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.
271 Enable FACK congestion avoidance and fast retransmission.
272 The value is not used, if tcp_sack is not enabled.
274 tcp_fin_timeout - INTEGER
275 The length of time an orphaned (no longer referenced by any
276 application) connection will remain in the FIN_WAIT_2 state
277 before it is aborted at the local end. While a perfectly
278 valid "receive only" state for an un-orphaned connection, an
279 orphaned connection in FIN_WAIT_2 state could otherwise wait
280 forever for the remote to close its end of the connection.
285 Enables Forward RTO-Recovery (F-RTO) defined in RFC5682.
286 F-RTO is an enhanced recovery algorithm for TCP retransmission
287 timeouts. It is particularly beneficial in networks where the
288 RTT fluctuates (e.g., wireless). F-RTO is sender-side only
289 modification. It does not require any support from the peer.
291 By default it's enabled with a non-zero value. 0 disables F-RTO.
293 tcp_keepalive_time - INTEGER
294 How often TCP sends out keepalive messages when keepalive is enabled.
297 tcp_keepalive_probes - INTEGER
298 How many keepalive probes TCP sends out, until it decides that the
299 connection is broken. Default value: 9.
301 tcp_keepalive_intvl - INTEGER
302 How frequently the probes are send out. Multiplied by
303 tcp_keepalive_probes it is time to kill not responding connection,
304 after probes started. Default value: 75sec i.e. connection
305 will be aborted after ~11 minutes of retries.
307 tcp_low_latency - BOOLEAN
308 If set, the TCP stack makes decisions that prefer lower
309 latency as opposed to higher throughput. By default, this
310 option is not set meaning that higher throughput is preferred.
311 An example of an application where this default should be
312 changed would be a Beowulf compute cluster.
315 tcp_max_orphans - INTEGER
316 Maximal number of TCP sockets not attached to any user file handle,
317 held by system. If this number is exceeded orphaned connections are
318 reset immediately and warning is printed. This limit exists
319 only to prevent simple DoS attacks, you _must_ not rely on this
320 or lower the limit artificially, but rather increase it
321 (probably, after increasing installed memory),
322 if network conditions require more than default value,
323 and tune network services to linger and kill such states
324 more aggressively. Let me to remind again: each orphan eats
325 up to ~64K of unswappable memory.
327 tcp_max_syn_backlog - INTEGER
328 Maximal number of remembered connection requests, which have not
329 received an acknowledgment from connecting client.
330 The minimal value is 128 for low memory machines, and it will
331 increase in proportion to the memory of machine.
332 If server suffers from overload, try increasing this number.
334 tcp_max_tw_buckets - INTEGER
335 Maximal number of timewait sockets held by system simultaneously.
336 If this number is exceeded time-wait socket is immediately destroyed
337 and warning is printed. This limit exists only to prevent
338 simple DoS attacks, you _must_ not lower the limit artificially,
339 but rather increase it (probably, after increasing installed memory),
340 if network conditions require more than default value.
342 tcp_mem - vector of 3 INTEGERs: min, pressure, max
343 min: below this number of pages TCP is not bothered about its
346 pressure: when amount of memory allocated by TCP exceeds this number
347 of pages, TCP moderates its memory consumption and enters memory
348 pressure mode, which is exited when memory consumption falls
351 max: number of pages allowed for queueing by all TCP sockets.
353 Defaults are calculated at boot time from amount of available
356 tcp_moderate_rcvbuf - BOOLEAN
357 If set, TCP performs receive buffer auto-tuning, attempting to
358 automatically size the buffer (no greater than tcp_rmem[2]) to
359 match the size required by the path for full throughput. Enabled by
362 tcp_mtu_probing - INTEGER
363 Controls TCP Packetization-Layer Path MTU Discovery. Takes three
366 1 - Disabled by default, enabled when an ICMP black hole detected
367 2 - Always enabled, use initial MSS of tcp_base_mss.
369 tcp_no_metrics_save - BOOLEAN
370 By default, TCP saves various connection metrics in the route cache
371 when the connection closes, so that connections established in the
372 near future can use these to set initial conditions. Usually, this
373 increases overall performance, but may sometimes cause performance
374 degradation. If set, TCP will not cache metrics on closing
377 tcp_orphan_retries - INTEGER
378 This value influences the timeout of a locally closed TCP connection,
379 when RTO retransmissions remain unacknowledged.
380 See tcp_retries2 for more details.
382 The default value is 8.
383 If your machine is a loaded WEB server,
384 you should think about lowering this value, such sockets
385 may consume significant resources. Cf. tcp_max_orphans.
387 tcp_reordering - INTEGER
388 Initial reordering level of packets in a TCP stream.
389 TCP stack can then dynamically adjust flow reordering level
390 between this initial value and tcp_max_reordering
393 tcp_max_reordering - INTEGER
394 Maximal reordering level of packets in a TCP stream.
395 300 is a fairly conservative value, but you might increase it
396 if paths are using per packet load balancing (like bonding rr mode)
399 tcp_retrans_collapse - BOOLEAN
400 Bug-to-bug compatibility with some broken printers.
401 On retransmit try to send bigger packets to work around bugs in
404 tcp_retries1 - INTEGER
405 This value influences the time, after which TCP decides, that
406 something is wrong due to unacknowledged RTO retransmissions,
407 and reports this suspicion to the network layer.
408 See tcp_retries2 for more details.
410 RFC 1122 recommends at least 3 retransmissions, which is the
413 tcp_retries2 - INTEGER
414 This value influences the timeout of an alive TCP connection,
415 when RTO retransmissions remain unacknowledged.
416 Given a value of N, a hypothetical TCP connection following
417 exponential backoff with an initial RTO of TCP_RTO_MIN would
418 retransmit N times before killing the connection at the (N+1)th RTO.
420 The default value of 15 yields a hypothetical timeout of 924.6
421 seconds and is a lower bound for the effective timeout.
422 TCP will effectively time out at the first RTO which exceeds the
423 hypothetical timeout.
425 RFC 1122 recommends at least 100 seconds for the timeout,
426 which corresponds to a value of at least 8.
428 tcp_rfc1337 - BOOLEAN
429 If set, the TCP stack behaves conforming to RFC1337. If unset,
430 we are not conforming to RFC, but prevent TCP TIME_WAIT
434 tcp_rmem - vector of 3 INTEGERs: min, default, max
435 min: Minimal size of receive buffer used by TCP sockets.
