| blob | c7712787933c1734c98a0191db23d9cb2886d0f8 |
1 /proc/sys/net/ipv4/* Variables:
3 ip_forward - BOOLEAN
4 0 - disabled (default)
5 not 0 - enabled
7 Forward Packets between interfaces.
9 This variable is special, its change resets all configuration
10 parameters to their default state (RFC1122 for hosts, RFC1812
11 for routers)
13 ip_default_ttl - INTEGER
14 default 64
16 ip_no_pmtu_disc - BOOLEAN
17 Disable Path MTU Discovery.
18 default FALSE
20 min_pmtu - INTEGER
21 default 562 - minimum discovered Path MTU
23 mtu_expires - INTEGER
24 Time, in seconds, that cached PMTU information is kept.
26 min_adv_mss - INTEGER
27 The advertised MSS depends on the first hop route MTU, but will
28 never be lower than this setting.
30 rt_cache_rebuild_count - INTEGER
31 The per net-namespace route cache emergency rebuild threshold.
32 Any net-namespace having its route cache rebuilt due to
33 a hash bucket chain being too long more than this many times
34 will have its route caching disabled
36 IP Fragmentation:
38 ipfrag_high_thresh - INTEGER
39 Maximum memory used to reassemble IP fragments. When
40 ipfrag_high_thresh bytes of memory is allocated for this purpose,
41 the fragment handler will toss packets until ipfrag_low_thresh
42 is reached.
44 ipfrag_low_thresh - INTEGER
45 See ipfrag_high_thresh
47 ipfrag_time - INTEGER
48 Time in seconds to keep an IP fragment in memory.
50 ipfrag_secret_interval - INTEGER
51 Regeneration interval (in seconds) of the hash secret (or lifetime
52 for the hash secret) for IP fragments.
53 Default: 600
55 ipfrag_max_dist - INTEGER
56 ipfrag_max_dist is a non-negative integer value which defines the
57 maximum "disorder" which is allowed among fragments which share a
58 common IP source address. Note that reordering of packets is
59 not unusual, but if a large number of fragments arrive from a source
60 IP address while a particular fragment queue remains incomplete, it
61 probably indicates that one or more fragments belonging to that queue
62 have been lost. When ipfrag_max_dist is positive, an additional check
63 is done on fragments before they are added to a reassembly queue - if
64 ipfrag_max_dist (or more) fragments have arrived from a particular IP
65 address between additions to any IP fragment queue using that source
66 address, it's presumed that one or more fragments in the queue are
67 lost. The existing fragment queue will be dropped, and a new one
68 started. An ipfrag_max_dist value of zero disables this check.
70 Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
71 result in unnecessarily dropping fragment queues when normal
72 reordering of packets occurs, which could lead to poor application
73 performance. Using a very large value, e.g. 50000, increases the
74 likelihood of incorrectly reassembling IP fragments that originate
75 from different IP datagrams, which could result in data corruption.
76 Default: 64
78 INET peer storage:
80 inet_peer_threshold - INTEGER
81 The approximate size of the storage. Starting from this threshold
82 entries will be thrown aggressively. This threshold also determines
83 entries' time-to-live and time intervals between garbage collection
84 passes. More entries, less time-to-live, less GC interval.
86 inet_peer_minttl - INTEGER
87 Minimum time-to-live of entries. Should be enough to cover fragment
88 time-to-live on the reassembling side. This minimum time-to-live is
89 guaranteed if the pool size is less than inet_peer_threshold.
90 Measured in seconds.
92 inet_peer_maxttl - INTEGER
93 Maximum time-to-live of entries. Unused entries will expire after
94 this period of time if there is no memory pressure on the pool (i.e.
95 when the number of entries in the pool is very small).
96 Measured in seconds.
98 inet_peer_gc_mintime - INTEGER
99 Minimum interval between garbage collection passes. This interval is
100 in effect under high memory pressure on the pool.
101 Measured in seconds.
103 inet_peer_gc_maxtime - INTEGER
104 Minimum interval between garbage collection passes. This interval is
105 in effect under low (or absent) memory pressure on the pool.
106 Measured in seconds.
108 TCP variables:
110 somaxconn - INTEGER
111 Limit of socket listen() backlog, known in userspace as SOMAXCONN.
112 Defaults to 128. See also tcp_max_syn_backlog for additional tuning
113 for TCP sockets.
115 tcp_abc - INTEGER
116 Controls Appropriate Byte Count (ABC) defined in RFC3465.
117 ABC is a way of increasing congestion window (cwnd) more slowly
118 in response to partial acknowledgments.
119 Possible values are:
120 0 increase cwnd once per acknowledgment (no ABC)
121 1 increase cwnd once per acknowledgment of full sized segment
122 2 allow increase cwnd by two if acknowledgment is
123 of two segments to compensate for delayed acknowledgments.
124 Default: 0 (off)
126 tcp_abort_on_overflow - BOOLEAN
127 If listening service is too slow to accept new connections,
128 reset them. Default state is FALSE. It means that if overflow
129 occurred due to a burst, connection will recover. Enable this
130 option _only_ if you are really sure that listening daemon
131 cannot be tuned to accept connections faster. Enabling this
132 option can harm clients of your server.
134 tcp_adv_win_scale - INTEGER
135 Count buffering overhead as bytes/2^tcp_adv_win_scale
136 (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
137 if it is <= 0.
138 Default: 2
140 tcp_allowed_congestion_control - STRING
141 Show/set the congestion control choices available to non-privileged
142 processes. The list is a subset of those listed in
143 tcp_available_congestion_control.
144 Default is "reno" and the default setting (tcp_congestion_control).
146 tcp_app_win - INTEGER
147 Reserve max(window/2^tcp_app_win, mss) of window for application
148 buffer. Value 0 is special, it means that nothing is reserved.
