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1 /proc/sys/net/ipv4/* Variables:
2
3 ip_forward - BOOLEAN
4 0 - disabled (default)
5 not 0 - enabled
6
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
13 ip_default_ttl - INTEGER
14 default 64
15
16 ip_no_pmtu_disc - BOOLEAN
17 Disable Path MTU Discovery.
18 default FALSE
19
20 min_pmtu - INTEGER
21 default 562 - minimum discovered Path MTU
22
23 mtu_expires - INTEGER
24 Time, in seconds, that cached PMTU information is kept.
25
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.
29
30 IP Fragmentation:
31
32 ipfrag_high_thresh - INTEGER
33 Maximum memory used to reassemble IP fragments. When
34 ipfrag_high_thresh bytes of memory is allocated for this purpose,
35 the fragment handler will toss packets until ipfrag_low_thresh
36 is reached.
37
38 ipfrag_low_thresh - INTEGER
39 See ipfrag_high_thresh
40
41 ipfrag_time - INTEGER
42 Time in seconds to keep an IP fragment in memory.
43
44 ipfrag_secret_interval - INTEGER
45 Regeneration interval (in seconds) of the hash secret (or lifetime
46 for the hash secret) for IP fragments.
47 Default: 600
48
49 ipfrag_max_dist - INTEGER
50 ipfrag_max_dist is a non-negative integer value which defines the
51 maximum "disorder" which is allowed among fragments which share a
52 common IP source address. Note that reordering of packets is
53 not unusual, but if a large number of fragments arrive from a source
54 IP address while a particular fragment queue remains incomplete, it
55 probably indicates that one or more fragments belonging to that queue
56 have been lost. When ipfrag_max_dist is positive, an additional check
57 is done on fragments before they are added to a reassembly queue - if
58 ipfrag_max_dist (or more) fragments have arrived from a particular IP
59 address between additions to any IP fragment queue using that source
60 address, it's presumed that one or more fragments in the queue are
61 lost. The existing fragment queue will be dropped, and a new one
62 started. An ipfrag_max_dist value of zero disables this check.
63
64 Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
65 result in unnecessarily dropping fragment queues when normal
66 reordering of packets occurs, which could lead to poor application
67 performance. Using a very large value, e.g. 50000, increases the
68 likelihood of incorrectly reassembling IP fragments that originate
69 from different IP datagrams, which could result in data corruption.
70 Default: 64
71
72 INET peer storage:
73
74 inet_peer_threshold - INTEGER
75 The approximate size of the storage. Starting from this threshold
76 entries will be thrown aggressively. This threshold also determines
77 entries' time-to-live and time intervals between garbage collection
78 passes. More entries, less time-to-live, less GC interval.
79
80 inet_peer_minttl - INTEGER
81 Minimum time-to-live of entries. Should be enough to cover fragment
82 time-to-live on the reassembling side. This minimum time-to-live is
83 guaranteed if the pool size is less than inet_peer_threshold.
84 Measured in jiffies(1).
85
86 inet_peer_maxttl - INTEGER
87 Maximum time-to-live of entries. Unused entries will expire after
88 this period of time if there is no memory pressure on the pool (i.e.
89 when the number of entries in the pool is very small).
90 Measured in jiffies(1).
91
92 inet_peer_gc_mintime - INTEGER
93 Minimum interval between garbage collection passes. This interval is
94 in effect under high memory pressure on the pool.
95 Measured in jiffies(1).
96
97 inet_peer_gc_maxtime - INTEGER
98 Minimum interval between garbage collection passes. This interval is
99 in effect under low (or absent) memory pressure on the pool.
100 Measured in jiffies(1).
101
102 TCP variables:
103
104 somaxconn - INTEGER
105 Limit of socket listen() backlog, known in userspace as SOMAXCONN.
106 Defaults to 128. See also tcp_max_syn_backlog for additional tuning
107 for TCP sockets.
108
109 tcp_abc - INTEGER
110 Controls Appropriate Byte Count (ABC) defined in RFC3465.
111 ABC is a way of increasing congestion window (cwnd) more slowly
112 in response to partial acknowledgments.
113 Possible values are:
114 0 increase cwnd once per acknowledgment (no ABC)
115 1 increase cwnd once per acknowledgment of full sized segment
116 2 allow increase cwnd by two if acknowledgment is
117 of two segments to compensate for delayed acknowledgments.
118 Default: 0 (off)
119
120 tcp_abort_on_overflow - BOOLEAN
121 If listening service is too slow to accept new connections,
122 reset them. Default state is FALSE. It means that if overflow
123 occurred due to a burst, connection will recover. Enable this
124 option _only_ if you are really sure that listening daemon
125 cannot be tuned to accept connections faster. Enabling this
126 option can harm clients of your server.
127
128 tcp_adv_win_scale - INTEGER
129 Count buffering overhead as bytes/2^tcp_adv_win_scale
130 (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
131 if it is <= 0.
132 Default: 2
133
134 tcp_allowed_congestion_control - STRING
135 Show/set the congestion control choices available to non-privileged
136 processes. The list is a subset of those listed in
137 tcp_available_congestion_control.
