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 Forward Packets between interfaces. 12 13 This variable is special, its change resets all configuration 14 parameters to their default state (RFC1122 for hosts, RFC1812 15 for routers) 16 17 Possible values: 18 19 - 0 (disabled) 20 - 1 (enabled) 21 22 Default: 0 (disabled) 23 24ip_default_ttl - INTEGER 25 Default value of TTL field (Time To Live) for outgoing (but not 26 forwarded) IP packets. Should be between 1 and 255 inclusive. 27 Default: 64 (as recommended by RFC1700) 28 29ip_no_pmtu_disc - INTEGER 30 Disable Path MTU Discovery. If enabled in mode 1 and a 31 fragmentation-required ICMP is received, the PMTU to this 32 destination will be set to the smallest of the old MTU to 33 this destination and min_pmtu (see below). You will need 34 to raise min_pmtu to the smallest interface MTU on your system 35 manually if you want to avoid locally generated fragments. 36 37 In mode 2 incoming Path MTU Discovery messages will be 38 discarded. Outgoing frames are handled the same as in mode 1, 39 implicitly setting IP_PMTUDISC_DONT on every created socket. 40 41 Mode 3 is a hardened pmtu discover mode. The kernel will only 42 accept fragmentation-needed errors if the underlying protocol 43 can verify them besides a plain socket lookup. Current 44 protocols for which pmtu events will be honored are TCP and 45 SCTP as they verify e.g. the sequence number or the 46 association. This mode should not be enabled globally but is 47 only intended to secure e.g. name servers in namespaces where 48 TCP path mtu must still work but path MTU information of other 49 protocols should be discarded. If enabled globally this mode 50 could break other protocols. 51 52 Possible values: 0-3 53 54 Default: FALSE 55 56min_pmtu - INTEGER 57 default 552 - minimum Path MTU. Unless this is changed manually, 58 each cached pmtu will never be lower than this setting. 59 60ip_forward_use_pmtu - BOOLEAN 61 By default we don't trust protocol path MTUs while forwarding 62 because they could be easily forged and can lead to unwanted 63 fragmentation by the router. 64 You only need to enable this if you have user-space software 65 which tries to discover path mtus by itself and depends on the 66 kernel honoring this information. This is normally not the 67 case. 68 69 Possible values: 70 71 - 0 (disabled) 72 - 1 (enabled) 73 74 Default: 0 (disabled) 75 76fwmark_reflect - BOOLEAN 77 Controls the fwmark of kernel-generated IPv4 reply packets that are not 78 associated with a socket for example, TCP RSTs or ICMP echo replies). 79 If disabled, these packets have a fwmark of zero. If enabled, they have the 80 fwmark of the packet they are replying to. 81 82 Possible values: 83 84 - 0 (disabled) 85 - 1 (enabled) 86 87 Default: 0 (disabled) 88 89fib_multipath_use_neigh - BOOLEAN 90 Use status of existing neighbor entry when determining nexthop for 91 multipath routes. If disabled, neighbor information is not used and 92 packets could be directed to a failed nexthop. Only valid for kernels 93 built with CONFIG_IP_ROUTE_MULTIPATH enabled. 94 95 Possible values: 96 97 - 0 (disabled) 98 - 1 (enabled) 99 100 Default: 0 (disabled) 101 102fib_multipath_hash_policy - INTEGER 103 Controls which hash policy to use for multipath routes. Only valid 104 for kernels built with CONFIG_IP_ROUTE_MULTIPATH enabled. 105 106 Default: 0 (Layer 3) 107 108 Possible values: 109 110 - 0 - Layer 3 111 - 1 - Layer 4 112 - 2 - Layer 3 or inner Layer 3 if present 113 - 3 - Custom multipath hash. Fields used for multipath hash calculation 114 are determined by fib_multipath_hash_fields sysctl 115 116fib_multipath_hash_fields - UNSIGNED INTEGER 117 When fib_multipath_hash_policy is set to 3 (custom multipath hash), the 118 fields used for multipath hash calculation are determined by this 119 sysctl. 120 121 This value is a bitmask which enables various fields for multipath hash 122 calculation. 123 124 Possible fields are: 125 126 ====== ============================ 127 0x0001 Source IP address 128 0x0002 Destination IP address 129 0x0004 IP protocol 130 0x0008 Unused (Flow Label) 131 0x0010 Source port 132 0x0020 Destination port 133 0x0040 Inner source IP address 134 0x0080 Inner destination IP address 135 0x0100 Inner IP protocol 136 0x0200 Inner Flow Label 137 0x0400 Inner source port 138 0x0800 Inner destination port 139 ====== ============================ 140 141 Default: 0x0007 (source IP, destination IP and IP protocol) 142 143fib_multipath_hash_seed - UNSIGNED INTEGER 144 The seed value used when calculating hash for multipath routes. Applies 145 to both IPv4 and IPv6 datapath. Only present for kernels built with 146 CONFIG_IP_ROUTE_MULTIPATH enabled. 147 148 When set to 0, the seed value used for multipath routing defaults to an 149 internal random-generated one. 150 151 The actual hashing algorithm is not specified -- there is no guarantee 152 that a next hop distribution effected by a given seed will keep stable 153 across kernel versions. 154 155 Default: 0 (random) 156 157fib_sync_mem - UNSIGNED INTEGER 158 Amount of dirty memory from fib entries that can be backlogged before 159 synchronize_rcu is forced. 160 161 Default: 512kB Minimum: 64kB Maximum: 64MB 162 163ip_forward_update_priority - INTEGER 164 Whether to update SKB priority from "TOS" field in IPv4 header after it 165 is forwarded. The new SKB priority is mapped from TOS field value 166 according to an rt_tos2priority table (see e.g. man tc-prio). 167 168 Default: 1 (Update priority.) 169 170 Possible values: 171 172 - 0 - Do not update priority. 173 - 1 - Update priority. 174 175route/max_size - INTEGER 176 Maximum number of routes allowed in the kernel. Increase 177 this when using large numbers of interfaces and/or routes. 178 179 From linux kernel 3.6 onwards, this is deprecated for ipv4 180 as route cache is no longer used. 181 182 From linux kernel 6.3 onwards, this is deprecated for ipv6 183 as garbage collection manages cached route entries. 184 185neigh/default/gc_thresh1 - INTEGER 186 Minimum number of entries to keep. Garbage collector will not 187 purge entries if there are fewer than this number. 188 189 Default: 128 190 191neigh/default/gc_thresh2 - INTEGER 192 Threshold when garbage collector becomes more aggressive about 193 purging entries. Entries older than 5 seconds will be cleared 194 when over this number. 195 196 Default: 512 197 198neigh/default/gc_thresh3 - INTEGER 199 Maximum number of non-PERMANENT neighbor entries allowed. Increase 200 this when using large numbers of interfaces and when communicating 201 with large numbers of directly-connected peers. 202 203 Default: 1024 204 205neigh/default/unres_qlen_bytes - INTEGER 206 The maximum number of bytes which may be used by packets 207 queued for each unresolved address by other network layers. 208 (added in linux 3.3) 209 210 Setting negative value is meaningless and will return error. 211 212 Default: SK_WMEM_DEFAULT, (same as net.core.wmem_default). 213 214 Exact value depends on architecture and kernel options, 215 but should be enough to allow queuing 256 packets 216 of medium size. 217 218neigh/default/unres_qlen - INTEGER 219 The maximum number of packets which may be queued for each 220 unresolved address by other network layers. 221 222 (deprecated in linux 3.3) : use unres_qlen_bytes instead. 223 224 Prior to linux 3.3, the default value is 3 which may cause 225 unexpected packet loss. The current default value is calculated 226 according to default value of unres_qlen_bytes and true size of 227 packet. 228 229 Default: 101 230 231neigh/default/interval_probe_time_ms - INTEGER 232 The probe interval for neighbor entries with NTF_MANAGED flag, 233 the min value is 1. 234 235 Default: 5000 236 237mtu_expires - INTEGER 238 Time, in seconds, that cached PMTU information is kept. 239 240min_adv_mss - INTEGER 241 The advertised MSS depends on the first hop route MTU, but will 242 never be lower than this setting. 243 244fib_notify_on_flag_change - INTEGER 245 Whether to emit RTM_NEWROUTE notifications whenever RTM_F_OFFLOAD/ 246 RTM_F_TRAP/RTM_F_OFFLOAD_FAILED flags are changed. 247 248 After installing a route to the kernel, user space receives an 249 acknowledgment, which means the route was installed in the kernel, 250 but not necessarily in hardware. 251 It is also possible for a route already installed in hardware to change 252 its action and therefore its flags. For example, a host route that is 253 trapping packets can be "promoted" to perform decapsulation following 254 the installation of an IPinIP/VXLAN tunnel. 255 The notifications will indicate to user-space the state of the route. 256 257 Default: 0 (Do not emit notifications.) 258 259 Possible values: 260 261 - 0 - Do not emit notifications. 262 - 1 - Emit notifications. 263 - 2 - Emit notifications only for RTM_F_OFFLOAD_FAILED flag change. 264 265IP Fragmentation: 266 267ipfrag_high_thresh - LONG INTEGER 268 Maximum memory used to reassemble IP fragments. 269 270ipfrag_low_thresh - LONG INTEGER 271 (Obsolete since linux-4.17) 272 Maximum memory used to reassemble IP fragments before the kernel 273 begins to remove incomplete fragment queues to free up resources. 274 The kernel still accepts new fragments for defragmentation. 275 276ipfrag_time - INTEGER 277 Time in seconds to keep an IP fragment in memory. 278 279ipfrag_max_dist - INTEGER 280 ipfrag_max_dist is a non-negative integer value which defines the 281 maximum "disorder" which is allowed among fragments which share a 282 common IP source address. Note that reordering of packets is 283 not unusual, but if a large number of fragments arrive from a source 284 IP address while a particular fragment queue remains incomplete, it 285 probably indicates that one or more fragments belonging to that queue 286 have been lost. When ipfrag_max_dist is positive, an additional check 287 is done on fragments before they are added to a reassembly queue - if 288 ipfrag_max_dist (or more) fragments have arrived from a particular IP 289 address between additions to any IP fragment queue using that source 290 address, it's presumed that one or more fragments in the queue are 291 lost. The existing fragment queue will be dropped, and a new one 292 started. An ipfrag_max_dist value of zero disables this check. 293 294 Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can 295 result in unnecessarily dropping fragment queues when normal 296 reordering of packets occurs, which could lead to poor application 297 performance. Using a very large value, e.g. 50000, increases the 298 likelihood of incorrectly reassembling IP fragments that originate 299 from different IP datagrams, which could result in data corruption. 300 Default: 64 301 302bc_forwarding - INTEGER 303 bc_forwarding enables the feature described in rfc1812#section-5.3.5.2 304 and rfc2644. It allows the router to forward directed broadcast. 305 To enable this feature, the 'all' entry and the input interface entry 306 should be set to 1. 307 Default: 0 308 309INET peer storage 310================= 311 312inet_peer_threshold - INTEGER 313 The approximate size of the storage. Starting from this threshold 314 entries will be thrown aggressively. This threshold also determines 315 entries' time-to-live and time intervals between garbage collection 316 passes. More entries, less time-to-live, less GC interval. 317 318inet_peer_minttl - INTEGER 319 Minimum time-to-live of entries. Should be enough to cover fragment 320 time-to-live on the reassembling side. This minimum time-to-live is 321 guaranteed if the pool size is less than inet_peer_threshold. 322 Measured in seconds. 323 324inet_peer_maxttl - INTEGER 325 Maximum time-to-live of entries. Unused entries will expire after 326 this period of time if there is no memory pressure on the pool (i.e. 327 when the number of entries in the pool is very small). 328 Measured in seconds. 329 330TCP variables 331============= 332 333somaxconn - INTEGER 334 Limit of socket listen() backlog, known in userspace as SOMAXCONN. 335 Defaults to 4096. (Was 128 before linux-5.4) 336 See also tcp_max_syn_backlog for additional tuning for TCP sockets. 337 338tcp_abort_on_overflow - BOOLEAN 339 If listening service is too slow to accept new connections, 340 reset them. Default state is FALSE. It means that if overflow 341 occurred due to a burst, connection will recover. Enable this 342 option _only_ if you are really sure that listening daemon 343 cannot be tuned to accept connections faster. Enabling this 344 option can harm clients of your server. 345 346tcp_adv_win_scale - INTEGER 347 Obsolete since linux-6.6 348 Count buffering overhead as bytes/2^tcp_adv_win_scale 349 (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale), 350 if it is <= 0. 351 352 Possible values are [-31, 31], inclusive. 353 354 Default: 1 355 356tcp_allowed_congestion_control - STRING 357 Show/set the congestion control choices available to non-privileged 358 processes. The list is a subset of those listed in 359 tcp_available_congestion_control. 360 361 Default is "reno" and the default setting (tcp_congestion_control). 362 363tcp_app_win - INTEGER 364 Reserve max(window/2^tcp_app_win, mss) of window for application 365 buffer. Value 0 is special, it means that nothing is reserved. 366 367 Possible values are [0, 31], inclusive. 368 369 Default: 31 370 371tcp_autocorking - BOOLEAN 372 Enable TCP auto corking : 373 When applications do consecutive small write()/sendmsg() system calls, 374 we try to coalesce these small writes as much as possible, to lower 375 total amount of sent packets. This is done if at least one prior 376 packet for the flow is waiting in Qdisc queues or device transmit 377 queue. Applications can still use TCP_CORK for optimal behavior 378 when they know how/when to uncork their sockets. 379 380 Possible values: 381 382 - 0 (disabled) 383 - 1 (enabled) 384 385 Default: 1 (enabled) 386 387tcp_available_congestion_control - STRING 388 Shows the available congestion control choices that are registered. 389 More congestion control algorithms may be available as modules, 390 but not loaded. 391 392tcp_base_mss - INTEGER 393 The initial value of search_low to be used by the packetization layer 394 Path MTU discovery (MTU probing). If MTU probing is enabled, 395 this is the initial MSS used by the connection. 396 397tcp_mtu_probe_floor - INTEGER 398 If MTU probing is enabled this caps the minimum MSS used for search_low 399 for the connection. 400 401 Default : 48 402 403tcp_min_snd_mss - INTEGER 404 TCP SYN and SYNACK messages usually advertise an ADVMSS option, 405 as described in RFC 1122 and RFC 6691. 406 407 If this ADVMSS option is smaller than tcp_min_snd_mss, 408 it is silently capped to tcp_min_snd_mss. 409 410 Default : 48 (at least 8 bytes of payload per segment) 411 412tcp_congestion_control - STRING 413 Set the congestion control algorithm to be used for new 414 connections. The algorithm "reno" is always available, but 415 additional choices may be available based on kernel configuration. 416 Default is set as part of kernel configuration. 417 For passive connections, the listener congestion control choice 418 is inherited. 419 420 [see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ] 421 422tcp_dsack - BOOLEAN 423 Allows TCP to send "duplicate" SACKs. 424 425 Possible values: 426 427 - 0 (disabled) 428 - 1 (enabled) 429 430 Default: 1 (enabled) 431 432tcp_early_retrans - INTEGER 433 Tail loss probe (TLP) converts RTOs occurring due to tail 434 losses into fast recovery (RFC8985). Note that 435 TLP requires RACK to function properly (see tcp_recovery below) 436 437 Possible values: 438 439 - 0 disables TLP 440 - 3 or 4 enables TLP 441 442 Default: 3 443 444tcp_ecn - INTEGER 445 Control use of Explicit Congestion Notification (ECN) by TCP. 446 ECN is used only when both ends of the TCP connection indicate support 447 for it. This feature is useful in avoiding losses due to congestion by 448 allowing supporting routers to signal congestion before having to drop 449 packets. A host that supports ECN both sends ECN at the IP layer and 450 feeds back ECN at the TCP layer. The highest variant of ECN feedback 451 that both peers support is chosen by the ECN negotiation (Accurate ECN, 452 ECN, or no ECN). 453 454 The highest negotiated variant for incoming connection requests 455 and the highest variant requested by outgoing connection 456 attempts: 457 458 ===== ==================== ==================== 459 Value Incoming connections Outgoing connections 460 ===== ==================== ==================== 461 0 No ECN No ECN 462 1 ECN ECN 463 2 ECN No ECN 464 3 AccECN AccECN 465 4 AccECN ECN 466 5 AccECN No ECN 467 ===== ==================== ==================== 468 469 Default: 2 470 471tcp_ecn_option - INTEGER 472 Control Accurate ECN (AccECN) option sending when AccECN has been 473 successfully negotiated during handshake. Send logic inhibits 474 sending AccECN options regarless of this setting when no AccECN 475 option has been seen for the reverse direction. 