1 /proc/sys/net/ipv4/* Variables:
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
13 ip_default_ttl - INTEGER
14 Default value of TTL field (Time To Live) for outgoing (but not
15 forwarded) IP packets. Should be between 1 and 255 inclusive.
16 Default: 64 (as recommended by RFC1700)
18 ip_no_pmtu_disc - INTEGER
19 Disable Path MTU Discovery. If enabled in mode 1 and a
20 fragmentation-required ICMP is received, the PMTU to this
21 destination will be set to min_pmtu (see below). You will need
22 to raise min_pmtu to the smallest interface MTU on your system
23 manually if you want to avoid locally generated fragments.
25 In mode 2 incoming Path MTU Discovery messages will be
26 discarded. Outgoing frames are handled the same as in mode 1,
27 implicitly setting IP_PMTUDISC_DONT on every created socket.
29 Mode 3 is a hardend pmtu discover mode. The kernel will only
30 accept fragmentation-needed errors if the underlying protocol
31 can verify them besides a plain socket lookup. Current
32 protocols for which pmtu events will be honored are TCP, SCTP
33 and DCCP as they verify e.g. the sequence number or the
34 association. This mode should not be enabled globally but is
35 only intended to secure e.g. name servers in namespaces where
36 TCP path mtu must still work but path MTU information of other
37 protocols should be discarded. If enabled globally this mode
38 could break other protocols.
44 default 552 - minimum discovered Path MTU
46 ip_forward_use_pmtu - BOOLEAN
47 By default we don't trust protocol path MTUs while forwarding
48 because they could be easily forged and can lead to unwanted
49 fragmentation by the router.
50 You only need to enable this if you have user-space software
51 which tries to discover path mtus by itself and depends on the
52 kernel honoring this information. This is normally not the
59 fwmark_reflect - BOOLEAN
60 Controls the fwmark of kernel-generated IPv4 reply packets that are not
61 associated with a socket for example, TCP RSTs or ICMP echo replies).
62 If unset, these packets have a fwmark of zero. If set, they have the
63 fwmark of the packet they are replying to.
66 route/max_size - INTEGER
67 Maximum number of routes allowed in the kernel. Increase
68 this when using large numbers of interfaces and/or routes.
69 From linux kernel 3.6 onwards, this is deprecated for ipv4
70 as route cache is no longer used.
72 neigh/default/gc_thresh1 - INTEGER
73 Minimum number of entries to keep. Garbage collector will not
74 purge entries if there are fewer than this number.
77 neigh/default/gc_thresh2 - INTEGER
78 Threshold when garbage collector becomes more aggressive about
79 purging entries. Entries older than 5 seconds will be cleared
80 when over this number.
83 neigh/default/gc_thresh3 - INTEGER
84 Maximum number of neighbor entries allowed. Increase this
85 when using large numbers of interfaces and when communicating
86 with large numbers of directly-connected peers.
89 neigh/default/unres_qlen_bytes - INTEGER
90 The maximum number of bytes which may be used by packets
91 queued for each unresolved address by other network layers.
93 Setting negative value is meaningless and will return error.
94 Default: 65536 Bytes(64KB)
96 neigh/default/unres_qlen - INTEGER
97 The maximum number of packets which may be queued for each
98 unresolved address by other network layers.
99 (deprecated in linux 3.3) : use unres_qlen_bytes instead.
100 Prior to linux 3.3, the default value is 3 which may cause
101 unexpected packet loss. The current default value is calculated
102 according to default value of unres_qlen_bytes and true size of
106 mtu_expires - INTEGER
107 Time, in seconds, that cached PMTU information is kept.
109 min_adv_mss - INTEGER
110 The advertised MSS depends on the first hop route MTU, but will
111 never be lower than this setting.
115 ipfrag_high_thresh - INTEGER
116 Maximum memory used to reassemble IP fragments. When
117 ipfrag_high_thresh bytes of memory is allocated for this purpose,
118 the fragment handler will toss packets until ipfrag_low_thresh
119 is reached. This also serves as a maximum limit to namespaces
120 different from the initial one.
122 ipfrag_low_thresh - INTEGER
123 Maximum memory used to reassemble IP fragments before the kernel
124 begins to remove incomplete fragment queues to free up resources.
125 The kernel still accepts new fragments for defragmentation.
127 ipfrag_time - INTEGER
128 Time in seconds to keep an IP fragment in memory.
130 ipfrag_max_dist - INTEGER
131 ipfrag_max_dist is a non-negative integer value which defines the
132 maximum "disorder" which is allowed among fragments which share a
133 common IP source address. Note that reordering of packets is
134 not unusual, but if a large number of fragments arrive from a source
135 IP address while a particular fragment queue remains incomplete, it
136 probably indicates that one or more fragments belonging to that queue
137 have been lost. When ipfrag_max_dist is positive, an additional check
138 is done on fragments before they are added to a reassembly queue - if
139 ipfrag_max_dist (or more) fragments have arrived from a particular IP
140 address between additions to any IP fragment queue using that source
141 address, it's presumed that one or more fragments in the queue are
142 lost. The existing fragment queue will be dropped, and a new one
143 started. An ipfrag_max_dist value of zero disables this check.
145 Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
146 result in unnecessarily dropping fragment queues when normal
147 reordering of packets occurs, which could lead to poor application
148 performance. Using a very large value, e.g. 50000, increases the
149 likelihood of incorrectly reassembling IP fragments that originate
150 from different IP datagrams, which could result in data corruption.
155 inet_peer_threshold - INTEGER
156 The approximate size of the storage. Starting from this threshold
157 entries will be thrown aggressively. This threshold also determines
158 entries' time-to-live and time intervals between garbage collection
159 passes. More entries, less time-to-live, less GC interval.
161 inet_peer_minttl - INTEGER
162 Minimum time-to-live of entries. Should be enough to cover fragment
163 time-to-live on the reassembling side. This minimum time-to-live is
164 guaranteed if the pool size is less than inet_peer_threshold.
167 inet_peer_maxttl - INTEGER
168 Maximum time-to-live of entries. Unused entries will expire after
169 this period of time if there is no memory pressure on the pool (i.e.
170 when the number of entries in the pool is very small).
176 Limit of socket listen() backlog, known in userspace as SOMAXCONN.
177 Defaults to 128. See also tcp_max_syn_backlog for additional tuning
180 tcp_abort_on_overflow - BOOLEAN
181 If listening service is too slow to accept new connections,
182 reset them. Default state is FALSE. It means that if overflow
183 occurred due to a burst, connection will recover. Enable this
184 option _only_ if you are really sure that listening daemon
185 cannot be tuned to accept connections faster. Enabling this
186 option can harm clients of your server.
188 tcp_adv_win_scale - INTEGER
189 Count buffering overhead as bytes/2^tcp_adv_win_scale
190 (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
192 Possible values are [-31, 31], inclusive.
195 tcp_allowed_congestion_control - STRING
196 Show/set the congestion control choices available to non-privileged
197 processes. The list is a subset of those listed in
198 tcp_available_congestion_control.
199 Default is "reno" and the default setting (tcp_congestion_control).
201 tcp_app_win - INTEGER
202 Reserve max(window/2^tcp_app_win, mss) of window for application
203 buffer. Value 0 is special, it means that nothing is reserved.
206 tcp_autocorking - BOOLEAN
207 Enable TCP auto corking :
208 When applications do consecutive small write()/sendmsg() system calls,
209 we try to coalesce these small writes as much as possible, to lower
210 total amount of sent packets. This is done if at least one prior
211 packet for the flow is waiting in Qdisc queues or device transmit
212 queue. Applications can still use TCP_CORK for optimal behavior
213 when they know how/when to uncork their sockets.
216 tcp_available_congestion_control - STRING
217 Shows the available congestion control choices that are registered.
218 More congestion control algorithms may be available as modules,
221 tcp_base_mss - INTEGER
222 The initial value of search_low to be used by the packetization layer
223 Path MTU discovery (MTU probing). If MTU probing is enabled,
224 this is the initial MSS used by the connection.
