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_rtt_percent - INTEGER 858 Percentage of SRTT used for the compressed SACK feature. 859 See tcp_comp_sack_nr, tcp_comp_sack_delay_ns, tcp_comp_sack_slack_ns. 860 861 Possible values : 1 - 1000 862 863 Default : 33 % 864 865tcp_comp_sack_delay_ns - LONG INTEGER 866 TCP tries to reduce number of SACK sent, using a timer based 867 on tcp_comp_sack_rtt_percent of SRTT, capped by this sysctl 868 in nano seconds. 869 The default is 1ms, based on TSO autosizing period. 870 871 Default : 1,000,000 ns (1 ms) 872 873tcp_comp_sack_slack_ns - LONG INTEGER 874 This sysctl control the slack used when arming the 875 timer used by SACK compression. This gives extra time 876 for small RTT flows, and reduces system overhead by allowing 877 opportunistic reduction of timer interrupts. 878 Too big values might reduce goodput. 879 880 Default : 10,000 ns (10 us) 881 882tcp_comp_sack_nr - INTEGER 883 Max number of SACK that can be compressed. 884 Using 0 disables SACK compression. 885 886 Default : 44 887 888tcp_backlog_ack_defer - BOOLEAN 889 If enabled, user thread processing socket backlog tries sending 890 one ACK for the whole queue. This helps to avoid potential 891 long latencies at end of a TCP socket syscall. 892 893 Possible values: 894 895 - 0 (disabled) 896 - 1 (enabled) 897 898 Default: 1 (enabled) 899 900tcp_slow_start_after_idle - BOOLEAN 901 If enabled, provide RFC2861 behavior and time out the congestion 902 window after an idle period. An idle period is defined at 903 the current RTO. If unset, the congestion window will not 904 be timed out after an idle period. 905 906 Possible values: 907 908 - 0 (disabled) 909 - 1 (enabled) 910 911 Default: 1 (enabled) 912 913tcp_stdurg - BOOLEAN 914 Use the Host requirements interpretation of the TCP urgent pointer field. 915 Most hosts use the older BSD interpretation, so if enabled, 916 Linux might not communicate correctly with them. 917 918 Possible values: 919 920 - 0 (disabled) 921 - 1 (enabled) 922 923 Default: 0 (disabled) 924 925tcp_synack_retries - INTEGER 926 Number of times SYNACKs for a passive TCP connection attempt will 927 be retransmitted. Should not be higher than 255. Default value 928 is 5, which corresponds to 31seconds till the last retransmission 929 with the current initial RTO of 1second. With this the final timeout 930 for a passive TCP connection will happen after 63seconds. 931 932tcp_syncookies - INTEGER 933 Only valid when the kernel was compiled with CONFIG_SYN_COOKIES 934 Send out syncookies when the syn backlog queue of a socket 935 overflows. This is to prevent against the common 'SYN flood attack' 936 Default: 1 937 938 Note, that syncookies is fallback facility. 939 It MUST NOT be used to help highly loaded servers to stand 940 against legal connection rate. If you see SYN flood warnings 941 in your logs, but investigation shows that they occur 942 because of overload with legal connections, you should tune 943 another parameters until this warning disappear. 944 See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow. 945 946 syncookies seriously violate TCP protocol, do not allow 947 to use TCP extensions, can result in serious degradation 948 of some services (f.e. SMTP relaying), visible not by you, 949 but your clients and relays, contacting you. While you see 950 SYN flood warnings in logs not being really flooded, your server 951 is seriously misconfigured. 952 953 If you want to test which effects syncookies have to your 954 network connections you can set this knob to 2 to enable 955 unconditionally generation of syncookies. 956 957tcp_migrate_req - BOOLEAN 958 The incoming connection is tied to a specific listening socket when 959 the initial SYN packet is received during the three-way handshake. 960 When a listener is closed, in-flight request sockets during the 961 handshake and established sockets in the accept queue are aborted. 962 963 If the listener has SO_REUSEPORT enabled, other listeners on the 964 same port should have been able to accept such connections. This 965 option makes it possible to migrate such child sockets to another 966 listener after close() or shutdown(). 967 968 The BPF_SK_REUSEPORT_SELECT_OR_MIGRATE type of eBPF program should 969 usually be used to define the policy to pick an alive listener. 970 Otherwise, the kernel will randomly pick an alive listener only if 971 this option is enabled. 972 973 Note that migration between listeners with different settings may 974 crash applications. Let's say migration happens from listener A to 975 B, and only B has TCP_SAVE_SYN enabled. B cannot read SYN data from 976 the requests migrated from A. To avoid such a situation, cancel 977 migration by returning SK_DROP in the type of eBPF program, or 978 disable this option. 979 980 Possible values: 981 982 - 0 (disabled) 983 - 1 (enabled) 984 985 Default: 0 (disabled) 986 987tcp_fastopen - INTEGER 988 Enable TCP Fast Open (RFC7413) to send and accept data in the opening 989 SYN packet. 990 991 The client support is enabled by flag 0x1 (on by default). The client 992 then must use sendmsg() or sendto() with the MSG_FASTOPEN flag, 993 rather than connect() to send data in SYN. 994 995 The server support is enabled by flag 0x2 (off by default). Then 996 either enable for all listeners with another flag (0x400) or 997 enable individual listeners via TCP_FASTOPEN socket option with 998 the option value being the length of the syn-data backlog. 999 1000 The values (bitmap) are 1001 1002 ===== ======== ====================================================== 1003 0x1 (client) enables sending data in the opening SYN on the client. 1004 0x2 (server) enables the server support, i.e., allowing data in 1005 a SYN packet to be accepted and passed to the 1006 application before 3-way handshake finishes. 1007 0x4 (client) send data in the opening SYN regardless of cookie 1008 availability and without a cookie option. 