476 477 Possible values are: 478 479 = ============================================================ 480 0 Never send AccECN option. This also disables sending AccECN 481 option in SYN/ACK during handshake. 482 1 Send AccECN option sparingly according to the minimum option 483 rules outlined in draft-ietf-tcpm-accurate-ecn. 484 2 Send AccECN option on every packet whenever it fits into TCP 485 option space. 486 = ============================================================ 487 488 Default: 2 489 490tcp_ecn_option_beacon - INTEGER 491 Control Accurate ECN (AccECN) option sending frequency per RTT and it 492 takes effect only when tcp_ecn_option is set to 2. 493 494 Default: 3 (AccECN will be send at least 3 times per RTT) 495 496tcp_ecn_fallback - BOOLEAN 497 If the kernel detects that ECN connection misbehaves, enable fall 498 back to non-ECN. Currently, this knob implements the fallback 499 from RFC3168, section 6.1.1.1., but we reserve that in future, 500 additional detection mechanisms could be implemented under this 501 knob. The value is not used, if tcp_ecn or per route (or congestion 502 control) ECN settings are disabled. 503 504 Possible values: 505 506 - 0 (disabled) 507 - 1 (enabled) 508 509 Default: 1 (enabled) 510 511tcp_fack - BOOLEAN 512 This is a legacy option, it has no effect anymore. 513 514tcp_fin_timeout - INTEGER 515 The length of time an orphaned (no longer referenced by any 516 application) connection will remain in the FIN_WAIT_2 state 517 before it is aborted at the local end. While a perfectly 518 valid "receive only" state for an un-orphaned connection, an 519 orphaned connection in FIN_WAIT_2 state could otherwise wait 520 forever for the remote to close its end of the connection. 521 522 Cf. tcp_max_orphans 523 524 Default: 60 seconds 525 526tcp_frto - INTEGER 527 Enables Forward RTO-Recovery (F-RTO) defined in RFC5682. 528 F-RTO is an enhanced recovery algorithm for TCP retransmission 529 timeouts. It is particularly beneficial in networks where the 530 RTT fluctuates (e.g., wireless). F-RTO is sender-side only 531 modification. It does not require any support from the peer. 532 533 By default it's enabled with a non-zero value. 0 disables F-RTO. 534 535tcp_fwmark_accept - BOOLEAN 536 If enabled, incoming connections to listening sockets that do not have a 537 socket mark will set the mark of the accepting socket to the fwmark of 538 the incoming SYN packet. This will cause all packets on that connection 539 (starting from the first SYNACK) to be sent with that fwmark. The 540 listening socket's mark is unchanged. Listening sockets that already 541 have a fwmark set via setsockopt(SOL_SOCKET, SO_MARK, ...) are 542 unaffected. 543 544 Possible values: 545 546 - 0 (disabled) 547 - 1 (enabled) 548 549 Default: 0 (disabled) 550 551tcp_invalid_ratelimit - INTEGER 552 Limit the maximal rate for sending duplicate acknowledgments 553 in response to incoming TCP packets that are for an existing 554 connection but that are invalid due to any of these reasons: 555 556 (a) out-of-window sequence number, 557 (b) out-of-window acknowledgment number, or 558 (c) PAWS (Protection Against Wrapped Sequence numbers) check failure 559 560 This can help mitigate simple "ack loop" DoS attacks, wherein 561 a buggy or malicious middlebox or man-in-the-middle can 562 rewrite TCP header fields in manner that causes each endpoint 563 to think that the other is sending invalid TCP segments, thus 564 causing each side to send an unterminating stream of duplicate 565 acknowledgments for invalid segments. 566 567 Using 0 disables rate-limiting of dupacks in response to 568 invalid segments; otherwise this value specifies the minimal 569 space between sending such dupacks, in milliseconds. 570 571 Default: 500 (milliseconds). 572 573tcp_keepalive_time - INTEGER 574 How often TCP sends out keepalive messages when keepalive is enabled. 575 Default: 2hours. 576 577tcp_keepalive_probes - INTEGER 578 How many keepalive probes TCP sends out, until it decides that the 579 connection is broken. Default value: 9. 580 581tcp_keepalive_intvl - INTEGER 582 How frequently the probes are send out. Multiplied by 583 tcp_keepalive_probes it is time to kill not responding connection, 584 after probes started. Default value: 75sec i.e. connection 585 will be aborted after ~11 minutes of retries. 586 587tcp_l3mdev_accept - BOOLEAN 588 Enables child sockets to inherit the L3 master device index. 589 Enabling this option allows a "global" listen socket to work 590 across L3 master domains (e.g., VRFs) with connected sockets 591 derived from the listen socket to be bound to the L3 domain in 592 which the packets originated. Only valid when the kernel was 593 compiled with CONFIG_NET_L3_MASTER_DEV. 594 595 Possible values: 596 597 - 0 (disabled) 598 - 1 (enabled) 599 600 Default: 0 (disabled) 601 602tcp_low_latency - BOOLEAN 603 This is a legacy option, it has no effect anymore. 604 605tcp_max_orphans - INTEGER 606 Maximal number of TCP sockets not attached to any user file handle, 607 held by system. If this number is exceeded orphaned connections are 608 reset immediately and warning is printed. This limit exists 609 only to prevent simple DoS attacks, you _must_ not rely on this 610 or lower the limit artificially, but rather increase it 611 (probably, after increasing installed memory), 612 if network conditions require more than default value, 613 and tune network services to linger and kill such states 614 more aggressively. Let me to remind again: each orphan eats 615 up to ~64K of unswappable memory. 616 617tcp_max_syn_backlog - INTEGER 618 Maximal number of remembered connection requests (SYN_RECV), 619 which have not received an acknowledgment from connecting client. 620 621 This is a per-listener limit. 622 623 The minimal value is 128 for low memory machines, and it will 624 increase in proportion to the memory of machine. 625 626 If server suffers from overload, try increasing this number. 627 628 Remember to also check /proc/sys/net/core/somaxconn 629 A SYN_RECV request socket consumes about 304 bytes of memory. 630 631tcp_max_tw_buckets - INTEGER 632 Maximal number of timewait sockets held by system simultaneously. 633 If this number is exceeded time-wait socket is immediately destroyed 634 and warning is printed. This limit exists only to prevent 635 simple DoS attacks, you _must_ not lower the limit artificially, 636 but rather increase it (probably, after increasing installed memory), 637 if network conditions require more than default value. 638 639tcp_mem - vector of 3 INTEGERs: min, pressure, max 640 min: below this number of pages TCP is not bothered about its 641 memory appetite. 642 643 pressure: when amount of memory allocated by TCP exceeds this number 644 of pages, TCP moderates its memory consumption and enters memory 645 pressure mode, which is exited when memory consumption falls 646 under "min". 647 648 max: number of pages allowed for queueing by all TCP sockets. 649 650 Defaults are calculated at boot time from amount of available 651 memory. 652 653tcp_min_rtt_wlen - INTEGER 654 The window length of the windowed min filter to track the minimum RTT. 655 A shorter window lets a flow more quickly pick up new (higher) 656 minimum RTT when it is moved to a longer path (e.g., due to traffic 657 engineering). A longer window makes the filter more resistant to RTT 658 inflations such as transient congestion. The unit is seconds. 659 660 Possible values: 0 - 86400 (1 day) 661 662 Default: 300 663 664tcp_moderate_rcvbuf - BOOLEAN 665 If enabled, TCP performs receive buffer auto-tuning, attempting to 666 automatically size the buffer (no greater than tcp_rmem[2]) to 667 match the size required by the path for full throughput. 668 669 Possible values: 670 671 - 0 (disabled) 672 - 1 (enabled) 673 674 Default: 1 (enabled) 675 676tcp_mtu_probing - INTEGER 677 Controls TCP Packetization-Layer Path MTU Discovery. Takes three 678 values: 679 680 - 0 - Disabled 681 - 1 - Disabled by default, enabled when an ICMP black hole detected 682 - 2 - Always enabled, use initial MSS of tcp_base_mss. 683 684tcp_probe_interval - UNSIGNED INTEGER 685 Controls how often to start TCP Packetization-Layer Path MTU 686 Discovery reprobe. The default is reprobing every 10 minutes as 687 per RFC4821. 688 689tcp_probe_threshold - INTEGER 690 Controls when TCP Packetization-Layer Path MTU Discovery probing 691 will stop in respect to the width of search range in bytes. Default 692 is 8 bytes. 693 694tcp_no_metrics_save - BOOLEAN 695 By default, TCP saves various connection metrics in the route cache 696 when the connection closes, so that connections established in the 697 near future can use these to set initial conditions. Usually, this 698 increases overall performance, but may sometimes cause performance 699 degradation. If enabled, TCP will not cache metrics on closing 700 connections. 701 702 Possible values: 703 704 - 0 (disabled) 705 - 1 (enabled) 706 707 Default: 0 (disabled) 708 709tcp_no_ssthresh_metrics_save - BOOLEAN 710 Controls whether TCP saves ssthresh metrics in the route cache. 711 If enabled, ssthresh metrics are disabled. 712 713 Possible values: 714 715 - 0 (disabled) 716 - 1 (enabled) 717 718 Default: 1 (enabled) 719 720tcp_orphan_retries - INTEGER 721 This value influences the timeout of a locally closed TCP connection, 722 when RTO retransmissions remain unacknowledged. 723 See tcp_retries2 for more details. 724 725 The default value is 8. 726 727 If your machine is a loaded WEB server, 728 you should think about lowering this value, such sockets 729 may consume significant resources. Cf. tcp_max_orphans. 730 731tcp_recovery - INTEGER 732 This value is a bitmap to enable various experimental loss recovery 733 features. 734 735 ========= ============================================================= 736 RACK: 0x1 enables RACK loss detection, for fast detection of lost 737 retransmissions and tail drops, and resilience to 738 reordering. currently, setting this bit to 0 has no 739 effect, since RACK is the only supported loss detection 740 algorithm. 741 742 RACK: 0x2 makes RACK's reordering window static (min_rtt/4). 743 744 RACK: 0x4 disables RACK's DUPACK threshold heuristic 745 ========= ============================================================= 746 747 Default: 0x1 748 749tcp_reflect_tos - BOOLEAN 750 For listening sockets, reuse the DSCP value of the initial SYN message 751 for outgoing packets. This allows to have both directions of a TCP 752 stream to use the same DSCP value, assuming DSCP remains unchanged for 753 the lifetime of the connection. 754 755 This options affects both IPv4 and IPv6. 756 757 Possible values: 758 759 - 0 (disabled) 760 - 1 (enabled) 761 762 Default: 0 (disabled) 763 764tcp_reordering - INTEGER 765 Initial reordering level of packets in a TCP stream. 766 TCP stack can then dynamically adjust flow reordering level 767 between this initial value and tcp_max_reordering 768 769 Default: 3 770 771tcp_max_reordering - INTEGER 772 Maximal reordering level of packets in a TCP stream. 773 300 is a fairly conservative value, but you might increase it 774 if paths are using per packet load balancing (like bonding rr mode) 775 776 Default: 300 777 778tcp_retrans_collapse - BOOLEAN 779 Bug-to-bug compatibility with some broken printers. 780 On retransmit try to send bigger packets to work around bugs in 781 certain TCP stacks. 782 783 Possible values: 784 785 - 0 (disabled) 786 - 1 (enabled) 787 788 Default: 1 (enabled) 789 790tcp_retries1 - INTEGER 791 This value influences the time, after which TCP decides, that 792 something is wrong due to unacknowledged RTO retransmissions, 793 and reports this suspicion to the network layer. 794 See tcp_retries2 for more details. 795 796 RFC 1122 recommends at least 3 retransmissions, which is the 797 default. 798 799tcp_retries2 - INTEGER 800 This value influences the timeout of an alive TCP connection, 801 when RTO retransmissions remain unacknowledged. 802 Given a value of N, a hypothetical TCP connection following 803 exponential backoff with an initial RTO of TCP_RTO_MIN would 804 retransmit N times before killing the connection at the (N+1)th RTO. 805 806 The default value of 15 yields a hypothetical timeout of 924.6 807 seconds and is a lower bound for the effective timeout. 808 TCP will effectively time out at the first RTO which exceeds the 809 hypothetical timeout. 810 If tcp_rto_max_ms is decreased, it is recommended to also 811 change tcp_retries2. 812 813 RFC 1122 recommends at least 100 seconds for the timeout, 814 which corresponds to a value of at least 8. 815 816tcp_rfc1337 - BOOLEAN 817 If enabled, the TCP stack behaves conforming to RFC1337. If unset, 818 we are not conforming to RFC, but prevent TCP TIME_WAIT 819 assassination. 820 821 Possible values: 822 823 - 0 (disabled) 824 - 1 (enabled) 825 826 Default: 0 (disabled) 827 828tcp_rmem - vector of 3 INTEGERs: min, default, max 829 min: Minimal size of receive buffer used by TCP sockets. 830 It is guaranteed to each TCP socket, even under moderate memory 831 pressure. 832 833 Default: 4K 834 835 default: initial size of receive buffer used by TCP sockets. 836 This value overrides net.core.rmem_default used by other protocols. 837 Default: 131072 bytes. 838 This value results in initial window of 65535. 839 840 max: maximal size of receive buffer allowed for automatically 841 selected receiver buffers for TCP socket. 842 Calling setsockopt() with SO_RCVBUF disables 843 automatic tuning of that socket's receive buffer size, in which 844 case this value is ignored. 845 Default: between 131072 and 32MB, depending on RAM size. 846 847tcp_sack - BOOLEAN 848 Enable select acknowledgments (SACKS). 849 850 Possible values: 851 852 - 0 (disabled) 853 - 1 (enabled) 854 855 Default: 1 (enabled) 856 857tcp_comp_sack_delay_ns - LONG INTEGER 858 TCP tries to reduce number of SACK sent, using a timer 859 based on 5% of SRTT, capped by this sysctl, in nano seconds. 860 The default is 1ms, based on TSO autosizing period. 861 862 Default : 1,000,000 ns (1 ms) 863 864tcp_comp_sack_slack_ns - LONG INTEGER 865 This sysctl control the slack used when arming the 866 timer used by SACK compression. This gives extra time 867 for small RTT flows, and reduces system overhead by allowing 868 opportunistic reduction of timer interrupts. 869 870 Default : 100,000 ns (100 us) 871 872tcp_comp_sack_nr - INTEGER 873 Max number of SACK that can be compressed. 874 Using 0 disables SACK compression. 875 876 Default : 44 877 878tcp_backlog_ack_defer - BOOLEAN 879 If enabled, user thread processing socket backlog tries sending 880 one ACK for the whole queue. This helps to avoid potential 881 long latencies at end of a TCP socket syscall. 882 883 Possible values: 884 885 - 0 (disabled) 886 - 1 (enabled) 887 888 Default: 1 (enabled) 889 890tcp_slow_start_after_idle - BOOLEAN 891 If enabled, provide RFC2861 behavior and time out the congestion 892 window after an idle period. An idle period is defined at 893 the current RTO. If unset, the congestion window will not 894 be timed out after an idle period. 895 896 Possible values: 897 898 - 0 (disabled) 899 - 1 (enabled) 900 901 Default: 1 (enabled) 902 903tcp_stdurg - BOOLEAN 904 Use the Host requirements interpretation of the TCP urgent pointer field. 905 Most hosts use the older BSD interpretation, so if enabled, 906 Linux might not communicate correctly with them. 907 908 Possible values: 909 910 - 0 (disabled) 911 - 1 (enabled) 912 913 Default: 0 (disabled) 914 915tcp_synack_retries - INTEGER 916 Number of times SYNACKs for a passive TCP connection attempt will 917 be retransmitted. Should not be higher than 255. Default value 918 is 5, which corresponds to 31seconds till the last retransmission 919 with the current initial RTO of 1second. With this the final timeout 920 for a passive TCP connection will happen after 63seconds. 921 922tcp_syncookies - INTEGER 923 Only valid when the kernel was compiled with CONFIG_SYN_COOKIES 924 Send out syncookies when the syn backlog queue of a socket 925 overflows. This is to prevent against the common 'SYN flood attack' 926 Default: 1 927 928 Note, that syncookies is fallback facility. 929 It MUST NOT be used to help highly loaded servers to stand 930 against legal connection rate. If you see SYN flood warnings 931 in your logs, but investigation shows that they occur 932 because of overload with legal connections, you should tune 933 another parameters until this warning disappear. 934 See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow. 935 936 syncookies seriously violate TCP protocol, do not allow 937 to use TCP extensions, can result in serious degradation 938 of some services (f.e. SMTP relaying), visible not by you, 939 but your clients and relays, contacting you. While you see 940 SYN flood warnings in logs not being really flooded, your server 941 is seriously misconfigured. 