226 tcp_congestion_control - STRING
227 Set the congestion control algorithm to be used for new
228 connections. The algorithm "reno" is always available, but
229 additional choices may be available based on kernel configuration.
230 Default is set as part of kernel configuration.
231 For passive connections, the listener congestion control choice
233 [see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ]
236 Allows TCP to send "duplicate" SACKs.
238 tcp_early_retrans - INTEGER
239 Enable Early Retransmit (ER), per RFC 5827. ER lowers the threshold
240 for triggering fast retransmit when the amount of outstanding data is
241 small and when no previously unsent data can be transmitted (such
242 that limited transmit could be used). Also controls the use of
243 Tail loss probe (TLP) that converts RTOs occurring due to tail
244 losses into fast recovery (draft-dukkipati-tcpm-tcp-loss-probe-01).
248 2 enables ER but delays fast recovery and fast retransmit
249 by a fourth of RTT. This mitigates connection falsely
250 recovers when network has a small degree of reordering
251 (less than 3 packets).
252 3 enables delayed ER and TLP.
257 Control use of Explicit Congestion Notification (ECN) by TCP.
258 ECN is used only when both ends of the TCP connection indicate
259 support for it. This feature is useful in avoiding losses due
260 to congestion by allowing supporting routers to signal
261 congestion before having to drop packets.
263 0 Disable ECN. Neither initiate nor accept ECN.
264 1 Enable ECN when requested by incoming connections and
265 also request ECN on outgoing connection attempts.
266 2 Enable ECN when requested by incoming connections
267 but do not request ECN on outgoing connections.
270 tcp_ecn_fallback - BOOLEAN
271 If the kernel detects that ECN connection misbehaves, enable fall
272 back to non-ECN. Currently, this knob implements the fallback
273 from RFC3168, section 6.1.1.1., but we reserve that in future,
274 additional detection mechanisms could be implemented under this
275 knob. The value is not used, if tcp_ecn or per route (or congestion
276 control) ECN settings are disabled.
277 Default: 1 (fallback enabled)
280 Enable FACK congestion avoidance and fast retransmission.
281 The value is not used, if tcp_sack is not enabled.
283 tcp_fin_timeout - INTEGER
284 The length of time an orphaned (no longer referenced by any
285 application) connection will remain in the FIN_WAIT_2 state
286 before it is aborted at the local end. While a perfectly
287 valid "receive only" state for an un-orphaned connection, an
288 orphaned connection in FIN_WAIT_2 state could otherwise wait
289 forever for the remote to close its end of the connection.
294 Enables Forward RTO-Recovery (F-RTO) defined in RFC5682.
295 F-RTO is an enhanced recovery algorithm for TCP retransmission
296 timeouts. It is particularly beneficial in networks where the
297 RTT fluctuates (e.g., wireless). F-RTO is sender-side only
298 modification. It does not require any support from the peer.
300 By default it's enabled with a non-zero value. 0 disables F-RTO.
302 tcp_invalid_ratelimit - INTEGER
303 Limit the maximal rate for sending duplicate acknowledgments
304 in response to incoming TCP packets that are for an existing
305 connection but that are invalid due to any of these reasons:
307 (a) out-of-window sequence number,
308 (b) out-of-window acknowledgment number, or
309 (c) PAWS (Protection Against Wrapped Sequence numbers) check failure
311 This can help mitigate simple "ack loop" DoS attacks, wherein
312 a buggy or malicious middlebox or man-in-the-middle can
313 rewrite TCP header fields in manner that causes each endpoint
314 to think that the other is sending invalid TCP segments, thus
315 causing each side to send an unterminating stream of duplicate
316 acknowledgments for invalid segments.
318 Using 0 disables rate-limiting of dupacks in response to
319 invalid segments; otherwise this value specifies the minimal
320 space between sending such dupacks, in milliseconds.
322 Default: 500 (milliseconds).
324 tcp_keepalive_time - INTEGER
325 How often TCP sends out keepalive messages when keepalive is enabled.
328 tcp_keepalive_probes - INTEGER
329 How many keepalive probes TCP sends out, until it decides that the
330 connection is broken. Default value: 9.
332 tcp_keepalive_intvl - INTEGER
333 How frequently the probes are send out. Multiplied by
334 tcp_keepalive_probes it is time to kill not responding connection,
335 after probes started. Default value: 75sec i.e. connection
336 will be aborted after ~11 minutes of retries.
338 tcp_low_latency - BOOLEAN
339 If set, the TCP stack makes decisions that prefer lower
340 latency as opposed to higher throughput. By default, this
341 option is not set meaning that higher throughput is preferred.
342 An example of an application where this default should be
343 changed would be a Beowulf compute cluster.
346 tcp_max_orphans - INTEGER
347 Maximal number of TCP sockets not attached to any user file handle,
348 held by system. If this number is exceeded orphaned connections are
349 reset immediately and warning is printed. This limit exists
350 only to prevent simple DoS attacks, you _must_ not rely on this
351 or lower the limit artificially, but rather increase it
352 (probably, after increasing installed memory),
353 if network conditions require more than default value,
354 and tune network services to linger and kill such states
355 more aggressively. Let me to remind again: each orphan eats
356 up to ~64K of unswappable memory.
358 tcp_max_syn_backlog - INTEGER
359 Maximal number of remembered connection requests, which have not
360 received an acknowledgment from connecting client.
361 The minimal value is 128 for low memory machines, and it will
362 increase in proportion to the memory of machine.
363 If server suffers from overload, try increasing this number.
365 tcp_max_tw_buckets - INTEGER
366 Maximal number of timewait sockets held by system simultaneously.
367 If this number is exceeded time-wait socket is immediately destroyed
368 and warning is printed. This limit exists only to prevent
369 simple DoS attacks, you _must_ not lower the limit artificially,
370 but rather increase it (probably, after increasing installed memory),
371 if network conditions require more than default value.
373 tcp_mem - vector of 3 INTEGERs: min, pressure, max
374 min: below this number of pages TCP is not bothered about its
377 pressure: when amount of memory allocated by TCP exceeds this number
378 of pages, TCP moderates its memory consumption and enters memory
379 pressure mode, which is exited when memory consumption falls
382 max: number of pages allowed for queueing by all TCP sockets.
384 Defaults are calculated at boot time from amount of available
387 tcp_moderate_rcvbuf - BOOLEAN
388 If set, TCP performs receive buffer auto-tuning, attempting to
389 automatically size the buffer (no greater than tcp_rmem[2]) to
390 match the size required by the path for full throughput. Enabled by
393 tcp_mtu_probing - INTEGER
394 Controls TCP Packetization-Layer Path MTU Discovery. Takes three
397 1 - Disabled by default, enabled when an ICMP black hole detected
398 2 - Always enabled, use initial MSS of tcp_base_mss.
400 tcp_probe_interval - INTEGER
401 Controls how often to start TCP Packetization-Layer Path MTU
402 Discovery reprobe. The default is reprobing every 10 minutes as
405 tcp_probe_threshold - INTEGER
406 Controls when TCP Packetization-Layer Path MTU Discovery probing
407 will stop in respect to the width of search range in bytes. Default
410 tcp_no_metrics_save - BOOLEAN
411 By default, TCP saves various connection metrics in the route cache
412 when the connection closes, so that connections established in the
413 near future can use these to set initial conditions. Usually, this
414 increases overall performance, but may sometimes cause performance
415 degradation. If set, TCP will not cache metrics on closing
418 tcp_orphan_retries - INTEGER
419 This value influences the timeout of a locally closed TCP connection,
420 when RTO retransmissions remain unacknowledged.
421 See tcp_retries2 for more details.
423 The default value is 8.
424 If your machine is a loaded WEB server,
425 you should think about lowering this value, such sockets
426 may consume significant resources. Cf. tcp_max_orphans.