149 Default: 31
151 tcp_available_congestion_control - STRING
152 Shows the available congestion control choices that are registered.
153 More congestion control algorithms may be available as modules,
154 but not loaded.
156 tcp_base_mss - INTEGER
157 The initial value of search_low to be used by the packetization layer
158 Path MTU discovery (MTU probing). If MTU probing is enabled,
159 this is the initial MSS used by the connection.
161 tcp_congestion_control - STRING
162 Set the congestion control algorithm to be used for new
163 connections. The algorithm "reno" is always available, but
164 additional choices may be available based on kernel configuration.
165 Default is set as part of kernel configuration.
167 tcp_dsack - BOOLEAN
168 Allows TCP to send "duplicate" SACKs.
170 tcp_ecn - BOOLEAN
171 Enable Explicit Congestion Notification in TCP.
173 tcp_fack - BOOLEAN
174 Enable FACK congestion avoidance and fast retransmission.
175 The value is not used, if tcp_sack is not enabled.
177 tcp_fin_timeout - INTEGER
178 Time to hold socket in state FIN-WAIT-2, if it was closed
179 by our side. Peer can be broken and never close its side,
180 or even died unexpectedly. Default value is 60sec.
181 Usual value used in 2.2 was 180 seconds, you may restore
182 it, but remember that if your machine is even underloaded WEB server,
183 you risk to overflow memory with kilotons of dead sockets,
184 FIN-WAIT-2 sockets are less dangerous than FIN-WAIT-1,
185 because they eat maximum 1.5K of memory, but they tend
186 to live longer. Cf. tcp_max_orphans.
188 tcp_frto - INTEGER
189 Enables Forward RTO-Recovery (F-RTO) defined in RFC4138.
190 F-RTO is an enhanced recovery algorithm for TCP retransmission
191 timeouts. It is particularly beneficial in wireless environments
192 where packet loss is typically due to random radio interference
193 rather than intermediate router congestion. F-RTO is sender-side
194 only modification. Therefore it does not require any support from
195 the peer.
197 If set to 1, basic version is enabled. 2 enables SACK enhanced
198 F-RTO if flow uses SACK. The basic version can be used also when
199 SACK is in use though scenario(s) with it exists where F-RTO
200 interacts badly with the packet counting of the SACK enabled TCP
201 flow.
203 tcp_frto_response - INTEGER
204 When F-RTO has detected that a TCP retransmission timeout was
205 spurious (i.e, the timeout would have been avoided had TCP set a
206 longer retransmission timeout), TCP has several options what to do
207 next. Possible values are:
208 0 Rate halving based; a smooth and conservative response,
209 results in halved cwnd and ssthresh after one RTT
210 1 Very conservative response; not recommended because even
211 though being valid, it interacts poorly with the rest of
212 Linux TCP, halves cwnd and ssthresh immediately
213 2 Aggressive response; undoes congestion control measures
214 that are now known to be unnecessary (ignoring the
215 possibility of a lost retransmission that would require
216 TCP to be more cautious), cwnd and ssthresh are restored
217 to the values prior timeout
218 Default: 0 (rate halving based)
220 tcp_keepalive_time - INTEGER
221 How often TCP sends out keepalive messages when keepalive is enabled.
222 Default: 2hours.
224 tcp_keepalive_probes - INTEGER
225 How many keepalive probes TCP sends out, until it decides that the
226 connection is broken. Default value: 9.
228 tcp_keepalive_intvl - INTEGER
229 How frequently the probes are send out. Multiplied by
230 tcp_keepalive_probes it is time to kill not responding connection,
231 after probes started. Default value: 75sec i.e. connection
232 will be aborted after ~11 minutes of retries.
234 tcp_low_latency - BOOLEAN
235 If set, the TCP stack makes decisions that prefer lower
236 latency as opposed to higher throughput. By default, this
237 option is not set meaning that higher throughput is preferred.
238 An example of an application where this default should be
239 changed would be a Beowulf compute cluster.
240 Default: 0
242 tcp_max_orphans - INTEGER
243 Maximal number of TCP sockets not attached to any user file handle,
244 held by system. If this number is exceeded orphaned connections are
245 reset immediately and warning is printed. This limit exists
246 only to prevent simple DoS attacks, you _must_ not rely on this
247 or lower the limit artificially, but rather increase it
248 (probably, after increasing installed memory),
249 if network conditions require more than default value,
250 and tune network services to linger and kill such states
251 more aggressively. Let me to remind again: each orphan eats
252 up to ~64K of unswappable memory.
254 tcp_max_syn_backlog - INTEGER
255 Maximal number of remembered connection requests, which are
256 still did not receive an acknowledgment from connecting client.
257 Default value is 1024 for systems with more than 128Mb of memory,
258 and 128 for low memory machines. If server suffers of overload,
259 try to increase this number.
261 tcp_max_tw_buckets - INTEGER
262 Maximal number of timewait sockets held by system simultaneously.
263 If this number is exceeded time-wait socket is immediately destroyed
264 and warning is printed. This limit exists only to prevent
265 simple DoS attacks, you _must_ not lower the limit artificially,
266 but rather increase it (probably, after increasing installed memory),
267 if network conditions require more than default value.
269 tcp_mem - vector of 3 INTEGERs: min, pressure, max
270 min: below this number of pages TCP is not bothered about its
271 memory appetite.
273 pressure: when amount of memory allocated by TCP exceeds this number
274 of pages, TCP moderates its memory consumption and enters memory
275 pressure mode, which is exited when memory consumption falls
276 under "min".
278 max: number of pages allowed for queueing by all TCP sockets.
280 Defaults are calculated at boot time from amount of available
281 memory.
