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 hardened 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 fib_multipath_use_neigh - BOOLEAN
67 Use status of existing neighbor entry when determining nexthop for
68 multipath routes. If disabled, neighbor information is not used and
69 packets could be directed to a failed nexthop. Only valid for kernels
70 built with CONFIG_IP_ROUTE_MULTIPATH enabled.
76 fib_multipath_hash_policy - INTEGER
77 Controls which hash policy to use for multipath routes. Only valid
78 for kernels built with CONFIG_IP_ROUTE_MULTIPATH enabled.
83 2 - Layer 3 or inner Layer 3 if present
85 fib_sync_mem - UNSIGNED INTEGER
86 Amount of dirty memory from fib entries that can be backlogged before
87 synchronize_rcu is forced.
88 Default: 512kB Minimum: 64kB Maximum: 64MB
90 ip_forward_update_priority - INTEGER
91 Whether to update SKB priority from "TOS" field in IPv4 header after it
92 is forwarded. The new SKB priority is mapped from TOS field value
93 according to an rt_tos2priority table (see e.g. man tc-prio).
94 Default: 1 (Update priority.)
96 0 - Do not update priority.
99 route/max_size - INTEGER
100 Maximum number of routes allowed in the kernel. Increase
101 this when using large numbers of interfaces and/or routes.
102 From linux kernel 3.6 onwards, this is deprecated for ipv4
103 as route cache is no longer used.
105 neigh/default/gc_thresh1 - INTEGER
106 Minimum number of entries to keep. Garbage collector will not
107 purge entries if there are fewer than this number.
110 neigh/default/gc_thresh2 - INTEGER
111 Threshold when garbage collector becomes more aggressive about
112 purging entries. Entries older than 5 seconds will be cleared
113 when over this number.
116 neigh/default/gc_thresh3 - INTEGER
117 Maximum number of non-PERMANENT neighbor entries allowed. Increase
118 this when using large numbers of interfaces and when communicating
119 with large numbers of directly-connected peers.
122 neigh/default/unres_qlen_bytes - INTEGER
123 The maximum number of bytes which may be used by packets
124 queued for each unresolved address by other network layers.
126 Setting negative value is meaningless and will return error.
127 Default: SK_WMEM_MAX, (same as net.core.wmem_default).
128 Exact value depends on architecture and kernel options,
129 but should be enough to allow queuing 256 packets
132 neigh/default/unres_qlen - INTEGER
133 The maximum number of packets which may be queued for each
134 unresolved address by other network layers.
135 (deprecated in linux 3.3) : use unres_qlen_bytes instead.
136 Prior to linux 3.3, the default value is 3 which may cause
137 unexpected packet loss. The current default value is calculated
138 according to default value of unres_qlen_bytes and true size of
142 mtu_expires - INTEGER
143 Time, in seconds, that cached PMTU information is kept.
145 min_adv_mss - INTEGER
146 The advertised MSS depends on the first hop route MTU, but will
147 never be lower than this setting.
151 ipfrag_high_thresh - LONG INTEGER
152 Maximum memory used to reassemble IP fragments.
154 ipfrag_low_thresh - LONG INTEGER
155 (Obsolete since linux-4.17)
156 Maximum memory used to reassemble IP fragments before the kernel
157 begins to remove incomplete fragment queues to free up resources.
158 The kernel still accepts new fragments for defragmentation.
160 ipfrag_time - INTEGER
161 Time in seconds to keep an IP fragment in memory.
163 ipfrag_max_dist - INTEGER
164 ipfrag_max_dist is a non-negative integer value which defines the
165 maximum "disorder" which is allowed among fragments which share a
166 common IP source address. Note that reordering of packets is
167 not unusual, but if a large number of fragments arrive from a source
168 IP address while a particular fragment queue remains incomplete, it
169 probably indicates that one or more fragments belonging to that queue
170 have been lost. When ipfrag_max_dist is positive, an additional check
171 is done on fragments before they are added to a reassembly queue - if
172 ipfrag_max_dist (or more) fragments have arrived from a particular IP
173 address between additions to any IP fragment queue using that source
174 address, it's presumed that one or more fragments in the queue are
175 lost. The existing fragment queue will be dropped, and a new one
176 started. An ipfrag_max_dist value of zero disables this check.
178 Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
179 result in unnecessarily dropping fragment queues when normal
180 reordering of packets occurs, which could lead to poor application
181 performance. Using a very large value, e.g. 50000, increases the
182 likelihood of incorrectly reassembling IP fragments that originate
183 from different IP datagrams, which could result in data corruption.
188 inet_peer_threshold - INTEGER
189 The approximate size of the storage. Starting from this threshold
190 entries will be thrown aggressively. This threshold also determines
191 entries' time-to-live and time intervals between garbage collection
192 passes. More entries, less time-to-live, less GC interval.
194 inet_peer_minttl - INTEGER
195 Minimum time-to-live of entries. Should be enough to cover fragment
196 time-to-live on the reassembling side. This minimum time-to-live is
197 guaranteed if the pool size is less than inet_peer_threshold.
200 inet_peer_maxttl - INTEGER
201 Maximum time-to-live of entries. Unused entries will expire after
202 this period of time if there is no memory pressure on the pool (i.e.
203 when the number of entries in the pool is very small).
209 Limit of socket listen() backlog, known in userspace as SOMAXCONN.
210 Defaults to 4096. (Was 128 before linux-5.4)
211 See also tcp_max_syn_backlog for additional tuning for TCP sockets.
213 tcp_abort_on_overflow - BOOLEAN
214 If listening service is too slow to accept new connections,
215 reset them. Default state is FALSE. It means that if overflow
216 occurred due to a burst, connection will recover. Enable this
217 option _only_ if you are really sure that listening daemon
218 cannot be tuned to accept connections faster. Enabling this
219 option can harm clients of your server.
221 tcp_adv_win_scale - INTEGER
222 Count buffering overhead as bytes/2^tcp_adv_win_scale
223 (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
225 Possible values are [-31, 31], inclusive.
228 tcp_allowed_congestion_control - STRING
229 Show/set the congestion control choices available to non-privileged
230 processes. The list is a subset of those listed in
231 tcp_available_congestion_control.
232 Default is "reno" and the default setting (tcp_congestion_control).
234 tcp_app_win - INTEGER
235 Reserve max(window/2^tcp_app_win, mss) of window for application
236 buffer. Value 0 is special, it means that nothing is reserved.
239 tcp_autocorking - BOOLEAN
240 Enable TCP auto corking :
241 When applications do consecutive small write()/sendmsg() system calls,
242 we try to coalesce these small writes as much as possible, to lower
243 total amount of sent packets. This is done if at least one prior
244 packet for the flow is waiting in Qdisc queues or device transmit
245 queue. Applications can still use TCP_CORK for optimal behavior
246 when they know how/when to uncork their sockets.
249 tcp_available_congestion_control - STRING
250 Shows the available congestion control choices that are registered.
251 More congestion control algorithms may be available as modules,
254 tcp_base_mss - INTEGER
255 The initial value of search_low to be used by the packetization layer
256 Path MTU discovery (MTU probing). If MTU probing is enabled,
257 this is the initial MSS used by the connection.
259 tcp_mtu_probe_floor - INTEGER
260 If MTU probing is enabled this caps the minimum MSS used for search_low
265 tcp_min_snd_mss - INTEGER
266 TCP SYN and SYNACK messages usually advertise an ADVMSS option,
267 as described in RFC 1122 and RFC 6691.
268 If this ADVMSS option is smaller than tcp_min_snd_mss,
269 it is silently capped to tcp_min_snd_mss.
271 Default : 48 (at least 8 bytes of payload per segment)
273 tcp_congestion_control - STRING
274 Set the congestion control algorithm to be used for new
275 connections. The algorithm "reno" is always available, but
276 additional choices may be available based on kernel configuration.
277 Default is set as part of kernel configuration.
278 For passive connections, the listener congestion control choice
280 [see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ]
283 Allows TCP to send "duplicate" SACKs.
285 tcp_early_retrans - INTEGER
286 Tail loss probe (TLP) converts RTOs occurring due to tail
287 losses into fast recovery (draft-ietf-tcpm-rack). Note that
288 TLP requires RACK to function properly (see tcp_recovery below)
295 Control use of Explicit Congestion Notification (ECN) by TCP.
296 ECN is used only when both ends of the TCP connection indicate
297 support for it. This feature is useful in avoiding losses due
298 to congestion by allowing supporting routers to signal
299 congestion before having to drop packets.
301 0 Disable ECN. Neither initiate nor accept ECN.
302 1 Enable ECN when requested by incoming connections and
303 also request ECN on outgoing connection attempts.
304 2 Enable ECN when requested by incoming connections
305 but do not request ECN on outgoing connections.
308 tcp_ecn_fallback - BOOLEAN
309 If the kernel detects that ECN connection misbehaves, enable fall
310 back to non-ECN. Currently, this knob implements the fallback
311 from RFC3168, section 6.1.1.1., but we reserve that in future,
312 additional detection mechanisms could be implemented under this
313 knob. The value is not used, if tcp_ecn or per route (or congestion
314 control) ECN settings are disabled.
315 Default: 1 (fallback enabled)
318 This is a legacy option, it has no effect anymore.
320 tcp_fin_timeout - INTEGER
321 The length of time an orphaned (no longer referenced by any
322 application) connection will remain in the FIN_WAIT_2 state
323 before it is aborted at the local end. While a perfectly
324 valid "receive only" state for an un-orphaned connection, an
325 orphaned connection in FIN_WAIT_2 state could otherwise wait
326 forever for the remote to close its end of the connection.
331 Enables Forward RTO-Recovery (F-RTO) defined in RFC5682.
332 F-RTO is an enhanced recovery algorithm for TCP retransmission
333 timeouts. It is particularly beneficial in networks where the
334 RTT fluctuates (e.g., wireless). F-RTO is sender-side only
335 modification. It does not require any support from the peer.