942 943 If you want to test which effects syncookies have to your 944 network connections you can set this knob to 2 to enable 945 unconditionally generation of syncookies. 946 947tcp_migrate_req - BOOLEAN 948 The incoming connection is tied to a specific listening socket when 949 the initial SYN packet is received during the three-way handshake. 950 When a listener is closed, in-flight request sockets during the 951 handshake and established sockets in the accept queue are aborted. 952 953 If the listener has SO_REUSEPORT enabled, other listeners on the 954 same port should have been able to accept such connections. This 955 option makes it possible to migrate such child sockets to another 956 listener after close() or shutdown(). 957 958 The BPF_SK_REUSEPORT_SELECT_OR_MIGRATE type of eBPF program should 959 usually be used to define the policy to pick an alive listener. 960 Otherwise, the kernel will randomly pick an alive listener only if 961 this option is enabled. 962 963 Note that migration between listeners with different settings may 964 crash applications. Let's say migration happens from listener A to 965 B, and only B has TCP_SAVE_SYN enabled. B cannot read SYN data from 966 the requests migrated from A. To avoid such a situation, cancel 967 migration by returning SK_DROP in the type of eBPF program, or 968 disable this option. 969 970 Possible values: 971 972 - 0 (disabled) 973 - 1 (enabled) 974 975 Default: 0 (disabled) 976 977tcp_fastopen - INTEGER 978 Enable TCP Fast Open (RFC7413) to send and accept data in the opening 979 SYN packet. 980 981 The client support is enabled by flag 0x1 (on by default). The client 982 then must use sendmsg() or sendto() with the MSG_FASTOPEN flag, 983 rather than connect() to send data in SYN. 984 985 The server support is enabled by flag 0x2 (off by default). Then 986 either enable for all listeners with another flag (0x400) or 987 enable individual listeners via TCP_FASTOPEN socket option with 988 the option value being the length of the syn-data backlog. 989 990 The values (bitmap) are 991 992 ===== ======== ====================================================== 993 0x1 (client) enables sending data in the opening SYN on the client. 994 0x2 (server) enables the server support, i.e., allowing data in 995 a SYN packet to be accepted and passed to the 996 application before 3-way handshake finishes. 997 0x4 (client) send data in the opening SYN regardless of cookie 998 availability and without a cookie option. 999 0x200 (server) accept data-in-SYN w/o any cookie option present. 1000 0x400 (server) enable all listeners to support Fast Open by 1001 default without explicit TCP_FASTOPEN socket option. 1002 ===== ======== ====================================================== 1003 1004 Default: 0x1 1005 1006 Note that additional client or server features are only 1007 effective if the basic support (0x1 and 0x2) are enabled respectively. 1008 1009tcp_fastopen_blackhole_timeout_sec - INTEGER 1010 Initial time period in second to disable Fastopen on active TCP sockets 1011 when a TFO firewall blackhole issue happens. 1012 This time period will grow exponentially when more blackhole issues 1013 get detected right after Fastopen is re-enabled and will reset to 1014 initial value when the blackhole issue goes away. 1015 0 to disable the blackhole detection. 1016 1017 By default, it is set to 0 (feature is disabled). 1018 1019tcp_fastopen_key - list of comma separated 32-digit hexadecimal INTEGERs 1020 The list consists of a primary key and an optional backup key. The 1021 primary key is used for both creating and validating cookies, while the 1022 optional backup key is only used for validating cookies. The purpose of 1023 the backup key is to maximize TFO validation when keys are rotated. 1024 1025 A randomly chosen primary key may be configured by the kernel if 1026 the tcp_fastopen sysctl is set to 0x400 (see above), or if the 1027 TCP_FASTOPEN setsockopt() optname is set and a key has not been 1028 previously configured via sysctl. If keys are configured via 1029 setsockopt() by using the TCP_FASTOPEN_KEY optname, then those 1030 per-socket keys will be used instead of any keys that are specified via 1031 sysctl. 1032 1033 A key is specified as 4 8-digit hexadecimal integers which are separated 1034 by a '-' as: xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx. Leading zeros may be 1035 omitted. A primary and a backup key may be specified by separating them 1036 by a comma. If only one key is specified, it becomes the primary key and 1037 any previously configured backup keys are removed. 1038 1039tcp_syn_retries - INTEGER 1040 Number of times initial SYNs for an active TCP connection attempt 1041 will be retransmitted. Should not be higher than 127. Default value 1042 is 6, which corresponds to 67seconds (with tcp_syn_linear_timeouts = 4) 1043 till the last retransmission with the current initial RTO of 1second. 1044 With this the final timeout for an active TCP connection attempt 1045 will happen after 131seconds. 1046 1047tcp_timestamps - INTEGER 1048 Enable timestamps as defined in RFC1323. 1049 1050 - 0: Disabled. 1051 - 1: Enable timestamps as defined in RFC1323 and use random offset for 1052 each connection rather than only using the current time. 1053 - 2: Like 1, but without random offsets. 1054 1055 Default: 1 1056 1057tcp_min_tso_segs - INTEGER 1058 Minimal number of segments per TSO frame. 1059 1060 Since linux-3.12, TCP does an automatic sizing of TSO frames, 1061 depending on flow rate, instead of filling 64Kbytes packets. 1062 For specific usages, it's possible to force TCP to build big 1063 TSO frames. Note that TCP stack might split too big TSO packets 1064 if available window is too small. 1065 1066 Default: 2 1067 1068tcp_tso_rtt_log - INTEGER 1069 Adjustment of TSO packet sizes based on min_rtt 1070 1071 Starting from linux-5.18, TCP autosizing can be tweaked 1072 for flows having small RTT. 1073 1074 Old autosizing was splitting the pacing budget to send 1024 TSO 1075 per second. 1076 1077 tso_packet_size = sk->sk_pacing_rate / 1024; 1078 1079 With the new mechanism, we increase this TSO sizing using: 1080 1081 distance = min_rtt_usec / (2^tcp_tso_rtt_log) 1082 tso_packet_size += gso_max_size >> distance; 1083 1084 This means that flows between very close hosts can use bigger 1085 TSO packets, reducing their cpu costs. 1086 1087 If you want to use the old autosizing, set this sysctl to 0. 1088 1089 Default: 9 (2^9 = 512 usec) 1090 1091tcp_pacing_ss_ratio - INTEGER 1092 sk->sk_pacing_rate is set by TCP stack using a ratio applied 1093 to current rate. (current_rate = cwnd * mss / srtt) 1094 If TCP is in slow start, tcp_pacing_ss_ratio is applied 1095 to let TCP probe for bigger speeds, assuming cwnd can be 1096 doubled every other RTT. 1097 1098 Default: 200 1099 1100tcp_pacing_ca_ratio - INTEGER 1101 sk->sk_pacing_rate is set by TCP stack using a ratio applied 1102 to current rate. (current_rate = cwnd * mss / srtt) 1103 If TCP is in congestion avoidance phase, tcp_pacing_ca_ratio 1104 is applied to conservatively probe for bigger throughput. 1105 1106 Default: 120 1107 1108tcp_syn_linear_timeouts - INTEGER 1109 The number of times for an active TCP connection to retransmit SYNs with 1110 a linear backoff timeout before defaulting to an exponential backoff 1111 timeout. This has no effect on SYNACK at the passive TCP side. 1112 1113 With an initial RTO of 1 and tcp_syn_linear_timeouts = 4 we would 1114 expect SYN RTOs to be: 1, 1, 1, 1, 1, 2, 4, ... (4 linear timeouts, 1115 and the first exponential backoff using 2^0 * initial_RTO). 1116 Default: 4 1117 1118tcp_tso_win_divisor - INTEGER 1119 This allows control over what percentage of the congestion window 1120 can be consumed by a single TSO frame. 1121 The setting of this parameter is a choice between burstiness and 1122 building larger TSO frames. 1123 1124 Default: 3 1125 1126tcp_tw_reuse - INTEGER 1127 Enable reuse of TIME-WAIT sockets for new connections when it is 1128 safe from protocol viewpoint. 1129 1130 - 0 - disable 1131 - 1 - global enable 1132 - 2 - enable for loopback traffic only 1133 1134 It should not be changed without advice/request of technical 1135 experts. 1136 1137 Default: 2 1138 1139tcp_tw_reuse_delay - UNSIGNED INTEGER 1140 The delay in milliseconds before a TIME-WAIT socket can be reused by a 1141 new connection, if TIME-WAIT socket reuse is enabled. The actual reuse 1142 threshold is within [N, N+1] range, where N is the requested delay in 1143 milliseconds, to ensure the delay interval is never shorter than the 1144 configured value. 1145 1146 This setting contains an assumption about the other TCP timestamp clock 1147 tick interval. It should not be set to a value lower than the peer's 1148 clock tick for PAWS (Protection Against Wrapped Sequence numbers) 1149 mechanism work correctly for the reused connection. 1150 1151 Default: 1000 (milliseconds) 1152 1153tcp_window_scaling - BOOLEAN 1154 Enable window scaling as defined in RFC1323. 1155 1156 Possible values: 1157 1158 - 0 (disabled) 1159 - 1 (enabled) 1160 1161 Default: 1 (enabled) 1162 1163tcp_shrink_window - BOOLEAN 1164 This changes how the TCP receive window is calculated. 1165 1166 RFC 7323, section 2.4, says there are instances when a retracted 1167 window can be offered, and that TCP implementations MUST ensure 1168 that they handle a shrinking window, as specified in RFC 1122. 1169 1170 Possible values: 1171 1172 - 0 (disabled) - The window is never shrunk. 1173 - 1 (enabled) - The window is shrunk when necessary to remain within 1174 the memory limit set by autotuning (sk_rcvbuf). 1175 This only occurs if a non-zero receive window 1176 scaling factor is also in effect. 1177 1178 Default: 0 (disabled) 1179 1180tcp_wmem - vector of 3 INTEGERs: min, default, max 1181 min: Amount of memory reserved for send buffers for TCP sockets. 1182 Each TCP socket has rights to use it due to fact of its birth. 1183 1184 Default: 4K 1185 1186 default: initial size of send buffer used by TCP sockets. This 1187 value overrides net.core.wmem_default used by other protocols. 1188 1189 It is usually lower than net.core.wmem_default. 1190 1191 Default: 16K 1192 1193 max: Maximal amount of memory allowed for automatically tuned 1194 send buffers for TCP sockets. This value does not override 1195 net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables 1196 automatic tuning of that socket's send buffer size, in which case 1197 this value is ignored. 1198 1199 Default: between 64K and 4MB, depending on RAM size. 1200 1201tcp_notsent_lowat - UNSIGNED INTEGER 1202 A TCP socket can control the amount of unsent bytes in its write queue, 1203 thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll() 1204 reports POLLOUT events if the amount of unsent bytes is below a per 1205 socket value, and if the write queue is not full. sendmsg() will 1206 also not add new buffers if the limit is hit. 1207 1208 This global variable controls the amount of unsent data for 1209 sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change 1210 to the global variable has immediate effect. 1211 1212 Default: UINT_MAX (0xFFFFFFFF) 1213 1214tcp_workaround_signed_windows - BOOLEAN 1215 If enabled, assume no receipt of a window scaling option means the 1216 remote TCP is broken and treats the window as a signed quantity. 1217 If disabled, assume the remote TCP is not broken even if we do 1218 not receive a window scaling option from them. 1219 1220 Possible values: 1221 1222 - 0 (disabled) 1223 - 1 (enabled) 1224 1225 Default: 0 (disabled) 1226 1227tcp_thin_linear_timeouts - BOOLEAN 1228 Enable dynamic triggering of linear timeouts for thin streams. 1229 If enabled, a check is performed upon retransmission by timeout to 1230 determine if the stream is thin (less than 4 packets in flight). 1231 As long as the stream is found to be thin, up to 6 linear 1232 timeouts may be performed before exponential backoff mode is 1233 initiated. This improves retransmission latency for 1234 non-aggressive thin streams, often found to be time-dependent. 1235 For more information on thin streams, see 1236 Documentation/networking/tcp-thin.rst 1237 1238 Possible values: 1239 1240 - 0 (disabled) 1241 - 1 (enabled) 1242 1243 Default: 0 (disabled) 1244 1245tcp_limit_output_bytes - INTEGER 1246 Controls TCP Small Queue limit per tcp socket. 1247 TCP bulk sender tends to increase packets in flight until it 1248 gets losses notifications. With SNDBUF autotuning, this can 1249 result in a large amount of packets queued on the local machine 1250 (e.g.: qdiscs, CPU backlog, or device) hurting latency of other 1251 flows, for typical pfifo_fast qdiscs. tcp_limit_output_bytes 1252 limits the number of bytes on qdisc or device to reduce artificial 1253 RTT/cwnd and reduce bufferbloat. 1254 1255 Default: 4194304 (4 MB) 1256 1257tcp_challenge_ack_limit - INTEGER 1258 Limits number of Challenge ACK sent per second, as recommended 1259 in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks) 1260 Note that this per netns rate limit can allow some side channel 1261 attacks and probably should not be enabled. 1262 TCP stack implements per TCP socket limits anyway. 1263 Default: INT_MAX (unlimited) 1264 1265tcp_ehash_entries - INTEGER 1266 Show the number of hash buckets for TCP sockets in the current 1267 networking namespace. 1268 1269 A negative value means the networking namespace does not own its 1270 hash buckets and shares the initial networking namespace's one. 1271 1272tcp_child_ehash_entries - INTEGER 1273 Control the number of hash buckets for TCP sockets in the child 1274 networking namespace, which must be set before clone() or unshare(). 1275 1276 If the value is not 0, the kernel uses a value rounded up to 2^n 1277 as the actual hash bucket size. 0 is a special value, meaning 1278 the child networking namespace will share the initial networking 1279 namespace's hash buckets. 1280 1281 Note that the child will use the global one in case the kernel 1282 fails to allocate enough memory. In addition, the global hash 1283 buckets are spread over available NUMA nodes, but the allocation 1284 of the child hash table depends on the current process's NUMA 1285 policy, which could result in performance differences. 1286 1287 Note also that the default value of tcp_max_tw_buckets and 1288 tcp_max_syn_backlog depend on the hash bucket size. 1289 1290 Possible values: 0, 2^n (n: 0 - 24 (16Mi)) 1291 1292 Default: 0 1293 1294tcp_plb_enabled - BOOLEAN 1295 If enabled and the underlying congestion control (e.g. DCTCP) supports 1296 and enables PLB feature, TCP PLB (Protective Load Balancing) is 1297 enabled. PLB is described in the following paper: 1298 https://doi.org/10.1145/3544216.3544226. Based on PLB parameters, 1299 upon sensing sustained congestion, TCP triggers a change in 1300 flow label field for outgoing IPv6 packets. A change in flow label 1301 field potentially changes the path of outgoing packets for switches 1302 that use ECMP/WCMP for routing. 1303 1304 PLB changes socket txhash which results in a change in IPv6 Flow Label 1305 field, and currently no-op for IPv4 headers. It is possible 1306 to apply PLB for IPv4 with other network header fields (e.g. TCP 1307 or IPv4 options) or using encapsulation where outer header is used 1308 by switches to determine next hop. In either case, further host 1309 and switch side changes will be needed. 1310 1311 If enabled, PLB assumes that congestion signal (e.g. ECN) is made 1312 available and used by congestion control module to estimate a 1313 congestion measure (e.g. ce_ratio). PLB needs a congestion measure to 1314 make repathing decisions. 1315 1316 Possible values: 1317 1318 - 0 (disabled) 1319 - 1 (enabled) 1320 1321 Default: 0 (disabled) 1322 1323tcp_plb_idle_rehash_rounds - INTEGER 1324 Number of consecutive congested rounds (RTT) seen after which 1325 a rehash can be performed, given there are no packets in flight. 1326 This is referred to as M in PLB paper: 1327 https://doi.org/10.1145/3544216.3544226. 1328 1329 Possible Values: 0 - 31 1330 1331 Default: 3 1332 1333tcp_plb_rehash_rounds - INTEGER 1334 Number of consecutive congested rounds (RTT) seen after which 1335 a forced rehash can be performed. Be careful when setting this 1336 parameter, as a small value increases the risk of retransmissions. 1337 This is referred to as N in PLB paper: 1338 https://doi.org/10.1145/3544216.3544226. 1339 1340 Possible Values: 0 - 31 1341 1342 Default: 12 1343 1344tcp_plb_suspend_rto_sec - INTEGER 1345 Time, in seconds, to suspend PLB in event of an RTO. In order to avoid 1346 having PLB repath onto a connectivity "black hole", after an RTO a TCP 1347 connection suspends PLB repathing for a random duration between 1x and 1348 2x of this parameter. Randomness is added to avoid concurrent rehashing 1349 of multiple TCP connections. This should be set corresponding to the 1350 amount of time it takes to repair a failed link. 1351 1352 Possible Values: 0 - 255 1353 1354 Default: 60 1355 1356tcp_plb_cong_thresh - INTEGER 1357 Fraction of packets marked with congestion over a round (RTT) to 1358 tag that round as congested. This is referred to as K in the PLB paper: 1359 https://doi.org/10.1145/3544216.3544226. 