283 tcp_moderate_rcvbuf - BOOLEAN
284 If set, TCP performs receive buffer auto-tuning, attempting to
285 automatically size the buffer (no greater than tcp_rmem[2]) to
286 match the size required by the path for full throughput. Enabled by
287 default.
289 tcp_mtu_probing - INTEGER
290 Controls TCP Packetization-Layer Path MTU Discovery. Takes three
291 values:
292 0 - Disabled
293 1 - Disabled by default, enabled when an ICMP black hole detected
294 2 - Always enabled, use initial MSS of tcp_base_mss.
296 tcp_no_metrics_save - BOOLEAN
297 By default, TCP saves various connection metrics in the route cache
298 when the connection closes, so that connections established in the
299 near future can use these to set initial conditions. Usually, this
300 increases overall performance, but may sometimes cause performance
301 degradation. If set, TCP will not cache metrics on closing
302 connections.
304 tcp_orphan_retries - INTEGER
305 How may times to retry before killing TCP connection, closed
306 by our side. Default value 7 corresponds to ~50sec-16min
307 depending on RTO. If you machine is loaded WEB server,
308 you should think about lowering this value, such sockets
309 may consume significant resources. Cf. tcp_max_orphans.
311 tcp_reordering - INTEGER
312 Maximal reordering of packets in a TCP stream.
313 Default: 3
315 tcp_retrans_collapse - BOOLEAN
316 Bug-to-bug compatibility with some broken printers.
317 On retransmit try to send bigger packets to work around bugs in
318 certain TCP stacks.
320 tcp_retries1 - INTEGER
321 How many times to retry before deciding that something is wrong
322 and it is necessary to report this suspicion to network layer.
323 Minimal RFC value is 3, it is default, which corresponds
324 to ~3sec-8min depending on RTO.
326 tcp_retries2 - INTEGER
327 How may times to retry before killing alive TCP connection.
328 RFC1122 says that the limit should be longer than 100 sec.
329 It is too small number. Default value 15 corresponds to ~13-30min
330 depending on RTO.
332 tcp_rfc1337 - BOOLEAN
333 If set, the TCP stack behaves conforming to RFC1337. If unset,
334 we are not conforming to RFC, but prevent TCP TIME_WAIT
335 assassination.
336 Default: 0
338 tcp_rmem - vector of 3 INTEGERs: min, default, max
339 min: Minimal size of receive buffer used by TCP sockets.
340 It is guaranteed to each TCP socket, even under moderate memory
341 pressure.
342 Default: 8K
344 default: initial size of receive buffer used by TCP sockets.
345 This value overrides net.core.rmem_default used by other protocols.
346 Default: 87380 bytes. This value results in window of 65535 with
347 default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
348 less for default tcp_app_win. See below about these variables.
350 max: maximal size of receive buffer allowed for automatically
351 selected receiver buffers for TCP socket. This value does not override
352 net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables
353 automatic tuning of that socket's receive buffer size, in which
354 case this value is ignored.
355 Default: between 87380B and 4MB, depending on RAM size.
357 tcp_sack - BOOLEAN
358 Enable select acknowledgments (SACKS).
360 tcp_slow_start_after_idle - BOOLEAN
361 If set, provide RFC2861 behavior and time out the congestion
362 window after an idle period. An idle period is defined at
363 the current RTO. If unset, the congestion window will not
364 be timed out after an idle period.
365 Default: 1
367 tcp_stdurg - BOOLEAN
368 Use the Host requirements interpretation of the TCP urgent pointer field.
369 Most hosts use the older BSD interpretation, so if you turn this on
370 Linux might not communicate correctly with them.
371 Default: FALSE
373 tcp_synack_retries - INTEGER
374 Number of times SYNACKs for a passive TCP connection attempt will
375 be retransmitted. Should not be higher than 255. Default value
376 is 5, which corresponds to ~180seconds.
378 tcp_syncookies - BOOLEAN
379 Only valid when the kernel was compiled with CONFIG_SYNCOOKIES
380 Send out syncookies when the syn backlog queue of a socket
381 overflows. This is to prevent against the common 'SYN flood attack'
382 Default: FALSE
384 Note, that syncookies is fallback facility.
385 It MUST NOT be used to help highly loaded servers to stand
386 against legal connection rate. If you see SYN flood warnings
387 in your logs, but investigation shows that they occur
388 because of overload with legal connections, you should tune
389 another parameters until this warning disappear.
390 See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
392 syncookies seriously violate TCP protocol, do not allow
393 to use TCP extensions, can result in serious degradation
394 of some services (f.e. SMTP relaying), visible not by you,
395 but your clients and relays, contacting you. While you see
396 SYN flood warnings in logs not being really flooded, your server
397 is seriously misconfigured.
399 tcp_syn_retries - INTEGER
400 Number of times initial SYNs for an active TCP connection attempt
401 will be retransmitted. Should not be higher than 255. Default value
402 is 5, which corresponds to ~180seconds.
404 tcp_timestamps - BOOLEAN
405 Enable timestamps as defined in RFC1323.
407 tcp_tso_win_divisor - INTEGER
408 This allows control over what percentage of the congestion window
409 can be consumed by a single TSO frame.
410 The setting of this parameter is a choice between burstiness and
411 building larger TSO frames.
412 Default: 3
414 tcp_tw_recycle - BOOLEAN
415 Enable fast recycling TIME-WAIT sockets. Default value is 0.
416 It should not be changed without advice/request of technical
417 experts.
419 tcp_tw_reuse - BOOLEAN
420 Allow to reuse TIME-WAIT sockets for new connections when it is
421 safe from protocol viewpoint. Default value is 0.
422 It should not be changed without advice/request of technical
423 experts.
425 tcp_window_scaling - BOOLEAN
426 Enable window scaling as defined in RFC1323.
428 tcp_wmem - vector of 3 INTEGERs: min, default, max
429 min: Amount of memory reserved for send buffers for TCP sockets.
