1 .. SPDX-License-Identifier: GPL-2.0
7 /proc/sys/net/ipv4/* Variables
8 ==============================
11 - 0 - disabled (default)
14 Forward Packets between interfaces.
16 This variable is special, its change resets all configuration
17 parameters to their default state (RFC1122 for hosts, RFC1812
20 ip_default_ttl - INTEGER
21 Default value of TTL field (Time To Live) for outgoing (but not
22 forwarded) IP packets. Should be between 1 and 255 inclusive.
23 Default: 64 (as recommended by RFC1700)
25 ip_no_pmtu_disc - INTEGER
26 Disable Path MTU Discovery. If enabled in mode 1 and a
27 fragmentation-required ICMP is received, the PMTU to this
28 destination will be set to the smallest of the old MTU to
29 this destination and min_pmtu (see below). You will need
30 to raise min_pmtu to the smallest interface MTU on your system
31 manually if you want to avoid locally generated fragments.
33 In mode 2 incoming Path MTU Discovery messages will be
34 discarded. Outgoing frames are handled the same as in mode 1,
35 implicitly setting IP_PMTUDISC_DONT on every created socket.
37 Mode 3 is a hardened pmtu discover mode. The kernel will only
38 accept fragmentation-needed errors if the underlying protocol
39 can verify them besides a plain socket lookup. Current
40 protocols for which pmtu events will be honored are TCP, SCTP
41 and DCCP as they verify e.g. the sequence number or the
42 association. This mode should not be enabled globally but is
43 only intended to secure e.g. name servers in namespaces where
44 TCP path mtu must still work but path MTU information of other
45 protocols should be discarded. If enabled globally this mode
46 could break other protocols.
53 default 552 - minimum Path MTU. Unless this is changed mannually,
54 each cached pmtu will never be lower than this setting.
56 ip_forward_use_pmtu - BOOLEAN
57 By default we don't trust protocol path MTUs while forwarding
58 because they could be easily forged and can lead to unwanted
59 fragmentation by the router.
60 You only need to enable this if you have user-space software
61 which tries to discover path mtus by itself and depends on the
62 kernel honoring this information. This is normally not the
72 fwmark_reflect - BOOLEAN
73 Controls the fwmark of kernel-generated IPv4 reply packets that are not
74 associated with a socket for example, TCP RSTs or ICMP echo replies).
75 If unset, these packets have a fwmark of zero. If set, they have the
76 fwmark of the packet they are replying to.
80 fib_multipath_use_neigh - BOOLEAN
81 Use status of existing neighbor entry when determining nexthop for
82 multipath routes. If disabled, neighbor information is not used and
83 packets could be directed to a failed nexthop. Only valid for kernels
84 built with CONFIG_IP_ROUTE_MULTIPATH enabled.
93 fib_multipath_hash_policy - INTEGER
94 Controls which hash policy to use for multipath routes. Only valid
95 for kernels built with CONFIG_IP_ROUTE_MULTIPATH enabled.
103 - 2 - Layer 3 or inner Layer 3 if present
104 - 3 - Custom multipath hash. Fields used for multipath hash calculation
105 are determined by fib_multipath_hash_fields sysctl
107 fib_multipath_hash_fields - UNSIGNED INTEGER
108 When fib_multipath_hash_policy is set to 3 (custom multipath hash), the
109 fields used for multipath hash calculation are determined by this
112 This value is a bitmask which enables various fields for multipath hash
117 ====== ============================
118 0x0001 Source IP address
119 0x0002 Destination IP address
121 0x0008 Unused (Flow Label)
123 0x0020 Destination port
124 0x0040 Inner source IP address
125 0x0080 Inner destination IP address
126 0x0100 Inner IP protocol
127 0x0200 Inner Flow Label
128 0x0400 Inner source port
129 0x0800 Inner destination port
130 ====== ============================
132 Default: 0x0007 (source IP, destination IP and IP protocol)
134 fib_sync_mem - UNSIGNED INTEGER
135 Amount of dirty memory from fib entries that can be backlogged before
136 synchronize_rcu is forced.
138 Default: 512kB Minimum: 64kB Maximum: 64MB
140 ip_forward_update_priority - INTEGER
141 Whether to update SKB priority from "TOS" field in IPv4 header after it
142 is forwarded. The new SKB priority is mapped from TOS field value
143 according to an rt_tos2priority table (see e.g. man tc-prio).
145 Default: 1 (Update priority.)
149 - 0 - Do not update priority.
150 - 1 - Update priority.
152 route/max_size - INTEGER
153 Maximum number of routes allowed in the kernel. Increase
154 this when using large numbers of interfaces and/or routes.
156 From linux kernel 3.6 onwards, this is deprecated for ipv4
157 as route cache is no longer used.
159 neigh/default/gc_thresh1 - INTEGER
160 Minimum number of entries to keep. Garbage collector will not
161 purge entries if there are fewer than this number.
165 neigh/default/gc_thresh2 - INTEGER
166 Threshold when garbage collector becomes more aggressive about
167 purging entries. Entries older than 5 seconds will be cleared
168 when over this number.
172 neigh/default/gc_thresh3 - INTEGER
173 Maximum number of non-PERMANENT neighbor entries allowed. Increase
174 this when using large numbers of interfaces and when communicating
175 with large numbers of directly-connected peers.
179 neigh/default/unres_qlen_bytes - INTEGER
180 The maximum number of bytes which may be used by packets
181 queued for each unresolved address by other network layers.
184 Setting negative value is meaningless and will return error.
186 Default: SK_WMEM_MAX, (same as net.core.wmem_default).
188 Exact value depends on architecture and kernel options,
189 but should be enough to allow queuing 256 packets
192 neigh/default/unres_qlen - INTEGER
193 The maximum number of packets which may be queued for each
194 unresolved address by other network layers.
196 (deprecated in linux 3.3) : use unres_qlen_bytes instead.
198 Prior to linux 3.3, the default value is 3 which may cause
199 unexpected packet loss. The current default value is calculated
200 according to default value of unres_qlen_bytes and true size of
205 neigh/default/interval_probe_time_ms - INTEGER
206 The probe interval for neighbor entries with NTF_MANAGED flag,
211 mtu_expires - INTEGER
212 Time, in seconds, that cached PMTU information is kept.
214 min_adv_mss - INTEGER
215 The advertised MSS depends on the first hop route MTU, but will
216 never be lower than this setting.
218 fib_notify_on_flag_change - INTEGER
219 Whether to emit RTM_NEWROUTE notifications whenever RTM_F_OFFLOAD/
220 RTM_F_TRAP/RTM_F_OFFLOAD_FAILED flags are changed.
222 After installing a route to the kernel, user space receives an
223 acknowledgment, which means the route was installed in the kernel,
224 but not necessarily in hardware.
225 It is also possible for a route already installed in hardware to change
226 its action and therefore its flags. For example, a host route that is
227 trapping packets can be "promoted" to perform decapsulation following
228 the installation of an IPinIP/VXLAN tunnel.
229 The notifications will indicate to user-space the state of the route.
231 Default: 0 (Do not emit notifications.)
235 - 0 - Do not emit notifications.
236 - 1 - Emit notifications.
237 - 2 - Emit notifications only for RTM_F_OFFLOAD_FAILED flag change.
241 ipfrag_high_thresh - LONG INTEGER
242 Maximum memory used to reassemble IP fragments.
244 ipfrag_low_thresh - LONG INTEGER
245 (Obsolete since linux-4.17)
246 Maximum memory used to reassemble IP fragments before the kernel
247 begins to remove incomplete fragment queues to free up resources.
248 The kernel still accepts new fragments for defragmentation.
250 ipfrag_time - INTEGER
251 Time in seconds to keep an IP fragment in memory.
253 ipfrag_max_dist - INTEGER
254 ipfrag_max_dist is a non-negative integer value which defines the
255 maximum "disorder" which is allowed among fragments which share a
256 common IP source address. Note that reordering of packets is
257 not unusual, but if a large number of fragments arrive from a source
258 IP address while a particular fragment queue remains incomplete, it
259 probably indicates that one or more fragments belonging to that queue
260 have been lost. When ipfrag_max_dist is positive, an additional check
261 is done on fragments before they are added to a reassembly queue - if
262 ipfrag_max_dist (or more) fragments have arrived from a particular IP
263 address between additions to any IP fragment queue using that source
264 address, it's presumed that one or more fragments in the queue are
265 lost. The existing fragment queue will be dropped, and a new one
266 started. An ipfrag_max_dist value of zero disables this check.
268 Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
269 result in unnecessarily dropping fragment queues when normal
270 reordering of packets occurs, which could lead to poor application
271 performance. Using a very large value, e.g. 50000, increases the
272 likelihood of incorrectly reassembling IP fragments that originate
273 from different IP datagrams, which could result in data corruption.
276 bc_forwarding - INTEGER
277 bc_forwarding enables the feature described in rfc1812#section-5.3.5.2
278 and rfc2644. It allows the router to forward directed broadcast.
279 To enable this feature, the 'all' entry and the input interface entry
286 inet_peer_threshold - INTEGER
287 The approximate size of the storage. Starting from this threshold
288 entries will be thrown aggressively. This threshold also determines
289 entries' time-to-live and time intervals between garbage collection
290 passes. More entries, less time-to-live, less GC interval.
292 inet_peer_minttl - INTEGER
293 Minimum time-to-live of entries. Should be enough to cover fragment
294 time-to-live on the reassembling side. This minimum time-to-live is
295 guaranteed if the pool size is less than inet_peer_threshold.
298 inet_peer_maxttl - INTEGER
299 Maximum time-to-live of entries. Unused entries will expire after
300 this period of time if there is no memory pressure on the pool (i.e.
301 when the number of entries in the pool is very small).
308 Limit of socket listen() backlog, known in userspace as SOMAXCONN.
309 Defaults to 4096. (Was 128 before linux-5.4)
310 See also tcp_max_syn_backlog for additional tuning for TCP sockets.
312 tcp_abort_on_overflow - BOOLEAN
313 If listening service is too slow to accept new connections,
314 reset them. Default state is FALSE. It means that if overflow
315 occurred due to a burst, connection will recover. Enable this
316 option _only_ if you are really sure that listening daemon
317 cannot be tuned to accept connections faster. Enabling this
318 option can harm clients of your server.
320 tcp_adv_win_scale - INTEGER
321 Count buffering overhead as bytes/2^tcp_adv_win_scale
322 (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
325 Possible values are [-31, 31], inclusive.
329 tcp_allowed_congestion_control - STRING
330 Show/set the congestion control choices available to non-privileged
331 processes. The list is a subset of those listed in
332 tcp_available_congestion_control.
334 Default is "reno" and the default setting (tcp_congestion_control).
336 tcp_app_win - INTEGER
337 Reserve max(window/2^tcp_app_win, mss) of window for application
338 buffer. Value 0 is special, it means that nothing is reserved.
342 tcp_autocorking - BOOLEAN
343 Enable TCP auto corking :
344 When applications do consecutive small write()/sendmsg() system calls,
345 we try to coalesce these small writes as much as possible, to lower
346 total amount of sent packets. This is done if at least one prior
347 packet for the flow is waiting in Qdisc queues or device transmit
348 queue. Applications can still use TCP_CORK for optimal behavior
349 when they know how/when to uncork their sockets.
353 tcp_available_congestion_control - STRING
354 Shows the available congestion control choices that are registered.
355 More congestion control algorithms may be available as modules,
358 tcp_base_mss - INTEGER
359 The initial value of search_low to be used by the packetization layer
360 Path MTU discovery (MTU probing). If MTU probing is enabled,
361 this is the initial MSS used by the connection.
363 tcp_mtu_probe_floor - INTEGER
364 If MTU probing is enabled this caps the minimum MSS used for search_low
369 tcp_min_snd_mss - INTEGER
370 TCP SYN and SYNACK messages usually advertise an ADVMSS option,
371 as described in RFC 1122 and RFC 6691.
373 If this ADVMSS option is smaller than tcp_min_snd_mss,
374 it is silently capped to tcp_min_snd_mss.
376 Default : 48 (at least 8 bytes of payload per segment)
378 tcp_congestion_control - STRING
379 Set the congestion control algorithm to be used for new
380 connections. The algorithm "reno" is always available, but
381 additional choices may be available based on kernel configuration.