337 By default it's enabled with a non-zero value. 0 disables F-RTO.
339 tcp_fwmark_accept - BOOLEAN
340 If set, incoming connections to listening sockets that do not have a
341 socket mark will set the mark of the accepting socket to the fwmark of
342 the incoming SYN packet. This will cause all packets on that connection
343 (starting from the first SYNACK) to be sent with that fwmark. The
344 listening socket's mark is unchanged. Listening sockets that already
345 have a fwmark set via setsockopt(SOL_SOCKET, SO_MARK, ...) are
350 tcp_invalid_ratelimit - INTEGER
351 Limit the maximal rate for sending duplicate acknowledgments
352 in response to incoming TCP packets that are for an existing
353 connection but that are invalid due to any of these reasons:
355 (a) out-of-window sequence number,
356 (b) out-of-window acknowledgment number, or
357 (c) PAWS (Protection Against Wrapped Sequence numbers) check failure
359 This can help mitigate simple "ack loop" DoS attacks, wherein
360 a buggy or malicious middlebox or man-in-the-middle can
361 rewrite TCP header fields in manner that causes each endpoint
362 to think that the other is sending invalid TCP segments, thus
363 causing each side to send an unterminating stream of duplicate
364 acknowledgments for invalid segments.
366 Using 0 disables rate-limiting of dupacks in response to
367 invalid segments; otherwise this value specifies the minimal
368 space between sending such dupacks, in milliseconds.
370 Default: 500 (milliseconds).
372 tcp_keepalive_time - INTEGER
373 How often TCP sends out keepalive messages when keepalive is enabled.
376 tcp_keepalive_probes - INTEGER
377 How many keepalive probes TCP sends out, until it decides that the
378 connection is broken. Default value: 9.
380 tcp_keepalive_intvl - INTEGER
381 How frequently the probes are send out. Multiplied by
382 tcp_keepalive_probes it is time to kill not responding connection,
383 after probes started. Default value: 75sec i.e. connection
384 will be aborted after ~11 minutes of retries.
386 tcp_l3mdev_accept - BOOLEAN
387 Enables child sockets to inherit the L3 master device index.
388 Enabling this option allows a "global" listen socket to work
389 across L3 master domains (e.g., VRFs) with connected sockets
390 derived from the listen socket to be bound to the L3 domain in
391 which the packets originated. Only valid when the kernel was
392 compiled with CONFIG_NET_L3_MASTER_DEV.
393 Default: 0 (disabled)
395 tcp_low_latency - BOOLEAN
396 This is a legacy option, it has no effect anymore.
398 tcp_max_orphans - INTEGER
399 Maximal number of TCP sockets not attached to any user file handle,
400 held by system. If this number is exceeded orphaned connections are
401 reset immediately and warning is printed. This limit exists
402 only to prevent simple DoS attacks, you _must_ not rely on this
403 or lower the limit artificially, but rather increase it
404 (probably, after increasing installed memory),
405 if network conditions require more than default value,
406 and tune network services to linger and kill such states
407 more aggressively. Let me to remind again: each orphan eats
408 up to ~64K of unswappable memory.
410 tcp_max_syn_backlog - INTEGER
411 Maximal number of remembered connection requests (SYN_RECV),
412 which have not received an acknowledgment from connecting client.
413 This is a per-listener limit.
414 The minimal value is 128 for low memory machines, and it will
415 increase in proportion to the memory of machine.
416 If server suffers from overload, try increasing this number.
417 Remember to also check /proc/sys/net/core/somaxconn
418 A SYN_RECV request socket consumes about 304 bytes of memory.
420 tcp_max_tw_buckets - INTEGER
421 Maximal number of timewait sockets held by system simultaneously.
422 If this number is exceeded time-wait socket is immediately destroyed
423 and warning is printed. This limit exists only to prevent
424 simple DoS attacks, you _must_ not lower the limit artificially,
425 but rather increase it (probably, after increasing installed memory),
426 if network conditions require more than default value.
428 tcp_mem - vector of 3 INTEGERs: min, pressure, max
429 min: below this number of pages TCP is not bothered about its
432 pressure: when amount of memory allocated by TCP exceeds this number
433 of pages, TCP moderates its memory consumption and enters memory
434 pressure mode, which is exited when memory consumption falls
437 max: number of pages allowed for queueing by all TCP sockets.
439 Defaults are calculated at boot time from amount of available
442 tcp_min_rtt_wlen - INTEGER
443 The window length of the windowed min filter to track the minimum RTT.
444 A shorter window lets a flow more quickly pick up new (higher)
445 minimum RTT when it is moved to a longer path (e.g., due to traffic
446 engineering). A longer window makes the filter more resistant to RTT
447 inflations such as transient congestion. The unit is seconds.
448 Possible values: 0 - 86400 (1 day)
451 tcp_moderate_rcvbuf - BOOLEAN
452 If set, TCP performs receive buffer auto-tuning, attempting to
453 automatically size the buffer (no greater than tcp_rmem[2]) to
454 match the size required by the path for full throughput. Enabled by
457 tcp_mtu_probing - INTEGER
458 Controls TCP Packetization-Layer Path MTU Discovery. Takes three
461 1 - Disabled by default, enabled when an ICMP black hole detected
462 2 - Always enabled, use initial MSS of tcp_base_mss.
464 tcp_probe_interval - UNSIGNED INTEGER
465 Controls how often to start TCP Packetization-Layer Path MTU
466 Discovery reprobe. The default is reprobing every 10 minutes as
469 tcp_probe_threshold - INTEGER
470 Controls when TCP Packetization-Layer Path MTU Discovery probing
471 will stop in respect to the width of search range in bytes. Default
474 tcp_no_metrics_save - BOOLEAN
475 By default, TCP saves various connection metrics in the route cache
476 when the connection closes, so that connections established in the
477 near future can use these to set initial conditions. Usually, this
478 increases overall performance, but may sometimes cause performance
479 degradation. If set, TCP will not cache metrics on closing
482 tcp_orphan_retries - INTEGER
483 This value influences the timeout of a locally closed TCP connection,
484 when RTO retransmissions remain unacknowledged.
485 See tcp_retries2 for more details.
487 The default value is 8.
488 If your machine is a loaded WEB server,
489 you should think about lowering this value, such sockets
490 may consume significant resources. Cf. tcp_max_orphans.
492 tcp_recovery - INTEGER
493 This value is a bitmap to enable various experimental loss recovery
496 RACK: 0x1 enables the RACK loss detection for fast detection of lost
497 retransmissions and tail drops. It also subsumes and disables
498 RFC6675 recovery for SACK connections.
499 RACK: 0x2 makes RACK's reordering window static (min_rtt/4).
500 RACK: 0x4 disables RACK's DUPACK threshold heuristic
504 tcp_reordering - INTEGER
505 Initial reordering level of packets in a TCP stream.
506 TCP stack can then dynamically adjust flow reordering level
507 between this initial value and tcp_max_reordering
510 tcp_max_reordering - INTEGER
511 Maximal reordering level of packets in a TCP stream.
512 300 is a fairly conservative value, but you might increase it
513 if paths are using per packet load balancing (like bonding rr mode)
516 tcp_retrans_collapse - BOOLEAN
517 Bug-to-bug compatibility with some broken printers.
518 On retransmit try to send bigger packets to work around bugs in
521 tcp_retries1 - INTEGER
522 This value influences the time, after which TCP decides, that
523 something is wrong due to unacknowledged RTO retransmissions,
524 and reports this suspicion to the network layer.
525 See tcp_retries2 for more details.
527 RFC 1122 recommends at least 3 retransmissions, which is the
530 tcp_retries2 - INTEGER
531 This value influences the timeout of an alive TCP connection,
532 when RTO retransmissions remain unacknowledged.
533 Given a value of N, a hypothetical TCP connection following
534 exponential backoff with an initial RTO of TCP_RTO_MIN would
535 retransmit N times before killing the connection at the (N+1)th RTO.
537 The default value of 15 yields a hypothetical timeout of 924.6
538 seconds and is a lower bound for the effective timeout.
539 TCP will effectively time out at the first RTO which exceeds the
540 hypothetical timeout.
542 RFC 1122 recommends at least 100 seconds for the timeout,
543 which corresponds to a value of at least 8.
545 tcp_rfc1337 - BOOLEAN
546 If set, the TCP stack behaves conforming to RFC1337. If unset,
547 we are not conforming to RFC, but prevent TCP TIME_WAIT
551 tcp_rmem - vector of 3 INTEGERs: min, default, max
552 min: Minimal size of receive buffer used by TCP sockets.
553 It is guaranteed to each TCP socket, even under moderate memory
557 default: initial size of receive buffer used by TCP sockets.
558 This value overrides net.core.rmem_default used by other protocols.
559 Default: 87380 bytes. This value results in window of 65535 with
560 default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
561 less for default tcp_app_win. See below about these variables.
563 max: maximal size of receive buffer allowed for automatically
564 selected receiver buffers for TCP socket. This value does not override
565 net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables
566 automatic tuning of that socket's receive buffer size, in which
567 case this value is ignored.
568 Default: between 87380B and 6MB, depending on RAM size.
571 Enable select acknowledgments (SACKS).
573 tcp_comp_sack_delay_ns - LONG INTEGER
574 TCP tries to reduce number of SACK sent, using a timer
575 based on 5% of SRTT, capped by this sysctl, in nano seconds.
576 The default is 1ms, based on TSO autosizing period.
578 Default : 1,000,000 ns (1 ms)
580 tcp_comp_sack_nr - INTEGER
581 Max number of SACK that can be compressed.
582 Using 0 disables SACK compression.
586 tcp_slow_start_after_idle - BOOLEAN
587 If set, provide RFC2861 behavior and time out the congestion
588 window after an idle period. An idle period is defined at
589 the current RTO. If unset, the congestion window will not
590 be timed out after an idle period.
594 Use the Host requirements interpretation of the TCP urgent pointer field.
595 Most hosts use the older BSD interpretation, so if you turn this on
596 Linux might not communicate correctly with them.
599 tcp_synack_retries - INTEGER
600 Number of times SYNACKs for a passive TCP connection attempt will
601 be retransmitted. Should not be higher than 255. Default value
602 is 5, which corresponds to 31seconds till the last retransmission
603 with the current initial RTO of 1second. With this the final timeout
604 for a passive TCP connection will happen after 63seconds.