1360 1361 The 0-1 fraction range is mapped to 0-256 range to avoid floating 1362 point operations. For example, 128 means that if at least 50% of 1363 the packets in a round were marked as congested then the round 1364 will be tagged as congested. 1365 1366 Setting threshold to 0 means that PLB repaths every RTT regardless 1367 of congestion. This is not intended behavior for PLB and should be 1368 used only for experimentation purpose. 1369 1370 Possible Values: 0 - 256 1371 1372 Default: 128 1373 1374tcp_pingpong_thresh - INTEGER 1375 The number of estimated data replies sent for estimated incoming data 1376 requests that must happen before TCP considers that a connection is a 1377 "ping-pong" (request-response) connection for which delayed 1378 acknowledgments can provide benefits. 1379 1380 This threshold is 1 by default, but some applications may need a higher 1381 threshold for optimal performance. 1382 1383 Possible Values: 1 - 255 1384 1385 Default: 1 1386 1387tcp_rto_min_us - INTEGER 1388 Minimal TCP retransmission timeout (in microseconds). Note that the 1389 rto_min route option has the highest precedence for configuring this 1390 setting, followed by the TCP_BPF_RTO_MIN and TCP_RTO_MIN_US socket 1391 options, followed by this tcp_rto_min_us sysctl. 1392 1393 The recommended practice is to use a value less or equal to 200000 1394 microseconds. 1395 1396 Possible Values: 1 - INT_MAX 1397 1398 Default: 200000 1399 1400tcp_rto_max_ms - INTEGER 1401 Maximal TCP retransmission timeout (in ms). 1402 Note that TCP_RTO_MAX_MS socket option has higher precedence. 1403 1404 When changing tcp_rto_max_ms, it is important to understand 1405 that tcp_retries2 might need a change. 1406 1407 Possible Values: 1000 - 120,000 1408 1409 Default: 120,000 1410 1411UDP variables 1412============= 1413 1414udp_l3mdev_accept - BOOLEAN 1415 Enabling this option allows a "global" bound socket to work 1416 across L3 master domains (e.g., VRFs) with packets capable of 1417 being received regardless of the L3 domain in which they 1418 originated. Only valid when the kernel was compiled with 1419 CONFIG_NET_L3_MASTER_DEV. 1420 1421 Possible values: 1422 1423 - 0 (disabled) 1424 - 1 (enabled) 1425 1426 Default: 0 (disabled) 1427 1428udp_mem - vector of 3 INTEGERs: min, pressure, max 1429 Number of pages allowed for queueing by all UDP sockets. 1430 1431 min: Number of pages allowed for queueing by all UDP sockets. 1432 1433 pressure: This value was introduced to follow format of tcp_mem. 1434 1435 max: This value was introduced to follow format of tcp_mem. 1436 1437 Default is calculated at boot time from amount of available memory. 1438 1439udp_rmem_min - INTEGER 1440 Minimal size of receive buffer used by UDP sockets in moderation. 1441 Each UDP socket is able to use the size for receiving data, even if 1442 total pages of UDP sockets exceed udp_mem pressure. The unit is byte. 1443 1444 Default: 4K 1445 1446udp_wmem_min - INTEGER 1447 UDP does not have tx memory accounting and this tunable has no effect. 1448 1449udp_hash_entries - INTEGER 1450 Show the number of hash buckets for UDP sockets in the current 1451 networking namespace. 1452 1453 A negative value means the networking namespace does not own its 1454 hash buckets and shares the initial networking namespace's one. 1455 1456udp_child_hash_entries - INTEGER 1457 Control the number of hash buckets for UDP sockets in the child 1458 networking namespace, which must be set before clone() or unshare(). 1459 1460 If the value is not 0, the kernel uses a value rounded up to 2^n 1461 as the actual hash bucket size. 0 is a special value, meaning 1462 the child networking namespace will share the initial networking 1463 namespace's hash buckets. 1464 1465 Note that the child will use the global one in case the kernel 1466 fails to allocate enough memory. In addition, the global hash 1467 buckets are spread over available NUMA nodes, but the allocation 1468 of the child hash table depends on the current process's NUMA 1469 policy, which could result in performance differences. 1470 1471 Possible values: 0, 2^n (n: 7 (128) - 16 (64K)) 1472 1473 Default: 0 1474 1475 1476RAW variables 1477============= 1478 1479raw_l3mdev_accept - BOOLEAN 1480 Enabling this option allows a "global" bound socket to work 1481 across L3 master domains (e.g., VRFs) with packets capable of 1482 being received regardless of the L3 domain in which they 1483 originated. Only valid when the kernel was compiled with 1484 CONFIG_NET_L3_MASTER_DEV. 1485 1486 Possible values: 1487 1488 - 0 (disabled) 1489 - 1 (enabled) 1490 1491 Default: 1 (enabled) 1492 1493CIPSOv4 Variables 1494================= 1495 1496cipso_cache_enable - BOOLEAN 1497 If enabled, enable additions to and lookups from the CIPSO label mapping 1498 cache. If disabled, additions are ignored and lookups always result in a 1499 miss. However, regardless of the setting the cache is still 1500 invalidated when required when means you can safely toggle this on and 1501 off and the cache will always be "safe". 1502 1503 Possible values: 1504 1505 - 0 (disabled) 1506 - 1 (enabled) 1507 1508 Default: 1 (enabled) 1509 1510cipso_cache_bucket_size - INTEGER 1511 The CIPSO label cache consists of a fixed size hash table with each 1512 hash bucket containing a number of cache entries. This variable limits 1513 the number of entries in each hash bucket; the larger the value is, the 1514 more CIPSO label mappings that can be cached. When the number of 1515 entries in a given hash bucket reaches this limit adding new entries 1516 causes the oldest entry in the bucket to be removed to make room. 1517 1518 Default: 10 1519 1520cipso_rbm_optfmt - BOOLEAN 1521 Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of 1522 the CIPSO draft specification (see Documentation/netlabel for details). 1523 This means that when set the CIPSO tag will be padded with empty 1524 categories in order to make the packet data 32-bit aligned. 1525 1526 Possible values: 1527 1528 - 0 (disabled) 1529 - 1 (enabled) 1530 1531 Default: 0 (disabled) 1532 1533cipso_rbm_strictvalid - BOOLEAN 1534 If enabled, do a very strict check of the CIPSO option when 1535 ip_options_compile() is called. If disabled, relax the checks done during 1536 ip_options_compile(). Either way is "safe" as errors are caught else 1537 where in the CIPSO processing code but setting this to 0 (False) should 1538 result in less work (i.e. it should be faster) but could cause problems 1539 with other implementations that require strict checking. 1540 1541 Possible values: 1542 1543 - 0 (disabled) 1544 - 1 (enabled) 1545 1546 Default: 0 (disabled) 1547 1548IP Variables 1549============ 1550 1551ip_local_port_range - 2 INTEGERS 1552 Defines the local port range that is used by TCP and UDP to 1553 choose the local port. The first number is the first, the 1554 second the last local port number. 1555 If possible, it is better these numbers have different parity 1556 (one even and one odd value). 1557 Must be greater than or equal to ip_unprivileged_port_start. 1558 The default values are 32768 and 60999 respectively. 1559 1560ip_local_reserved_ports - list of comma separated ranges 1561 Specify the ports which are reserved for known third-party 1562 applications. These ports will not be used by automatic port 1563 assignments (e.g. when calling connect() or bind() with port 1564 number 0). Explicit port allocation behavior is unchanged. 1565 1566 The format used for both input and output is a comma separated 1567 list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and 1568 10). Writing to the file will clear all previously reserved 1569 ports and update the current list with the one given in the 1570 input. 1571 1572 Note that ip_local_port_range and ip_local_reserved_ports 1573 settings are independent and both are considered by the kernel 1574 when determining which ports are available for automatic port 1575 assignments. 1576 1577 You can reserve ports which are not in the current 1578 ip_local_port_range, e.g.:: 1579 1580 $ cat /proc/sys/net/ipv4/ip_local_port_range 1581 32000 60999 1582 $ cat /proc/sys/net/ipv4/ip_local_reserved_ports 1583 8080,9148 1584 1585 although this is redundant. However such a setting is useful 1586 if later the port range is changed to a value that will 1587 include the reserved ports. Also keep in mind, that overlapping 1588 of these ranges may affect probability of selecting ephemeral 1589 ports which are right after block of reserved ports. 1590 1591 Default: Empty 1592 1593ip_unprivileged_port_start - INTEGER 1594 This is a per-namespace sysctl. It defines the first 1595 unprivileged port in the network namespace. Privileged ports 1596 require root or CAP_NET_BIND_SERVICE in order to bind to them. 1597 To disable all privileged ports, set this to 0. They must not 1598 overlap with the ip_local_port_range. 1599 1600 Default: 1024 1601 1602ip_nonlocal_bind - BOOLEAN 1603 If enabled, allows processes to bind() to non-local IP addresses, 1604 which can be quite useful - but may break some applications. 1605 1606 Possible values: 1607 1608 - 0 (disabled) 1609 - 1 (enabled) 1610 1611 Default: 0 (disabled) 1612 1613ip_autobind_reuse - BOOLEAN 1614 By default, bind() does not select the ports automatically even if 1615 the new socket and all sockets bound to the port have SO_REUSEADDR. 1616 ip_autobind_reuse allows bind() to reuse the port and this is useful 1617 when you use bind()+connect(), but may break some applications. 1618 The preferred solution is to use IP_BIND_ADDRESS_NO_PORT and this 1619 option should only be set by experts. 1620 1621 Possible values: 1622 1623 - 0 (disabled) 1624 - 1 (enabled) 1625 1626 Default: 0 (disabled) 1627 1628ip_dynaddr - INTEGER 1629 If set non-zero, enables support for dynamic addresses. 1630 If set to a non-zero value larger than 1, a kernel log 1631 message will be printed when dynamic address rewriting 1632 occurs. 1633 1634 Default: 0 1635 1636ip_early_demux - BOOLEAN 1637 Optimize input packet processing down to one demux for 1638 certain kinds of local sockets. Currently we only do this 1639 for established TCP and connected UDP sockets. 1640 1641 It may add an additional cost for pure routing workloads that 1642 reduces overall throughput, in such case you should disable it. 1643 1644 Possible values: 1645 1646 - 0 (disabled) 1647 - 1 (enabled) 1648 1649 Default: 1 (enabled) 1650 1651ping_group_range - 2 INTEGERS 1652 Restrict ICMP_PROTO datagram sockets to users in the group range. 1653 The default is "1 0", meaning, that nobody (not even root) may 1654 create ping sockets. Setting it to "100 100" would grant permissions 1655 to the single group. "0 4294967294" would enable it for the world, "100 1656 4294967294" would enable it for the users, but not daemons. 1657 1658tcp_early_demux - BOOLEAN 1659 Enable early demux for established TCP sockets. 1660 1661 Possible values: 1662 1663 - 0 (disabled) 1664 - 1 (enabled) 1665 1666 Default: 1 (enabled) 1667 1668udp_early_demux - BOOLEAN 1669 Enable early demux for connected UDP sockets. Disable this if 1670 your system could experience more unconnected load. 1671 1672 Possible values: 1673 1674 - 0 (disabled) 1675 - 1 (enabled) 1676 1677 Default: 1 (enabled) 1678 1679icmp_echo_ignore_all - BOOLEAN 1680 If enabled, then the kernel will ignore all ICMP ECHO 1681 requests sent to it. 1682 1683 Possible values: 1684 1685 - 0 (disabled) 1686 - 1 (enabled) 1687 1688 Default: 0 (disabled) 1689 1690icmp_echo_enable_probe - BOOLEAN 1691 If enabled, then the kernel will respond to RFC 8335 PROBE 1692 requests sent to it. 1693 1694 Possible values: 1695 1696 - 0 (disabled) 1697 - 1 (enabled) 1698 1699 Default: 0 (disabled) 1700 1701icmp_echo_ignore_broadcasts - BOOLEAN 1702 If enabled, then the kernel will ignore all ICMP ECHO and 1703 TIMESTAMP requests sent to it via broadcast/multicast. 1704 1705 Possible values: 1706 1707 - 0 (disabled) 1708 - 1 (enabled) 1709 1710 Default: 1 (enabled) 1711 1712icmp_ratelimit - INTEGER 1713 Limit the maximal rates for sending ICMP packets whose type matches 1714 icmp_ratemask (see below) to specific targets. 1715 0 to disable any limiting, 1716 otherwise the minimal space between responses in milliseconds. 1717 Note that another sysctl, icmp_msgs_per_sec limits the number 1718 of ICMP packets sent on all targets. 1719 1720 Default: 1000 1721 1722icmp_msgs_per_sec - INTEGER 1723 Limit maximal number of ICMP packets sent per second from this host. 1724 Only messages whose type matches icmp_ratemask (see below) are 1725 controlled by this limit. For security reasons, the precise count 1726 of messages per second is randomized. 1727 1728 Default: 1000 1729 1730icmp_msgs_burst - INTEGER 1731 icmp_msgs_per_sec controls number of ICMP packets sent per second, 1732 while icmp_msgs_burst controls the burst size of these packets. 1733 For security reasons, the precise burst size is randomized. 1734 1735 Default: 50 1736 1737icmp_ratemask - INTEGER 1738 Mask made of ICMP types for which rates are being limited. 1739 1740 Significant bits: IHGFEDCBA9876543210 1741 1742 Default mask: 0000001100000011000 (6168) 1743 1744 Bit definitions (see include/linux/icmp.h): 1745 1746 = ========================= 1747 0 Echo Reply 1748 3 Destination Unreachable [1]_ 1749 4 Source Quench [1]_ 1750 5 Redirect 1751 8 Echo Request 1752 B Time Exceeded [1]_ 1753 C Parameter Problem [1]_ 1754 D Timestamp Request 1755 E Timestamp Reply 1756 F Info Request 1757 G Info Reply 1758 H Address Mask Request 1759 I Address Mask Reply 1760 = ========================= 1761 1762 .. [1] These are rate limited by default (see default mask above) 1763 1764icmp_ignore_bogus_error_responses - BOOLEAN 1765 Some routers violate RFC1122 by sending bogus responses to broadcast 1766 frames. Such violations are normally logged via a kernel warning. 1767 If enabled, the kernel will not give such warnings, which 1768 will avoid log file clutter. 1769 1770 Possible values: 1771 1772 - 0 (disabled) 1773 - 1 (enabled) 1774 1775 Default: 1 (enabled) 1776 1777icmp_errors_use_inbound_ifaddr - BOOLEAN 1778 1779 If disabled, icmp error messages are sent with the primary address of 1780 the exiting interface. 1781 1782 If enabled, the message will be sent with the primary address of 1783 the interface that received the packet that caused the icmp error. 1784 This is the behaviour many network administrators will expect from 1785 a router. And it can make debugging complicated network layouts 1786 much easier. 1787 1788 Note that if no primary address exists for the interface selected, 1789 then the primary address of the first non-loopback interface that 1790 has one will be used regardless of this setting. 1791 1792 Possible values: 1793 1794 - 0 (disabled) 1795 - 1 (enabled) 1796 1797 Default: 0 (disabled) 1798 1799icmp_errors_extension_mask - UNSIGNED INTEGER 1800 Bitmask of ICMP extensions to append to ICMPv4 error messages 1801 ("Destination Unreachable", "Time Exceeded" and "Parameter Problem"). 1802 The original datagram is trimmed / padded to 128 bytes in order to be 1803 compatible with applications that do not comply with RFC 4884. 1804 1805 Possible extensions are: 1806 1807 ==== ============================================================== 1808 0x01 Incoming IP interface information according to RFC 5837. 1809 Extension will include the index, IPv4 address (if present), 1810 name and MTU of the IP interface that received the datagram 1811 which elicited the ICMP error. 1812 ==== ============================================================== 1813 1814 Default: 0x00 (no extensions) 1815 1816igmp_max_memberships - INTEGER 1817 Change the maximum number of multicast groups we can subscribe to. 1818 Default: 20 1819 1820 Theoretical maximum value is bounded by having to send a membership 1821 report in a single datagram (i.e. the report can't span multiple 1822 datagrams, or risk confusing the switch and leaving groups you don't 1823 intend to). 1824 1825 The number of supported groups 'M' is bounded by the number of group 1826 report entries you can fit into a single datagram of 65535 bytes. 1827 1828 M = 65536-sizeof (ip header)/(sizeof(Group record)) 1829 1830 Group records are variable length, with a minimum of 12 bytes. 1831 So net.ipv4.igmp_max_memberships should not be set higher than: 1832 1833 (65536-24) / 12 = 5459 1834 1835 The value 5459 assumes no IP header options, so in practice 1836 this number may be lower. 1837 1838igmp_max_msf - INTEGER 1839 Maximum number of addresses allowed in the source filter list for a 1840 multicast group. 