382 Default is set as part of kernel configuration.
383 For passive connections, the listener congestion control choice
386 [see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ]
389 Allows TCP to send "duplicate" SACKs.
391 tcp_early_retrans - INTEGER
392 Tail loss probe (TLP) converts RTOs occurring due to tail
393 losses into fast recovery (draft-ietf-tcpm-rack). Note that
394 TLP requires RACK to function properly (see tcp_recovery below)
404 Control use of Explicit Congestion Notification (ECN) by TCP.
405 ECN is used only when both ends of the TCP connection indicate
406 support for it. This feature is useful in avoiding losses due
407 to congestion by allowing supporting routers to signal
408 congestion before having to drop packets.
412 = =====================================================
413 0 Disable ECN. Neither initiate nor accept ECN.
414 1 Enable ECN when requested by incoming connections and
415 also request ECN on outgoing connection attempts.
416 2 Enable ECN when requested by incoming connections
417 but do not request ECN on outgoing connections.
418 = =====================================================
422 tcp_ecn_fallback - BOOLEAN
423 If the kernel detects that ECN connection misbehaves, enable fall
424 back to non-ECN. Currently, this knob implements the fallback
425 from RFC3168, section 6.1.1.1., but we reserve that in future,
426 additional detection mechanisms could be implemented under this
427 knob. The value is not used, if tcp_ecn or per route (or congestion
428 control) ECN settings are disabled.
430 Default: 1 (fallback enabled)
433 This is a legacy option, it has no effect anymore.
435 tcp_fin_timeout - INTEGER
436 The length of time an orphaned (no longer referenced by any
437 application) connection will remain in the FIN_WAIT_2 state
438 before it is aborted at the local end. While a perfectly
439 valid "receive only" state for an un-orphaned connection, an
440 orphaned connection in FIN_WAIT_2 state could otherwise wait
441 forever for the remote to close its end of the connection.
448 Enables Forward RTO-Recovery (F-RTO) defined in RFC5682.
449 F-RTO is an enhanced recovery algorithm for TCP retransmission
450 timeouts. It is particularly beneficial in networks where the
451 RTT fluctuates (e.g., wireless). F-RTO is sender-side only
452 modification. It does not require any support from the peer.
454 By default it's enabled with a non-zero value. 0 disables F-RTO.
456 tcp_fwmark_accept - BOOLEAN
457 If set, incoming connections to listening sockets that do not have a
458 socket mark will set the mark of the accepting socket to the fwmark of
459 the incoming SYN packet. This will cause all packets on that connection
460 (starting from the first SYNACK) to be sent with that fwmark. The
461 listening socket's mark is unchanged. Listening sockets that already
462 have a fwmark set via setsockopt(SOL_SOCKET, SO_MARK, ...) are
467 tcp_invalid_ratelimit - INTEGER
468 Limit the maximal rate for sending duplicate acknowledgments
469 in response to incoming TCP packets that are for an existing
470 connection but that are invalid due to any of these reasons:
472 (a) out-of-window sequence number,
473 (b) out-of-window acknowledgment number, or
474 (c) PAWS (Protection Against Wrapped Sequence numbers) check failure
476 This can help mitigate simple "ack loop" DoS attacks, wherein
477 a buggy or malicious middlebox or man-in-the-middle can
478 rewrite TCP header fields in manner that causes each endpoint
479 to think that the other is sending invalid TCP segments, thus
480 causing each side to send an unterminating stream of duplicate
481 acknowledgments for invalid segments.
483 Using 0 disables rate-limiting of dupacks in response to
484 invalid segments; otherwise this value specifies the minimal
485 space between sending such dupacks, in milliseconds.
487 Default: 500 (milliseconds).
489 tcp_keepalive_time - INTEGER
490 How often TCP sends out keepalive messages when keepalive is enabled.
493 tcp_keepalive_probes - INTEGER
494 How many keepalive probes TCP sends out, until it decides that the
495 connection is broken. Default value: 9.
497 tcp_keepalive_intvl - INTEGER
498 How frequently the probes are send out. Multiplied by
499 tcp_keepalive_probes it is time to kill not responding connection,
500 after probes started. Default value: 75sec i.e. connection
501 will be aborted after ~11 minutes of retries.
503 tcp_l3mdev_accept - BOOLEAN
504 Enables child sockets to inherit the L3 master device index.
505 Enabling this option allows a "global" listen socket to work
506 across L3 master domains (e.g., VRFs) with connected sockets
507 derived from the listen socket to be bound to the L3 domain in
508 which the packets originated. Only valid when the kernel was
509 compiled with CONFIG_NET_L3_MASTER_DEV.
511 Default: 0 (disabled)
513 tcp_low_latency - BOOLEAN
514 This is a legacy option, it has no effect anymore.
516 tcp_max_orphans - INTEGER
517 Maximal number of TCP sockets not attached to any user file handle,
518 held by system. If this number is exceeded orphaned connections are
519 reset immediately and warning is printed. This limit exists
520 only to prevent simple DoS attacks, you _must_ not rely on this
521 or lower the limit artificially, but rather increase it
522 (probably, after increasing installed memory),
523 if network conditions require more than default value,
524 and tune network services to linger and kill such states
525 more aggressively. Let me to remind again: each orphan eats
526 up to ~64K of unswappable memory.
528 tcp_max_syn_backlog - INTEGER
529 Maximal number of remembered connection requests (SYN_RECV),
530 which have not received an acknowledgment from connecting client.
532 This is a per-listener limit.
534 The minimal value is 128 for low memory machines, and it will
535 increase in proportion to the memory of machine.
537 If server suffers from overload, try increasing this number.
539 Remember to also check /proc/sys/net/core/somaxconn
540 A SYN_RECV request socket consumes about 304 bytes of memory.
542 tcp_max_tw_buckets - INTEGER
543 Maximal number of timewait sockets held by system simultaneously.
544 If this number is exceeded time-wait socket is immediately destroyed
545 and warning is printed. This limit exists only to prevent
546 simple DoS attacks, you _must_ not lower the limit artificially,
547 but rather increase it (probably, after increasing installed memory),
548 if network conditions require more than default value.
550 tcp_mem - vector of 3 INTEGERs: min, pressure, max
551 min: below this number of pages TCP is not bothered about its
554 pressure: when amount of memory allocated by TCP exceeds this number
555 of pages, TCP moderates its memory consumption and enters memory
556 pressure mode, which is exited when memory consumption falls
559 max: number of pages allowed for queueing by all TCP sockets.
561 Defaults are calculated at boot time from amount of available
564 tcp_min_rtt_wlen - INTEGER
565 The window length of the windowed min filter to track the minimum RTT.
566 A shorter window lets a flow more quickly pick up new (higher)
567 minimum RTT when it is moved to a longer path (e.g., due to traffic
568 engineering). A longer window makes the filter more resistant to RTT
569 inflations such as transient congestion. The unit is seconds.
571 Possible values: 0 - 86400 (1 day)
575 tcp_moderate_rcvbuf - BOOLEAN
576 If set, TCP performs receive buffer auto-tuning, attempting to
577 automatically size the buffer (no greater than tcp_rmem[2]) to
578 match the size required by the path for full throughput. Enabled by
581 tcp_mtu_probing - INTEGER
582 Controls TCP Packetization-Layer Path MTU Discovery. Takes three
586 - 1 - Disabled by default, enabled when an ICMP black hole detected
587 - 2 - Always enabled, use initial MSS of tcp_base_mss.
589 tcp_probe_interval - UNSIGNED INTEGER
590 Controls how often to start TCP Packetization-Layer Path MTU
591 Discovery reprobe. The default is reprobing every 10 minutes as
594 tcp_probe_threshold - INTEGER
595 Controls when TCP Packetization-Layer Path MTU Discovery probing
596 will stop in respect to the width of search range in bytes. Default
599 tcp_no_metrics_save - BOOLEAN
600 By default, TCP saves various connection metrics in the route cache
601 when the connection closes, so that connections established in the
602 near future can use these to set initial conditions. Usually, this
603 increases overall performance, but may sometimes cause performance
604 degradation. If set, TCP will not cache metrics on closing
607 tcp_no_ssthresh_metrics_save - BOOLEAN
608 Controls whether TCP saves ssthresh metrics in the route cache.
610 Default is 1, which disables ssthresh metrics.
612 tcp_orphan_retries - INTEGER
613 This value influences the timeout of a locally closed TCP connection,
614 when RTO retransmissions remain unacknowledged.
615 See tcp_retries2 for more details.
617 The default value is 8.
619 If your machine is a loaded WEB server,
620 you should think about lowering this value, such sockets
621 may consume significant resources. Cf. tcp_max_orphans.
623 tcp_recovery - INTEGER
624 This value is a bitmap to enable various experimental loss recovery
627 ========= =============================================================
628 RACK: 0x1 enables the RACK loss detection for fast detection of lost
629 retransmissions and tail drops. It also subsumes and disables
630 RFC6675 recovery for SACK connections.
632 RACK: 0x2 makes RACK's reordering window static (min_rtt/4).
634 RACK: 0x4 disables RACK's DUPACK threshold heuristic
635 ========= =============================================================
639 tcp_reflect_tos - BOOLEAN
640 For listening sockets, reuse the DSCP value of the initial SYN message
641 for outgoing packets. This allows to have both directions of a TCP
642 stream to use the same DSCP value, assuming DSCP remains unchanged for
643 the lifetime of the connection.
645 This options affects both IPv4 and IPv6.
647 Default: 0 (disabled)
649 tcp_reordering - INTEGER
650 Initial reordering level of packets in a TCP stream.
651 TCP stack can then dynamically adjust flow reordering level
652 between this initial value and tcp_max_reordering
656 tcp_max_reordering - INTEGER
657 Maximal reordering level of packets in a TCP stream.
658 300 is a fairly conservative value, but you might increase it
659 if paths are using per packet load balancing (like bonding rr mode)
663 tcp_retrans_collapse - BOOLEAN
664 Bug-to-bug compatibility with some broken printers.
665 On retransmit try to send bigger packets to work around bugs in
668 tcp_retries1 - INTEGER
669 This value influences the time, after which TCP decides, that
670 something is wrong due to unacknowledged RTO retransmissions,
671 and reports this suspicion to the network layer.
672 See tcp_retries2 for more details.
674 RFC 1122 recommends at least 3 retransmissions, which is the
677 tcp_retries2 - INTEGER
678 This value influences the timeout of an alive TCP connection,
679 when RTO retransmissions remain unacknowledged.
680 Given a value of N, a hypothetical TCP connection following
681 exponential backoff with an initial RTO of TCP_RTO_MIN would
682 retransmit N times before killing the connection at the (N+1)th RTO.
684 The default value of 15 yields a hypothetical timeout of 924.6
685 seconds and is a lower bound for the effective timeout.
686 TCP will effectively time out at the first RTO which exceeds the
687 hypothetical timeout.
689 RFC 1122 recommends at least 100 seconds for the timeout,
690 which corresponds to a value of at least 8.
692 tcp_rfc1337 - BOOLEAN
693 If set, the TCP stack behaves conforming to RFC1337. If unset,
694 we are not conforming to RFC, but prevent TCP TIME_WAIT
699 tcp_rmem - vector of 3 INTEGERs: min, default, max
700 min: Minimal size of receive buffer used by TCP sockets.
701 It is guaranteed to each TCP socket, even under moderate memory
706 default: initial size of receive buffer used by TCP sockets.
707 This value overrides net.core.rmem_default used by other protocols.
708 Default: 131072 bytes.
709 This value results in initial window of 65535.
711 max: maximal size of receive buffer allowed for automatically
712 selected receiver buffers for TCP socket. This value does not override
713 net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables
714 automatic tuning of that socket's receive buffer size, in which
715 case this value is ignored.
716 Default: between 131072 and 6MB, depending on RAM size.
719 Enable select acknowledgments (SACKS).
721 tcp_comp_sack_delay_ns - LONG INTEGER
722 TCP tries to reduce number of SACK sent, using a timer
723 based on 5% of SRTT, capped by this sysctl, in nano seconds.
724 The default is 1ms, based on TSO autosizing period.
726 Default : 1,000,000 ns (1 ms)
728 tcp_comp_sack_slack_ns - LONG INTEGER
729 This sysctl control the slack used when arming the
730 timer used by SACK compression. This gives extra time
731 for small RTT flows, and reduces system overhead by allowing
732 opportunistic reduction of timer interrupts.
