| blob | fd3c0c012351b7f15716d9314ffcb404c54f1693 |
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 IP Fragmentation:
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.
38 ipfrag_low_thresh - INTEGER
39 See ipfrag_high_thresh
41 ipfrag_time - INTEGER
42 Time in seconds to keep an IP fragment in memory.
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
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.
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
72 INET peer storage:
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.
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).
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).
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).
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).
102 TCP variables:
104 tcp_abc - INTEGER
105 Controls Appropriate Byte Count (ABC) defined in RFC3465.
106 ABC is a way of increasing congestion window (cwnd) more slowly
107 in response to partial acknowledgments.
108 Possible values are:
109 0 increase cwnd once per acknowledgment (no ABC)
110 1 increase cwnd once per acknowledgment of full sized segment
111 2 allow increase cwnd by two if acknowledgment is
112 of two segments to compensate for delayed acknowledgments.
113 Default: 0 (off)
115 tcp_syn_retries - INTEGER
116 Number of times initial SYNs for an active TCP connection attempt
117 will be retransmitted. Should not be higher than 255. Default value
118 is 5, which corresponds to ~180seconds.
120 tcp_synack_retries - INTEGER
121 Number of times SYNACKs for a passive TCP connection attempt will
122 be retransmitted. Should not be higher than 255. Default value
123 is 5, which corresponds to ~180seconds.
125 tcp_keepalive_time - INTEGER
126 How often TCP sends out keepalive messages when keepalive is enabled.
127 Default: 2hours.
129 tcp_keepalive_probes - INTEGER
130 How many keepalive probes TCP sends out, until it decides that the
131 connection is broken. Default value: 9.
133 tcp_keepalive_intvl - INTEGER
134 How frequently the probes are send out. Multiplied by
135 tcp_keepalive_probes it is time to kill not responding connection,
136 after probes started. Default value: 75sec i.e. connection
137 will be aborted after ~11 minutes of retries.
139 tcp_retries1 - INTEGER
140 How many times to retry before deciding that something is wrong
141 and it is necessary to report this suspicion to network layer.
142 Minimal RFC value is 3, it is default, which corresponds
143 to ~3sec-8min depending on RTO.
145 tcp_retries2 - INTEGER
146 How may times to retry before killing alive TCP connection.
147 RFC1122 says that the limit should be longer than 100 sec.
148 It is too small number. Default value 15 corresponds to ~13-30min
149 depending on RTO.
151 tcp_orphan_retries - INTEGER
152 How may times to retry before killing TCP connection, closed
153 by our side. Default value 7 corresponds to ~50sec-16min
154 depending on RTO. If you machine is loaded WEB server,
155 you should think about lowering this value, such sockets
156 may consume significant resources. Cf. tcp_max_orphans.
158 tcp_fin_timeout - INTEGER
159 Time to hold socket in state FIN-WAIT-2, if it was closed
160 by our side. Peer can be broken and never close its side,
161 or even died unexpectedly. Default value is 60sec.
162 Usual value used in 2.2 was 180 seconds, you may restore
163 it, but remember that if your machine is even underloaded WEB server,
164 you risk to overflow memory with kilotons of dead sockets,
165 FIN-WAIT-2 sockets are less dangerous than FIN-WAIT-1,
166 because they eat maximum 1.5K of memory, but they tend
167 to live longer. Cf. tcp_max_orphans.
169 tcp_max_tw_buckets - INTEGER
170 Maximal number of timewait sockets held by system simultaneously.
171 If this number is exceeded time-wait socket is immediately destroyed
172 and warning is printed. This limit exists only to prevent
173 simple DoS attacks, you _must_ not lower the limit artificially,
174 but rather increase it (probably, after increasing installed memory),
175 if network conditions require more than default value.
177 tcp_tw_recycle - BOOLEAN
178 Enable fast recycling TIME-WAIT sockets. Default value is 0.
179 It should not be changed without advice/request of technical
180 experts.
182 tcp_tw_reuse - BOOLEAN
183 Allow to reuse TIME-WAIT sockets for new connections when it is
184 safe from protocol viewpoint. Default value is 0.
