-08-28 23:47:33 +00001193 It also determines whether or not to transmit Router
1194 Solicitations. If and only if the functional setting is to
1195 accept Router Advertisements, Router Solicitations will be
1196 transmitted.
1197
Thomas Grafae8abfa2010-09-03 05:47:30 +00001198 Possible values are:
1199 0 Do not accept Router Advertisements.
1200 1 Accept Router Advertisements if forwarding is disabled.
1201 2 Overrule forwarding behaviour. Accept Router Advertisements
1202 even if forwarding is enabled.
1203
Linus Torvalds1da177e2005-04-16 15:20:36 -07001204 Functional default: enabled if local forwarding is disabled.
1205 disabled if local forwarding is enabled.
1206
YOSHIFUJI Hideaki65f5c7c2006-03-20 16:55:08 -08001207accept_ra_defrtr - BOOLEAN
1208 Learn default router in Router Advertisement.
1209
1210 Functional default: enabled if accept_ra is enabled.
1211 disabled if accept_ra is disabled.
1212
YOSHIFUJI Hideakic4fd30e2006-03-20 16:55:26 -08001213accept_ra_pinfo - BOOLEAN
Matt LaPlante2fe0ae72006-10-03 22:50:39 +02001214 Learn Prefix Information in Router Advertisement.
YOSHIFUJI Hideakic4fd30e2006-03-20 16:55:26 -08001215
1216 Functional default: enabled if accept_ra is enabled.
1217 disabled if accept_ra is disabled.
1218
YOSHIFUJI Hideaki09c884d2006-03-20 17:07:03 -08001219accept_ra_rt_info_max_plen - INTEGER
1220 Maximum prefix length of Route Information in RA.
1221
1222 Route Information w/ prefix larger than or equal to this
1223 variable shall be ignored.
1224
1225 Functional default: 0 if accept_ra_rtr_pref is enabled.
1226 -1 if accept_ra_rtr_pref is disabled.
1227
YOSHIFUJI Hideaki930d6ff2006-03-20 17:05:30 -08001228accept_ra_rtr_pref - BOOLEAN
1229 Accept Router Preference in RA.
1230
1231 Functional default: enabled if accept_ra is enabled.
1232 disabled if accept_ra is disabled.
1233
Linus Torvalds1da177e2005-04-16 15:20:36 -07001234accept_redirects - BOOLEAN
1235 Accept Redirects.
1236
1237 Functional default: enabled if local forwarding is disabled.
1238 disabled if local forwarding is enabled.
1239
YOSHIFUJI Hideaki0bcbc922007-04-24 14:58:30 -07001240accept_source_route - INTEGER
1241 Accept source routing (routing extension header).
1242
YOSHIFUJI Hideakibb4dbf92007-07-10 22:55:49 -07001243 >= 0: Accept only routing header type 2.
YOSHIFUJI Hideaki0bcbc922007-04-24 14:58:30 -07001244 < 0: Do not accept routing header.
1245
1246 Default: 0
1247
Linus Torvalds1da177e2005-04-16 15:20:36 -07001248autoconf - BOOLEAN
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001249 Autoconfigure addresses using Prefix Information in Router
Linus Torvalds1da177e2005-04-16 15:20:36 -07001250 Advertisements.
1251
YOSHIFUJI Hideakic4fd30e2006-03-20 16:55:26 -08001252 Functional default: enabled if accept_ra_pinfo is enabled.
1253 disabled if accept_ra_pinfo is disabled.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001254
1255dad_transmits - INTEGER
1256 The amount of Duplicate Address Detection probes to send.
1257 Default: 1
Linus Torvalds1da177e2005-04-16 15:20:36 -07001258
Roy.Li605b91c2011-09-28 19:51:54 +00001259forwarding - INTEGER
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001260 Configure interface-specific Host/Router behaviour.
1261
1262 Note: It is recommended to have the same setting on all
Linus Torvalds1da177e2005-04-16 15:20:36 -07001263 interfaces; mixed router/host scenarios are rather uncommon.