138 Default is "reno" and the default setting (tcp_congestion_control).
139
140 tcp_app_win - INTEGER
141 Reserve max(window/2^tcp_app_win, mss) of window for application
142 buffer. Value 0 is special, it means that nothing is reserved.
143 Default: 31
144
145 tcp_available_congestion_control - STRING
146 Shows the available congestion control choices that are registered.
147 More congestion control algorithms may be available as modules,
148 but not loaded.
149
150 tcp_base_mss - INTEGER
151 The initial value of search_low to be used by Packetization Layer
152 Path MTU Discovery (MTU probing). If MTU probing is enabled,
153 this is the inital MSS used by the connection.
154
155 tcp_congestion_control - STRING
156 Set the congestion control algorithm to be used for new
157 connections. The algorithm "reno" is always available, but
158 additional choices may be available based on kernel configuration.
159 Default is set as part of kernel configuration.
160
161 tcp_dsack - BOOLEAN
162 Allows TCP to send "duplicate" SACKs.
163
164 tcp_ecn - BOOLEAN
165 Enable Explicit Congestion Notification in TCP.
166
167 tcp_fack - BOOLEAN
168 Enable FACK congestion avoidance and fast retransmission.
169 The value is not used, if tcp_sack is not enabled.
170
171 tcp_fin_timeout - INTEGER
172 Time to hold socket in state FIN-WAIT-2, if it was closed
173 by our side. Peer can be broken and never close its side,
174 or even died unexpectedly. Default value is 60sec.
175 Usual value used in 2.2 was 180 seconds, you may restore
176 it, but remember that if your machine is even underloaded WEB server,
177 you risk to overflow memory with kilotons of dead sockets,
178 FIN-WAIT-2 sockets are less dangerous than FIN-WAIT-1,
179 because they eat maximum 1.5K of memory, but they tend
180 to live longer. Cf. tcp_max_orphans.
181
182 tcp_frto - INTEGER
183 Enables Forward RTO-Recovery (F-RTO) defined in RFC4138.
184 F-RTO is an enhanced recovery algorithm for TCP retransmission
185 timeouts. It is particularly beneficial in wireless environments
186 where packet loss is typically due to random radio interference
187 rather than intermediate router congestion. FRTO is sender-side
188 only modification. Therefore it does not require any support from
189 the peer, but in a typical case, however, where wireless link is
190 the local access link and most of the data flows downlink, the
191 faraway servers should have FRTO enabled to take advantage of it.
192 If set to 1, basic version is enabled. 2 enables SACK enhanced
193 F-RTO if flow uses SACK. The basic version can be used also when
194 SACK is in use though scenario(s) with it exists where FRTO
195 interacts badly with the packet counting of the SACK enabled TCP
196 flow.
197
198 tcp_frto_response - INTEGER
199 When F-RTO has detected that a TCP retransmission timeout was
200 spurious (i.e, the timeout would have been avoided had TCP set a
201 longer retransmission timeout), TCP has several options what to do
202 next. Possible values are:
203 0 Rate halving based; a smooth and conservative response,
204 results in halved cwnd and ssthresh after one RTT
205 1 Very conservative response; not recommended because even
206 though being valid, it interacts poorly with the rest of
207 Linux TCP, halves cwnd and ssthresh immediately
208 2 Aggressive response; undoes congestion control measures
209 that are now known to be unnecessary (ignoring the
210 possibility of a lost retransmission that would require
211 TCP to be more cautious), cwnd and ssthresh are restored
212 to the values prior timeout
213 Default: 0 (rate halving based)
214
215 tcp_keepalive_time - INTEGER
216 How often TCP sends out keepalive messages when keepalive is enabled.
217 Default: 2hours.
218
219 tcp_keepalive_probes - INTEGER
220 How many keepalive probes TCP sends out, until it decides that the
221 connection is broken. Default value: 9.
222
223 tcp_keepalive_intvl - INTEGER
224 How frequently the probes are send out. Multiplied by
225 tcp_keepalive_probes it is time to kill not responding connection,
226 after probes started. Default value: 75sec i.e. connection
227 will be aborted after ~11 minutes of retries.
228
229 tcp_low_latency - BOOLEAN
230 If set, the TCP stack makes decisions that prefer lower
231 latency as opposed to higher throughput. By default, this
232 option is not set meaning that higher throughput is preferred.
233 An example of an application where this default should be
234 changed would be a Beowulf compute cluster.
235 Default: 0
236
237 tcp_max_orphans - INTEGER
238 Maximal number of TCP sockets not attached to any user file handle,
239 held by system. If this number is exceeded orphaned connections are
240 reset immediately and warning is printed. This limit exists
241 only to prevent simple DoS attacks, you _must_ not rely on this
242 or lower the limit artificially, but rather increase it
243 (probably, after increasing installed memory),
244 if network conditions require more than default value,
245 and tune network services to linger and kill such states
246 more aggressively. Let me to remind again: each orphan eats
247 up to ~64K of unswappable memory.