734 Default : 100,000 ns (100 us)
736 tcp_comp_sack_nr - INTEGER
737 Max number of SACK that can be compressed.
738 Using 0 disables SACK compression.
742 tcp_slow_start_after_idle - BOOLEAN
743 If set, provide RFC2861 behavior and time out the congestion
744 window after an idle period. An idle period is defined at
745 the current RTO. If unset, the congestion window will not
746 be timed out after an idle period.
751 Use the Host requirements interpretation of the TCP urgent pointer field.
752 Most hosts use the older BSD interpretation, so if you turn this on
753 Linux might not communicate correctly with them.
757 tcp_synack_retries - INTEGER
758 Number of times SYNACKs for a passive TCP connection attempt will
759 be retransmitted. Should not be higher than 255. Default value
760 is 5, which corresponds to 31seconds till the last retransmission
761 with the current initial RTO of 1second. With this the final timeout
762 for a passive TCP connection will happen after 63seconds.
764 tcp_syncookies - INTEGER
765 Only valid when the kernel was compiled with CONFIG_SYN_COOKIES
766 Send out syncookies when the syn backlog queue of a socket
767 overflows. This is to prevent against the common 'SYN flood attack'
770 Note, that syncookies is fallback facility.
771 It MUST NOT be used to help highly loaded servers to stand
772 against legal connection rate. If you see SYN flood warnings
773 in your logs, but investigation shows that they occur
774 because of overload with legal connections, you should tune
775 another parameters until this warning disappear.
776 See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
778 syncookies seriously violate TCP protocol, do not allow
779 to use TCP extensions, can result in serious degradation
780 of some services (f.e. SMTP relaying), visible not by you,
781 but your clients and relays, contacting you. While you see
782 SYN flood warnings in logs not being really flooded, your server
783 is seriously misconfigured.
785 If you want to test which effects syncookies have to your
786 network connections you can set this knob to 2 to enable
787 unconditionally generation of syncookies.
789 tcp_migrate_req - BOOLEAN
790 The incoming connection is tied to a specific listening socket when
791 the initial SYN packet is received during the three-way handshake.
792 When a listener is closed, in-flight request sockets during the
793 handshake and established sockets in the accept queue are aborted.
795 If the listener has SO_REUSEPORT enabled, other listeners on the
796 same port should have been able to accept such connections. This
797 option makes it possible to migrate such child sockets to another
798 listener after close() or shutdown().
800 The BPF_SK_REUSEPORT_SELECT_OR_MIGRATE type of eBPF program should
801 usually be used to define the policy to pick an alive listener.
802 Otherwise, the kernel will randomly pick an alive listener only if
803 this option is enabled.
805 Note that migration between listeners with different settings may
806 crash applications. Let's say migration happens from listener A to
807 B, and only B has TCP_SAVE_SYN enabled. B cannot read SYN data from
808 the requests migrated from A. To avoid such a situation, cancel
809 migration by returning SK_DROP in the type of eBPF program, or
814 tcp_fastopen - INTEGER
815 Enable TCP Fast Open (RFC7413) to send and accept data in the opening
818 The client support is enabled by flag 0x1 (on by default). The client
819 then must use sendmsg() or sendto() with the MSG_FASTOPEN flag,
820 rather than connect() to send data in SYN.
822 The server support is enabled by flag 0x2 (off by default). Then
823 either enable for all listeners with another flag (0x400) or
824 enable individual listeners via TCP_FASTOPEN socket option with
825 the option value being the length of the syn-data backlog.
827 The values (bitmap) are
829 ===== ======== ======================================================
830 0x1 (client) enables sending data in the opening SYN on the client.
831 0x2 (server) enables the server support, i.e., allowing data in
832 a SYN packet to be accepted and passed to the
833 application before 3-way handshake finishes.
834 0x4 (client) send data in the opening SYN regardless of cookie
835 availability and without a cookie option.
836 0x200 (server) accept data-in-SYN w/o any cookie option present.
837 0x400 (server) enable all listeners to support Fast Open by
838 default without explicit TCP_FASTOPEN socket option.
839 ===== ======== ======================================================
843 Note that additional client or server features are only
844 effective if the basic support (0x1 and 0x2) are enabled respectively.
846 tcp_fastopen_blackhole_timeout_sec - INTEGER
847 Initial time period in second to disable Fastopen on active TCP sockets
848 when a TFO firewall blackhole issue happens.
849 This time period will grow exponentially when more blackhole issues
850 get detected right after Fastopen is re-enabled and will reset to
851 initial value when the blackhole issue goes away.
852 0 to disable the blackhole detection.
854 By default, it is set to 0 (feature is disabled).
856 tcp_fastopen_key - list of comma separated 32-digit hexadecimal INTEGERs
857 The list consists of a primary key and an optional backup key. The
858 primary key is used for both creating and validating cookies, while the
859 optional backup key is only used for validating cookies. The purpose of
860 the backup key is to maximize TFO validation when keys are rotated.
862 A randomly chosen primary key may be configured by the kernel if
863 the tcp_fastopen sysctl is set to 0x400 (see above), or if the
864 TCP_FASTOPEN setsockopt() optname is set and a key has not been
865 previously configured via sysctl. If keys are configured via
866 setsockopt() by using the TCP_FASTOPEN_KEY optname, then those
867 per-socket keys will be used instead of any keys that are specified via
870 A key is specified as 4 8-digit hexadecimal integers which are separated
871 by a '-' as: xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx. Leading zeros may be
872 omitted. A primary and a backup key may be specified by separating them
873 by a comma. If only one key is specified, it becomes the primary key and
874 any previously configured backup keys are removed.
876 tcp_syn_retries - INTEGER
877 Number of times initial SYNs for an active TCP connection attempt
878 will be retransmitted. Should not be higher than 127. Default value
879 is 6, which corresponds to 63seconds till the last retransmission
880 with the current initial RTO of 1second. With this the final timeout
881 for an active TCP connection attempt will happen after 127seconds.
883 tcp_timestamps - INTEGER
884 Enable timestamps as defined in RFC1323.
887 - 1: Enable timestamps as defined in RFC1323 and use random offset for
888 each connection rather than only using the current time.
889 - 2: Like 1, but without random offsets.
893 tcp_min_tso_segs - INTEGER
894 Minimal number of segments per TSO frame.
896 Since linux-3.12, TCP does an automatic sizing of TSO frames,
897 depending on flow rate, instead of filling 64Kbytes packets.
898 For specific usages, it's possible to force TCP to build big
899 TSO frames. Note that TCP stack might split too big TSO packets
900 if available window is too small.
904 tcp_tso_rtt_log - INTEGER
905 Adjustment of TSO packet sizes based on min_rtt
907 Starting from linux-5.18, TCP autosizing can be tweaked
908 for flows having small RTT.
910 Old autosizing was splitting the pacing budget to send 1024 TSO
913 tso_packet_size = sk->sk_pacing_rate / 1024;
915 With the new mechanism, we increase this TSO sizing using:
917 distance = min_rtt_usec / (2^tcp_tso_rtt_log)
918 tso_packet_size += gso_max_size >> distance;
920 This means that flows between very close hosts can use bigger
921 TSO packets, reducing their cpu costs.
923 If you want to use the old autosizing, set this sysctl to 0.
925 Default: 9 (2^9 = 512 usec)
927 tcp_pacing_ss_ratio - INTEGER
928 sk->sk_pacing_rate is set by TCP stack using a ratio applied
929 to current rate. (current_rate = cwnd * mss / srtt)
930 If TCP is in slow start, tcp_pacing_ss_ratio is applied
931 to let TCP probe for bigger speeds, assuming cwnd can be
932 doubled every other RTT.
936 tcp_pacing_ca_ratio - INTEGER
937 sk->sk_pacing_rate is set by TCP stack using a ratio applied
938 to current rate. (current_rate = cwnd * mss / srtt)
939 If TCP is in congestion avoidance phase, tcp_pacing_ca_ratio
940 is applied to conservatively probe for bigger throughput.
944 tcp_tso_win_divisor - INTEGER
945 This allows control over what percentage of the congestion window
946 can be consumed by a single TSO frame.
947 The setting of this parameter is a choice between burstiness and
948 building larger TSO frames.
952 tcp_tw_reuse - INTEGER
953 Enable reuse of TIME-WAIT sockets for new connections when it is
954 safe from protocol viewpoint.
958 - 2 - enable for loopback traffic only
960 It should not be changed without advice/request of technical
965 tcp_window_scaling - BOOLEAN
966 Enable window scaling as defined in RFC1323.
968 tcp_wmem - vector of 3 INTEGERs: min, default, max
969 min: Amount of memory reserved for send buffers for TCP sockets.
970 Each TCP socket has rights to use it due to fact of its birth.
974 default: initial size of send buffer used by TCP sockets. This
975 value overrides net.core.wmem_default used by other protocols.
977 It is usually lower than net.core.wmem_default.
981 max: Maximal amount of memory allowed for automatically tuned
982 send buffers for TCP sockets. This value does not override
983 net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables
984 automatic tuning of that socket's send buffer size, in which case
985 this value is ignored.
987 Default: between 64K and 4MB, depending on RAM size.
989 tcp_notsent_lowat - UNSIGNED INTEGER
990 A TCP socket can control the amount of unsent bytes in its write queue,
991 thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll()
992 reports POLLOUT events if the amount of unsent bytes is below a per
993 socket value, and if the write queue is not full. sendmsg() will
994 also not add new buffers if the limit is hit.
996 This global variable controls the amount of unsent data for
997 sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change
998 to the global variable has immediate effect.
1000 Default: UINT_MAX (0xFFFFFFFF)
1002 tcp_workaround_signed_windows - BOOLEAN
1003 If set, assume no receipt of a window scaling option means the
1004 remote TCP is broken and treats the window as a signed quantity.
1005 If unset, assume the remote TCP is not broken even if we do
1006 not receive a window scaling option from them.
1010 tcp_thin_linear_timeouts - BOOLEAN
1011 Enable dynamic triggering of linear timeouts for thin streams.
1012 If set, a check is performed upon retransmission by timeout to
1013 determine if the stream is thin (less than 4 packets in flight).
1014 As long as the stream is found to be thin, up to 6 linear
1015 timeouts may be performed before exponential backoff mode is
1016 initiated. This improves retransmission latency for
1017 non-aggressive thin streams, often found to be time-dependent.
1018 For more information on thin streams, see
1019 Documentation/networking/tcp-thin.rst
1023 tcp_limit_output_bytes - INTEGER
1024 Controls TCP Small Queue limit per tcp socket.
1025 TCP bulk sender tends to increase packets in flight until it
1026 gets losses notifications. With SNDBUF autotuning, this can
1027 result in a large amount of packets queued on the local machine
1028 (e.g.: qdiscs, CPU backlog, or device) hurting latency of other
1029 flows, for typical pfifo_fast qdiscs. tcp_limit_output_bytes
1030 limits the number of bytes on qdisc or device to reduce artificial
1031 RTT/cwnd and reduce bufferbloat.
1033 Default: 1048576 (16 * 65536)
1035 tcp_challenge_ack_limit - INTEGER
1036 Limits number of Challenge ACK sent per second, as recommended
1037 in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
1038 Note that this per netns rate limit can allow some side channel
1039 attacks and probably should not be enabled.
1040 TCP stack implements per TCP socket limits anyway.
1041 Default: INT_MAX (unlimited)
1046 udp_l3mdev_accept - BOOLEAN
1047 Enabling this option allows a "global" bound socket to work
1048 across L3 master domains (e.g., VRFs) with packets capable of
1049 being received regardless of the L3 domain in which they
1050 originated. Only valid when the kernel was compiled with
1051 CONFIG_NET_L3_MASTER_DEV.
1053 Default: 0 (disabled)
1055 udp_mem - vector of 3 INTEGERs: min, pressure, max
1056 Number of pages allowed for queueing by all UDP sockets.
1058 min: Number of pages allowed for queueing by all UDP sockets.
1060 pressure: This value was introduced to follow format of tcp_mem.
1062 max: This value was introduced to follow format of tcp_mem.