436 It is guaranteed to each TCP socket, even under moderate memory
440 default: initial size of receive buffer used by TCP sockets.
441 This value overrides net.core.rmem_default used by other protocols.
442 Default: 87380 bytes. This value results in window of 65535 with
443 default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
444 less for default tcp_app_win. See below about these variables.
446 max: maximal size of receive buffer allowed for automatically
447 selected receiver buffers for TCP socket. This value does not override
448 net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables
449 automatic tuning of that socket's receive buffer size, in which
450 case this value is ignored.
451 Default: between 87380B and 6MB, depending on RAM size.
454 Enable select acknowledgments (SACKS).
456 tcp_slow_start_after_idle - BOOLEAN
457 If set, provide RFC2861 behavior and time out the congestion
458 window after an idle period. An idle period is defined at
459 the current RTO. If unset, the congestion window will not
460 be timed out after an idle period.
464 Use the Host requirements interpretation of the TCP urgent pointer field.
465 Most hosts use the older BSD interpretation, so if you turn this on
466 Linux might not communicate correctly with them.
469 tcp_synack_retries - INTEGER
470 Number of times SYNACKs for a passive TCP connection attempt will
471 be retransmitted. Should not be higher than 255. Default value
472 is 5, which corresponds to 31seconds till the last retransmission
473 with the current initial RTO of 1second. With this the final timeout
474 for a passive TCP connection will happen after 63seconds.
476 tcp_syncookies - BOOLEAN
477 Only valid when the kernel was compiled with CONFIG_SYN_COOKIES
478 Send out syncookies when the syn backlog queue of a socket
479 overflows. This is to prevent against the common 'SYN flood attack'
482 Note, that syncookies is fallback facility.
483 It MUST NOT be used to help highly loaded servers to stand
484 against legal connection rate. If you see SYN flood warnings
485 in your logs, but investigation shows that they occur
486 because of overload with legal connections, you should tune
487 another parameters until this warning disappear.
488 See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
490 syncookies seriously violate TCP protocol, do not allow
491 to use TCP extensions, can result in serious degradation
492 of some services (f.e. SMTP relaying), visible not by you,
493 but your clients and relays, contacting you. While you see
494 SYN flood warnings in logs not being really flooded, your server
495 is seriously misconfigured.
497 If you want to test which effects syncookies have to your
498 network connections you can set this knob to 2 to enable
499 unconditionally generation of syncookies.
501 tcp_fastopen - INTEGER
502 Enable TCP Fast Open feature (draft-ietf-tcpm-fastopen) to send data
503 in the opening SYN packet. To use this feature, the client application
504 must use sendmsg() or sendto() with MSG_FASTOPEN flag rather than
505 connect() to perform a TCP handshake automatically.
507 The values (bitmap) are
508 1: Enables sending data in the opening SYN on the client w/ MSG_FASTOPEN.
509 2: Enables TCP Fast Open on the server side, i.e., allowing data in
510 a SYN packet to be accepted and passed to the application before
511 3-way hand shake finishes.
512 4: Send data in the opening SYN regardless of cookie availability and
513 without a cookie option.
514 0x100: Accept SYN data w/o validating the cookie.
515 0x200: Accept data-in-SYN w/o any cookie option present.
516 0x400/0x800: Enable Fast Open on all listeners regardless of the
517 TCP_FASTOPEN socket option. The two different flags designate two
518 different ways of setting max_qlen without the TCP_FASTOPEN socket
523 Note that the client & server side Fast Open flags (1 and 2
524 respectively) must be also enabled before the rest of flags can take
527 See include/net/tcp.h and the code for more details.
529 tcp_syn_retries - INTEGER
530 Number of times initial SYNs for an active TCP connection attempt
531 will be retransmitted. Should not be higher than 255. Default value
532 is 6, which corresponds to 63seconds till the last retransmission
533 with the current initial RTO of 1second. With this the final timeout
534 for an active TCP connection attempt will happen after 127seconds.
536 tcp_timestamps - BOOLEAN
537 Enable timestamps as defined in RFC1323.
539 tcp_min_tso_segs - INTEGER
540 Minimal number of segments per TSO frame.
541 Since linux-3.12, TCP does an automatic sizing of TSO frames,
542 depending on flow rate, instead of filling 64Kbytes packets.
543 For specific usages, it's possible to force TCP to build big
544 TSO frames. Note that TCP stack might split too big TSO packets
545 if available window is too small.
548 tcp_tso_win_divisor - INTEGER
549 This allows control over what percentage of the congestion window
550 can be consumed by a single TSO frame.
551 The setting of this parameter is a choice between burstiness and
552 building larger TSO frames.
555 tcp_tw_recycle - BOOLEAN
556 Enable fast recycling TIME-WAIT sockets. Default value is 0.
557 It should not be changed without advice/request of technical
560 tcp_tw_reuse - BOOLEAN
561 Allow to reuse TIME-WAIT sockets for new connections when it is
562 safe from protocol viewpoint. Default value is 0.
563 It should not be changed without advice/request of technical
566 tcp_window_scaling - BOOLEAN
567 Enable window scaling as defined in RFC1323.
569 tcp_wmem - vector of 3 INTEGERs: min, default, max
570 min: Amount of memory reserved for send buffers for TCP sockets.
571 Each TCP socket has rights to use it due to fact of its birth.
574 default: initial size of send buffer used by TCP sockets. This
575 value overrides net.core.wmem_default used by other protocols.
576 It is usually lower than net.core.wmem_default.
579 max: Maximal amount of memory allowed for automatically tuned
580 send buffers for TCP sockets. This value does not override
581 net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables
582 automatic tuning of that socket's send buffer size, in which case
583 this value is ignored.
584 Default: between 64K and 4MB, depending on RAM size.
586 tcp_notsent_lowat - UNSIGNED INTEGER
587 A TCP socket can control the amount of unsent bytes in its write queue,
588 thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll()
589 reports POLLOUT events if the amount of unsent bytes is below a per
590 socket value, and if the write queue is not full. sendmsg() will
591 also not add new buffers if the limit is hit.
593 This global variable controls the amount of unsent data for
594 sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change
595 to the global variable has immediate effect.