1841 1842 Default: 10 1843 1844igmp_qrv - INTEGER 1845 Controls the IGMP query robustness variable (see RFC2236 8.1). 1846 1847 Default: 2 (as specified by RFC2236 8.1) 1848 1849 Minimum: 1 (as specified by RFC6636 4.5) 1850 1851force_igmp_version - INTEGER 1852 - 0 - (default) No enforcement of a IGMP version, IGMPv1/v2 fallback 1853 allowed. Will back to IGMPv3 mode again if all IGMPv1/v2 Querier 1854 Present timer expires. 1855 - 1 - Enforce to use IGMP version 1. Will also reply IGMPv1 report if 1856 receive IGMPv2/v3 query. 1857 - 2 - Enforce to use IGMP version 2. Will fallback to IGMPv1 if receive 1858 IGMPv1 query message. Will reply report if receive IGMPv3 query. 1859 - 3 - Enforce to use IGMP version 3. The same react with default 0. 1860 1861 .. note:: 1862 1863 this is not the same with force_mld_version because IGMPv3 RFC3376 1864 Security Considerations does not have clear description that we could 1865 ignore other version messages completely as MLDv2 RFC3810. So make 1866 this value as default 0 is recommended. 1867 1868``conf/interface/*`` 1869 changes special settings per interface (where 1870 interface" is the name of your network interface) 1871 1872``conf/all/*`` 1873 is special, changes the settings for all interfaces 1874 1875log_martians - BOOLEAN 1876 Log packets with impossible addresses to kernel log. 1877 log_martians for the interface will be enabled if at least one of 1878 conf/{all,interface}/log_martians is set to TRUE, 1879 it will be disabled otherwise 1880 1881accept_redirects - BOOLEAN 1882 Accept ICMP redirect messages. 1883 accept_redirects for the interface will be enabled if: 1884 1885 - both conf/{all,interface}/accept_redirects are TRUE in the case 1886 forwarding for the interface is enabled 1887 1888 or 1889 1890 - at least one of conf/{all,interface}/accept_redirects is TRUE in the 1891 case forwarding for the interface is disabled 1892 1893 accept_redirects for the interface will be disabled otherwise 1894 1895 default: 1896 1897 - TRUE (host) 1898 - FALSE (router) 1899 1900forwarding - BOOLEAN 1901 Enable IP forwarding on this interface. This controls whether packets 1902 received _on_ this interface can be forwarded. 1903 1904mc_forwarding - BOOLEAN 1905 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE 1906 and a multicast routing daemon is required. 1907 conf/all/mc_forwarding must also be set to TRUE to enable multicast 1908 routing for the interface 1909 1910medium_id - INTEGER 1911 Integer value used to differentiate the devices by the medium they 1912 are attached to. Two devices can have different id values when 1913 the broadcast packets are received only on one of them. 1914 The default value 0 means that the device is the only interface 1915 to its medium, value of -1 means that medium is not known. 1916 1917 Currently, it is used to change the proxy_arp behavior: 1918 the proxy_arp feature is enabled for packets forwarded between 1919 two devices attached to different media. 1920 1921proxy_arp - BOOLEAN 1922 Do proxy arp. 1923 1924 proxy_arp for the interface will be enabled if at least one of 1925 conf/{all,interface}/proxy_arp is set to TRUE, 1926 it will be disabled otherwise 1927 1928proxy_arp_pvlan - BOOLEAN 1929 Private VLAN proxy arp. 1930 1931 Basically allow proxy arp replies back to the same interface 1932 (from which the ARP request/solicitation was received). 1933 1934 This is done to support (ethernet) switch features, like RFC 1935 3069, where the individual ports are NOT allowed to 1936 communicate with each other, but they are allowed to talk to 1937 the upstream router. As described in RFC 3069, it is possible 1938 to allow these hosts to communicate through the upstream 1939 router by proxy_arp'ing. Don't need to be used together with 1940 proxy_arp. 1941 1942 This technology is known by different names: 1943 1944 - In RFC 3069 it is called VLAN Aggregation. 1945 - Cisco and Allied Telesyn call it Private VLAN. 1946 - Hewlett-Packard call it Source-Port filtering or port-isolation. 1947 - Ericsson call it MAC-Forced Forwarding (RFC Draft). 1948 1949proxy_delay - INTEGER 1950 Delay proxy response. 1951 1952 Delay response to a neighbor solicitation when proxy_arp 1953 or proxy_ndp is enabled. A random value between [0, proxy_delay) 1954 will be chosen, setting to zero means reply with no delay. 1955 Value in jiffies. Defaults to 80. 1956 1957shared_media - BOOLEAN 1958 Send(router) or accept(host) RFC1620 shared media redirects. 1959 Overrides secure_redirects. 1960 1961 shared_media for the interface will be enabled if at least one of 1962 conf/{all,interface}/shared_media is set to TRUE, 1963 it will be disabled otherwise 1964 1965 default TRUE 1966 1967secure_redirects - BOOLEAN 1968 Accept ICMP redirect messages only to gateways listed in the 1969 interface's current gateway list. Even if disabled, RFC1122 redirect 1970 rules still apply. 1971 1972 Overridden by shared_media. 1973 1974 secure_redirects for the interface will be enabled if at least one of 1975 conf/{all,interface}/secure_redirects is set to TRUE, 1976 it will be disabled otherwise 1977 1978 default TRUE 1979 1980send_redirects - BOOLEAN 1981 Send redirects, if router. 1982 1983 send_redirects for the interface will be enabled if at least one of 1984 conf/{all,interface}/send_redirects is set to TRUE, 1985 it will be disabled otherwise 1986 1987 Default: TRUE 1988 1989bootp_relay - BOOLEAN 1990 Accept packets with source address 0.b.c.d destined 1991 not to this host as local ones. It is supposed, that 1992 BOOTP relay daemon will catch and forward such packets. 1993 conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay 1994 for the interface 1995 1996 default FALSE 1997 1998 Not Implemented Yet. 1999 2000accept_source_route - BOOLEAN 2001 Accept packets with SRR option. 2002 conf/all/accept_source_route must also be set to TRUE to accept packets 2003 with SRR option on the interface 2004 2005 default 2006 2007 - TRUE (router) 2008 - FALSE (host) 2009 2010accept_local - BOOLEAN 2011 Accept packets with local source addresses. In combination with 2012 suitable routing, this can be used to direct packets between two 2013 local interfaces over the wire and have them accepted properly. 2014 default FALSE 2015 2016route_localnet - BOOLEAN 2017 Do not consider loopback addresses as martian source or destination 2018 while routing. This enables the use of 127/8 for local routing purposes. 2019 2020 default FALSE 2021 2022rp_filter - INTEGER 2023 - 0 - No source validation. 2024 - 1 - Strict mode as defined in RFC3704 Strict Reverse Path 2025 Each incoming packet is tested against the FIB and if the interface 2026 is not the best reverse path the packet check will fail. 2027 By default failed packets are discarded. 2028 - 2 - Loose mode as defined in RFC3704 Loose Reverse Path 2029 Each incoming packet's source address is also tested against the FIB 2030 and if the source address is not reachable via any interface 2031 the packet check will fail. 2032 2033 Current recommended practice in RFC3704 is to enable strict mode 2034 to prevent IP spoofing from DDos attacks. If using asymmetric routing 2035 or other complicated routing, then loose mode is recommended. 2036 2037 The max value from conf/{all,interface}/rp_filter is used 2038 when doing source validation on the {interface}. 2039 2040 Default value is 0. Note that some distributions enable it 2041 in startup scripts. 2042 2043src_valid_mark - BOOLEAN 2044 - 0 - The fwmark of the packet is not included in reverse path 2045 route lookup. This allows for asymmetric routing configurations 2046 utilizing the fwmark in only one direction, e.g., transparent 2047 proxying. 2048 2049 - 1 - The fwmark of the packet is included in reverse path route 2050 lookup. This permits rp_filter to function when the fwmark is 2051 used for routing traffic in both directions. 2052 2053 This setting also affects the utilization of fmwark when 2054 performing source address selection for ICMP replies, or 2055 determining addresses stored for the IPOPT_TS_TSANDADDR and 2056 IPOPT_RR IP options. 2057 2058 The max value from conf/{all,interface}/src_valid_mark is used. 2059 2060 Default value is 0. 2061 2062arp_filter - BOOLEAN 2063 - 1 - Allows you to have multiple network interfaces on the same 2064 subnet, and have the ARPs for each interface be answered 2065 based on whether or not the kernel would route a packet from 2066 the ARP'd IP out that interface (therefore you must use source 2067 based routing for this to work). In other words it allows control 2068 of which cards (usually 1) will respond to an arp request. 2069 2070 - 0 - (default) The kernel can respond to arp requests with addresses 2071 from other interfaces. This may seem wrong but it usually makes 2072 sense, because it increases the chance of successful communication. 2073 IP addresses are owned by the complete host on Linux, not by 2074 particular interfaces. Only for more complex setups like load- 2075 balancing, does this behaviour cause problems. 2076 2077 arp_filter for the interface will be enabled if at least one of 2078 conf/{all,interface}/arp_filter is set to TRUE, 2079 it will be disabled otherwise 2080 2081arp_announce - INTEGER 2082 Define different restriction levels for announcing the local 2083 source IP address from IP packets in ARP requests sent on 2084 interface: 2085 2086 - 0 - (default) Use any local address, configured on any interface 2087 - 1 - Try to avoid local addresses that are not in the target's 2088 subnet for this interface. This mode is useful when target 2089 hosts reachable via this interface require the source IP 2090 address in ARP requests to be part of their logical network 2091 configured on the receiving interface. When we generate the 2092 request we will check all our subnets that include the 2093 target IP and will preserve the source address if it is from 2094 such subnet. If there is no such subnet we select source 2095 address according to the rules for level 2. 2096 - 2 - Always use the best local address for this target. 2097 In this mode we ignore the source address in the IP packet 2098 and try to select local address that we prefer for talks with 2099 the target host. Such local address is selected by looking 2100 for primary IP addresses on all our subnets on the outgoing 2101 interface that include the target IP address. If no suitable 2102 local address is found we select the first local address 2103 we have on the outgoing interface or on all other interfaces, 2104 with the hope we will receive reply for our request and 2105 even sometimes no matter the source IP address we announce. 2106 2107 The max value from conf/{all,interface}/arp_announce is used. 2108 2109 Increasing the restriction level gives more chance for 2110 receiving answer from the resolved target while decreasing 2111 the level announces more valid sender's information. 2112 2113arp_ignore - INTEGER 2114 Define different modes for sending replies in response to 2115 received ARP requests that resolve local target IP addresses: 2116 2117 - 0 - (default): reply for any local target IP address, configured 2118 on any interface 2119 - 1 - reply only if the target IP address is local address 2120 configured on the incoming interface 2121 - 2 - reply only if the target IP address is local address 2122 configured on the incoming interface and both with the 2123 sender's IP address are part from same subnet on this interface 2124 - 3 - do not reply for local addresses configured with scope host, 2125 only resolutions for global and link addresses are replied 2126 - 4-7 - reserved 2127 - 8 - do not reply for all local addresses 2128 2129 The max value from conf/{all,interface}/arp_ignore is used 2130 when ARP request is received on the {interface} 2131 2132arp_notify - BOOLEAN 2133 Define mode for notification of address and device changes. 2134 2135 == ========================================================== 2136 0 (default): do nothing 2137 1 Generate gratuitous arp requests when device is brought up 2138 or hardware address changes. 2139 == ========================================================== 2140 2141arp_accept - INTEGER 2142 Define behavior for accepting gratuitous ARP (garp) frames from devices 2143 that are not already present in the ARP table: 2144 2145 - 0 - don't create new entries in the ARP table 2146 - 1 - create new entries in the ARP table 2147 - 2 - create new entries only if the source IP address is in the same 2148 subnet as an address configured on the interface that received the 2149 garp message. 2150 2151 Both replies and requests type gratuitous arp will trigger the 2152 ARP table to be updated, if this setting is on. 2153 2154 If the ARP table already contains the IP address of the 2155 gratuitous arp frame, the arp table will be updated regardless 2156 if this setting is on or off. 2157 2158arp_evict_nocarrier - BOOLEAN 2159 Clears the ARP cache on NOCARRIER events. This option is important for 2160 wireless devices where the ARP cache should not be cleared when roaming 2161 between access points on the same network. In most cases this should 2162 remain as the default (1). 2163 2164 Possible values: 2165 2166 - 0 (disabled) - Do not clear ARP cache on NOCARRIER events 2167 - 1 (enabled) - Clear the ARP cache on NOCARRIER events 2168 2169 Default: 1 (enabled) 2170 2171mcast_solicit - INTEGER 2172 The maximum number of multicast probes in INCOMPLETE state, 2173 when the associated hardware address is unknown. Defaults 2174 to 3. 2175 2176ucast_solicit - INTEGER 2177 The maximum number of unicast probes in PROBE state, when 2178 the hardware address is being reconfirmed. Defaults to 3. 2179 2180app_solicit - INTEGER 2181 The maximum number of probes to send to the user space ARP daemon 2182 via netlink before dropping back to multicast probes (see 2183 mcast_resolicit). Defaults to 0. 2184 2185mcast_resolicit - INTEGER 2186 The maximum number of multicast probes after unicast and 2187 app probes in PROBE state. Defaults to 0. 2188 2189disable_policy - BOOLEAN 2190 Disable IPSEC policy (SPD) for this interface 2191 2192 Possible values: 2193 2194 - 0 (disabled) 2195 - 1 (enabled) 2196 2197 Default: 0 (disabled) 2198 2199disable_xfrm - BOOLEAN 2200 Disable IPSEC encryption on this interface, whatever the policy 2201 2202 Possible values: 2203 2204 - 0 (disabled) 2205 - 1 (enabled) 2206 2207 Default: 0 (disabled) 2208 2209igmpv2_unsolicited_report_interval - INTEGER 2210 The interval in milliseconds in which the next unsolicited 2211 IGMPv1 or IGMPv2 report retransmit will take place. 2212 2213 Default: 10000 (10 seconds) 2214 2215igmpv3_unsolicited_report_interval - INTEGER 2216 The interval in milliseconds in which the next unsolicited 2217 IGMPv3 report retransmit will take place. 2218 2219 Default: 1000 (1 seconds) 2220 2221ignore_routes_with_linkdown - BOOLEAN 2222 Ignore routes whose link is down when performing a FIB lookup. 2223 2224 Possible values: 2225 2226 - 0 (disabled) 2227 - 1 (enabled) 2228 2229 Default: 0 (disabled) 2230 2231promote_secondaries - BOOLEAN 2232 When a primary IP address is removed from this interface 2233 promote a corresponding secondary IP address instead of 2234 removing all the corresponding secondary IP addresses. 2235 2236 Possible values: 2237 2238 - 0 (disabled) 2239 - 1 (enabled) 2240 2241 Default: 0 (disabled) 2242 2243drop_unicast_in_l2_multicast - BOOLEAN 2244 Drop any unicast IP packets that are received in link-layer 2245 multicast (or broadcast) frames. 2246 2247 This behavior (for multicast) is actually a SHOULD in RFC 2248 1122, but is disabled by default for compatibility reasons. 2249 2250 Possible values: 2251 2252 - 0 (disabled) 2253 - 1 (enabled) 2254 2255 Default: 0 (disabled) 2256 2257drop_gratuitous_arp - BOOLEAN 2258 Drop all gratuitous ARP frames, for example if there's a known 2259 good ARP proxy on the network and such frames need not be used 2260 (or in the case of 802.11, must not be used to prevent attacks.) 2261 2262 Possible values: 2263 2264 - 0 (disabled) 2265 - 1 (enabled) 2266 2267 Default: 0 (disabled) 2268 2269 2270tag - INTEGER 2271 Allows you to write a number, which can be used as required. 2272 2273 Default value is 0. 2274 2275xfrm4_gc_thresh - INTEGER 2276 (Obsolete since linux-4.14) 2277 The threshold at which we will start garbage collecting for IPv4 2278 destination cache entries. At twice this value the system will 2279 refuse new allocations. 2280 2281igmp_link_local_mcast_reports - BOOLEAN 2282 Enable IGMP reports for link local multicast groups in the 2283 224.0.0.X range. 2284 2285 Default TRUE 2286 2287Alexey Kuznetsov. 2288kuznet@ms2.inr.ac.ru 2289 2290Updated by: 2291 2292- Andi Kleen 2293 ak@muc.de 2294- Nicolas Delon 2295 delon.nicolas@wanadoo.fr 2296 2297 2298 2299 2300/proc/sys/net/ipv6/* Variables 2301============================== 2302 2303IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also 2304apply to IPv6 [XXX?]