430 Each TCP socket has rights to use it due to fact of its birth.
431 Default: 4K
433 default: initial size of send buffer used by TCP sockets. This
434 value overrides net.core.wmem_default used by other protocols.
435 It is usually lower than net.core.wmem_default.
436 Default: 16K
438 max: Maximal amount of memory allowed for automatically tuned
439 send buffers for TCP sockets. This value does not override
440 net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables
441 automatic tuning of that socket's send buffer size, in which case
442 this value is ignored.
443 Default: between 64K and 4MB, depending on RAM size.
445 tcp_workaround_signed_windows - BOOLEAN
446 If set, assume no receipt of a window scaling option means the
447 remote TCP is broken and treats the window as a signed quantity.
448 If unset, assume the remote TCP is not broken even if we do
449 not receive a window scaling option from them.
450 Default: 0
452 tcp_dma_copybreak - INTEGER
453 Lower limit, in bytes, of the size of socket reads that will be
454 offloaded to a DMA copy engine, if one is present in the system
455 and CONFIG_NET_DMA is enabled.
456 Default: 4096
458 UDP variables:
460 udp_mem - vector of 3 INTEGERs: min, pressure, max
461 Number of pages allowed for queueing by all UDP sockets.
463 min: Below this number of pages UDP is not bothered about its
464 memory appetite. When amount of memory allocated by UDP exceeds
465 this number, UDP starts to moderate memory usage.
467 pressure: This value was introduced to follow format of tcp_mem.
469 max: Number of pages allowed for queueing by all UDP sockets.
471 Default is calculated at boot time from amount of available memory.
473 udp_rmem_min - INTEGER
474 Minimal size of receive buffer used by UDP sockets in moderation.
475 Each UDP socket is able to use the size for receiving data, even if
476 total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
477 Default: 4096
479 udp_wmem_min - INTEGER
480 Minimal size of send buffer used by UDP sockets in moderation.
481 Each UDP socket is able to use the size for sending data, even if
482 total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
483 Default: 4096
485 CIPSOv4 Variables:
487 cipso_cache_enable - BOOLEAN
488 If set, enable additions to and lookups from the CIPSO label mapping
489 cache. If unset, additions are ignored and lookups always result in a
490 miss. However, regardless of the setting the cache is still
491 invalidated when required when means you can safely toggle this on and
492 off and the cache will always be "safe".
493 Default: 1
495 cipso_cache_bucket_size - INTEGER
496 The CIPSO label cache consists of a fixed size hash table with each
497 hash bucket containing a number of cache entries. This variable limits
498 the number of entries in each hash bucket; the larger the value the
499 more CIPSO label mappings that can be cached. When the number of
500 entries in a given hash bucket reaches this limit adding new entries
501 causes the oldest entry in the bucket to be removed to make room.
502 Default: 10
504 cipso_rbm_optfmt - BOOLEAN
505 Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
506 the CIPSO draft specification (see Documentation/netlabel for details).
507 This means that when set the CIPSO tag will be padded with empty
508 categories in order to make the packet data 32-bit aligned.
509 Default: 0
511 cipso_rbm_structvalid - BOOLEAN
512 If set, do a very strict check of the CIPSO option when
513 ip_options_compile() is called. If unset, relax the checks done during
514 ip_options_compile(). Either way is "safe" as errors are caught else
515 where in the CIPSO processing code but setting this to 0 (False) should
516 result in less work (i.e. it should be faster) but could cause problems
517 with other implementations that require strict checking.
518 Default: 0
520 IP Variables:
522 ip_local_port_range - 2 INTEGERS
523 Defines the local port range that is used by TCP and UDP to
524 choose the local port. The first number is the first, the
525 second the last local port number. Default value depends on
526 amount of memory available on the system:
527 > 128Mb 32768-61000
528 < 128Mb 1024-4999 or even less.
529 This number defines number of active connections, which this
530 system can issue simultaneously to systems not supporting
531 TCP extensions (timestamps). With tcp_tw_recycle enabled
532 (i.e. by default) range 1024-4999 is enough to issue up to
533 2000 connections per second to systems supporting timestamps.
535 ip_nonlocal_bind - BOOLEAN
536 If set, allows processes to bind() to non-local IP addresses,
537 which can be quite useful - but may break some applications.
538 Default: 0
540 ip_dynaddr - BOOLEAN
541 If set non-zero, enables support for dynamic addresses.
542 If set to a non-zero value larger than 1, a kernel log
543 message will be printed when dynamic address rewriting
544 occurs.
545 Default: 0
547 icmp_echo_ignore_all - BOOLEAN
548 If set non-zero, then the kernel will ignore all ICMP ECHO
549 requests sent to it.
550 Default: 0
552 icmp_echo_ignore_broadcasts - BOOLEAN
553 If set non-zero, then the kernel will ignore all ICMP ECHO and
554 TIMESTAMP requests sent to it via broadcast/multicast.
555 Default: 1
557 icmp_ratelimit - INTEGER
558 Limit the maximal rates for sending ICMP packets whose type matches
559 icmp_ratemask (see below) to specific targets.
560 0 to disable any limiting,
561 otherwise the minimal space between responses in milliseconds.
562 Default: 1000
564 icmp_ratemask - INTEGER
565 Mask made of ICMP types for which rates are being limited.
566 Significant bits: IHGFEDCBA9876543210
567 Default mask: 0000001100000011000 (6168)
569 Bit definitions (see include/linux/icmp.h):
570 0 Echo Reply
571 3 Destination Unreachable *
572 4 Source Quench *
573 5 Redirect
574 8 Echo Request
575 B Time Exceeded *
576 C Parameter Problem *
577 D Timestamp Request
578 E Timestamp Reply
579 F Info Request
580 G Info Reply
581 H Address Mask Request
582 I Address Mask Reply
584 * These are rate limited by default (see default mask above)
586 icmp_ignore_bogus_error_responses - BOOLEAN
587 Some routers violate RFC1122 by sending bogus responses to broadcast
588 frames. Such violations are normally logged via a kernel warning.
