1.. SPDX-License-Identifier: GPL-2.0 2 3========= 4IP Sysctl 5========= 6 7/proc/sys/net/ipv4/* Variables 8============================== 9 10ip_forward - BOOLEAN 11 - 0 - disabled (default) 12 - not 0 - enabled 13 14 Forward Packets between interfaces. 15 16 This variable is special, its change resets all configuration 17 parameters to their default state (RFC1122 for hosts, RFC1812 18 for routers) 19 20ip_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) 24 25ip_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 min_pmtu (see below). You will need 29 to raise min_pmtu to the smallest interface MTU on your system 30 manually if you want to avoid locally generated fragments. 31 32 In mode 2 incoming Path MTU Discovery messages will be 33 discarded. Outgoing frames are handled the same as in mode 1, 34 implicitly setting IP_PMTUDISC_DONT on every created socket. 35 36 Mode 3 is a hardened pmtu discover mode. The kernel will only 37 accept fragmentation-needed errors if the underlying protocol 38 can verify them besides a plain socket lookup. Current 39 protocols for which pmtu events will be honored are TCP, SCTP 40 and DCCP as they verify e.g. the sequence number or the 41 association. This mode should not be enabled globally but is 42 only intended to secure e.g. name servers in namespaces where 43 TCP path mtu must still work but path MTU information of other 44 protocols should be discarded. If enabled globally this mode 45 could break other protocols. 46 47 Possible values: 0-3 48 49 Default: FALSE 50 51min_pmtu - INTEGER 52 default 552 - minimum discovered Path MTU 53 54ip_forward_use_pmtu - BOOLEAN 55 By default we don't trust protocol path MTUs while forwarding 56 because they could be easily forged and can lead to unwanted 57 fragmentation by the router. 58 You only need to enable this if you have user-space software 59 which tries to discover path mtus by itself and depends on the 60 kernel honoring this information. This is normally not the 61 case. 62 63 Default: 0 (disabled) 64 65 Possible values: 66 67 - 0 - disabled 68 - 1 - enabled 69 70fwmark_reflect - BOOLEAN 71 Controls the fwmark of kernel-generated IPv4 reply packets that are not 72 associated with a socket for example, TCP RSTs or ICMP echo replies). 73 If unset, these packets have a fwmark of zero. If set, they have the 74 fwmark of the packet they are replying to. 75 76 Default: 0 77 78fib_multipath_use_neigh - BOOLEAN 79 Use status of existing neighbor entry when determining nexthop for 80 multipath routes. If disabled, neighbor information is not used and 81 packets could be directed to a failed nexthop. Only valid for kernels 82 built with CONFIG_IP_ROUTE_MULTIPATH enabled. 83 84 Default: 0 (disabled) 85 86 Possible values: 87 88 - 0 - disabled 89 - 1 - enabled 90 91fib_multipath_hash_policy - INTEGER 92 Controls which hash policy to use for multipath routes. Only valid 93 for kernels built with CONFIG_IP_ROUTE_MULTIPATH enabled. 94 95 Default: 0 (Layer 3) 96 97 Possible values: 98 99 - 0 - Layer 3 100 - 1 - Layer 4 101 - 2 - Layer 3 or inner Layer 3 if present 102 103fib_sync_mem - UNSIGNED INTEGER 104 Amount of dirty memory from fib entries that can be backlogged before 105 synchronize_rcu is forced. 106 107 Default: 512kB Minimum: 64kB Maximum: 64MB 108 109ip_forward_update_priority - INTEGER 110 Whether to update SKB priority from "TOS" field in IPv4 header after it 111 is forwarded. The new SKB priority is mapped from TOS field value 112 according to an rt_tos2priority table (see e.g. man tc-prio). 113 114 Default: 1 (Update priority.) 115 116 Possible values: 117 118 - 0 - Do not update priority. 119 - 1 - Update priority. 120 121route/max_size - INTEGER 122 Maximum number of routes allowed in the kernel. Increase 123 this when using large numbers of interfaces and/or routes. 124 125 From linux kernel 3.6 onwards, this is deprecated for ipv4 126 as route cache is no longer used. 127 128neigh/default/gc_thresh1 - INTEGER 129 Minimum number of entries to keep. Garbage collector will not 130 purge entries if there are fewer than this number. 131 132 Default: 128 133 134neigh/default/gc_thresh2 - INTEGER 135 Threshold when garbage collector becomes more aggressive about 136 purging entries. Entries older than 5 seconds will be cleared 137 when over this number. 138 139 Default: 512 140 141neigh/default/gc_thresh3 - INTEGER 142 Maximum number of non-PERMANENT neighbor entries allowed. Increase 143 this when using large numbers of interfaces and when communicating 144 with large numbers of directly-connected peers. 145 146 Default: 1024 147 148neigh/default/unres_qlen_bytes - INTEGER 149 The maximum number of bytes which may be used by packets 150 queued for each unresolved address by other network layers. 151 (added in linux 3.3) 152 153 Setting negative value is meaningless and will return error. 154 155 Default: SK_WMEM_MAX, (same as net.core.wmem_default). 156 157 Exact value depends on architecture and kernel options, 158 but should be enough to allow queuing 256 packets 159 of medium size. 160 161neigh/default/unres_qlen - INTEGER 162 The maximum number of packets which may be queued for each 163 unresolved address by other network layers. 164 165 (deprecated in linux 3.3) : use unres_qlen_bytes instead. 166 167 Prior to linux 3.3, the default value is 3 which may cause 168 unexpected packet loss. The current default value is calculated 169 according to default value of unres_qlen_bytes and true size of 170 packet. 171 172 Default: 101 173 174mtu_expires - INTEGER 175 Time, in seconds, that cached PMTU information is kept. 176 177min_adv_mss - INTEGER 178 The advertised MSS depends on the first hop route MTU, but will 179 never be lower than this setting. 180 181IP Fragmentation: 182 183ipfrag_high_thresh - LONG INTEGER 184 Maximum memory used to reassemble IP fragments. 185 186ipfrag_low_thresh - LONG INTEGER 187 (Obsolete since linux-4.17) 188 Maximum memory used to reassemble IP fragments before the kernel 189 begins to remove incomplete fragment queues to free up resources. 190 The kernel still accepts new fragments for defragmentation. 191 192ipfrag_time - INTEGER 193 Time in seconds to keep an IP fragment in memory. 194 195ipfrag_max_dist - INTEGER 196 ipfrag_max_dist is a non-negative integer value which defines the 197 maximum "disorder" which is allowed among fragments which share a 198 common IP source address. Note that reordering of packets is 199 not unusual, but if a large number of fragments arrive from a source 200 IP address while a particular fragment queue remains incomplete, it 201 probably indicates that one or more fragments belonging to that queue 202 have been lost. When ipfrag_max_dist is positive, an additional check 203 is done on fragments before they are added to a reassembly queue - if 204 ipfrag_max_dist (or more) fragments have arrived from a particular IP 205 address between additions to any IP fragment queue using that source 206 address, it's presumed that one or more fragments in the queue are 207 lost. The existing fragment queue will be dropped, and a new one 208 started. An ipfrag_max_dist value of zero disables this check. 209 210 Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can 211 result in unnecessarily dropping fragment queues when normal 212 reordering of packets occurs, which could lead to poor application 213 performance. Using a very large value, e.g. 50000, increases the 214 likelihood of incorrectly reassembling IP fragments that originate 215 from different IP datagrams, which could result in data corruption. 216 Default: 64 217 218INET peer storage 219================= 220 221inet_peer_threshold - INTEGER 222 The approximate size of the storage. Starting from this threshold 223 entries will be thrown aggressively. This threshold also determines 224 entries' time-to-live and time intervals between garbage collection 225 passes. More entries, less time-to-live, less GC interval. 226 227inet_peer_minttl - INTEGER 228 Minimum time-to-live of entries. Should be enough to cover fragment 229 time-to-live on the reassembling side. This minimum time-to-live is 230 guaranteed if the pool size is less than inet_peer_threshold. 231 Measured in seconds. 232 233inet_peer_maxttl - INTEGER 234 Maximum time-to-live of entries. Unused entries will expire after 235 this period of time if there is no memory pressure on the pool (i.e. 236 when the number of entries in the pool is very small). 237 Measured in seconds. 238 239TCP variables 240============= 241 242somaxconn - INTEGER 243 Limit of socket listen() backlog, known in userspace as SOMAXCONN. 244 Defaults to 4096. (Was 128 before linux-5.4) 245 See also tcp_max_syn_backlog for additional tuning for TCP sockets. 246 247tcp_abort_on_overflow - BOOLEAN 248 If listening service is too slow to accept new connections, 249 reset them. Default state is FALSE. It means that if overflow 250 occurred due to a burst, connection will recover. Enable this 251 option _only_ if you are really sure that listening daemon 252 cannot be tuned to accept connections faster. Enabling this 253 option can harm clients of your server. 254 255tcp_adv_win_scale - INTEGER 256 Count buffering overhead as bytes/2^tcp_adv_win_scale 257 (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale), 258 if it is <= 0. 259 260 Possible values are [-31, 31], inclusive. 261 262 Default: 1 263 264tcp_allowed_congestion_control - STRING 265 Show/set the congestion control choices available to non-privileged 266 processes. The list is a subset of those listed in 267 tcp_available_congestion_control. 268 269 Default is "reno" and the default setting (tcp_congestion_control). 270 271tcp_app_win - INTEGER 272 Reserve max(window/2^tcp_app_win, mss) of window for application 273 buffer. Value 0 is special, it means that nothing is reserved. 274 275 Default: 31 276 277tcp_autocorking - BOOLEAN 278 Enable TCP auto corking : 279 When applications do consecutive small write()/sendmsg() system calls, 280 we try to coalesce these small writes as much as possible, to lower 281 total amount of sent packets. This is done if at least one prior 282 packet for the flow is waiting in Qdisc queues or device transmit 283 queue. Applications can still use TCP_CORK for optimal behavior 284 when they know how/when to uncork their sockets. 285 286 Default : 1 287 288tcp_available_congestion_control - STRING 289 Shows the available congestion control choices that are registered. 290 More congestion control algorithms may be available as modules, 291 but not loaded. 292 293tcp_base_mss - INTEGER 294 The initial value of search_low to be used by the packetization layer 295 Path MTU discovery (MTU probing). If MTU probing is enabled, 296 this is the initial MSS used by the connection. 297 298tcp_mtu_probe_floor - INTEGER 299 If MTU probing is enabled this caps the minimum MSS used for search_low 300 for the connection. 301 302 Default : 48 303 304tcp_min_snd_mss - INTEGER 305 TCP SYN and SYNACK messages usually advertise an ADVMSS option, 306 as described in RFC 1122 and RFC 6691. 307 308 If this ADVMSS option is smaller than tcp_min_snd_mss, 309 it is silently capped to tcp_min_snd_mss. 310 311 Default : 48 (at least 8 bytes of payload per segment) 312 313tcp_congestion_control - STRING 314 Set the congestion control algorithm to be used for new 315 connections. The algorithm "reno" is always available, but 316 additional choices may be available based on kernel configuration. 317 Default is set as part of kernel configuration. 318 For passive connections, the listener congestion control choice 319 is inherited. 320 321 [see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ] 322 323tcp_dsack - BOOLEAN 324 Allows TCP to send "duplicate" SACKs. 325 326tcp_early_retrans - INTEGER 327 Tail loss probe (TLP) converts RTOs occurring due to tail 328 losses into fast recovery (draft-ietf-tcpm-rack). Note that 329 TLP requires RACK to function properly (see tcp_recovery below) 330 331 Possible values: 332 333 - 0 disables TLP 334 - 3 or 4 enables TLP 335 336 Default: 3 337 338tcp_ecn - INTEGER 339 Control use of Explicit Congestion Notification (ECN) by TCP. 340 ECN is used only when both ends of the TCP connection indicate 341 support for it. This feature is useful in avoiding losses due 342 to congestion by allowing supporting routers to signal 343 congestion before having to drop packets. 