428 tcp_reordering - INTEGER
429 Initial reordering level of packets in a TCP stream.
430 TCP stack can then dynamically adjust flow reordering level
431 between this initial value and tcp_max_reordering
434 tcp_max_reordering - INTEGER
435 Maximal reordering level of packets in a TCP stream.
436 300 is a fairly conservative value, but you might increase it
437 if paths are using per packet load balancing (like bonding rr mode)
440 tcp_retrans_collapse - BOOLEAN
441 Bug-to-bug compatibility with some broken printers.
442 On retransmit try to send bigger packets to work around bugs in
445 tcp_retries1 - INTEGER
446 This value influences the time, after which TCP decides, that
447 something is wrong due to unacknowledged RTO retransmissions,
448 and reports this suspicion to the network layer.
449 See tcp_retries2 for more details.
451 RFC 1122 recommends at least 3 retransmissions, which is the
454 tcp_retries2 - INTEGER
455 This value influences the timeout of an alive TCP connection,
456 when RTO retransmissions remain unacknowledged.
457 Given a value of N, a hypothetical TCP connection following
458 exponential backoff with an initial RTO of TCP_RTO_MIN would
459 retransmit N times before killing the connection at the (N+1)th RTO.
461 The default value of 15 yields a hypothetical timeout of 924.6
462 seconds and is a lower bound for the effective timeout.
463 TCP will effectively time out at the first RTO which exceeds the
464 hypothetical timeout.
466 RFC 1122 recommends at least 100 seconds for the timeout,
467 which corresponds to a value of at least 8.
469 tcp_rfc1337 - BOOLEAN
470 If set, the TCP stack behaves conforming to RFC1337. If unset,
471 we are not conforming to RFC, but prevent TCP TIME_WAIT
475 tcp_rmem - vector of 3 INTEGERs: min, default, max
476 min: Minimal size of receive buffer used by TCP sockets.
477 It is guaranteed to each TCP socket, even under moderate memory
481 default: initial size of receive buffer used by TCP sockets.
482 This value overrides net.core.rmem_default used by other protocols.
483 Default: 87380 bytes. This value results in window of 65535 with
484 default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
485 less for default tcp_app_win. See below about these variables.
487 max: maximal size of receive buffer allowed for automatically
488 selected receiver buffers for TCP socket. This value does not override
489 net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables
490 automatic tuning of that socket's receive buffer size, in which
491 case this value is ignored.
492 Default: between 87380B and 6MB, depending on RAM size.
495 Enable select acknowledgments (SACKS).
497 tcp_slow_start_after_idle - BOOLEAN
498 If set, provide RFC2861 behavior and time out the congestion
499 window after an idle period. An idle period is defined at
500 the current RTO. If unset, the congestion window will not
501 be timed out after an idle period.
505 Use the Host requirements interpretation of the TCP urgent pointer field.
506 Most hosts use the older BSD interpretation, so if you turn this on
507 Linux might not communicate correctly with them.
510 tcp_synack_retries - INTEGER
511 Number of times SYNACKs for a passive TCP connection attempt will
512 be retransmitted. Should not be higher than 255. Default value
513 is 5, which corresponds to 31seconds till the last retransmission
514 with the current initial RTO of 1second. With this the final timeout
515 for a passive TCP connection will happen after 63seconds.
517 tcp_syncookies - BOOLEAN
518 Only valid when the kernel was compiled with CONFIG_SYN_COOKIES
519 Send out syncookies when the syn backlog queue of a socket
520 overflows. This is to prevent against the common 'SYN flood attack'
523 Note, that syncookies is fallback facility.
524 It MUST NOT be used to help highly loaded servers to stand
525 against legal connection rate. If you see SYN flood warnings
526 in your logs, but investigation shows that they occur
527 because of overload with legal connections, you should tune
528 another parameters until this warning disappear.
529 See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
531 syncookies seriously violate TCP protocol, do not allow
532 to use TCP extensions, can result in serious degradation
533 of some services (f.e. SMTP relaying), visible not by you,
534 but your clients and relays, contacting you. While you see
535 SYN flood warnings in logs not being really flooded, your server
536 is seriously misconfigured.
538 If you want to test which effects syncookies have to your
539 network connections you can set this knob to 2 to enable
540 unconditionally generation of syncookies.
542 tcp_fastopen - INTEGER
543 Enable TCP Fast Open feature (draft-ietf-tcpm-fastopen) to send data
544 in the opening SYN packet. To use this feature, the client application
545 must use sendmsg() or sendto() with MSG_FASTOPEN flag rather than
546 connect() to perform a TCP handshake automatically.
548 The values (bitmap) are
549 1: Enables sending data in the opening SYN on the client w/ MSG_FASTOPEN.
550 2: Enables TCP Fast Open on the server side, i.e., allowing data in
551 a SYN packet to be accepted and passed to the application before
552 3-way hand shake finishes.
553 4: Send data in the opening SYN regardless of cookie availability and
554 without a cookie option.
555 0x100: Accept SYN data w/o validating the cookie.
556 0x200: Accept data-in-SYN w/o any cookie option present.
557 0x400/0x800: Enable Fast Open on all listeners regardless of the
558 TCP_FASTOPEN socket option. The two different flags designate two
559 different ways of setting max_qlen without the TCP_FASTOPEN socket
564 Note that the client & server side Fast Open flags (1 and 2
565 respectively) must be also enabled before the rest of flags can take
568 See include/net/tcp.h and the code for more details.
570 tcp_syn_retries - INTEGER
571 Number of times initial SYNs for an active TCP connection attempt
572 will be retransmitted. Should not be higher than 255. Default value
573 is 6, which corresponds to 63seconds till the last retransmission
574 with the current initial RTO of 1second. With this the final timeout
575 for an active TCP connection attempt will happen after 127seconds.
577 tcp_timestamps - BOOLEAN
578 Enable timestamps as defined in RFC1323.
580 tcp_min_tso_segs - INTEGER
581 Minimal number of segments per TSO frame.
582 Since linux-3.12, TCP does an automatic sizing of TSO frames,
583 depending on flow rate, instead of filling 64Kbytes packets.
584 For specific usages, it's possible to force TCP to build big
585 TSO frames. Note that TCP stack might split too big TSO packets
586 if available window is too small.
589 tcp_tso_win_divisor - INTEGER
590 This allows control over what percentage of the congestion window
591 can be consumed by a single TSO frame.
592 The setting of this parameter is a choice between burstiness and
593 building larger TSO frames.
596 tcp_tw_recycle - BOOLEAN
597 Enable fast recycling TIME-WAIT sockets. Default value is 0.
598 It should not be changed without advice/request of technical
601 tcp_tw_reuse - BOOLEAN
602 Allow to reuse TIME-WAIT sockets for new connections when it is
603 safe from protocol viewpoint. Default value is 0.
604 It should not be changed without advice/request of technical
607 tcp_window_scaling - BOOLEAN
608 Enable window scaling as defined in RFC1323.
610 tcp_wmem - vector of 3 INTEGERs: min, default, max
611 min: Amount of memory reserved for send buffers for TCP sockets.
612 Each TCP socket has rights to use it due to fact of its birth.
615 default: initial size of send buffer used by TCP sockets. This
616 value overrides net.core.wmem_default used by other protocols.
617 It is usually lower than net.core.wmem_default.
620 max: Maximal amount of memory allowed for automatically tuned
621 send buffers for TCP sockets. This value does not override
622 net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables
623 automatic tuning of that socket's send buffer size, in which case
624 this value is ignored.
625 Default: between 64K and 4MB, depending on RAM size.
627 tcp_notsent_lowat - UNSIGNED INTEGER
628 A TCP socket can control the amount of unsent bytes in its write queue,
629 thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll()
630 reports POLLOUT events if the amount of unsent bytes is below a per
631 socket value, and if the write queue is not full. sendmsg() will
632 also not add new buffers if the limit is hit.
634 This global variable controls the amount of unsent data for
635 sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change
636 to the global variable has immediate effect.