248
249 tcp_max_syn_backlog - INTEGER
250 Maximal number of remembered connection requests, which are
251 still did not receive an acknowledgment from connecting client.
252 Default value is 1024 for systems with more than 128Mb of memory,
253 and 128 for low memory machines. If server suffers of overload,
254 try to increase this number.
255
256 tcp_max_tw_buckets - INTEGER
257 Maximal number of timewait sockets held by system simultaneously.
258 If this number is exceeded time-wait socket is immediately destroyed
259 and warning is printed. This limit exists only to prevent
260 simple DoS attacks, you _must_ not lower the limit artificially,
261 but rather increase it (probably, after increasing installed memory),
262 if network conditions require more than default value.
263
264 tcp_mem - vector of 3 INTEGERs: min, pressure, max
265 min: below this number of pages TCP is not bothered about its
266 memory appetite.
267
268 pressure: when amount of memory allocated by TCP exceeds this number
269 of pages, TCP moderates its memory consumption and enters memory
270 pressure mode, which is exited when memory consumption falls
271 under "min".
272
273 max: number of pages allowed for queueing by all TCP sockets.
274
275 Defaults are calculated at boot time from amount of available
276 memory.
277
278 tcp_moderate_rcvbuf - BOOLEAN
279 If set, TCP performs receive buffer autotuning, attempting to
280 automatically size the buffer (no greater than tcp_rmem[2]) to
281 match the size required by the path for full throughput. Enabled by
282 default.
283
284 tcp_mtu_probing - INTEGER
285 Controls TCP Packetization-Layer Path MTU Discovery. Takes three
286 values:
287 0 - Disabled
288 1 - Disabled by default, enabled when an ICMP black hole detected
289 2 - Always enabled, use initial MSS of tcp_base_mss.
290
291 tcp_no_metrics_save - BOOLEAN
292 By default, TCP saves various connection metrics in the route cache
293 when the connection closes, so that connections established in the
294 near future can use these to set initial conditions. Usually, this
295 increases overall performance, but may sometimes cause performance
296 degradation. If set, TCP will not cache metrics on closing
297 connections.
298
299 tcp_orphan_retries - INTEGER
300 How may times to retry before killing TCP connection, closed
301 by our side. Default value 7 corresponds to ~50sec-16min
302 depending on RTO. If you machine is loaded WEB server,
303 you should think about lowering this value, such sockets
304 may consume significant resources. Cf. tcp_max_orphans.
305
306 tcp_reordering - INTEGER
307 Maximal reordering of packets in a TCP stream.
308 Default: 3
309
310 tcp_retrans_collapse - BOOLEAN
311 Bug-to-bug compatibility with some broken printers.
312 On retransmit try to send bigger packets to work around bugs in
313 certain TCP stacks.
314
315 tcp_retries1 - INTEGER
316 How many times to retry before deciding that something is wrong
317 and it is necessary to report this suspicion to network layer.
318 Minimal RFC value is 3, it is default, which corresponds
319 to ~3sec-8min depending on RTO.
320
321 tcp_retries2 - INTEGER
322 How may times to retry before killing alive TCP connection.
323 RFC1122 says that the limit should be longer than 100 sec.
324 It is too small number. Default value 15 corresponds to ~13-30min
325 depending on RTO.
326
327 tcp_rfc1337 - BOOLEAN
328 If set, the TCP stack behaves conforming to RFC1337. If unset,
329 we are not conforming to RFC, but prevent TCP TIME_WAIT
330 assassination.
331 Default: 0
332
333 tcp_rmem - vector of 3 INTEGERs: min, default, max
334 min: Minimal size of receive buffer used by TCP sockets.
335 It is guaranteed to each TCP socket, even under moderate memory
336 pressure.
337 Default: 8K
338
339 default: default size of receive buffer used by TCP sockets.
340 This value overrides net.core.rmem_default used by other protocols.
341 Default: 87380 bytes. This value results in window of 65535 with
342 default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
343 less for default tcp_app_win. See below about these variables.
344
345 max: maximal size of receive buffer allowed for automatically
346 selected receiver buffers for TCP socket. This value does not override
347 net.core.rmem_max, "static" selection via SO_RCVBUF does not use this.
348 Default: 87380*2 bytes.
349
350 tcp_sack - BOOLEAN
351 Enable select acknowledgments (SACKS).
352
353 tcp_slow_start_after_idle - BOOLEAN
354 If set, provide RFC2861 behavior and time out the congestion
355 window after an idle period. An idle period is defined at
356 the current RTO. If unset, the congestion window will not
357 be timed out after an idle period.
358 Default: 1
359
360 tcp_stdurg - BOOLEAN
361 Use the Host requirements interpretation of the TCP urg pointer field.
362 Most hosts use the older BSD interpretation, so if you turn this on
363 Linux might not communicate correctly with them.
364 Default: FALSE
365
366 tcp_synack_retries - INTEGER
367 Number of times SYNACKs for a passive TCP connection attempt will
368 be retransmitted. Should not be higher than 255. Default value
369 is 5, which corresponds to ~180seconds.