344 345 Possible values are: 346 347 = ===================================================== 348 0 Disable ECN. Neither initiate nor accept ECN. 349 1 Enable ECN when requested by incoming connections and 350 also request ECN on outgoing connection attempts. 351 2 Enable ECN when requested by incoming connections 352 but do not request ECN on outgoing connections. 353 = ===================================================== 354 355 Default: 2 356 357tcp_ecn_fallback - BOOLEAN 358 If the kernel detects that ECN connection misbehaves, enable fall 359 back to non-ECN. Currently, this knob implements the fallback 360 from RFC3168, section 6.1.1.1., but we reserve that in future, 361 additional detection mechanisms could be implemented under this 362 knob. The value is not used, if tcp_ecn or per route (or congestion 363 control) ECN settings are disabled. 364 365 Default: 1 (fallback enabled) 366 367tcp_fack - BOOLEAN 368 This is a legacy option, it has no effect anymore. 369 370tcp_fin_timeout - INTEGER 371 The length of time an orphaned (no longer referenced by any 372 application) connection will remain in the FIN_WAIT_2 state 373 before it is aborted at the local end. While a perfectly 374 valid "receive only" state for an un-orphaned connection, an 375 orphaned connection in FIN_WAIT_2 state could otherwise wait 376 forever for the remote to close its end of the connection. 377 378 Cf. tcp_max_orphans 379 380 Default: 60 seconds 381 382tcp_frto - INTEGER 383 Enables Forward RTO-Recovery (F-RTO) defined in RFC5682. 384 F-RTO is an enhanced recovery algorithm for TCP retransmission 385 timeouts. It is particularly beneficial in networks where the 386 RTT fluctuates (e.g., wireless). F-RTO is sender-side only 387 modification. It does not require any support from the peer. 388 389 By default it's enabled with a non-zero value. 0 disables F-RTO. 390 391tcp_fwmark_accept - BOOLEAN 392 If set, incoming connections to listening sockets that do not have a 393 socket mark will set the mark of the accepting socket to the fwmark of 394 the incoming SYN packet. This will cause all packets on that connection 395 (starting from the first SYNACK) to be sent with that fwmark. The 396 listening socket's mark is unchanged. Listening sockets that already 397 have a fwmark set via setsockopt(SOL_SOCKET, SO_MARK, ...) are 398 unaffected. 399 400 Default: 0 401 402tcp_invalid_ratelimit - INTEGER 403 Limit the maximal rate for sending duplicate acknowledgments 404 in response to incoming TCP packets that are for an existing 405 connection but that are invalid due to any of these reasons: 406 407 (a) out-of-window sequence number, 408 (b) out-of-window acknowledgment number, or 409 (c) PAWS (Protection Against Wrapped Sequence numbers) check failure 410 411 This can help mitigate simple "ack loop" DoS attacks, wherein 412 a buggy or malicious middlebox or man-in-the-middle can 413 rewrite TCP header fields in manner that causes each endpoint 414 to think that the other is sending invalid TCP segments, thus 415 causing each side to send an unterminating stream of duplicate 416 acknowledgments for invalid segments. 417 418 Using 0 disables rate-limiting of dupacks in response to 419 invalid segments; otherwise this value specifies the minimal 420 space between sending such dupacks, in milliseconds. 421 422 Default: 500 (milliseconds). 423 424tcp_keepalive_time - INTEGER 425 How often TCP sends out keepalive messages when keepalive is enabled. 426 Default: 2hours. 427 428tcp_keepalive_probes - INTEGER 429 How many keepalive probes TCP sends out, until it decides that the 430 connection is broken. Default value: 9. 431 432tcp_keepalive_intvl - INTEGER 433 How frequently the probes are send out. Multiplied by 434 tcp_keepalive_probes it is time to kill not responding connection, 435 after probes started. Default value: 75sec i.e. connection 436 will be aborted after ~11 minutes of retries. 437 438tcp_l3mdev_accept - BOOLEAN 439 Enables child sockets to inherit the L3 master device index. 440 Enabling this option allows a "global" listen socket to work 441 across L3 master domains (e.g., VRFs) with connected sockets 442 derived from the listen socket to be bound to the L3 domain in 443 which the packets originated. Only valid when the kernel was 444 compiled with CONFIG_NET_L3_MASTER_DEV. 445 446 Default: 0 (disabled) 447 448tcp_low_latency - BOOLEAN 449 This is a legacy option, it has no effect anymore. 450 451tcp_max_orphans - INTEGER 452 Maximal number of TCP sockets not attached to any user file handle, 453 held by system. If this number is exceeded orphaned connections are 454 reset immediately and warning is printed. This limit exists 455 only to prevent simple DoS attacks, you _must_ not rely on this 456 or lower the limit artificially, but rather increase it 457 (probably, after increasing installed memory), 458 if network conditions require more than default value, 459 and tune network services to linger and kill such states 460 more aggressively. Let me to remind again: each orphan eats 461 up to ~64K of unswappable memory. 462 463tcp_max_syn_backlog - INTEGER 464 Maximal number of remembered connection requests (SYN_RECV), 465 which have not received an acknowledgment from connecting client. 466 467 This is a per-listener limit. 468 469 The minimal value is 128 for low memory machines, and it will 470 increase in proportion to the memory of machine. 471 472 If server suffers from overload, try increasing this number. 473 474 Remember to also check /proc/sys/net/core/somaxconn 475 A SYN_RECV request socket consumes about 304 bytes of memory. 476 477tcp_max_tw_buckets - INTEGER 478 Maximal number of timewait sockets held by system simultaneously. 479 If this number is exceeded time-wait socket is immediately destroyed 480 and warning is printed. This limit exists only to prevent 481 simple DoS attacks, you _must_ not lower the limit artificially, 482 but rather increase it (probably, after increasing installed memory), 483 if network conditions require more than default value. 484 485tcp_mem - vector of 3 INTEGERs: min, pressure, max 486 min: below this number of pages TCP is not bothered about its 487 memory appetite. 488 489 pressure: when amount of memory allocated by TCP exceeds this number 490 of pages, TCP moderates its memory consumption and enters memory 491 pressure mode, which is exited when memory consumption falls 492 under "min". 493 494 max: number of pages allowed for queueing by all TCP sockets. 495 496 Defaults are calculated at boot time from amount of available 497 memory. 498 499tcp_min_rtt_wlen - INTEGER 500 The window length of the windowed min filter to track the minimum RTT. 501 A shorter window lets a flow more quickly pick up new (higher) 502 minimum RTT when it is moved to a longer path (e.g., due to traffic 503 engineering). A longer window makes the filter more resistant to RTT 504 inflations such as transient congestion. The unit is seconds. 505 506 Possible values: 0 - 86400 (1 day) 507 508 Default: 300 509 510tcp_moderate_rcvbuf - BOOLEAN 511 If set, TCP performs receive buffer auto-tuning, attempting to 512 automatically size the buffer (no greater than tcp_rmem[2]) to 513 match the size required by the path for full throughput. Enabled by 514 default. 515 516tcp_mtu_probing - INTEGER 517 Controls TCP Packetization-Layer Path MTU Discovery. Takes three 518 values: 519 520 - 0 - Disabled 521 - 1 - Disabled by default, enabled when an ICMP black hole detected 522 - 2 - Always enabled, use initial MSS of tcp_base_mss. 523 524tcp_probe_interval - UNSIGNED INTEGER 525 Controls how often to start TCP Packetization-Layer Path MTU 526 Discovery reprobe. The default is reprobing every 10 minutes as 527 per RFC4821. 528 529tcp_probe_threshold - INTEGER 530 Controls when TCP Packetization-Layer Path MTU Discovery probing 531 will stop in respect to the width of search range in bytes. Default 532 is 8 bytes. 533 534tcp_no_metrics_save - BOOLEAN 535 By default, TCP saves various connection metrics in the route cache 536 when the connection closes, so that connections established in the 537 near future can use these to set initial conditions. Usually, this 538 increases overall performance, but may sometimes cause performance 539 degradation. If set, TCP will not cache metrics on closing 540 connections. 541 542tcp_no_ssthresh_metrics_save - BOOLEAN 543 Controls whether TCP saves ssthresh metrics in the route cache. 544 545 Default is 1, which disables ssthresh metrics. 546 547tcp_orphan_retries - INTEGER 548 This value influences the timeout of a locally closed TCP connection, 549 when RTO retransmissions remain unacknowledged. 550 See tcp_retries2 for more details. 551 552 The default value is 8. 553 554 If your machine is a loaded WEB server, 555 you should think about lowering this value, such sockets 556 may consume significant resources. Cf. tcp_max_orphans. 557 558tcp_recovery - INTEGER 559 This value is a bitmap to enable various experimental loss recovery 560 features. 561 562 ========= ============================================================= 563 RACK: 0x1 enables the RACK loss detection for fast detection of lost 564 retransmissions and tail drops. It also subsumes and disables 565 RFC6675 recovery for SACK connections. 566 567 RACK: 0x2 makes RACK's reordering window static (min_rtt/4). 568 569 RACK: 0x4 disables RACK's DUPACK threshold heuristic 570 ========= ============================================================= 571 572 Default: 0x1 573 574tcp_reordering - INTEGER 575 Initial reordering level of packets in a TCP stream. 576 TCP stack can then dynamically adjust flow reordering level 577 between this initial value and tcp_max_reordering 578 579 Default: 3 580 581tcp_max_reordering - INTEGER 582 Maximal reordering level of packets in a TCP stream. 583 300 is a fairly conservative value, but you might increase it 584 if paths are using per packet load balancing (like bonding rr mode) 585 586 Default: 300 587 588tcp_retrans_collapse - BOOLEAN 589 Bug-to-bug compatibility with some broken printers. 590 On retransmit try to send bigger packets to work around bugs in 591 certain TCP stacks. 592 593tcp_retries1 - INTEGER 594 This value influences the time, after which TCP decides, that 595 something is wrong due to unacknowledged RTO retransmissions, 596 and reports this suspicion to the network layer. 597 See tcp_retries2 for more details. 598 599 RFC 1122 recommends at least 3 retransmissions, which is the 600 default. 601 602tcp_retries2 - INTEGER 603 This value influences the timeout of an alive TCP connection, 604 when RTO retransmissions remain unacknowledged. 605 Given a value of N, a hypothetical TCP connection following 606 exponential backoff with an initial RTO of TCP_RTO_MIN would 607 retransmit N times before killing the connection at the (N+1)th RTO. 608 609 The default value of 15 yields a hypothetical timeout of 924.6 610 seconds and is a lower bound for the effective timeout. 611 TCP will effectively time out at the first RTO which exceeds the 612 hypothetical timeout. 613 614 RFC 1122 recommends at least 100 seconds for the timeout, 615 which corresponds to a value of at least 8. 616 617tcp_rfc1337 - BOOLEAN 618 If set, the TCP stack behaves conforming to RFC1337. If unset, 619 we are not conforming to RFC, but prevent TCP TIME_WAIT 620 assassination. 621 622 Default: 0 623 624tcp_rmem - vector of 3 INTEGERs: min, default, max 625 min: Minimal size of receive buffer used by TCP sockets. 626 It is guaranteed to each TCP socket, even under moderate memory 627 pressure. 628 629 Default: 4K 630 631 default: initial size of receive buffer used by TCP sockets. 632 This value overrides net.core.rmem_default used by other protocols. 633 Default: 87380 bytes. This value results in window of 65535 with 634 default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit 635 less for default tcp_app_win. See below about these variables. 636 637 max: maximal size of receive buffer allowed for automatically 638 selected receiver buffers for TCP socket. This value does not override 639 net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables 640 automatic tuning of that socket's receive buffer size, in which 641 case this value is ignored. 