606 tcp_syncookies - INTEGER
607 Only valid when the kernel was compiled with CONFIG_SYN_COOKIES
608 Send out syncookies when the syn backlog queue of a socket
609 overflows. This is to prevent against the common 'SYN flood attack'
612 Note, that syncookies is fallback facility.
613 It MUST NOT be used to help highly loaded servers to stand
614 against legal connection rate. If you see SYN flood warnings
615 in your logs, but investigation shows that they occur
616 because of overload with legal connections, you should tune
617 another parameters until this warning disappear.
618 See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
620 syncookies seriously violate TCP protocol, do not allow
621 to use TCP extensions, can result in serious degradation
622 of some services (f.e. SMTP relaying), visible not by you,
623 but your clients and relays, contacting you. While you see
624 SYN flood warnings in logs not being really flooded, your server
625 is seriously misconfigured.
627 If you want to test which effects syncookies have to your
628 network connections you can set this knob to 2 to enable
629 unconditionally generation of syncookies.
631 tcp_fastopen - INTEGER
632 Enable TCP Fast Open (RFC7413) to send and accept data in the opening
635 The client support is enabled by flag 0x1 (on by default). The client
636 then must use sendmsg() or sendto() with the MSG_FASTOPEN flag,
637 rather than connect() to send data in SYN.
639 The server support is enabled by flag 0x2 (off by default). Then
640 either enable for all listeners with another flag (0x400) or
641 enable individual listeners via TCP_FASTOPEN socket option with
642 the option value being the length of the syn-data backlog.
644 The values (bitmap) are
645 0x1: (client) enables sending data in the opening SYN on the client.
646 0x2: (server) enables the server support, i.e., allowing data in
647 a SYN packet to be accepted and passed to the
648 application before 3-way handshake finishes.
649 0x4: (client) send data in the opening SYN regardless of cookie
650 availability and without a cookie option.
651 0x200: (server) accept data-in-SYN w/o any cookie option present.
652 0x400: (server) enable all listeners to support Fast Open by
653 default without explicit TCP_FASTOPEN socket option.
657 Note that that additional client or server features are only
658 effective if the basic support (0x1 and 0x2) are enabled respectively.
660 tcp_fastopen_blackhole_timeout_sec - INTEGER
661 Initial time period in second to disable Fastopen on active TCP sockets
662 when a TFO firewall blackhole issue happens.
663 This time period will grow exponentially when more blackhole issues
664 get detected right after Fastopen is re-enabled and will reset to
665 initial value when the blackhole issue goes away.
666 0 to disable the blackhole detection.
667 By default, it is set to 1hr.
669 tcp_fastopen_key - list of comma separated 32-digit hexadecimal INTEGERs
670 The list consists of a primary key and an optional backup key. The
671 primary key is used for both creating and validating cookies, while the
672 optional backup key is only used for validating cookies. The purpose of
673 the backup key is to maximize TFO validation when keys are rotated.
675 A randomly chosen primary key may be configured by the kernel if
676 the tcp_fastopen sysctl is set to 0x400 (see above), or if the
677 TCP_FASTOPEN setsockopt() optname is set and a key has not been
678 previously configured via sysctl. If keys are configured via
679 setsockopt() by using the TCP_FASTOPEN_KEY optname, then those
680 per-socket keys will be used instead of any keys that are specified via
683 A key is specified as 4 8-digit hexadecimal integers which are separated
684 by a '-' as: xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx. Leading zeros may be
685 omitted. A primary and a backup key may be specified by separating them
686 by a comma. If only one key is specified, it becomes the primary key and
687 any previously configured backup keys are removed.
689 tcp_syn_retries - INTEGER
690 Number of times initial SYNs for an active TCP connection attempt
691 will be retransmitted. Should not be higher than 127. Default value
692 is 6, which corresponds to 63seconds till the last retransmission
693 with the current initial RTO of 1second. With this the final timeout
694 for an active TCP connection attempt will happen after 127seconds.
696 tcp_timestamps - INTEGER
697 Enable timestamps as defined in RFC1323.
699 1: Enable timestamps as defined in RFC1323 and use random offset for
700 each connection rather than only using the current time.
701 2: Like 1, but without random offsets.
704 tcp_min_tso_segs - INTEGER
705 Minimal number of segments per TSO frame.
706 Since linux-3.12, TCP does an automatic sizing of TSO frames,
707 depending on flow rate, instead of filling 64Kbytes packets.
708 For specific usages, it's possible to force TCP to build big
709 TSO frames. Note that TCP stack might split too big TSO packets
710 if available window is too small.
713 tcp_pacing_ss_ratio - INTEGER
714 sk->sk_pacing_rate is set by TCP stack using a ratio applied
715 to current rate. (current_rate = cwnd * mss / srtt)
716 If TCP is in slow start, tcp_pacing_ss_ratio is applied
717 to let TCP probe for bigger speeds, assuming cwnd can be
718 doubled every other RTT.
721 tcp_pacing_ca_ratio - INTEGER
722 sk->sk_pacing_rate is set by TCP stack using a ratio applied
723 to current rate. (current_rate = cwnd * mss / srtt)
724 If TCP is in congestion avoidance phase, tcp_pacing_ca_ratio
725 is applied to conservatively probe for bigger throughput.
728 tcp_tso_win_divisor - INTEGER
729 This allows control over what percentage of the congestion window
730 can be consumed by a single TSO frame.
731 The setting of this parameter is a choice between burstiness and
732 building larger TSO frames.
735 tcp_tw_reuse - INTEGER
736 Enable reuse of TIME-WAIT sockets for new connections when it is
737 safe from protocol viewpoint.
740 2 - enable for loopback traffic only
741 It should not be changed without advice/request of technical
745 tcp_window_scaling - BOOLEAN
746 Enable window scaling as defined in RFC1323.
748 tcp_wmem - vector of 3 INTEGERs: min, default, max
749 min: Amount of memory reserved for send buffers for TCP sockets.
750 Each TCP socket has rights to use it due to fact of its birth.
753 default: initial size of send buffer used by TCP sockets. This
754 value overrides net.core.wmem_default used by other protocols.
755 It is usually lower than net.core.wmem_default.
758 max: Maximal amount of memory allowed for automatically tuned
759 send buffers for TCP sockets. This value does not override
760 net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables
761 automatic tuning of that socket's send buffer size, in which case
762 this value is ignored.
763 Default: between 64K and 4MB, depending on RAM size.
765 tcp_notsent_lowat - UNSIGNED INTEGER
766 A TCP socket can control the amount of unsent bytes in its write queue,
767 thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll()
768 reports POLLOUT events if the amount of unsent bytes is below a per
769 socket value, and if the write queue is not full. sendmsg() will
770 also not add new buffers if the limit is hit.
772 This global variable controls the amount of unsent data for
773 sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change
774 to the global variable has immediate effect.
776 Default: UINT_MAX (0xFFFFFFFF)
778 tcp_workaround_signed_windows - BOOLEAN
779 If set, assume no receipt of a window scaling option means the
780 remote TCP is broken and treats the window as a signed quantity.
781 If unset, assume the remote TCP is not broken even if we do
782 not receive a window scaling option from them.
785 tcp_thin_linear_timeouts - BOOLEAN
786 Enable dynamic triggering of linear timeouts for thin streams.
787 If set, a check is performed upon retransmission by timeout to
788 determine if the stream is thin (less than 4 packets in flight).
789 As long as the stream is found to be thin, up to 6 linear
790 timeouts may be performed before exponential backoff mode is
791 initiated. This improves retransmission latency for
792 non-aggressive thin streams, often found to be time-dependent.
793 For more information on thin streams, see
794 Documentation/networking/tcp-thin.txt
797 tcp_limit_output_bytes - INTEGER
798 Controls TCP Small Queue limit per tcp socket.
799 TCP bulk sender tends to increase packets in flight until it
800 gets losses notifications. With SNDBUF autotuning, this can
801 result in a large amount of packets queued on the local machine
802 (e.g.: qdiscs, CPU backlog, or device) hurting latency of other
803 flows, for typical pfifo_fast qdiscs. tcp_limit_output_bytes
804 limits the number of bytes on qdisc or device to reduce artificial
805 RTT/cwnd and reduce bufferbloat.
806 Default: 1048576 (16 * 65536)
808 tcp_challenge_ack_limit - INTEGER
809 Limits number of Challenge ACK sent per second, as recommended
810 in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
813 tcp_rx_skb_cache - BOOLEAN
814 Controls a per TCP socket cache of one skb, that might help
815 performance of some workloads. This might be dangerous
816 on systems with a lot of TCP sockets, since it increases
819 Default: 0 (disabled)
823 udp_l3mdev_accept - BOOLEAN
824 Enabling this option allows a "global" bound socket to work
825 across L3 master domains (e.g., VRFs) with packets capable of
826 being received regardless of the L3 domain in which they
827 originated. Only valid when the kernel was compiled with
828 CONFIG_NET_L3_MASTER_DEV.
829 Default: 0 (disabled)
831 udp_mem - vector of 3 INTEGERs: min, pressure, max
832 Number of pages allowed for queueing by all UDP sockets.
834 min: Below this number of pages UDP is not bothered about its
835 memory appetite. When amount of memory allocated by UDP exceeds
836 this number, UDP starts to moderate memory usage.
838 pressure: This value was introduced to follow format of tcp_mem.
840 max: Number of pages allowed for queueing by all UDP sockets.