597 Default: UINT_MAX (0xFFFFFFFF)
599 tcp_workaround_signed_windows - BOOLEAN
600 If set, assume no receipt of a window scaling option means the
601 remote TCP is broken and treats the window as a signed quantity.
602 If unset, assume the remote TCP is not broken even if we do
603 not receive a window scaling option from them.
606 tcp_thin_linear_timeouts - BOOLEAN
607 Enable dynamic triggering of linear timeouts for thin streams.
608 If set, a check is performed upon retransmission by timeout to
609 determine if the stream is thin (less than 4 packets in flight).
610 As long as the stream is found to be thin, up to 6 linear
611 timeouts may be performed before exponential backoff mode is
612 initiated. This improves retransmission latency for
613 non-aggressive thin streams, often found to be time-dependent.
614 For more information on thin streams, see
615 Documentation/networking/tcp-thin.txt
618 tcp_thin_dupack - BOOLEAN
619 Enable dynamic triggering of retransmissions after one dupACK
620 for thin streams. If set, a check is performed upon reception
621 of a dupACK to determine if the stream is thin (less than 4
622 packets in flight). As long as the stream is found to be thin,
623 data is retransmitted on the first received dupACK. This
624 improves retransmission latency for non-aggressive thin
625 streams, often found to be time-dependent.
626 For more information on thin streams, see
627 Documentation/networking/tcp-thin.txt
630 tcp_limit_output_bytes - INTEGER
631 Controls TCP Small Queue limit per tcp socket.
632 TCP bulk sender tends to increase packets in flight until it
633 gets losses notifications. With SNDBUF autotuning, this can
634 result in a large amount of packets queued in qdisc/device
635 on the local machine, hurting latency of other flows, for
636 typical pfifo_fast qdiscs.
637 tcp_limit_output_bytes limits the number of bytes on qdisc
638 or device to reduce artificial RTT/cwnd and reduce bufferbloat.
641 tcp_challenge_ack_limit - INTEGER
642 Limits number of Challenge ACK sent per second, as recommended
643 in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
648 udp_mem - vector of 3 INTEGERs: min, pressure, max
649 Number of pages allowed for queueing by all UDP sockets.
651 min: Below this number of pages UDP is not bothered about its
652 memory appetite. When amount of memory allocated by UDP exceeds
653 this number, UDP starts to moderate memory usage.
655 pressure: This value was introduced to follow format of tcp_mem.
657 max: Number of pages allowed for queueing by all UDP sockets.
659 Default is calculated at boot time from amount of available memory.
661 udp_rmem_min - INTEGER
662 Minimal size of receive buffer used by UDP sockets in moderation.
663 Each UDP socket is able to use the size for receiving data, even if
664 total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
667 udp_wmem_min - INTEGER
668 Minimal size of send buffer used by UDP sockets in moderation.
669 Each UDP socket is able to use the size for sending data, even if
670 total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
675 cipso_cache_enable - BOOLEAN
676 If set, enable additions to and lookups from the CIPSO label mapping
677 cache. If unset, additions are ignored and lookups always result in a
678 miss. However, regardless of the setting the cache is still
679 invalidated when required when means you can safely toggle this on and
680 off and the cache will always be "safe".
683 cipso_cache_bucket_size - INTEGER
684 The CIPSO label cache consists of a fixed size hash table with each
685 hash bucket containing a number of cache entries. This variable limits
686 the number of entries in each hash bucket; the larger the value the
687 more CIPSO label mappings that can be cached. When the number of
688 entries in a given hash bucket reaches this limit adding new entries
689 causes the oldest entry in the bucket to be removed to make room.
692 cipso_rbm_optfmt - BOOLEAN
693 Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
694 the CIPSO draft specification (see Documentation/netlabel for details).
695 This means that when set the CIPSO tag will be padded with empty
696 categories in order to make the packet data 32-bit aligned.
699 cipso_rbm_structvalid - BOOLEAN
700 If set, do a very strict check of the CIPSO option when
701 ip_options_compile() is called. If unset, relax the checks done during
702 ip_options_compile(). Either way is "safe" as errors are caught else
703 where in the CIPSO processing code but setting this to 0 (False) should
704 result in less work (i.e. it should be faster) but could cause problems
705 with other implementations that require strict checking.
710 ip_local_port_range - 2 INTEGERS
711 Defines the local port range that is used by TCP and UDP to
712 choose the local port. The first number is the first, the
713 second the last local port number. The default values are
714 32768 and 61000 respectively.
716 ip_local_reserved_ports - list of comma separated ranges
717 Specify the ports which are reserved for known third-party
718 applications. These ports will not be used by automatic port
719 assignments (e.g. when calling connect() or bind() with port
720 number 0). Explicit port allocation behavior is unchanged.
722 The format used for both input and output is a comma separated
723 list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and
724 10). Writing to the file will clear all previously reserved
725 ports and update the current list with the one given in the
728 Note that ip_local_port_range and ip_local_reserved_ports
729 settings are independent and both are considered by the kernel
730 when determining which ports are available for automatic port
733 You can reserve ports which are not in the current
734 ip_local_port_range, e.g.:
736 $ cat /proc/sys/net/ipv4/ip_local_port_range
738 $ cat /proc/sys/net/ipv4/ip_local_reserved_ports
741 although this is redundant. However such a setting is useful
742 if later the port range is changed to a value that will
743 include the reserved ports.
747 ip_nonlocal_bind - BOOLEAN
748 If set, allows processes to bind() to non-local IP addresses,
749 which can be quite useful - but may break some applications.
753 If set non-zero, enables support for dynamic addresses.
754 If set to a non-zero value larger than 1, a kernel log
755 message will be printed when dynamic address rewriting
759 ip_early_demux - BOOLEAN
760 Optimize input packet processing down to one demux for
761 certain kinds of local sockets. Currently we only do this
762 for established TCP sockets.
764 It may add an additional cost for pure routing workloads that
765 reduces overall throughput, in such case you should disable it.
768 icmp_echo_ignore_all - BOOLEAN
769 If set non-zero, then the kernel will ignore all ICMP ECHO
773 icmp_echo_ignore_broadcasts - BOOLEAN
774 If set non-zero, then the kernel will ignore all ICMP ECHO and
775 TIMESTAMP requests sent to it via broadcast/multicast.
778 icmp_ratelimit - INTEGER
779 Limit the maximal rates for sending ICMP packets whose type matches
780 icmp_ratemask (see below) to specific targets.