1064 Default is calculated at boot time from amount of available memory.
1066 udp_rmem_min - INTEGER
1067 Minimal size of receive buffer used by UDP sockets in moderation.
1068 Each UDP socket is able to use the size for receiving data, even if
1069 total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
1073 udp_wmem_min - INTEGER
1074 UDP does not have tx memory accounting and this tunable has no effect.
1079 raw_l3mdev_accept - BOOLEAN
1080 Enabling this option allows a "global" bound socket to work
1081 across L3 master domains (e.g., VRFs) with packets capable of
1082 being received regardless of the L3 domain in which they
1083 originated. Only valid when the kernel was compiled with
1084 CONFIG_NET_L3_MASTER_DEV.
1086 Default: 1 (enabled)
1091 cipso_cache_enable - BOOLEAN
1092 If set, enable additions to and lookups from the CIPSO label mapping
1093 cache. If unset, additions are ignored and lookups always result in a
1094 miss. However, regardless of the setting the cache is still
1095 invalidated when required when means you can safely toggle this on and
1096 off and the cache will always be "safe".
1100 cipso_cache_bucket_size - INTEGER
1101 The CIPSO label cache consists of a fixed size hash table with each
1102 hash bucket containing a number of cache entries. This variable limits
1103 the number of entries in each hash bucket; the larger the value is, the
1104 more CIPSO label mappings that can be cached. When the number of
1105 entries in a given hash bucket reaches this limit adding new entries
1106 causes the oldest entry in the bucket to be removed to make room.
1110 cipso_rbm_optfmt - BOOLEAN
1111 Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
1112 the CIPSO draft specification (see Documentation/netlabel for details).
1113 This means that when set the CIPSO tag will be padded with empty
1114 categories in order to make the packet data 32-bit aligned.
1118 cipso_rbm_structvalid - BOOLEAN
1119 If set, do a very strict check of the CIPSO option when
1120 ip_options_compile() is called. If unset, relax the checks done during
1121 ip_options_compile(). Either way is "safe" as errors are caught else
1122 where in the CIPSO processing code but setting this to 0 (False) should
1123 result in less work (i.e. it should be faster) but could cause problems
1124 with other implementations that require strict checking.
1131 ip_local_port_range - 2 INTEGERS
1132 Defines the local port range that is used by TCP and UDP to
1133 choose the local port. The first number is the first, the
1134 second the last local port number.
1135 If possible, it is better these numbers have different parity
1136 (one even and one odd value).
1137 Must be greater than or equal to ip_unprivileged_port_start.
1138 The default values are 32768 and 60999 respectively.
1140 ip_local_reserved_ports - list of comma separated ranges
1141 Specify the ports which are reserved for known third-party
1142 applications. These ports will not be used by automatic port
1143 assignments (e.g. when calling connect() or bind() with port
1144 number 0). Explicit port allocation behavior is unchanged.
1146 The format used for both input and output is a comma separated
1147 list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and
1148 10). Writing to the file will clear all previously reserved
1149 ports and update the current list with the one given in the
1152 Note that ip_local_port_range and ip_local_reserved_ports
1153 settings are independent and both are considered by the kernel
1154 when determining which ports are available for automatic port
1157 You can reserve ports which are not in the current
1158 ip_local_port_range, e.g.::
1160 $ cat /proc/sys/net/ipv4/ip_local_port_range
1162 $ cat /proc/sys/net/ipv4/ip_local_reserved_ports
1165 although this is redundant. However such a setting is useful
1166 if later the port range is changed to a value that will
1167 include the reserved ports. Also keep in mind, that overlapping
1168 of these ranges may affect probability of selecting ephemeral
1169 ports which are right after block of reserved ports.
1173 ip_unprivileged_port_start - INTEGER
1174 This is a per-namespace sysctl. It defines the first
1175 unprivileged port in the network namespace. Privileged ports
1176 require root or CAP_NET_BIND_SERVICE in order to bind to them.
1177 To disable all privileged ports, set this to 0. They must not
1178 overlap with the ip_local_port_range.
1182 ip_nonlocal_bind - BOOLEAN
1183 If set, allows processes to bind() to non-local IP addresses,
1184 which can be quite useful - but may break some applications.
1188 ip_autobind_reuse - BOOLEAN
1189 By default, bind() does not select the ports automatically even if
1190 the new socket and all sockets bound to the port have SO_REUSEADDR.
1191 ip_autobind_reuse allows bind() to reuse the port and this is useful
1192 when you use bind()+connect(), but may break some applications.
1193 The preferred solution is to use IP_BIND_ADDRESS_NO_PORT and this
1194 option should only be set by experts.
1197 ip_dynaddr - INTEGER
1198 If set non-zero, enables support for dynamic addresses.
1199 If set to a non-zero value larger than 1, a kernel log
1200 message will be printed when dynamic address rewriting
1205 ip_early_demux - BOOLEAN
1206 Optimize input packet processing down to one demux for
1207 certain kinds of local sockets. Currently we only do this
1208 for established TCP and connected UDP sockets.
1210 It may add an additional cost for pure routing workloads that
1211 reduces overall throughput, in such case you should disable it.
1215 ping_group_range - 2 INTEGERS
1216 Restrict ICMP_PROTO datagram sockets to users in the group range.
1217 The default is "1 0", meaning, that nobody (not even root) may
1218 create ping sockets. Setting it to "100 100" would grant permissions
1219 to the single group. "0 4294967295" would enable it for the world, "100
1220 4294967295" would enable it for the users, but not daemons.
1222 tcp_early_demux - BOOLEAN
1223 Enable early demux for established TCP sockets.
1227 udp_early_demux - BOOLEAN
1228 Enable early demux for connected UDP sockets. Disable this if
1229 your system could experience more unconnected load.
1233 icmp_echo_ignore_all - BOOLEAN
1234 If set non-zero, then the kernel will ignore all ICMP ECHO
1235 requests sent to it.
1239 icmp_echo_enable_probe - BOOLEAN
1240 If set to one, then the kernel will respond to RFC 8335 PROBE
1241 requests sent to it.
1245 icmp_echo_ignore_broadcasts - BOOLEAN
1246 If set non-zero, then the kernel will ignore all ICMP ECHO and
1247 TIMESTAMP requests sent to it via broadcast/multicast.
1251 icmp_ratelimit - INTEGER
1252 Limit the maximal rates for sending ICMP packets whose type matches
1253 icmp_ratemask (see below) to specific targets.
1254 0 to disable any limiting,
1255 otherwise the minimal space between responses in milliseconds.
1256 Note that another sysctl, icmp_msgs_per_sec limits the number
1257 of ICMP packets sent on all targets.
1261 icmp_msgs_per_sec - INTEGER
1262 Limit maximal number of ICMP packets sent per second from this host.
1263 Only messages whose type matches icmp_ratemask (see below) are
1264 controlled by this limit. For security reasons, the precise count
1265 of messages per second is randomized.
1269 icmp_msgs_burst - INTEGER
1270 icmp_msgs_per_sec controls number of ICMP packets sent per second,
1271 while icmp_msgs_burst controls the burst size of these packets.
1272 For security reasons, the precise burst size is randomized.
1276 icmp_ratemask - INTEGER
1277 Mask made of ICMP types for which rates are being limited.
1279 Significant bits: IHGFEDCBA9876543210
1281 Default mask: 0000001100000011000 (6168)
1283 Bit definitions (see include/linux/icmp.h):
1285 = =========================
1287 3 Destination Unreachable [1]_
1288 4 Source Quench [1]_
1291 B Time Exceeded [1]_
1292 C Parameter Problem [1]_
1297 H Address Mask Request
1298 I Address Mask Reply
1299 = =========================
1301 .. [1] These are rate limited by default (see default mask above)
1303 icmp_ignore_bogus_error_responses - BOOLEAN
1304 Some routers violate RFC1122 by sending bogus responses to broadcast
1305 frames. Such violations are normally logged via a kernel warning.
1306 If this is set to TRUE, the kernel will not give such warnings, which
1307 will avoid log file clutter.
1311 icmp_errors_use_inbound_ifaddr - BOOLEAN
1313 If zero, icmp error messages are sent with the primary address of
1314 the exiting interface.
1316 If non-zero, the message will be sent with the primary address of
1317 the interface that received the packet that caused the icmp error.
1318 This is the behaviour many network administrators will expect from
1319 a router. And it can make debugging complicated network layouts
1322 Note that if no primary address exists for the interface selected,
1323 then the primary address of the first non-loopback interface that
1324 has one will be used regardless of this setting.
1328 igmp_max_memberships - INTEGER
1329 Change the maximum number of multicast groups we can subscribe to.
1332 Theoretical maximum value is bounded by having to send a membership
1333 report in a single datagram (i.e. the report can't span multiple
1334 datagrams, or risk confusing the switch and leaving groups you don't
1337 The number of supported groups 'M' is bounded by the number of group
1338 report entries you can fit into a single datagram of 65535 bytes.
1340 M = 65536-sizeof (ip header)/(sizeof(Group record))
1342 Group records are variable length, with a minimum of 12 bytes.
1343 So net.ipv4.igmp_max_memberships should not be set higher than:
1345 (65536-24) / 12 = 5459
1347 The value 5459 assumes no IP header options, so in practice
1348 this number may be lower.
1350 igmp_max_msf - INTEGER
1351 Maximum number of addresses allowed in the source filter list for a
1357 Controls the IGMP query robustness variable (see RFC2236 8.1).
1359 Default: 2 (as specified by RFC2236 8.1)
1361 Minimum: 1 (as specified by RFC6636 4.5)
1363 force_igmp_version - INTEGER
1364 - 0 - (default) No enforcement of a IGMP version, IGMPv1/v2 fallback
1365 allowed. Will back to IGMPv3 mode again if all IGMPv1/v2 Querier
1366 Present timer expires.
1367 - 1 - Enforce to use IGMP version 1. Will also reply IGMPv1 report if
1368 receive IGMPv2/v3 query.
1369 - 2 - Enforce to use IGMP version 2. Will fallback to IGMPv1 if receive
1370 IGMPv1 query message. Will reply report if receive IGMPv3 query.
1371 - 3 - Enforce to use IGMP version 3. The same react with default 0.
1375 this is not the same with force_mld_version because IGMPv3 RFC3376
1376 Security Considerations does not have clear description that we could
1377 ignore other version messages completely as MLDv2 RFC3810. So make
1378 this value as default 0 is recommended.
1380 ``conf/interface/*``
1381 changes special settings per interface (where
1382 interface" is the name of your network interface)
1385 is special, changes the settings for all interfaces
1387 log_martians - BOOLEAN
1388 Log packets with impossible addresses to kernel log.
1389 log_martians for the interface will be enabled if at least one of
1390 conf/{all,interface}/log_martians is set to TRUE,
1391 it will be disabled otherwise
1393 accept_redirects - BOOLEAN
1394 Accept ICMP redirect messages.
1395 accept_redirects for the interface will be enabled if:
1397 - both conf/{all,interface}/accept_redirects are TRUE in the case
1398 forwarding for the interface is enabled
1402 - at least one of conf/{all,interface}/accept_redirects is TRUE in the
1403 case forwarding for the interface is disabled
1405 accept_redirects for the interface will be disabled otherwise
1412 forwarding - BOOLEAN
1413 Enable IP forwarding on this interface. This controls whether packets
1414 received _on_ this interface can be forwarded.
1416 mc_forwarding - BOOLEAN
1417 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
1418 and a multicast routing daemon is required.
1419 conf/all/mc_forwarding must also be set to TRUE to enable multicast
1420 routing for the interface
1423 Integer value used to differentiate the devices by the medium they
1424 are attached to. Two devices can have different id values when
1425 the broadcast packets are received only on one of them.
1426 The default value 0 means that the device is the only interface
1427 to its medium, value of -1 means that medium is not known.
1429 Currently, it is used to change the proxy_arp behavior:
1430 the proxy_arp feature is enabled for packets forwarded between
1431 two devices attached to different media.
1436 proxy_arp for the interface will be enabled if at least one of
1437 conf/{all,interface}/proxy_arp is set to TRUE,
1438 it will be disabled otherwise
1440 proxy_arp_pvlan - BOOLEAN
1441 Private VLAN proxy arp.
1443 Basically allow proxy arp replies back to the same interface
1444 (from which the ARP request/solicitation was received).