1009 0x200 (server) accept data-in-SYN w/o any cookie option present. 1010 0x400 (server) enable all listeners to support Fast Open by 1011 default without explicit TCP_FASTOPEN socket option. 1012 ===== ======== ====================================================== 1013 1014 Default: 0x1 1015 1016 Note that additional client or server features are only 1017 effective if the basic support (0x1 and 0x2) are enabled respectively. 1018 1019tcp_fastopen_blackhole_timeout_sec - INTEGER 1020 Initial time period in second to disable Fastopen on active TCP sockets 1021 when a TFO firewall blackhole issue happens. 1022 This time period will grow exponentially when more blackhole issues 1023 get detected right after Fastopen is re-enabled and will reset to 1024 initial value when the blackhole issue goes away. 1025 0 to disable the blackhole detection. 1026 1027 By default, it is set to 0 (feature is disabled). 1028 1029tcp_fastopen_key - list of comma separated 32-digit hexadecimal INTEGERs 1030 The list consists of a primary key and an optional backup key. The 1031 primary key is used for both creating and validating cookies, while the 1032 optional backup key is only used for validating cookies. The purpose of 1033 the backup key is to maximize TFO validation when keys are rotated. 1034 1035 A randomly chosen primary key may be configured by the kernel if 1036 the tcp_fastopen sysctl is set to 0x400 (see above), or if the 1037 TCP_FASTOPEN setsockopt() optname is set and a key has not been 1038 previously configured via sysctl. If keys are configured via 1039 setsockopt() by using the TCP_FASTOPEN_KEY optname, then those 1040 per-socket keys will be used instead of any keys that are specified via 1041 sysctl. 1042 1043 A key is specified as 4 8-digit hexadecimal integers which are separated 1044 by a '-' as: xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx. Leading zeros may be 1045 omitted. A primary and a backup key may be specified by separating them 1046 by a comma. If only one key is specified, it becomes the primary key and 1047 any previously configured backup keys are removed. 1048 1049tcp_syn_retries - INTEGER 1050 Number of times initial SYNs for an active TCP connection attempt 1051 will be retransmitted. Should not be higher than 127. Default value 1052 is 6, which corresponds to 67seconds (with tcp_syn_linear_timeouts = 4) 1053 till the last retransmission with the current initial RTO of 1second. 1054 With this the final timeout for an active TCP connection attempt 1055 will happen after 131seconds. 1056 1057tcp_timestamps - INTEGER 1058 Enable timestamps as defined in RFC1323. 1059 1060 - 0: Disabled. 1061 - 1: Enable timestamps as defined in RFC1323 and use random offset for 1062 each connection rather than only using the current time. 1063 - 2: Like 1, but without random offsets. 1064 1065 Default: 1 1066 1067tcp_min_tso_segs - INTEGER 1068 Minimal number of segments per TSO frame. 1069 1070 Since linux-3.12, TCP does an automatic sizing of TSO frames, 1071 depending on flow rate, instead of filling 64Kbytes packets. 1072 For specific usages, it's possible to force TCP to build big 1073 TSO frames. Note that TCP stack might split too big TSO packets 1074 if available window is too small. 1075 1076 Default: 2 1077 1078tcp_tso_rtt_log - INTEGER 1079 Adjustment of TSO packet sizes based on min_rtt 1080 1081 Starting from linux-5.18, TCP autosizing can be tweaked 1082 for flows having small RTT. 1083 1084 Old autosizing was splitting the pacing budget to send 1024 TSO 1085 per second. 1086 1087 tso_packet_size = sk->sk_pacing_rate / 1024; 1088 1089 With the new mechanism, we increase this TSO sizing using: 1090 1091 distance = min_rtt_usec / (2^tcp_tso_rtt_log) 1092 tso_packet_size += gso_max_size >> distance; 1093 1094 This means that flows between very close hosts can use bigger 1095 TSO packets, reducing their cpu costs. 1096 1097 If you want to use the old autosizing, set this sysctl to 0. 1098 1099 Default: 9 (2^9 = 512 usec) 1100 1101tcp_pacing_ss_ratio - INTEGER 1102 sk->sk_pacing_rate is set by TCP stack using a ratio applied 1103 to current rate. (current_rate = cwnd * mss / srtt) 1104 If TCP is in slow start, tcp_pacing_ss_ratio is applied 1105 to let TCP probe for bigger speeds, assuming cwnd can be 1106 doubled every other RTT. 1107 1108 Default: 200 1109 1110tcp_pacing_ca_ratio - INTEGER 1111 sk->sk_pacing_rate is set by TCP stack using a ratio applied 1112 to current rate. (current_rate = cwnd * mss / srtt) 1113 If TCP is in congestion avoidance phase, tcp_pacing_ca_ratio 1114 is applied to conservatively probe for bigger throughput. 1115 1116 Default: 120 1117 1118tcp_syn_linear_timeouts - INTEGER 1119 The number of times for an active TCP connection to retransmit SYNs with 1120 a linear backoff timeout before defaulting to an exponential backoff 1121 timeout. This has no effect on SYNACK at the passive TCP side. 1122 1123 With an initial RTO of 1 and tcp_syn_linear_timeouts = 4 we would 1124 expect SYN RTOs to be: 1, 1, 1, 1, 1, 2, 4, ... (4 linear timeouts, 1125 and the first exponential backoff using 2^0 * initial_RTO). 1126 Default: 4 1127 1128tcp_tso_win_divisor - INTEGER 1129 This allows control over what percentage of the congestion window 1130 can be consumed by a single TSO frame. 1131 The setting of this parameter is a choice between burstiness and 1132 building larger TSO frames. 1133 1134 Default: 3 1135 1136tcp_tw_reuse - INTEGER 1137 Enable reuse of TIME-WAIT sockets for new connections when it is 1138 safe from protocol viewpoint. 1139 1140 - 0 - disable 1141 - 1 - global enable 1142 - 2 - enable for loopback traffic only 1143 1144 It should not be changed without advice/request of technical 1145 experts. 1146 1147 Default: 2 1148 1149tcp_tw_reuse_delay - UNSIGNED INTEGER 1150 The delay in milliseconds before a TIME-WAIT socket can be reused by a 1151 new connection, if TIME-WAIT socket reuse is enabled. The actual reuse 1152 threshold is within [N, N+1] range, where N is the requested delay in 1153 milliseconds, to ensure the delay interval is never shorter than the 1154 configured value. 