781 0 to disable any limiting,
782 otherwise the minimal space between responses in milliseconds.
783 Note that another sysctl, icmp_msgs_per_sec limits the number
784 of ICMP packets sent on all targets.
787 icmp_msgs_per_sec - INTEGER
788 Limit maximal number of ICMP packets sent per second from this host.
789 Only messages whose type matches icmp_ratemask (see below) are
790 controlled by this limit.
793 icmp_msgs_burst - INTEGER
794 icmp_msgs_per_sec controls number of ICMP packets sent per second,
795 while icmp_msgs_burst controls the burst size of these packets.
798 icmp_ratemask - INTEGER
799 Mask made of ICMP types for which rates are being limited.
800 Significant bits: IHGFEDCBA9876543210
801 Default mask: 0000001100000011000 (6168)
803 Bit definitions (see include/linux/icmp.h):
805 3 Destination Unreachable *
810 C Parameter Problem *
815 H Address Mask Request
818 * These are rate limited by default (see default mask above)
820 icmp_ignore_bogus_error_responses - BOOLEAN
821 Some routers violate RFC1122 by sending bogus responses to broadcast
822 frames. Such violations are normally logged via a kernel warning.
823 If this is set to TRUE, the kernel will not give such warnings, which
824 will avoid log file clutter.
827 icmp_errors_use_inbound_ifaddr - BOOLEAN
829 If zero, icmp error messages are sent with the primary address of
830 the exiting interface.
832 If non-zero, the message will be sent with the primary address of
833 the interface that received the packet that caused the icmp error.
834 This is the behaviour network many administrators will expect from
835 a router. And it can make debugging complicated network layouts
838 Note that if no primary address exists for the interface selected,
839 then the primary address of the first non-loopback interface that
840 has one will be used regardless of this setting.
844 igmp_max_memberships - INTEGER
845 Change the maximum number of multicast groups we can subscribe to.
848 Theoretical maximum value is bounded by having to send a membership
849 report in a single datagram (i.e. the report can't span multiple
850 datagrams, or risk confusing the switch and leaving groups you don't
853 The number of supported groups 'M' is bounded by the number of group
854 report entries you can fit into a single datagram of 65535 bytes.
856 M = 65536-sizeof (ip header)/(sizeof(Group record))
858 Group records are variable length, with a minimum of 12 bytes.
859 So net.ipv4.igmp_max_memberships should not be set higher than:
861 (65536-24) / 12 = 5459
863 The value 5459 assumes no IP header options, so in practice
864 this number may be lower.
866 conf/interface/* changes special settings per interface (where
867 "interface" is the name of your network interface)
869 conf/all/* is special, changes the settings for all interfaces
872 Controls the IGMP query robustness variable (see RFC2236 8.1).
873 Default: 2 (as specified by RFC2236 8.1)
874 Minimum: 1 (as specified by RFC6636 4.5)
876 log_martians - BOOLEAN
877 Log packets with impossible addresses to kernel log.
878 log_martians for the interface will be enabled if at least one of
879 conf/{all,interface}/log_martians is set to TRUE,
880 it will be disabled otherwise
882 accept_redirects - BOOLEAN
883 Accept ICMP redirect messages.
884 accept_redirects for the interface will be enabled if:
885 - both conf/{all,interface}/accept_redirects are TRUE in the case
886 forwarding for the interface is enabled
888 - at least one of conf/{all,interface}/accept_redirects is TRUE in the
889 case forwarding for the interface is disabled
890 accept_redirects for the interface will be disabled otherwise
895 Enable IP forwarding on this interface.
897 mc_forwarding - BOOLEAN
898 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
899 and a multicast routing daemon is required.
900 conf/all/mc_forwarding must also be set to TRUE to enable multicast
901 routing for the interface
904 Integer value used to differentiate the devices by the medium they
905 are attached to. Two devices can have different id values when
906 the broadcast packets are received only on one of them.
907 The default value 0 means that the device is the only interface
908 to its medium, value of -1 means that medium is not known.
910 Currently, it is used to change the proxy_arp behavior:
911 the proxy_arp feature is enabled for packets forwarded between
912 two devices attached to different media.
916 proxy_arp for the interface will be enabled if at least one of
917 conf/{all,interface}/proxy_arp is set to TRUE,
918 it will be disabled otherwise
920 proxy_arp_pvlan - BOOLEAN
921 Private VLAN proxy arp.
922 Basically allow proxy arp replies back to the same interface
923 (from which the ARP request/solicitation was received).
925 This is done to support (ethernet) switch features, like RFC
926 3069, where the individual ports are NOT allowed to
927 communicate with each other, but they are allowed to talk to
928 the upstream router. As described in RFC 3069, it is possible
929 to allow these hosts to communicate through the upstream
930 router by proxy_arp'ing. Don't need to be used together with
933 This technology is known by different names:
934 In RFC 3069 it is called VLAN Aggregation.
935 Cisco and Allied Telesyn call it Private VLAN.
936 Hewlett-Packard call it Source-Port filtering or port-isolation.
937 Ericsson call it MAC-Forced Forwarding (RFC Draft).
939 shared_media - BOOLEAN
940 Send(router) or accept(host) RFC1620 shared media redirects.
941 Overrides ip_secure_redirects.
942 shared_media for the interface will be enabled if at least one of
943 conf/{all,interface}/shared_media is set to TRUE,
944 it will be disabled otherwise
947 secure_redirects - BOOLEAN
948 Accept ICMP redirect messages only for gateways,
949 listed in default gateway list.
950 secure_redirects for the interface will be enabled if at least one of
951 conf/{all,interface}/secure_redirects is set to TRUE,
952 it will be disabled otherwise
955 send_redirects - BOOLEAN
956 Send redirects, if router.
957 send_redirects for the interface will be enabled if at least one of
958 conf/{all,interface}/send_redirects is set to TRUE,
959 it will be disabled otherwise
962 bootp_relay - BOOLEAN
963 Accept packets with source address 0.b.c.d destined
964 not to this host as local ones. It is supposed, that
965 BOOTP relay daemon will catch and forward such packets.
966 conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
971 accept_source_route - BOOLEAN
972 Accept packets with SRR option.
973 conf/all/accept_source_route must also be set to TRUE to accept packets
974 with SRR option on the interface
975 default TRUE (router)
978 accept_local - BOOLEAN
979 Accept packets with local source addresses. In combination with
980 suitable routing, this can be used to direct packets between two
981 local interfaces over the wire and have them accepted properly.