370
371 tcp_syncookies - BOOLEAN
372 Only valid when the kernel was compiled with CONFIG_SYNCOOKIES
373 Send out syncookies when the syn backlog queue of a socket
374 overflows. This is to prevent against the common 'syn flood attack'
375 Default: FALSE
376
377 Note, that syncookies is fallback facility.
378 It MUST NOT be used to help highly loaded servers to stand
379 against legal connection rate. If you see synflood warnings
380 in your logs, but investigation shows that they occur
381 because of overload with legal connections, you should tune
382 another parameters until this warning disappear.
383 See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
384
385 syncookies seriously violate TCP protocol, do not allow
386 to use TCP extensions, can result in serious degradation
387 of some services (f.e. SMTP relaying), visible not by you,
388 but your clients and relays, contacting you. While you see
389 synflood warnings in logs not being really flooded, your server
390 is seriously misconfigured.
391
392 tcp_syn_retries - INTEGER
393 Number of times initial SYNs for an active TCP connection attempt
394 will be retransmitted. Should not be higher than 255. Default value
395 is 5, which corresponds to ~180seconds.
396
397 tcp_timestamps - BOOLEAN
398 Enable timestamps as defined in RFC1323.
399
400 tcp_tso_win_divisor - INTEGER
401 This allows control over what percentage of the congestion window
402 can be consumed by a single TSO frame.
403 The setting of this parameter is a choice between burstiness and
404 building larger TSO frames.
405 Default: 3
406
407 tcp_tw_recycle - BOOLEAN
408 Enable fast recycling TIME-WAIT sockets. Default value is 0.
409 It should not be changed without advice/request of technical
410 experts.
411
412 tcp_tw_reuse - BOOLEAN
413 Allow to reuse TIME-WAIT sockets for new connections when it is
414 safe from protocol viewpoint. Default value is 0.
415 It should not be changed without advice/request of technical
416 experts.
417
418 tcp_window_scaling - BOOLEAN
419 Enable window scaling as defined in RFC1323.
420
421 tcp_wmem - vector of 3 INTEGERs: min, default, max
422 min: Amount of memory reserved for send buffers for TCP socket.
423 Each TCP socket has rights to use it due to fact of its birth.
424 Default: 4K
425
426 default: Amount of memory allowed for send buffers for TCP socket
427 by default. This value overrides net.core.wmem_default used
428 by other protocols, it is usually lower than net.core.wmem_default.
429 Default: 16K
430
431 max: Maximal amount of memory allowed for automatically selected
432 send buffers for TCP socket. This value does not override
433 net.core.wmem_max, "static" selection via SO_SNDBUF does not use this.
434 Default: 128K
435
436 tcp_workaround_signed_windows - BOOLEAN
437 If set, assume no receipt of a window scaling option means the
438 remote TCP is broken and treats the window as a signed quantity.
439 If unset, assume the remote TCP is not broken even if we do
440 not receive a window scaling option from them.
441 Default: 0
442
443 tcp_dma_copybreak - INTEGER
444 Lower limit, in bytes, of the size of socket reads that will be
445 offloaded to a DMA copy engine, if one is present in the system
446 and CONFIG_NET_DMA is enabled.
447 Default: 4096
448
449 CIPSOv4 Variables:
450
451 cipso_cache_enable - BOOLEAN
452 If set, enable additions to and lookups from the CIPSO label mapping
453 cache. If unset, additions are ignored and lookups always result in a
454 miss. However, regardless of the setting the cache is still
455 invalidated when required when means you can safely toggle this on and
456 off and the cache will always be "safe".
457 Default: 1
458
459 cipso_cache_bucket_size - INTEGER
460 The CIPSO label cache consists of a fixed size hash table with each
461 hash bucket containing a number of cache entries. This variable limits
462 the number of entries in each hash bucket; the larger the value the
463 more CIPSO label mappings that can be cached. When the number of
464 entries in a given hash bucket reaches this limit adding new entries
465 causes the oldest entry in the bucket to be removed to make room.
466 Default: 10
467
468 cipso_rbm_optfmt - BOOLEAN
469 Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
470 the CIPSO draft specification (see Documentation/netlabel for details).
471 This means that when set the CIPSO tag will be padded with empty
472 categories in order to make the packet data 32-bit aligned.
473 Default: 0
474
475 cipso_rbm_structvalid - BOOLEAN
476 If set, do a very strict check of the CIPSO option when
477 ip_options_compile() is called. If unset, relax the checks done during
478 ip_options_compile(). Either way is "safe" as errors are caught else
479 where in the CIPSO processing code but setting this to 0 (False) should
480 result in less work (i.e. it should be faster) but could cause problems
481 with other implementations that require strict checking.
482 Default: 0
483
484 IP Variables:
485
486 ip_local_port_range - 2 INTEGERS
487 Defines the local port range that is used by TCP and UDP to
488 choose the local port. The first number is the first, the
489 second the last local port number. Default value depends on
490 amount of memory available on the system:
491 > 128Mb 32768-61000
492 < 128Mb 1024-4999 or even less.