1446 This is done to support (ethernet) switch features, like RFC
1447 3069, where the individual ports are NOT allowed to
1448 communicate with each other, but they are allowed to talk to
1449 the upstream router. As described in RFC 3069, it is possible
1450 to allow these hosts to communicate through the upstream
1451 router by proxy_arp'ing. Don't need to be used together with
1454 This technology is known by different names:
1456 In RFC 3069 it is called VLAN Aggregation.
1457 Cisco and Allied Telesyn call it Private VLAN.
1458 Hewlett-Packard call it Source-Port filtering or port-isolation.
1459 Ericsson call it MAC-Forced Forwarding (RFC Draft).
1461 shared_media - BOOLEAN
1462 Send(router) or accept(host) RFC1620 shared media redirects.
1463 Overrides secure_redirects.
1465 shared_media for the interface will be enabled if at least one of
1466 conf/{all,interface}/shared_media is set to TRUE,
1467 it will be disabled otherwise
1471 secure_redirects - BOOLEAN
1472 Accept ICMP redirect messages only to gateways listed in the
1473 interface's current gateway list. Even if disabled, RFC1122 redirect
1476 Overridden by shared_media.
1478 secure_redirects for the interface will be enabled if at least one of
1479 conf/{all,interface}/secure_redirects is set to TRUE,
1480 it will be disabled otherwise
1484 send_redirects - BOOLEAN
1485 Send redirects, if router.
1487 send_redirects for the interface will be enabled if at least one of
1488 conf/{all,interface}/send_redirects is set to TRUE,
1489 it will be disabled otherwise
1493 bootp_relay - BOOLEAN
1494 Accept packets with source address 0.b.c.d destined
1495 not to this host as local ones. It is supposed, that
1496 BOOTP relay daemon will catch and forward such packets.
1497 conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
1502 Not Implemented Yet.
1504 accept_source_route - BOOLEAN
1505 Accept packets with SRR option.
1506 conf/all/accept_source_route must also be set to TRUE to accept packets
1507 with SRR option on the interface
1514 accept_local - BOOLEAN
1515 Accept packets with local source addresses. In combination with
1516 suitable routing, this can be used to direct packets between two
1517 local interfaces over the wire and have them accepted properly.
1520 route_localnet - BOOLEAN
1521 Do not consider loopback addresses as martian source or destination
1522 while routing. This enables the use of 127/8 for local routing purposes.
1527 - 0 - No source validation.
1528 - 1 - Strict mode as defined in RFC3704 Strict Reverse Path
1529 Each incoming packet is tested against the FIB and if the interface
1530 is not the best reverse path the packet check will fail.
1531 By default failed packets are discarded.
1532 - 2 - Loose mode as defined in RFC3704 Loose Reverse Path
1533 Each incoming packet's source address is also tested against the FIB
1534 and if the source address is not reachable via any interface
1535 the packet check will fail.
1537 Current recommended practice in RFC3704 is to enable strict mode
1538 to prevent IP spoofing from DDos attacks. If using asymmetric routing
1539 or other complicated routing, then loose mode is recommended.
1541 The max value from conf/{all,interface}/rp_filter is used
1542 when doing source validation on the {interface}.
1544 Default value is 0. Note that some distributions enable it
1547 src_valid_mark - BOOLEAN
1548 - 0 - The fwmark of the packet is not included in reverse path
1549 route lookup. This allows for asymmetric routing configurations
1550 utilizing the fwmark in only one direction, e.g., transparent
1553 - 1 - The fwmark of the packet is included in reverse path route
1554 lookup. This permits rp_filter to function when the fwmark is
1555 used for routing traffic in both directions.
1557 This setting also affects the utilization of fmwark when
1558 performing source address selection for ICMP replies, or
1559 determining addresses stored for the IPOPT_TS_TSANDADDR and
1560 IPOPT_RR IP options.
1562 The max value from conf/{all,interface}/src_valid_mark is used.
1566 arp_filter - BOOLEAN
1567 - 1 - Allows you to have multiple network interfaces on the same
1568 subnet, and have the ARPs for each interface be answered
1569 based on whether or not the kernel would route a packet from
1570 the ARP'd IP out that interface (therefore you must use source
1571 based routing for this to work). In other words it allows control
1572 of which cards (usually 1) will respond to an arp request.
1574 - 0 - (default) The kernel can respond to arp requests with addresses
1575 from other interfaces. This may seem wrong but it usually makes
1576 sense, because it increases the chance of successful communication.
1577 IP addresses are owned by the complete host on Linux, not by
1578 particular interfaces. Only for more complex setups like load-
1579 balancing, does this behaviour cause problems.
1581 arp_filter for the interface will be enabled if at least one of
1582 conf/{all,interface}/arp_filter is set to TRUE,
1583 it will be disabled otherwise
1585 arp_announce - INTEGER
1586 Define different restriction levels for announcing the local
1587 source IP address from IP packets in ARP requests sent on
1590 - 0 - (default) Use any local address, configured on any interface
1591 - 1 - Try to avoid local addresses that are not in the target's
1592 subnet for this interface. This mode is useful when target
1593 hosts reachable via this interface require the source IP
1594 address in ARP requests to be part of their logical network
1595 configured on the receiving interface. When we generate the
1596 request we will check all our subnets that include the
1597 target IP and will preserve the source address if it is from
1598 such subnet. If there is no such subnet we select source
1599 address according to the rules for level 2.
1600 - 2 - Always use the best local address for this target.
1601 In this mode we ignore the source address in the IP packet
1602 and try to select local address that we prefer for talks with
1603 the target host. Such local address is selected by looking
1604 for primary IP addresses on all our subnets on the outgoing
1605 interface that include the target IP address. If no suitable
1606 local address is found we select the first local address
1607 we have on the outgoing interface or on all other interfaces,
1608 with the hope we will receive reply for our request and
1609 even sometimes no matter the source IP address we announce.
1611 The max value from conf/{all,interface}/arp_announce is used.
1613 Increasing the restriction level gives more chance for
1614 receiving answer from the resolved target while decreasing
1615 the level announces more valid sender's information.
1617 arp_ignore - INTEGER
1618 Define different modes for sending replies in response to
1619 received ARP requests that resolve local target IP addresses:
1621 - 0 - (default): reply for any local target IP address, configured
1623 - 1 - reply only if the target IP address is local address
1624 configured on the incoming interface
1625 - 2 - reply only if the target IP address is local address
1626 configured on the incoming interface and both with the
1627 sender's IP address are part from same subnet on this interface
1628 - 3 - do not reply for local addresses configured with scope host,
1629 only resolutions for global and link addresses are replied
1631 - 8 - do not reply for all local addresses
1633 The max value from conf/{all,interface}/arp_ignore is used
1634 when ARP request is received on the {interface}
1636 arp_notify - BOOLEAN
1637 Define mode for notification of address and device changes.
1639 == ==========================================================
1640 0 (default): do nothing
1641 1 Generate gratuitous arp requests when device is brought up
1642 or hardware address changes.
1643 == ==========================================================
1645 arp_accept - INTEGER
1646 Define behavior for accepting gratuitous ARP (garp) frames from devices
1647 that are not already present in the ARP table:
1649 - 0 - don't create new entries in the ARP table
1650 - 1 - create new entries in the ARP table
1651 - 2 - create new entries only if the source IP address is in the same
1652 subnet as an address configured on the interface that received the
1655 Both replies and requests type gratuitous arp will trigger the
1656 ARP table to be updated, if this setting is on.
1658 If the ARP table already contains the IP address of the
1659 gratuitous arp frame, the arp table will be updated regardless
1660 if this setting is on or off.
1662 arp_evict_nocarrier - BOOLEAN
1663 Clears the ARP cache on NOCARRIER events. This option is important for
1664 wireless devices where the ARP cache should not be cleared when roaming
1665 between access points on the same network. In most cases this should
1666 remain as the default (1).
1668 - 1 - (default): Clear the ARP cache on NOCARRIER events
1669 - 0 - Do not clear ARP cache on NOCARRIER events
1671 mcast_solicit - INTEGER
1672 The maximum number of multicast probes in INCOMPLETE state,
1673 when the associated hardware address is unknown. Defaults
1676 ucast_solicit - INTEGER
1677 The maximum number of unicast probes in PROBE state, when
1678 the hardware address is being reconfirmed. Defaults to 3.
1680 app_solicit - INTEGER
1681 The maximum number of probes to send to the user space ARP daemon
1682 via netlink before dropping back to multicast probes (see
1683 mcast_resolicit). Defaults to 0.
1685 mcast_resolicit - INTEGER
1686 The maximum number of multicast probes after unicast and
1687 app probes in PROBE state. Defaults to 0.
1689 disable_policy - BOOLEAN
1690 Disable IPSEC policy (SPD) for this interface
1692 disable_xfrm - BOOLEAN
1693 Disable IPSEC encryption on this interface, whatever the policy
1695 igmpv2_unsolicited_report_interval - INTEGER
1696 The interval in milliseconds in which the next unsolicited
1697 IGMPv1 or IGMPv2 report retransmit will take place.
1699 Default: 10000 (10 seconds)
1701 igmpv3_unsolicited_report_interval - INTEGER
1702 The interval in milliseconds in which the next unsolicited
1703 IGMPv3 report retransmit will take place.
1705 Default: 1000 (1 seconds)
1707 ignore_routes_with_linkdown - BOOLEAN
1708 Ignore routes whose link is down when performing a FIB lookup.
1710 promote_secondaries - BOOLEAN
1711 When a primary IP address is removed from this interface
1712 promote a corresponding secondary IP address instead of
1713 removing all the corresponding secondary IP addresses.
1715 drop_unicast_in_l2_multicast - BOOLEAN
1716 Drop any unicast IP packets that are received in link-layer
1717 multicast (or broadcast) frames.
1719 This behavior (for multicast) is actually a SHOULD in RFC
1720 1122, but is disabled by default for compatibility reasons.
1724 drop_gratuitous_arp - BOOLEAN
1725 Drop all gratuitous ARP frames, for example if there's a known
1726 good ARP proxy on the network and such frames need not be used
1727 (or in the case of 802.11, must not be used to prevent attacks.)
1733 Allows you to write a number, which can be used as required.
1737 xfrm4_gc_thresh - INTEGER
1738 (Obsolete since linux-4.14)
1739 The threshold at which we will start garbage collecting for IPv4
1740 destination cache entries. At twice this value the system will
1741 refuse new allocations.
1743 igmp_link_local_mcast_reports - BOOLEAN
1744 Enable IGMP reports for link local multicast groups in the
1750 kuznet@ms2.inr.ac.ru
1757 delon.nicolas@wanadoo.fr
1762 /proc/sys/net/ipv6/* Variables
1763 ==============================
1765 IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also
1766 apply to IPv6 [XXX?].
1768 bindv6only - BOOLEAN
1769 Default value for IPV6_V6ONLY socket option,
1770 which restricts use of the IPv6 socket to IPv6 communication
1773 - TRUE: disable IPv4-mapped address feature
1774 - FALSE: enable IPv4-mapped address feature
1776 Default: FALSE (as specified in RFC3493)
1778 flowlabel_consistency - BOOLEAN
1779 Protect the consistency (and unicity) of flow label.
1780 You have to disable it to use IPV6_FL_F_REFLECT flag on the
1788 auto_flowlabels - INTEGER
1789 Automatically generate flow labels based on a flow hash of the
1790 packet. This allows intermediate devices, such as routers, to
1791 identify packet flows for mechanisms like Equal Cost Multipath
1792 Routing (see RFC 6438).
1794 = ===========================================================
1795 0 automatic flow labels are completely disabled
1796 1 automatic flow labels are enabled by default, they can be
1797 disabled on a per socket basis using the IPV6_AUTOFLOWLABEL
1799 2 automatic flow labels are allowed, they may be enabled on a
1800 per socket basis using the IPV6_AUTOFLOWLABEL socket option
1801 3 automatic flow labels are enabled and enforced, they cannot
1802 be disabled by the socket option
1803 = ===========================================================
1807 flowlabel_state_ranges - BOOLEAN
1808 Split the flow label number space into two ranges. 0-0x7FFFF is
1809 reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF
1810 is reserved for stateless flow labels as described in RFC6437.
1817 flowlabel_reflect - INTEGER
1818 Control flow label reflection. Needed for Path MTU
1819 Discovery to work with Equal Cost Multipath Routing in anycast
1820 environments. See RFC 7690 and:
1821 https://tools.ietf.org/html/draft-wang-6man-flow-label-reflection-01
1825 - 1: enabled for established flows
1827 Note that this prevents automatic flowlabel changes, as done
1828 in "tcp: change IPv6 flow-label upon receiving spurious retransmission"
1829 and "tcp: Change txhash on every SYN and RTO retransmit"
1831 - 2: enabled for TCP RESET packets (no active listener)
1832 If set, a RST packet sent in response to a SYN packet on a closed
1833 port will reflect the incoming flow label.