984 route_localnet - BOOLEAN
985 Do not consider loopback addresses as martian source or destination
986 while routing. This enables the use of 127/8 for local routing purposes.
990 0 - No source validation.
991 1 - Strict mode as defined in RFC3704 Strict Reverse Path
992 Each incoming packet is tested against the FIB and if the interface
993 is not the best reverse path the packet check will fail.
994 By default failed packets are discarded.
995 2 - Loose mode as defined in RFC3704 Loose Reverse Path
996 Each incoming packet's source address is also tested against the FIB
997 and if the source address is not reachable via any interface
998 the packet check will fail.
1000 Current recommended practice in RFC3704 is to enable strict mode
1001 to prevent IP spoofing from DDos attacks. If using asymmetric routing
1002 or other complicated routing, then loose mode is recommended.
1004 The max value from conf/{all,interface}/rp_filter is used
1005 when doing source validation on the {interface}.
1007 Default value is 0. Note that some distributions enable it
1010 arp_filter - BOOLEAN
1011 1 - Allows you to have multiple network interfaces on the same
1012 subnet, and have the ARPs for each interface be answered
1013 based on whether or not the kernel would route a packet from
1014 the ARP'd IP out that interface (therefore you must use source
1015 based routing for this to work). In other words it allows control
1016 of which cards (usually 1) will respond to an arp request.
1018 0 - (default) The kernel can respond to arp requests with addresses
1019 from other interfaces. This may seem wrong but it usually makes
1020 sense, because it increases the chance of successful communication.
1021 IP addresses are owned by the complete host on Linux, not by
1022 particular interfaces. Only for more complex setups like load-
1023 balancing, does this behaviour cause problems.
1025 arp_filter for the interface will be enabled if at least one of
1026 conf/{all,interface}/arp_filter is set to TRUE,
1027 it will be disabled otherwise
1029 arp_announce - INTEGER
1030 Define different restriction levels for announcing the local
1031 source IP address from IP packets in ARP requests sent on
1033 0 - (default) Use any local address, configured on any interface
1034 1 - Try to avoid local addresses that are not in the target's
1035 subnet for this interface. This mode is useful when target
1036 hosts reachable via this interface require the source IP
1037 address in ARP requests to be part of their logical network
1038 configured on the receiving interface. When we generate the
1039 request we will check all our subnets that include the
1040 target IP and will preserve the source address if it is from
1041 such subnet. If there is no such subnet we select source
1042 address according to the rules for level 2.
1043 2 - Always use the best local address for this target.
1044 In this mode we ignore the source address in the IP packet
1045 and try to select local address that we prefer for talks with
1046 the target host. Such local address is selected by looking
1047 for primary IP addresses on all our subnets on the outgoing
1048 interface that include the target IP address. If no suitable
1049 local address is found we select the first local address
1050 we have on the outgoing interface or on all other interfaces,
1051 with the hope we will receive reply for our request and
1052 even sometimes no matter the source IP address we announce.
1054 The max value from conf/{all,interface}/arp_announce is used.
1056 Increasing the restriction level gives more chance for
1057 receiving answer from the resolved target while decreasing
1058 the level announces more valid sender's information.
1060 arp_ignore - INTEGER
1061 Define different modes for sending replies in response to
1062 received ARP requests that resolve local target IP addresses:
1063 0 - (default): reply for any local target IP address, configured
1065 1 - reply only if the target IP address is local address
1066 configured on the incoming interface
1067 2 - reply only if the target IP address is local address
1068 configured on the incoming interface and both with the
1069 sender's IP address are part from same subnet on this interface
1070 3 - do not reply for local addresses configured with scope host,
1071 only resolutions for global and link addresses are replied
1073 8 - do not reply for all local addresses
1075 The max value from conf/{all,interface}/arp_ignore is used
1076 when ARP request is received on the {interface}
1078 arp_notify - BOOLEAN
1079 Define mode for notification of address and device changes.
1080 0 - (default): do nothing
1081 1 - Generate gratuitous arp requests when device is brought up
1082 or hardware address changes.
1084 arp_accept - BOOLEAN
1085 Define behavior for gratuitous ARP frames who's IP is not
1086 already present in the ARP table:
1087 0 - don't create new entries in the ARP table
1088 1 - create new entries in the ARP table
1090 Both replies and requests type gratuitous arp will trigger the
1091 ARP table to be updated, if this setting is on.
1093 If the ARP table already contains the IP address of the
1094 gratuitous arp frame, the arp table will be updated regardless
1095 if this setting is on or off.
1098 app_solicit - INTEGER
1099 The maximum number of probes to send to the user space ARP daemon
1100 via netlink before dropping back to multicast probes (see
1101 mcast_solicit). Defaults to 0.
1103 disable_policy - BOOLEAN
1104 Disable IPSEC policy (SPD) for this interface
1106 disable_xfrm - BOOLEAN
1107 Disable IPSEC encryption on this interface, whatever the policy
1109 igmpv2_unsolicited_report_interval - INTEGER
1110 The interval in milliseconds in which the next unsolicited
1111 IGMPv1 or IGMPv2 report retransmit will take place.
1112 Default: 10000 (10 seconds)
1114 igmpv3_unsolicited_report_interval - INTEGER
1115 The interval in milliseconds in which the next unsolicited
1116 IGMPv3 report retransmit will take place.
1117 Default: 1000 (1 seconds)
1119 promote_secondaries - BOOLEAN
1120 When a primary IP address is removed from this interface
1121 promote a corresponding secondary IP address instead of
1122 removing all the corresponding secondary IP addresses.
1126 Allows you to write a number, which can be used as required.
1130 kuznet@ms2.inr.ac.ru
1136 delon.nicolas@wanadoo.fr
1141 /proc/sys/net/ipv6/* Variables:
1143 IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also
1144 apply to IPv6 [XXX?].