493 This number defines number of active connections, which this
494 system can issue simultaneously to systems not supporting
495 TCP extensions (timestamps). With tcp_tw_recycle enabled
496 (i.e. by default) range 1024-4999 is enough to issue up to
497 2000 connections per second to systems supporting timestamps.
498
499 ip_nonlocal_bind - BOOLEAN
500 If set, allows processes to bind() to non-local IP addresses,
501 which can be quite useful - but may break some applications.
502 Default: 0
503
504 ip_dynaddr - BOOLEAN
505 If set non-zero, enables support for dynamic addresses.
506 If set to a non-zero value larger than 1, a kernel log
507 message will be printed when dynamic address rewriting
508 occurs.
509 Default: 0
510
511 icmp_echo_ignore_all - BOOLEAN
512 If set non-zero, then the kernel will ignore all ICMP ECHO
513 requests sent to it.
514 Default: 0
515
516 icmp_echo_ignore_broadcasts - BOOLEAN
517 If set non-zero, then the kernel will ignore all ICMP ECHO and
518 TIMESTAMP requests sent to it via broadcast/multicast.
519 Default: 1
520
521 icmp_ratelimit - INTEGER
522 Limit the maximal rates for sending ICMP packets whose type matches
523 icmp_ratemask (see below) to specific targets.
524 0 to disable any limiting, otherwise the maximal rate in jiffies(1)
525 Default: 100
526
527 icmp_ratemask - INTEGER
528 Mask made of ICMP types for which rates are being limited.
529 Significant bits: IHGFEDCBA9876543210
530 Default mask: 0000001100000011000 (6168)
531
532 Bit definitions (see include/linux/icmp.h):
533 0 Echo Reply
534 3 Destination Unreachable *
535 4 Source Quench *
536 5 Redirect
537 8 Echo Request
538 B Time Exceeded *
539 C Parameter Problem *
540 D Timestamp Request
541 E Timestamp Reply
542 F Info Request
543 G Info Reply
544 H Address Mask Request
545 I Address Mask Reply
546
547 * These are rate limited by default (see default mask above)
548
549 icmp_ignore_bogus_error_responses - BOOLEAN
550 Some routers violate RFC1122 by sending bogus responses to broadcast
551 frames. Such violations are normally logged via a kernel warning.
552 If this is set to TRUE, the kernel will not give such warnings, which
553 will avoid log file clutter.
554 Default: FALSE
555
556 icmp_errors_use_inbound_ifaddr - BOOLEAN
557
558 If zero, icmp error messages are sent with the primary address of
559 the exiting interface.
560
561 If non-zero, the message will be sent with the primary address of
562 the interface that received the packet that caused the icmp error.
563 This is the behaviour network many administrators will expect from
564 a router. And it can make debugging complicated network layouts
565 much easier.
566
567 Note that if no primary address exists for the interface selected,
568 then the primary address of the first non-loopback interface that
569 has one will be used regardless of this setting.
570
571 Default: 0
572
573 igmp_max_memberships - INTEGER
574 Change the maximum number of multicast groups we can subscribe to.
575 Default: 20
576
577 conf/interface/* changes special settings per interface (where "interface" is
578 the name of your network interface)
579 conf/all/* is special, changes the settings for all interfaces
580
581
582 log_martians - BOOLEAN
583 Log packets with impossible addresses to kernel log.
584 log_martians for the interface will be enabled if at least one of
585 conf/{all,interface}/log_martians is set to TRUE,
586 it will be disabled otherwise
587
588 accept_redirects - BOOLEAN
589 Accept ICMP redirect messages.
590 accept_redirects for the interface will be enabled if:
591 - both conf/{all,interface}/accept_redirects are TRUE in the case forwarding
592 for the interface is enabled
593 or
594 - at least one of conf/{all,interface}/accept_redirects is TRUE in the case
595 forwarding for the interface is disabled
596 accept_redirects for the interface will be disabled otherwise
597 default TRUE (host)
598 FALSE (router)
599
600 forwarding - BOOLEAN
601 Enable IP forwarding on this interface.
602
603 mc_forwarding - BOOLEAN
604 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
605 and a multicast routing daemon is required.
606 conf/all/mc_forwarding must also be set to TRUE to enable multicast routing
607 for the interface
608
609 medium_id - INTEGER
610 Integer value used to differentiate the devices by the medium they
611 are attached to. Two devices can have different id values when
612 the broadcast packets are received only on one of them.
613 The default value 0 means that the device is the only interface
614 to its medium, value of -1 means that medium is not known.
615
616 Currently, it is used to change the proxy_arp behavior:
617 the proxy_arp feature is enabled for packets forwarded between
618 two devices attached to different media.