185 It should not be changed without advice/request of technical
186 experts.
188 tcp_max_orphans - INTEGER
189 Maximal number of TCP sockets not attached to any user file handle,
190 held by system. If this number is exceeded orphaned connections are
191 reset immediately and warning is printed. This limit exists
192 only to prevent simple DoS attacks, you _must_ not rely on this
193 or lower the limit artificially, but rather increase it
194 (probably, after increasing installed memory),
195 if network conditions require more than default value,
196 and tune network services to linger and kill such states
197 more aggressively. Let me to remind again: each orphan eats
198 up to ~64K of unswappable memory.
200 tcp_abort_on_overflow - BOOLEAN
201 If listening service is too slow to accept new connections,
202 reset them. Default state is FALSE. It means that if overflow
203 occurred due to a burst, connection will recover. Enable this
204 option _only_ if you are really sure that listening daemon
205 cannot be tuned to accept connections faster. Enabling this
206 option can harm clients of your server.
208 tcp_syncookies - BOOLEAN
209 Only valid when the kernel was compiled with CONFIG_SYNCOOKIES
210 Send out syncookies when the syn backlog queue of a socket
211 overflows. This is to prevent against the common 'syn flood attack'
212 Default: FALSE
214 Note, that syncookies is fallback facility.
215 It MUST NOT be used to help highly loaded servers to stand
216 against legal connection rate. If you see synflood warnings
217 in your logs, but investigation shows that they occur
218 because of overload with legal connections, you should tune
219 another parameters until this warning disappear.
220 See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
222 syncookies seriously violate TCP protocol, do not allow
223 to use TCP extensions, can result in serious degradation
224 of some services (f.e. SMTP relaying), visible not by you,
225 but your clients and relays, contacting you. While you see
226 synflood warnings in logs not being really flooded, your server
227 is seriously misconfigured.
229 tcp_stdurg - BOOLEAN
230 Use the Host requirements interpretation of the TCP urg pointer field.
231 Most hosts use the older BSD interpretation, so if you turn this on
232 Linux might not communicate correctly with them.
233 Default: FALSE
235 tcp_max_syn_backlog - INTEGER
236 Maximal number of remembered connection requests, which are
237 still did not receive an acknowledgment from connecting client.
238 Default value is 1024 for systems with more than 128Mb of memory,
239 and 128 for low memory machines. If server suffers of overload,
240 try to increase this number.
242 tcp_window_scaling - BOOLEAN
243 Enable window scaling as defined in RFC1323.
245 tcp_timestamps - BOOLEAN
246 Enable timestamps as defined in RFC1323.
248 tcp_sack - BOOLEAN
249 Enable select acknowledgments (SACKS).
251 tcp_fack - BOOLEAN
252 Enable FACK congestion avoidance and fast retransmission.
253 The value is not used, if tcp_sack is not enabled.
255 tcp_dsack - BOOLEAN
256 Allows TCP to send "duplicate" SACKs.
258 tcp_ecn - BOOLEAN
259 Enable Explicit Congestion Notification in TCP.
261 tcp_reordering - INTEGER
262 Maximal reordering of packets in a TCP stream.
263 Default: 3
265 tcp_retrans_collapse - BOOLEAN
266 Bug-to-bug compatibility with some broken printers.
267 On retransmit try to send bigger packets to work around bugs in
268 certain TCP stacks.
270 tcp_wmem - vector of 3 INTEGERs: min, default, max
271 min: Amount of memory reserved for send buffers for TCP socket.
272 Each TCP socket has rights to use it due to fact of its birth.
273 Default: 4K
275 default: Amount of memory allowed for send buffers for TCP socket
276 by default. This value overrides net.core.wmem_default used
277 by other protocols, it is usually lower than net.core.wmem_default.
278 Default: 16K
280 max: Maximal amount of memory allowed for automatically selected
281 send buffers for TCP socket. This value does not override
282 net.core.wmem_max, "static" selection via SO_SNDBUF does not use this.