842 Default is calculated at boot time from amount of available memory.
844 udp_rmem_min - INTEGER
845 Minimal size of receive buffer used by UDP sockets in moderation.
846 Each UDP socket is able to use the size for receiving data, even if
847 total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
850 udp_wmem_min - INTEGER
851 Minimal size of send buffer used by UDP sockets in moderation.
852 Each UDP socket is able to use the size for sending data, even if
853 total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
858 raw_l3mdev_accept - BOOLEAN
859 Enabling this option allows a "global" bound socket to work
860 across L3 master domains (e.g., VRFs) with packets capable of
861 being received regardless of the L3 domain in which they
862 originated. Only valid when the kernel was compiled with
863 CONFIG_NET_L3_MASTER_DEV.
868 cipso_cache_enable - BOOLEAN
869 If set, enable additions to and lookups from the CIPSO label mapping
870 cache. If unset, additions are ignored and lookups always result in a
871 miss. However, regardless of the setting the cache is still
872 invalidated when required when means you can safely toggle this on and
873 off and the cache will always be "safe".
876 cipso_cache_bucket_size - INTEGER
877 The CIPSO label cache consists of a fixed size hash table with each
878 hash bucket containing a number of cache entries. This variable limits
879 the number of entries in each hash bucket; the larger the value the
880 more CIPSO label mappings that can be cached. When the number of
881 entries in a given hash bucket reaches this limit adding new entries
882 causes the oldest entry in the bucket to be removed to make room.
885 cipso_rbm_optfmt - BOOLEAN
886 Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
887 the CIPSO draft specification (see Documentation/netlabel for details).
888 This means that when set the CIPSO tag will be padded with empty
889 categories in order to make the packet data 32-bit aligned.
892 cipso_rbm_structvalid - BOOLEAN
893 If set, do a very strict check of the CIPSO option when
894 ip_options_compile() is called. If unset, relax the checks done during
895 ip_options_compile(). Either way is "safe" as errors are caught else
896 where in the CIPSO processing code but setting this to 0 (False) should
897 result in less work (i.e. it should be faster) but could cause problems
898 with other implementations that require strict checking.
903 ip_local_port_range - 2 INTEGERS
904 Defines the local port range that is used by TCP and UDP to
905 choose the local port. The first number is the first, the
906 second the last local port number.
907 If possible, it is better these numbers have different parity
908 (one even and one odd value).
909 Must be greater than or equal to ip_unprivileged_port_start.
910 The default values are 32768 and 60999 respectively.
912 ip_local_reserved_ports - list of comma separated ranges
913 Specify the ports which are reserved for known third-party
914 applications. These ports will not be used by automatic port
915 assignments (e.g. when calling connect() or bind() with port
916 number 0). Explicit port allocation behavior is unchanged.
918 The format used for both input and output is a comma separated
919 list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and
920 10). Writing to the file will clear all previously reserved
921 ports and update the current list with the one given in the
924 Note that ip_local_port_range and ip_local_reserved_ports
925 settings are independent and both are considered by the kernel
926 when determining which ports are available for automatic port
929 You can reserve ports which are not in the current
930 ip_local_port_range, e.g.:
932 $ cat /proc/sys/net/ipv4/ip_local_port_range
934 $ cat /proc/sys/net/ipv4/ip_local_reserved_ports
937 although this is redundant. However such a setting is useful
938 if later the port range is changed to a value that will
939 include the reserved ports.
943 ip_unprivileged_port_start - INTEGER
944 This is a per-namespace sysctl. It defines the first
945 unprivileged port in the network namespace. Privileged ports
946 require root or CAP_NET_BIND_SERVICE in order to bind to them.
947 To disable all privileged ports, set this to 0. They must not
948 overlap with the ip_local_port_range.
952 ip_nonlocal_bind - BOOLEAN
953 If set, allows processes to bind() to non-local IP addresses,
954 which can be quite useful - but may break some applications.
958 If set non-zero, enables support for dynamic addresses.
959 If set to a non-zero value larger than 1, a kernel log
960 message will be printed when dynamic address rewriting
964 ip_early_demux - BOOLEAN
965 Optimize input packet processing down to one demux for
966 certain kinds of local sockets. Currently we only do this
967 for established TCP and connected UDP sockets.
969 It may add an additional cost for pure routing workloads that
970 reduces overall throughput, in such case you should disable it.
973 tcp_early_demux - BOOLEAN
974 Enable early demux for established TCP sockets.
977 udp_early_demux - BOOLEAN
978 Enable early demux for connected UDP sockets. Disable this if
979 your system could experience more unconnected load.
982 icmp_echo_ignore_all - BOOLEAN
983 If set non-zero, then the kernel will ignore all ICMP ECHO
987 icmp_echo_ignore_broadcasts - BOOLEAN
988 If set non-zero, then the kernel will ignore all ICMP ECHO and
989 TIMESTAMP requests sent to it via broadcast/multicast.
992 icmp_ratelimit - INTEGER
993 Limit the maximal rates for sending ICMP packets whose type matches
994 icmp_ratemask (see below) to specific targets.
995 0 to disable any limiting,
996 otherwise the minimal space between responses in milliseconds.
997 Note that another sysctl, icmp_msgs_per_sec limits the number
998 of ICMP packets sent on all targets.
1001 icmp_msgs_per_sec - INTEGER
1002 Limit maximal number of ICMP packets sent per second from this host.
1003 Only messages whose type matches icmp_ratemask (see below) are
1004 controlled by this limit.
1007 icmp_msgs_burst - INTEGER
1008 icmp_msgs_per_sec controls number of ICMP packets sent per second,
1009 while icmp_msgs_burst controls the burst size of these packets.
1012 icmp_ratemask - INTEGER
1013 Mask made of ICMP types for which rates are being limited.
1014 Significant bits: IHGFEDCBA9876543210
1015 Default mask: 0000001100000011000 (6168)
1017 Bit definitions (see include/linux/icmp.h):
1019 3 Destination Unreachable *
1024 C Parameter Problem *
1029 H Address Mask Request
1030 I Address Mask Reply
1032 * These are rate limited by default (see default mask above)
1034 icmp_ignore_bogus_error_responses - BOOLEAN
1035 Some routers violate RFC1122 by sending bogus responses to broadcast
1036 frames. Such violations are normally logged via a kernel warning.
1037 If this is set to TRUE, the kernel will not give such warnings, which
1038 will avoid log file clutter.
1041 icmp_errors_use_inbound_ifaddr - BOOLEAN
1043 If zero, icmp error messages are sent with the primary address of
1044 the exiting interface.
1046 If non-zero, the message will be sent with the primary address of
1047 the interface that received the packet that caused the icmp error.
1048 This is the behaviour network many administrators will expect from
1049 a router. And it can make debugging complicated network layouts
1052 Note that if no primary address exists for the interface selected,
1053 then the primary address of the first non-loopback interface that
1054 has one will be used regardless of this setting.
1058 igmp_max_memberships - INTEGER
1059 Change the maximum number of multicast groups we can subscribe to.
1062 Theoretical maximum value is bounded by having to send a membership
1063 report in a single datagram (i.e. the report can't span multiple
1064 datagrams, or risk confusing the switch and leaving groups you don't
1067 The number of supported groups 'M' is bounded by the number of group
1068 report entries you can fit into a single datagram of 65535 bytes.
1070 M = 65536-sizeof (ip header)/(sizeof(Group record))
1072 Group records are variable length, with a minimum of 12 bytes.
1073 So net.ipv4.igmp_max_memberships should not be set higher than:
1075 (65536-24) / 12 = 5459
1077 The value 5459 assumes no IP header options, so in practice
1078 this number may be lower.
1080 igmp_max_msf - INTEGER
1081 Maximum number of addresses allowed in the source filter list for a
1086 Controls the IGMP query robustness variable (see RFC2236 8.1).
1087 Default: 2 (as specified by RFC2236 8.1)
1088 Minimum: 1 (as specified by RFC6636 4.5)
1090 force_igmp_version - INTEGER
1091 0 - (default) No enforcement of a IGMP version, IGMPv1/v2 fallback
1092 allowed. Will back to IGMPv3 mode again if all IGMPv1/v2 Querier
1093 Present timer expires.
1094 1 - Enforce to use IGMP version 1. Will also reply IGMPv1 report if
1095 receive IGMPv2/v3 query.
1096 2 - Enforce to use IGMP version 2. Will fallback to IGMPv1 if receive
1097 IGMPv1 query message. Will reply report if receive IGMPv3 query.
1098 3 - Enforce to use IGMP version 3. The same react with default 0.
1100 Note: this is not the same with force_mld_version because IGMPv3 RFC3376
1101 Security Considerations does not have clear description that we could
1102 ignore other version messages completely as MLDv2 RFC3810. So make
1103 this value as default 0 is recommended.
1105 conf/interface/* changes special settings per interface (where
1106 "interface" is the name of your network interface)
1108 conf/all/* is special, changes the settings for all interfaces
1110 log_martians - BOOLEAN
1111 Log packets with impossible addresses to kernel log.
1112 log_martians for the interface will be enabled if at least one of
1113 conf/{all,interface}/log_martians is set to TRUE,
1114 it will be disabled otherwise
1116 accept_redirects - BOOLEAN
1117 Accept ICMP redirect messages.
1118 accept_redirects for the interface will be enabled if:
1119 - both conf/{all,interface}/accept_redirects are TRUE in the case
1120 forwarding for the interface is enabled
1122 - at least one of conf/{all,interface}/accept_redirects is TRUE in the
1123 case forwarding for the interface is disabled
1124 accept_redirects for the interface will be disabled otherwise
1128 forwarding - BOOLEAN
1129 Enable IP forwarding on this interface. This controls whether packets
1130 received _on_ this interface can be forwarded.
1132 mc_forwarding - BOOLEAN
1133 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
1134 and a multicast routing daemon is required.
1135 conf/all/mc_forwarding must also be set to TRUE to enable multicast
1136 routing for the interface
1139 Integer value used to differentiate the devices by the medium they
1140 are attached to. Two devices can have different id values when
1141 the broadcast packets are received only on one of them.
1142 The default value 0 means that the device is the only interface
1143 to its medium, value of -1 means that medium is not known.
1145 Currently, it is used to change the proxy_arp behavior:
1146 the proxy_arp feature is enabled for packets forwarded between
1147 two devices attached to different media.
1151 proxy_arp for the interface will be enabled if at least one of
1152 conf/{all,interface}/proxy_arp is set to TRUE,
1153 it will be disabled otherwise
1155 proxy_arp_pvlan - BOOLEAN
1156 Private VLAN proxy arp.
1157 Basically allow proxy arp replies back to the same interface
1158 (from which the ARP request/solicitation was received).