619
620 proxy_arp - BOOLEAN
621 Do proxy arp.
622 proxy_arp for the interface will be enabled if at least one of
623 conf/{all,interface}/proxy_arp is set to TRUE,
624 it will be disabled otherwise
625
626 shared_media - BOOLEAN
627 Send(router) or accept(host) RFC1620 shared media redirects.
628 Overrides ip_secure_redirects.
629 shared_media for the interface will be enabled if at least one of
630 conf/{all,interface}/shared_media is set to TRUE,
631 it will be disabled otherwise
632 default TRUE
633
634 secure_redirects - BOOLEAN
635 Accept ICMP redirect messages only for gateways,
636 listed in default gateway list.
637 secure_redirects for the interface will be enabled if at least one of
638 conf/{all,interface}/secure_redirects is set to TRUE,
639 it will be disabled otherwise
640 default TRUE
641
642 send_redirects - BOOLEAN
643 Send redirects, if router.
644 send_redirects for the interface will be enabled if at least one of
645 conf/{all,interface}/send_redirects is set to TRUE,
646 it will be disabled otherwise
647 Default: TRUE
648
649 bootp_relay - BOOLEAN
650 Accept packets with source address 0.b.c.d destined
651 not to this host as local ones. It is supposed, that
652 BOOTP relay daemon will catch and forward such packets.
653 conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
654 for the interface
655 default FALSE
656 Not Implemented Yet.
657
658 accept_source_route - BOOLEAN
659 Accept packets with SRR option.
660 conf/all/accept_source_route must also be set to TRUE to accept packets
661 with SRR option on the interface
662 default TRUE (router)
663 FALSE (host)
664
665 rp_filter - BOOLEAN
666 1 - do source validation by reversed path, as specified in RFC1812
667 Recommended option for single homed hosts and stub network
668 routers. Could cause troubles for complicated (not loop free)
669 networks running a slow unreliable protocol (sort of RIP),
670 or using static routes.
671
672 0 - No source validation.
673
674 conf/all/rp_filter must also be set to TRUE to do source validation
675 on the interface
676
677 Default value is 0. Note that some distributions enable it
678 in startup scripts.
679
680 arp_filter - BOOLEAN
681 1 - Allows you to have multiple network interfaces on the same
682 subnet, and have the ARPs for each interface be answered
683 based on whether or not the kernel would route a packet from
684 the ARP'd IP out that interface (therefore you must use source
685 based routing for this to work). In other words it allows control
686 of which cards (usually 1) will respond to an arp request.
687
688 0 - (default) The kernel can respond to arp requests with addresses
689 from other interfaces. This may seem wrong but it usually makes
690 sense, because it increases the chance of successful communication.
691 IP addresses are owned by the complete host on Linux, not by
692 particular interfaces. Only for more complex setups like load-
693 balancing, does this behaviour cause problems.
694
695 arp_filter for the interface will be enabled if at least one of
696 conf/{all,interface}/arp_filter is set to TRUE,
697 it will be disabled otherwise
698
699 arp_announce - INTEGER
700 Define different restriction levels for announcing the local
701 source IP address from IP packets in ARP requests sent on
702 interface:
703 0 - (default) Use any local address, configured on any interface
704 1 - Try to avoid local addresses that are not in the target's
705 subnet for this interface. This mode is useful when target
706 hosts reachable via this interface require the source IP
707 address in ARP requests to be part of their logical network
708 configured on the receiving interface. When we generate the
709 request we will check all our subnets that include the
710 target IP and will preserve the source address if it is from
711 such subnet. If there is no such subnet we select source
712 address according to the rules for level 2.
713 2 - Always use the best local address for this target.
714 In this mode we ignore the source address in the IP packet
715 and try to select local address that we prefer for talks with
716 the target host. Such local address is selected by looking
717 for primary IP addresses on all our subnets on the outgoing
718 interface that include the target IP address. If no suitable
719 local address is found we select the first local address
720 we have on the outgoing interface or on all other interfaces,
721 with the hope we will receive reply for our request and
722 even sometimes no matter the source IP address we announce.
723
724 The max value from conf/{all,interface}/arp_announce is used.
725
726 Increasing the restriction level gives more chance for
727 receiving answer from the resolved target while decreasing
728 the level announces more valid sender's information.
729
730 arp_ignore - INTEGER
731 Define different modes for sending replies in response to
732 received ARP requests that resolve local target IP addresses:
733 0 - (default): reply for any local target IP address, configured
734 on any interface
735 1 - reply only if the target IP address is local address
736 configured on the incoming interface
737 2 - reply only if the target IP address is local address
738 configured on the incoming interface and both with the
739 sender's IP address are part from same subnet on this interface
740 3 - do not reply for local addresses configured with scope host,
741 only resolutions for global and link addresses are replied
742 4-7 - reserved
743 8 - do not reply for all local addresses
744
745 The max value from conf/{all,interface}/arp_ignore is used
746 when ARP request is received on the {interface}
747
748 arp_accept - BOOLEAN
749 Define behavior when gratuitous arp replies are received:
750 0 - drop gratuitous arp frames
751 1 - accept gratuitous arp frames
752
753 app_solicit - INTEGER
754 The maximum number of probes to send to the user space ARP daemon
755 via netlink before dropping back to multicast probes (see
756 mcast_solicit). Defaults to 0.