283 Default: 128K
285 tcp_rmem - vector of 3 INTEGERs: min, default, max
286 min: Minimal size of receive buffer used by TCP sockets.
287 It is guaranteed to each TCP socket, even under moderate memory
288 pressure.
289 Default: 8K
291 default: default size of receive buffer used by TCP sockets.
292 This value overrides net.core.rmem_default used by other protocols.
293 Default: 87380 bytes. This value results in window of 65535 with
294 default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
295 less for default tcp_app_win. See below about these variables.
297 max: maximal size of receive buffer allowed for automatically
298 selected receiver buffers for TCP socket. This value does not override
299 net.core.rmem_max, "static" selection via SO_RCVBUF does not use this.
300 Default: 87380*2 bytes.
302 tcp_mem - vector of 3 INTEGERs: min, pressure, max
303 min: below this number of pages TCP is not bothered about its
304 memory appetite.
306 pressure: when amount of memory allocated by TCP exceeds this number
307 of pages, TCP moderates its memory consumption and enters memory
308 pressure mode, which is exited when memory consumption falls
309 under "min".
311 max: number of pages allowed for queueing by all TCP sockets.
313 Defaults are calculated at boot time from amount of available
314 memory.
316 tcp_app_win - INTEGER
317 Reserve max(window/2^tcp_app_win, mss) of window for application
318 buffer. Value 0 is special, it means that nothing is reserved.
319 Default: 31
321 tcp_adv_win_scale - INTEGER
322 Count buffering overhead as bytes/2^tcp_adv_win_scale
323 (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
324 if it is <= 0.
325 Default: 2
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
333 tcp_low_latency - BOOLEAN
334 If set, the TCP stack makes decisions that prefer lower
335 latency as opposed to higher throughput. By default, this
336 option is not set meaning that higher throughput is preferred.
337 An example of an application where this default should be
338 changed would be a Beowulf compute cluster.
339 Default: 0
341 tcp_tso_win_divisor - INTEGER
342 This allows control over what percentage of the congestion window
343 can be consumed by a single TSO frame.
344 The setting of this parameter is a choice between burstiness and
345 building larger TSO frames.
346 Default: 3
348 tcp_frto - BOOLEAN
349 Enables F-RTO, an enhanced recovery algorithm for TCP retransmission
350 timeouts. It is particularly beneficial in wireless environments
351 where packet loss is typically due to random radio interference
352 rather than intermediate router congestion.
354 tcp_congestion_control - STRING
355 Set the congestion control algorithm to be used for new
356 connections. The algorithm "reno" is always available, but
357 additional choices may be available based on kernel configuration.
359 somaxconn - INTEGER
360 Limit of socket listen() backlog, known in userspace as SOMAXCONN.
361 Defaults to 128. See also tcp_max_syn_backlog for additional tuning
362 for TCP sockets.
364 tcp_workaround_signed_windows - BOOLEAN
365 If set, assume no receipt of a window scaling option means the
366 remote TCP is broken and treats the window as a signed quantity.
367 If unset, assume the remote TCP is not broken even if we do
368 not receive a window scaling option from them.
369 Default: 0
371 tcp_slow_start_after_idle - BOOLEAN
372 If set, provide RFC2861 behavior and time out the congestion
373 window after an idle period. An idle period is defined at
374 the current RTO. If unset, the congestion window will not
375 be timed out after an idle period.
376 Default: 1
378 CIPSOv4 Variables:
380 cipso_cache_enable - BOOLEAN
381 If set, enable additions to and lookups from the CIPSO label mapping
382 cache. If unset, additions are ignored and lookups always result in a
383 miss. However, regardless of the setting the cache is still
384 invalidated when required when means you can safely toggle this on and
385 off and the cache will always be "safe".
386 Default: 1
388 cipso_cache_bucket_size - INTEGER
389 The CIPSO label cache consists of a fixed size hash table with each
390 hash bucket containing a number of cache entries. This variable limits
391 the number of entries in each hash bucket; the larger the value the
392 more CIPSO label mappings that can be cached. When the number of
393 entries in a given hash bucket reaches this limit adding new entries
394 causes the oldest entry in the bucket to be removed to make room.