1264
Thomas Grafae8abfa2010-09-03 05:47:30 +00001265 Possible values are:
1266 0 Forwarding disabled
1267 1 Forwarding enabled
Thomas Grafae8abfa2010-09-03 05:47:30 +00001268
1269 FALSE (0):
Linus Torvalds1da177e2005-04-16 15:20:36 -07001270
1271 By default, Host behaviour is assumed. This means:
1272
1273 1. IsRouter flag is not set in Neighbour Advertisements.
Tore Anderson026359b2011-08-28 23:47:33 +00001274 2. If accept_ra is TRUE (default), transmit Router
1275 Solicitations.
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001276 3. If accept_ra is TRUE (default), accept Router
Linus Torvalds1da177e2005-04-16 15:20:36 -07001277 Advertisements (and do autoconfiguration).
1278 4. If accept_redirects is TRUE (default), accept Redirects.
1279
Thomas Grafae8abfa2010-09-03 05:47:30 +00001280 TRUE (1):
Linus Torvalds1da177e2005-04-16 15:20:36 -07001281
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001282 If local forwarding is enabled, Router behaviour is assumed.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001283 This means exactly the reverse from the above:
1284
1285 1. IsRouter flag is set in Neighbour Advertisements.
Tore Anderson026359b2011-08-28 23:47:33 +00001286 2. Router Solicitations are not sent unless accept_ra is 2.
Thomas Grafae8abfa2010-09-03 05:47:30 +00001287 3. Router Advertisements are ignored unless accept_ra is 2.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001288 4. Redirects are ignored.
1289
Thomas Grafae8abfa2010-09-03 05:47:30 +00001290 Default: 0 (disabled) if global forwarding is disabled (default),
1291 otherwise 1 (enabled).
Linus Torvalds1da177e2005-04-16 15:20:36 -07001292
1293hop_limit - INTEGER
1294 Default Hop Limit to set.
1295 Default: 64
1296
1297mtu - INTEGER
1298 Default Maximum Transfer Unit
1299 Default: 1280 (IPv6 required minimum)
1300
YOSHIFUJI Hideaki52e16352006-03-20 17:05:47 -08001301router_probe_interval - INTEGER
1302 Minimum interval (in seconds) between Router Probing described
1303 in RFC4191.
1304
1305 Default: 60
1306
Linus Torvalds1da177e2005-04-16 15:20:36 -07001307router_solicitation_delay - INTEGER
1308 Number of seconds to wait after interface is brought up
1309 before sending Router Solicitations.
1310 Default: 1
1311
1312router_solicitation_interval - INTEGER
1313 Number of seconds to wait between Router Solicitations.
1314 Default: 4
1315
1316router_solicitations - INTEGER
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001317 Number of Router Solicitations to send until assuming no
Linus Torvalds1da177e2005-04-16 15:20:36 -07001318 routers are present.
1319 Default: 3
1320
1321use_tempaddr - INTEGER
1322 Preference for Privacy Extensions (RFC3041).
1323 <= 0 : disable Privacy Extensions
1324 == 1 : enable Privacy Extensions, but prefer public
1325 addresses over temporary addresses.
1326 > 1 : enable Privacy Extensions and prefer temporary
1327 addresses over public addresses.
1328 Default: 0 (for most devices)
1329 -1 (for point-to-point devices and loopback devices)
1330
1331temp_valid_lft - INTEGER
1332 valid lifetime (in seconds) for temporary addresses.
1333 Default: 604800 (7 days)
1334
1335temp_prefered_lft - INTEGER
1336 Preferred lifetime (in seconds) for temporary addresses.
1337 Default: 86400 (1 day)
1338
1339max_desync_factor - INTEGER
1340 Maximum value for DESYNC_FACTOR, which is a random value
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001341 that ensures that clients don't synchronize with each
Linus Torvalds1da177e2005-04-16 15:20:36 -07001342 other and generate new addresses at exactly the same time.
1343 value is in seconds.
1344 Default: 600
Jesper Dangaard Brouere18f5fe2009-02-23 04:39:04 +00001345
Linus Torvalds1da177e2005-04-16 15:20:36 -07001346regen_max_retry - INTEGER
1347 Number of attempts before give up attempting to generate
1348 valid temporary addresses.