1160 This is done to support (ethernet) switch features, like RFC
1161 3069, where the individual ports are NOT allowed to
1162 communicate with each other, but they are allowed to talk to
1163 the upstream router. As described in RFC 3069, it is possible
1164 to allow these hosts to communicate through the upstream
1165 router by proxy_arp'ing. Don't need to be used together with
1168 This technology is known by different names:
1169 In RFC 3069 it is called VLAN Aggregation.
1170 Cisco and Allied Telesyn call it Private VLAN.
1171 Hewlett-Packard call it Source-Port filtering or port-isolation.
1172 Ericsson call it MAC-Forced Forwarding (RFC Draft).
1174 shared_media - BOOLEAN
1175 Send(router) or accept(host) RFC1620 shared media redirects.
1176 Overrides secure_redirects.
1177 shared_media for the interface will be enabled if at least one of
1178 conf/{all,interface}/shared_media is set to TRUE,
1179 it will be disabled otherwise
1182 secure_redirects - BOOLEAN
1183 Accept ICMP redirect messages only to gateways listed in the
1184 interface's current gateway list. Even if disabled, RFC1122 redirect
1186 Overridden by shared_media.
1187 secure_redirects for the interface will be enabled if at least one of
1188 conf/{all,interface}/secure_redirects is set to TRUE,
1189 it will be disabled otherwise
1192 send_redirects - BOOLEAN
1193 Send redirects, if router.
1194 send_redirects for the interface will be enabled if at least one of
1195 conf/{all,interface}/send_redirects is set to TRUE,
1196 it will be disabled otherwise
1199 bootp_relay - BOOLEAN
1200 Accept packets with source address 0.b.c.d destined
1201 not to this host as local ones. It is supposed, that
1202 BOOTP relay daemon will catch and forward such packets.
1203 conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
1206 Not Implemented Yet.
1208 accept_source_route - BOOLEAN
1209 Accept packets with SRR option.
1210 conf/all/accept_source_route must also be set to TRUE to accept packets
1211 with SRR option on the interface
1212 default TRUE (router)
1215 accept_local - BOOLEAN
1216 Accept packets with local source addresses. In combination with
1217 suitable routing, this can be used to direct packets between two
1218 local interfaces over the wire and have them accepted properly.
1221 route_localnet - BOOLEAN
1222 Do not consider loopback addresses as martian source or destination
1223 while routing. This enables the use of 127/8 for local routing purposes.
1227 0 - No source validation.
1228 1 - Strict mode as defined in RFC3704 Strict Reverse Path
1229 Each incoming packet is tested against the FIB and if the interface
1230 is not the best reverse path the packet check will fail.
1231 By default failed packets are discarded.
1232 2 - Loose mode as defined in RFC3704 Loose Reverse Path
1233 Each incoming packet's source address is also tested against the FIB
1234 and if the source address is not reachable via any interface
1235 the packet check will fail.
1237 Current recommended practice in RFC3704 is to enable strict mode
1238 to prevent IP spoofing from DDos attacks. If using asymmetric routing
1239 or other complicated routing, then loose mode is recommended.
1241 The max value from conf/{all,interface}/rp_filter is used
1242 when doing source validation on the {interface}.
1244 Default value is 0. Note that some distributions enable it
1247 arp_filter - BOOLEAN
1248 1 - Allows you to have multiple network interfaces on the same
1249 subnet, and have the ARPs for each interface be answered
1250 based on whether or not the kernel would route a packet from
1251 the ARP'd IP out that interface (therefore you must use source
1252 based routing for this to work). In other words it allows control
1253 of which cards (usually 1) will respond to an arp request.
1255 0 - (default) The kernel can respond to arp requests with addresses
1256 from other interfaces. This may seem wrong but it usually makes
1257 sense, because it increases the chance of successful communication.
1258 IP addresses are owned by the complete host on Linux, not by
1259 particular interfaces. Only for more complex setups like load-
1260 balancing, does this behaviour cause problems.
1262 arp_filter for the interface will be enabled if at least one of
1263 conf/{all,interface}/arp_filter is set to TRUE,
1264 it will be disabled otherwise
1266 arp_announce - INTEGER
1267 Define different restriction levels for announcing the local
1268 source IP address from IP packets in ARP requests sent on
1270 0 - (default) Use any local address, configured on any interface
1271 1 - Try to avoid local addresses that are not in the target's
1272 subnet for this interface. This mode is useful when target
1273 hosts reachable via this interface require the source IP
1274 address in ARP requests to be part of their logical network
1275 configured on the receiving interface. When we generate the
1276 request we will check all our subnets that include the
1277 target IP and will preserve the source address if it is from
1278 such subnet. If there is no such subnet we select source
1279 address according to the rules for level 2.
1280 2 - Always use the best local address for this target.
1281 In this mode we ignore the source address in the IP packet
1282 and try to select local address that we prefer for talks with
1283 the target host. Such local address is selected by looking
1284 for primary IP addresses on all our subnets on the outgoing
1285 interface that include the target IP address. If no suitable
1286 local address is found we select the first local address
1287 we have on the outgoing interface or on all other interfaces,
1288 with the hope we will receive reply for our request and
1289 even sometimes no matter the source IP address we announce.
1291 The max value from conf/{all,interface}/arp_announce is used.
1293 Increasing the restriction level gives more chance for
1294 receiving answer from the resolved target while decreasing
1295 the level announces more valid sender's information.
1297 arp_ignore - INTEGER
1298 Define different modes for sending replies in response to
1299 received ARP requests that resolve local target IP addresses:
1300 0 - (default): reply for any local target IP address, configured
1302 1 - reply only if the target IP address is local address
1303 configured on the incoming interface
1304 2 - reply only if the target IP address is local address
1305 configured on the incoming interface and both with the
1306 sender's IP address are part from same subnet on this interface
1307 3 - do not reply for local addresses configured with scope host,
1308 only resolutions for global and link addresses are replied
1310 8 - do not reply for all local addresses
1312 The max value from conf/{all,interface}/arp_ignore is used
1313 when ARP request is received on the {interface}
1315 arp_notify - BOOLEAN
1316 Define mode for notification of address and device changes.
1317 0 - (default): do nothing
1318 1 - Generate gratuitous arp requests when device is brought up
1319 or hardware address changes.
1321 arp_accept - BOOLEAN
1322 Define behavior for gratuitous ARP frames who's IP is not
1323 already present in the ARP table:
1324 0 - don't create new entries in the ARP table
1325 1 - create new entries in the ARP table
1327 Both replies and requests type gratuitous arp will trigger the
1328 ARP table to be updated, if this setting is on.
1330 If the ARP table already contains the IP address of the
1331 gratuitous arp frame, the arp table will be updated regardless
1332 if this setting is on or off.
1334 mcast_solicit - INTEGER
1335 The maximum number of multicast probes in INCOMPLETE state,
1336 when the associated hardware address is unknown. Defaults
1339 ucast_solicit - INTEGER
1340 The maximum number of unicast probes in PROBE state, when
1341 the hardware address is being reconfirmed. Defaults to 3.
1343 app_solicit - INTEGER
1344 The maximum number of probes to send to the user space ARP daemon
1345 via netlink before dropping back to multicast probes (see
1346 mcast_resolicit). Defaults to 0.
1348 mcast_resolicit - INTEGER
1349 The maximum number of multicast probes after unicast and
1350 app probes in PROBE state. Defaults to 0.
1352 disable_policy - BOOLEAN
1353 Disable IPSEC policy (SPD) for this interface
1355 disable_xfrm - BOOLEAN
1356 Disable IPSEC encryption on this interface, whatever the policy
1358 igmpv2_unsolicited_report_interval - INTEGER
1359 The interval in milliseconds in which the next unsolicited
1360 IGMPv1 or IGMPv2 report retransmit will take place.
1361 Default: 10000 (10 seconds)
1363 igmpv3_unsolicited_report_interval - INTEGER
1364 The interval in milliseconds in which the next unsolicited
1365 IGMPv3 report retransmit will take place.
1366 Default: 1000 (1 seconds)
1368 promote_secondaries - BOOLEAN
1369 When a primary IP address is removed from this interface
1370 promote a corresponding secondary IP address instead of
1371 removing all the corresponding secondary IP addresses.
1373 drop_unicast_in_l2_multicast - BOOLEAN
1374 Drop any unicast IP packets that are received in link-layer
1375 multicast (or broadcast) frames.
1376 This behavior (for multicast) is actually a SHOULD in RFC
1377 1122, but is disabled by default for compatibility reasons.
1380 drop_gratuitous_arp - BOOLEAN
1381 Drop all gratuitous ARP frames, for example if there's a known
1382 good ARP proxy on the network and such frames need not be used
1383 (or in the case of 802.11, must not be used to prevent attacks.)
1388 Allows you to write a number, which can be used as required.
1391 xfrm4_gc_thresh - INTEGER
1392 (Obsolete since linux-4.14)
1393 The threshold at which we will start garbage collecting for IPv4
1394 destination cache entries. At twice this value the system will
1395 refuse new allocations.
1397 igmp_link_local_mcast_reports - BOOLEAN
1398 Enable IGMP reports for link local multicast groups in the
1403 kuznet@ms2.inr.ac.ru
1409 delon.nicolas@wanadoo.fr
1414 /proc/sys/net/ipv6/* Variables:
1416 IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also
1417 apply to IPv6 [XXX?].