1155 1156 This setting contains an assumption about the other TCP timestamp clock 1157 tick interval. It should not be set to a value lower than the peer's 1158 clock tick for PAWS (Protection Against Wrapped Sequence numbers) 1159 mechanism work correctly for the reused connection. 1160 1161 Default: 1000 (milliseconds) 1162 1163tcp_window_scaling - BOOLEAN 1164 Enable window scaling as defined in RFC1323. 1165 1166 Possible values: 1167 1168 - 0 (disabled) 1169 - 1 (enabled) 1170 1171 Default: 1 (enabled) 1172 1173tcp_shrink_window - BOOLEAN 1174 This changes how the TCP receive window is calculated. 1175 1176 RFC 7323, section 2.4, says there are instances when a retracted 1177 window can be offered, and that TCP implementations MUST ensure 1178 that they handle a shrinking window, as specified in RFC 1122. 1179 1180 Possible values: 1181 1182 - 0 (disabled) - The window is never shrunk. 1183 - 1 (enabled) - The window is shrunk when necessary to remain within 1184 the memory limit set by autotuning (sk_rcvbuf). 1185 This only occurs if a non-zero receive window 1186 scaling factor is also in effect. 1187 1188 Default: 0 (disabled) 1189 1190tcp_wmem - vector of 3 INTEGERs: min, default, max 1191 min: Amount of memory reserved for send buffers for TCP sockets. 1192 Each TCP socket has rights to use it due to fact of its birth. 1193 1194 Default: 4K 1195 1196 default: initial size of send buffer used by TCP sockets. This 1197 value overrides net.core.wmem_default used by other protocols. 1198 1199 It is usually lower than net.core.wmem_default. 1200 1201 Default: 16K 1202 1203 max: Maximal amount of memory allowed for automatically tuned 1204 send buffers for TCP sockets. This value does not override 1205 net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables 1206 automatic tuning of that socket's send buffer size, in which case 1207 this value is ignored. 1208 1209 Default: between 64K and 4MB, depending on RAM size. 1210 1211tcp_notsent_lowat - UNSIGNED INTEGER 1212 A TCP socket can control the amount of unsent bytes in its write queue, 1213 thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll() 1214 reports POLLOUT events if the amount of unsent bytes is below a per 1215 socket value, and if the write queue is not full. sendmsg() will 1216 also not add new buffers if the limit is hit. 1217 1218 This global variable controls the amount of unsent data for 1219 sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change 1220 to the global variable has immediate effect. 1221 1222 Default: UINT_MAX (0xFFFFFFFF) 1223 1224tcp_workaround_signed_windows - BOOLEAN 1225 If enabled, assume no receipt of a window scaling option means the 1226 remote TCP is broken and treats the window as a signed quantity. 1227 If disabled, assume the remote TCP is not broken even if we do 1228 not receive a window scaling option from them. 1229 1230 Possible values: 1231 1232 - 0 (disabled) 1233 - 1 (enabled) 1234 1235 Default: 0 (disabled) 1236 1237tcp_thin_linear_timeouts - BOOLEAN 1238 Enable dynamic triggering of linear timeouts for thin streams. 1239 If enabled, a check is performed upon retransmission by timeout to 1240 determine if the stream is thin (less than 4 packets in flight). 1241 As long as the stream is found to be thin, up to 6 linear 1242 timeouts may be performed before exponential backoff mode is 1243 initiated. This improves retransmission latency for 1244 non-aggressive thin streams, often found to be time-dependent. 1245 For more information on thin streams, see 1246 Documentation/networking/tcp-thin.rst 1247 1248 Possible values: 1249 1250 - 0 (disabled) 1251 - 1 (enabled) 1252 1253 Default: 0 (disabled) 1254 1255tcp_limit_output_bytes - INTEGER 1256 Controls TCP Small Queue limit per tcp socket. 1257 TCP bulk sender tends to increase packets in flight until it 1258 gets losses notifications. With SNDBUF autotuning, this can 1259 result in a large amount of packets queued on the local machine 1260 (e.g.: qdiscs, CPU backlog, or device) hurting latency of other 1261 flows, for typical pfifo_fast qdiscs. tcp_limit_output_bytes 1262 limits the number of bytes on qdisc or device to reduce artificial 1263 RTT/cwnd and reduce bufferbloat. 1264 1265 Default: 4194304 (4 MB) 1266 1267tcp_challenge_ack_limit - INTEGER 1268 Limits number of Challenge ACK sent per second, as recommended 1269 in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks) 1270 Note that this per netns rate limit can allow some side channel 1271 attacks and probably should not be enabled. 1272 TCP stack implements per TCP socket limits anyway. 1273 Default: INT_MAX (unlimited) 1274 1275tcp_ehash_entries - INTEGER 1276 Show the number of hash buckets for TCP sockets in the current 1277 networking namespace. 1278 1279 A negative value means the networking namespace does not own its 1280 hash buckets and shares the initial networking namespace's one. 1281 1282tcp_child_ehash_entries - INTEGER 1283 Control the number of hash buckets for TCP sockets in the child 1284 networking namespace, which must be set before clone() or unshare(). 1285 1286 If the value is not 0, the kernel uses a value rounded up to 2^n 1287 as the actual hash bucket size. 0 is a special value, meaning 1288 the child networking namespace will share the initial networking 1289 namespace's hash buckets. 1290 1291 Note that the child will use the global one in case the kernel 1292 fails to allocate enough memory. In addition, the global hash 1293 buckets are spread over available NUMA nodes, but the allocation 1294 of the child hash table depends on the current process's NUMA 1295 policy, which could result in performance differences. 