589 If this is set to TRUE, the kernel will not give such warnings, which
590 will avoid log file clutter.
591 Default: FALSE
593 icmp_errors_use_inbound_ifaddr - BOOLEAN
595 If zero, icmp error messages are sent with the primary address of
596 the exiting interface.
598 If non-zero, the message will be sent with the primary address of
599 the interface that received the packet that caused the icmp error.
600 This is the behaviour network many administrators will expect from
601 a router. And it can make debugging complicated network layouts
602 much easier.
604 Note that if no primary address exists for the interface selected,
605 then the primary address of the first non-loopback interface that
606 has one will be used regardless of this setting.
608 Default: 0
610 igmp_max_memberships - INTEGER
611 Change the maximum number of multicast groups we can subscribe to.
612 Default: 20
614 conf/interface/* changes special settings per interface (where "interface" is
615 the name of your network interface)
616 conf/all/* is special, changes the settings for all interfaces
619 log_martians - BOOLEAN
620 Log packets with impossible addresses to kernel log.
621 log_martians for the interface will be enabled if at least one of
622 conf/{all,interface}/log_martians is set to TRUE,
623 it will be disabled otherwise
625 accept_redirects - BOOLEAN
626 Accept ICMP redirect messages.
627 accept_redirects for the interface will be enabled if:
628 - both conf/{all,interface}/accept_redirects are TRUE in the case forwarding
629 for the interface is enabled
630 or
631 - at least one of conf/{all,interface}/accept_redirects is TRUE in the case
632 forwarding for the interface is disabled
633 accept_redirects for the interface will be disabled otherwise
634 default TRUE (host)
635 FALSE (router)
637 forwarding - BOOLEAN
638 Enable IP forwarding on this interface.
640 mc_forwarding - BOOLEAN
641 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
642 and a multicast routing daemon is required.
643 conf/all/mc_forwarding must also be set to TRUE to enable multicast routing
644 for the interface
646 medium_id - INTEGER
647 Integer value used to differentiate the devices by the medium they
648 are attached to. Two devices can have different id values when
649 the broadcast packets are received only on one of them.
650 The default value 0 means that the device is the only interface
651 to its medium, value of -1 means that medium is not known.
653 Currently, it is used to change the proxy_arp behavior:
654 the proxy_arp feature is enabled for packets forwarded between
655 two devices attached to different media.
657 proxy_arp - BOOLEAN
658 Do proxy arp.
659 proxy_arp for the interface will be enabled if at least one of
660 conf/{all,interface}/proxy_arp is set to TRUE,
661 it will be disabled otherwise
663 shared_media - BOOLEAN
664 Send(router) or accept(host) RFC1620 shared media redirects.
665 Overrides ip_secure_redirects.
666 shared_media for the interface will be enabled if at least one of
667 conf/{all,interface}/shared_media is set to TRUE,
668 it will be disabled otherwise
669 default TRUE
671 secure_redirects - BOOLEAN
672 Accept ICMP redirect messages only for gateways,
673 listed in default gateway list.
674 secure_redirects for the interface will be enabled if at least one of
675 conf/{all,interface}/secure_redirects is set to TRUE,
676 it will be disabled otherwise
677 default TRUE
679 send_redirects - BOOLEAN
680 Send redirects, if router.
681 send_redirects for the interface will be enabled if at least one of
682 conf/{all,interface}/send_redirects is set to TRUE,
683 it will be disabled otherwise
684 Default: TRUE
686 bootp_relay - BOOLEAN
687 Accept packets with source address 0.b.c.d destined
688 not to this host as local ones. It is supposed, that
689 BOOTP relay daemon will catch and forward such packets.
690 conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
691 for the interface
692 default FALSE
693 Not Implemented Yet.
695 accept_source_route - BOOLEAN
696 Accept packets with SRR option.
697 conf/all/accept_source_route must also be set to TRUE to accept packets
698 with SRR option on the interface
699 default TRUE (router)
700 FALSE (host)
702 rp_filter - BOOLEAN
703 1 - do source validation by reversed path, as specified in RFC1812
704 Recommended option for single homed hosts and stub network
705 routers. Could cause troubles for complicated (not loop free)
706 networks running a slow unreliable protocol (sort of RIP),
707 or using static routes.
709 0 - No source validation.
711 conf/all/rp_filter must also be set to TRUE to do source validation
712 on the interface
714 Default value is 0. Note that some distributions enable it
715 in startup scripts.
717 arp_filter - BOOLEAN
718 1 - Allows you to have multiple network interfaces on the same
719 subnet, and have the ARPs for each interface be answered
720 based on whether or not the kernel would route a packet from
721 the ARP'd IP out that interface (therefore you must use source
722 based routing for this to work). In other words it allows control
723 of which cards (usually 1) will respond to an arp request.
725 0 - (default) The kernel can respond to arp requests with addresses
726 from other interfaces. This may seem wrong but it usually makes
727 sense, because it increases the chance of successful communication.
728 IP addresses are owned by the complete host on Linux, not by
729 particular interfaces. Only for more complex setups like load-
730 balancing, does this behaviour cause problems.