638 Default: UINT_MAX (0xFFFFFFFF)
640 tcp_workaround_signed_windows - BOOLEAN
641 If set, assume no receipt of a window scaling option means the
642 remote TCP is broken and treats the window as a signed quantity.
643 If unset, assume the remote TCP is not broken even if we do
644 not receive a window scaling option from them.
647 tcp_thin_linear_timeouts - BOOLEAN
648 Enable dynamic triggering of linear timeouts for thin streams.
649 If set, a check is performed upon retransmission by timeout to
650 determine if the stream is thin (less than 4 packets in flight).
651 As long as the stream is found to be thin, up to 6 linear
652 timeouts may be performed before exponential backoff mode is
653 initiated. This improves retransmission latency for
654 non-aggressive thin streams, often found to be time-dependent.
655 For more information on thin streams, see
656 Documentation/networking/tcp-thin.txt
659 tcp_thin_dupack - BOOLEAN
660 Enable dynamic triggering of retransmissions after one dupACK
661 for thin streams. If set, a check is performed upon reception
662 of a dupACK to determine if the stream is thin (less than 4
663 packets in flight). As long as the stream is found to be thin,
664 data is retransmitted on the first received dupACK. This
665 improves retransmission latency for non-aggressive thin
666 streams, often found to be time-dependent.
667 For more information on thin streams, see
668 Documentation/networking/tcp-thin.txt
671 tcp_limit_output_bytes - INTEGER
672 Controls TCP Small Queue limit per tcp socket.
673 TCP bulk sender tends to increase packets in flight until it
674 gets losses notifications. With SNDBUF autotuning, this can
675 result in a large amount of packets queued in qdisc/device
676 on the local machine, hurting latency of other flows, for
677 typical pfifo_fast qdiscs.
678 tcp_limit_output_bytes limits the number of bytes on qdisc
679 or device to reduce artificial RTT/cwnd and reduce bufferbloat.
682 tcp_challenge_ack_limit - INTEGER
683 Limits number of Challenge ACK sent per second, as recommended
684 in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
689 udp_mem - vector of 3 INTEGERs: min, pressure, max
690 Number of pages allowed for queueing by all UDP sockets.
692 min: Below this number of pages UDP is not bothered about its
693 memory appetite. When amount of memory allocated by UDP exceeds
694 this number, UDP starts to moderate memory usage.
696 pressure: This value was introduced to follow format of tcp_mem.
698 max: Number of pages allowed for queueing by all UDP sockets.
700 Default is calculated at boot time from amount of available memory.
702 udp_rmem_min - INTEGER
703 Minimal size of receive buffer used by UDP sockets in moderation.
704 Each UDP socket is able to use the size for receiving data, even if
705 total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
708 udp_wmem_min - INTEGER
709 Minimal size of send buffer used by UDP sockets in moderation.
710 Each UDP socket is able to use the size for sending data, even if
711 total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
716 cipso_cache_enable - BOOLEAN
717 If set, enable additions to and lookups from the CIPSO label mapping
718 cache. If unset, additions are ignored and lookups always result in a
719 miss. However, regardless of the setting the cache is still
720 invalidated when required when means you can safely toggle this on and
721 off and the cache will always be "safe".
724 cipso_cache_bucket_size - INTEGER
725 The CIPSO label cache consists of a fixed size hash table with each
726 hash bucket containing a number of cache entries. This variable limits
727 the number of entries in each hash bucket; the larger the value the
728 more CIPSO label mappings that can be cached. When the number of
729 entries in a given hash bucket reaches this limit adding new entries
730 causes the oldest entry in the bucket to be removed to make room.
733 cipso_rbm_optfmt - BOOLEAN
734 Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
735 the CIPSO draft specification (see Documentation/netlabel for details).
736 This means that when set the CIPSO tag will be padded with empty
737 categories in order to make the packet data 32-bit aligned.
740 cipso_rbm_structvalid - BOOLEAN
741 If set, do a very strict check of the CIPSO option when
742 ip_options_compile() is called. If unset, relax the checks done during
743 ip_options_compile(). Either way is "safe" as errors are caught else
744 where in the CIPSO processing code but setting this to 0 (False) should
745 result in less work (i.e. it should be faster) but could cause problems
746 with other implementations that require strict checking.
751 ip_local_port_range - 2 INTEGERS
752 Defines the local port range that is used by TCP and UDP to
753 choose the local port. The first number is the first, the
754 second the last local port number. The default values are
755 32768 and 61000 respectively.
757 ip_local_reserved_ports - list of comma separated ranges
758 Specify the ports which are reserved for known third-party
759 applications. These ports will not be used by automatic port
760 assignments (e.g. when calling connect() or bind() with port
761 number 0). Explicit port allocation behavior is unchanged.
763 The format used for both input and output is a comma separated
764 list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and
765 10). Writing to the file will clear all previously reserved
766 ports and update the current list with the one given in the
769 Note that ip_local_port_range and ip_local_reserved_ports
770 settings are independent and both are considered by the kernel
771 when determining which ports are available for automatic port
774 You can reserve ports which are not in the current
775 ip_local_port_range, e.g.:
777 $ cat /proc/sys/net/ipv4/ip_local_port_range
779 $ cat /proc/sys/net/ipv4/ip_local_reserved_ports
782 although this is redundant. However such a setting is useful
783 if later the port range is changed to a value that will
784 include the reserved ports.
788 ip_nonlocal_bind - BOOLEAN
789 If set, allows processes to bind() to non-local IP addresses,
790 which can be quite useful - but may break some applications.
794 If set non-zero, enables support for dynamic addresses.
795 If set to a non-zero value larger than 1, a kernel log
796 message will be printed when dynamic address rewriting
800 ip_early_demux - BOOLEAN
801 Optimize input packet processing down to one demux for
802 certain kinds of local sockets. Currently we only do this
803 for established TCP sockets.
805 It may add an additional cost for pure routing workloads that
806 reduces overall throughput, in such case you should disable it.
809 icmp_echo_ignore_all - BOOLEAN
810 If set non-zero, then the kernel will ignore all ICMP ECHO
814 icmp_echo_ignore_broadcasts - BOOLEAN
815 If set non-zero, then the kernel will ignore all ICMP ECHO and
816 TIMESTAMP requests sent to it via broadcast/multicast.
819 icmp_ratelimit - INTEGER
820 Limit the maximal rates for sending ICMP packets whose type matches
821 icmp_ratemask (see below) to specific targets.
822 0 to disable any limiting,
823 otherwise the minimal space between responses in milliseconds.
824 Note that another sysctl, icmp_msgs_per_sec limits the number
825 of ICMP packets sent on all targets.
828 icmp_msgs_per_sec - INTEGER
829 Limit maximal number of ICMP packets sent per second from this host.
830 Only messages whose type matches icmp_ratemask (see below) are
831 controlled by this limit.
834 icmp_msgs_burst - INTEGER
835 icmp_msgs_per_sec controls number of ICMP packets sent per second,
836 while icmp_msgs_burst controls the burst size of these packets.
839 icmp_ratemask - INTEGER
840 Mask made of ICMP types for which rates are being limited.
841 Significant bits: IHGFEDCBA9876543210
842 Default mask: 0000001100000011000 (6168)
844 Bit definitions (see include/linux/icmp.h):
846 3 Destination Unreachable *
851 C Parameter Problem *
856 H Address Mask Request
859 * These are rate limited by default (see default mask above)
861 icmp_ignore_bogus_error_responses - BOOLEAN
862 Some routers violate RFC1122 by sending bogus responses to broadcast
863 frames. Such violations are normally logged via a kernel warning.
864 If this is set to TRUE, the kernel will not give such warnings, which
865 will avoid log file clutter.
868 icmp_errors_use_inbound_ifaddr - BOOLEAN
870 If zero, icmp error messages are sent with the primary address of
871 the exiting interface.
873 If non-zero, the message will be sent with the primary address of
874 the interface that received the packet that caused the icmp error.
875 This is the behaviour network many administrators will expect from
876 a router. And it can make debugging complicated network layouts
879 Note that if no primary address exists for the interface selected,
880 then the primary address of the first non-loopback interface that
881 has one will be used regardless of this setting.