642 Default: between 87380B and 6MB, depending on RAM size. 643 644tcp_sack - BOOLEAN 645 Enable select acknowledgments (SACKS). 646 647tcp_comp_sack_delay_ns - LONG INTEGER 648 TCP tries to reduce number of SACK sent, using a timer 649 based on 5% of SRTT, capped by this sysctl, in nano seconds. 650 The default is 1ms, based on TSO autosizing period. 651 652 Default : 1,000,000 ns (1 ms) 653 654tcp_comp_sack_nr - INTEGER 655 Max number of SACK that can be compressed. 656 Using 0 disables SACK compression. 657 658 Default : 44 659 660tcp_slow_start_after_idle - BOOLEAN 661 If set, provide RFC2861 behavior and time out the congestion 662 window after an idle period. An idle period is defined at 663 the current RTO. If unset, the congestion window will not 664 be timed out after an idle period. 665 666 Default: 1 667 668tcp_stdurg - BOOLEAN 669 Use the Host requirements interpretation of the TCP urgent pointer field. 670 Most hosts use the older BSD interpretation, so if you turn this on 671 Linux might not communicate correctly with them. 672 673 Default: FALSE 674 675tcp_synack_retries - INTEGER 676 Number of times SYNACKs for a passive TCP connection attempt will 677 be retransmitted. Should not be higher than 255. Default value 678 is 5, which corresponds to 31seconds till the last retransmission 679 with the current initial RTO of 1second. With this the final timeout 680 for a passive TCP connection will happen after 63seconds. 681 682tcp_syncookies - INTEGER 683 Only valid when the kernel was compiled with CONFIG_SYN_COOKIES 684 Send out syncookies when the syn backlog queue of a socket 685 overflows. This is to prevent against the common 'SYN flood attack' 686 Default: 1 687 688 Note, that syncookies is fallback facility. 689 It MUST NOT be used to help highly loaded servers to stand 690 against legal connection rate. If you see SYN flood warnings 691 in your logs, but investigation shows that they occur 692 because of overload with legal connections, you should tune 693 another parameters until this warning disappear. 694 See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow. 695 696 syncookies seriously violate TCP protocol, do not allow 697 to use TCP extensions, can result in serious degradation 698 of some services (f.e. SMTP relaying), visible not by you, 699 but your clients and relays, contacting you. While you see 700 SYN flood warnings in logs not being really flooded, your server 701 is seriously misconfigured. 702 703 If you want to test which effects syncookies have to your 704 network connections you can set this knob to 2 to enable 705 unconditionally generation of syncookies. 706 707tcp_fastopen - INTEGER 708 Enable TCP Fast Open (RFC7413) to send and accept data in the opening 709 SYN packet. 710 711 The client support is enabled by flag 0x1 (on by default). The client 712 then must use sendmsg() or sendto() with the MSG_FASTOPEN flag, 713 rather than connect() to send data in SYN. 714 715 The server support is enabled by flag 0x2 (off by default). Then 716 either enable for all listeners with another flag (0x400) or 717 enable individual listeners via TCP_FASTOPEN socket option with 718 the option value being the length of the syn-data backlog. 719 720 The values (bitmap) are 721 722 ===== ======== ====================================================== 723 0x1 (client) enables sending data in the opening SYN on the client. 724 0x2 (server) enables the server support, i.e., allowing data in 725 a SYN packet to be accepted and passed to the 726 application before 3-way handshake finishes. 727 0x4 (client) send data in the opening SYN regardless of cookie 728 availability and without a cookie option. 729 0x200 (server) accept data-in-SYN w/o any cookie option present. 730 0x400 (server) enable all listeners to support Fast Open by 731 default without explicit TCP_FASTOPEN socket option. 732 ===== ======== ====================================================== 733 734 Default: 0x1 735 736 Note that that additional client or server features are only 737 effective if the basic support (0x1 and 0x2) are enabled respectively. 738 739tcp_fastopen_blackhole_timeout_sec - INTEGER 740 Initial time period in second to disable Fastopen on active TCP sockets 741 when a TFO firewall blackhole issue happens. 742 This time period will grow exponentially when more blackhole issues 743 get detected right after Fastopen is re-enabled and will reset to 744 initial value when the blackhole issue goes away. 745 0 to disable the blackhole detection. 746 747 By default, it is set to 1hr. 748 749tcp_fastopen_key - list of comma separated 32-digit hexadecimal INTEGERs 750 The list consists of a primary key and an optional backup key. The 751 primary key is used for both creating and validating cookies, while the 752 optional backup key is only used for validating cookies. The purpose of 753 the backup key is to maximize TFO validation when keys are rotated. 754 755 A randomly chosen primary key may be configured by the kernel if 756 the tcp_fastopen sysctl is set to 0x400 (see above), or if the 757 TCP_FASTOPEN setsockopt() optname is set and a key has not been 758 previously configured via sysctl. If keys are configured via 759 setsockopt() by using the TCP_FASTOPEN_KEY optname, then those 760 per-socket keys will be used instead of any keys that are specified via 761 sysctl. 762 763 A key is specified as 4 8-digit hexadecimal integers which are separated 764 by a '-' as: xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx. Leading zeros may be 765 omitted. A primary and a backup key may be specified by separating them 766 by a comma. If only one key is specified, it becomes the primary key and 767 any previously configured backup keys are removed. 768 769tcp_syn_retries - INTEGER 770 Number of times initial SYNs for an active TCP connection attempt 771 will be retransmitted. Should not be higher than 127. Default value 772 is 6, which corresponds to 63seconds till the last retransmission 773 with the current initial RTO of 1second. With this the final timeout 774 for an active TCP connection attempt will happen after 127seconds. 775 776tcp_timestamps - INTEGER 777 Enable timestamps as defined in RFC1323. 778 779 - 0: Disabled. 780 - 1: Enable timestamps as defined in RFC1323 and use random offset for 781 each connection rather than only using the current time. 782 - 2: Like 1, but without random offsets. 783 784 Default: 1 785 786tcp_min_tso_segs - INTEGER 787 Minimal number of segments per TSO frame. 788 789 Since linux-3.12, TCP does an automatic sizing of TSO frames, 790 depending on flow rate, instead of filling 64Kbytes packets. 791 For specific usages, it's possible to force TCP to build big 792 TSO frames. Note that TCP stack might split too big TSO packets 793 if available window is too small. 794 795 Default: 2 796 797tcp_pacing_ss_ratio - INTEGER 798 sk->sk_pacing_rate is set by TCP stack using a ratio applied 799 to current rate. (current_rate = cwnd * mss / srtt) 800 If TCP is in slow start, tcp_pacing_ss_ratio is applied 801 to let TCP probe for bigger speeds, assuming cwnd can be 802 doubled every other RTT. 803 804 Default: 200 805 806tcp_pacing_ca_ratio - INTEGER 807 sk->sk_pacing_rate is set by TCP stack using a ratio applied 808 to current rate. (current_rate = cwnd * mss / srtt) 809 If TCP is in congestion avoidance phase, tcp_pacing_ca_ratio 810 is applied to conservatively probe for bigger throughput. 811 812 Default: 120 813 814tcp_tso_win_divisor - INTEGER 815 This allows control over what percentage of the congestion window 816 can be consumed by a single TSO frame. 817 The setting of this parameter is a choice between burstiness and 818 building larger TSO frames. 819 820 Default: 3 821 822tcp_tw_reuse - INTEGER 823 Enable reuse of TIME-WAIT sockets for new connections when it is 824 safe from protocol viewpoint. 825 826 - 0 - disable 827 - 1 - global enable 828 - 2 - enable for loopback traffic only 829 830 It should not be changed without advice/request of technical 831 experts. 832 833 Default: 2 834 835tcp_window_scaling - BOOLEAN 836 Enable window scaling as defined in RFC1323. 837 838tcp_wmem - vector of 3 INTEGERs: min, default, max 839 min: Amount of memory reserved for send buffers for TCP sockets. 840 Each TCP socket has rights to use it due to fact of its birth. 841 842 Default: 4K 843 844 default: initial size of send buffer used by TCP sockets. This 845 value overrides net.core.wmem_default used by other protocols. 846 847 It is usually lower than net.core.wmem_default. 848 849 Default: 16K 850 851 max: Maximal amount of memory allowed for automatically tuned 852 send buffers for TCP sockets. This value does not override 853 net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables 854 automatic tuning of that socket's send buffer size, in which case 855 this value is ignored. 856 857 Default: between 64K and 4MB, depending on RAM size. 858 859tcp_notsent_lowat - UNSIGNED INTEGER 860 A TCP socket can control the amount of unsent bytes in its write queue, 861 thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll() 862 reports POLLOUT events if the amount of unsent bytes is below a per 863 socket value, and if the write queue is not full. sendmsg() will 864 also not add new buffers if the limit is hit. 865 866 This global variable controls the amount of unsent data for 867 sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change 868 to the global variable has immediate effect. 869 870 Default: UINT_MAX (0xFFFFFFFF) 871 872tcp_workaround_signed_windows - BOOLEAN 873 If set, assume no receipt of a window scaling option means the 874 remote TCP is broken and treats the window as a signed quantity. 875 If unset, assume the remote TCP is not broken even if we do 876 not receive a window scaling option from them. 877 878 Default: 0 879 880tcp_thin_linear_timeouts - BOOLEAN 881 Enable dynamic triggering of linear timeouts for thin streams. 882 If set, a check is performed upon retransmission by timeout to 883 determine if the stream is thin (less than 4 packets in flight). 884 As long as the stream is found to be thin, up to 6 linear 885 timeouts may be performed before exponential backoff mode is 886 initiated. This improves retransmission latency for 887 non-aggressive thin streams, often found to be time-dependent. 888 For more information on thin streams, see 889 Documentation/networking/tcp-thin.txt 890 891 Default: 0 892 893tcp_limit_output_bytes - INTEGER 894 Controls TCP Small Queue limit per tcp socket. 895 TCP bulk sender tends to increase packets in flight until it 896 gets losses notifications. With SNDBUF autotuning, this can 897 result in a large amount of packets queued on the local machine 898 (e.g.: qdiscs, CPU backlog, or device) hurting latency of other 899 flows, for typical pfifo_fast qdiscs. tcp_limit_output_bytes 900 limits the number of bytes on qdisc or device to reduce artificial 901 RTT/cwnd and reduce bufferbloat. 902 903 Default: 1048576 (16 * 65536) 904 905tcp_challenge_ack_limit - INTEGER 906 Limits number of Challenge ACK sent per second, as recommended 907 in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks) 908 Default: 1000 909 910tcp_rx_skb_cache - BOOLEAN 911 Controls a per TCP socket cache of one skb, that might help 912 performance of some workloads. This might be dangerous 913 on systems with a lot of TCP sockets, since it increases 914 memory usage. 915 916 Default: 0 (disabled) 917 918UDP variables 919============= 920 921udp_l3mdev_accept - BOOLEAN 922 Enabling this option allows a "global" bound socket to work 923 across L3 master domains (e.g., VRFs) with packets capable of 924 being received regardless of the L3 domain in which they 925 originated. Only valid when the kernel was compiled with 926 CONFIG_NET_L3_MASTER_DEV. 927 928 Default: 0 (disabled) 929 930udp_mem - vector of 3 INTEGERs: min, pressure, max 931 Number of pages allowed for queueing by all UDP sockets. 932 933 min: Below this number of pages UDP is not bothered about its 934 memory appetite. When amount of memory allocated by UDP exceeds 935 this number, UDP starts to moderate memory usage. 936 937 pressure: This value was introduced to follow format of tcp_mem. 938 939 max: Number of pages allowed for queueing by all UDP sockets. 940 941 Default is calculated at boot time from amount of available memory. 942 943udp_rmem_min - INTEGER 944 Minimal size of receive buffer used by UDP sockets in moderation. 