1146 bindv6only - BOOLEAN
1147 Default value for IPV6_V6ONLY socket option,
1148 which restricts use of the IPv6 socket to IPv6 communication
1150 TRUE: disable IPv4-mapped address feature
1151 FALSE: enable IPv4-mapped address feature
1153 Default: FALSE (as specified in RFC3493)
1155 flowlabel_consistency - BOOLEAN
1156 Protect the consistency (and unicity) of flow label.
1157 You have to disable it to use IPV6_FL_F_REFLECT flag on the
1163 auto_flowlabels - BOOLEAN
1164 Automatically generate flow labels based based on a flow hash
1165 of the packet. This allows intermediate devices, such as routers,
1166 to idenfify packet flows for mechanisms like Equal Cost Multipath
1167 Routing (see RFC 6438).
1172 anycast_src_echo_reply - BOOLEAN
1173 Controls the use of anycast addresses as source addresses for ICMPv6
1180 Controls the MLD query robustness variable (see RFC3810 9.1).
1181 Default: 2 (as specified by RFC3810 9.1)
1182 Minimum: 1 (as specified by RFC6636 4.5)
1186 ip6frag_high_thresh - INTEGER
1187 Maximum memory used to reassemble IPv6 fragments. When
1188 ip6frag_high_thresh bytes of memory is allocated for this purpose,
1189 the fragment handler will toss packets until ip6frag_low_thresh
1192 ip6frag_low_thresh - INTEGER
1193 See ip6frag_high_thresh
1195 ip6frag_time - INTEGER
1196 Time in seconds to keep an IPv6 fragment in memory.
1199 Change the interface-specific default settings.
1203 Change all the interface-specific settings.
1205 [XXX: Other special features than forwarding?]
1207 conf/all/forwarding - BOOLEAN
1208 Enable global IPv6 forwarding between all interfaces.
1210 IPv4 and IPv6 work differently here; e.g. netfilter must be used
1211 to control which interfaces may forward packets and which not.
1213 This also sets all interfaces' Host/Router setting
1214 'forwarding' to the specified value. See below for details.
1216 This referred to as global forwarding.
1221 fwmark_reflect - BOOLEAN
1222 Controls the fwmark of kernel-generated IPv6 reply packets that are not
1223 associated with a socket for example, TCP RSTs or ICMPv6 echo replies).
1224 If unset, these packets have a fwmark of zero. If set, they have the
1225 fwmark of the packet they are replying to.
1229 Change special settings per interface.
1231 The functional behaviour for certain settings is different
1232 depending on whether local forwarding is enabled or not.
1235 Accept Router Advertisements; autoconfigure using them.
1237 It also determines whether or not to transmit Router
1238 Solicitations. If and only if the functional setting is to
1239 accept Router Advertisements, Router Solicitations will be
1242 Possible values are:
1243 0 Do not accept Router Advertisements.
1244 1 Accept Router Advertisements if forwarding is disabled.
1245 2 Overrule forwarding behaviour. Accept Router Advertisements
1246 even if forwarding is enabled.
1248 Functional default: enabled if local forwarding is disabled.
1249 disabled if local forwarding is enabled.
1251 accept_ra_defrtr - BOOLEAN
1252 Learn default router in Router Advertisement.
1254 Functional default: enabled if accept_ra is enabled.
1255 disabled if accept_ra is disabled.
1257 accept_ra_from_local - BOOLEAN
1258 Accept RA with source-address that is found on local machine
1259 if the RA is otherwise proper and able to be accepted.
1260 Default is to NOT accept these as it may be an un-intended
1264 enabled if accept_ra_from_local is enabled
1265 on a specific interface.
1266 disabled if accept_ra_from_local is disabled
1267 on a specific interface.
1269 accept_ra_pinfo - BOOLEAN
1270 Learn Prefix Information in Router Advertisement.
1272 Functional default: enabled if accept_ra is enabled.
1273 disabled if accept_ra is disabled.
1275 accept_ra_rt_info_max_plen - INTEGER
1276 Maximum prefix length of Route Information in RA.
1278 Route Information w/ prefix larger than or equal to this
1279 variable shall be ignored.
1281 Functional default: 0 if accept_ra_rtr_pref is enabled.
1282 -1 if accept_ra_rtr_pref is disabled.
1284 accept_ra_rtr_pref - BOOLEAN
1285 Accept Router Preference in RA.
1287 Functional default: enabled if accept_ra is enabled.
1288 disabled if accept_ra is disabled.
1290 accept_redirects - BOOLEAN
1293 Functional default: enabled if local forwarding is disabled.
1294 disabled if local forwarding is enabled.
1296 accept_source_route - INTEGER
1297 Accept source routing (routing extension header).
1299 >= 0: Accept only routing header type 2.
1300 < 0: Do not accept routing header.
1305 Autoconfigure addresses using Prefix Information in Router
1308 Functional default: enabled if accept_ra_pinfo is enabled.
1309 disabled if accept_ra_pinfo is disabled.
1311 dad_transmits - INTEGER
1312 The amount of Duplicate Address Detection probes to send.
1315 forwarding - INTEGER
1316 Configure interface-specific Host/Router behaviour.
1318 Note: It is recommended to have the same setting on all
1319 interfaces; mixed router/host scenarios are rather uncommon.
1321 Possible values are:
1322 0 Forwarding disabled
1323 1 Forwarding enabled
1327 By default, Host behaviour is assumed. This means:
1329 1. IsRouter flag is not set in Neighbour Advertisements.
1330 2. If accept_ra is TRUE (default), transmit Router
1332 3. If accept_ra is TRUE (default), accept Router
1333 Advertisements (and do autoconfiguration).
1334 4. If accept_redirects is TRUE (default), accept Redirects.
1338 If local forwarding is enabled, Router behaviour is assumed.
1339 This means exactly the reverse from the above:
1341 1. IsRouter flag is set in Neighbour Advertisements.
1342 2. Router Solicitations are not sent unless accept_ra is 2.
1343 3. Router Advertisements are ignored unless accept_ra is 2.
1344 4. Redirects are ignored.
1346 Default: 0 (disabled) if global forwarding is disabled (default),
1347 otherwise 1 (enabled).
1350 Default Hop Limit to set.
1354 Default Maximum Transfer Unit
1355 Default: 1280 (IPv6 required minimum)
1357 router_probe_interval - INTEGER
1358 Minimum interval (in seconds) between Router Probing described
1363 router_solicitation_delay - INTEGER
1364 Number of seconds to wait after interface is brought up
1365 before sending Router Solicitations.
1368 router_solicitation_interval - INTEGER
1369 Number of seconds to wait between Router Solicitations.
1372 router_solicitations - INTEGER
1373 Number of Router Solicitations to send until assuming no
1374 routers are present.