757
758 disable_policy - BOOLEAN
759 Disable IPSEC policy (SPD) for this interface
760
761 disable_xfrm - BOOLEAN
762 Disable IPSEC encryption on this interface, whatever the policy
763
764
765
766 tag - INTEGER
767 Allows you to write a number, which can be used as required.
768 Default value is 0.
769
770 (1) Jiffie: internal timeunit for the kernel. On the i386 1/100s, on the
771 Alpha 1/1024s. See the HZ define in /usr/include/asm/param.h for the exact
772 value on your system.
773
774 Alexey Kuznetsov.
775 kuznet@ms2.inr.ac.ru
776
777 Updated by:
778 Andi Kleen
779 ak@muc.de
780 Nicolas Delon
781 delon.nicolas@wanadoo.fr
782
783
784
785
786 /proc/sys/net/ipv6/* Variables:
787
788 IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also
789 apply to IPv6 [XXX?].
790
791 bindv6only - BOOLEAN
792 Default value for IPV6_V6ONLY socket option,
793 which restricts use of the IPv6 socket to IPv6 communication
794 only.
795 TRUE: disable IPv4-mapped address feature
796 FALSE: enable IPv4-mapped address feature
797
798 Default: FALSE (as specified in RFC2553bis)
799
800 IPv6 Fragmentation:
801
802 ip6frag_high_thresh - INTEGER
803 Maximum memory used to reassemble IPv6 fragments. When
804 ip6frag_high_thresh bytes of memory is allocated for this purpose,
805 the fragment handler will toss packets until ip6frag_low_thresh
806 is reached.
807
808 ip6frag_low_thresh - INTEGER
809 See ip6frag_high_thresh
810
811 ip6frag_time - INTEGER
812 Time in seconds to keep an IPv6 fragment in memory.
813
814 ip6frag_secret_interval - INTEGER
815 Regeneration interval (in seconds) of the hash secret (or lifetime
816 for the hash secret) for IPv6 fragments.
817 Default: 600
818
819 conf/default/*:
820 Change the interface-specific default settings.
821
822
823 conf/all/*:
824 Change all the interface-specific settings.
825
826 [XXX: Other special features than forwarding?]
827
828 conf/all/forwarding - BOOLEAN
829 Enable global IPv6 forwarding between all interfaces.
830
831 IPv4 and IPv6 work differently here; e.g. netfilter must be used
832 to control which interfaces may forward packets and which not.
833
834 This also sets all interfaces' Host/Router setting
835 'forwarding' to the specified value. See below for details.
836
837 This referred to as global forwarding.
838
839 proxy_ndp - BOOLEAN
840 Do proxy ndp.
841
842 conf/interface/*:
843 Change special settings per interface.
844
845 The functional behaviour for certain settings is different
846 depending on whether local forwarding is enabled or not.
847
848 accept_ra - BOOLEAN
849 Accept Router Advertisements; autoconfigure using them.
850
851 Functional default: enabled if local forwarding is disabled.
852 disabled if local forwarding is enabled.
853
854 accept_ra_defrtr - BOOLEAN
855 Learn default router in Router Advertisement.
856
857 Functional default: enabled if accept_ra is enabled.
858 disabled if accept_ra is disabled.
859
860 accept_ra_pinfo - BOOLEAN
861 Learn Prefix Information in Router Advertisement.
862
863 Functional default: enabled if accept_ra is enabled.
864 disabled if accept_ra is disabled.
865
866 accept_ra_rt_info_max_plen - INTEGER
867 Maximum prefix length of Route Information in RA.
868
869 Route Information w/ prefix larger than or equal to this
870 variable shall be ignored.
871
872 Functional default: 0 if accept_ra_rtr_pref is enabled.
873 -1 if accept_ra_rtr_pref is disabled.
874
875 accept_ra_rtr_pref - BOOLEAN
876 Accept Router Preference in RA.
877
878 Functional default: enabled if accept_ra is enabled.
879 disabled if accept_ra is disabled.
880
881 accept_redirects - BOOLEAN
882 Accept Redirects.
883
884 Functional default: enabled if local forwarding is disabled.
885 disabled if local forwarding is enabled.
886
887 accept_source_route - INTEGER
888 Accept source routing (routing extension header).
889
890 >= 0: Accept only routing header type 2.
891 < 0: Do not accept routing header.
892
893 Default: 0
894
895 autoconf - BOOLEAN
896 Autoconfigure addresses using Prefix Information in Router
897 Advertisements.
898
899 Functional default: enabled if accept_ra_pinfo is enabled.
900 disabled if accept_ra_pinfo is disabled.
901
902 dad_transmits - INTEGER
903 The amount of Duplicate Address Detection probes to send.
904 Default: 1
905
906 forwarding - BOOLEAN
907 Configure interface-specific Host/Router behaviour.
908
909 Note: It is recommended to have the same setting on all
910 interfaces; mixed router/host scenarios are rather uncommon.