732 arp_filter for the interface will be enabled if at least one of
733 conf/{all,interface}/arp_filter is set to TRUE,
734 it will be disabled otherwise
736 arp_announce - INTEGER
737 Define different restriction levels for announcing the local
738 source IP address from IP packets in ARP requests sent on
739 interface:
740 0 - (default) Use any local address, configured on any interface
741 1 - Try to avoid local addresses that are not in the target's
742 subnet for this interface. This mode is useful when target
743 hosts reachable via this interface require the source IP
744 address in ARP requests to be part of their logical network
745 configured on the receiving interface. When we generate the
746 request we will check all our subnets that include the
747 target IP and will preserve the source address if it is from
748 such subnet. If there is no such subnet we select source
749 address according to the rules for level 2.
750 2 - Always use the best local address for this target.
751 In this mode we ignore the source address in the IP packet
752 and try to select local address that we prefer for talks with
753 the target host. Such local address is selected by looking
754 for primary IP addresses on all our subnets on the outgoing
755 interface that include the target IP address. If no suitable
756 local address is found we select the first local address
757 we have on the outgoing interface or on all other interfaces,
758 with the hope we will receive reply for our request and
759 even sometimes no matter the source IP address we announce.
761 The max value from conf/{all,interface}/arp_announce is used.
763 Increasing the restriction level gives more chance for
764 receiving answer from the resolved target while decreasing
765 the level announces more valid sender's information.
767 arp_ignore - INTEGER
768 Define different modes for sending replies in response to
769 received ARP requests that resolve local target IP addresses:
770 0 - (default): reply for any local target IP address, configured
771 on any interface
772 1 - reply only if the target IP address is local address
773 configured on the incoming interface
774 2 - reply only if the target IP address is local address
775 configured on the incoming interface and both with the
776 sender's IP address are part from same subnet on this interface
777 3 - do not reply for local addresses configured with scope host,
778 only resolutions for global and link addresses are replied
779 4-7 - reserved
780 8 - do not reply for all local addresses
782 The max value from conf/{all,interface}/arp_ignore is used
783 when ARP request is received on the {interface}
785 arp_accept - BOOLEAN
786 Define behavior when gratuitous arp replies are received:
787 0 - drop gratuitous arp frames
788 1 - accept gratuitous arp frames
790 app_solicit - INTEGER
791 The maximum number of probes to send to the user space ARP daemon
792 via netlink before dropping back to multicast probes (see
793 mcast_solicit). Defaults to 0.
795 disable_policy - BOOLEAN
796 Disable IPSEC policy (SPD) for this interface
798 disable_xfrm - BOOLEAN
799 Disable IPSEC encryption on this interface, whatever the policy
803 tag - INTEGER
804 Allows you to write a number, which can be used as required.
805 Default value is 0.
807 Alexey Kuznetsov.
808 kuznet@ms2.inr.ac.ru
810 Updated by:
811 Andi Kleen
812 ak@muc.de
813 Nicolas Delon
814 delon.nicolas@wanadoo.fr
819 /proc/sys/net/ipv6/* Variables:
821 IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also
822 apply to IPv6 [XXX?].
824 bindv6only - BOOLEAN
825 Default value for IPV6_V6ONLY socket option,
826 which restricts use of the IPv6 socket to IPv6 communication
827 only.
828 TRUE: disable IPv4-mapped address feature
829 FALSE: enable IPv4-mapped address feature
831 Default: FALSE (as specified in RFC2553bis)
833 IPv6 Fragmentation:
835 ip6frag_high_thresh - INTEGER
836 Maximum memory used to reassemble IPv6 fragments. When
837 ip6frag_high_thresh bytes of memory is allocated for this purpose,
838 the fragment handler will toss packets until ip6frag_low_thresh
839 is reached.
841 ip6frag_low_thresh - INTEGER
842 See ip6frag_high_thresh
844 ip6frag_time - INTEGER
845 Time in seconds to keep an IPv6 fragment in memory.
847 ip6frag_secret_interval - INTEGER
848 Regeneration interval (in seconds) of the hash secret (or lifetime
849 for the hash secret) for IPv6 fragments.
850 Default: 600
852 conf/default/*:
853 Change the interface-specific default settings.
856 conf/all/*:
857 Change all the interface-specific settings.
859 [XXX: Other special features than forwarding?]
861 conf/all/forwarding - BOOLEAN
862 Enable global IPv6 forwarding between all interfaces.
864 IPv4 and IPv6 work differently here; e.g. netfilter must be used
865 to control which interfaces may forward packets and which not.
867 This also sets all interfaces' Host/Router setting
868 'forwarding' to the specified value. See below for details.
870 This referred to as global forwarding.
872 proxy_ndp - BOOLEAN
873 Do proxy ndp.
875 conf/interface/*:
876 Change special settings per interface.
878 The functional behaviour for certain settings is different
879 depending on whether local forwarding is enabled or not.
881 accept_ra - BOOLEAN
882 Accept Router Advertisements; autoconfigure using them.
884 Functional default: enabled if local forwarding is disabled.
885 disabled if local forwarding is enabled.
887 accept_ra_defrtr - BOOLEAN
888 Learn default router in Router Advertisement.
890 Functional default: enabled if accept_ra is enabled.
891 disabled if accept_ra is disabled.
893 accept_ra_pinfo - BOOLEAN
894 Learn Prefix Information in Router Advertisement.
896 Functional default: enabled if accept_ra is enabled.
897 disabled if accept_ra is disabled.
899 accept_ra_rt_info_max_plen - INTEGER
900 Maximum prefix length of Route Information in RA.
902 Route Information w/ prefix larger than or equal to this
903 variable shall be ignored.
905 Functional default: 0 if accept_ra_rtr_pref is enabled.
906 -1 if accept_ra_rtr_pref is disabled.
908 accept_ra_rtr_pref - BOOLEAN
909 Accept Router Preference in RA.
911 Functional default: enabled if accept_ra is enabled.
912 disabled if accept_ra is disabled.