1377 use_tempaddr - INTEGER
1378 Preference for Privacy Extensions (RFC3041).
1379 <= 0 : disable Privacy Extensions
1380 == 1 : enable Privacy Extensions, but prefer public
1381 addresses over temporary addresses.
1382 > 1 : enable Privacy Extensions and prefer temporary
1383 addresses over public addresses.
1384 Default: 0 (for most devices)
1385 -1 (for point-to-point devices and loopback devices)
1387 temp_valid_lft - INTEGER
1388 valid lifetime (in seconds) for temporary addresses.
1389 Default: 604800 (7 days)
1391 temp_prefered_lft - INTEGER
1392 Preferred lifetime (in seconds) for temporary addresses.
1393 Default: 86400 (1 day)
1395 max_desync_factor - INTEGER
1396 Maximum value for DESYNC_FACTOR, which is a random value
1397 that ensures that clients don't synchronize with each
1398 other and generate new addresses at exactly the same time.
1399 value is in seconds.
1402 regen_max_retry - INTEGER
1403 Number of attempts before give up attempting to generate
1404 valid temporary addresses.
1407 max_addresses - INTEGER
1408 Maximum number of autoconfigured addresses per interface. Setting
1409 to zero disables the limitation. It is not recommended to set this
1410 value too large (or to zero) because it would be an easy way to
1411 crash the kernel by allowing too many addresses to be created.
1414 disable_ipv6 - BOOLEAN
1415 Disable IPv6 operation. If accept_dad is set to 2, this value
1416 will be dynamically set to TRUE if DAD fails for the link-local
1418 Default: FALSE (enable IPv6 operation)
1420 When this value is changed from 1 to 0 (IPv6 is being enabled),
1421 it will dynamically create a link-local address on the given
1422 interface and start Duplicate Address Detection, if necessary.
1424 When this value is changed from 0 to 1 (IPv6 is being disabled),
1425 it will dynamically delete all address on the given interface.
1427 accept_dad - INTEGER
1428 Whether to accept DAD (Duplicate Address Detection).
1430 1: Enable DAD (default)
1431 2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
1432 link-local address has been found.
1434 force_tllao - BOOLEAN
1435 Enable sending the target link-layer address option even when
1436 responding to a unicast neighbor solicitation.
1439 Quoting from RFC 2461, section 4.4, Target link-layer address:
1441 "The option MUST be included for multicast solicitations in order to
1442 avoid infinite Neighbor Solicitation "recursion" when the peer node
1443 does not have a cache entry to return a Neighbor Advertisements
1444 message. When responding to unicast solicitations, the option can be
1445 omitted since the sender of the solicitation has the correct link-
1446 layer address; otherwise it would not have be able to send the unicast
1447 solicitation in the first place. However, including the link-layer
1448 address in this case adds little overhead and eliminates a potential
1449 race condition where the sender deletes the cached link-layer address
1450 prior to receiving a response to a previous solicitation."
1452 ndisc_notify - BOOLEAN
1453 Define mode for notification of address and device changes.
1454 0 - (default): do nothing
1455 1 - Generate unsolicited neighbour advertisements when device is brought
1456 up or hardware address changes.
1458 mldv1_unsolicited_report_interval - INTEGER
1459 The interval in milliseconds in which the next unsolicited
1460 MLDv1 report retransmit will take place.
1461 Default: 10000 (10 seconds)
1463 mldv2_unsolicited_report_interval - INTEGER
1464 The interval in milliseconds in which the next unsolicited
1465 MLDv2 report retransmit will take place.
1466 Default: 1000 (1 second)
1468 force_mld_version - INTEGER
1469 0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed
1470 1 - Enforce to use MLD version 1
1471 2 - Enforce to use MLD version 2
1473 suppress_frag_ndisc - INTEGER
1474 Control RFC 6980 (Security Implications of IPv6 Fragmentation
1475 with IPv6 Neighbor Discovery) behavior:
1476 1 - (default) discard fragmented neighbor discovery packets
1477 0 - allow fragmented neighbor discovery packets
1479 optimistic_dad - BOOLEAN
1480 Whether to perform Optimistic Duplicate Address Detection (RFC 4429).
1481 0: disabled (default)
1484 use_optimistic - BOOLEAN
1485 If enabled, do not classify optimistic addresses as deprecated during
1486 source address selection. Preferred addresses will still be chosen
1487 before optimistic addresses, subject to other ranking in the source
1488 address selection algorithm.
1489 0: disabled (default)
1494 Limit the maximal rates for sending ICMPv6 packets.
1495 0 to disable any limiting,
1496 otherwise the minimal space between responses in milliseconds.
1501 Pekka Savola <pekkas@netcore.fi>
1502 YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
1505 /proc/sys/net/bridge/* Variables:
1507 bridge-nf-call-arptables - BOOLEAN
1508 1 : pass bridged ARP traffic to arptables' FORWARD chain.
1512 bridge-nf-call-iptables - BOOLEAN
1513 1 : pass bridged IPv4 traffic to iptables' chains.
1517 bridge-nf-call-ip6tables - BOOLEAN
1518 1 : pass bridged IPv6 traffic to ip6tables' chains.
1522 bridge-nf-filter-vlan-tagged - BOOLEAN
1523 1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
1527 bridge-nf-filter-pppoe-tagged - BOOLEAN
1528 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
1532 bridge-nf-pass-vlan-input-dev - BOOLEAN
1533 1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan
1534 interface on the bridge and set the netfilter input device to the vlan.
1535 This allows use of e.g. "iptables -i br0.1" and makes the REDIRECT
1536 target work with vlan-on-top-of-bridge interfaces. When no matching
1537 vlan interface is found, or this switch is off, the input device is
1538 set to the bridge interface.
1539 0: disable bridge netfilter vlan interface lookup.
1542 proc/sys/net/sctp/* Variables:
1544 addip_enable - BOOLEAN
1545 Enable or disable extension of Dynamic Address Reconfiguration
1546 (ADD-IP) functionality specified in RFC5061. This extension provides
1547 the ability to dynamically add and remove new addresses for the SCTP
1550 1: Enable extension.
1552 0: Disable extension.