885 igmp_max_memberships - INTEGER
886 Change the maximum number of multicast groups we can subscribe to.
889 Theoretical maximum value is bounded by having to send a membership
890 report in a single datagram (i.e. the report can't span multiple
891 datagrams, or risk confusing the switch and leaving groups you don't
894 The number of supported groups 'M' is bounded by the number of group
895 report entries you can fit into a single datagram of 65535 bytes.
897 M = 65536-sizeof (ip header)/(sizeof(Group record))
899 Group records are variable length, with a minimum of 12 bytes.
900 So net.ipv4.igmp_max_memberships should not be set higher than:
902 (65536-24) / 12 = 5459
904 The value 5459 assumes no IP header options, so in practice
905 this number may be lower.
907 conf/interface/* changes special settings per interface (where
908 "interface" is the name of your network interface)
910 conf/all/* is special, changes the settings for all interfaces
913 Controls the IGMP query robustness variable (see RFC2236 8.1).
914 Default: 2 (as specified by RFC2236 8.1)
915 Minimum: 1 (as specified by RFC6636 4.5)
917 log_martians - BOOLEAN
918 Log packets with impossible addresses to kernel log.
919 log_martians for the interface will be enabled if at least one of
920 conf/{all,interface}/log_martians is set to TRUE,
921 it will be disabled otherwise
923 accept_redirects - BOOLEAN
924 Accept ICMP redirect messages.
925 accept_redirects for the interface will be enabled if:
926 - both conf/{all,interface}/accept_redirects are TRUE in the case
927 forwarding for the interface is enabled
929 - at least one of conf/{all,interface}/accept_redirects is TRUE in the
930 case forwarding for the interface is disabled
931 accept_redirects for the interface will be disabled otherwise
936 Enable IP forwarding on this interface.
938 mc_forwarding - BOOLEAN
939 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
940 and a multicast routing daemon is required.
941 conf/all/mc_forwarding must also be set to TRUE to enable multicast
942 routing for the interface
945 Integer value used to differentiate the devices by the medium they
946 are attached to. Two devices can have different id values when
947 the broadcast packets are received only on one of them.
948 The default value 0 means that the device is the only interface
949 to its medium, value of -1 means that medium is not known.
951 Currently, it is used to change the proxy_arp behavior:
952 the proxy_arp feature is enabled for packets forwarded between
953 two devices attached to different media.
957 proxy_arp for the interface will be enabled if at least one of
958 conf/{all,interface}/proxy_arp is set to TRUE,
959 it will be disabled otherwise
961 proxy_arp_pvlan - BOOLEAN
962 Private VLAN proxy arp.
963 Basically allow proxy arp replies back to the same interface
964 (from which the ARP request/solicitation was received).
966 This is done to support (ethernet) switch features, like RFC
967 3069, where the individual ports are NOT allowed to
968 communicate with each other, but they are allowed to talk to
969 the upstream router. As described in RFC 3069, it is possible
970 to allow these hosts to communicate through the upstream
971 router by proxy_arp'ing. Don't need to be used together with
974 This technology is known by different names:
975 In RFC 3069 it is called VLAN Aggregation.
976 Cisco and Allied Telesyn call it Private VLAN.
977 Hewlett-Packard call it Source-Port filtering or port-isolation.
978 Ericsson call it MAC-Forced Forwarding (RFC Draft).
980 shared_media - BOOLEAN
981 Send(router) or accept(host) RFC1620 shared media redirects.
982 Overrides ip_secure_redirects.
983 shared_media for the interface will be enabled if at least one of
984 conf/{all,interface}/shared_media is set to TRUE,
985 it will be disabled otherwise
988 secure_redirects - BOOLEAN
989 Accept ICMP redirect messages only for gateways,
990 listed in default gateway list.
991 secure_redirects for the interface will be enabled if at least one of
992 conf/{all,interface}/secure_redirects is set to TRUE,
993 it will be disabled otherwise
996 send_redirects - BOOLEAN
997 Send redirects, if router.
998 send_redirects for the interface will be enabled if at least one of
999 conf/{all,interface}/send_redirects is set to TRUE,
1000 it will be disabled otherwise
1003 bootp_relay - BOOLEAN
1004 Accept packets with source address 0.b.c.d destined
1005 not to this host as local ones. It is supposed, that
1006 BOOTP relay daemon will catch and forward such packets.
1007 conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
1010 Not Implemented Yet.
1012 accept_source_route - BOOLEAN
1013 Accept packets with SRR option.
1014 conf/all/accept_source_route must also be set to TRUE to accept packets
1015 with SRR option on the interface
1016 default TRUE (router)
1019 accept_local - BOOLEAN
1020 Accept packets with local source addresses. In combination with
1021 suitable routing, this can be used to direct packets between two
1022 local interfaces over the wire and have them accepted properly.
1025 route_localnet - BOOLEAN
1026 Do not consider loopback addresses as martian source or destination
1027 while routing. This enables the use of 127/8 for local routing purposes.
1031 0 - No source validation.
1032 1 - Strict mode as defined in RFC3704 Strict Reverse Path
1033 Each incoming packet is tested against the FIB and if the interface
1034 is not the best reverse path the packet check will fail.
1035 By default failed packets are discarded.
1036 2 - Loose mode as defined in RFC3704 Loose Reverse Path
1037 Each incoming packet's source address is also tested against the FIB
1038 and if the source address is not reachable via any interface
1039 the packet check will fail.
1041 Current recommended practice in RFC3704 is to enable strict mode
1042 to prevent IP spoofing from DDos attacks. If using asymmetric routing
1043 or other complicated routing, then loose mode is recommended.
1045 The max value from conf/{all,interface}/rp_filter is used
1046 when doing source validation on the {interface}.
1048 Default value is 0. Note that some distributions enable it
1051 arp_filter - BOOLEAN
1052 1 - Allows you to have multiple network interfaces on the same
1053 subnet, and have the ARPs for each interface be answered
1054 based on whether or not the kernel would route a packet from
1055 the ARP'd IP out that interface (therefore you must use source
1056 based routing for this to work). In other words it allows control
1057 of which cards (usually 1) will respond to an arp request.
1059 0 - (default) The kernel can respond to arp requests with addresses
1060 from other interfaces. This may seem wrong but it usually makes
1061 sense, because it increases the chance of successful communication.
1062 IP addresses are owned by the complete host on Linux, not by
1063 particular interfaces. Only for more complex setups like load-
1064 balancing, does this behaviour cause problems.
1066 arp_filter for the interface will be enabled if at least one of
1067 conf/{all,interface}/arp_filter is set to TRUE,
1068 it will be disabled otherwise
1070 arp_announce - INTEGER
1071 Define different restriction levels for announcing the local
1072 source IP address from IP packets in ARP requests sent on
1074 0 - (default) Use any local address, configured on any interface
1075 1 - Try to avoid local addresses that are not in the target's
1076 subnet for this interface. This mode is useful when target
1077 hosts reachable via this interface require the source IP
1078 address in ARP requests to be part of their logical network
1079 configured on the receiving interface. When we generate the
1080 request we will check all our subnets that include the
1081 target IP and will preserve the source address if it is from
1082 such subnet. If there is no such subnet we select source
1083 address according to the rules for level 2.
1084 2 - Always use the best local address for this target.
1085 In this mode we ignore the source address in the IP packet
1086 and try to select local address that we prefer for talks with
1087 the target host. Such local address is selected by looking
1088 for primary IP addresses on all our subnets on the outgoing
1089 interface that include the target IP address. If no suitable
1090 local address is found we select the first local address
1091 we have on the outgoing interface or on all other interfaces,
1092 with the hope we will receive reply for our request and
1093 even sometimes no matter the source IP address we announce.
1095 The max value from conf/{all,interface}/arp_announce is used.
1097 Increasing the restriction level gives more chance for
1098 receiving answer from the resolved target while decreasing
1099 the level announces more valid sender's information.