1419 bindv6only - BOOLEAN
1420 Default value for IPV6_V6ONLY socket option,
1421 which restricts use of the IPv6 socket to IPv6 communication
1423 TRUE: disable IPv4-mapped address feature
1424 FALSE: enable IPv4-mapped address feature
1426 Default: FALSE (as specified in RFC3493)
1428 flowlabel_consistency - BOOLEAN
1429 Protect the consistency (and unicity) of flow label.
1430 You have to disable it to use IPV6_FL_F_REFLECT flag on the
1436 auto_flowlabels - INTEGER
1437 Automatically generate flow labels based on a flow hash of the
1438 packet. This allows intermediate devices, such as routers, to
1439 identify packet flows for mechanisms like Equal Cost Multipath
1440 Routing (see RFC 6438).
1441 0: automatic flow labels are completely disabled
1442 1: automatic flow labels are enabled by default, they can be
1443 disabled on a per socket basis using the IPV6_AUTOFLOWLABEL
1445 2: automatic flow labels are allowed, they may be enabled on a
1446 per socket basis using the IPV6_AUTOFLOWLABEL socket option
1447 3: automatic flow labels are enabled and enforced, they cannot
1448 be disabled by the socket option
1451 flowlabel_state_ranges - BOOLEAN
1452 Split the flow label number space into two ranges. 0-0x7FFFF is
1453 reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF
1454 is reserved for stateless flow labels as described in RFC6437.
1459 flowlabel_reflect - INTEGER
1460 Control flow label reflection. Needed for Path MTU
1461 Discovery to work with Equal Cost Multipath Routing in anycast
1462 environments. See RFC 7690 and:
1463 https://tools.ietf.org/html/draft-wang-6man-flow-label-reflection-01
1466 1: enabled for established flows
1468 Note that this prevents automatic flowlabel changes, as done
1469 in "tcp: change IPv6 flow-label upon receiving spurious retransmission"
1470 and "tcp: Change txhash on every SYN and RTO retransmit"
1472 2: enabled for TCP RESET packets (no active listener)
1473 If set, a RST packet sent in response to a SYN packet on a closed
1474 port will reflect the incoming flow label.
1476 4: enabled for ICMPv6 echo reply messages.
1480 fib_multipath_hash_policy - INTEGER
1481 Controls which hash policy to use for multipath routes.
1482 Default: 0 (Layer 3)
1484 0 - Layer 3 (source and destination addresses plus flow label)
1485 1 - Layer 4 (standard 5-tuple)
1486 2 - Layer 3 or inner Layer 3 if present
1488 anycast_src_echo_reply - BOOLEAN
1489 Controls the use of anycast addresses as source addresses for ICMPv6
1495 idgen_delay - INTEGER
1496 Controls the delay in seconds after which time to retry
1497 privacy stable address generation if a DAD conflict is
1499 Default: 1 (as specified in RFC7217)
1501 idgen_retries - INTEGER
1502 Controls the number of retries to generate a stable privacy
1503 address if a DAD conflict is detected.
1504 Default: 3 (as specified in RFC7217)
1507 Controls the MLD query robustness variable (see RFC3810 9.1).
1508 Default: 2 (as specified by RFC3810 9.1)
1509 Minimum: 1 (as specified by RFC6636 4.5)
1511 max_dst_opts_number - INTEGER
1512 Maximum number of non-padding TLVs allowed in a Destination
1513 options extension header. If this value is less than zero
1514 then unknown options are disallowed and the number of known
1515 TLVs allowed is the absolute value of this number.
1518 max_hbh_opts_number - INTEGER
1519 Maximum number of non-padding TLVs allowed in a Hop-by-Hop
1520 options extension header. If this value is less than zero
1521 then unknown options are disallowed and the number of known
1522 TLVs allowed is the absolute value of this number.
1525 max_dst_opts_length - INTEGER
1526 Maximum length allowed for a Destination options extension
1528 Default: INT_MAX (unlimited)
1530 max_hbh_length - INTEGER
1531 Maximum length allowed for a Hop-by-Hop options extension
1533 Default: INT_MAX (unlimited)
1535 skip_notify_on_dev_down - BOOLEAN
1536 Controls whether an RTM_DELROUTE message is generated for routes
1537 removed when a device is taken down or deleted. IPv4 does not
1538 generate this message; IPv6 does by default. Setting this sysctl
1539 to true skips the message, making IPv4 and IPv6 on par in relying
1540 on userspace caches to track link events and evict routes.
1541 Default: false (generate message)
1545 ip6frag_high_thresh - INTEGER
1546 Maximum memory used to reassemble IPv6 fragments. When
1547 ip6frag_high_thresh bytes of memory is allocated for this purpose,
1548 the fragment handler will toss packets until ip6frag_low_thresh
1551 ip6frag_low_thresh - INTEGER
1552 See ip6frag_high_thresh
1554 ip6frag_time - INTEGER
1555 Time in seconds to keep an IPv6 fragment in memory.
1557 IPv6 Segment Routing:
1559 seg6_flowlabel - INTEGER
1560 Controls the behaviour of computing the flowlabel of outer
1561 IPv6 header in case of SR T.encaps
1563 -1 set flowlabel to zero.
1564 0 copy flowlabel from Inner packet in case of Inner IPv6
1565 (Set flowlabel to 0 in case IPv4/L2)
1566 1 Compute the flowlabel using seg6_make_flowlabel()
1571 Change the interface-specific default settings.
1575 Change all the interface-specific settings.
1577 [XXX: Other special features than forwarding?]
1579 conf/all/forwarding - BOOLEAN
1580 Enable global IPv6 forwarding between all interfaces.
1582 IPv4 and IPv6 work differently here; e.g. netfilter must be used
1583 to control which interfaces may forward packets and which not.
1585 This also sets all interfaces' Host/Router setting
1586 'forwarding' to the specified value. See below for details.
1588 This referred to as global forwarding.
1593 fwmark_reflect - BOOLEAN
1594 Controls the fwmark of kernel-generated IPv6 reply packets that are not
1595 associated with a socket for example, TCP RSTs or ICMPv6 echo replies).
1596 If unset, these packets have a fwmark of zero. If set, they have the
1597 fwmark of the packet they are replying to.
1601 Change special settings per interface.
1603 The functional behaviour for certain settings is different
1604 depending on whether local forwarding is enabled or not.
1607 Accept Router Advertisements; autoconfigure using them.
1609 It also determines whether or not to transmit Router
1610 Solicitations. If and only if the functional setting is to
1611 accept Router Advertisements, Router Solicitations will be
1614 Possible values are:
1615 0 Do not accept Router Advertisements.
1616 1 Accept Router Advertisements if forwarding is disabled.
1617 2 Overrule forwarding behaviour. Accept Router Advertisements
1618 even if forwarding is enabled.
1620 Functional default: enabled if local forwarding is disabled.
1621 disabled if local forwarding is enabled.
1623 accept_ra_defrtr - BOOLEAN
1624 Learn default router in Router Advertisement.
1626 Functional default: enabled if accept_ra is enabled.
1627 disabled if accept_ra is disabled.
1629 accept_ra_from_local - BOOLEAN
1630 Accept RA with source-address that is found on local machine
1631 if the RA is otherwise proper and able to be accepted.
1632 Default is to NOT accept these as it may be an un-intended
1636 enabled if accept_ra_from_local is enabled
1637 on a specific interface.
1638 disabled if accept_ra_from_local is disabled
1639 on a specific interface.
1641 accept_ra_min_hop_limit - INTEGER
1642 Minimum hop limit Information in Router Advertisement.
1644 Hop limit Information in Router Advertisement less than this
1645 variable shall be ignored.
1649 accept_ra_pinfo - BOOLEAN
1650 Learn Prefix Information in Router Advertisement.
1652 Functional default: enabled if accept_ra is enabled.
1653 disabled if accept_ra is disabled.
1655 accept_ra_rt_info_min_plen - INTEGER
1656 Minimum prefix length of Route Information in RA.
1658 Route Information w/ prefix smaller than this variable shall
1661 Functional default: 0 if accept_ra_rtr_pref is enabled.
1662 -1 if accept_ra_rtr_pref is disabled.
1664 accept_ra_rt_info_max_plen - INTEGER
1665 Maximum prefix length of Route Information in RA.
1667 Route Information w/ prefix larger than this variable shall
1670 Functional default: 0 if accept_ra_rtr_pref is enabled.
1671 -1 if accept_ra_rtr_pref is disabled.
1673 accept_ra_rtr_pref - BOOLEAN
1674 Accept Router Preference in RA.
1676 Functional default: enabled if accept_ra is enabled.
1677 disabled if accept_ra is disabled.
1679 accept_ra_mtu - BOOLEAN
1680 Apply the MTU value specified in RA option 5 (RFC4861). If
1681 disabled, the MTU specified in the RA will be ignored.
1683 Functional default: enabled if accept_ra is enabled.
1684 disabled if accept_ra is disabled.
1686 accept_redirects - BOOLEAN
1689 Functional default: enabled if local forwarding is disabled.
1690 disabled if local forwarding is enabled.
1692 accept_source_route - INTEGER
1693 Accept source routing (routing extension header).
1695 >= 0: Accept only routing header type 2.
1696 < 0: Do not accept routing header.
1701 Autoconfigure addresses using Prefix Information in Router
1704 Functional default: enabled if accept_ra_pinfo is enabled.
1705 disabled if accept_ra_pinfo is disabled.
1707 dad_transmits - INTEGER
1708 The amount of Duplicate Address Detection probes to send.
1711 forwarding - INTEGER
1712 Configure interface-specific Host/Router behaviour.
1714 Note: It is recommended to have the same setting on all
1715 interfaces; mixed router/host scenarios are rather uncommon.
1717 Possible values are:
1718 0 Forwarding disabled
1719 1 Forwarding enabled
1723 By default, Host behaviour is assumed. This means:
1725 1. IsRouter flag is not set in Neighbour Advertisements.
1726 2. If accept_ra is TRUE (default), transmit Router
1728 3. If accept_ra is TRUE (default), accept Router
1729 Advertisements (and do autoconfiguration).
1730 4. If accept_redirects is TRUE (default), accept Redirects.
1734 If local forwarding is enabled, Router behaviour is assumed.
1735 This means exactly the reverse from the above:
1737 1. IsRouter flag is set in Neighbour Advertisements.
1738 2. Router Solicitations are not sent unless accept_ra is 2.
1739 3. Router Advertisements are ignored unless accept_ra is 2.
1740 4. Redirects are ignored.
1742 Default: 0 (disabled) if global forwarding is disabled (default),
1743 otherwise 1 (enabled).