945 Each UDP socket is able to use the size for receiving data, even if 946 total pages of UDP sockets exceed udp_mem pressure. The unit is byte. 947 948 Default: 4K 949 950udp_wmem_min - INTEGER 951 Minimal size of send buffer used by UDP sockets in moderation. 952 Each UDP socket is able to use the size for sending data, even if 953 total pages of UDP sockets exceed udp_mem pressure. The unit is byte. 954 955 Default: 4K 956 957RAW variables 958============= 959 960raw_l3mdev_accept - BOOLEAN 961 Enabling this option allows a "global" bound socket to work 962 across L3 master domains (e.g., VRFs) with packets capable of 963 being received regardless of the L3 domain in which they 964 originated. Only valid when the kernel was compiled with 965 CONFIG_NET_L3_MASTER_DEV. 966 967 Default: 1 (enabled) 968 969CIPSOv4 Variables 970================= 971 972cipso_cache_enable - BOOLEAN 973 If set, enable additions to and lookups from the CIPSO label mapping 974 cache. If unset, additions are ignored and lookups always result in a 975 miss. However, regardless of the setting the cache is still 976 invalidated when required when means you can safely toggle this on and 977 off and the cache will always be "safe". 978 979 Default: 1 980 981cipso_cache_bucket_size - INTEGER 982 The CIPSO label cache consists of a fixed size hash table with each 983 hash bucket containing a number of cache entries. This variable limits 984 the number of entries in each hash bucket; the larger the value the 985 more CIPSO label mappings that can be cached. When the number of 986 entries in a given hash bucket reaches this limit adding new entries 987 causes the oldest entry in the bucket to be removed to make room. 988 989 Default: 10 990 991cipso_rbm_optfmt - BOOLEAN 992 Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of 993 the CIPSO draft specification (see Documentation/netlabel for details). 994 This means that when set the CIPSO tag will be padded with empty 995 categories in order to make the packet data 32-bit aligned. 996 997 Default: 0 998 999cipso_rbm_structvalid - BOOLEAN 1000 If set, do a very strict check of the CIPSO option when 1001 ip_options_compile() is called. If unset, relax the checks done during 1002 ip_options_compile(). Either way is "safe" as errors are caught else 1003 where in the CIPSO processing code but setting this to 0 (False) should 1004 result in less work (i.e. it should be faster) but could cause problems 1005 with other implementations that require strict checking. 1006 1007 Default: 0 1008 1009IP Variables 1010============ 1011 1012ip_local_port_range - 2 INTEGERS 1013 Defines the local port range that is used by TCP and UDP to 1014 choose the local port. The first number is the first, the 1015 second the last local port number. 1016 If possible, it is better these numbers have different parity 1017 (one even and one odd value). 1018 Must be greater than or equal to ip_unprivileged_port_start. 1019 The default values are 32768 and 60999 respectively. 1020 1021ip_local_reserved_ports - list of comma separated ranges 1022 Specify the ports which are reserved for known third-party 1023 applications. These ports will not be used by automatic port 1024 assignments (e.g. when calling connect() or bind() with port 1025 number 0). Explicit port allocation behavior is unchanged. 1026 1027 The format used for both input and output is a comma separated 1028 list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and 1029 10). Writing to the file will clear all previously reserved 1030 ports and update the current list with the one given in the 1031 input. 1032 1033 Note that ip_local_port_range and ip_local_reserved_ports 1034 settings are independent and both are considered by the kernel 1035 when determining which ports are available for automatic port 1036 assignments. 1037 1038 You can reserve ports which are not in the current 1039 ip_local_port_range, e.g.:: 1040 1041 $ cat /proc/sys/net/ipv4/ip_local_port_range 1042 32000 60999 1043 $ cat /proc/sys/net/ipv4/ip_local_reserved_ports 1044 8080,9148 1045 1046 although this is redundant. However such a setting is useful 1047 if later the port range is changed to a value that will 1048 include the reserved ports. 1049 1050 Default: Empty 1051 1052ip_unprivileged_port_start - INTEGER 1053 This is a per-namespace sysctl. It defines the first 1054 unprivileged port in the network namespace. Privileged ports 1055 require root or CAP_NET_BIND_SERVICE in order to bind to them. 1056 To disable all privileged ports, set this to 0. They must not 1057 overlap with the ip_local_port_range. 1058 1059 Default: 1024 1060 1061ip_nonlocal_bind - BOOLEAN 1062 If set, allows processes to bind() to non-local IP addresses, 1063 which can be quite useful - but may break some applications. 1064 1065 Default: 0 1066 1067ip_autobind_reuse - BOOLEAN 1068 By default, bind() does not select the ports automatically even if 1069 the new socket and all sockets bound to the port have SO_REUSEADDR. 1070 ip_autobind_reuse allows bind() to reuse the port and this is useful 1071 when you use bind()+connect(), but may break some applications. 1072 The preferred solution is to use IP_BIND_ADDRESS_NO_PORT and this 1073 option should only be set by experts. 1074 Default: 0 1075 1076ip_dynaddr - BOOLEAN 1077 If set non-zero, enables support for dynamic addresses. 1078 If set to a non-zero value larger than 1, a kernel log 1079 message will be printed when dynamic address rewriting 1080 occurs. 1081 1082 Default: 0 1083 1084ip_early_demux - BOOLEAN 1085 Optimize input packet processing down to one demux for 1086 certain kinds of local sockets. Currently we only do this 1087 for established TCP and connected UDP sockets. 1088 1089 It may add an additional cost for pure routing workloads that 1090 reduces overall throughput, in such case you should disable it. 1091 1092 Default: 1 1093 1094ping_group_range - 2 INTEGERS 1095 Restrict ICMP_PROTO datagram sockets to users in the group range. 1096 The default is "1 0", meaning, that nobody (not even root) may 1097 create ping sockets. Setting it to "100 100" would grant permissions 1098 to the single group. "0 4294967295" would enable it for the world, "100 1099 4294967295" would enable it for the users, but not daemons. 1100 1101tcp_early_demux - BOOLEAN 1102 Enable early demux for established TCP sockets. 1103 1104 Default: 1 1105 1106udp_early_demux - BOOLEAN 1107 Enable early demux for connected UDP sockets. Disable this if 1108 your system could experience more unconnected load. 1109 1110 Default: 1 1111 1112icmp_echo_ignore_all - BOOLEAN 1113 If set non-zero, then the kernel will ignore all ICMP ECHO 1114 requests sent to it. 1115 1116 Default: 0 1117 1118icmp_echo_ignore_broadcasts - BOOLEAN 1119 If set non-zero, then the kernel will ignore all ICMP ECHO and 1120 TIMESTAMP requests sent to it via broadcast/multicast. 1121 1122 Default: 1 1123 1124icmp_ratelimit - INTEGER 1125 Limit the maximal rates for sending ICMP packets whose type matches 1126 icmp_ratemask (see below) to specific targets. 1127 0 to disable any limiting, 1128 otherwise the minimal space between responses in milliseconds. 1129 Note that another sysctl, icmp_msgs_per_sec limits the number 1130 of ICMP packets sent on all targets. 1131 1132 Default: 1000 1133 1134icmp_msgs_per_sec - INTEGER 1135 Limit maximal number of ICMP packets sent per second from this host. 1136 Only messages whose type matches icmp_ratemask (see below) are 1137 controlled by this limit. 1138 1139 Default: 1000 1140 1141icmp_msgs_burst - INTEGER 1142 icmp_msgs_per_sec controls number of ICMP packets sent per second, 1143 while icmp_msgs_burst controls the burst size of these packets. 1144 1145 Default: 50 1146 1147icmp_ratemask - INTEGER 1148 Mask made of ICMP types for which rates are being limited. 1149 1150 Significant bits: IHGFEDCBA9876543210 1151 1152 Default mask: 0000001100000011000 (6168) 1153 1154 Bit definitions (see include/linux/icmp.h): 1155 1156 = ========================= 1157 0 Echo Reply 1158 3 Destination Unreachable [1]_ 1159 4 Source Quench [1]_ 1160 5 Redirect 1161 8 Echo Request 1162 B Time Exceeded [1]_ 1163 C Parameter Problem [1]_ 1164 D Timestamp Request 1165 E Timestamp Reply 1166 F Info Request 1167 G Info Reply 1168 H Address Mask Request 1169 I Address Mask Reply 1170 = ========================= 1171 1172 .. [1] These are rate limited by default (see default mask above) 1173 1174icmp_ignore_bogus_error_responses - BOOLEAN 1175 Some routers violate RFC1122 by sending bogus responses to broadcast 1176 frames. Such violations are normally logged via a kernel warning. 1177 If this is set to TRUE, the kernel will not give such warnings, which 1178 will avoid log file clutter. 1179 1180 Default: 1 1181 1182icmp_errors_use_inbound_ifaddr - BOOLEAN 1183 1184 If zero, icmp error messages are sent with the primary address of 1185 the exiting interface. 1186 1187 If non-zero, the message will be sent with the primary address of 1188 the interface that received the packet that caused the icmp error. 1189 This is the behaviour network many administrators will expect from 1190 a router. And it can make debugging complicated network layouts 1191 much easier. 1192 1193 Note that if no primary address exists for the interface selected, 1194 then the primary address of the first non-loopback interface that 1195 has one will be used regardless of this setting. 1196 1197 Default: 0 1198 1199igmp_max_memberships - INTEGER 1200 Change the maximum number of multicast groups we can subscribe to. 1201 Default: 20 1202 1203 Theoretical maximum value is bounded by having to send a membership 1204 report in a single datagram (i.e. the report can't span multiple 1205 datagrams, or risk confusing the switch and leaving groups you don't 1206 intend to). 1207 1208 The number of supported groups 'M' is bounded by the number of group 1209 report entries you can fit into a single datagram of 65535 bytes. 1210 1211 M = 65536-sizeof (ip header)/(sizeof(Group record)) 1212 1213 Group records are variable length, with a minimum of 12 bytes. 1214 So net.ipv4.igmp_max_memberships should not be set higher than: 1215 1216 (65536-24) / 12 = 5459 1217 1218 The value 5459 assumes no IP header options, so in practice 1219 this number may be lower. 1220 1221igmp_max_msf - INTEGER 1222 Maximum number of addresses allowed in the source filter list for a 1223 multicast group. 1224 1225 Default: 10 1226 1227igmp_qrv - INTEGER 1228 Controls the IGMP query robustness variable (see RFC2236 8.1). 1229 1230 Default: 2 (as specified by RFC2236 8.1) 1231 1232 Minimum: 1 (as specified by RFC6636 4.5) 1233 1234force_igmp_version - INTEGER 1235 - 0 - (default) No enforcement of a IGMP version, IGMPv1/v2 fallback 1236 allowed. Will back to IGMPv3 mode again if all IGMPv1/v2 Querier 1237 Present timer expires. 1238 - 1 - Enforce to use IGMP version 1. Will also reply IGMPv1 report if 1239 receive IGMPv2/v3 query. 1240 - 2 - Enforce to use IGMP version 2. Will fallback to IGMPv1 if receive 1241 IGMPv1 query message. Will reply report if receive IGMPv3 query. 1242 - 3 - Enforce to use IGMP version 3. The same react with default 0. 1243 1244 .. note:: 1245 1246 this is not the same with force_mld_version because IGMPv3 RFC3376 1247 Security Considerations does not have clear description that we could 1248 ignore other version messages completely as MLDv2 RFC3810. So make 1249 this value as default 0 is recommended. 1250 1251``conf/interface/*`` 1252 changes special settings per interface (where 1253 interface" is the name of your network interface) 1254 1255``conf/all/*`` 1256 is special, changes the settings for all interfaces 1257 1258log_martians - BOOLEAN 1259 Log packets with impossible addresses to kernel log. 1260 log_martians for the interface will be enabled if at least one of 1261 conf/{all,interface}/log_martians is set to TRUE, 1262 it will be disabled otherwise 1263 1264accept_redirects - BOOLEAN 1265 Accept ICMP redirect messages. 