1296 1297 Note also that the default value of tcp_max_tw_buckets and 1298 tcp_max_syn_backlog depend on the hash bucket size. 1299 1300 Possible values: 0, 2^n (n: 0 - 24 (16Mi)) 1301 1302 Default: 0 1303 1304tcp_plb_enabled - BOOLEAN 1305 If enabled and the underlying congestion control (e.g. DCTCP) supports 1306 and enables PLB feature, TCP PLB (Protective Load Balancing) is 1307 enabled. PLB is described in the following paper: 1308 https://doi.org/10.1145/3544216.3544226. Based on PLB parameters, 1309 upon sensing sustained congestion, TCP triggers a change in 1310 flow label field for outgoing IPv6 packets. A change in flow label 1311 field potentially changes the path of outgoing packets for switches 1312 that use ECMP/WCMP for routing. 1313 1314 PLB changes socket txhash which results in a change in IPv6 Flow Label 1315 field, and currently no-op for IPv4 headers. It is possible 1316 to apply PLB for IPv4 with other network header fields (e.g. TCP 1317 or IPv4 options) or using encapsulation where outer header is used 1318 by switches to determine next hop. In either case, further host 1319 and switch side changes will be needed. 1320 1321 If enabled, PLB assumes that congestion signal (e.g. ECN) is made 1322 available and used by congestion control module to estimate a 1323 congestion measure (e.g. ce_ratio). PLB needs a congestion measure to 1324 make repathing decisions. 1325 1326 Possible values: 1327 1328 - 0 (disabled) 1329 - 1 (enabled) 1330 1331 Default: 0 (disabled) 1332 1333tcp_plb_idle_rehash_rounds - INTEGER 1334 Number of consecutive congested rounds (RTT) seen after which 1335 a rehash can be performed, given there are no packets in flight. 1336 This is referred to as M in PLB paper: 1337 https://doi.org/10.1145/3544216.3544226. 1338 1339 Possible Values: 0 - 31 1340 1341 Default: 3 1342 1343tcp_plb_rehash_rounds - INTEGER 1344 Number of consecutive congested rounds (RTT) seen after which 1345 a forced rehash can be performed. Be careful when setting this 1346 parameter, as a small value increases the risk of retransmissions. 1347 This is referred to as N in PLB paper: 1348 https://doi.org/10.1145/3544216.3544226. 1349 1350 Possible Values: 0 - 31 1351 1352 Default: 12 1353 1354tcp_plb_suspend_rto_sec - INTEGER 1355 Time, in seconds, to suspend PLB in event of an RTO. In order to avoid 1356 having PLB repath onto a connectivity "black hole", after an RTO a TCP 1357 connection suspends PLB repathing for a random duration between 1x and 1358 2x of this parameter. Randomness is added to avoid concurrent rehashing 1359 of multiple TCP connections. This should be set corresponding to the 1360 amount of time it takes to repair a failed link. 1361 1362 Possible Values: 0 - 255 1363 1364 Default: 60 1365 1366tcp_plb_cong_thresh - INTEGER 1367 Fraction of packets marked with congestion over a round (RTT) to 1368 tag that round as congested. This is referred to as K in the PLB paper: 1369 https://doi.org/10.1145/3544216.3544226. 1370 1371 The 0-1 fraction range is mapped to 0-256 range to avoid floating 1372 point operations. For example, 128 means that if at least 50% of 1373 the packets in a round were marked as congested then the round 1374 will be tagged as congested. 1375 1376 Setting threshold to 0 means that PLB repaths every RTT regardless 1377 of congestion. This is not intended behavior for PLB and should be 1378 used only for experimentation purpose. 1379 1380 Possible Values: 0 - 256 1381 1382 Default: 128 1383 1384tcp_pingpong_thresh - INTEGER 1385 The number of estimated data replies sent for estimated incoming data 1386 requests that must happen before TCP considers that a connection is a 1387 "ping-pong" (request-response) connection for which delayed 1388 acknowledgments can provide benefits. 1389 1390 This threshold is 1 by default, but some applications may need a higher 1391 threshold for optimal performance. 1392 1393 Possible Values: 1 - 255 1394 1395 Default: 1 1396 1397tcp_rto_min_us - INTEGER 1398 Minimal TCP retransmission timeout (in microseconds). Note that the 1399 rto_min route option has the highest precedence for configuring this 1400 setting, followed by the TCP_BPF_RTO_MIN and TCP_RTO_MIN_US socket 1401 options, followed by this tcp_rto_min_us sysctl. 1402 1403 The recommended practice is to use a value less or equal to 200000 1404 microseconds. 1405 1406 Possible Values: 1 - INT_MAX 1407 1408 Default: 200000 1409 1410tcp_rto_max_ms - INTEGER 1411 Maximal TCP retransmission timeout (in ms). 1412 Note that TCP_RTO_MAX_MS socket option has higher precedence. 1413 1414 When changing tcp_rto_max_ms, it is important to understand 1415 that tcp_retries2 might need a change. 1416 1417 Possible Values: 1000 - 120,000 1418 1419 Default: 120,000 1420 1421UDP variables 1422============= 1423 1424udp_l3mdev_accept - BOOLEAN 1425 Enabling this option allows a "global" bound socket to work 1426 across L3 master domains (e.g., VRFs) with packets capable of 1427 being received regardless of the L3 domain in which they 1428 originated. Only valid when the kernel was compiled with 1429 CONFIG_NET_L3_MASTER_DEV. 1430 1431 Possible values: 1432 1433 - 0 (disabled) 1434 - 1 (enabled) 1435 1436 Default: 0 (disabled) 1437 1438udp_mem - vector of 3 INTEGERs: min, pressure, max 1439 Number of pages allowed for queueing by all UDP sockets. 1440 1441 min: Number of pages allowed for queueing by all UDP sockets. 1442 1443 pressure: This value was introduced to follow format of tcp_mem. 1444 1445 max: This value was introduced to follow format of tcp_mem. 1446 1447 Default is calculated at boot time from amount of available memory. 1448 1449udp_rmem_min - INTEGER 1450 Minimal size of receive buffer used by UDP sockets in moderation. 1451 Each UDP socket is able to use the size for receiving data, even if 1452 total pages of UDP sockets exceed udp_mem pressure. The unit is byte. 1453 1454 Default: 4K 1455 1456udp_wmem_min - INTEGER 1457 UDP does not have tx memory accounting and this tunable has no effect. 1458 1459udp_hash_entries - INTEGER 1460 Show the number of hash buckets for UDP sockets in the current 1461 networking namespace. 