1349 Default: 5
1350
1351max_addresses - INTEGER
Brian Haleye79dc482010-02-22 12:27:21 +00001352 Maximum number of autoconfigured addresses per interface. Setting
1353 to zero disables the limitation. It is not recommended to set this
1354 value too large (or to zero) because it would be an easy way to
1355 crash the kernel by allowing too many addresses to be created.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001356 Default: 16
1357
YOSHIFUJI Hideaki778d80b2008-06-28 14:17:11 +09001358disable_ipv6 - BOOLEAN
Brian Haley9bdd8d42009-03-18 18:22:48 -07001359 Disable IPv6 operation. If accept_dad is set to 2, this value
1360 will be dynamically set to TRUE if DAD fails for the link-local
1361 address.
YOSHIFUJI Hideaki778d80b2008-06-28 14:17:11 +09001362 Default: FALSE (enable IPv6 operation)
1363
Brian Haley56d417b2009-06-01 03:07:33 -07001364 When this value is changed from 1 to 0 (IPv6 is being enabled),
1365 it will dynamically create a link-local address on the given
1366 interface and start Duplicate Address Detection, if necessary.
1367
1368 When this value is changed from 0 to 1 (IPv6 is being disabled),
1369 it will dynamically delete all address on the given interface.
1370
YOSHIFUJI Hideaki1b34be72008-06-28 14:18:38 +09001371accept_dad - INTEGER
1372 Whether to accept DAD (Duplicate Address Detection).
1373 0: Disable DAD
1374 1: Enable DAD (default)
1375 2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
1376 link-local address has been found.
1377
Octavian Purdilaf7734fd2009-10-02 11:39:15 +00001378force_tllao - BOOLEAN
1379 Enable sending the target link-layer address option even when
1380 responding to a unicast neighbor solicitation.
1381 Default: FALSE
1382
1383 Quoting from RFC 2461, section 4.4, Target link-layer address:
1384
1385 "The option MUST be included for multicast solicitations in order to
1386 avoid infinite Neighbor Solicitation "recursion" when the peer node
1387 does not have a cache entry to return a Neighbor Advertisements
1388 message. When responding to unicast solicitations, the option can be
1389 omitted since the sender of the solicitation has the correct link-
1390 layer address; otherwise it would not have be able to send the unicast
1391 solicitation in the first place. However, including the link-layer
1392 address in this case adds little overhead and eliminates a potential
1393 race condition where the sender deletes the cached link-layer address
1394 prior to receiving a response to a previous solicitation."
1395
Hannes Frederic Sowadb2b6202013-01-01 00:35:31 +00001396ndisc_notify - BOOLEAN
1397 Define mode for notification of address and device changes.
1398 0 - (default): do nothing
1399 1 - Generate unsolicited neighbour advertisements when device is brought
1400 up or hardware address changes.
1401
Hannes Frederic Sowafc4eba52013-08-14 01:03:46 +02001402mldv1_unsolicited_report_interval - INTEGER
1403 The interval in milliseconds in which the next unsolicited
1404 MLDv1 report retransmit will take place.
1405 Default: 10000 (10 seconds)
1406
1407mldv2_unsolicited_report_interval - INTEGER
1408 The interval in milliseconds in which the next unsolicited
1409 MLDv2 report retransmit will take place.
1410 Default: 1000 (1 second)
1411
Daniel Borkmannf2127812013-09-04 00:19:44 +02001412force_mld_version - INTEGER
1413 0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed
1414 1 - Enforce to use MLD version 1
1415 2 - Enforce to use MLD version 2
1416
Hannes Frederic Sowab800c3b2013-08-27 01:36:51 +02001417suppress_frag_ndisc - INTEGER
1418 Control RFC 6980 (Security Implications of IPv6 Fragmentation
1419 with IPv6 Neighbor Discovery) behavior:
1420 1 - (default) discard fragmented neighbor discovery packets
1421 0 - allow fragmented neighbor discovery packets
1422
Linus Torvalds1da177e2005-04-16 15:20:36 -07001423icmp/*:
1424ratelimit - INTEGER
1425 Limit the maximal rates for sending ICMPv6 packets.
Stephen Hemminger6dbf4bc2008-07-01 19:29:07 -07001426 0 to disable any limiting,
1427 otherwise the minimal space between responses in milliseconds.