1266 accept_redirects for the interface will be enabled if: 1267 1268 - both conf/{all,interface}/accept_redirects are TRUE in the case 1269 forwarding for the interface is enabled 1270 1271 or 1272 1273 - at least one of conf/{all,interface}/accept_redirects is TRUE in the 1274 case forwarding for the interface is disabled 1275 1276 accept_redirects for the interface will be disabled otherwise 1277 1278 default: 1279 1280 - TRUE (host) 1281 - FALSE (router) 1282 1283forwarding - BOOLEAN 1284 Enable IP forwarding on this interface. This controls whether packets 1285 received _on_ this interface can be forwarded. 1286 1287mc_forwarding - BOOLEAN 1288 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE 1289 and a multicast routing daemon is required. 1290 conf/all/mc_forwarding must also be set to TRUE to enable multicast 1291 routing for the interface 1292 1293medium_id - INTEGER 1294 Integer value used to differentiate the devices by the medium they 1295 are attached to. Two devices can have different id values when 1296 the broadcast packets are received only on one of them. 1297 The default value 0 means that the device is the only interface 1298 to its medium, value of -1 means that medium is not known. 1299 1300 Currently, it is used to change the proxy_arp behavior: 1301 the proxy_arp feature is enabled for packets forwarded between 1302 two devices attached to different media. 1303 1304proxy_arp - BOOLEAN 1305 Do proxy arp. 1306 1307 proxy_arp for the interface will be enabled if at least one of 1308 conf/{all,interface}/proxy_arp is set to TRUE, 1309 it will be disabled otherwise 1310 1311proxy_arp_pvlan - BOOLEAN 1312 Private VLAN proxy arp. 1313 1314 Basically allow proxy arp replies back to the same interface 1315 (from which the ARP request/solicitation was received). 1316 1317 This is done to support (ethernet) switch features, like RFC 1318 3069, where the individual ports are NOT allowed to 1319 communicate with each other, but they are allowed to talk to 1320 the upstream router. As described in RFC 3069, it is possible 1321 to allow these hosts to communicate through the upstream 1322 router by proxy_arp'ing. Don't need to be used together with 1323 proxy_arp. 1324 1325 This technology is known by different names: 1326 1327 In RFC 3069 it is called VLAN Aggregation. 1328 Cisco and Allied Telesyn call it Private VLAN. 1329 Hewlett-Packard call it Source-Port filtering or port-isolation. 1330 Ericsson call it MAC-Forced Forwarding (RFC Draft). 1331 1332shared_media - BOOLEAN 1333 Send(router) or accept(host) RFC1620 shared media redirects. 1334 Overrides secure_redirects. 1335 1336 shared_media for the interface will be enabled if at least one of 1337 conf/{all,interface}/shared_media is set to TRUE, 1338 it will be disabled otherwise 1339 1340 default TRUE 1341 1342secure_redirects - BOOLEAN 1343 Accept ICMP redirect messages only to gateways listed in the 1344 interface's current gateway list. Even if disabled, RFC1122 redirect 1345 rules still apply. 1346 1347 Overridden by shared_media. 1348 1349 secure_redirects for the interface will be enabled if at least one of 1350 conf/{all,interface}/secure_redirects is set to TRUE, 1351 it will be disabled otherwise 1352 1353 default TRUE 1354 1355send_redirects - BOOLEAN 1356 Send redirects, if router. 1357 1358 send_redirects for the interface will be enabled if at least one of 1359 conf/{all,interface}/send_redirects is set to TRUE, 1360 it will be disabled otherwise 1361 1362 Default: TRUE 1363 1364bootp_relay - BOOLEAN 1365 Accept packets with source address 0.b.c.d destined 1366 not to this host as local ones. It is supposed, that 1367 BOOTP relay daemon will catch and forward such packets. 1368 conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay 1369 for the interface 1370 1371 default FALSE 1372 1373 Not Implemented Yet. 1374 1375accept_source_route - BOOLEAN 1376 Accept packets with SRR option. 1377 conf/all/accept_source_route must also be set to TRUE to accept packets 1378 with SRR option on the interface 1379 1380 default 1381 1382 - TRUE (router) 1383 - FALSE (host) 1384 1385accept_local - BOOLEAN 1386 Accept packets with local source addresses. In combination with 1387 suitable routing, this can be used to direct packets between two 1388 local interfaces over the wire and have them accepted properly. 1389 default FALSE 1390 1391route_localnet - BOOLEAN 1392 Do not consider loopback addresses as martian source or destination 1393 while routing. This enables the use of 127/8 for local routing purposes. 1394 1395 default FALSE 1396 1397rp_filter - INTEGER 1398 - 0 - No source validation. 1399 - 1 - Strict mode as defined in RFC3704 Strict Reverse Path 1400 Each incoming packet is tested against the FIB and if the interface 1401 is not the best reverse path the packet check will fail. 1402 By default failed packets are discarded. 1403 - 2 - Loose mode as defined in RFC3704 Loose Reverse Path 1404 Each incoming packet's source address is also tested against the FIB 1405 and if the source address is not reachable via any interface 1406 the packet check will fail. 1407 1408 Current recommended practice in RFC3704 is to enable strict mode 1409 to prevent IP spoofing from DDos attacks. If using asymmetric routing 1410 or other complicated routing, then loose mode is recommended. 1411 1412 The max value from conf/{all,interface}/rp_filter is used 1413 when doing source validation on the {interface}. 1414 1415 Default value is 0. Note that some distributions enable it 1416 in startup scripts. 1417 1418arp_filter - BOOLEAN 1419 - 1 - Allows you to have multiple network interfaces on the same 1420 subnet, and have the ARPs for each interface be answered 1421 based on whether or not the kernel would route a packet from 1422 the ARP'd IP out that interface (therefore you must use source 1423 based routing for this to work). In other words it allows control 1424 of which cards (usually 1) will respond to an arp request. 1425 1426 - 0 - (default) The kernel can respond to arp requests with addresses 1427 from other interfaces. This may seem wrong but it usually makes 1428 sense, because it increases the chance of successful communication. 1429 IP addresses are owned by the complete host on Linux, not by 1430 particular interfaces. Only for more complex setups like load- 1431 balancing, does this behaviour cause problems. 1432 1433 arp_filter for the interface will be enabled if at least one of 1434 conf/{all,interface}/arp_filter is set to TRUE, 1435 it will be disabled otherwise 1436 1437arp_announce - INTEGER 1438 Define different restriction levels for announcing the local 1439 source IP address from IP packets in ARP requests sent on 1440 interface: 1441 1442 - 0 - (default) Use any local address, configured on any interface 1443 - 1 - Try to avoid local addresses that are not in the target's 1444 subnet for this interface. This mode is useful when target 1445 hosts reachable via this interface require the source IP 1446 address in ARP requests to be part of their logical network 1447 configured on the receiving interface. When we generate the 1448 request we will check all our subnets that include the 1449 target IP and will preserve the source address if it is from 1450 such subnet. If there is no such subnet we select source 1451 address according to the rules for level 2. 1452 - 2 - Always use the best local address for this target. 1453 In this mode we ignore the source address in the IP packet 1454 and try to select local address that we prefer for talks with 1455 the target host. Such local address is selected by looking 1456 for primary IP addresses on all our subnets on the outgoing 1457 interface that include the target IP address. If no suitable 1458 local address is found we select the first local address 1459 we have on the outgoing interface or on all other interfaces, 1460 with the hope we will receive reply for our request and 1461 even sometimes no matter the source IP address we announce. 1462 1463 The max value from conf/{all,interface}/arp_announce is used. 1464 1465 Increasing the restriction level gives more chance for 1466 receiving answer from the resolved target while decreasing 1467 the level announces more valid sender's information. 1468 1469arp_ignore - INTEGER 1470 Define different modes for sending replies in response to 1471 received ARP requests that resolve local target IP addresses: 1472 1473 - 0 - (default): reply for any local target IP address, configured 1474 on any interface 1475 - 1 - reply only if the target IP address is local address 1476 configured on the incoming interface 1477 - 2 - reply only if the target IP address is local address 1478 configured on the incoming interface and both with the 1479 sender's IP address are part from same subnet on this interface 1480 - 3 - do not reply for local addresses configured with scope host, 1481 only resolutions for global and link addresses are replied 1482 - 4-7 - reserved 1483 - 8 - do not reply for all local addresses 1484 1485 The max value from conf/{all,interface}/arp_ignore is used 1486 when ARP request is received on the {interface} 1487 1488arp_notify - BOOLEAN 1489 Define mode for notification of address and device changes. 1490 1491 == ========================================================== 1492 0 (default): do nothing 1493 1 Generate gratuitous arp requests when device is brought up 1494 or hardware address changes. 1495 == ========================================================== 1496 1497arp_accept - BOOLEAN 1498 Define behavior for gratuitous ARP frames who's IP is not 1499 already present in the ARP table: 1500 1501 - 0 - don't create new entries in the ARP table 1502 - 1 - create new entries in the ARP table 1503 1504 Both replies and requests type gratuitous arp will trigger the 1505 ARP table to be updated, if this setting is on. 1506 1507 If the ARP table already contains the IP address of the 1508 gratuitous arp frame, the arp table will be updated regardless 1509 if this setting is on or off. 1510 1511mcast_solicit - INTEGER 1512 The maximum number of multicast probes in INCOMPLETE state, 1513 when the associated hardware address is unknown. Defaults 1514 to 3. 1515 1516ucast_solicit - INTEGER 1517 The maximum number of unicast probes in PROBE state, when 1518 the hardware address is being reconfirmed. Defaults to 3. 1519 1520app_solicit - INTEGER 1521 The maximum number of probes to send to the user space ARP daemon 1522 via netlink before dropping back to multicast probes (see 1523 mcast_resolicit). Defaults to 0. 1524 1525mcast_resolicit - INTEGER 1526 The maximum number of multicast probes after unicast and 1527 app probes in PROBE state. Defaults to 0. 1528 1529disable_policy - BOOLEAN 1530 Disable IPSEC policy (SPD) for this interface 1531 1532disable_xfrm - BOOLEAN 1533 Disable IPSEC encryption on this interface, whatever the policy 1534 1535igmpv2_unsolicited_report_interval - INTEGER 1536 The interval in milliseconds in which the next unsolicited 1537 IGMPv1 or IGMPv2 report retransmit will take place. 1538 1539 Default: 10000 (10 seconds) 1540 1541igmpv3_unsolicited_report_interval - INTEGER 1542 The interval in milliseconds in which the next unsolicited 1543 IGMPv3 report retransmit will take place. 1544 1545 Default: 1000 (1 seconds) 1546 1547promote_secondaries - BOOLEAN 1548 When a primary IP address is removed from this interface 1549 promote a corresponding secondary IP address instead of 1550 removing all the corresponding secondary IP addresses. 1551 1552drop_unicast_in_l2_multicast - BOOLEAN 1553 Drop any unicast IP packets that are received in link-layer 1554 multicast (or broadcast) frames. 1555 1556 This behavior (for multicast) is actually a SHOULD in RFC 1557 1122, but is disabled by default for compatibility reasons. 1558 1559 Default: off (0) 1560 1561drop_gratuitous_arp - BOOLEAN 1562 Drop all gratuitous ARP frames, for example if there's a known 1563 good ARP proxy on the network and such frames need not be used 1564 (or in the case of 802.11, must not be used to prevent attacks.) 1565 1566 Default: off (0) 1567 1568 1569tag - INTEGER 1570 Allows you to write a number, which can be used as required. 1571 1572 Default value is 0. 1573 1574xfrm4_gc_thresh - INTEGER 1575 (Obsolete since linux-4.14) 1576 The threshold at which we will start garbage collecting for IPv4 1577 destination cache entries. At twice this value the system will 1578 refuse new allocations. 1579 1580igmp_link_local_mcast_reports - BOOLEAN 1581 Enable IGMP reports for link local multicast groups in the 1582 224.0.0.X range. 1583 1584 Default TRUE 1585 1586Alexey Kuznetsov. 