1835 - 4: enabled for ICMPv6 echo reply messages.
1839 fib_multipath_hash_policy - INTEGER
1840 Controls which hash policy to use for multipath routes.
1842 Default: 0 (Layer 3)
1846 - 0 - Layer 3 (source and destination addresses plus flow label)
1847 - 1 - Layer 4 (standard 5-tuple)
1848 - 2 - Layer 3 or inner Layer 3 if present
1849 - 3 - Custom multipath hash. Fields used for multipath hash calculation
1850 are determined by fib_multipath_hash_fields sysctl
1852 fib_multipath_hash_fields - UNSIGNED INTEGER
1853 When fib_multipath_hash_policy is set to 3 (custom multipath hash), the
1854 fields used for multipath hash calculation are determined by this
1857 This value is a bitmask which enables various fields for multipath hash
1860 Possible fields are:
1862 ====== ============================
1863 0x0001 Source IP address
1864 0x0002 Destination IP address
1868 0x0020 Destination port
1869 0x0040 Inner source IP address
1870 0x0080 Inner destination IP address
1871 0x0100 Inner IP protocol
1872 0x0200 Inner Flow Label
1873 0x0400 Inner source port
1874 0x0800 Inner destination port
1875 ====== ============================
1877 Default: 0x0007 (source IP, destination IP and IP protocol)
1879 anycast_src_echo_reply - BOOLEAN
1880 Controls the use of anycast addresses as source addresses for ICMPv6
1888 idgen_delay - INTEGER
1889 Controls the delay in seconds after which time to retry
1890 privacy stable address generation if a DAD conflict is
1893 Default: 1 (as specified in RFC7217)
1895 idgen_retries - INTEGER
1896 Controls the number of retries to generate a stable privacy
1897 address if a DAD conflict is detected.
1899 Default: 3 (as specified in RFC7217)
1902 Controls the MLD query robustness variable (see RFC3810 9.1).
1904 Default: 2 (as specified by RFC3810 9.1)
1906 Minimum: 1 (as specified by RFC6636 4.5)
1908 max_dst_opts_number - INTEGER
1909 Maximum number of non-padding TLVs allowed in a Destination
1910 options extension header. If this value is less than zero
1911 then unknown options are disallowed and the number of known
1912 TLVs allowed is the absolute value of this number.
1916 max_hbh_opts_number - INTEGER
1917 Maximum number of non-padding TLVs allowed in a Hop-by-Hop
1918 options extension header. If this value is less than zero
1919 then unknown options are disallowed and the number of known
1920 TLVs allowed is the absolute value of this number.
1924 max_dst_opts_length - INTEGER
1925 Maximum length allowed for a Destination options extension
1928 Default: INT_MAX (unlimited)
1930 max_hbh_length - INTEGER
1931 Maximum length allowed for a Hop-by-Hop options extension
1934 Default: INT_MAX (unlimited)
1936 skip_notify_on_dev_down - BOOLEAN
1937 Controls whether an RTM_DELROUTE message is generated for routes
1938 removed when a device is taken down or deleted. IPv4 does not
1939 generate this message; IPv6 does by default. Setting this sysctl
1940 to true skips the message, making IPv4 and IPv6 on par in relying
1941 on userspace caches to track link events and evict routes.
1943 Default: false (generate message)
1945 nexthop_compat_mode - BOOLEAN
1946 New nexthop API provides a means for managing nexthops independent of
1947 prefixes. Backwards compatibilty with old route format is enabled by
1948 default which means route dumps and notifications contain the new
1949 nexthop attribute but also the full, expanded nexthop definition.
1950 Further, updates or deletes of a nexthop configuration generate route
1951 notifications for each fib entry using the nexthop. Once a system
1952 understands the new API, this sysctl can be disabled to achieve full
1953 performance benefits of the new API by disabling the nexthop expansion
1954 and extraneous notifications.
1955 Default: true (backward compat mode)
1957 fib_notify_on_flag_change - INTEGER
1958 Whether to emit RTM_NEWROUTE notifications whenever RTM_F_OFFLOAD/
1959 RTM_F_TRAP/RTM_F_OFFLOAD_FAILED flags are changed.
1961 After installing a route to the kernel, user space receives an
1962 acknowledgment, which means the route was installed in the kernel,
1963 but not necessarily in hardware.
1964 It is also possible for a route already installed in hardware to change
1965 its action and therefore its flags. For example, a host route that is
1966 trapping packets can be "promoted" to perform decapsulation following
1967 the installation of an IPinIP/VXLAN tunnel.
1968 The notifications will indicate to user-space the state of the route.
1970 Default: 0 (Do not emit notifications.)
1974 - 0 - Do not emit notifications.
1975 - 1 - Emit notifications.
1976 - 2 - Emit notifications only for RTM_F_OFFLOAD_FAILED flag change.
1979 Define the IOAM id of this node. Uses only 24 bits out of 32 in total.
1986 ioam6_id_wide - LONG INTEGER
1987 Define the wide IOAM id of this node. Uses only 56 bits out of 64 in
1988 total. Can be different from ioam6_id.
1991 Max: 0xFFFFFFFFFFFFFF
1993 Default: 0xFFFFFFFFFFFFFF
1997 ip6frag_high_thresh - INTEGER
1998 Maximum memory used to reassemble IPv6 fragments. When
1999 ip6frag_high_thresh bytes of memory is allocated for this purpose,
2000 the fragment handler will toss packets until ip6frag_low_thresh
2003 ip6frag_low_thresh - INTEGER
2004 See ip6frag_high_thresh
2006 ip6frag_time - INTEGER
2007 Time in seconds to keep an IPv6 fragment in memory.
2010 Change the interface-specific default settings.
2012 These settings would be used during creating new interfaces.
2016 Change all the interface-specific settings.
2018 [XXX: Other special features than forwarding?]
2020 conf/all/disable_ipv6 - BOOLEAN
2021 Changing this value is same as changing ``conf/default/disable_ipv6``
2022 setting and also all per-interface ``disable_ipv6`` settings to the same
2025 Reading this value does not have any particular meaning. It does not say
2026 whether IPv6 support is enabled or disabled. Returned value can be 1
2027 also in the case when some interface has ``disable_ipv6`` set to 0 and
2028 has configured IPv6 addresses.
2030 conf/all/forwarding - BOOLEAN
2031 Enable global IPv6 forwarding between all interfaces.
2033 IPv4 and IPv6 work differently here; e.g. netfilter must be used
2034 to control which interfaces may forward packets and which not.
2036 This also sets all interfaces' Host/Router setting
2037 'forwarding' to the specified value. See below for details.
2039 This referred to as global forwarding.
2044 fwmark_reflect - BOOLEAN
2045 Controls the fwmark of kernel-generated IPv6 reply packets that are not
2046 associated with a socket for example, TCP RSTs or ICMPv6 echo replies).
2047 If unset, these packets have a fwmark of zero. If set, they have the
2048 fwmark of the packet they are replying to.
2052 ``conf/interface/*``:
2053 Change special settings per interface.
2055 The functional behaviour for certain settings is different
2056 depending on whether local forwarding is enabled or not.
2059 Accept Router Advertisements; autoconfigure using them.
2061 It also determines whether or not to transmit Router
2062 Solicitations. If and only if the functional setting is to
2063 accept Router Advertisements, Router Solicitations will be
2066 Possible values are:
2068 == ===========================================================
2069 0 Do not accept Router Advertisements.
2070 1 Accept Router Advertisements if forwarding is disabled.
2071 2 Overrule forwarding behaviour. Accept Router Advertisements
2072 even if forwarding is enabled.
2073 == ===========================================================
2077 - enabled if local forwarding is disabled.
2078 - disabled if local forwarding is enabled.
2080 accept_ra_defrtr - BOOLEAN
2081 Learn default router in Router Advertisement.
2085 - enabled if accept_ra is enabled.
2086 - disabled if accept_ra is disabled.
2088 ra_defrtr_metric - UNSIGNED INTEGER
2089 Route metric for default route learned in Router Advertisement. This value
2090 will be assigned as metric for the default route learned via IPv6 Router
2091 Advertisement. Takes affect only if accept_ra_defrtr is enabled.
2096 Default: IP6_RT_PRIO_USER i.e. 1024.
2098 accept_ra_from_local - BOOLEAN
2099 Accept RA with source-address that is found on local machine
2100 if the RA is otherwise proper and able to be accepted.
2102 Default is to NOT accept these as it may be an un-intended
2107 - enabled if accept_ra_from_local is enabled
2108 on a specific interface.
2109 - disabled if accept_ra_from_local is disabled
2110 on a specific interface.
2112 accept_ra_min_hop_limit - INTEGER
2113 Minimum hop limit Information in Router Advertisement.
2115 Hop limit Information in Router Advertisement less than this
2116 variable shall be ignored.
2120 accept_ra_pinfo - BOOLEAN
2121 Learn Prefix Information in Router Advertisement.
2125 - enabled if accept_ra is enabled.
2126 - disabled if accept_ra is disabled.
2128 accept_ra_rt_info_min_plen - INTEGER
2129 Minimum prefix length of Route Information in RA.
2131 Route Information w/ prefix smaller than this variable shall
2136 * 0 if accept_ra_rtr_pref is enabled.
2137 * -1 if accept_ra_rtr_pref is disabled.
2139 accept_ra_rt_info_max_plen - INTEGER
2140 Maximum prefix length of Route Information in RA.
2142 Route Information w/ prefix larger than this variable shall
2147 * 0 if accept_ra_rtr_pref is enabled.
2148 * -1 if accept_ra_rtr_pref is disabled.
2150 accept_ra_rtr_pref - BOOLEAN
2151 Accept Router Preference in RA.
2155 - enabled if accept_ra is enabled.
2156 - disabled if accept_ra is disabled.
2158 accept_ra_mtu - BOOLEAN
2159 Apply the MTU value specified in RA option 5 (RFC4861). If
2160 disabled, the MTU specified in the RA will be ignored.
2164 - enabled if accept_ra is enabled.
2165 - disabled if accept_ra is disabled.
2167 accept_redirects - BOOLEAN
2172 - enabled if local forwarding is disabled.
2173 - disabled if local forwarding is enabled.
2175 accept_source_route - INTEGER
2176 Accept source routing (routing extension header).
2178 - >= 0: Accept only routing header type 2.
2179 - < 0: Do not accept routing header.
2184 Autoconfigure addresses using Prefix Information in Router
2189 - enabled if accept_ra_pinfo is enabled.
2190 - disabled if accept_ra_pinfo is disabled.
2192 dad_transmits - INTEGER
2193 The amount of Duplicate Address Detection probes to send.
2197 forwarding - INTEGER
2198 Configure interface-specific Host/Router behaviour.
2202 It is recommended to have the same setting on all
2203 interfaces; mixed router/host scenarios are rather uncommon.
2205 Possible values are:
2207 - 0 Forwarding disabled
2208 - 1 Forwarding enabled
2212 By default, Host behaviour is assumed. This means:
2214 1. IsRouter flag is not set in Neighbour Advertisements.
2215 2. If accept_ra is TRUE (default), transmit Router
2217 3. If accept_ra is TRUE (default), accept Router
2218 Advertisements (and do autoconfiguration).
2219 4. If accept_redirects is TRUE (default), accept Redirects.
2223 If local forwarding is enabled, Router behaviour is assumed.
2224 This means exactly the reverse from the above:
2226 1. IsRouter flag is set in Neighbour Advertisements.
2227 2. Router Solicitations are not sent unless accept_ra is 2.
2228 3. Router Advertisements are ignored unless accept_ra is 2.
2229 4. Redirects are ignored.
2231 Default: 0 (disabled) if global forwarding is disabled (default),
2232 otherwise 1 (enabled).
2235 Default Hop Limit to set.
2240 Default Maximum Transfer Unit
2242 Default: 1280 (IPv6 required minimum)
2244 ip_nonlocal_bind - BOOLEAN
2245 If set, allows processes to bind() to non-local IPv6 addresses,
2246 which can be quite useful - but may break some applications.
2250 router_probe_interval - INTEGER
2251 Minimum interval (in seconds) between Router Probing described
2256 router_solicitation_delay - INTEGER
2257 Number of seconds to wait after interface is brought up
2258 before sending Router Solicitations.