1746 Default Hop Limit to set.
1750 Default Maximum Transfer Unit
1751 Default: 1280 (IPv6 required minimum)
1753 ip_nonlocal_bind - BOOLEAN
1754 If set, allows processes to bind() to non-local IPv6 addresses,
1755 which can be quite useful - but may break some applications.
1758 router_probe_interval - INTEGER
1759 Minimum interval (in seconds) between Router Probing described
1764 router_solicitation_delay - INTEGER
1765 Number of seconds to wait after interface is brought up
1766 before sending Router Solicitations.
1769 router_solicitation_interval - INTEGER
1770 Number of seconds to wait between Router Solicitations.
1773 router_solicitations - INTEGER
1774 Number of Router Solicitations to send until assuming no
1775 routers are present.
1778 use_oif_addrs_only - BOOLEAN
1779 When enabled, the candidate source addresses for destinations
1780 routed via this interface are restricted to the set of addresses
1781 configured on this interface (vis. RFC 6724, section 4).
1785 use_tempaddr - INTEGER
1786 Preference for Privacy Extensions (RFC3041).
1787 <= 0 : disable Privacy Extensions
1788 == 1 : enable Privacy Extensions, but prefer public
1789 addresses over temporary addresses.
1790 > 1 : enable Privacy Extensions and prefer temporary
1791 addresses over public addresses.
1792 Default: 0 (for most devices)
1793 -1 (for point-to-point devices and loopback devices)
1795 temp_valid_lft - INTEGER
1796 valid lifetime (in seconds) for temporary addresses.
1797 Default: 604800 (7 days)
1799 temp_prefered_lft - INTEGER
1800 Preferred lifetime (in seconds) for temporary addresses.
1801 Default: 86400 (1 day)
1803 keep_addr_on_down - INTEGER
1804 Keep all IPv6 addresses on an interface down event. If set static
1805 global addresses with no expiration time are not flushed.
1810 Default: 0 (addresses are removed)
1812 max_desync_factor - INTEGER
1813 Maximum value for DESYNC_FACTOR, which is a random value
1814 that ensures that clients don't synchronize with each
1815 other and generate new addresses at exactly the same time.
1816 value is in seconds.
1819 regen_max_retry - INTEGER
1820 Number of attempts before give up attempting to generate
1821 valid temporary addresses.
1824 max_addresses - INTEGER
1825 Maximum number of autoconfigured addresses per interface. Setting
1826 to zero disables the limitation. It is not recommended to set this
1827 value too large (or to zero) because it would be an easy way to
1828 crash the kernel by allowing too many addresses to be created.
1831 disable_ipv6 - BOOLEAN
1832 Disable IPv6 operation. If accept_dad is set to 2, this value
1833 will be dynamically set to TRUE if DAD fails for the link-local
1835 Default: FALSE (enable IPv6 operation)
1837 When this value is changed from 1 to 0 (IPv6 is being enabled),
1838 it will dynamically create a link-local address on the given
1839 interface and start Duplicate Address Detection, if necessary.
1841 When this value is changed from 0 to 1 (IPv6 is being disabled),
1842 it will dynamically delete all addresses and routes on the given
1843 interface. From now on it will not possible to add addresses/routes
1844 to the selected interface.
1846 accept_dad - INTEGER
1847 Whether to accept DAD (Duplicate Address Detection).
1849 1: Enable DAD (default)
1850 2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
1851 link-local address has been found.
1853 DAD operation and mode on a given interface will be selected according
1854 to the maximum value of conf/{all,interface}/accept_dad.
1856 force_tllao - BOOLEAN
1857 Enable sending the target link-layer address option even when
1858 responding to a unicast neighbor solicitation.
1861 Quoting from RFC 2461, section 4.4, Target link-layer address:
1863 "The option MUST be included for multicast solicitations in order to
1864 avoid infinite Neighbor Solicitation "recursion" when the peer node
1865 does not have a cache entry to return a Neighbor Advertisements
1866 message. When responding to unicast solicitations, the option can be
1867 omitted since the sender of the solicitation has the correct link-
1868 layer address; otherwise it would not have be able to send the unicast
1869 solicitation in the first place. However, including the link-layer
1870 address in this case adds little overhead and eliminates a potential
1871 race condition where the sender deletes the cached link-layer address
1872 prior to receiving a response to a previous solicitation."
1874 ndisc_notify - BOOLEAN
1875 Define mode for notification of address and device changes.
1876 0 - (default): do nothing
1877 1 - Generate unsolicited neighbour advertisements when device is brought
1878 up or hardware address changes.
1880 ndisc_tclass - INTEGER
1881 The IPv6 Traffic Class to use by default when sending IPv6 Neighbor
1882 Discovery (Router Solicitation, Router Advertisement, Neighbor
1883 Solicitation, Neighbor Advertisement, Redirect) messages.
1884 These 8 bits can be interpreted as 6 high order bits holding the DSCP
1885 value and 2 low order bits representing ECN (which you probably want
1889 mldv1_unsolicited_report_interval - INTEGER
1890 The interval in milliseconds in which the next unsolicited
1891 MLDv1 report retransmit will take place.
1892 Default: 10000 (10 seconds)
1894 mldv2_unsolicited_report_interval - INTEGER
1895 The interval in milliseconds in which the next unsolicited
1896 MLDv2 report retransmit will take place.
1897 Default: 1000 (1 second)
1899 force_mld_version - INTEGER
1900 0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed
1901 1 - Enforce to use MLD version 1
1902 2 - Enforce to use MLD version 2
1904 suppress_frag_ndisc - INTEGER
1905 Control RFC 6980 (Security Implications of IPv6 Fragmentation
1906 with IPv6 Neighbor Discovery) behavior:
1907 1 - (default) discard fragmented neighbor discovery packets
1908 0 - allow fragmented neighbor discovery packets
1910 optimistic_dad - BOOLEAN
1911 Whether to perform Optimistic Duplicate Address Detection (RFC 4429).
1912 0: disabled (default)
1915 Optimistic Duplicate Address Detection for the interface will be enabled
1916 if at least one of conf/{all,interface}/optimistic_dad is set to 1,
1917 it will be disabled otherwise.
1919 use_optimistic - BOOLEAN
1920 If enabled, do not classify optimistic addresses as deprecated during
1921 source address selection. Preferred addresses will still be chosen
1922 before optimistic addresses, subject to other ranking in the source
1923 address selection algorithm.
1924 0: disabled (default)
1927 This will be enabled if at least one of
1928 conf/{all,interface}/use_optimistic is set to 1, disabled otherwise.
1930 stable_secret - IPv6 address
1931 This IPv6 address will be used as a secret to generate IPv6
1932 addresses for link-local addresses and autoconfigured
1933 ones. All addresses generated after setting this secret will
1934 be stable privacy ones by default. This can be changed via the
1935 addrgenmode ip-link. conf/default/stable_secret is used as the
1936 secret for the namespace, the interface specific ones can
1937 overwrite that. Writes to conf/all/stable_secret are refused.
1939 It is recommended to generate this secret during installation
1940 of a system and keep it stable after that.
1942 By default the stable secret is unset.
1944 addr_gen_mode - INTEGER
1945 Defines how link-local and autoconf addresses are generated.
1947 0: generate address based on EUI64 (default)
1948 1: do no generate a link-local address, use EUI64 for addresses generated
1950 2: generate stable privacy addresses, using the secret from
1951 stable_secret (RFC7217)
1952 3: generate stable privacy addresses, using a random secret if unset
1954 drop_unicast_in_l2_multicast - BOOLEAN
1955 Drop any unicast IPv6 packets that are received in link-layer
1956 multicast (or broadcast) frames.
1958 By default this is turned off.
1960 drop_unsolicited_na - BOOLEAN
1961 Drop all unsolicited neighbor advertisements, for example if there's
1962 a known good NA proxy on the network and such frames need not be used
1963 (or in the case of 802.11, must not be used to prevent attacks.)
1965 By default this is turned off.
1967 enhanced_dad - BOOLEAN
1968 Include a nonce option in the IPv6 neighbor solicitation messages used for
1969 duplicate address detection per RFC7527. A received DAD NS will only signal
1970 a duplicate address if the nonce is different. This avoids any false
1971 detection of duplicates due to loopback of the NS messages that we send.
1972 The nonce option will be sent on an interface unless both of
1973 conf/{all,interface}/enhanced_dad are set to FALSE.
1978 Limit the maximal rates for sending ICMPv6 messages.
1979 0 to disable any limiting,
1980 otherwise the minimal space between responses in milliseconds.
1983 ratemask - list of comma separated ranges
1984 For ICMPv6 message types matching the ranges in the ratemask, limit
1985 the sending of the message according to ratelimit parameter.
1987 The format used for both input and output is a comma separated
1988 list of ranges (e.g. "0-127,129" for ICMPv6 message type 0 to 127 and
1989 129). Writing to the file will clear all previous ranges of ICMPv6
1990 message types and update the current list with the input.
1992 Refer to: https://www.iana.org/assignments/icmpv6-parameters/icmpv6-parameters.xhtml
1993 for numerical values of ICMPv6 message types, e.g. echo request is 128
1994 and echo reply is 129.
1996 Default: 0-1,3-127 (rate limit ICMPv6 errors except Packet Too Big)
1998 echo_ignore_all - BOOLEAN
1999 If set non-zero, then the kernel will ignore all ICMP ECHO
2000 requests sent to it over the IPv6 protocol.
2003 echo_ignore_multicast - BOOLEAN
2004 If set non-zero, then the kernel will ignore all ICMP ECHO
2005 requests sent to it over the IPv6 protocol via multicast.
2008 echo_ignore_anycast - BOOLEAN
2009 If set non-zero, then the kernel will ignore all ICMP ECHO
2010 requests sent to it over the IPv6 protocol destined to anycast address.
2013 xfrm6_gc_thresh - INTEGER
2014 (Obsolete since linux-4.14)
2015 The threshold at which we will start garbage collecting for IPv6
2016 destination cache entries. At twice this value the system will
2017 refuse new allocations.