1428 Default: 1000
Linus Torvalds1da177e2005-04-16 15:20:36 -07001429
1430
1431IPv6 Update by:
1432Pekka Savola <pekkas@netcore.fi>
1433YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
1434
1435
1436/proc/sys/net/bridge/* Variables:
1437
1438bridge-nf-call-arptables - BOOLEAN
1439 1 : pass bridged ARP traffic to arptables' FORWARD chain.
1440 0 : disable this.
1441 Default: 1
1442
1443bridge-nf-call-iptables - BOOLEAN
1444 1 : pass bridged IPv4 traffic to iptables' chains.
1445 0 : disable this.
1446 Default: 1
1447
1448bridge-nf-call-ip6tables - BOOLEAN
1449 1 : pass bridged IPv6 traffic to ip6tables' chains.
1450 0 : disable this.
1451 Default: 1
1452
1453bridge-nf-filter-vlan-tagged - BOOLEAN
Michael Milner516299d2007-04-12 22:14:23 -07001454 1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
1455 0 : disable this.
Pablo Neira Ayuso49816822012-05-08 19:36:44 +02001456 Default: 0
Michael Milner516299d2007-04-12 22:14:23 -07001457
1458bridge-nf-filter-pppoe-tagged - BOOLEAN
1459 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001460 0 : disable this.
Pablo Neira Ayuso49816822012-05-08 19:36:44 +02001461 Default: 0
Linus Torvalds1da177e2005-04-16 15:20:36 -07001462
Pablo Neira Ayuso49816822012-05-08 19:36:44 +02001463bridge-nf-pass-vlan-input-dev - BOOLEAN
1464 1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan
1465 interface on the bridge and set the netfilter input device to the vlan.
1466 This allows use of e.g. "iptables -i br0.1" and makes the REDIRECT
1467 target work with vlan-on-top-of-bridge interfaces. When no matching
1468 vlan interface is found, or this switch is off, the input device is
1469 set to the bridge interface.
1470 0: disable bridge netfilter vlan interface lookup.
1471 Default: 0
Linus Torvalds1da177e2005-04-16 15:20:36 -07001472
Vlad Yasevich32e8d492008-07-08 16:43:29 -07001473proc/sys/net/sctp/* Variables:
1474
1475addip_enable - BOOLEAN
1476 Enable or disable extension of Dynamic Address Reconfiguration
1477 (ADD-IP) functionality specified in RFC5061. This extension provides
1478 the ability to dynamically add and remove new addresses for the SCTP
1479 associations.
1480
1481 1: Enable extension.
1482
1483 0: Disable extension.
1484
1485 Default: 0
1486
1487addip_noauth_enable - BOOLEAN
1488 Dynamic Address Reconfiguration (ADD-IP) requires the use of
1489 authentication to protect the operations of adding or removing new
1490 addresses. This requirement is mandated so that unauthorized hosts
1491 would not be able to hijack associations. However, older
1492 implementations may not have implemented this requirement while
1493 allowing the ADD-IP extension. For reasons of interoperability,
1494 we provide this variable to control the enforcement of the
1495 authentication requirement.
1496
1497 1: Allow ADD-IP extension to be used without authentication. This
1498 should only be set in a closed environment for interoperability
1499 with older implementations.
1500
1501 0: Enforce the authentication requirement
1502
1503 Default: 0
1504
1505auth_enable - BOOLEAN
1506 Enable or disable Authenticated Chunks extension. This extension
1507 provides the ability to send and receive authenticated chunks and is
1508 required for secure operation of Dynamic Address Reconfiguration
1509 (ADD-IP) extension.
1510
1511 1: Enable this extension.
1512 0: Disable this extension.
1513
1514 Default: 0
1515
1516prsctp_enable - BOOLEAN
1517 Enable or disable the Partial Reliability extension (RFC3758) which
1518 is used to notify peers that a given DATA should no longer be expected.