914 accept_redirects - BOOLEAN
915 Accept Redirects.
917 Functional default: enabled if local forwarding is disabled.
918 disabled if local forwarding is enabled.
920 accept_source_route - INTEGER
921 Accept source routing (routing extension header).
923 >= 0: Accept only routing header type 2.
924 < 0: Do not accept routing header.
926 Default: 0
928 autoconf - BOOLEAN
929 Autoconfigure addresses using Prefix Information in Router
930 Advertisements.
932 Functional default: enabled if accept_ra_pinfo is enabled.
933 disabled if accept_ra_pinfo is disabled.
935 dad_transmits - INTEGER
936 The amount of Duplicate Address Detection probes to send.
937 Default: 1
939 forwarding - BOOLEAN
940 Configure interface-specific Host/Router behaviour.
942 Note: It is recommended to have the same setting on all
943 interfaces; mixed router/host scenarios are rather uncommon.
945 FALSE:
947 By default, Host behaviour is assumed. This means:
949 1. IsRouter flag is not set in Neighbour Advertisements.
950 2. Router Solicitations are being sent when necessary.
951 3. If accept_ra is TRUE (default), accept Router
952 Advertisements (and do autoconfiguration).
953 4. If accept_redirects is TRUE (default), accept Redirects.
955 TRUE:
957 If local forwarding is enabled, Router behaviour is assumed.
958 This means exactly the reverse from the above:
960 1. IsRouter flag is set in Neighbour Advertisements.
961 2. Router Solicitations are not sent.
962 3. Router Advertisements are ignored.
963 4. Redirects are ignored.
965 Default: FALSE if global forwarding is disabled (default),
966 otherwise TRUE.
968 hop_limit - INTEGER
969 Default Hop Limit to set.
970 Default: 64
972 mtu - INTEGER
973 Default Maximum Transfer Unit
974 Default: 1280 (IPv6 required minimum)
976 router_probe_interval - INTEGER
977 Minimum interval (in seconds) between Router Probing described
978 in RFC4191.
980 Default: 60
982 router_solicitation_delay - INTEGER
983 Number of seconds to wait after interface is brought up
984 before sending Router Solicitations.
985 Default: 1
987 router_solicitation_interval - INTEGER
988 Number of seconds to wait between Router Solicitations.
989 Default: 4
991 router_solicitations - INTEGER
992 Number of Router Solicitations to send until assuming no
993 routers are present.
994 Default: 3
996 use_tempaddr - INTEGER
997 Preference for Privacy Extensions (RFC3041).
998 <= 0 : disable Privacy Extensions
999 == 1 : enable Privacy Extensions, but prefer public
1000 addresses over temporary addresses.
1001 > 1 : enable Privacy Extensions and prefer temporary
1002 addresses over public addresses.
1003 Default: 0 (for most devices)
1004 -1 (for point-to-point devices and loopback devices)
1006 temp_valid_lft - INTEGER
1007 valid lifetime (in seconds) for temporary addresses.
1008 Default: 604800 (7 days)
1010 temp_prefered_lft - INTEGER
1011 Preferred lifetime (in seconds) for temporary addresses.
1012 Default: 86400 (1 day)
1014 max_desync_factor - INTEGER
1015 Maximum value for DESYNC_FACTOR, which is a random value
1016 that ensures that clients don't synchronize with each
1017 other and generate new addresses at exactly the same time.
1018 value is in seconds.
1019 Default: 600
1021 regen_max_retry - INTEGER
1022 Number of attempts before give up attempting to generate
1023 valid temporary addresses.
1024 Default: 5
1026 max_addresses - INTEGER
1027 Number of maximum addresses per interface. 0 disables limitation.
1028 It is recommended not set too large value (or 0) because it would
1029 be too easy way to crash kernel to allow to create too much of
1030 autoconfigured addresses.
1031 Default: 16
1033 disable_ipv6 - BOOLEAN
1034 Disable IPv6 operation.
1035 Default: FALSE (enable IPv6 operation)
1037 accept_dad - INTEGER
1038 Whether to accept DAD (Duplicate Address Detection).
1039 0: Disable DAD
1040 1: Enable DAD (default)
1041 2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
1042 link-local address has been found.
1044 icmp/*:
1045 ratelimit - INTEGER
1046 Limit the maximal rates for sending ICMPv6 packets.
1047 0 to disable any limiting,
1048 otherwise the minimal space between responses in milliseconds.
1049 Default: 1000
1052 IPv6 Update by:
1053 Pekka Savola <pekkas@netcore.fi>
1054 YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
1057 /proc/sys/net/bridge/* Variables:
1059 bridge-nf-call-arptables - BOOLEAN
1060 1 : pass bridged ARP traffic to arptables' FORWARD chain.
1061 0 : disable this.
1062 Default: 1
1064 bridge-nf-call-iptables - BOOLEAN
1065 1 : pass bridged IPv4 traffic to iptables' chains.
1066 0 : disable this.
1067 Default: 1
1069 bridge-nf-call-ip6tables - BOOLEAN
1070 1 : pass bridged IPv6 traffic to ip6tables' chains.
1071 0 : disable this.
1072 Default: 1
1074 bridge-nf-filter-vlan-tagged - BOOLEAN
1075 1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
1076 0 : disable this.
1077 Default: 1
1079 bridge-nf-filter-pppoe-tagged - BOOLEAN
1080 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
1081 0 : disable this.
1082 Default: 1
1085 proc/sys/net/sctp/* Variables:
1087 addip_enable - BOOLEAN
1088 Enable or disable extension of Dynamic Address Reconfiguration
1089 (ADD-IP) functionality specified in RFC5061. This extension provides
1090 the ability to dynamically add and remove new addresses for the SCTP
1091 associations.
1093 1: Enable extension.
1095 0: Disable extension.