1462 1463 A negative value means the networking namespace does not own its 1464 hash buckets and shares the initial networking namespace's one. 1465 1466udp_child_hash_entries - INTEGER 1467 Control the number of hash buckets for UDP sockets in the child 1468 networking namespace, which must be set before clone() or unshare(). 1469 1470 If the value is not 0, the kernel uses a value rounded up to 2^n 1471 as the actual hash bucket size. 0 is a special value, meaning 1472 the child networking namespace will share the initial networking 1473 namespace's hash buckets. 1474 1475 Note that the child will use the global one in case the kernel 1476 fails to allocate enough memory. In addition, the global hash 1477 buckets are spread over available NUMA nodes, but the allocation 1478 of the child hash table depends on the current process's NUMA 1479 policy, which could result in performance differences. 1480 1481 Possible values: 0, 2^n (n: 7 (128) - 16 (64K)) 1482 1483 Default: 0 1484 1485 1486RAW variables 1487============= 1488 1489raw_l3mdev_accept - BOOLEAN 1490 Enabling this option allows a "global" bound socket to work 1491 across L3 master domains (e.g., VRFs) with packets capable of 1492 being received regardless of the L3 domain in which they 1493 originated. Only valid when the kernel was compiled with 1494 CONFIG_NET_L3_MASTER_DEV. 1495 1496 Possible values: 1497 1498 - 0 (disabled) 1499 - 1 (enabled) 1500 1501 Default: 1 (enabled) 1502 1503CIPSOv4 Variables 1504================= 1505 1506cipso_cache_enable - BOOLEAN 1507 If enabled, enable additions to and lookups from the CIPSO label mapping 1508 cache. If disabled, additions are ignored and lookups always result in a 1509 miss. However, regardless of the setting the cache is still 1510 invalidated when required when means you can safely toggle this on and 1511 off and the cache will always be "safe". 1512 1513 Possible values: 1514 1515 - 0 (disabled) 1516 - 1 (enabled) 1517 1518 Default: 1 (enabled) 1519 1520cipso_cache_bucket_size - INTEGER 1521 The CIPSO label cache consists of a fixed size hash table with each 1522 hash bucket containing a number of cache entries. This variable limits 1523 the number of entries in each hash bucket; the larger the value is, the 1524 more CIPSO label mappings that can be cached. When the number of 1525 entries in a given hash bucket reaches this limit adding new entries 1526 causes the oldest entry in the bucket to be removed to make room. 1527 1528 Default: 10 1529 1530cipso_rbm_optfmt - BOOLEAN 1531 Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of 1532 the CIPSO draft specification (see Documentation/netlabel for details). 1533 This means that when set the CIPSO tag will be padded with empty 1534 categories in order to make the packet data 32-bit aligned. 1535 1536 Possible values: 1537 1538 - 0 (disabled) 1539 - 1 (enabled) 1540 1541 Default: 0 (disabled) 1542 1543cipso_rbm_strictvalid - BOOLEAN 1544 If enabled, do a very strict check of the CIPSO option when 1545 ip_options_compile() is called. If disabled, relax the checks done during 1546 ip_options_compile(). Either way is "safe" as errors are caught else 1547 where in the CIPSO processing code but setting this to 0 (False) should 1548 result in less work (i.e. it should be faster) but could cause problems 1549 with other implementations that require strict checking. 1550 1551 Possible values: 1552 1553 - 0 (disabled) 1554 - 1 (enabled) 1555 1556 Default: 0 (disabled) 1557 1558IP Variables 1559============ 1560 1561ip_local_port_range - 2 INTEGERS 1562 Defines the local port range that is used by TCP and UDP to 1563 choose the local port. The first number is the first, the 1564 second the last local port number. 1565 If possible, it is better these numbers have different parity 1566 (one even and one odd value). 1567 Must be greater than or equal to ip_unprivileged_port_start. 1568 The default values are 32768 and 60999 respectively. 1569 1570ip_local_reserved_ports - list of comma separated ranges 1571 Specify the ports which are reserved for known third-party 1572 applications. These ports will not be used by automatic port 1573 assignments (e.g. when calling connect() or bind() with port 1574 number 0). Explicit port allocation behavior is unchanged. 1575 1576 The format used for both input and output is a comma separated 1577 list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and 1578 10). Writing to the file will clear all previously reserved 1579 ports and update the current list with the one given in the 1580 input. 1581 1582 Note that ip_local_port_range and ip_local_reserved_ports 1583 settings are independent and both are considered by the kernel 1584 when determining which ports are available for automatic port 1585 assignments. 1586 1587 You can reserve ports which are not in the current 1588 ip_local_port_range, e.g.:: 1589 1590 $ cat /proc/sys/net/ipv4/ip_local_port_range 1591 32000 60999 1592 $ cat /proc/sys/net/ipv4/ip_local_reserved_ports 1593 8080,9148 1594 1595 although this is redundant. However such a setting is useful 1596 if later the port range is changed to a value that will 1597 include the reserved ports. Also keep in mind, that overlapping 1598 of these ranges may affect probability of selecting ephemeral 1599 ports which are right after block of reserved ports. 1600 1601 Default: Empty 1602 1603ip_unprivileged_port_start - INTEGER 1604 This is a per-namespace sysctl. It defines the first 1605 unprivileged port in the network namespace. Privileged ports 1606 require root or CAP_NET_BIND_SERVICE in order to bind to them. 1607 To disable all privileged ports, set this to 0. They must not 1608 overlap with the ip_local_port_range. 1609 1610 Default: 1024 1611 1612ip_nonlocal_bind - BOOLEAN 1613 If enabled, allows processes to bind() to non-local IP addresses, 1614 which can be quite useful - but may break some applications. 