1556 addip_noauth_enable - BOOLEAN
1557 Dynamic Address Reconfiguration (ADD-IP) requires the use of
1558 authentication to protect the operations of adding or removing new
1559 addresses. This requirement is mandated so that unauthorized hosts
1560 would not be able to hijack associations. However, older
1561 implementations may not have implemented this requirement while
1562 allowing the ADD-IP extension. For reasons of interoperability,
1563 we provide this variable to control the enforcement of the
1564 authentication requirement.
1566 1: Allow ADD-IP extension to be used without authentication. This
1567 should only be set in a closed environment for interoperability
1568 with older implementations.
1570 0: Enforce the authentication requirement
1574 auth_enable - BOOLEAN
1575 Enable or disable Authenticated Chunks extension. This extension
1576 provides the ability to send and receive authenticated chunks and is
1577 required for secure operation of Dynamic Address Reconfiguration
1580 1: Enable this extension.
1581 0: Disable this extension.
1585 prsctp_enable - BOOLEAN
1586 Enable or disable the Partial Reliability extension (RFC3758) which
1587 is used to notify peers that a given DATA should no longer be expected.
1595 The limit of the number of new packets that can be initially sent. It
1596 controls how bursty the generated traffic can be.
1600 association_max_retrans - INTEGER
1601 Set the maximum number for retransmissions that an association can
1602 attempt deciding that the remote end is unreachable. If this value
1603 is exceeded, the association is terminated.
1607 max_init_retransmits - INTEGER
1608 The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
1609 that an association will attempt before declaring the destination
1610 unreachable and terminating.
1614 path_max_retrans - INTEGER
1615 The maximum number of retransmissions that will be attempted on a given
1616 path. Once this threshold is exceeded, the path is considered
1617 unreachable, and new traffic will use a different path when the
1618 association is multihomed.
1622 pf_retrans - INTEGER
1623 The number of retransmissions that will be attempted on a given path
1624 before traffic is redirected to an alternate transport (should one
1625 exist). Note this is distinct from path_max_retrans, as a path that
1626 passes the pf_retrans threshold can still be used. Its only
1627 deprioritized when a transmission path is selected by the stack. This
1628 setting is primarily used to enable fast failover mechanisms without
1629 having to reduce path_max_retrans to a very low value. See:
1630 http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt
1631 for details. Note also that a value of pf_retrans > path_max_retrans
1632 disables this feature
1636 rto_initial - INTEGER
1637 The initial round trip timeout value in milliseconds that will be used
1638 in calculating round trip times. This is the initial time interval
1639 for retransmissions.
1644 The maximum value (in milliseconds) of the round trip timeout. This
1645 is the largest time interval that can elapse between retransmissions.
1650 The minimum value (in milliseconds) of the round trip timeout. This
1651 is the smallest time interval the can elapse between retransmissions.
1655 hb_interval - INTEGER
1656 The interval (in milliseconds) between HEARTBEAT chunks. These chunks
1657 are sent at the specified interval on idle paths to probe the state of
1658 a given path between 2 associations.
1662 sack_timeout - INTEGER
1663 The amount of time (in milliseconds) that the implementation will wait
1668 valid_cookie_life - INTEGER
1669 The default lifetime of the SCTP cookie (in milliseconds). The cookie
1670 is used during association establishment.
1674 cookie_preserve_enable - BOOLEAN
1675 Enable or disable the ability to extend the lifetime of the SCTP cookie
1676 that is used during the establishment phase of SCTP association
1678 1: Enable cookie lifetime extension.
1683 cookie_hmac_alg - STRING
1684 Select the hmac algorithm used when generating the cookie value sent by
1685 a listening sctp socket to a connecting client in the INIT-ACK chunk.
1690 Ability to assign md5 or sha1 as the selected alg is predicated on the
1691 configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and
1692 CONFIG_CRYPTO_SHA1).
1694 Default: Dependent on configuration. MD5 if available, else SHA1 if
1695 available, else none.
1697 rcvbuf_policy - INTEGER
1698 Determines if the receive buffer is attributed to the socket or to
1699 association. SCTP supports the capability to create multiple
1700 associations on a single socket. When using this capability, it is
1701 possible that a single stalled association that's buffering a lot
1702 of data may block other associations from delivering their data by
1703 consuming all of the receive buffer space. To work around this,
1704 the rcvbuf_policy could be set to attribute the receiver buffer space
1705 to each association instead of the socket. This prevents the described
1708 1: rcvbuf space is per association
1709 0: rcvbuf space is per socket
1713 sndbuf_policy - INTEGER
1714 Similar to rcvbuf_policy above, this applies to send buffer space.
1716 1: Send buffer is tracked per association
1717 0: Send buffer is tracked per socket.
1721 sctp_mem - vector of 3 INTEGERs: min, pressure, max
1722 Number of pages allowed for queueing by all SCTP sockets.
1724 min: Below this number of pages SCTP is not bothered about its
1725 memory appetite. When amount of memory allocated by SCTP exceeds
1726 this number, SCTP starts to moderate memory usage.
1728 pressure: This value was introduced to follow format of tcp_mem.
1730 max: Number of pages allowed for queueing by all SCTP sockets.
1732 Default is calculated at boot time from amount of available memory.
1734 sctp_rmem - vector of 3 INTEGERs: min, default, max
1735 Only the first value ("min") is used, "default" and "max" are
1738 min: Minimal size of receive buffer used by SCTP socket.
1739 It is guaranteed to each SCTP socket (but not association) even
1740 under moderate memory pressure.
1744 sctp_wmem - vector of 3 INTEGERs: min, default, max
1745 Currently this tunable has no effect.
1747 addr_scope_policy - INTEGER
1748 Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00
1750 0 - Disable IPv4 address scoping
1751 1 - Enable IPv4 address scoping
1752 2 - Follow draft but allow IPv4 private addresses
1753 3 - Follow draft but allow IPv4 link local addresses
1758 /proc/sys/net/core/*
1759 Please see: Documentation/sysctl/net.txt for descriptions of these entries.
1762 /proc/sys/net/unix/*
1763 max_dgram_qlen - INTEGER
1764 The maximum length of dgram socket receive queue
1771 /proc/sys/net/irda/*
1772 fast_poll_increase FIXME
1773 warn_noreply_time FIXME
1774 discovery_slots FIXME
1777 discovery_timeout FIXME
1778 lap_keepalive_time FIXME
1779 max_noreply_time FIXME
1780 max_tx_data_size FIXME
1782 min_tx_turn_time FIXME