1101 arp_ignore - INTEGER
1102 Define different modes for sending replies in response to
1103 received ARP requests that resolve local target IP addresses:
1104 0 - (default): reply for any local target IP address, configured
1106 1 - reply only if the target IP address is local address
1107 configured on the incoming interface
1108 2 - reply only if the target IP address is local address
1109 configured on the incoming interface and both with the
1110 sender's IP address are part from same subnet on this interface
1111 3 - do not reply for local addresses configured with scope host,
1112 only resolutions for global and link addresses are replied
1114 8 - do not reply for all local addresses
1116 The max value from conf/{all,interface}/arp_ignore is used
1117 when ARP request is received on the {interface}
1119 arp_notify - BOOLEAN
1120 Define mode for notification of address and device changes.
1121 0 - (default): do nothing
1122 1 - Generate gratuitous arp requests when device is brought up
1123 or hardware address changes.
1125 arp_accept - BOOLEAN
1126 Define behavior for gratuitous ARP frames who's IP is not
1127 already present in the ARP table:
1128 0 - don't create new entries in the ARP table
1129 1 - create new entries in the ARP table
1131 Both replies and requests type gratuitous arp will trigger the
1132 ARP table to be updated, if this setting is on.
1134 If the ARP table already contains the IP address of the
1135 gratuitous arp frame, the arp table will be updated regardless
1136 if this setting is on or off.
1138 mcast_solicit - INTEGER
1139 The maximum number of multicast probes in INCOMPLETE state,
1140 when the associated hardware address is unknown. Defaults
1143 ucast_solicit - INTEGER
1144 The maximum number of unicast probes in PROBE state, when
1145 the hardware address is being reconfirmed. Defaults to 3.
1147 app_solicit - INTEGER
1148 The maximum number of probes to send to the user space ARP daemon
1149 via netlink before dropping back to multicast probes (see
1150 mcast_resolicit). Defaults to 0.
1152 mcast_resolicit - INTEGER
1153 The maximum number of multicast probes after unicast and
1154 app probes in PROBE state. Defaults to 0.
1156 disable_policy - BOOLEAN
1157 Disable IPSEC policy (SPD) for this interface
1159 disable_xfrm - BOOLEAN
1160 Disable IPSEC encryption on this interface, whatever the policy
1162 igmpv2_unsolicited_report_interval - INTEGER
1163 The interval in milliseconds in which the next unsolicited
1164 IGMPv1 or IGMPv2 report retransmit will take place.
1165 Default: 10000 (10 seconds)
1167 igmpv3_unsolicited_report_interval - INTEGER
1168 The interval in milliseconds in which the next unsolicited
1169 IGMPv3 report retransmit will take place.
1170 Default: 1000 (1 seconds)
1172 promote_secondaries - BOOLEAN
1173 When a primary IP address is removed from this interface
1174 promote a corresponding secondary IP address instead of
1175 removing all the corresponding secondary IP addresses.
1179 Allows you to write a number, which can be used as required.
1183 kuznet@ms2.inr.ac.ru
1189 delon.nicolas@wanadoo.fr
1194 /proc/sys/net/ipv6/* Variables:
1196 IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also
1197 apply to IPv6 [XXX?].
1199 bindv6only - BOOLEAN
1200 Default value for IPV6_V6ONLY socket option,
1201 which restricts use of the IPv6 socket to IPv6 communication
1203 TRUE: disable IPv4-mapped address feature
1204 FALSE: enable IPv4-mapped address feature
1206 Default: FALSE (as specified in RFC3493)
1208 flowlabel_consistency - BOOLEAN
1209 Protect the consistency (and unicity) of flow label.
1210 You have to disable it to use IPV6_FL_F_REFLECT flag on the
1216 auto_flowlabels - BOOLEAN
1217 Automatically generate flow labels based based on a flow hash
1218 of the packet. This allows intermediate devices, such as routers,
1219 to idenfify packet flows for mechanisms like Equal Cost Multipath
1220 Routing (see RFC 6438).
1225 flowlabel_state_ranges - BOOLEAN
1226 Split the flow label number space into two ranges. 0-0x7FFFF is
1227 reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF
1228 is reserved for stateless flow labels as described in RFC6437.
1233 anycast_src_echo_reply - BOOLEAN
1234 Controls the use of anycast addresses as source addresses for ICMPv6
1240 idgen_delay - INTEGER
1241 Controls the delay in seconds after which time to retry
1242 privacy stable address generation if a DAD conflict is
1244 Default: 1 (as specified in RFC7217)
1246 idgen_retries - INTEGER
1247 Controls the number of retries to generate a stable privacy
1248 address if a DAD conflict is detected.
1249 Default: 3 (as specified in RFC7217)
1252 Controls the MLD query robustness variable (see RFC3810 9.1).
1253 Default: 2 (as specified by RFC3810 9.1)
1254 Minimum: 1 (as specified by RFC6636 4.5)
1258 ip6frag_high_thresh - INTEGER
1259 Maximum memory used to reassemble IPv6 fragments. When
1260 ip6frag_high_thresh bytes of memory is allocated for this purpose,
1261 the fragment handler will toss packets until ip6frag_low_thresh
1264 ip6frag_low_thresh - INTEGER
1265 See ip6frag_high_thresh
1267 ip6frag_time - INTEGER
1268 Time in seconds to keep an IPv6 fragment in memory.
1271 Change the interface-specific default settings.
1275 Change all the interface-specific settings.
1277 [XXX: Other special features than forwarding?]
1279 conf/all/forwarding - BOOLEAN
1280 Enable global IPv6 forwarding between all interfaces.
1282 IPv4 and IPv6 work differently here; e.g. netfilter must be used
1283 to control which interfaces may forward packets and which not.
1285 This also sets all interfaces' Host/Router setting
1286 'forwarding' to the specified value. See below for details.
1288 This referred to as global forwarding.
1293 fwmark_reflect - BOOLEAN
1294 Controls the fwmark of kernel-generated IPv6 reply packets that are not
1295 associated with a socket for example, TCP RSTs or ICMPv6 echo replies).
1296 If unset, these packets have a fwmark of zero. If set, they have the
1297 fwmark of the packet they are replying to.
1301 Change special settings per interface.
1303 The functional behaviour for certain settings is different
1304 depending on whether local forwarding is enabled or not.
1307 Accept Router Advertisements; autoconfigure using them.
1309 It also determines whether or not to transmit Router
1310 Solicitations. If and only if the functional setting is to
1311 accept Router Advertisements, Router Solicitations will be
1314 Possible values are:
1315 0 Do not accept Router Advertisements.
1316 1 Accept Router Advertisements if forwarding is disabled.
1317 2 Overrule forwarding behaviour. Accept Router Advertisements
1318 even if forwarding is enabled.
1320 Functional default: enabled if local forwarding is disabled.
1321 disabled if local forwarding is enabled.
1323 accept_ra_defrtr - BOOLEAN
1324 Learn default router in Router Advertisement.
1326 Functional default: enabled if accept_ra is enabled.
1327 disabled if accept_ra is disabled.
1329 accept_ra_from_local - BOOLEAN
1330 Accept RA with source-address that is found on local machine
1331 if the RA is otherwise proper and able to be accepted.
1332 Default is to NOT accept these as it may be an un-intended
1336 enabled if accept_ra_from_local is enabled
1337 on a specific interface.
1338 disabled if accept_ra_from_local is disabled
1339 on a specific interface.
1341 accept_ra_pinfo - BOOLEAN
1342 Learn Prefix Information in Router Advertisement.
1344 Functional default: enabled if accept_ra is enabled.
1345 disabled if accept_ra is disabled.
1347 accept_ra_rt_info_max_plen - INTEGER
1348 Maximum prefix length of Route Information in RA.
1350 Route Information w/ prefix larger than or equal to this
1351 variable shall be ignored.
1353 Functional default: 0 if accept_ra_rtr_pref is enabled.
1354 -1 if accept_ra_rtr_pref is disabled.