1615 1616 Possible values: 1617 1618 - 0 (disabled) 1619 - 1 (enabled) 1620 1621 Default: 0 (disabled) 1622 1623ip_autobind_reuse - BOOLEAN 1624 By default, bind() does not select the ports automatically even if 1625 the new socket and all sockets bound to the port have SO_REUSEADDR. 1626 ip_autobind_reuse allows bind() to reuse the port and this is useful 1627 when you use bind()+connect(), but may break some applications. 1628 The preferred solution is to use IP_BIND_ADDRESS_NO_PORT and this 1629 option should only be set by experts. 1630 1631 Possible values: 1632 1633 - 0 (disabled) 1634 - 1 (enabled) 1635 1636 Default: 0 (disabled) 1637 1638ip_dynaddr - INTEGER 1639 If set non-zero, enables support for dynamic addresses. 1640 If set to a non-zero value larger than 1, a kernel log 1641 message will be printed when dynamic address rewriting 1642 occurs. 1643 1644 Default: 0 1645 1646ip_early_demux - BOOLEAN 1647 Optimize input packet processing down to one demux for 1648 certain kinds of local sockets. Currently we only do this 1649 for established TCP and connected UDP sockets. 1650 1651 It may add an additional cost for pure routing workloads that 1652 reduces overall throughput, in such case you should disable it. 1653 1654 Possible values: 1655 1656 - 0 (disabled) 1657 - 1 (enabled) 1658 1659 Default: 1 (enabled) 1660 1661ping_group_range - 2 INTEGERS 1662 Restrict ICMP_PROTO datagram sockets to users in the group range. 1663 The default is "1 0", meaning, that nobody (not even root) may 1664 create ping sockets. Setting it to "100 100" would grant permissions 1665 to the single group. "0 4294967294" would enable it for the world, "100 1666 4294967294" would enable it for the users, but not daemons. 1667 1668tcp_early_demux - BOOLEAN 1669 Enable early demux for established TCP sockets. 1670 1671 Possible values: 1672 1673 - 0 (disabled) 1674 - 1 (enabled) 1675 1676 Default: 1 (enabled) 1677 1678udp_early_demux - BOOLEAN 1679 Enable early demux for connected UDP sockets. Disable this if 1680 your system could experience more unconnected load. 1681 1682 Possible values: 1683 1684 - 0 (disabled) 1685 - 1 (enabled) 1686 1687 Default: 1 (enabled) 1688 1689icmp_echo_ignore_all - BOOLEAN 1690 If enabled, then the kernel will ignore all ICMP ECHO 1691 requests sent to it. 1692 1693 Possible values: 1694 1695 - 0 (disabled) 1696 - 1 (enabled) 1697 1698 Default: 0 (disabled) 1699 1700icmp_echo_enable_probe - BOOLEAN 1701 If enabled, then the kernel will respond to RFC 8335 PROBE 1702 requests sent to it. 1703 1704 Possible values: 1705 1706 - 0 (disabled) 1707 - 1 (enabled) 1708 1709 Default: 0 (disabled) 1710 1711icmp_echo_ignore_broadcasts - BOOLEAN 1712 If enabled, then the kernel will ignore all ICMP ECHO and 1713 TIMESTAMP requests sent to it via broadcast/multicast. 1714 1715 Possible values: 1716 1717 - 0 (disabled) 1718 - 1 (enabled) 1719 1720 Default: 1 (enabled) 1721 1722icmp_ratelimit - INTEGER 1723 Limit the maximal rates for sending ICMP packets whose type matches 1724 icmp_ratemask (see below) to specific targets. 1725 0 to disable any limiting, 1726 otherwise the minimal space between responses in milliseconds. 1727 Note that another sysctl, icmp_msgs_per_sec limits the number 1728 of ICMP packets sent on all targets. 1729 1730 Default: 1000 1731 1732icmp_msgs_per_sec - INTEGER 1733 Limit maximal number of ICMP packets sent per second from this host. 1734 Only messages whose type matches icmp_ratemask (see below) are 1735 controlled by this limit. For security reasons, the precise count 1736 of messages per second is randomized. 1737 1738 Default: 1000 1739 1740icmp_msgs_burst - INTEGER 1741 icmp_msgs_per_sec controls number of ICMP packets sent per second, 1742 while icmp_msgs_burst controls the burst size of these packets. 1743 For security reasons, the precise burst size is randomized. 1744 1745 Default: 50 1746 1747icmp_ratemask - INTEGER 1748 Mask made of ICMP types for which rates are being limited. 1749 1750 Significant bits: IHGFEDCBA9876543210 1751 1752 Default mask: 0000001100000011000 (6168) 1753 1754 Bit definitions (see include/linux/icmp.h): 1755 1756 = ========================= 1757 0 Echo Reply 1758 3 Destination Unreachable [1]_ 1759 4 Source Quench [1]_ 1760 5 Redirect 1761 8 Echo Request 1762 B Time Exceeded [1]_ 1763 C Parameter Problem [1]_ 1764 D Timestamp Request 1765 E Timestamp Reply 1766 F Info Request 1767 G Info Reply 1768 H Address Mask Request 1769 I Address Mask Reply 1770 = ========================= 1771 1772 .. [1] These are rate limited by default (see default mask above) 1773 1774icmp_ignore_bogus_error_responses - BOOLEAN 1775 Some routers violate RFC1122 by sending bogus responses to broadcast 1776 frames. Such violations are normally logged via a kernel warning. 1777 If enabled, the kernel will not give such warnings, which 1778 will avoid log file clutter. 1779 1780 Possible values: 1781 1782 - 0 (disabled) 1783 - 1 (enabled) 1784 1785 Default: 1 (enabled) 1786 1787icmp_errors_use_inbound_ifaddr - BOOLEAN 1788 1789 If disabled, icmp error messages are sent with the primary address of 1790 the exiting interface. 1791 1792 If enabled, the message will be sent with the primary address of 1793 the interface that received the packet that caused the icmp error. 1794 This is the behaviour many network administrators will expect from 1795 a router. And it can make debugging complicated network layouts 1796 much easier. 1797 1798 Note that if no primary address exists for the interface selected, 1799 then the primary address of the first non-loopback interface that 1800 has one will be used regardless of this setting. 1801 1802 Possible values: 1803 1804 - 0 (disabled) 1805 - 1 (enabled) 1806 1807 Default: 0 (disabled) 1808 1809icmp_errors_extension_mask - UNSIGNED INTEGER 1810 Bitmask of ICMP extensions to append to ICMPv4 error messages 1811 ("Destination Unreachable", "Time Exceeded" and "Parameter Problem"). 