1587kuznet@ms2.inr.ac.ru 1588 1589Updated by: 1590 1591- Andi Kleen 1592 ak@muc.de 1593- Nicolas Delon 1594 delon.nicolas@wanadoo.fr 1595 1596 1597 1598 1599/proc/sys/net/ipv6/* Variables 1600============================== 1601 1602IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also 1603apply to IPv6 [XXX?]. 1604 1605bindv6only - BOOLEAN 1606 Default value for IPV6_V6ONLY socket option, 1607 which restricts use of the IPv6 socket to IPv6 communication 1608 only. 1609 1610 - TRUE: disable IPv4-mapped address feature 1611 - FALSE: enable IPv4-mapped address feature 1612 1613 Default: FALSE (as specified in RFC3493) 1614 1615flowlabel_consistency - BOOLEAN 1616 Protect the consistency (and unicity) of flow label. 1617 You have to disable it to use IPV6_FL_F_REFLECT flag on the 1618 flow label manager. 1619 1620 - TRUE: enabled 1621 - FALSE: disabled 1622 1623 Default: TRUE 1624 1625auto_flowlabels - INTEGER 1626 Automatically generate flow labels based on a flow hash of the 1627 packet. This allows intermediate devices, such as routers, to 1628 identify packet flows for mechanisms like Equal Cost Multipath 1629 Routing (see RFC 6438). 1630 1631 = =========================================================== 1632 0 automatic flow labels are completely disabled 1633 1 automatic flow labels are enabled by default, they can be 1634 disabled on a per socket basis using the IPV6_AUTOFLOWLABEL 1635 socket option 1636 2 automatic flow labels are allowed, they may be enabled on a 1637 per socket basis using the IPV6_AUTOFLOWLABEL socket option 1638 3 automatic flow labels are enabled and enforced, they cannot 1639 be disabled by the socket option 1640 = =========================================================== 1641 1642 Default: 1 1643 1644flowlabel_state_ranges - BOOLEAN 1645 Split the flow label number space into two ranges. 0-0x7FFFF is 1646 reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF 1647 is reserved for stateless flow labels as described in RFC6437. 1648 1649 - TRUE: enabled 1650 - FALSE: disabled 1651 1652 Default: true 1653 1654flowlabel_reflect - INTEGER 1655 Control flow label reflection. Needed for Path MTU 1656 Discovery to work with Equal Cost Multipath Routing in anycast 1657 environments. See RFC 7690 and: 1658 https://tools.ietf.org/html/draft-wang-6man-flow-label-reflection-01 1659 1660 This is a bitmask. 1661 1662 - 1: enabled for established flows 1663 1664 Note that this prevents automatic flowlabel changes, as done 1665 in "tcp: change IPv6 flow-label upon receiving spurious retransmission" 1666 and "tcp: Change txhash on every SYN and RTO retransmit" 1667 1668 - 2: enabled for TCP RESET packets (no active listener) 1669 If set, a RST packet sent in response to a SYN packet on a closed 1670 port will reflect the incoming flow label. 1671 1672 - 4: enabled for ICMPv6 echo reply messages. 1673 1674 Default: 0 1675 1676fib_multipath_hash_policy - INTEGER 1677 Controls which hash policy to use for multipath routes. 1678 1679 Default: 0 (Layer 3) 1680 1681 Possible values: 1682 1683 - 0 - Layer 3 (source and destination addresses plus flow label) 1684 - 1 - Layer 4 (standard 5-tuple) 1685 - 2 - Layer 3 or inner Layer 3 if present 1686 1687anycast_src_echo_reply - BOOLEAN 1688 Controls the use of anycast addresses as source addresses for ICMPv6 1689 echo reply 1690 1691 - TRUE: enabled 1692 - FALSE: disabled 1693 1694 Default: FALSE 1695 1696idgen_delay - INTEGER 1697 Controls the delay in seconds after which time to retry 1698 privacy stable address generation if a DAD conflict is 1699 detected. 1700 1701 Default: 1 (as specified in RFC7217) 1702 1703idgen_retries - INTEGER 1704 Controls the number of retries to generate a stable privacy 1705 address if a DAD conflict is detected. 1706 1707 Default: 3 (as specified in RFC7217) 1708 1709mld_qrv - INTEGER 1710 Controls the MLD query robustness variable (see RFC3810 9.1). 1711 1712 Default: 2 (as specified by RFC3810 9.1) 1713 1714 Minimum: 1 (as specified by RFC6636 4.5) 1715 1716max_dst_opts_number - INTEGER 1717 Maximum number of non-padding TLVs allowed in a Destination 1718 options extension header. If this value is less than zero 1719 then unknown options are disallowed and the number of known 1720 TLVs allowed is the absolute value of this number. 1721 1722 Default: 8 1723 1724max_hbh_opts_number - INTEGER 1725 Maximum number of non-padding TLVs allowed in a Hop-by-Hop 1726 options extension header. If this value is less than zero 1727 then unknown options are disallowed and the number of known 1728 TLVs allowed is the absolute value of this number. 1729 1730 Default: 8 1731 1732max_dst_opts_length - INTEGER 1733 Maximum length allowed for a Destination options extension 1734 header. 1735 1736 Default: INT_MAX (unlimited) 1737 1738max_hbh_length - INTEGER 1739 Maximum length allowed for a Hop-by-Hop options extension 1740 header. 1741 1742 Default: INT_MAX (unlimited) 1743 1744skip_notify_on_dev_down - BOOLEAN 1745 Controls whether an RTM_DELROUTE message is generated for routes 1746 removed when a device is taken down or deleted. IPv4 does not 1747 generate this message; IPv6 does by default. Setting this sysctl 1748 to true skips the message, making IPv4 and IPv6 on par in relying 1749 on userspace caches to track link events and evict routes. 1750 1751 Default: false (generate message) 1752 1753nexthop_compat_mode - BOOLEAN 1754 New nexthop API provides a means for managing nexthops independent of 1755 prefixes. Backwards compatibilty with old route format is enabled by 1756 default which means route dumps and notifications contain the new 1757 nexthop attribute but also the full, expanded nexthop definition. 1758 Further, updates or deletes of a nexthop configuration generate route 1759 notifications for each fib entry using the nexthop. Once a system 1760 understands the new API, this sysctl can be disabled to achieve full 1761 performance benefits of the new API by disabling the nexthop expansion 1762 and extraneous notifications. 1763 Default: true (backward compat mode) 1764 1765IPv6 Fragmentation: 1766 1767ip6frag_high_thresh - INTEGER 1768 Maximum memory used to reassemble IPv6 fragments. When 1769 ip6frag_high_thresh bytes of memory is allocated for this purpose, 1770 the fragment handler will toss packets until ip6frag_low_thresh 1771 is reached. 1772 1773ip6frag_low_thresh - INTEGER 1774 See ip6frag_high_thresh 1775 1776ip6frag_time - INTEGER 1777 Time in seconds to keep an IPv6 fragment in memory. 1778 1779IPv6 Segment Routing: 1780 1781seg6_flowlabel - INTEGER 1782 Controls the behaviour of computing the flowlabel of outer 1783 IPv6 header in case of SR T.encaps 1784 1785 == ======================================================= 1786 -1 set flowlabel to zero. 1787 0 copy flowlabel from Inner packet in case of Inner IPv6 1788 (Set flowlabel to 0 in case IPv4/L2) 1789 1 Compute the flowlabel using seg6_make_flowlabel() 1790 == ======================================================= 1791 1792 Default is 0. 1793 1794``conf/default/*``: 1795 Change the interface-specific default settings. 1796 1797 1798``conf/all/*``: 1799 Change all the interface-specific settings. 1800 1801 [XXX: Other special features than forwarding?] 1802 1803conf/all/forwarding - BOOLEAN 1804 Enable global IPv6 forwarding between all interfaces. 1805 1806 IPv4 and IPv6 work differently here; e.g. netfilter must be used 1807 to control which interfaces may forward packets and which not. 1808 1809 This also sets all interfaces' Host/Router setting 1810 'forwarding' to the specified value. See below for details. 1811 1812 This referred to as global forwarding. 1813 1814proxy_ndp - BOOLEAN 1815 Do proxy ndp. 1816 1817fwmark_reflect - BOOLEAN 1818 Controls the fwmark of kernel-generated IPv6 reply packets that are not 1819 associated with a socket for example, TCP RSTs or ICMPv6 echo replies). 1820 If unset, these packets have a fwmark of zero. If set, they have the 1821 fwmark of the packet they are replying to. 1822 1823 Default: 0 1824 1825``conf/interface/*``: 1826 Change special settings per interface. 1827 1828 The functional behaviour for certain settings is different 1829 depending on whether local forwarding is enabled or not. 1830 1831accept_ra - INTEGER 1832 Accept Router Advertisements; autoconfigure using them. 1833 1834 It also determines whether or not to transmit Router 1835 Solicitations. If and only if the functional setting is to 1836 accept Router Advertisements, Router Solicitations will be 1837 transmitted. 1838 1839 Possible values are: 1840 1841 == =========================================================== 1842 0 Do not accept Router Advertisements. 1843 1 Accept Router Advertisements if forwarding is disabled. 1844 2 Overrule forwarding behaviour. Accept Router Advertisements 1845 even if forwarding is enabled. 1846 == =========================================================== 1847 1848 Functional default: 1849 1850 - enabled if local forwarding is disabled. 1851 - disabled if local forwarding is enabled. 1852 1853accept_ra_defrtr - BOOLEAN 1854 Learn default router in Router Advertisement. 1855 1856 Functional default: 1857 1858 - enabled if accept_ra is enabled. 1859 - disabled if accept_ra is disabled. 1860 1861accept_ra_from_local - BOOLEAN 1862 Accept RA with source-address that is found on local machine 1863 if the RA is otherwise proper and able to be accepted. 1864 1865 Default is to NOT accept these as it may be an un-intended 1866 network loop. 1867 1868 Functional default: 1869 1870 - enabled if accept_ra_from_local is enabled 1871 on a specific interface. 1872 - disabled if accept_ra_from_local is disabled 1873 on a specific interface. 1874 1875accept_ra_min_hop_limit - INTEGER 1876 Minimum hop limit Information in Router Advertisement. 1877 1878 Hop limit Information in Router Advertisement less than this 1879 variable shall be ignored. 1880 1881 Default: 1 1882 1883accept_ra_pinfo - BOOLEAN 1884 Learn Prefix Information in Router Advertisement. 1885 1886 Functional default: 1887 1888 - enabled if accept_ra is enabled. 1889 - disabled if accept_ra is disabled. 1890 1891accept_ra_rt_info_min_plen - INTEGER 1892 Minimum prefix length of Route Information in RA. 1893 1894 Route Information w/ prefix smaller than this variable shall 1895 be ignored. 1896 1897 Functional default: 1898 1899 * 0 if accept_ra_rtr_pref is enabled. 1900 * -1 if accept_ra_rtr_pref is disabled. 1901 1902accept_ra_rt_info_max_plen - INTEGER 1903 Maximum prefix length of Route Information in RA. 1904 1905 Route Information w/ prefix larger than this variable shall 1906 be ignored. 1907 1908 Functional default: 1909 1910 * 0 if accept_ra_rtr_pref is enabled. 1911 * -1 if accept_ra_rtr_pref is disabled. 1912 1913accept_ra_rtr_pref - BOOLEAN 1914 Accept Router Preference in RA. 1915 1916 Functional default: 1917 1918 - enabled if accept_ra is enabled. 1919 - disabled if accept_ra is disabled. 1920 1921accept_ra_mtu - BOOLEAN 1922 Apply the MTU value specified in RA option 5 (RFC4861). If 1923 disabled, the MTU specified in the RA will be ignored. 1924 1925 Functional default: 1926 1927 - enabled if accept_ra is enabled. 1928 - disabled if accept_ra is disabled. 1929 1930accept_redirects - BOOLEAN 1931 Accept Redirects. 1932 1933 Functional default: 1934 1935 - enabled if local forwarding is disabled. 1936 - disabled if local forwarding is enabled. 1937 1938accept_source_route - INTEGER 1939 Accept source routing (routing extension header). 1940 1941 - >= 0: Accept only routing header type 2. 1942 - < 0: Do not accept routing header. 1943 1944 Default: 0 1945 1946autoconf - BOOLEAN 1947 Autoconfigure addresses using Prefix Information in Router 1948 Advertisements. 1949 1950 Functional default: 1951 1952 - enabled if accept_ra_pinfo is enabled. 1953 - disabled if accept_ra_pinfo is disabled. 1954 1955dad_transmits - INTEGER 1956 The amount of Duplicate Address Detection probes to send. 1957 1958 Default: 1 1959 1960forwarding - INTEGER 1961 Configure interface-specific Host/Router behaviour. 1962 1963 .. note:: 1964 1965 It is recommended to have the same setting on all 1966 interfaces; mixed router/host scenarios are rather uncommon. 1967 1968 Possible values are: 1969 1970 - 0 Forwarding disabled 1971 - 1 Forwarding enabled 1972 1973 **FALSE (0)**: 1974 1975 By default, Host behaviour is assumed. This means: 1976 1977 1. IsRouter flag is not set in Neighbour Advertisements. 