395 Default: 10
397 cipso_rbm_optfmt - BOOLEAN
398 Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
399 the CIPSO draft specification (see Documentation/netlabel for details).
400 This means that when set the CIPSO tag will be padded with empty
401 categories in order to make the packet data 32-bit aligned.
402 Default: 0
404 cipso_rbm_structvalid - BOOLEAN
405 If set, do a very strict check of the CIPSO option when
406 ip_options_compile() is called. If unset, relax the checks done during
407 ip_options_compile(). Either way is "safe" as errors are caught else
408 where in the CIPSO processing code but setting this to 0 (False) should
409 result in less work (i.e. it should be faster) but could cause problems
410 with other implementations that require strict checking.
411 Default: 0
413 IP Variables:
415 ip_local_port_range - 2 INTEGERS
416 Defines the local port range that is used by TCP and UDP to
417 choose the local port. The first number is the first, the
418 second the last local port number. Default value depends on
419 amount of memory available on the system:
420 > 128Mb 32768-61000
421 < 128Mb 1024-4999 or even less.
422 This number defines number of active connections, which this
423 system can issue simultaneously to systems not supporting
424 TCP extensions (timestamps). With tcp_tw_recycle enabled
425 (i.e. by default) range 1024-4999 is enough to issue up to
426 2000 connections per second to systems supporting timestamps.
428 ip_nonlocal_bind - BOOLEAN
429 If set, allows processes to bind() to non-local IP addresses,
430 which can be quite useful - but may break some applications.
431 Default: 0
433 ip_dynaddr - BOOLEAN
434 If set non-zero, enables support for dynamic addresses.
435 If set to a non-zero value larger than 1, a kernel log
436 message will be printed when dynamic address rewriting
437 occurs.
438 Default: 0
440 icmp_echo_ignore_all - BOOLEAN
441 If set non-zero, then the kernel will ignore all ICMP ECHO
442 requests sent to it.
443 Default: 0
445 icmp_echo_ignore_broadcasts - BOOLEAN
446 If set non-zero, then the kernel will ignore all ICMP ECHO and
447 TIMESTAMP requests sent to it via broadcast/multicast.
448 Default: 1
450 icmp_ratelimit - INTEGER
451 Limit the maximal rates for sending ICMP packets whose type matches
452 icmp_ratemask (see below) to specific targets.
453 0 to disable any limiting, otherwise the maximal rate in jiffies(1)
454 Default: 100
456 icmp_ratemask - INTEGER
457 Mask made of ICMP types for which rates are being limited.
458 Significant bits: IHGFEDCBA9876543210
459 Default mask: 0000001100000011000 (6168)
461 Bit definitions (see include/linux/icmp.h):
462 0 Echo Reply
463 3 Destination Unreachable *
464 4 Source Quench *
465 5 Redirect
466 8 Echo Request
467 B Time Exceeded *
468 C Parameter Problem *
469 D Timestamp Request
470 E Timestamp Reply
471 F Info Request
472 G Info Reply
473 H Address Mask Request
474 I Address Mask Reply
476 * These are rate limited by default (see default mask above)
478 icmp_ignore_bogus_error_responses - BOOLEAN
479 Some routers violate RFC1122 by sending bogus responses to broadcast
480 frames. Such violations are normally logged via a kernel warning.
481 If this is set to TRUE, the kernel will not give such warnings, which
482 will avoid log file clutter.
483 Default: FALSE
485 icmp_errors_use_inbound_ifaddr - BOOLEAN
487 If zero, icmp error messages are sent with the primary address of
488 the exiting interface.
490 If non-zero, the message will be sent with the primary address of
491 the interface that received the packet that caused the icmp error.
492 This is the behaviour network many administrators will expect from
493 a router. And it can make debugging complicated network layouts
494 much easier.
496 Note that if no primary address exists for the interface selected,
497 then the primary address of the first non-loopback interface that
498 has one will be used regardless of this setting.