1812 The original datagram is trimmed / padded to 128 bytes in order to be 1813 compatible with applications that do not comply with RFC 4884. 1814 1815 Possible extensions are: 1816 1817 ==== ============================================================== 1818 0x01 Incoming IP interface information according to RFC 5837. 1819 Extension will include the index, IPv4 address (if present), 1820 name and MTU of the IP interface that received the datagram 1821 which elicited the ICMP error. 1822 ==== ============================================================== 1823 1824 Default: 0x00 (no extensions) 1825 1826igmp_max_memberships - INTEGER 1827 Change the maximum number of multicast groups we can subscribe to. 1828 Default: 20 1829 1830 Theoretical maximum value is bounded by having to send a membership 1831 report in a single datagram (i.e. the report can't span multiple 1832 datagrams, or risk confusing the switch and leaving groups you don't 1833 intend to). 1834 1835 The number of supported groups 'M' is bounded by the number of group 1836 report entries you can fit into a single datagram of 65535 bytes. 1837 1838 M = 65536-sizeof (ip header)/(sizeof(Group record)) 1839 1840 Group records are variable length, with a minimum of 12 bytes. 1841 So net.ipv4.igmp_max_memberships should not be set higher than: 1842 1843 (65536-24) / 12 = 5459 1844 1845 The value 5459 assumes no IP header options, so in practice 1846 this number may be lower. 1847 1848igmp_max_msf - INTEGER 1849 Maximum number of addresses allowed in the source filter list for a 1850 multicast group. 1851 1852 Default: 10 1853 1854igmp_qrv - INTEGER 1855 Controls the IGMP query robustness variable (see RFC2236 8.1). 1856 1857 Default: 2 (as specified by RFC2236 8.1) 1858 1859 Minimum: 1 (as specified by RFC6636 4.5) 1860 1861force_igmp_version - INTEGER 1862 - 0 - (default) No enforcement of a IGMP version, IGMPv1/v2 fallback 1863 allowed. Will back to IGMPv3 mode again if all IGMPv1/v2 Querier 1864 Present timer expires. 1865 - 1 - Enforce to use IGMP version 1. Will also reply IGMPv1 report if 1866 receive IGMPv2/v3 query. 1867 - 2 - Enforce to use IGMP version 2. Will fallback to IGMPv1 if receive 1868 IGMPv1 query message. Will reply report if receive IGMPv3 query. 1869 - 3 - Enforce to use IGMP version 3. The same react with default 0. 1870 1871 .. note:: 1872 1873 this is not the same with force_mld_version because IGMPv3 RFC3376 1874 Security Considerations does not have clear description that we could 1875 ignore other version messages completely as MLDv2 RFC3810. So make 1876 this value as default 0 is recommended. 1877 1878``conf/interface/*`` 1879 changes special settings per interface (where 1880 interface" is the name of your network interface) 1881 1882``conf/all/*`` 1883 is special, changes the settings for all interfaces 1884 1885log_martians - BOOLEAN 1886 Log packets with impossible addresses to kernel log. 1887 log_martians for the interface will be enabled if at least one of 1888 conf/{all,interface}/log_martians is set to TRUE, 1889 it will be disabled otherwise 1890 1891accept_redirects - BOOLEAN 1892 Accept ICMP redirect messages. 1893 accept_redirects for the interface will be enabled if: 1894 1895 - both conf/{all,interface}/accept_redirects are TRUE in the case 1896 forwarding for the interface is enabled 1897 1898 or 1899 1900 - at least one of conf/{all,interface}/accept_redirects is TRUE in the 1901 case forwarding for the interface is disabled 1902 1903 accept_redirects for the interface will be disabled otherwise 1904 1905 default: 1906 1907 - TRUE (host) 1908 - FALSE (router) 1909 1910forwarding - BOOLEAN 1911 Enable IP forwarding on this interface. This controls whether packets 1912 received _on_ this interface can be forwarded. 1913 1914mc_forwarding - BOOLEAN 1915 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE 1916 and a multicast routing daemon is required. 1917 conf/all/mc_forwarding must also be set to TRUE to enable multicast 1918 routing for the interface 1919 1920medium_id - INTEGER 1921 Integer value used to differentiate the devices by the medium they 1922 are attached to. Two devices can have different id values when 1923 the broadcast packets are received only on one of them. 1924 The default value 0 means that the device is the only interface 1925 to its medium, value of -1 means that medium is not known. 1926 1927 Currently, it is used to change the proxy_arp behavior: 1928 the proxy_arp feature is enabled for packets forwarded between 1929 two devices attached to different media. 1930 1931proxy_arp - BOOLEAN 1932 Do proxy arp. 1933 1934 proxy_arp for the interface will be enabled if at least one of 1935 conf/{all,interface}/proxy_arp is set to TRUE, 1936 it will be disabled otherwise 1937 1938proxy_arp_pvlan - BOOLEAN 1939 Private VLAN proxy arp. 1940 1941 Basically allow proxy arp replies back to the same interface 1942 (from which the ARP request/solicitation was received). 1943 1944 This is done to support (ethernet) switch features, like RFC 1945 3069, where the individual ports are NOT allowed to 1946 communicate with each other, but they are allowed to talk to 1947 the upstream router. As described in RFC 3069, it is possible 1948 to allow these hosts to communicate through the upstream 1949 router by proxy_arp'ing. Don't need to be used together with 1950 proxy_arp. 1951 1952 This technology is known by different names: 1953 1954 - In RFC 3069 it is called VLAN Aggregation. 1955 - Cisco and Allied Telesyn call it Private VLAN. 1956 - Hewlett-Packard call it Source-Port filtering or port-isolation. 1957 - Ericsson call it MAC-Forced Forwarding (RFC Draft). 1958 1959proxy_delay - INTEGER 1960 Delay proxy response. 1961 1962 Delay response to a neighbor solicitation when proxy_arp 1963 or proxy_ndp is enabled. A random value between [0, proxy_delay) 1964 will be chosen, setting to zero means reply with no delay. 1965 Value in jiffies. Defaults to 80. 