1978 2. If accept_ra is TRUE (default), transmit Router 1979 Solicitations. 1980 3. If accept_ra is TRUE (default), accept Router 1981 Advertisements (and do autoconfiguration). 1982 4. If accept_redirects is TRUE (default), accept Redirects. 1983 1984 **TRUE (1)**: 1985 1986 If local forwarding is enabled, Router behaviour is assumed. 1987 This means exactly the reverse from the above: 1988 1989 1. IsRouter flag is set in Neighbour Advertisements. 1990 2. Router Solicitations are not sent unless accept_ra is 2. 1991 3. Router Advertisements are ignored unless accept_ra is 2. 1992 4. Redirects are ignored. 1993 1994 Default: 0 (disabled) if global forwarding is disabled (default), 1995 otherwise 1 (enabled). 1996 1997hop_limit - INTEGER 1998 Default Hop Limit to set. 1999 2000 Default: 64 2001 2002mtu - INTEGER 2003 Default Maximum Transfer Unit 2004 2005 Default: 1280 (IPv6 required minimum) 2006 2007ip_nonlocal_bind - BOOLEAN 2008 If set, allows processes to bind() to non-local IPv6 addresses, 2009 which can be quite useful - but may break some applications. 2010 2011 Default: 0 2012 2013router_probe_interval - INTEGER 2014 Minimum interval (in seconds) between Router Probing described 2015 in RFC4191. 2016 2017 Default: 60 2018 2019router_solicitation_delay - INTEGER 2020 Number of seconds to wait after interface is brought up 2021 before sending Router Solicitations. 2022 2023 Default: 1 2024 2025router_solicitation_interval - INTEGER 2026 Number of seconds to wait between Router Solicitations. 2027 2028 Default: 4 2029 2030router_solicitations - INTEGER 2031 Number of Router Solicitations to send until assuming no 2032 routers are present. 2033 2034 Default: 3 2035 2036use_oif_addrs_only - BOOLEAN 2037 When enabled, the candidate source addresses for destinations 2038 routed via this interface are restricted to the set of addresses 2039 configured on this interface (vis. RFC 6724, section 4). 2040 2041 Default: false 2042 2043use_tempaddr - INTEGER 2044 Preference for Privacy Extensions (RFC3041). 2045 2046 * <= 0 : disable Privacy Extensions 2047 * == 1 : enable Privacy Extensions, but prefer public 2048 addresses over temporary addresses. 2049 * > 1 : enable Privacy Extensions and prefer temporary 2050 addresses over public addresses. 2051 2052 Default: 2053 2054 * 0 (for most devices) 2055 * -1 (for point-to-point devices and loopback devices) 2056 2057temp_valid_lft - INTEGER 2058 valid lifetime (in seconds) for temporary addresses. 2059 2060 Default: 604800 (7 days) 2061 2062temp_prefered_lft - INTEGER 2063 Preferred lifetime (in seconds) for temporary addresses. 2064 2065 Default: 86400 (1 day) 2066 2067keep_addr_on_down - INTEGER 2068 Keep all IPv6 addresses on an interface down event. If set static 2069 global addresses with no expiration time are not flushed. 2070 2071 * >0 : enabled 2072 * 0 : system default 2073 * <0 : disabled 2074 2075 Default: 0 (addresses are removed) 2076 2077max_desync_factor - INTEGER 2078 Maximum value for DESYNC_FACTOR, which is a random value 2079 that ensures that clients don't synchronize with each 2080 other and generate new addresses at exactly the same time. 2081 value is in seconds. 2082 2083 Default: 600 2084 2085regen_max_retry - INTEGER 2086 Number of attempts before give up attempting to generate 2087 valid temporary addresses. 2088 2089 Default: 5 2090 2091max_addresses - INTEGER 2092 Maximum number of autoconfigured addresses per interface. Setting 2093 to zero disables the limitation. It is not recommended to set this 2094 value too large (or to zero) because it would be an easy way to 2095 crash the kernel by allowing too many addresses to be created. 2096 2097 Default: 16 2098 2099disable_ipv6 - BOOLEAN 2100 Disable IPv6 operation. If accept_dad is set to 2, this value 2101 will be dynamically set to TRUE if DAD fails for the link-local 2102 address. 2103 2104 Default: FALSE (enable IPv6 operation) 2105 2106 When this value is changed from 1 to 0 (IPv6 is being enabled), 2107 it will dynamically create a link-local address on the given 2108 interface and start Duplicate Address Detection, if necessary. 2109 2110 When this value is changed from 0 to 1 (IPv6 is being disabled), 2111 it will dynamically delete all addresses and routes on the given 2112 interface. From now on it will not possible to add addresses/routes 2113 to the selected interface. 2114 2115accept_dad - INTEGER 2116 Whether to accept DAD (Duplicate Address Detection). 2117 2118 == ============================================================== 2119 0 Disable DAD 2120 1 Enable DAD (default) 2121 2 Enable DAD, and disable IPv6 operation if MAC-based duplicate 2122 link-local address has been found. 2123 == ============================================================== 2124 2125 DAD operation and mode on a given interface will be selected according 2126 to the maximum value of conf/{all,interface}/accept_dad. 2127 2128force_tllao - BOOLEAN 2129 Enable sending the target link-layer address option even when 2130 responding to a unicast neighbor solicitation. 2131 2132 Default: FALSE 2133 2134 Quoting from RFC 2461, section 4.4, Target link-layer address: 2135 2136 "The option MUST be included for multicast solicitations in order to 2137 avoid infinite Neighbor Solicitation "recursion" when the peer node 2138 does not have a cache entry to return a Neighbor Advertisements 2139 message. When responding to unicast solicitations, the option can be 2140 omitted since the sender of the solicitation has the correct link- 2141 layer address; otherwise it would not have be able to send the unicast 2142 solicitation in the first place. However, including the link-layer 2143 address in this case adds little overhead and eliminates a potential 2144 race condition where the sender deletes the cached link-layer address 2145 prior to receiving a response to a previous solicitation." 2146 2147ndisc_notify - BOOLEAN 2148 Define mode for notification of address and device changes. 2149 2150 * 0 - (default): do nothing 2151 * 1 - Generate unsolicited neighbour advertisements when device is brought 2152 up or hardware address changes. 2153 2154ndisc_tclass - INTEGER 2155 The IPv6 Traffic Class to use by default when sending IPv6 Neighbor 2156 Discovery (Router Solicitation, Router Advertisement, Neighbor 2157 Solicitation, Neighbor Advertisement, Redirect) messages. 2158 These 8 bits can be interpreted as 6 high order bits holding the DSCP 2159 value and 2 low order bits representing ECN (which you probably want 2160 to leave cleared). 2161 2162 * 0 - (default) 2163 2164mldv1_unsolicited_report_interval - INTEGER 2165 The interval in milliseconds in which the next unsolicited 2166 MLDv1 report retransmit will take place. 2167 2168 Default: 10000 (10 seconds) 2169 2170mldv2_unsolicited_report_interval - INTEGER 2171 The interval in milliseconds in which the next unsolicited 2172 MLDv2 report retransmit will take place. 2173 2174 Default: 1000 (1 second) 2175 2176force_mld_version - INTEGER 2177 * 0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed 2178 * 1 - Enforce to use MLD version 1 2179 * 2 - Enforce to use MLD version 2 2180 2181suppress_frag_ndisc - INTEGER 2182 Control RFC 6980 (Security Implications of IPv6 Fragmentation 2183 with IPv6 Neighbor Discovery) behavior: 2184 2185 * 1 - (default) discard fragmented neighbor discovery packets 2186 * 0 - allow fragmented neighbor discovery packets 2187 2188optimistic_dad - BOOLEAN 2189 Whether to perform Optimistic Duplicate Address Detection (RFC 4429). 2190 2191 * 0: disabled (default) 2192 * 1: enabled 2193 2194 Optimistic Duplicate Address Detection for the interface will be enabled 2195 if at least one of conf/{all,interface}/optimistic_dad is set to 1, 2196 it will be disabled otherwise. 2197 2198use_optimistic - BOOLEAN 2199 If enabled, do not classify optimistic addresses as deprecated during 2200 source address selection. Preferred addresses will still be chosen 2201 before optimistic addresses, subject to other ranking in the source 2202 address selection algorithm. 2203 2204 * 0: disabled (default) 2205 * 1: enabled 2206 2207 This will be enabled if at least one of 2208 conf/{all,interface}/use_optimistic is set to 1, disabled otherwise. 2209 2210stable_secret - IPv6 address 2211 This IPv6 address will be used as a secret to generate IPv6 2212 addresses for link-local addresses and autoconfigured 2213 ones. All addresses generated after setting this secret will 2214 be stable privacy ones by default. This can be changed via the 2215 addrgenmode ip-link. conf/default/stable_secret is used as the 2216 secret for the namespace, the interface specific ones can 2217 overwrite that. Writes to conf/all/stable_secret are refused. 2218 2219 It is recommended to generate this secret during installation 2220 of a system and keep it stable after that. 2221 2222 By default the stable secret is unset. 2223 2224addr_gen_mode - INTEGER 2225 Defines how link-local and autoconf addresses are generated. 2226 2227 = ================================================================= 2228 0 generate address based on EUI64 (default) 2229 1 do no generate a link-local address, use EUI64 for addresses 2230 generated from autoconf 2231 2 generate stable privacy addresses, using the secret from 2232 stable_secret (RFC7217) 2233 3 generate stable privacy addresses, using a random secret if unset 2234 = ================================================================= 2235 2236drop_unicast_in_l2_multicast - BOOLEAN 2237 Drop any unicast IPv6 packets that are received in link-layer 2238 multicast (or broadcast) frames. 2239 2240 By default this is turned off. 2241 2242drop_unsolicited_na - BOOLEAN 2243 Drop all unsolicited neighbor advertisements, for example if there's 2244 a known good NA proxy on the network and such frames need not be used 2245 (or in the case of 802.11, must not be used to prevent attacks.) 2246 2247 By default this is turned off. 2248 2249enhanced_dad - BOOLEAN 2250 Include a nonce option in the IPv6 neighbor solicitation messages used for 2251 duplicate address detection per RFC7527. A received DAD NS will only signal 2252 a duplicate address if the nonce is different. This avoids any false 2253 detection of duplicates due to loopback of the NS messages that we send. 2254 The nonce option will be sent on an interface unless both of 2255 conf/{all,interface}/enhanced_dad are set to FALSE. 2256 2257 Default: TRUE 2258 2259``icmp/*``: 2260=========== 2261 2262ratelimit - INTEGER 2263 Limit the maximal rates for sending ICMPv6 messages. 2264 2265 0 to disable any limiting, 2266 otherwise the minimal space between responses in milliseconds. 2267 2268 Default: 1000 2269 2270ratemask - list of comma separated ranges 2271 For ICMPv6 message types matching the ranges in the ratemask, limit 2272 the sending of the message according to ratelimit parameter. 2273 2274 The format used for both input and output is a comma separated 2275 list of ranges (e.g. "0-127,129" for ICMPv6 message type 0 to 127 and 2276 129). Writing to the file will clear all previous ranges of ICMPv6 2277 message types and update the current list with the input. 2278 2279 Refer to: https://www.iana.org/assignments/icmpv6-parameters/icmpv6-parameters.xhtml 2280 for numerical values of ICMPv6 message types, e.g. echo request is 128 2281 and echo reply is 129. 2282 2283 Default: 0-1,3-127 (rate limit ICMPv6 errors except Packet Too Big) 2284 2285echo_ignore_all - BOOLEAN 2286 If set non-zero, then the kernel will ignore all ICMP ECHO 2287 requests sent to it over the IPv6 protocol. 2288 2289 Default: 0 2290 2291echo_ignore_multicast - BOOLEAN 2292 If set non-zero, then the kernel will ignore all ICMP ECHO 2293 requests sent to it over the IPv6 protocol via multicast. 2294 2295 Default: 0 2296 2297echo_ignore_anycast - BOOLEAN 2298 If set non-zero, then the kernel will ignore all ICMP ECHO 2299 requests sent to it over the IPv6 protocol destined to anycast address. 2300 2301 Default: 0 2302 2303xfrm6_gc_thresh - INTEGER 2304 (Obsolete since linux-4.14) 2305 The threshold at which we will start garbage collecting for IPv6 2306 destination cache entries. At twice this value the system will 2307 refuse new allocations. 