1519
1520 1: Enable extension
1521 0: Disable
1522
1523 Default: 1
1524
1525max_burst - INTEGER
1526 The limit of the number of new packets that can be initially sent. It
1527 controls how bursty the generated traffic can be.
1528
1529 Default: 4
1530
1531association_max_retrans - INTEGER
1532 Set the maximum number for retransmissions that an association can
1533 attempt deciding that the remote end is unreachable. If this value
1534 is exceeded, the association is terminated.
1535
1536 Default: 10
1537
1538max_init_retransmits - INTEGER
1539 The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
1540 that an association will attempt before declaring the destination
1541 unreachable and terminating.
1542
1543 Default: 8
1544
1545path_max_retrans - INTEGER
1546 The maximum number of retransmissions that will be attempted on a given
1547 path. Once this threshold is exceeded, the path is considered
1548 unreachable, and new traffic will use a different path when the
1549 association is multihomed.
1550
1551 Default: 5
1552
Neil Horman5aa93bc2012-07-21 07:56:07 +00001553pf_retrans - INTEGER
1554 The number of retransmissions that will be attempted on a given path
1555 before traffic is redirected to an alternate transport (should one
1556 exist). Note this is distinct from path_max_retrans, as a path that
1557 passes the pf_retrans threshold can still be used. Its only
1558 deprioritized when a transmission path is selected by the stack. This
1559 setting is primarily used to enable fast failover mechanisms without
1560 having to reduce path_max_retrans to a very low value. See:
1561 http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt
1562 for details. Note also that a value of pf_retrans > path_max_retrans
1563 disables this feature
1564
1565 Default: 0
1566
Vlad Yasevich32e8d492008-07-08 16:43:29 -07001567rto_initial - INTEGER
1568 The initial round trip timeout value in milliseconds that will be used
1569 in calculating round trip times. This is the initial time interval
1570 for retransmissions.
1571
1572 Default: 3000
1573
1574rto_max - INTEGER
1575 The maximum value (in milliseconds) of the round trip timeout. This
1576 is the largest time interval that can elapse between retransmissions.
1577
1578 Default: 60000
1579
1580rto_min - INTEGER
1581 The minimum value (in milliseconds) of the round trip timeout. This
1582 is the smallest time interval the can elapse between retransmissions.
1583
1584 Default: 1000
1585
1586hb_interval - INTEGER
1587 The interval (in milliseconds) between HEARTBEAT chunks. These chunks
1588 are sent at the specified interval on idle paths to probe the state of
1589 a given path between 2 associations.
1590
1591 Default: 30000
1592
1593sack_timeout - INTEGER
1594 The amount of time (in milliseconds) that the implementation will wait
1595 to send a SACK.
1596
1597 Default: 200
1598
1599valid_cookie_life - INTEGER
1600 The default lifetime of the SCTP cookie (in milliseconds). The cookie
1601 is used during association establishment.
1602
1603 Default: 60000
1604
1605cookie_preserve_enable - BOOLEAN
1606 Enable or disable the ability to extend the lifetime of the SCTP cookie
1607 that is used during the establishment phase of SCTP association
1608
1609 1: Enable cookie lifetime extension.
1610 0: Disable
1611
1612 Default: 1
1613
Neil Horman3c681982012-10-24 09:20:03 +00001614cookie_hmac_alg - STRING
1615 Select the hmac algorithm used when generating the cookie value sent by
1616 a listening sctp socket to a connecting client in the INIT-ACK chunk.
1617 Valid values are:
1618 * md5
1619 * sha1
1620 * none
1621 Ability to assign md5 or sha1 as the selected alg is predicated on the
stephen hemminger3b09adc2013-01-03 07:50:29 +00001622 configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and
Neil Horman3c681982012-10-24 09:20:03 +00001623 CONFIG_CRYPTO_SHA1).
1624
1625 Default: Dependent on configuration. MD5 if available, else SHA1 if
1626 available, else none.