500 Default: 0
502 igmp_max_memberships - INTEGER
503 Change the maximum number of multicast groups we can subscribe to.
504 Default: 20
506 conf/interface/* changes special settings per interface (where "interface" is
507 the name of your network interface)
508 conf/all/* is special, changes the settings for all interfaces
511 log_martians - BOOLEAN
512 Log packets with impossible addresses to kernel log.
513 log_martians for the interface will be enabled if at least one of
514 conf/{all,interface}/log_martians is set to TRUE,
515 it will be disabled otherwise
517 accept_redirects - BOOLEAN
518 Accept ICMP redirect messages.
519 accept_redirects for the interface will be enabled if:
520 - both conf/{all,interface}/accept_redirects are TRUE in the case forwarding
521 for the interface is enabled
522 or
523 - at least one of conf/{all,interface}/accept_redirects is TRUE in the case
524 forwarding for the interface is disabled
525 accept_redirects for the interface will be disabled otherwise
526 default TRUE (host)
527 FALSE (router)
529 forwarding - BOOLEAN
530 Enable IP forwarding on this interface.
532 mc_forwarding - BOOLEAN
533 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
534 and a multicast routing daemon is required.
535 conf/all/mc_forwarding must also be set to TRUE to enable multicast routing
536 for the interface
538 medium_id - INTEGER
539 Integer value used to differentiate the devices by the medium they
540 are attached to. Two devices can have different id values when
541 the broadcast packets are received only on one of them.
542 The default value 0 means that the device is the only interface
543 to its medium, value of -1 means that medium is not known.
545 Currently, it is used to change the proxy_arp behavior:
546 the proxy_arp feature is enabled for packets forwarded between
547 two devices attached to different media.
549 proxy_arp - BOOLEAN
550 Do proxy arp.
551 proxy_arp for the interface will be enabled if at least one of
552 conf/{all,interface}/proxy_arp is set to TRUE,
553 it will be disabled otherwise
555 shared_media - BOOLEAN
556 Send(router) or accept(host) RFC1620 shared media redirects.
557 Overrides ip_secure_redirects.
558 shared_media for the interface will be enabled if at least one of
559 conf/{all,interface}/shared_media is set to TRUE,
560 it will be disabled otherwise
561 default TRUE
563 secure_redirects - BOOLEAN
564 Accept ICMP redirect messages only for gateways,
565 listed in default gateway list.
566 secure_redirects for the interface will be enabled if at least one of
567 conf/{all,interface}/secure_redirects is set to TRUE,
568 it will be disabled otherwise
569 default TRUE
571 send_redirects - BOOLEAN
572 Send redirects, if router.
573 send_redirects for the interface will be enabled if at least one of
574 conf/{all,interface}/send_redirects is set to TRUE,
575 it will be disabled otherwise
576 Default: TRUE
578 bootp_relay - BOOLEAN
579 Accept packets with source address 0.b.c.d destined
580 not to this host as local ones. It is supposed, that
581 BOOTP relay daemon will catch and forward such packets.
582 conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
583 for the interface
584 default FALSE
585 Not Implemented Yet.
587 accept_source_route - BOOLEAN
588 Accept packets with SRR option.
589 conf/all/accept_source_route must also be set to TRUE to accept packets
590 with SRR option on the interface
591 default TRUE (router)
592 FALSE (host)
594 rp_filter - BOOLEAN
595 1 - do source validation by reversed path, as specified in RFC1812
596 Recommended option for single homed hosts and stub network
597 routers. Could cause troubles for complicated (not loop free)
598 networks running a slow unreliable protocol (sort of RIP),
599 or using static routes.
601 0 - No source validation.
603 conf/all/rp_filter must also be set to TRUE to do source validation
604 on the interface
606 Default value is 0. Note that some distributions enable it
607 in startup scripts.
609 arp_filter - BOOLEAN
610 1 - Allows you to have multiple network interfaces on the same
611 subnet, and have the ARPs for each interface be answered
612 based on whether or not the kernel would route a packet from
613 the ARP'd IP out that interface (therefore you must use source
614 based routing for this to work). In other words it allows control
615 of which cards (usually 1) will respond to an arp request.