. 2305 2306bindv6only - BOOLEAN 2307 Default value for IPV6_V6ONLY socket option, 2308 which restricts use of the IPv6 socket to IPv6 communication 2309 only. 2310 2311 Possible values: 2312 2313 - 0 (disabled) - enable IPv4-mapped address feature 2314 - 1 (enabled) - disable IPv4-mapped address feature 2315 2316 Default: 0 (disabled) 2317 2318flowlabel_consistency - BOOLEAN 2319 Protect the consistency (and unicity) of flow label. 2320 You have to disable it to use IPV6_FL_F_REFLECT flag on the 2321 flow label manager. 2322 2323 Possible values: 2324 2325 - 0 (disabled) 2326 - 1 (enabled) 2327 2328 Default: 1 (enabled) 2329 2330auto_flowlabels - INTEGER 2331 Automatically generate flow labels based on a flow hash of the 2332 packet. This allows intermediate devices, such as routers, to 2333 identify packet flows for mechanisms like Equal Cost Multipath 2334 Routing (see RFC 6438). 2335 2336 = =========================================================== 2337 0 automatic flow labels are completely disabled 2338 1 automatic flow labels are enabled by default, they can be 2339 disabled on a per socket basis using the IPV6_AUTOFLOWLABEL 2340 socket option 2341 2 automatic flow labels are allowed, they may be enabled on a 2342 per socket basis using the IPV6_AUTOFLOWLABEL socket option 2343 3 automatic flow labels are enabled and enforced, they cannot 2344 be disabled by the socket option 2345 = =========================================================== 2346 2347 Default: 1 2348 2349flowlabel_state_ranges - BOOLEAN 2350 Split the flow label number space into two ranges. 0-0x7FFFF is 2351 reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF 2352 is reserved for stateless flow labels as described in RFC6437. 2353 2354 Possible values: 2355 2356 - 0 (disabled) 2357 - 1 (enabled) 2358 2359 Default: 1 (enabled) 2360 2361 2362flowlabel_reflect - INTEGER 2363 Control flow label reflection. Needed for Path MTU 2364 Discovery to work with Equal Cost Multipath Routing in anycast 2365 environments. See RFC 7690 and: 2366 https://tools.ietf.org/html/draft-wang-6man-flow-label-reflection-01 2367 2368 This is a bitmask. 2369 2370 - 1: enabled for established flows 2371 2372 Note that this prevents automatic flowlabel changes, as done 2373 in "tcp: change IPv6 flow-label upon receiving spurious retransmission" 2374 and "tcp: Change txhash on every SYN and RTO retransmit" 2375 2376 - 2: enabled for TCP RESET packets (no active listener) 2377 If set, a RST packet sent in response to a SYN packet on a closed 2378 port will reflect the incoming flow label. 2379 2380 - 4: enabled for ICMPv6 echo reply messages. 2381 2382 Default: 0 2383 2384fib_multipath_hash_policy - INTEGER 2385 Controls which hash policy to use for multipath routes. 2386 2387 Default: 0 (Layer 3) 2388 2389 Possible values: 2390 2391 - 0 - Layer 3 (source and destination addresses plus flow label) 2392 - 1 - Layer 4 (standard 5-tuple) 2393 - 2 - Layer 3 or inner Layer 3 if present 2394 - 3 - Custom multipath hash. Fields used for multipath hash calculation 2395 are determined by fib_multipath_hash_fields sysctl 2396 2397fib_multipath_hash_fields - UNSIGNED INTEGER 2398 When fib_multipath_hash_policy is set to 3 (custom multipath hash), the 2399 fields used for multipath hash calculation are determined by this 2400 sysctl. 2401 2402 This value is a bitmask which enables various fields for multipath hash 2403 calculation. 2404 2405 Possible fields are: 2406 2407 ====== ============================ 2408 0x0001 Source IP address 2409 0x0002 Destination IP address 2410 0x0004 IP protocol 2411 0x0008 Flow Label 2412 0x0010 Source port 2413 0x0020 Destination port 2414 0x0040 Inner source IP address 2415 0x0080 Inner destination IP address 2416 0x0100 Inner IP protocol 2417 0x0200 Inner Flow Label 2418 0x0400 Inner source port 2419 0x0800 Inner destination port 2420 ====== ============================ 2421 2422 Default: 0x0007 (source IP, destination IP and IP protocol) 2423 2424anycast_src_echo_reply - BOOLEAN 2425 Controls the use of anycast addresses as source addresses for ICMPv6 2426 echo reply 2427 2428 Possible values: 2429 2430 - 0 (disabled) 2431 - 1 (enabled) 2432 2433 Default: 0 (disabled) 2434 2435 2436idgen_delay - INTEGER 2437 Controls the delay in seconds after which time to retry 2438 privacy stable address generation if a DAD conflict is 2439 detected. 2440 2441 Default: 1 (as specified in RFC7217) 2442 2443idgen_retries - INTEGER 2444 Controls the number of retries to generate a stable privacy 2445 address if a DAD conflict is detected. 2446 2447 Default: 3 (as specified in RFC7217) 2448 2449mld_qrv - INTEGER 2450 Controls the MLD query robustness variable (see RFC3810 9.1). 2451 2452 Default: 2 (as specified by RFC3810 9.1) 2453 2454 Minimum: 1 (as specified by RFC6636 4.5) 2455 2456max_dst_opts_number - INTEGER 2457 Maximum number of non-padding TLVs allowed in a Destination 2458 options extension header. If this value is less than zero 2459 then unknown options are disallowed and the number of known 2460 TLVs allowed is the absolute value of this number. 2461 2462 Default: 8 2463 2464max_hbh_opts_number - INTEGER 2465 Maximum number of non-padding TLVs allowed in a Hop-by-Hop 2466 options extension header. If this value is less than zero 2467 then unknown options are disallowed and the number of known 2468 TLVs allowed is the absolute value of this number. 2469 2470 Default: 8 2471 2472max_dst_opts_length - INTEGER 2473 Maximum length allowed for a Destination options extension 2474 header. 2475 2476 Default: INT_MAX (unlimited) 2477 2478max_hbh_length - INTEGER 2479 Maximum length allowed for a Hop-by-Hop options extension 2480 header. 2481 2482 Default: INT_MAX (unlimited) 2483 2484skip_notify_on_dev_down - BOOLEAN 2485 Controls whether an RTM_DELROUTE message is generated for routes 2486 removed when a device is taken down or deleted. IPv4 does not 2487 generate this message; IPv6 does by default. Setting this sysctl 2488 to true skips the message, making IPv4 and IPv6 on par in relying 2489 on userspace caches to track link events and evict routes. 2490 2491 Possible values: 2492 2493 - 0 (disabled) - generate the message 2494 - 1 (enabled) - skip generating the message 2495 2496 Default: 0 (disabled) 2497 2498nexthop_compat_mode - BOOLEAN 2499 New nexthop API provides a means for managing nexthops independent of 2500 prefixes. Backwards compatibility with old route format is enabled by 2501 default which means route dumps and notifications contain the new 2502 nexthop attribute but also the full, expanded nexthop definition. 2503 Further, updates or deletes of a nexthop configuration generate route 2504 notifications for each fib entry using the nexthop. Once a system 2505 understands the new API, this sysctl can be disabled to achieve full 2506 performance benefits of the new API by disabling the nexthop expansion 2507 and extraneous notifications. 2508 2509 Note that as a backward-compatible mode, dumping of modern features 2510 might be incomplete or wrong. For example, resilient groups will not be 2511 shown as such, but rather as just a list of next hops. Also weights that 2512 do not fit into 8 bits will show incorrectly. 2513 2514 Default: true (backward compat mode) 2515 2516fib_notify_on_flag_change - INTEGER 2517 Whether to emit RTM_NEWROUTE notifications whenever RTM_F_OFFLOAD/ 2518 RTM_F_TRAP/RTM_F_OFFLOAD_FAILED flags are changed. 2519 2520 After installing a route to the kernel, user space receives an 2521 acknowledgment, which means the route was installed in the kernel, 2522 but not necessarily in hardware. 2523 It is also possible for a route already installed in hardware to change 2524 its action and therefore its flags. For example, a host route that is 2525 trapping packets can be "promoted" to perform decapsulation following 2526 the installation of an IPinIP/VXLAN tunnel. 2527 The notifications will indicate to user-space the state of the route. 2528 2529 Default: 0 (Do not emit notifications.) 2530 2531 Possible values: 2532 2533 - 0 - Do not emit notifications. 2534 - 1 - Emit notifications. 2535 - 2 - Emit notifications only for RTM_F_OFFLOAD_FAILED flag change. 2536 2537ioam6_id - INTEGER 2538 Define the IOAM id of this node. Uses only 24 bits out of 32 in total. 2539 2540 Possible value range: 2541 2542 - Min: 0 2543 - Max: 0xFFFFFF 2544 2545 Default: 0xFFFFFF 2546 2547ioam6_id_wide - LONG INTEGER 2548 Define the wide IOAM id of this node. Uses only 56 bits out of 64 in 2549 total. Can be different from ioam6_id. 2550 2551 Possible value range: 2552 2553 - Min: 0 2554 - Max: 0xFFFFFFFFFFFFFF 2555 2556 Default: 0xFFFFFFFFFFFFFF 2557 2558IPv6 Fragmentation: 2559 2560ip6frag_high_thresh - INTEGER 2561 Maximum memory used to reassemble IPv6 fragments. When 2562 ip6frag_high_thresh bytes of memory is allocated for this purpose, 2563 the fragment handler will toss packets until ip6frag_low_thresh 2564 is reached. 2565 2566ip6frag_low_thresh - INTEGER 2567 See ip6frag_high_thresh 2568 2569ip6frag_time - INTEGER 2570 Time in seconds to keep an IPv6 fragment in memory. 2571 2572``conf/default/*``: 2573 Change the interface-specific default settings. 2574 2575 These settings would be used during creating new interfaces. 2576 2577 2578``conf/all/*``: 2579 Change all the interface-specific settings. 2580 2581 [XXX: Other special features than forwarding?] 2582 2583conf/all/disable_ipv6 - BOOLEAN 2584 Changing this value is same as changing ``conf/default/disable_ipv6`` 2585 setting and also all per-interface ``disable_ipv6`` settings to the same 2586 value. 2587 2588 Reading this value does not have any particular meaning. It does not say 2589 whether IPv6 support is enabled or disabled. Returned value can be 1 2590 also in the case when some interface has ``disable_ipv6`` set to 0 and 2591 has configured IPv6 addresses. 2592 2593conf/all/forwarding - BOOLEAN 2594 Enable global IPv6 forwarding between all interfaces. 2595 2596 IPv4 and IPv6 work differently here; the ``force_forwarding`` flag must 2597 be used to control which interfaces may forward packets. 2598 2599 This also sets all interfaces' Host/Router setting 2600 'forwarding' to the specified value. See below for details. 2601 2602 This referred to as global forwarding. 2603 2604proxy_ndp - BOOLEAN 2605 Do proxy ndp. 2606 2607 Possible values: 2608 2609 - 0 (disabled) 2610 - 1 (enabled) 2611 2612 Default: 0 (disabled) 2613 2614force_forwarding - BOOLEAN 2615 Enable forwarding on this interface only -- regardless of the setting on 2616 ``conf/all/forwarding``. When setting ``conf.all.forwarding`` to 0, 2617 the ``force_forwarding`` flag will be reset on all interfaces. 2618 2619fwmark_reflect - BOOLEAN 2620 Controls the fwmark of kernel-generated IPv6 reply packets that are not 2621 associated with a socket for example, TCP RSTs or ICMPv6 echo replies). 2622 If disabled, these packets have a fwmark of zero. If enabled, they have the 2623 fwmark of the packet they are replying to. 2624 2625 Possible values: 2626 2627 - 0 (disabled) 2628 - 1 (enabled) 2629 2630 Default: 0 (disabled) 2631 2632``conf/interface/*``: 2633 Change special settings per interface. 2634 2635 The functional behaviour for certain settings is different 2636 depending on whether local forwarding is enabled or not. 2637 2638accept_ra - INTEGER 2639 Accept Router Advertisements; autoconfigure using them. 2640 2641 It also determines whether or not to transmit Router 2642 Solicitations. If and only if the functional setting is to 2643 accept Router Advertisements, Router Solicitations will be 2644 transmitted. 2645 2646 Possible values are: 2647 2648 == =========================================================== 2649 0 Do not accept Router Advertisements. 2650 1 Accept Router Advertisements if forwarding is disabled. 2651 2 Overrule forwarding behaviour. Accept Router Advertisements 2652 even if forwarding is enabled. 2653 == =========================================================== 2654 2655 Functional default: 2656 2657 - enabled if local forwarding is disabled. 2658 - disabled if local forwarding is enabled. 2659 2660accept_ra_defrtr - BOOLEAN 2661 Learn default router in Router Advertisement. 2662 2663 Functional default: 2664 2665 - enabled if accept_ra is enabled. 2666 - disabled if accept_ra is disabled. 2667 2668ra_defrtr_metric - UNSIGNED INTEGER 2669 Route metric for default route learned in Router Advertisement. This value 2670 will be assigned as metric for the default route learned via IPv6 Router 2671 Advertisement. Takes affect only if accept_ra_defrtr is enabled. 2672 2673 Possible values: 2674 1 to 0xFFFFFFFF 2675 2676 Default: IP6_RT_PRIO_USER i.e. 1024. 2677 2678accept_ra_from_local - BOOLEAN 2679 Accept RA with source-address that is found on local machine 2680 if the RA is otherwise proper and able to be accepted. 2681 2682 Default is to NOT accept these as it may be an un-intended 2683 network loop. 2684 2685 Functional default: 2686 2687 - enabled if accept_ra_from_local is enabled 2688 on a specific interface. 2689 - disabled if accept_ra_from_local is disabled 2690 on a specific interface. 2691 2692accept_ra_min_hop_limit - INTEGER 2693 Minimum hop limit Information in Router Advertisement. 2694 2695 Hop limit Information in Router Advertisement less than this 2696 variable shall be ignored. 2697 2698 Default: 1 2699 2700accept_ra_min_lft - INTEGER 2701 Minimum acceptable lifetime value in Router Advertisement. 2702 2703 RA sections with a lifetime less than this value shall be 2704 ignored. Zero lifetimes stay unaffected. 2705 2706 Default: 0 2707 2708accept_ra_pinfo - BOOLEAN 2709 Learn Prefix Information in Router Advertisement. 2710 2711 Functional default: 2712 2713 - enabled if accept_ra is enabled. 2714 - disabled if accept_ra is disabled. 2715 2716ra_honor_pio_life - BOOLEAN 2717 Whether to use RFC4862 Section 5.5.3e to determine the valid 2718 lifetime of an address matching a prefix sent in a Router 2719 Advertisement Prefix Information Option. 2720 2721 Possible values: 2722 2723 - 0 (disabled) - RFC4862 section 5.5.3e is used to determine 2724 the valid lifetime of the address. 2725 - 1 (enabled) - the PIO valid lifetime will always be honored. 2726 2727 Default: 0 (disabled) 2728 2729ra_honor_pio_pflag - BOOLEAN 2730 The Prefix Information Option P-flag indicates the network can 2731 allocate a unique IPv6 prefix per client using DHCPv6-PD. 2732 This sysctl can be enabled when a userspace DHCPv6-PD client 2733 is running to cause the P-flag to take effect: i.e. the 2734 P-flag suppresses any effects of the A-flag within the same 2735 PIO. For a given PIO, P=1 and A=1 is treated as A=0. 2736 2737 Possible values: 2738 2739 - 0 (disabled) - the P-flag is ignored. 2740 - 1 (enabled) - the P-flag will disable SLAAC autoconfiguration 2741 for the given Prefix Information Option. 2742 2743 Default: 0 (disabled) 2744 2745accept_ra_rt_info_min_plen - INTEGER 2746 Minimum prefix length of Route Information in RA. 2747 2748 Route Information w/ prefix smaller than this variable shall 2749 be ignored. 2750 2751 Functional default: 2752 2753 * 0 if accept_ra_rtr_pref is enabled. 2754 * -1 if accept_ra_rtr_pref is disabled. 2755 2756accept_ra_rt_info_max_plen - INTEGER 2757 Maximum prefix length of Route Information in RA. 2758 2759 Route Information w/ prefix larger than this variable shall 2760 be ignored. 2761 2762 Functional default: 2763 2764 * 0 if accept_ra_rtr_pref is enabled. 2765 * -1 if accept_ra_rtr_pref is disabled. 2766 2767accept_ra_rtr_pref - BOOLEAN 2768 Accept Router Preference in RA. 2769 2770 Functional default: 2771 2772 - enabled if accept_ra is enabled. 2773 - disabled if accept_ra is disabled. 2774 2775accept_ra_mtu - BOOLEAN 2776 Apply the MTU value specified in RA option 5 (RFC4861). If 2777 disabled, the MTU specified in the RA will be ignored. 2778 2779 Functional default: 2780 2781 - enabled if accept_ra is enabled. 2782 - disabled if accept_ra is disabled. 2783 2784accept_redirects - BOOLEAN 2785 Accept Redirects. 2786 2787 Functional default: 2788 2789 - enabled if local forwarding is disabled. 2790 - disabled if local forwarding is enabled. 2791 2792accept_source_route - INTEGER 2793 Accept source routing (routing extension header). 2794 2795 - >= 0: Accept only routing header type 2. 2796 - < 0: Do not accept routing header. 2797 2798 Default: 0 2799 2800autoconf - BOOLEAN 2801 Autoconfigure addresses using Prefix Information in Router 2802 Advertisements. 2803 2804 Functional default: 2805 2806 - enabled if accept_ra_pinfo is enabled. 2807 - disabled if accept_ra_pinfo is disabled. 2808 2809dad_transmits - INTEGER 2810 The amount of Duplicate Address Detection probes to send. 2811 2812 Default: 1 2813 2814forwarding - INTEGER 2815 Configure interface-specific Host/Router behaviour. 2816 2817 .. note:: 2818 2819 It is recommended to have the same setting on all 2820 interfaces; mixed router/host scenarios are rather uncommon. 