1627
Vlad Yasevich32e8d492008-07-08 16:43:29 -07001628rcvbuf_policy - INTEGER
1629 Determines if the receive buffer is attributed to the socket or to
1630 association. SCTP supports the capability to create multiple
1631 associations on a single socket. When using this capability, it is
1632 possible that a single stalled association that's buffering a lot
1633 of data may block other associations from delivering their data by
1634 consuming all of the receive buffer space. To work around this,
1635 the rcvbuf_policy could be set to attribute the receiver buffer space
1636 to each association instead of the socket. This prevents the described
1637 blocking.
1638
1639 1: rcvbuf space is per association
stephen hemminger3b09adc2013-01-03 07:50:29 +00001640 0: rcvbuf space is per socket
Vlad Yasevich32e8d492008-07-08 16:43:29 -07001641
1642 Default: 0
1643
1644sndbuf_policy - INTEGER
1645 Similar to rcvbuf_policy above, this applies to send buffer space.
1646
1647 1: Send buffer is tracked per association
1648 0: Send buffer is tracked per socket.
1649
1650 Default: 0
1651
1652sctp_mem - vector of 3 INTEGERs: min, pressure, max
1653 Number of pages allowed for queueing by all SCTP sockets.
1654
1655 min: Below this number of pages SCTP is not bothered about its
1656 memory appetite. When amount of memory allocated by SCTP exceeds
1657 this number, SCTP starts to moderate memory usage.
1658
1659 pressure: This value was introduced to follow format of tcp_mem.
1660
1661 max: Number of pages allowed for queueing by all SCTP sockets.
1662
1663 Default is calculated at boot time from amount of available memory.
1664
1665sctp_rmem - vector of 3 INTEGERs: min, default, max
Max Matveeva6e12042011-06-19 22:08:10 +00001666 Only the first value ("min") is used, "default" and "max" are
1667 ignored.
1668
1669 min: Minimal size of receive buffer used by SCTP socket.
1670 It is guaranteed to each SCTP socket (but not association) even
1671 under moderate memory pressure.
1672
1673 Default: 1 page
Vlad Yasevich32e8d492008-07-08 16:43:29 -07001674
1675sctp_wmem - vector of 3 INTEGERs: min, default, max
Max Matveeva6e12042011-06-19 22:08:10 +00001676 Currently this tunable has no effect.
Vlad Yasevich32e8d492008-07-08 16:43:29 -07001677
Bhaskar Dutta72388432009-09-03 17:25:47 +05301678addr_scope_policy - INTEGER
1679 Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00
1680
1681 0 - Disable IPv4 address scoping
1682 1 - Enable IPv4 address scoping
1683 2 - Follow draft but allow IPv4 private addresses
1684 3 - Follow draft but allow IPv4 link local addresses
1685
1686 Default: 1
1687
Linus Torvalds1da177e2005-04-16 15:20:36 -07001688
Stephen Hemminger4edc2f32008-07-10 16:50:26 -07001689/proc/sys/net/core/*
Shan Weic60f6aa2012-04-26 16:52:52 +00001690 Please see: Documentation/sysctl/net.txt for descriptions of these entries.
Wang Tinggong705efc32009-05-14 22:49:36 +00001691
Linus Torvalds1da177e2005-04-16 15:20:36 -07001692
Stephen Hemminger4edc2f32008-07-10 16:50:26 -07001693/proc/sys/net/unix/*
Wang Tinggong705efc32009-05-14 22:49:36 +00001694max_dgram_qlen - INTEGER
1695 The maximum length of dgram socket receive queue
1696
1697 Default: 10
1698
1699
1700UNDOCUMENTED:
Stephen Hemminger4edc2f32008-07-10 16:50:26 -07001701
1702/proc/sys/net/irda/*
1703 fast_poll_increase FIXME
1704 warn_noreply_time FIXME
1705 discovery_slots FIXME
1706 slot_timeout FIXME
1707 max_baud_rate FIXME
1708 discovery_timeout FIXME
1709 lap_keepalive_time FIXME
1710 max_noreply_time FIXME
1711 max_tx_data_size FIXME
1712 max_tx_window FIXME
1713 min_tx_turn_time FIXME