617 0 - (default) The kernel can respond to arp requests with addresses
618 from other interfaces. This may seem wrong but it usually makes
619 sense, because it increases the chance of successful communication.
620 IP addresses are owned by the complete host on Linux, not by
621 particular interfaces. Only for more complex setups like load-
622 balancing, does this behaviour cause problems.
624 arp_filter for the interface will be enabled if at least one of
625 conf/{all,interface}/arp_filter is set to TRUE,
626 it will be disabled otherwise
628 arp_announce - INTEGER
629 Define different restriction levels for announcing the local
630 source IP address from IP packets in ARP requests sent on
631 interface:
632 0 - (default) Use any local address, configured on any interface
633 1 - Try to avoid local addresses that are not in the target's
634 subnet for this interface. This mode is useful when target
635 hosts reachable via this interface require the source IP
636 address in ARP requests to be part of their logical network
637 configured on the receiving interface. When we generate the
638 request we will check all our subnets that include the
639 target IP and will preserve the source address if it is from
640 such subnet. If there is no such subnet we select source
641 address according to the rules for level 2.
642 2 - Always use the best local address for this target.
643 In this mode we ignore the source address in the IP packet
644 and try to select local address that we prefer for talks with
645 the target host. Such local address is selected by looking
646 for primary IP addresses on all our subnets on the outgoing
647 interface that include the target IP address. If no suitable
648 local address is found we select the first local address
649 we have on the outgoing interface or on all other interfaces,
650 with the hope we will receive reply for our request and
651 even sometimes no matter the source IP address we announce.
653 The max value from conf/{all,interface}/arp_announce is used.
655 Increasing the restriction level gives more chance for
656 receiving answer from the resolved target while decreasing
657 the level announces more valid sender's information.
659 arp_ignore - INTEGER
660 Define different modes for sending replies in response to
661 received ARP requests that resolve local target IP addresses:
662 0 - (default): reply for any local target IP address, configured
663 on any interface
664 1 - reply only if the target IP address is local address
665 configured on the incoming interface
666 2 - reply only if the target IP address is local address
667 configured on the incoming interface and both with the
668 sender's IP address are part from same subnet on this interface
669 3 - do not reply for local addresses configured with scope host,
670 only resolutions for global and link addresses are replied
671 4-7 - reserved
672 8 - do not reply for all local addresses
674 The max value from conf/{all,interface}/arp_ignore is used
675 when ARP request is received on the {interface}
677 arp_accept - BOOLEAN
678 Define behavior when gratuitous arp replies are received:
679 0 - drop gratuitous arp frames
680 1 - accept gratuitous arp frames
682 app_solicit - INTEGER
683 The maximum number of probes to send to the user space ARP daemon
684 via netlink before dropping back to multicast probes (see
685 mcast_solicit). Defaults to 0.
687 disable_policy - BOOLEAN
688 Disable IPSEC policy (SPD) for this interface
690 disable_xfrm - BOOLEAN
691 Disable IPSEC encryption on this interface, whatever the policy
695 tag - INTEGER
696 Allows you to write a number, which can be used as required.
697 Default value is 0.
699 (1) Jiffie: internal timeunit for the kernel. On the i386 1/100s, on the
700 Alpha 1/1024s. See the HZ define in /usr/include/asm/param.h for the exact
701 value on your system.
703 Alexey Kuznetsov.
704 kuznet@ms2.inr.ac.ru
706 Updated by:
707 Andi Kleen
708 ak@muc.de
709 Nicolas Delon
710 delon.nicolas@wanadoo.fr
715 /proc/sys/net/ipv6/* Variables:
717 IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also
718 apply to IPv6 [XXX?].
720 bindv6only - BOOLEAN
721 Default value for IPV6_V6ONLY socket option,
722 which restricts use of the IPv6 socket to IPv6 communication
723 only.