2262 router_solicitation_interval - INTEGER
2263 Number of seconds to wait between Router Solicitations.
2267 router_solicitations - INTEGER
2268 Number of Router Solicitations to send until assuming no
2269 routers are present.
2273 use_oif_addrs_only - BOOLEAN
2274 When enabled, the candidate source addresses for destinations
2275 routed via this interface are restricted to the set of addresses
2276 configured on this interface (vis. RFC 6724, section 4).
2280 use_tempaddr - INTEGER
2281 Preference for Privacy Extensions (RFC3041).
2283 * <= 0 : disable Privacy Extensions
2284 * == 1 : enable Privacy Extensions, but prefer public
2285 addresses over temporary addresses.
2286 * > 1 : enable Privacy Extensions and prefer temporary
2287 addresses over public addresses.
2291 * 0 (for most devices)
2292 * -1 (for point-to-point devices and loopback devices)
2294 temp_valid_lft - INTEGER
2295 valid lifetime (in seconds) for temporary addresses.
2297 Default: 172800 (2 days)
2299 temp_prefered_lft - INTEGER
2300 Preferred lifetime (in seconds) for temporary addresses.
2302 Default: 86400 (1 day)
2304 keep_addr_on_down - INTEGER
2305 Keep all IPv6 addresses on an interface down event. If set static
2306 global addresses with no expiration time are not flushed.
2309 * 0 : system default
2312 Default: 0 (addresses are removed)
2314 max_desync_factor - INTEGER
2315 Maximum value for DESYNC_FACTOR, which is a random value
2316 that ensures that clients don't synchronize with each
2317 other and generate new addresses at exactly the same time.
2318 value is in seconds.
2322 regen_max_retry - INTEGER
2323 Number of attempts before give up attempting to generate
2324 valid temporary addresses.
2328 max_addresses - INTEGER
2329 Maximum number of autoconfigured addresses per interface. Setting
2330 to zero disables the limitation. It is not recommended to set this
2331 value too large (or to zero) because it would be an easy way to
2332 crash the kernel by allowing too many addresses to be created.
2336 disable_ipv6 - BOOLEAN
2337 Disable IPv6 operation. If accept_dad is set to 2, this value
2338 will be dynamically set to TRUE if DAD fails for the link-local
2341 Default: FALSE (enable IPv6 operation)
2343 When this value is changed from 1 to 0 (IPv6 is being enabled),
2344 it will dynamically create a link-local address on the given
2345 interface and start Duplicate Address Detection, if necessary.
2347 When this value is changed from 0 to 1 (IPv6 is being disabled),
2348 it will dynamically delete all addresses and routes on the given
2349 interface. From now on it will not possible to add addresses/routes
2350 to the selected interface.
2352 accept_dad - INTEGER
2353 Whether to accept DAD (Duplicate Address Detection).
2355 == ==============================================================
2357 1 Enable DAD (default)
2358 2 Enable DAD, and disable IPv6 operation if MAC-based duplicate
2359 link-local address has been found.
2360 == ==============================================================
2362 DAD operation and mode on a given interface will be selected according
2363 to the maximum value of conf/{all,interface}/accept_dad.
2365 force_tllao - BOOLEAN
2366 Enable sending the target link-layer address option even when
2367 responding to a unicast neighbor solicitation.
2371 Quoting from RFC 2461, section 4.4, Target link-layer address:
2373 "The option MUST be included for multicast solicitations in order to
2374 avoid infinite Neighbor Solicitation "recursion" when the peer node
2375 does not have a cache entry to return a Neighbor Advertisements
2376 message. When responding to unicast solicitations, the option can be
2377 omitted since the sender of the solicitation has the correct link-
2378 layer address; otherwise it would not have be able to send the unicast
2379 solicitation in the first place. However, including the link-layer
2380 address in this case adds little overhead and eliminates a potential
2381 race condition where the sender deletes the cached link-layer address
2382 prior to receiving a response to a previous solicitation."
2384 ndisc_notify - BOOLEAN
2385 Define mode for notification of address and device changes.
2387 * 0 - (default): do nothing
2388 * 1 - Generate unsolicited neighbour advertisements when device is brought
2389 up or hardware address changes.
2391 ndisc_tclass - INTEGER
2392 The IPv6 Traffic Class to use by default when sending IPv6 Neighbor
2393 Discovery (Router Solicitation, Router Advertisement, Neighbor
2394 Solicitation, Neighbor Advertisement, Redirect) messages.
2395 These 8 bits can be interpreted as 6 high order bits holding the DSCP
2396 value and 2 low order bits representing ECN (which you probably want
2401 ndisc_evict_nocarrier - BOOLEAN
2402 Clears the neighbor discovery table on NOCARRIER events. This option is
2403 important for wireless devices where the neighbor discovery cache should
2404 not be cleared when roaming between access points on the same network.
2405 In most cases this should remain as the default (1).
2407 - 1 - (default): Clear neighbor discover cache on NOCARRIER events.
2408 - 0 - Do not clear neighbor discovery cache on NOCARRIER events.
2410 mldv1_unsolicited_report_interval - INTEGER
2411 The interval in milliseconds in which the next unsolicited
2412 MLDv1 report retransmit will take place.
2414 Default: 10000 (10 seconds)
2416 mldv2_unsolicited_report_interval - INTEGER
2417 The interval in milliseconds in which the next unsolicited
2418 MLDv2 report retransmit will take place.
2420 Default: 1000 (1 second)
2422 force_mld_version - INTEGER
2423 * 0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed
2424 * 1 - Enforce to use MLD version 1
2425 * 2 - Enforce to use MLD version 2
2427 suppress_frag_ndisc - INTEGER
2428 Control RFC 6980 (Security Implications of IPv6 Fragmentation
2429 with IPv6 Neighbor Discovery) behavior:
2431 * 1 - (default) discard fragmented neighbor discovery packets
2432 * 0 - allow fragmented neighbor discovery packets
2434 optimistic_dad - BOOLEAN
2435 Whether to perform Optimistic Duplicate Address Detection (RFC 4429).
2437 * 0: disabled (default)
2440 Optimistic Duplicate Address Detection for the interface will be enabled
2441 if at least one of conf/{all,interface}/optimistic_dad is set to 1,
2442 it will be disabled otherwise.
2444 use_optimistic - BOOLEAN
2445 If enabled, do not classify optimistic addresses as deprecated during
2446 source address selection. Preferred addresses will still be chosen
2447 before optimistic addresses, subject to other ranking in the source
2448 address selection algorithm.
2450 * 0: disabled (default)
2453 This will be enabled if at least one of
2454 conf/{all,interface}/use_optimistic is set to 1, disabled otherwise.
2456 stable_secret - IPv6 address
2457 This IPv6 address will be used as a secret to generate IPv6
2458 addresses for link-local addresses and autoconfigured
2459 ones. All addresses generated after setting this secret will
2460 be stable privacy ones by default. This can be changed via the
2461 addrgenmode ip-link. conf/default/stable_secret is used as the
2462 secret for the namespace, the interface specific ones can
2463 overwrite that. Writes to conf/all/stable_secret are refused.
2465 It is recommended to generate this secret during installation
2466 of a system and keep it stable after that.
2468 By default the stable secret is unset.
2470 addr_gen_mode - INTEGER
2471 Defines how link-local and autoconf addresses are generated.
2473 = =================================================================
2474 0 generate address based on EUI64 (default)
2475 1 do no generate a link-local address, use EUI64 for addresses
2476 generated from autoconf
2477 2 generate stable privacy addresses, using the secret from
2478 stable_secret (RFC7217)
2479 3 generate stable privacy addresses, using a random secret if unset
2480 = =================================================================
2482 drop_unicast_in_l2_multicast - BOOLEAN
2483 Drop any unicast IPv6 packets that are received in link-layer
2484 multicast (or broadcast) frames.
2486 By default this is turned off.
2488 drop_unsolicited_na - BOOLEAN
2489 Drop all unsolicited neighbor advertisements, for example if there's
2490 a known good NA proxy on the network and such frames need not be used
2491 (or in the case of 802.11, must not be used to prevent attacks.)
2493 By default this is turned off.
2495 accept_untracked_na - INTEGER
2496 Define behavior for accepting neighbor advertisements from devices that
2497 are absent in the neighbor cache:
2499 - 0 - (default) Do not accept unsolicited and untracked neighbor
2502 - 1 - Add a new neighbor cache entry in STALE state for routers on
2503 receiving a neighbor advertisement (either solicited or unsolicited)
2504 with target link-layer address option specified if no neighbor entry
2505 is already present for the advertised IPv6 address. Without this knob,
2506 NAs received for untracked addresses (absent in neighbor cache) are
2509 This is as per router-side behavior documented in RFC9131.
2511 This has lower precedence than drop_unsolicited_na.
2513 This will optimize the return path for the initial off-link
2514 communication that is initiated by a directly connected host, by
2515 ensuring that the first-hop router which turns on this setting doesn't
2516 have to buffer the initial return packets to do neighbor-solicitation.
2517 The prerequisite is that the host is configured to send unsolicited
2518 neighbor advertisements on interface bringup. This setting should be
2519 used in conjunction with the ndisc_notify setting on the host to
2520 satisfy this prerequisite.
2522 - 2 - Extend option (1) to add a new neighbor cache entry only if the
2523 source IP address is in the same subnet as an address configured on
2524 the interface that received the neighbor advertisement.
2526 enhanced_dad - BOOLEAN
2527 Include a nonce option in the IPv6 neighbor solicitation messages used for
2528 duplicate address detection per RFC7527. A received DAD NS will only signal
2529 a duplicate address if the nonce is different. This avoids any false
2530 detection of duplicates due to loopback of the NS messages that we send.
2531 The nonce option will be sent on an interface unless both of
2532 conf/{all,interface}/enhanced_dad are set to FALSE.
2540 Limit the maximal rates for sending ICMPv6 messages.
2542 0 to disable any limiting,
2543 otherwise the minimal space between responses in milliseconds.
2547 ratemask - list of comma separated ranges
2548 For ICMPv6 message types matching the ranges in the ratemask, limit
2549 the sending of the message according to ratelimit parameter.
2551 The format used for both input and output is a comma separated
2552 list of ranges (e.g. "0-127,129" for ICMPv6 message type 0 to 127 and
2553 129). Writing to the file will clear all previous ranges of ICMPv6
2554 message types and update the current list with the input.
2556 Refer to: https://www.iana.org/assignments/icmpv6-parameters/icmpv6-parameters.xhtml
2557 for numerical values of ICMPv6 message types, e.g. echo request is 128
2558 and echo reply is 129.
2560 Default: 0-1,3-127 (rate limit ICMPv6 errors except Packet Too Big)
2562 echo_ignore_all - BOOLEAN
2563 If set non-zero, then the kernel will ignore all ICMP ECHO
2564 requests sent to it over the IPv6 protocol.
2568 echo_ignore_multicast - BOOLEAN
2569 If set non-zero, then the kernel will ignore all ICMP ECHO
2570 requests sent to it over the IPv6 protocol via multicast.
2574 echo_ignore_anycast - BOOLEAN
2575 If set non-zero, then the kernel will ignore all ICMP ECHO
2576 requests sent to it over the IPv6 protocol destined to anycast address.
2580 xfrm6_gc_thresh - INTEGER
2581 (Obsolete since linux-4.14)
2582 The threshold at which we will start garbage collecting for IPv6
2583 destination cache entries. At twice this value the system will
2584 refuse new allocations.
2588 Pekka Savola <pekkas@netcore.fi>
2589 YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
2592 /proc/sys/net/bridge/* Variables:
2593 =================================
2595 bridge-nf-call-arptables - BOOLEAN
2596 - 1 : pass bridged ARP traffic to arptables' FORWARD chain.
2601 bridge-nf-call-iptables - BOOLEAN
2602 - 1 : pass bridged IPv4 traffic to iptables' chains.
2607 bridge-nf-call-ip6tables - BOOLEAN
2608 - 1 : pass bridged IPv6 traffic to ip6tables' chains.
2613 bridge-nf-filter-vlan-tagged - BOOLEAN
2614 - 1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
2619 bridge-nf-filter-pppoe-tagged - BOOLEAN
2620 - 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
2625 bridge-nf-pass-vlan-input-dev - BOOLEAN
2626 - 1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan
2627 interface on the bridge and set the netfilter input device to the
2628 vlan. This allows use of e.g. "iptables -i br0.1" and makes the
2629 REDIRECT target work with vlan-on-top-of-bridge interfaces. When no
2630 matching vlan interface is found, or this switch is off, the input
2631 device is set to the bridge interface.