2821 2822 Possible values are: 2823 2824 - 0 Forwarding disabled 2825 - 1 Forwarding enabled 2826 2827 **FALSE (0)**: 2828 2829 By default, Host behaviour is assumed. This means: 2830 2831 1. IsRouter flag is not set in Neighbour Advertisements. 2832 2. If accept_ra is TRUE (default), transmit Router 2833 Solicitations. 2834 3. If accept_ra is TRUE (default), accept Router 2835 Advertisements (and do autoconfiguration). 2836 4. If accept_redirects is TRUE (default), accept Redirects. 2837 2838 **TRUE (1)**: 2839 2840 If local forwarding is enabled, Router behaviour is assumed. 2841 This means exactly the reverse from the above: 2842 2843 1. IsRouter flag is set in Neighbour Advertisements. 2844 2. Router Solicitations are not sent unless accept_ra is 2. 2845 3. Router Advertisements are ignored unless accept_ra is 2. 2846 4. Redirects are ignored. 2847 2848 Default: 0 (disabled) if global forwarding is disabled (default), 2849 otherwise 1 (enabled). 2850 2851hop_limit - INTEGER 2852 Default Hop Limit to set. 2853 2854 Default: 64 2855 2856mtu - INTEGER 2857 Default Maximum Transfer Unit 2858 2859 Default: 1280 (IPv6 required minimum) 2860 2861ip_nonlocal_bind - BOOLEAN 2862 If enabled, allows processes to bind() to non-local IPv6 addresses, 2863 which can be quite useful - but may break some applications. 2864 2865 Possible values: 2866 2867 - 0 (disabled) 2868 - 1 (enabled) 2869 2870 Default: 0 (disabled) 2871 2872router_probe_interval - INTEGER 2873 Minimum interval (in seconds) between Router Probing described 2874 in RFC4191. 2875 2876 Default: 60 2877 2878router_solicitation_delay - INTEGER 2879 Number of seconds to wait after interface is brought up 2880 before sending Router Solicitations. 2881 2882 Default: 1 2883 2884router_solicitation_interval - INTEGER 2885 Number of seconds to wait between Router Solicitations. 2886 2887 Default: 4 2888 2889router_solicitations - INTEGER 2890 Number of Router Solicitations to send until assuming no 2891 routers are present. 2892 2893 Default: 3 2894 2895use_oif_addrs_only - BOOLEAN 2896 When enabled, the candidate source addresses for destinations 2897 routed via this interface are restricted to the set of addresses 2898 configured on this interface (vis. RFC 6724, section 4). 2899 2900 Possible values: 2901 2902 - 0 (disabled) 2903 - 1 (enabled) 2904 2905 Default: 0 (disabled) 2906 2907use_tempaddr - INTEGER 2908 Preference for Privacy Extensions (RFC3041). 2909 2910 * <= 0 : disable Privacy Extensions 2911 * == 1 : enable Privacy Extensions, but prefer public 2912 addresses over temporary addresses. 2913 * > 1 : enable Privacy Extensions and prefer temporary 2914 addresses over public addresses. 2915 2916 Default: 2917 2918 * 0 (for most devices) 2919 * -1 (for point-to-point devices and loopback devices) 2920 2921temp_valid_lft - INTEGER 2922 valid lifetime (in seconds) for temporary addresses. If less than the 2923 minimum required lifetime (typically 5-7 seconds), temporary addresses 2924 will not be created. 2925 2926 Default: 172800 (2 days) 2927 2928temp_prefered_lft - INTEGER 2929 Preferred lifetime (in seconds) for temporary addresses. If 2930 temp_prefered_lft is less than the minimum required lifetime (typically 2931 5-7 seconds), the preferred lifetime is the minimum required. If 2932 temp_prefered_lft is greater than temp_valid_lft, the preferred lifetime 2933 is temp_valid_lft. 2934 2935 Default: 86400 (1 day) 2936 2937keep_addr_on_down - INTEGER 2938 Keep all IPv6 addresses on an interface down event. If set static 2939 global addresses with no expiration time are not flushed. 2940 2941 * >0 : enabled 2942 * 0 : system default 2943 * <0 : disabled 2944 2945 Default: 0 (addresses are removed) 2946 2947max_desync_factor - INTEGER 2948 Maximum value for DESYNC_FACTOR, which is a random value 2949 that ensures that clients don't synchronize with each 2950 other and generate new addresses at exactly the same time. 2951 value is in seconds. 2952 2953 Default: 600 2954 2955regen_min_advance - INTEGER 2956 How far in advance (in seconds), at minimum, to create a new temporary 2957 address before the current one is deprecated. This value is added to 2958 the amount of time that may be required for duplicate address detection 2959 to determine when to create a new address. Linux permits setting this 2960 value to less than the default of 2 seconds, but a value less than 2 2961 does not conform to RFC 8981. 2962 2963 Default: 2 2964 2965regen_max_retry - INTEGER 2966 Number of attempts before give up attempting to generate 2967 valid temporary addresses. 2968 2969 Default: 5 2970 2971max_addresses - INTEGER 2972 Maximum number of autoconfigured addresses per interface. Setting 2973 to zero disables the limitation. It is not recommended to set this 2974 value too large (or to zero) because it would be an easy way to 2975 crash the kernel by allowing too many addresses to be created. 2976 2977 Default: 16 2978 2979disable_ipv6 - BOOLEAN 2980 Disable IPv6 operation. If accept_dad is set to 2, this value 2981 will be dynamically set to TRUE if DAD fails for the link-local 2982 address. 2983 2984 Default: FALSE (enable IPv6 operation) 2985 2986 When this value is changed from 1 to 0 (IPv6 is being enabled), 2987 it will dynamically create a link-local address on the given 2988 interface and start Duplicate Address Detection, if necessary. 2989 2990 When this value is changed from 0 to 1 (IPv6 is being disabled), 2991 it will dynamically delete all addresses and routes on the given 2992 interface. From now on it will not possible to add addresses/routes 2993 to the selected interface. 2994 2995accept_dad - INTEGER 2996 Whether to accept DAD (Duplicate Address Detection). 2997 2998 == ============================================================== 2999 0 Disable DAD 3000 1 Enable DAD (default) 3001 2 Enable DAD, and disable IPv6 operation if MAC-based duplicate 3002 link-local address has been found. 3003 == ============================================================== 3004 3005 DAD operation and mode on a given interface will be selected according 3006 to the maximum value of conf/{all,interface}/accept_dad. 3007 3008force_tllao - BOOLEAN 3009 Enable sending the target link-layer address option even when 3010 responding to a unicast neighbor solicitation. 3011 3012 Default: FALSE 3013 3014 Quoting from RFC 2461, section 4.4, Target link-layer address: 3015 3016 "The option MUST be included for multicast solicitations in order to 3017 avoid infinite Neighbor Solicitation "recursion" when the peer node 3018 does not have a cache entry to return a Neighbor Advertisements 3019 message. When responding to unicast solicitations, the option can be 3020 omitted since the sender of the solicitation has the correct link- 3021 layer address; otherwise it would not have be able to send the unicast 3022 solicitation in the first place. However, including the link-layer 3023 address in this case adds little overhead and eliminates a potential 3024 race condition where the sender deletes the cached link-layer address 3025 prior to receiving a response to a previous solicitation." 3026 3027ndisc_notify - BOOLEAN 3028 Define mode for notification of address and device changes. 3029 3030 Possible values: 3031 3032 - 0 (disabled) - do nothing 3033 - 1 (enabled) - Generate unsolicited neighbour advertisements when device is brought 3034 up or hardware address changes. 3035 3036 Default: 0 (disabled) 3037 3038ndisc_tclass - INTEGER 3039 The IPv6 Traffic Class to use by default when sending IPv6 Neighbor 3040 Discovery (Router Solicitation, Router Advertisement, Neighbor 3041 Solicitation, Neighbor Advertisement, Redirect) messages. 3042 These 8 bits can be interpreted as 6 high order bits holding the DSCP 3043 value and 2 low order bits representing ECN (which you probably want 3044 to leave cleared). 3045 3046 * 0 - (default) 3047 3048ndisc_evict_nocarrier - BOOLEAN 3049 Clears the neighbor discovery table on NOCARRIER events. This option is 3050 important for wireless devices where the neighbor discovery cache should 3051 not be cleared when roaming between access points on the same network. 3052 In most cases this should remain as the default (1). 3053 3054 Possible values: 3055 3056 - 0 (disabled) - Do not clear neighbor discovery cache on NOCARRIER events. 3057 - 1 (enabled) - Clear neighbor discover cache on NOCARRIER events. 3058 3059 Default: 1 (enabled) 3060 3061mldv1_unsolicited_report_interval - INTEGER 3062 The interval in milliseconds in which the next unsolicited 3063 MLDv1 report retransmit will take place. 3064 3065 Default: 10000 (10 seconds) 3066 3067mldv2_unsolicited_report_interval - INTEGER 3068 The interval in milliseconds in which the next unsolicited 3069 MLDv2 report retransmit will take place. 3070 3071 Default: 1000 (1 second) 3072 3073force_mld_version - INTEGER 3074 * 0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed 3075 * 1 - Enforce to use MLD version 1 3076 * 2 - Enforce to use MLD version 2 3077 3078suppress_frag_ndisc - INTEGER 3079 Control RFC 6980 (Security Implications of IPv6 Fragmentation 3080 with IPv6 Neighbor Discovery) behavior: 3081 3082 * 1 - (default) discard fragmented neighbor discovery packets 3083 * 0 - allow fragmented neighbor discovery packets 3084 3085optimistic_dad - BOOLEAN 3086 Whether to perform Optimistic Duplicate Address Detection (RFC 4429). 3087 3088 Optimistic Duplicate Address Detection for the interface will be enabled 3089 if at least one of conf/{all,interface}/optimistic_dad is set to 1, 3090 it will be disabled otherwise. 3091 3092 Possible values: 3093 3094 - 0 (disabled) 3095 - 1 (enabled) 3096 3097 Default: 0 (disabled) 3098 3099 3100use_optimistic - BOOLEAN 3101 If enabled, do not classify optimistic addresses as deprecated during 3102 source address selection. Preferred addresses will still be chosen 3103 before optimistic addresses, subject to other ranking in the source 3104 address selection algorithm. 3105 3106 This will be enabled if at least one of 3107 conf/{all,interface}/use_optimistic is set to 1, disabled otherwise. 3108 3109 Possible values: 3110 3111 - 0 (disabled) 3112 - 1 (enabled) 3113 3114 Default: 0 (disabled) 3115 3116stable_secret - IPv6 address 3117 This IPv6 address will be used as a secret to generate IPv6 3118 addresses for link-local addresses and autoconfigured 3119 ones. All addresses generated after setting this secret will 3120 be stable privacy ones by default. This can be changed via the 3121 addrgenmode ip-link. conf/default/stable_secret is used as the 3122 secret for the namespace, the interface specific ones can 3123 overwrite that. Writes to conf/all/stable_secret are refused. 3124 3125 It is recommended to generate this secret during installation 3126 of a system and keep it stable after that. 3127 3128 By default the stable secret is unset. 3129 3130addr_gen_mode - INTEGER 3131 Defines how link-local and autoconf addresses are generated. 3132 3133 = ================================================================= 3134 0 generate address based on EUI64 (default) 3135 1 do no generate a link-local address, use EUI64 for addresses 3136 generated from autoconf 3137 2 generate stable privacy addresses, using the secret from 3138 stable_secret (RFC7217) 3139 3 generate stable privacy addresses, using a random secret if unset 3140 = ================================================================= 3141 3142drop_unicast_in_l2_multicast - BOOLEAN 3143 Drop any unicast IPv6 packets that are received in link-layer 3144 multicast (or broadcast) frames. 3145 3146 Possible values: 3147 3148 - 0 (disabled) 3149 - 1 (enabled) 3150 3151 Default: 0 (disabled) 3152 3153drop_unsolicited_na - BOOLEAN 3154 Drop all unsolicited neighbor advertisements, for example if there's 3155 a known good NA proxy on the network and such frames need not be used 3156 (or in the case of 802.11, must not be used to prevent attacks.) 3157 3158 Possible values: 3159 3160 - 0 (disabled) 3161 - 1 (enabled) 3162 3163 Default: 0 (disabled). 3164 3165accept_untracked_na - INTEGER 3166 Define behavior for accepting neighbor advertisements from devices that 3167 are absent in the neighbor cache: 3168 3169 - 0 - (default) Do not accept unsolicited and untracked neighbor 3170 advertisements. 3171 3172 - 1 - Add a new neighbor cache entry in STALE state for routers on 3173 receiving a neighbor advertisement (either solicited or unsolicited) 3174 with target link-layer address option specified if no neighbor entry 3175 is already present for the advertised IPv6 address. Without this knob, 3176 NAs received for untracked addresses (absent in neighbor cache) are 3177 silently ignored. 3178 3179 This is as per router-side behavior documented in RFC9131. 3180 3181 This has lower precedence than drop_unsolicited_na. 3182 3183 This will optimize the return path for the initial off-link 3184 communication that is initiated by a directly connected host, by 3185 ensuring that the first-hop router which turns on this setting doesn't 3186 have to buffer the initial return packets to do neighbor-solicitation. 3187 The prerequisite is that the host is configured to send unsolicited 3188 neighbor advertisements on interface bringup. This setting should be 3189 used in conjunction with the ndisc_notify setting on the host to 3190 satisfy this prerequisite. 3191 3192 - 2 - Extend option (1) to add a new neighbor cache entry only if the 3193 source IP address is in the same subnet as an address configured on 3194 the interface that received the neighbor advertisement. 3195 3196enhanced_dad - BOOLEAN 3197 Include a nonce option in the IPv6 neighbor solicitation messages used for 3198 duplicate address detection per RFC7527. A received DAD NS will only signal 3199 a duplicate address if the nonce is different. This avoids any false 3200 detection of duplicates due to loopback of the NS messages that we send. 3201 The nonce option will be sent on an interface unless both of 3202 conf/{all,interface}/enhanced_dad are set to FALSE. 3203 3204 Possible values: 3205 3206 - 0 (disabled) 3207 - 1 (enabled) 3208 3209 Default: 1 (enabled) 3210 3211``icmp/*``: 3212=========== 3213 3214ratelimit - INTEGER 3215 Limit the maximal rates for sending ICMPv6 messages. 3216 3217 0 to disable any limiting, 3218 otherwise the minimal space between responses in milliseconds. 3219 3220 Default: 1000 3221 3222ratemask - list of comma separated ranges 3223 For ICMPv6 message types matching the ranges in the ratemask, limit 3224 the sending of the message according to ratelimit parameter. 3225 3226 The format used for both input and output is a comma separated 3227 list of ranges (e.g. "0-127,129" for ICMPv6 message type 0 to 127 and 3228 129). Writing to the file will clear all previous ranges of ICMPv6 3229 message types and update the current list with the input. 3230 3231 Refer to: https://www.iana.org/assignments/icmpv6-parameters/icmpv6-parameters.xhtml 3232 for numerical values of ICMPv6 message types, e.g. echo request is 128 3233 and echo reply is 129. 3234 3235 Default: 0-1,3-127 (rate limit ICMPv6 errors except Packet Too Big) 3236 3237echo_ignore_all - BOOLEAN 3238 If enabled, then the kernel will ignore all ICMP ECHO 3239 requests sent to it over the IPv6 protocol. 3240 3241 Possible values: 3242 3243 - 0 (disabled) 3244 - 1 (enabled) 3245 3246 Default: 0 (disabled) 3247 3248echo_ignore_multicast - BOOLEAN 3249 If enabled, then the kernel will ignore all ICMP ECHO 3250 requests sent to it over the IPv6 protocol via multicast. 3251 3252 Possible values: 3253 3254 - 0 (disabled) 3255 - 1 (enabled) 3256 3257 Default: 0 (disabled) 3258 3259echo_ignore_anycast - BOOLEAN 3260 If enabled, then the kernel will ignore all ICMP ECHO 3261 requests sent to it over the IPv6 protocol destined to anycast address. 3262 3263 Possible values: 3264 3265 - 0 (disabled) 3266 - 1 (enabled) 3267 3268 Default: 0 (disabled) 3269 3270error_anycast_as_unicast - BOOLEAN 3271 If enabled, then the kernel will respond with ICMP Errors 3272 resulting from requests sent to it over the IPv6 protocol destined 3273 to anycast address essentially treating anycast as unicast. 3274 3275 Possible values: 3276 3277 - 0 (disabled) 3278 - 1 (enabled) 3279 3280 Default: 0 (disabled) 3281 3282errors_extension_mask - UNSIGNED INTEGER 3283 Bitmask of ICMP extensions to append to ICMPv6 error messages 3284 ("Destination Unreachable" and "Time Exceeded"). The original datagram 3285 is trimmed / padded to 128 bytes in order to be compatible with 3286 applications that do not comply with RFC 4884. 3287 3288 Possible extensions are: 3289 3290 ==== ============================================================== 3291 0x01 Incoming IP interface information according to RFC 5837. 3292 Extension will include the index, IPv6 address (if present), 3293 name and MTU of the IP interface that received the datagram 3294 which elicited the ICMP error. 