724 TRUE: disable IPv4-mapped address feature
725 FALSE: enable IPv4-mapped address feature
727 Default: FALSE (as specified in RFC2553bis)
729 IPv6 Fragmentation:
731 ip6frag_high_thresh - INTEGER
732 Maximum memory used to reassemble IPv6 fragments. When
733 ip6frag_high_thresh bytes of memory is allocated for this purpose,
734 the fragment handler will toss packets until ip6frag_low_thresh
735 is reached.
737 ip6frag_low_thresh - INTEGER
738 See ip6frag_high_thresh
740 ip6frag_time - INTEGER
741 Time in seconds to keep an IPv6 fragment in memory.
743 ip6frag_secret_interval - INTEGER
744 Regeneration interval (in seconds) of the hash secret (or lifetime
745 for the hash secret) for IPv6 fragments.
746 Default: 600
748 conf/default/*:
749 Change the interface-specific default settings.
752 conf/all/*:
753 Change all the interface-specific settings.
755 [XXX: Other special features than forwarding?]
757 conf/all/forwarding - BOOLEAN
758 Enable global IPv6 forwarding between all interfaces.
760 IPv4 and IPv6 work differently here; e.g. netfilter must be used
761 to control which interfaces may forward packets and which not.
763 This also sets all interfaces' Host/Router setting
764 'forwarding' to the specified value. See below for details.
766 This referred to as global forwarding.
768 proxy_ndp - BOOLEAN
769 Do proxy ndp.
771 conf/interface/*:
772 Change special settings per interface.
774 The functional behaviour for certain settings is different
775 depending on whether local forwarding is enabled or not.
777 accept_ra - BOOLEAN
778 Accept Router Advertisements; autoconfigure using them.
780 Functional default: enabled if local forwarding is disabled.
781 disabled if local forwarding is enabled.
783 accept_ra_defrtr - BOOLEAN
784 Learn default router in Router Advertisement.
786 Functional default: enabled if accept_ra is enabled.
787 disabled if accept_ra is disabled.
789 accept_ra_pinfo - BOOLEAN
790 Learn Prefix Information in Router Advertisement.
792 Functional default: enabled if accept_ra is enabled.
793 disabled if accept_ra is disabled.
795 accept_ra_rt_info_max_plen - INTEGER
796 Maximum prefix length of Route Information in RA.
798 Route Information w/ prefix larger than or equal to this
799 variable shall be ignored.
801 Functional default: 0 if accept_ra_rtr_pref is enabled.
802 -1 if accept_ra_rtr_pref is disabled.
804 accept_ra_rtr_pref - BOOLEAN
805 Accept Router Preference in RA.
807 Functional default: enabled if accept_ra is enabled.
808 disabled if accept_ra is disabled.
810 accept_redirects - BOOLEAN
811 Accept Redirects.
813 Functional default: enabled if local forwarding is disabled.
814 disabled if local forwarding is enabled.
816 autoconf - BOOLEAN
817 Autoconfigure addresses using Prefix Information in Router
818 Advertisements.
820 Functional default: enabled if accept_ra_pinfo is enabled.
821 disabled if accept_ra_pinfo is disabled.
823 dad_transmits - INTEGER
824 The amount of Duplicate Address Detection probes to send.
825 Default: 1
827 forwarding - BOOLEAN
828 Configure interface-specific Host/Router behaviour.
830 Note: It is recommended to have the same setting on all
831 interfaces; mixed router/host scenarios are rather uncommon.
833 FALSE:
835 By default, Host behaviour is assumed. This means:
837 1. IsRouter flag is not set in Neighbour Advertisements.
838 2. Router Solicitations are being sent when necessary.
839 3. If accept_ra is TRUE (default), accept Router
840 Advertisements (and do autoconfiguration).
841 4. If accept_redirects is TRUE (default), accept Redirects.
843 TRUE:
845 If local forwarding is enabled, Router behaviour is assumed.
846 This means exactly the reverse from the above:
848 1. IsRouter flag is set in Neighbour Advertisements.
849 2. Router Solicitations are not sent.
850 3. Router Advertisements are ignored.
851 4. Redirects are ignored.