1356 accept_ra_rtr_pref - BOOLEAN
1357 Accept Router Preference in RA.
1359 Functional default: enabled if accept_ra is enabled.
1360 disabled if accept_ra is disabled.
1362 accept_ra_mtu - BOOLEAN
1363 Apply the MTU value specified in RA option 5 (RFC4861). If
1364 disabled, the MTU specified in the RA will be ignored.
1366 Functional default: enabled if accept_ra is enabled.
1367 disabled if accept_ra is disabled.
1369 accept_redirects - BOOLEAN
1372 Functional default: enabled if local forwarding is disabled.
1373 disabled if local forwarding is enabled.
1375 accept_source_route - INTEGER
1376 Accept source routing (routing extension header).
1378 >= 0: Accept only routing header type 2.
1379 < 0: Do not accept routing header.
1384 Autoconfigure addresses using Prefix Information in Router
1387 Functional default: enabled if accept_ra_pinfo is enabled.
1388 disabled if accept_ra_pinfo is disabled.
1390 dad_transmits - INTEGER
1391 The amount of Duplicate Address Detection probes to send.
1394 forwarding - INTEGER
1395 Configure interface-specific Host/Router behaviour.
1397 Note: It is recommended to have the same setting on all
1398 interfaces; mixed router/host scenarios are rather uncommon.
1400 Possible values are:
1401 0 Forwarding disabled
1402 1 Forwarding enabled
1406 By default, Host behaviour is assumed. This means:
1408 1. IsRouter flag is not set in Neighbour Advertisements.
1409 2. If accept_ra is TRUE (default), transmit Router
1411 3. If accept_ra is TRUE (default), accept Router
1412 Advertisements (and do autoconfiguration).
1413 4. If accept_redirects is TRUE (default), accept Redirects.
1417 If local forwarding is enabled, Router behaviour is assumed.
1418 This means exactly the reverse from the above:
1420 1. IsRouter flag is set in Neighbour Advertisements.
1421 2. Router Solicitations are not sent unless accept_ra is 2.
1422 3. Router Advertisements are ignored unless accept_ra is 2.
1423 4. Redirects are ignored.
1425 Default: 0 (disabled) if global forwarding is disabled (default),
1426 otherwise 1 (enabled).
1429 Default Hop Limit to set.
1433 Default Maximum Transfer Unit
1434 Default: 1280 (IPv6 required minimum)
1436 router_probe_interval - INTEGER
1437 Minimum interval (in seconds) between Router Probing described
1442 router_solicitation_delay - INTEGER
1443 Number of seconds to wait after interface is brought up
1444 before sending Router Solicitations.
1447 router_solicitation_interval - INTEGER
1448 Number of seconds to wait between Router Solicitations.
1451 router_solicitations - INTEGER
1452 Number of Router Solicitations to send until assuming no
1453 routers are present.
1456 use_tempaddr - INTEGER
1457 Preference for Privacy Extensions (RFC3041).
1458 <= 0 : disable Privacy Extensions
1459 == 1 : enable Privacy Extensions, but prefer public
1460 addresses over temporary addresses.
1461 > 1 : enable Privacy Extensions and prefer temporary
1462 addresses over public addresses.
1463 Default: 0 (for most devices)
1464 -1 (for point-to-point devices and loopback devices)
1466 temp_valid_lft - INTEGER
1467 valid lifetime (in seconds) for temporary addresses.
1468 Default: 604800 (7 days)
1470 temp_prefered_lft - INTEGER
1471 Preferred lifetime (in seconds) for temporary addresses.
1472 Default: 86400 (1 day)
1474 max_desync_factor - INTEGER
1475 Maximum value for DESYNC_FACTOR, which is a random value
1476 that ensures that clients don't synchronize with each
1477 other and generate new addresses at exactly the same time.
1478 value is in seconds.
1481 regen_max_retry - INTEGER
1482 Number of attempts before give up attempting to generate
1483 valid temporary addresses.
1486 max_addresses - INTEGER
1487 Maximum number of autoconfigured addresses per interface. Setting
1488 to zero disables the limitation. It is not recommended to set this
1489 value too large (or to zero) because it would be an easy way to
1490 crash the kernel by allowing too many addresses to be created.
1493 disable_ipv6 - BOOLEAN
1494 Disable IPv6 operation. If accept_dad is set to 2, this value
1495 will be dynamically set to TRUE if DAD fails for the link-local
1497 Default: FALSE (enable IPv6 operation)
1499 When this value is changed from 1 to 0 (IPv6 is being enabled),
1500 it will dynamically create a link-local address on the given
1501 interface and start Duplicate Address Detection, if necessary.
1503 When this value is changed from 0 to 1 (IPv6 is being disabled),
1504 it will dynamically delete all address on the given interface.
1506 accept_dad - INTEGER
1507 Whether to accept DAD (Duplicate Address Detection).
1509 1: Enable DAD (default)
1510 2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
1511 link-local address has been found.
1513 force_tllao - BOOLEAN
1514 Enable sending the target link-layer address option even when
1515 responding to a unicast neighbor solicitation.
1518 Quoting from RFC 2461, section 4.4, Target link-layer address:
1520 "The option MUST be included for multicast solicitations in order to
1521 avoid infinite Neighbor Solicitation "recursion" when the peer node
1522 does not have a cache entry to return a Neighbor Advertisements
1523 message. When responding to unicast solicitations, the option can be
1524 omitted since the sender of the solicitation has the correct link-
1525 layer address; otherwise it would not have be able to send the unicast
1526 solicitation in the first place. However, including the link-layer
1527 address in this case adds little overhead and eliminates a potential
1528 race condition where the sender deletes the cached link-layer address
1529 prior to receiving a response to a previous solicitation."
1531 ndisc_notify - BOOLEAN
1532 Define mode for notification of address and device changes.
1533 0 - (default): do nothing
1534 1 - Generate unsolicited neighbour advertisements when device is brought
1535 up or hardware address changes.
1537 mldv1_unsolicited_report_interval - INTEGER
1538 The interval in milliseconds in which the next unsolicited
1539 MLDv1 report retransmit will take place.
1540 Default: 10000 (10 seconds)
1542 mldv2_unsolicited_report_interval - INTEGER
1543 The interval in milliseconds in which the next unsolicited
1544 MLDv2 report retransmit will take place.
1545 Default: 1000 (1 second)
1547 force_mld_version - INTEGER
1548 0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed
1549 1 - Enforce to use MLD version 1
1550 2 - Enforce to use MLD version 2
1552 suppress_frag_ndisc - INTEGER
1553 Control RFC 6980 (Security Implications of IPv6 Fragmentation
1554 with IPv6 Neighbor Discovery) behavior:
1555 1 - (default) discard fragmented neighbor discovery packets
1556 0 - allow fragmented neighbor discovery packets
1558 optimistic_dad - BOOLEAN
1559 Whether to perform Optimistic Duplicate Address Detection (RFC 4429).
1560 0: disabled (default)
1563 use_optimistic - BOOLEAN
1564 If enabled, do not classify optimistic addresses as deprecated during
1565 source address selection. Preferred addresses will still be chosen
1566 before optimistic addresses, subject to other ranking in the source
1567 address selection algorithm.
1568 0: disabled (default)
1571 stable_secret - IPv6 address
1572 This IPv6 address will be used as a secret to generate IPv6
1573 addresses for link-local addresses and autoconfigured
1574 ones. All addresses generated after setting this secret will
1575 be stable privacy ones by default. This can be changed via the
1576 addrgenmode ip-link. conf/default/stable_secret is used as the
1577 secret for the namespace, the interface specific ones can
1578 overwrite that. Writes to conf/all/stable_secret are refused.
1580 It is recommended to generate this secret during installation
1581 of a system and keep it stable after that.
1583 By default the stable secret is unset.
1587 Limit the maximal rates for sending ICMPv6 packets.
1588 0 to disable any limiting,
1589 otherwise the minimal space between responses in milliseconds.