2021 Pekka Savola <pekkas@netcore.fi>
2022 YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
2025 /proc/sys/net/bridge/* Variables:
2027 bridge-nf-call-arptables - BOOLEAN
2028 1 : pass bridged ARP traffic to arptables' FORWARD chain.
2032 bridge-nf-call-iptables - BOOLEAN
2033 1 : pass bridged IPv4 traffic to iptables' chains.
2037 bridge-nf-call-ip6tables - BOOLEAN
2038 1 : pass bridged IPv6 traffic to ip6tables' chains.
2042 bridge-nf-filter-vlan-tagged - BOOLEAN
2043 1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
2047 bridge-nf-filter-pppoe-tagged - BOOLEAN
2048 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
2052 bridge-nf-pass-vlan-input-dev - BOOLEAN
2053 1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan
2054 interface on the bridge and set the netfilter input device to the vlan.
2055 This allows use of e.g. "iptables -i br0.1" and makes the REDIRECT
2056 target work with vlan-on-top-of-bridge interfaces. When no matching
2057 vlan interface is found, or this switch is off, the input device is
2058 set to the bridge interface.
2059 0: disable bridge netfilter vlan interface lookup.
2062 proc/sys/net/sctp/* Variables:
2064 addip_enable - BOOLEAN
2065 Enable or disable extension of Dynamic Address Reconfiguration
2066 (ADD-IP) functionality specified in RFC5061. This extension provides
2067 the ability to dynamically add and remove new addresses for the SCTP
2070 1: Enable extension.
2072 0: Disable extension.
2077 Enable or disable pf (pf is short for potentially failed) state. A value
2078 of pf_retrans > path_max_retrans also disables pf state. That is, one of
2079 both pf_enable and pf_retrans > path_max_retrans can disable pf state.
2080 Since pf_retrans and path_max_retrans can be changed by userspace
2081 application, sometimes user expects to disable pf state by the value of
2082 pf_retrans > path_max_retrans, but occasionally the value of pf_retrans
2083 or path_max_retrans is changed by the user application, this pf state is
2084 enabled. As such, it is necessary to add this to dynamically enable
2085 and disable pf state. See:
2086 https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover for
2096 Unset or enable/disable pf (pf is short for potentially failed) state
2097 exposure. Applications can control the exposure of the PF path state
2098 in the SCTP_PEER_ADDR_CHANGE event and the SCTP_GET_PEER_ADDR_INFO
2099 sockopt. When it's unset, no SCTP_PEER_ADDR_CHANGE event with
2100 SCTP_ADDR_PF state will be sent and a SCTP_PF-state transport info
2101 can be got via SCTP_GET_PEER_ADDR_INFO sockopt; When it's enabled,
2102 a SCTP_PEER_ADDR_CHANGE event will be sent for a transport becoming
2103 SCTP_PF state and a SCTP_PF-state transport info can be got via
2104 SCTP_GET_PEER_ADDR_INFO sockopt; When it's diabled, no
2105 SCTP_PEER_ADDR_CHANGE event will be sent and it returns -EACCES when
2106 trying to get a SCTP_PF-state transport info via SCTP_GET_PEER_ADDR_INFO
2109 0: Unset pf state exposure, Compatible with old applications.
2111 1: Disable pf state exposure.
2113 2: Enable pf state exposure.
2117 addip_noauth_enable - BOOLEAN
2118 Dynamic Address Reconfiguration (ADD-IP) requires the use of
2119 authentication to protect the operations of adding or removing new
2120 addresses. This requirement is mandated so that unauthorized hosts
2121 would not be able to hijack associations. However, older
2122 implementations may not have implemented this requirement while
2123 allowing the ADD-IP extension. For reasons of interoperability,
2124 we provide this variable to control the enforcement of the
2125 authentication requirement.
2127 1: Allow ADD-IP extension to be used without authentication. This
2128 should only be set in a closed environment for interoperability
2129 with older implementations.
2131 0: Enforce the authentication requirement
2135 auth_enable - BOOLEAN
2136 Enable or disable Authenticated Chunks extension. This extension
2137 provides the ability to send and receive authenticated chunks and is
2138 required for secure operation of Dynamic Address Reconfiguration
2141 1: Enable this extension.
2142 0: Disable this extension.
2146 prsctp_enable - BOOLEAN
2147 Enable or disable the Partial Reliability extension (RFC3758) which
2148 is used to notify peers that a given DATA should no longer be expected.
2156 The limit of the number of new packets that can be initially sent. It
2157 controls how bursty the generated traffic can be.
2161 association_max_retrans - INTEGER
2162 Set the maximum number for retransmissions that an association can
2163 attempt deciding that the remote end is unreachable. If this value
2164 is exceeded, the association is terminated.
2168 max_init_retransmits - INTEGER
2169 The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
2170 that an association will attempt before declaring the destination
2171 unreachable and terminating.
2175 path_max_retrans - INTEGER
2176 The maximum number of retransmissions that will be attempted on a given
2177 path. Once this threshold is exceeded, the path is considered
2178 unreachable, and new traffic will use a different path when the
2179 association is multihomed.
2183 pf_retrans - INTEGER
2184 The number of retransmissions that will be attempted on a given path
2185 before traffic is redirected to an alternate transport (should one
2186 exist). Note this is distinct from path_max_retrans, as a path that
2187 passes the pf_retrans threshold can still be used. Its only
2188 deprioritized when a transmission path is selected by the stack. This
2189 setting is primarily used to enable fast failover mechanisms without
2190 having to reduce path_max_retrans to a very low value. See:
2191 http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt
2192 for details. Note also that a value of pf_retrans > path_max_retrans
2193 disables this feature. Since both pf_retrans and path_max_retrans can
2194 be changed by userspace application, a variable pf_enable is used to
2199 ps_retrans - INTEGER
2200 Primary.Switchover.Max.Retrans (PSMR), it's a tunable parameter coming
2201 from section-5 "Primary Path Switchover" in rfc7829. The primary path
2202 will be changed to another active path when the path error counter on
2203 the old primary path exceeds PSMR, so that "the SCTP sender is allowed
2204 to continue data transmission on a new working path even when the old
2205 primary destination address becomes active again". Note this feature
2206 is disabled by initializing 'ps_retrans' per netns as 0xffff by default,
2207 and its value can't be less than 'pf_retrans' when changing by sysctl.
2211 rto_initial - INTEGER
2212 The initial round trip timeout value in milliseconds that will be used
2213 in calculating round trip times. This is the initial time interval
2214 for retransmissions.
2219 The maximum value (in milliseconds) of the round trip timeout. This
2220 is the largest time interval that can elapse between retransmissions.
2225 The minimum value (in milliseconds) of the round trip timeout. This
2226 is the smallest time interval the can elapse between retransmissions.
2230 hb_interval - INTEGER
2231 The interval (in milliseconds) between HEARTBEAT chunks. These chunks
2232 are sent at the specified interval on idle paths to probe the state of
2233 a given path between 2 associations.
2237 sack_timeout - INTEGER
2238 The amount of time (in milliseconds) that the implementation will wait
2243 valid_cookie_life - INTEGER
2244 The default lifetime of the SCTP cookie (in milliseconds). The cookie
2245 is used during association establishment.
2249 cookie_preserve_enable - BOOLEAN
2250 Enable or disable the ability to extend the lifetime of the SCTP cookie
2251 that is used during the establishment phase of SCTP association
2253 1: Enable cookie lifetime extension.
2258 cookie_hmac_alg - STRING
2259 Select the hmac algorithm used when generating the cookie value sent by
2260 a listening sctp socket to a connecting client in the INIT-ACK chunk.
2265 Ability to assign md5 or sha1 as the selected alg is predicated on the
2266 configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and
2267 CONFIG_CRYPTO_SHA1).
2269 Default: Dependent on configuration. MD5 if available, else SHA1 if
2270 available, else none.
2272 rcvbuf_policy - INTEGER
2273 Determines if the receive buffer is attributed to the socket or to
2274 association. SCTP supports the capability to create multiple
2275 associations on a single socket. When using this capability, it is
2276 possible that a single stalled association that's buffering a lot
2277 of data may block other associations from delivering their data by
2278 consuming all of the receive buffer space. To work around this,
2279 the rcvbuf_policy could be set to attribute the receiver buffer space
2280 to each association instead of the socket. This prevents the described
2283 1: rcvbuf space is per association
2284 0: rcvbuf space is per socket
2288 sndbuf_policy - INTEGER
2289 Similar to rcvbuf_policy above, this applies to send buffer space.
2291 1: Send buffer is tracked per association
2292 0: Send buffer is tracked per socket.
2296 sctp_mem - vector of 3 INTEGERs: min, pressure, max
2297 Number of pages allowed for queueing by all SCTP sockets.
2299 min: Below this number of pages SCTP is not bothered about its
2300 memory appetite. When amount of memory allocated by SCTP exceeds
2301 this number, SCTP starts to moderate memory usage.
2303 pressure: This value was introduced to follow format of tcp_mem.
2305 max: Number of pages allowed for queueing by all SCTP sockets.
2307 Default is calculated at boot time from amount of available memory.
2309 sctp_rmem - vector of 3 INTEGERs: min, default, max
2310 Only the first value ("min") is used, "default" and "max" are
2313 min: Minimal size of receive buffer used by SCTP socket.
2314 It is guaranteed to each SCTP socket (but not association) even
2315 under moderate memory pressure.
2319 sctp_wmem - vector of 3 INTEGERs: min, default, max
2320 Currently this tunable has no effect.
2322 addr_scope_policy - INTEGER
2323 Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00
2325 0 - Disable IPv4 address scoping
2326 1 - Enable IPv4 address scoping
2327 2 - Follow draft but allow IPv4 private addresses
2328 3 - Follow draft but allow IPv4 link local addresses
2333 /proc/sys/net/core/*
2334 Please see: Documentation/admin-guide/sysctl/net.rst for descriptions of these entries.
2337 /proc/sys/net/unix/*
2338 max_dgram_qlen - INTEGER
2339 The maximum length of dgram socket receive queue