1097 Default: 0
1099 addip_noauth_enable - BOOLEAN
1100 Dynamic Address Reconfiguration (ADD-IP) requires the use of
1101 authentication to protect the operations of adding or removing new
1102 addresses. This requirement is mandated so that unauthorized hosts
1103 would not be able to hijack associations. However, older
1104 implementations may not have implemented this requirement while
1105 allowing the ADD-IP extension. For reasons of interoperability,
1106 we provide this variable to control the enforcement of the
1107 authentication requirement.
1109 1: Allow ADD-IP extension to be used without authentication. This
1110 should only be set in a closed environment for interoperability
1111 with older implementations.
1113 0: Enforce the authentication requirement
1115 Default: 0
1117 auth_enable - BOOLEAN
1118 Enable or disable Authenticated Chunks extension. This extension
1119 provides the ability to send and receive authenticated chunks and is
1120 required for secure operation of Dynamic Address Reconfiguration
1121 (ADD-IP) extension.
1123 1: Enable this extension.
1124 0: Disable this extension.
1126 Default: 0
1128 prsctp_enable - BOOLEAN
1129 Enable or disable the Partial Reliability extension (RFC3758) which
1130 is used to notify peers that a given DATA should no longer be expected.
1132 1: Enable extension
1133 0: Disable
1135 Default: 1
1137 max_burst - INTEGER
1138 The limit of the number of new packets that can be initially sent. It
1139 controls how bursty the generated traffic can be.
1141 Default: 4
1143 association_max_retrans - INTEGER
1144 Set the maximum number for retransmissions that an association can
1145 attempt deciding that the remote end is unreachable. If this value
1146 is exceeded, the association is terminated.
1148 Default: 10
1150 max_init_retransmits - INTEGER
1151 The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
1152 that an association will attempt before declaring the destination
1153 unreachable and terminating.
1155 Default: 8
1157 path_max_retrans - INTEGER
1158 The maximum number of retransmissions that will be attempted on a given
1159 path. Once this threshold is exceeded, the path is considered
1160 unreachable, and new traffic will use a different path when the
1161 association is multihomed.
1163 Default: 5
1165 rto_initial - INTEGER
1166 The initial round trip timeout value in milliseconds that will be used
1167 in calculating round trip times. This is the initial time interval
1168 for retransmissions.
1170 Default: 3000
1172 rto_max - INTEGER
1173 The maximum value (in milliseconds) of the round trip timeout. This
1174 is the largest time interval that can elapse between retransmissions.
1176 Default: 60000
1178 rto_min - INTEGER
1179 The minimum value (in milliseconds) of the round trip timeout. This
1180 is the smallest time interval the can elapse between retransmissions.
1182 Default: 1000
1184 hb_interval - INTEGER
1185 The interval (in milliseconds) between HEARTBEAT chunks. These chunks
1186 are sent at the specified interval on idle paths to probe the state of
1187 a given path between 2 associations.
1189 Default: 30000
1191 sack_timeout - INTEGER
1192 The amount of time (in milliseconds) that the implementation will wait
1193 to send a SACK.
1195 Default: 200
1197 valid_cookie_life - INTEGER
1198 The default lifetime of the SCTP cookie (in milliseconds). The cookie
1199 is used during association establishment.
1201 Default: 60000
1203 cookie_preserve_enable - BOOLEAN
1204 Enable or disable the ability to extend the lifetime of the SCTP cookie
1205 that is used during the establishment phase of SCTP association
1207 1: Enable cookie lifetime extension.
1208 0: Disable
1210 Default: 1
1212 rcvbuf_policy - INTEGER
1213 Determines if the receive buffer is attributed to the socket or to
1214 association. SCTP supports the capability to create multiple
1215 associations on a single socket. When using this capability, it is
1216 possible that a single stalled association that's buffering a lot
1217 of data may block other associations from delivering their data by
1218 consuming all of the receive buffer space. To work around this,
1219 the rcvbuf_policy could be set to attribute the receiver buffer space
1220 to each association instead of the socket. This prevents the described
1221 blocking.
1223 1: rcvbuf space is per association
1224 0: recbuf space is per socket
1226 Default: 0
1228 sndbuf_policy - INTEGER
1229 Similar to rcvbuf_policy above, this applies to send buffer space.
1231 1: Send buffer is tracked per association
1232 0: Send buffer is tracked per socket.
1234 Default: 0
1236 sctp_mem - vector of 3 INTEGERs: min, pressure, max
1237 Number of pages allowed for queueing by all SCTP sockets.
1239 min: Below this number of pages SCTP is not bothered about its
1240 memory appetite. When amount of memory allocated by SCTP exceeds
1241 this number, SCTP starts to moderate memory usage.
1243 pressure: This value was introduced to follow format of tcp_mem.
1245 max: Number of pages allowed for queueing by all SCTP sockets.
1247 Default is calculated at boot time from amount of available memory.
1249 sctp_rmem - vector of 3 INTEGERs: min, default, max
1250 See tcp_rmem for a description.
1252 sctp_wmem - vector of 3 INTEGERs: min, default, max
1253 See tcp_wmem for a description.
1255 UNDOCUMENTED:
1257 /proc/sys/net/core/*
1258 dev_weight FIXME
1260 /proc/sys/net/unix/*
1261 max_dgram_qlen FIXME
1263 /proc/sys/net/irda/*
1264 fast_poll_increase FIXME
1265 warn_noreply_time FIXME
1266 discovery_slots FIXME
1267 slot_timeout FIXME
1268 max_baud_rate FIXME
1269 discovery_timeout FIXME
1270 lap_keepalive_time FIXME
1271 max_noreply_time FIXME
1272 max_tx_data_size FIXME
1273 max_tx_window FIXME
1274 min_tx_turn_time FIXME