853 Default: FALSE if global forwarding is disabled (default),
854 otherwise TRUE.
856 hop_limit - INTEGER
857 Default Hop Limit to set.
858 Default: 64
860 mtu - INTEGER
861 Default Maximum Transfer Unit
862 Default: 1280 (IPv6 required minimum)
864 router_probe_interval - INTEGER
865 Minimum interval (in seconds) between Router Probing described
866 in RFC4191.
868 Default: 60
870 router_solicitation_delay - INTEGER
871 Number of seconds to wait after interface is brought up
872 before sending Router Solicitations.
873 Default: 1
875 router_solicitation_interval - INTEGER
876 Number of seconds to wait between Router Solicitations.
877 Default: 4
879 router_solicitations - INTEGER
880 Number of Router Solicitations to send until assuming no
881 routers are present.
882 Default: 3
884 use_tempaddr - INTEGER
885 Preference for Privacy Extensions (RFC3041).
886 <= 0 : disable Privacy Extensions
887 == 1 : enable Privacy Extensions, but prefer public
888 addresses over temporary addresses.
889 > 1 : enable Privacy Extensions and prefer temporary
890 addresses over public addresses.
891 Default: 0 (for most devices)
892 -1 (for point-to-point devices and loopback devices)
894 temp_valid_lft - INTEGER
895 valid lifetime (in seconds) for temporary addresses.
896 Default: 604800 (7 days)
898 temp_prefered_lft - INTEGER
899 Preferred lifetime (in seconds) for temporary addresses.
900 Default: 86400 (1 day)
902 max_desync_factor - INTEGER
903 Maximum value for DESYNC_FACTOR, which is a random value
904 that ensures that clients don't synchronize with each
905 other and generate new addresses at exactly the same time.
906 value is in seconds.
907 Default: 600
909 regen_max_retry - INTEGER
910 Number of attempts before give up attempting to generate
911 valid temporary addresses.
912 Default: 5
914 max_addresses - INTEGER
915 Number of maximum addresses per interface. 0 disables limitation.
916 It is recommended not set too large value (or 0) because it would
917 be too easy way to crash kernel to allow to create too much of
918 autoconfigured addresses.
919 Default: 16
921 icmp/*:
922 ratelimit - INTEGER
923 Limit the maximal rates for sending ICMPv6 packets.
924 0 to disable any limiting, otherwise the maximal rate in jiffies(1)
925 Default: 100
928 IPv6 Update by:
929 Pekka Savola <pekkas@netcore.fi>
930 YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
933 /proc/sys/net/bridge/* Variables:
935 bridge-nf-call-arptables - BOOLEAN
936 1 : pass bridged ARP traffic to arptables' FORWARD chain.
937 0 : disable this.
938 Default: 1
940 bridge-nf-call-iptables - BOOLEAN
941 1 : pass bridged IPv4 traffic to iptables' chains.
942 0 : disable this.
943 Default: 1
945 bridge-nf-call-ip6tables - BOOLEAN
946 1 : pass bridged IPv6 traffic to ip6tables' chains.
947 0 : disable this.
948 Default: 1
950 bridge-nf-filter-vlan-tagged - BOOLEAN
951 1 : pass bridged vlan-tagged ARP/IP traffic to arptables/iptables.
952 0 : disable this.
953 Default: 1
956 UNDOCUMENTED:
958 dev_weight FIXME
959 discovery_slots FIXME
960 discovery_timeout FIXME
961 fast_poll_increase FIXME
962 ip6_queue_maxlen FIXME
963 lap_keepalive_time FIXME
964 lo_cong FIXME
965 max_baud_rate FIXME
966 max_dgram_qlen FIXME
967 max_noreply_time FIXME
968 max_tx_data_size FIXME
969 max_tx_window FIXME
970 min_tx_turn_time FIXME
971 mod_cong FIXME
972 no_cong FIXME
973 no_cong_thresh FIXME
974 slot_timeout FIXME
975 warn_noreply_time FIXME
977 $Id: ip-sysctl.txt,v 1.20 2001/12/13 09:00:18 davem Exp $