911
912 FALSE:
913
914 By default, Host behaviour is assumed. This means:
915
916 1. IsRouter flag is not set in Neighbour Advertisements.
917 2. Router Solicitations are being sent when necessary.
918 3. If accept_ra is TRUE (default), accept Router
919 Advertisements (and do autoconfiguration).
920 4. If accept_redirects is TRUE (default), accept Redirects.
921
922 TRUE:
923
924 If local forwarding is enabled, Router behaviour is assumed.
925 This means exactly the reverse from the above:
926
927 1. IsRouter flag is set in Neighbour Advertisements.
928 2. Router Solicitations are not sent.
929 3. Router Advertisements are ignored.
930 4. Redirects are ignored.
931
932 Default: FALSE if global forwarding is disabled (default),
933 otherwise TRUE.
934
935 hop_limit - INTEGER
936 Default Hop Limit to set.
937 Default: 64
938
939 mtu - INTEGER
940 Default Maximum Transfer Unit
941 Default: 1280 (IPv6 required minimum)
942
943 router_probe_interval - INTEGER
944 Minimum interval (in seconds) between Router Probing described
945 in RFC4191.
946
947 Default: 60
948
949 router_solicitation_delay - INTEGER
950 Number of seconds to wait after interface is brought up
951 before sending Router Solicitations.
952 Default: 1
953
954 router_solicitation_interval - INTEGER
955 Number of seconds to wait between Router Solicitations.
956 Default: 4
957
958 router_solicitations - INTEGER
959 Number of Router Solicitations to send until assuming no
960 routers are present.
961 Default: 3
962
963 use_tempaddr - INTEGER
964 Preference for Privacy Extensions (RFC3041).
965 <= 0 : disable Privacy Extensions
966 == 1 : enable Privacy Extensions, but prefer public
967 addresses over temporary addresses.
968 > 1 : enable Privacy Extensions and prefer temporary
969 addresses over public addresses.
970 Default: 0 (for most devices)
971 -1 (for point-to-point devices and loopback devices)
972
973 temp_valid_lft - INTEGER
974 valid lifetime (in seconds) for temporary addresses.
975 Default: 604800 (7 days)
976
977 temp_prefered_lft - INTEGER
978 Preferred lifetime (in seconds) for temporary addresses.
979 Default: 86400 (1 day)
980
981 max_desync_factor - INTEGER
982 Maximum value for DESYNC_FACTOR, which is a random value
983 that ensures that clients don't synchronize with each
984 other and generate new addresses at exactly the same time.
985 value is in seconds.
986 Default: 600
987
988 regen_max_retry - INTEGER
989 Number of attempts before give up attempting to generate
990 valid temporary addresses.
991 Default: 5
992
993 max_addresses - INTEGER
994 Number of maximum addresses per interface. 0 disables limitation.
995 It is recommended not set too large value (or 0) because it would
996 be too easy way to crash kernel to allow to create too much of
997 autoconfigured addresses.
998 Default: 16
999
1000 icmp/*:
1001 ratelimit - INTEGER
1002 Limit the maximal rates for sending ICMPv6 packets.
1003 0 to disable any limiting, otherwise the maximal rate in jiffies(1)
1004 Default: 100
1005
1006
1007 IPv6 Update by:
1008 Pekka Savola <pekkas@netcore.fi>
1009 YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
1010
1011
1012 /proc/sys/net/bridge/* Variables:
1013
1014 bridge-nf-call-arptables - BOOLEAN
1015 1 : pass bridged ARP traffic to arptables' FORWARD chain.
1016 0 : disable this.
1017 Default: 1
1018
1019 bridge-nf-call-iptables - BOOLEAN
1020 1 : pass bridged IPv4 traffic to iptables' chains.
1021 0 : disable this.
1022 Default: 1
1023
1024 bridge-nf-call-ip6tables - BOOLEAN
1025 1 : pass bridged IPv6 traffic to ip6tables' chains.
1026 0 : disable this.
1027 Default: 1
1028
1029 bridge-nf-filter-vlan-tagged - BOOLEAN
1030 1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
1031 0 : disable this.
1032 Default: 1
1033
1034 bridge-nf-filter-pppoe-tagged - BOOLEAN
1035 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
1036 0 : disable this.
1037 Default: 1
1038
1039
1040 UNDOCUMENTED:
1041
1042 dev_weight FIXME
1043 discovery_slots FIXME
1044 discovery_timeout FIXME
1045 fast_poll_increase FIXME
1046 ip6_queue_maxlen FIXME
1047 lap_keepalive_time FIXME
1048 lo_cong FIXME
1049 max_baud_rate FIXME
1050 max_dgram_qlen FIXME
1051 max_noreply_time FIXME
1052 max_tx_data_size FIXME
1053 max_tx_window FIXME
1054 min_tx_turn_time FIXME
1055 mod_cong FIXME
1056 no_cong FIXME
1057 no_cong_thresh FIXME
1058 slot_timeout FIXME
1059 warn_noreply_time FIXME
1060