2308 2309 2310IPv6 Update by: 2311Pekka Savola <pekkas@netcore.fi> 2312YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org> 2313 2314 2315/proc/sys/net/bridge/* Variables: 2316================================= 2317 2318bridge-nf-call-arptables - BOOLEAN 2319 - 1 : pass bridged ARP traffic to arptables' FORWARD chain. 2320 - 0 : disable this. 2321 2322 Default: 1 2323 2324bridge-nf-call-iptables - BOOLEAN 2325 - 1 : pass bridged IPv4 traffic to iptables' chains. 2326 - 0 : disable this. 2327 2328 Default: 1 2329 2330bridge-nf-call-ip6tables - BOOLEAN 2331 - 1 : pass bridged IPv6 traffic to ip6tables' chains. 2332 - 0 : disable this. 2333 2334 Default: 1 2335 2336bridge-nf-filter-vlan-tagged - BOOLEAN 2337 - 1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables. 2338 - 0 : disable this. 2339 2340 Default: 0 2341 2342bridge-nf-filter-pppoe-tagged - BOOLEAN 2343 - 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables. 2344 - 0 : disable this. 2345 2346 Default: 0 2347 2348bridge-nf-pass-vlan-input-dev - BOOLEAN 2349 - 1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan 2350 interface on the bridge and set the netfilter input device to the 2351 vlan. This allows use of e.g. "iptables -i br0.1" and makes the 2352 REDIRECT target work with vlan-on-top-of-bridge interfaces. When no 2353 matching vlan interface is found, or this switch is off, the input 2354 device is set to the bridge interface. 2355 2356 - 0: disable bridge netfilter vlan interface lookup. 2357 2358 Default: 0 2359 2360``proc/sys/net/sctp/*`` Variables: 2361================================== 2362 2363addip_enable - BOOLEAN 2364 Enable or disable extension of Dynamic Address Reconfiguration 2365 (ADD-IP) functionality specified in RFC5061. This extension provides 2366 the ability to dynamically add and remove new addresses for the SCTP 2367 associations. 2368 2369 1: Enable extension. 2370 2371 0: Disable extension. 2372 2373 Default: 0 2374 2375pf_enable - INTEGER 2376 Enable or disable pf (pf is short for potentially failed) state. A value 2377 of pf_retrans > path_max_retrans also disables pf state. That is, one of 2378 both pf_enable and pf_retrans > path_max_retrans can disable pf state. 2379 Since pf_retrans and path_max_retrans can be changed by userspace 2380 application, sometimes user expects to disable pf state by the value of 2381 pf_retrans > path_max_retrans, but occasionally the value of pf_retrans 2382 or path_max_retrans is changed by the user application, this pf state is 2383 enabled. As such, it is necessary to add this to dynamically enable 2384 and disable pf state. See: 2385 https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover for 2386 details. 2387 2388 1: Enable pf. 2389 2390 0: Disable pf. 2391 2392 Default: 1 2393 2394pf_expose - INTEGER 2395 Unset or enable/disable pf (pf is short for potentially failed) state 2396 exposure. Applications can control the exposure of the PF path state 2397 in the SCTP_PEER_ADDR_CHANGE event and the SCTP_GET_PEER_ADDR_INFO 2398 sockopt. When it's unset, no SCTP_PEER_ADDR_CHANGE event with 2399 SCTP_ADDR_PF state will be sent and a SCTP_PF-state transport info 2400 can be got via SCTP_GET_PEER_ADDR_INFO sockopt; When it's enabled, 2401 a SCTP_PEER_ADDR_CHANGE event will be sent for a transport becoming 2402 SCTP_PF state and a SCTP_PF-state transport info can be got via 2403 SCTP_GET_PEER_ADDR_INFO sockopt; When it's diabled, no 2404 SCTP_PEER_ADDR_CHANGE event will be sent and it returns -EACCES when 2405 trying to get a SCTP_PF-state transport info via SCTP_GET_PEER_ADDR_INFO 2406 sockopt. 2407 2408 0: Unset pf state exposure, Compatible with old applications. 2409 2410 1: Disable pf state exposure. 2411 2412 2: Enable pf state exposure. 2413 2414 Default: 0 2415 2416addip_noauth_enable - BOOLEAN 2417 Dynamic Address Reconfiguration (ADD-IP) requires the use of 2418 authentication to protect the operations of adding or removing new 2419 addresses. This requirement is mandated so that unauthorized hosts 2420 would not be able to hijack associations. However, older 2421 implementations may not have implemented this requirement while 2422 allowing the ADD-IP extension. For reasons of interoperability, 2423 we provide this variable to control the enforcement of the 2424 authentication requirement. 2425 2426 == =============================================================== 2427 1 Allow ADD-IP extension to be used without authentication. This 2428 should only be set in a closed environment for interoperability 2429 with older implementations. 2430 2431 0 Enforce the authentication requirement 2432 == =============================================================== 2433 2434 Default: 0 2435 2436auth_enable - BOOLEAN 2437 Enable or disable Authenticated Chunks extension. This extension 2438 provides the ability to send and receive authenticated chunks and is 2439 required for secure operation of Dynamic Address Reconfiguration 2440 (ADD-IP) extension. 2441 2442 - 1: Enable this extension. 2443 - 0: Disable this extension. 2444 2445 Default: 0 2446 2447prsctp_enable - BOOLEAN 2448 Enable or disable the Partial Reliability extension (RFC3758) which 2449 is used to notify peers that a given DATA should no longer be expected. 2450 2451 - 1: Enable extension 2452 - 0: Disable 2453 2454 Default: 1 2455 2456max_burst - INTEGER 2457 The limit of the number of new packets that can be initially sent. It 2458 controls how bursty the generated traffic can be. 2459 2460 Default: 4 2461 2462association_max_retrans - INTEGER 2463 Set the maximum number for retransmissions that an association can 2464 attempt deciding that the remote end is unreachable. If this value 2465 is exceeded, the association is terminated. 2466 2467 Default: 10 2468 2469max_init_retransmits - INTEGER 2470 The maximum number of retransmissions of INIT and COOKIE-ECHO chunks 2471 that an association will attempt before declaring the destination 2472 unreachable and terminating. 2473 2474 Default: 8 2475 2476path_max_retrans - INTEGER 2477 The maximum number of retransmissions that will be attempted on a given 2478 path. Once this threshold is exceeded, the path is considered 2479 unreachable, and new traffic will use a different path when the 2480 association is multihomed. 2481 2482 Default: 5 2483 2484pf_retrans - INTEGER 2485 The number of retransmissions that will be attempted on a given path 2486 before traffic is redirected to an alternate transport (should one 2487 exist). Note this is distinct from path_max_retrans, as a path that 2488 passes the pf_retrans threshold can still be used. Its only 2489 deprioritized when a transmission path is selected by the stack. This 2490 setting is primarily used to enable fast failover mechanisms without 2491 having to reduce path_max_retrans to a very low value. See: 2492 http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt 2493 for details. Note also that a value of pf_retrans > path_max_retrans 2494 disables this feature. Since both pf_retrans and path_max_retrans can 2495 be changed by userspace application, a variable pf_enable is used to 2496 disable pf state. 2497 2498 Default: 0 2499 2500ps_retrans - INTEGER 2501 Primary.Switchover.Max.Retrans (PSMR), it's a tunable parameter coming 2502 from section-5 "Primary Path Switchover" in rfc7829. The primary path 2503 will be changed to another active path when the path error counter on 2504 the old primary path exceeds PSMR, so that "the SCTP sender is allowed 2505 to continue data transmission on a new working path even when the old 2506 primary destination address becomes active again". Note this feature 2507 is disabled by initializing 'ps_retrans' per netns as 0xffff by default, 2508 and its value can't be less than 'pf_retrans' when changing by sysctl. 2509 2510 Default: 0xffff 2511 2512rto_initial - INTEGER 2513 The initial round trip timeout value in milliseconds that will be used 2514 in calculating round trip times. This is the initial time interval 2515 for retransmissions. 2516 2517 Default: 3000 2518 2519rto_max - INTEGER 2520 The maximum value (in milliseconds) of the round trip timeout. This 2521 is the largest time interval that can elapse between retransmissions. 2522 2523 Default: 60000 2524 2525rto_min - INTEGER 2526 The minimum value (in milliseconds) of the round trip timeout. This 2527 is the smallest time interval the can elapse between retransmissions. 2528 2529 Default: 1000 2530 2531hb_interval - INTEGER 2532 The interval (in milliseconds) between HEARTBEAT chunks. These chunks 2533 are sent at the specified interval on idle paths to probe the state of 2534 a given path between 2 associations. 2535 2536 Default: 30000 2537 2538sack_timeout - INTEGER 2539 The amount of time (in milliseconds) that the implementation will wait 2540 to send a SACK. 2541 2542 Default: 200 2543 2544valid_cookie_life - INTEGER 2545 The default lifetime of the SCTP cookie (in milliseconds). The cookie 2546 is used during association establishment. 2547 2548 Default: 60000 2549 2550cookie_preserve_enable - BOOLEAN 2551 Enable or disable the ability to extend the lifetime of the SCTP cookie 2552 that is used during the establishment phase of SCTP association 2553 2554 - 1: Enable cookie lifetime extension. 2555 - 0: Disable 2556 2557 Default: 1 2558 2559cookie_hmac_alg - STRING 2560 Select the hmac algorithm used when generating the cookie value sent by 2561 a listening sctp socket to a connecting client in the INIT-ACK chunk. 2562 Valid values are: 2563 2564 * md5 2565 * sha1 2566 * none 2567 2568 Ability to assign md5 or sha1 as the selected alg is predicated on the 2569 configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and 2570 CONFIG_CRYPTO_SHA1). 2571 2572 Default: Dependent on configuration. MD5 if available, else SHA1 if 2573 available, else none. 2574 2575rcvbuf_policy - INTEGER 2576 Determines if the receive buffer is attributed to the socket or to 2577 association. SCTP supports the capability to create multiple 2578 associations on a single socket. When using this capability, it is 2579 possible that a single stalled association that's buffering a lot 2580 of data may block other associations from delivering their data by 2581 consuming all of the receive buffer space. To work around this, 2582 the rcvbuf_policy could be set to attribute the receiver buffer space 2583 to each association instead of the socket. This prevents the described 2584 blocking. 2585 2586 - 1: rcvbuf space is per association 2587 - 0: rcvbuf space is per socket 2588 2589 Default: 0 2590 2591sndbuf_policy - INTEGER 2592 Similar to rcvbuf_policy above, this applies to send buffer space. 2593 2594 - 1: Send buffer is tracked per association 2595 - 0: Send buffer is tracked per socket. 2596 2597 Default: 0 2598 2599sctp_mem - vector of 3 INTEGERs: min, pressure, max 2600 Number of pages allowed for queueing by all SCTP sockets. 2601 2602 min: Below this number of pages SCTP is not bothered about its 2603 memory appetite. When amount of memory allocated by SCTP exceeds 2604 this number, SCTP starts to moderate memory usage. 2605 2606 pressure: This value was introduced to follow format of tcp_mem. 2607 2608 max: Number of pages allowed for queueing by all SCTP sockets. 2609 2610 Default is calculated at boot time from amount of available memory. 2611 2612sctp_rmem - vector of 3 INTEGERs: min, default, max 2613 Only the first value ("min") is used, "default" and "max" are 2614 ignored. 2615 2616 min: Minimal size of receive buffer used by SCTP socket. 2617 It is guaranteed to each SCTP socket (but not association) even 2618 under moderate memory pressure. 2619 2620 Default: 4K 2621 2622sctp_wmem - vector of 3 INTEGERs: min, default, max 2623 Currently this tunable has no effect. 2624 2625addr_scope_policy - INTEGER 2626 Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00 2627 2628 - 0 - Disable IPv4 address scoping 2629 - 1 - Enable IPv4 address scoping 2630 - 2 - Follow draft but allow IPv4 private addresses 2631 - 3 - Follow draft but allow IPv4 link local addresses 2632 2633 Default: 1 2634 2635 2636``/proc/sys/net/core/*`` 2637======================== 2638 2639 Please see: Documentation/admin-guide/sysctl/net.rst for descriptions of these entries. 2640 2641 2642``/proc/sys/net/unix/*`` 2643======================== 2644 2645max_dgram_qlen - INTEGER 2646 The maximum length of dgram socket receive queue 2647 2648 Default: 10 2649 2650