3295 ==== ============================================================== 3296 3297 Default: 0x00 (no extensions) 3298 3299xfrm6_gc_thresh - INTEGER 3300 (Obsolete since linux-4.14) 3301 The threshold at which we will start garbage collecting for IPv6 3302 destination cache entries. At twice this value the system will 3303 refuse new allocations. 3304 3305 3306IPv6 Update by: 3307Pekka Savola <pekkas@netcore.fi> 3308YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org> 3309 3310 3311/proc/sys/net/bridge/* Variables: 3312================================= 3313 3314bridge-nf-call-arptables - BOOLEAN 3315 3316 Possible values: 3317 3318 - 0 (disabled) - disable this. 3319 - 1 (enabled) - pass bridged ARP traffic to arptables' FORWARD chain. 3320 3321 Default: 1 (enabled) 3322 3323bridge-nf-call-iptables - BOOLEAN 3324 3325 Possible values: 3326 3327 - 0 (disabled) - disable this. 3328 - 1 (enabled) - pass bridged IPv4 traffic to iptables' chains. 3329 3330 Default: 1 (enabled) 3331 3332bridge-nf-call-ip6tables - BOOLEAN 3333 3334 Possible values: 3335 3336 - 0 (disabled) - disable this. 3337 - 1 (enabled) - pass bridged IPv6 traffic to ip6tables' chains. 3338 3339 Default: 1 (enabled) 3340 3341bridge-nf-filter-vlan-tagged - BOOLEAN 3342 3343 Possible values: 3344 3345 - 0 (disabled) - disable this. 3346 - 1 (enabled) - pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables 3347 3348 Default: 0 (disabled) 3349 3350bridge-nf-filter-pppoe-tagged - BOOLEAN 3351 3352 Possible values: 3353 3354 - 0 (disabled) - disable this. 3355 - 1 (enabled) - pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables. 3356 3357 Default: 0 (disabled) 3358 3359bridge-nf-pass-vlan-input-dev - BOOLEAN 3360 - 1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan 3361 interface on the bridge and set the netfilter input device to the 3362 vlan. This allows use of e.g. "iptables -i br0.1" and makes the 3363 REDIRECT target work with vlan-on-top-of-bridge interfaces. When no 3364 matching vlan interface is found, or this switch is off, the input 3365 device is set to the bridge interface. 3366 3367 - 0: disable bridge netfilter vlan interface lookup. 3368 3369 Default: 0 3370 3371``proc/sys/net/sctp/*`` Variables: 3372================================== 3373 3374addip_enable - BOOLEAN 3375 Enable or disable extension of Dynamic Address Reconfiguration 3376 (ADD-IP) functionality specified in RFC5061. This extension provides 3377 the ability to dynamically add and remove new addresses for the SCTP 3378 associations. 3379 3380 Possible values: 3381 3382 - 0 (disabled) - disable extension. 3383 - 1 (enabled) - enable extension 3384 3385 Default: 0 (disabled) 3386 3387pf_enable - INTEGER 3388 Enable or disable pf (pf is short for potentially failed) state. A value 3389 of pf_retrans > path_max_retrans also disables pf state. That is, one of 3390 both pf_enable and pf_retrans > path_max_retrans can disable pf state. 3391 Since pf_retrans and path_max_retrans can be changed by userspace 3392 application, sometimes user expects to disable pf state by the value of 3393 pf_retrans > path_max_retrans, but occasionally the value of pf_retrans 3394 or path_max_retrans is changed by the user application, this pf state is 3395 enabled. As such, it is necessary to add this to dynamically enable 3396 and disable pf state. See: 3397 https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover for 3398 details. 3399 3400 Possible values: 3401 3402 - 1: Enable pf. 3403 - 0: Disable pf. 3404 3405 Default: 1 3406 3407pf_expose - INTEGER 3408 Unset or enable/disable pf (pf is short for potentially failed) state 3409 exposure. Applications can control the exposure of the PF path state 3410 in the SCTP_PEER_ADDR_CHANGE event and access of SCTP_PF-state 3411 transport info via SCTP_GET_PEER_ADDR_INFO sockopt. 3412 3413 Possible values: 3414 3415 - 0: Unset pf state exposure (compatible with old applications). No 3416 event will be sent but the transport info can be queried. 3417 - 1: Disable pf state exposure. No event will be sent and trying to 3418 obtain transport info will return -EACCESS. 3419 - 2: Enable pf state exposure. The event will be sent for a transport 3420 becoming SCTP_PF state and transport info can be obtained. 3421 3422 Default: 0 3423 3424addip_noauth_enable - BOOLEAN 3425 Dynamic Address Reconfiguration (ADD-IP) requires the use of 3426 authentication to protect the operations of adding or removing new 3427 addresses. This requirement is mandated so that unauthorized hosts 3428 would not be able to hijack associations. However, older 3429 implementations may not have implemented this requirement while 3430 allowing the ADD-IP extension. For reasons of interoperability, 3431 we provide this variable to control the enforcement of the 3432 authentication requirement. 3433 3434 == =============================================================== 3435 1 Allow ADD-IP extension to be used without authentication. This 3436 should only be set in a closed environment for interoperability 3437 with older implementations. 3438 3439 0 Enforce the authentication requirement 3440 == =============================================================== 3441 3442 Default: 0 3443 3444auth_enable - BOOLEAN 3445 Enable or disable Authenticated Chunks extension. This extension 3446 provides the ability to send and receive authenticated chunks and is 3447 required for secure operation of Dynamic Address Reconfiguration 3448 (ADD-IP) extension. 3449 3450 Possible values: 3451 3452 - 0 (disabled) - disable extension. 3453 - 1 (enabled) - enable extension 3454 3455 Default: 0 (disabled) 3456 3457prsctp_enable - BOOLEAN 3458 Enable or disable the Partial Reliability extension (RFC3758) which 3459 is used to notify peers that a given DATA should no longer be expected. 3460 3461 Possible values: 3462 3463 - 0 (disabled) - disable extension. 3464 - 1 (enabled) - enable extension 3465 3466 Default: 1 (enabled) 3467 3468max_burst - INTEGER 3469 The limit of the number of new packets that can be initially sent. It 3470 controls how bursty the generated traffic can be. 3471 3472 Default: 4 3473 3474association_max_retrans - INTEGER 3475 Set the maximum number for retransmissions that an association can 3476 attempt deciding that the remote end is unreachable. If this value 3477 is exceeded, the association is terminated. 3478 3479 Default: 10 3480 3481max_init_retransmits - INTEGER 3482 The maximum number of retransmissions of INIT and COOKIE-ECHO chunks 3483 that an association will attempt before declaring the destination 3484 unreachable and terminating. 3485 3486 Default: 8 3487 3488path_max_retrans - INTEGER 3489 The maximum number of retransmissions that will be attempted on a given 3490 path. Once this threshold is exceeded, the path is considered 3491 unreachable, and new traffic will use a different path when the 3492 association is multihomed. 3493 3494 Default: 5 3495 3496pf_retrans - INTEGER 3497 The number of retransmissions that will be attempted on a given path 3498 before traffic is redirected to an alternate transport (should one 3499 exist). Note this is distinct from path_max_retrans, as a path that 3500 passes the pf_retrans threshold can still be used. Its only 3501 deprioritized when a transmission path is selected by the stack. This 3502 setting is primarily used to enable fast failover mechanisms without 3503 having to reduce path_max_retrans to a very low value. See: 3504 http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt 3505 for details. Note also that a value of pf_retrans > path_max_retrans 3506 disables this feature. Since both pf_retrans and path_max_retrans can 3507 be changed by userspace application, a variable pf_enable is used to 3508 disable pf state. 3509 3510 Default: 0 3511 3512ps_retrans - INTEGER 3513 Primary.Switchover.Max.Retrans (PSMR), it's a tunable parameter coming 3514 from section-5 "Primary Path Switchover" in rfc7829. The primary path 3515 will be changed to another active path when the path error counter on 3516 the old primary path exceeds PSMR, so that "the SCTP sender is allowed 3517 to continue data transmission on a new working path even when the old 3518 primary destination address becomes active again". Note this feature 3519 is disabled by initializing 'ps_retrans' per netns as 0xffff by default, 3520 and its value can't be less than 'pf_retrans' when changing by sysctl. 3521 3522 Default: 0xffff 3523 3524rto_initial - INTEGER 3525 The initial round trip timeout value in milliseconds that will be used 3526 in calculating round trip times. This is the initial time interval 3527 for retransmissions. 3528 3529 Default: 3000 3530 3531rto_max - INTEGER 3532 The maximum value (in milliseconds) of the round trip timeout. This 3533 is the largest time interval that can elapse between retransmissions. 3534 3535 Default: 60000 3536 3537rto_min - INTEGER 3538 The minimum value (in milliseconds) of the round trip timeout. This 3539 is the smallest time interval the can elapse between retransmissions. 3540 3541 Default: 1000 3542 3543hb_interval - INTEGER 3544 The interval (in milliseconds) between HEARTBEAT chunks. These chunks 3545 are sent at the specified interval on idle paths to probe the state of 3546 a given path between 2 associations. 3547 3548 Default: 30000 3549 3550sack_timeout - INTEGER 3551 The amount of time (in milliseconds) that the implementation will wait 3552 to send a SACK. 3553 3554 Default: 200 3555 3556valid_cookie_life - INTEGER 3557 The default lifetime of the SCTP cookie (in milliseconds). The cookie 3558 is used during association establishment. 3559 3560 Default: 60000 3561 3562cookie_preserve_enable - BOOLEAN 3563 Enable or disable the ability to extend the lifetime of the SCTP cookie 3564 that is used during the establishment phase of SCTP association 3565 3566 Possible values: 3567 3568 - 0 (disabled) - disable. 3569 - 1 (enabled) - enable cookie lifetime extension. 3570 3571 Default: 1 (enabled) 3572 3573cookie_hmac_alg - STRING 3574 Select the hmac algorithm used when generating the cookie value sent by 3575 a listening sctp socket to a connecting client in the INIT-ACK chunk. 3576 Valid values are: 3577 3578 * sha256 3579 * none 3580 3581 Default: sha256 3582 3583rcvbuf_policy - INTEGER 3584 Determines if the receive buffer is attributed to the socket or to 3585 association. SCTP supports the capability to create multiple 3586 associations on a single socket. When using this capability, it is 3587 possible that a single stalled association that's buffering a lot 3588 of data may block other associations from delivering their data by 3589 consuming all of the receive buffer space. To work around this, 3590 the rcvbuf_policy could be set to attribute the receiver buffer space 3591 to each association instead of the socket. This prevents the described 3592 blocking. 3593 3594 - 1: rcvbuf space is per association 3595 - 0: rcvbuf space is per socket 3596 3597 Default: 0 3598 3599sndbuf_policy - INTEGER 3600 Similar to rcvbuf_policy above, this applies to send buffer space. 3601 3602 - 1: Send buffer is tracked per association 3603 - 0: Send buffer is tracked per socket. 3604 3605 Default: 0 3606 3607sctp_mem - vector of 3 INTEGERs: min, pressure, max 3608 Number of pages allowed for queueing by all SCTP sockets. 3609 3610 * min: Below this number of pages SCTP is not bothered about its 3611 memory usage. When amount of memory allocated by SCTP exceeds 3612 this number, SCTP starts to moderate memory usage. 3613 * pressure: This value was introduced to follow format of tcp_mem. 3614 * max: Maximum number of allowed pages. 3615 3616 Default is calculated at boot time from amount of available memory. 3617 3618sctp_rmem - vector of 3 INTEGERs: min, default, max 3619 Only the first value ("min") is used, "default" and "max" are 3620 ignored. 3621 3622 * min: Minimal size of receive buffer used by SCTP socket. 3623 It is guaranteed to each SCTP socket (but not association) even 3624 under moderate memory pressure. 3625 3626 Default: 4K 3627 3628sctp_wmem - vector of 3 INTEGERs: min, default, max 3629 Only the first value ("min") is used, "default" and "max" are 3630 ignored. 3631 3632 * min: Minimum size of send buffer that can be used by SCTP sockets. 3633 It is guaranteed to each SCTP socket (but not association) even 3634 under moderate memory pressure. 3635 3636 Default: 4K 3637 3638addr_scope_policy - INTEGER 3639 Control IPv4 address scoping (see 3640 https://datatracker.ietf.org/doc/draft-stewart-tsvwg-sctp-ipv4/00/ 3641 for details). 3642 3643 - 0 - Disable IPv4 address scoping 3644 - 1 - Enable IPv4 address scoping 3645 - 2 - Follow draft but allow IPv4 private addresses 3646 - 3 - Follow draft but allow IPv4 link local addresses 3647 3648 Default: 1 3649 3650udp_port - INTEGER 3651 The listening port for the local UDP tunneling sock. Normally it's 3652 using the IANA-assigned UDP port number 9899 (sctp-tunneling). 3653 3654 This UDP sock is used for processing the incoming UDP-encapsulated 3655 SCTP packets (from RFC6951), and shared by all applications in the 3656 same net namespace. This UDP sock will be closed when the value is 3657 set to 0. 3658 3659 The value will also be used to set the src port of the UDP header 3660 for the outgoing UDP-encapsulated SCTP packets. For the dest port, 3661 please refer to 'encap_port' below. 3662 3663 Default: 0 3664 3665encap_port - INTEGER 3666 The default remote UDP encapsulation port. 3667 3668 This value is used to set the dest port of the UDP header for the 3669 outgoing UDP-encapsulated SCTP packets by default. Users can also 3670 change the value for each sock/asoc/transport by using setsockopt. 3671 For further information, please refer to RFC6951. 3672 3673 Note that when connecting to a remote server, the client should set 3674 this to the port that the UDP tunneling sock on the peer server is 3675 listening to and the local UDP tunneling sock on the client also 3676 must be started. On the server, it would get the encap_port from 3677 the incoming packet's source port. 3678 3679 Default: 0 3680 3681plpmtud_probe_interval - INTEGER 3682 The time interval (in milliseconds) for the PLPMTUD probe timer, 3683 which is configured to expire after this period to receive an 3684 acknowledgment to a probe packet. This is also the time interval 3685 between the probes for the current pmtu when the probe search 3686 is done. 3687 3688 PLPMTUD will be disabled when 0 is set, and other values for it 3689 must be >= 5000. 3690 3691 Default: 0 3692 3693reconf_enable - BOOLEAN 3694 Enable or disable extension of Stream Reconfiguration functionality 3695 specified in RFC6525. This extension provides the ability to "reset" 3696 a stream, and it includes the Parameters of "Outgoing/Incoming SSN 3697 Reset", "SSN/TSN Reset" and "Add Outgoing/Incoming Streams". 3698 3699 Possible values: 3700 3701 - 0 (disabled) - Disable extension. 3702 - 1 (enabled) - Enable extension. 3703 3704 Default: 0 (disabled) 3705 3706intl_enable - BOOLEAN 3707 Enable or disable extension of User Message Interleaving functionality 3708 specified in RFC8260. This extension allows the interleaving of user 3709 messages sent on different streams. With this feature enabled, I-DATA 3710 chunk will replace DATA chunk to carry user messages if also supported 3711 by the peer. Note that to use this feature, one needs to set this option 3712 to 1 and also needs to set socket options SCTP_FRAGMENT_INTERLEAVE to 2 3713 and SCTP_INTERLEAVING_SUPPORTED to 1. 3714 3715 Possible values: 3716 3717 - 0 (disabled) - Disable extension. 3718 - 1 (enabled) - Enable extension. 3719 3720 Default: 0 (disabled) 3721 3722ecn_enable - BOOLEAN 3723 Control use of Explicit Congestion Notification (ECN) by SCTP. 3724 Like in TCP, ECN is used only when both ends of the SCTP connection 3725 indicate support for it. This feature is useful in avoiding losses 3726 due to congestion by allowing supporting routers to signal congestion 3727 before having to drop packets. 3728 3729 Possible values: 3730 3731 - 0 (disabled) - Disable ecn. 3732 - 1 (enabled) - Enable ecn. 3733 3734 Default: 1 (enabled) 3735 3736l3mdev_accept - BOOLEAN 3737 Enabling this option allows a "global" bound socket to work 3738 across L3 master domains (e.g., VRFs) with packets capable of 3739 being received regardless of the L3 domain in which they 3740 originated. Only valid when the kernel was compiled with 3741 CONFIG_NET_L3_MASTER_DEV. 3742 3743 Possible values: 3744 3745 - 0 (disabled) 3746 - 1 (enabled) 3747 3748 Default: 1 (enabled) 3749 3750 3751``/proc/sys/net/core/*`` 3752======================== 3753 3754 Please see: Documentation/admin-guide/sysctl/net.rst for descriptions of these entries. 3755 3756 3757``/proc/sys/net/unix/*`` 3758======================== 3759 3760max_dgram_qlen - INTEGER 3761 The maximum length of dgram socket receive queue 3762 3763 Default: 10 3764 3765