2633 - 0: disable bridge netfilter vlan interface lookup.
2637 ``proc/sys/net/sctp/*`` Variables:
2638 ==================================
2640 addip_enable - BOOLEAN
2641 Enable or disable extension of Dynamic Address Reconfiguration
2642 (ADD-IP) functionality specified in RFC5061. This extension provides
2643 the ability to dynamically add and remove new addresses for the SCTP
2646 1: Enable extension.
2648 0: Disable extension.
2653 Enable or disable pf (pf is short for potentially failed) state. A value
2654 of pf_retrans > path_max_retrans also disables pf state. That is, one of
2655 both pf_enable and pf_retrans > path_max_retrans can disable pf state.
2656 Since pf_retrans and path_max_retrans can be changed by userspace
2657 application, sometimes user expects to disable pf state by the value of
2658 pf_retrans > path_max_retrans, but occasionally the value of pf_retrans
2659 or path_max_retrans is changed by the user application, this pf state is
2660 enabled. As such, it is necessary to add this to dynamically enable
2661 and disable pf state. See:
2662 https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover for
2672 Unset or enable/disable pf (pf is short for potentially failed) state
2673 exposure. Applications can control the exposure of the PF path state
2674 in the SCTP_PEER_ADDR_CHANGE event and the SCTP_GET_PEER_ADDR_INFO
2675 sockopt. When it's unset, no SCTP_PEER_ADDR_CHANGE event with
2676 SCTP_ADDR_PF state will be sent and a SCTP_PF-state transport info
2677 can be got via SCTP_GET_PEER_ADDR_INFO sockopt; When it's enabled,
2678 a SCTP_PEER_ADDR_CHANGE event will be sent for a transport becoming
2679 SCTP_PF state and a SCTP_PF-state transport info can be got via
2680 SCTP_GET_PEER_ADDR_INFO sockopt; When it's diabled, no
2681 SCTP_PEER_ADDR_CHANGE event will be sent and it returns -EACCES when
2682 trying to get a SCTP_PF-state transport info via SCTP_GET_PEER_ADDR_INFO
2685 0: Unset pf state exposure, Compatible with old applications.
2687 1: Disable pf state exposure.
2689 2: Enable pf state exposure.
2693 addip_noauth_enable - BOOLEAN
2694 Dynamic Address Reconfiguration (ADD-IP) requires the use of
2695 authentication to protect the operations of adding or removing new
2696 addresses. This requirement is mandated so that unauthorized hosts
2697 would not be able to hijack associations. However, older
2698 implementations may not have implemented this requirement while
2699 allowing the ADD-IP extension. For reasons of interoperability,
2700 we provide this variable to control the enforcement of the
2701 authentication requirement.
2703 == ===============================================================
2704 1 Allow ADD-IP extension to be used without authentication. This
2705 should only be set in a closed environment for interoperability
2706 with older implementations.
2708 0 Enforce the authentication requirement
2709 == ===============================================================
2713 auth_enable - BOOLEAN
2714 Enable or disable Authenticated Chunks extension. This extension
2715 provides the ability to send and receive authenticated chunks and is
2716 required for secure operation of Dynamic Address Reconfiguration
2719 - 1: Enable this extension.
2720 - 0: Disable this extension.
2724 prsctp_enable - BOOLEAN
2725 Enable or disable the Partial Reliability extension (RFC3758) which
2726 is used to notify peers that a given DATA should no longer be expected.
2728 - 1: Enable extension
2734 The limit of the number of new packets that can be initially sent. It
2735 controls how bursty the generated traffic can be.
2739 association_max_retrans - INTEGER
2740 Set the maximum number for retransmissions that an association can
2741 attempt deciding that the remote end is unreachable. If this value
2742 is exceeded, the association is terminated.
2746 max_init_retransmits - INTEGER
2747 The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
2748 that an association will attempt before declaring the destination
2749 unreachable and terminating.
2753 path_max_retrans - INTEGER
2754 The maximum number of retransmissions that will be attempted on a given
2755 path. Once this threshold is exceeded, the path is considered
2756 unreachable, and new traffic will use a different path when the
2757 association is multihomed.
2761 pf_retrans - INTEGER
2762 The number of retransmissions that will be attempted on a given path
2763 before traffic is redirected to an alternate transport (should one
2764 exist). Note this is distinct from path_max_retrans, as a path that
2765 passes the pf_retrans threshold can still be used. Its only
2766 deprioritized when a transmission path is selected by the stack. This
2767 setting is primarily used to enable fast failover mechanisms without
2768 having to reduce path_max_retrans to a very low value. See:
2769 http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt
2770 for details. Note also that a value of pf_retrans > path_max_retrans
2771 disables this feature. Since both pf_retrans and path_max_retrans can
2772 be changed by userspace application, a variable pf_enable is used to
2777 ps_retrans - INTEGER
2778 Primary.Switchover.Max.Retrans (PSMR), it's a tunable parameter coming
2779 from section-5 "Primary Path Switchover" in rfc7829. The primary path
2780 will be changed to another active path when the path error counter on
2781 the old primary path exceeds PSMR, so that "the SCTP sender is allowed
2782 to continue data transmission on a new working path even when the old
2783 primary destination address becomes active again". Note this feature
2784 is disabled by initializing 'ps_retrans' per netns as 0xffff by default,
2785 and its value can't be less than 'pf_retrans' when changing by sysctl.
2789 rto_initial - INTEGER
2790 The initial round trip timeout value in milliseconds that will be used
2791 in calculating round trip times. This is the initial time interval
2792 for retransmissions.
2797 The maximum value (in milliseconds) of the round trip timeout. This
2798 is the largest time interval that can elapse between retransmissions.
2803 The minimum value (in milliseconds) of the round trip timeout. This
2804 is the smallest time interval the can elapse between retransmissions.
2808 hb_interval - INTEGER
2809 The interval (in milliseconds) between HEARTBEAT chunks. These chunks
2810 are sent at the specified interval on idle paths to probe the state of
2811 a given path between 2 associations.
2815 sack_timeout - INTEGER
2816 The amount of time (in milliseconds) that the implementation will wait
2821 valid_cookie_life - INTEGER
2822 The default lifetime of the SCTP cookie (in milliseconds). The cookie
2823 is used during association establishment.
2827 cookie_preserve_enable - BOOLEAN
2828 Enable or disable the ability to extend the lifetime of the SCTP cookie
2829 that is used during the establishment phase of SCTP association
2831 - 1: Enable cookie lifetime extension.
2836 cookie_hmac_alg - STRING
2837 Select the hmac algorithm used when generating the cookie value sent by
2838 a listening sctp socket to a connecting client in the INIT-ACK chunk.
2845 Ability to assign md5 or sha1 as the selected alg is predicated on the
2846 configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and
2847 CONFIG_CRYPTO_SHA1).
2849 Default: Dependent on configuration. MD5 if available, else SHA1 if
2850 available, else none.
2852 rcvbuf_policy - INTEGER
2853 Determines if the receive buffer is attributed to the socket or to
2854 association. SCTP supports the capability to create multiple
2855 associations on a single socket. When using this capability, it is
2856 possible that a single stalled association that's buffering a lot
2857 of data may block other associations from delivering their data by
2858 consuming all of the receive buffer space. To work around this,
2859 the rcvbuf_policy could be set to attribute the receiver buffer space
2860 to each association instead of the socket. This prevents the described
2863 - 1: rcvbuf space is per association
2864 - 0: rcvbuf space is per socket
2868 sndbuf_policy - INTEGER
2869 Similar to rcvbuf_policy above, this applies to send buffer space.
2871 - 1: Send buffer is tracked per association
2872 - 0: Send buffer is tracked per socket.
2876 sctp_mem - vector of 3 INTEGERs: min, pressure, max
2877 Number of pages allowed for queueing by all SCTP sockets.
2879 min: Below this number of pages SCTP is not bothered about its
2880 memory appetite. When amount of memory allocated by SCTP exceeds
2881 this number, SCTP starts to moderate memory usage.
2883 pressure: This value was introduced to follow format of tcp_mem.
2885 max: Number of pages allowed for queueing by all SCTP sockets.
2887 Default is calculated at boot time from amount of available memory.
2889 sctp_rmem - vector of 3 INTEGERs: min, default, max
2890 Only the first value ("min") is used, "default" and "max" are
2893 min: Minimal size of receive buffer used by SCTP socket.
2894 It is guaranteed to each SCTP socket (but not association) even
2895 under moderate memory pressure.
2899 sctp_wmem - vector of 3 INTEGERs: min, default, max
2900 Only the first value ("min") is used, "default" and "max" are
2903 min: Minimum size of send buffer that can be used by SCTP sockets.
2904 It is guaranteed to each SCTP socket (but not association) even
2905 under moderate memory pressure.
2909 addr_scope_policy - INTEGER
2910 Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00
2912 - 0 - Disable IPv4 address scoping
2913 - 1 - Enable IPv4 address scoping
2914 - 2 - Follow draft but allow IPv4 private addresses
2915 - 3 - Follow draft but allow IPv4 link local addresses
2920 The listening port for the local UDP tunneling sock. Normally it's
2921 using the IANA-assigned UDP port number 9899 (sctp-tunneling).
2923 This UDP sock is used for processing the incoming UDP-encapsulated
2924 SCTP packets (from RFC6951), and shared by all applications in the
2925 same net namespace. This UDP sock will be closed when the value is
2928 The value will also be used to set the src port of the UDP header
2929 for the outgoing UDP-encapsulated SCTP packets. For the dest port,
2930 please refer to 'encap_port' below.
2934 encap_port - INTEGER
2935 The default remote UDP encapsulation port.
2937 This value is used to set the dest port of the UDP header for the
2938 outgoing UDP-encapsulated SCTP packets by default. Users can also
2939 change the value for each sock/asoc/transport by using setsockopt.
2940 For further information, please refer to RFC6951.
2942 Note that when connecting to a remote server, the client should set
2943 this to the port that the UDP tunneling sock on the peer server is
2944 listening to and the local UDP tunneling sock on the client also
2945 must be started. On the server, it would get the encap_port from
2946 the incoming packet's source port.
2950 plpmtud_probe_interval - INTEGER
2951 The time interval (in milliseconds) for the PLPMTUD probe timer,
2952 which is configured to expire after this period to receive an
2953 acknowledgment to a probe packet. This is also the time interval
2954 between the probes for the current pmtu when the probe search
2957 PLPMTUD will be disabled when 0 is set, and other values for it
2962 reconf_enable - BOOLEAN
2963 Enable or disable extension of Stream Reconfiguration functionality
2964 specified in RFC6525. This extension provides the ability to "reset"
2965 a stream, and it includes the Parameters of "Outgoing/Incoming SSN
2966 Reset", "SSN/TSN Reset" and "Add Outgoing/Incoming Streams".
2968 - 1: Enable extension.
2969 - 0: Disable extension.
2973 intl_enable - BOOLEAN
2974 Enable or disable extension of User Message Interleaving functionality
2975 specified in RFC8260. This extension allows the interleaving of user
2976 messages sent on different streams. With this feature enabled, I-DATA
2977 chunk will replace DATA chunk to carry user messages if also supported
2978 by the peer. Note that to use this feature, one needs to set this option
2979 to 1 and also needs to set socket options SCTP_FRAGMENT_INTERLEAVE to 2
2980 and SCTP_INTERLEAVING_SUPPORTED to 1.
2982 - 1: Enable extension.
2983 - 0: Disable extension.
2987 ecn_enable - BOOLEAN
2988 Control use of Explicit Congestion Notification (ECN) by SCTP.
2989 Like in TCP, ECN is used only when both ends of the SCTP connection
2990 indicate support for it. This feature is useful in avoiding losses
2991 due to congestion by allowing supporting routers to signal congestion
2992 before having to drop packets.
3000 ``/proc/sys/net/core/*``
3001 ========================
3003 Please see: Documentation/admin-guide/sysctl/net.rst for descriptions of these entries.
3006 ``/proc/sys/net/unix/*``
3007 ========================
3009 max_dgram_qlen - INTEGER
3010 The maximum length of dgram socket receive queue