1594 Pekka Savola <pekkas@netcore.fi>
1595 YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
1598 /proc/sys/net/bridge/* Variables:
1600 bridge-nf-call-arptables - BOOLEAN
1601 1 : pass bridged ARP traffic to arptables' FORWARD chain.
1605 bridge-nf-call-iptables - BOOLEAN
1606 1 : pass bridged IPv4 traffic to iptables' chains.
1610 bridge-nf-call-ip6tables - BOOLEAN
1611 1 : pass bridged IPv6 traffic to ip6tables' chains.
1615 bridge-nf-filter-vlan-tagged - BOOLEAN
1616 1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
1620 bridge-nf-filter-pppoe-tagged - BOOLEAN
1621 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
1625 bridge-nf-pass-vlan-input-dev - BOOLEAN
1626 1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan
1627 interface on the bridge and set the netfilter input device to the vlan.
1628 This allows use of e.g. "iptables -i br0.1" and makes the REDIRECT
1629 target work with vlan-on-top-of-bridge interfaces. When no matching
1630 vlan interface is found, or this switch is off, the input device is
1631 set to the bridge interface.
1632 0: disable bridge netfilter vlan interface lookup.
1635 proc/sys/net/sctp/* Variables:
1637 addip_enable - BOOLEAN
1638 Enable or disable extension of Dynamic Address Reconfiguration
1639 (ADD-IP) functionality specified in RFC5061. This extension provides
1640 the ability to dynamically add and remove new addresses for the SCTP
1643 1: Enable extension.
1645 0: Disable extension.
1649 addip_noauth_enable - BOOLEAN
1650 Dynamic Address Reconfiguration (ADD-IP) requires the use of
1651 authentication to protect the operations of adding or removing new
1652 addresses. This requirement is mandated so that unauthorized hosts
1653 would not be able to hijack associations. However, older
1654 implementations may not have implemented this requirement while
1655 allowing the ADD-IP extension. For reasons of interoperability,
1656 we provide this variable to control the enforcement of the
1657 authentication requirement.
1659 1: Allow ADD-IP extension to be used without authentication. This
1660 should only be set in a closed environment for interoperability
1661 with older implementations.
1663 0: Enforce the authentication requirement
1667 auth_enable - BOOLEAN
1668 Enable or disable Authenticated Chunks extension. This extension
1669 provides the ability to send and receive authenticated chunks and is
1670 required for secure operation of Dynamic Address Reconfiguration
1673 1: Enable this extension.
1674 0: Disable this extension.
1678 prsctp_enable - BOOLEAN
1679 Enable or disable the Partial Reliability extension (RFC3758) which
1680 is used to notify peers that a given DATA should no longer be expected.
1688 The limit of the number of new packets that can be initially sent. It
1689 controls how bursty the generated traffic can be.
1693 association_max_retrans - INTEGER
1694 Set the maximum number for retransmissions that an association can
1695 attempt deciding that the remote end is unreachable. If this value
1696 is exceeded, the association is terminated.
1700 max_init_retransmits - INTEGER
1701 The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
1702 that an association will attempt before declaring the destination
1703 unreachable and terminating.
1707 path_max_retrans - INTEGER
1708 The maximum number of retransmissions that will be attempted on a given
1709 path. Once this threshold is exceeded, the path is considered
1710 unreachable, and new traffic will use a different path when the
1711 association is multihomed.
1715 pf_retrans - INTEGER
1716 The number of retransmissions that will be attempted on a given path
1717 before traffic is redirected to an alternate transport (should one
1718 exist). Note this is distinct from path_max_retrans, as a path that
1719 passes the pf_retrans threshold can still be used. Its only
1720 deprioritized when a transmission path is selected by the stack. This
1721 setting is primarily used to enable fast failover mechanisms without
1722 having to reduce path_max_retrans to a very low value. See:
1723 http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt
1724 for details. Note also that a value of pf_retrans > path_max_retrans
1725 disables this feature
1729 rto_initial - INTEGER
1730 The initial round trip timeout value in milliseconds that will be used
1731 in calculating round trip times. This is the initial time interval
1732 for retransmissions.
1737 The maximum value (in milliseconds) of the round trip timeout. This
1738 is the largest time interval that can elapse between retransmissions.
1743 The minimum value (in milliseconds) of the round trip timeout. This
1744 is the smallest time interval the can elapse between retransmissions.
1748 hb_interval - INTEGER
1749 The interval (in milliseconds) between HEARTBEAT chunks. These chunks
1750 are sent at the specified interval on idle paths to probe the state of
1751 a given path between 2 associations.
1755 sack_timeout - INTEGER
1756 The amount of time (in milliseconds) that the implementation will wait
1761 valid_cookie_life - INTEGER
1762 The default lifetime of the SCTP cookie (in milliseconds). The cookie
1763 is used during association establishment.
1767 cookie_preserve_enable - BOOLEAN
1768 Enable or disable the ability to extend the lifetime of the SCTP cookie
1769 that is used during the establishment phase of SCTP association
1771 1: Enable cookie lifetime extension.
1776 cookie_hmac_alg - STRING
1777 Select the hmac algorithm used when generating the cookie value sent by
1778 a listening sctp socket to a connecting client in the INIT-ACK chunk.
1783 Ability to assign md5 or sha1 as the selected alg is predicated on the
1784 configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and
1785 CONFIG_CRYPTO_SHA1).
1787 Default: Dependent on configuration. MD5 if available, else SHA1 if
1788 available, else none.
1790 rcvbuf_policy - INTEGER
1791 Determines if the receive buffer is attributed to the socket or to
1792 association. SCTP supports the capability to create multiple
1793 associations on a single socket. When using this capability, it is
1794 possible that a single stalled association that's buffering a lot
1795 of data may block other associations from delivering their data by
1796 consuming all of the receive buffer space. To work around this,
1797 the rcvbuf_policy could be set to attribute the receiver buffer space
1798 to each association instead of the socket. This prevents the described
1801 1: rcvbuf space is per association
1802 0: rcvbuf space is per socket
1806 sndbuf_policy - INTEGER
1807 Similar to rcvbuf_policy above, this applies to send buffer space.
1809 1: Send buffer is tracked per association
1810 0: Send buffer is tracked per socket.
1814 sctp_mem - vector of 3 INTEGERs: min, pressure, max
1815 Number of pages allowed for queueing by all SCTP sockets.
1817 min: Below this number of pages SCTP is not bothered about its
1818 memory appetite. When amount of memory allocated by SCTP exceeds
1819 this number, SCTP starts to moderate memory usage.
1821 pressure: This value was introduced to follow format of tcp_mem.
1823 max: Number of pages allowed for queueing by all SCTP sockets.
1825 Default is calculated at boot time from amount of available memory.
1827 sctp_rmem - vector of 3 INTEGERs: min, default, max
1828 Only the first value ("min") is used, "default" and "max" are
1831 min: Minimal size of receive buffer used by SCTP socket.
1832 It is guaranteed to each SCTP socket (but not association) even
1833 under moderate memory pressure.
1837 sctp_wmem - vector of 3 INTEGERs: min, default, max
1838 Currently this tunable has no effect.
1840 addr_scope_policy - INTEGER
1841 Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00
1843 0 - Disable IPv4 address scoping
1844 1 - Enable IPv4 address scoping
1845 2 - Follow draft but allow IPv4 private addresses
1846 3 - Follow draft but allow IPv4 link local addresses
1851 /proc/sys/net/core/*
1852 Please see: Documentation/sysctl/net.txt for descriptions of these entries.
1855 /proc/sys/net/unix/*
1856 max_dgram_qlen - INTEGER
1857 The maximum length of dgram socket receive queue
1864 /proc/sys/net/irda/*
1865 fast_poll_increase FIXME
1866 warn_noreply_time FIXME
1867 discovery_slots FIXME
1870 discovery_timeout FIXME
1871 lap_keepalive_time FIXME
1872 max_noreply_time FIXME
1873 max_tx_data_size FIXME
1875 min_tx_turn_time FIXME