1966 1967shared_media - BOOLEAN 1968 Send(router) or accept(host) RFC1620 shared media redirects. 1969 Overrides secure_redirects. 1970 1971 shared_media for the interface will be enabled if at least one of 1972 conf/{all,interface}/shared_media is set to TRUE, 1973 it will be disabled otherwise 1974 1975 default TRUE 1976 1977secure_redirects - BOOLEAN 1978 Accept ICMP redirect messages only to gateways listed in the 1979 interface's current gateway list. Even if disabled, RFC1122 redirect 1980 rules still apply. 1981 1982 Overridden by shared_media. 1983 1984 secure_redirects for the interface will be enabled if at least one of 1985 conf/{all,interface}/secure_redirects is set to TRUE, 1986 it will be disabled otherwise 1987 1988 default TRUE 1989 1990send_redirects - BOOLEAN 1991 Send redirects, if router. 1992 1993 send_redirects for the interface will be enabled if at least one of 1994 conf/{all,interface}/send_redirects is set to TRUE, 1995 it will be disabled otherwise 1996 1997 Default: TRUE 1998 1999bootp_relay - BOOLEAN 2000 Accept packets with source address 0.b.c.d destined 2001 not to this host as local ones. It is supposed, that 2002 BOOTP relay daemon will catch and forward such packets. 2003 conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay 2004 for the interface 2005 2006 default FALSE 2007 2008 Not Implemented Yet. 2009 2010accept_source_route - BOOLEAN 2011 Accept packets with SRR option. 2012 conf/all/accept_source_route must also be set to TRUE to accept packets 2013 with SRR option on the interface 2014 2015 default 2016 2017 - TRUE (router) 2018 - FALSE (host) 2019 2020accept_local - BOOLEAN 2021 Accept packets with local source addresses. In combination with 2022 suitable routing, this can be used to direct packets between two 2023 local interfaces over the wire and have them accepted properly. 2024 default FALSE 2025 2026route_localnet - BOOLEAN 2027 Do not consider loopback addresses as martian source or destination 2028 while routing. This enables the use of 127/8 for local routing purposes. 2029 2030 default FALSE 2031 2032rp_filter - INTEGER 2033 - 0 - No source validation. 2034 - 1 - Strict mode as defined in RFC3704 Strict Reverse Path 2035 Each incoming packet is tested against the FIB and if the interface 2036 is not the best reverse path the packet check will fail. 2037 By default failed packets are discarded. 2038 - 2 - Loose mode as defined in RFC3704 Loose Reverse Path 2039 Each incoming packet's source address is also tested against the FIB 2040 and if the source address is not reachable via any interface 2041 the packet check will fail. 2042 2043 Current recommended practice in RFC3704 is to enable strict mode 2044 to prevent IP spoofing from DDos attacks. If using asymmetric routing 2045 or other complicated routing, then loose mode is recommended. 2046 2047 The max value from conf/{all,interface}/rp_filter is used 2048 when doing source validation on the {interface}. 2049 2050 Default value is 0. Note that some distributions enable it 2051 in startup scripts. 2052 2053src_valid_mark - BOOLEAN 2054 - 0 - The fwmark of the packet is not included in reverse path 2055 route lookup. This allows for asymmetric routing configurations 2056 utilizing the fwmark in only one direction, e.g., transparent 2057 proxying. 2058 2059 - 1 - The fwmark of the packet is included in reverse path route 2060 lookup. This permits rp_filter to function when the fwmark is 2061 used for routing traffic in both directions. 2062 2063 This setting also affects the utilization of fmwark when 2064 performing source address selection for ICMP replies, or 2065 determining addresses stored for the IPOPT_TS_TSANDADDR and 2066 IPOPT_RR IP options. 2067 2068 The max value from conf/{all,interface}/src_valid_mark is used. 2069 2070 Default value is 0. 2071 2072arp_filter - BOOLEAN 2073 - 1 - Allows you to have multiple network interfaces on the same 2074 subnet, and have the ARPs for each interface be answered 2075 based on whether or not the kernel would route a packet from 2076 the ARP'd IP out that interface (therefore you must use source 2077 based routing for this to work). In other words it allows control 2078 of which cards (usually 1) will respond to an arp request. 2079 2080 - 0 - (default) The kernel can respond to arp requests with addresses 2081 from other interfaces. This may seem wrong but it usually makes 2082 sense, because it increases the chance of successful communication. 2083 IP addresses are owned by the complete host on Linux, not by 2084 particular interfaces. Only for more complex setups like load- 2085 balancing, does this behaviour cause problems. 2086 2087 arp_filter for the interface will be enabled if at least one of 2088 conf/{all,interface}/arp_filter is set to TRUE, 2089 it will be disabled otherwise 2090 2091arp_announce - INTEGER 2092 Define different restriction levels for announcing the local 2093 source IP address from IP packets in ARP requests sent on 2094 interface: 2095 2096 - 0 - (default) Use any local address, configured on any interface 2097 - 1 - Try to avoid local addresses that are not in the target's 2098 subnet for this interface. This mode is useful when target 2099 hosts reachable via this interface require the source IP 2100 address in ARP requests to be part of their logical network 2101 configured on the receiving interface. When we generate the 2102 request we will check all our subnets that include the 2103 target IP and will preserve the source address if it is from 2104 such subnet. If there is no such subnet we select source 2105 address according to the rules for level 2. 2106 - 2 - Always use the best local address for this target. 2107 In this mode we ignore the source address in the IP packet 2108 and try to select local address that we prefer for talks with 2109 the target host. Such local address is selected by looking 2110 for primary IP addresses on all our subnets on the outgoing 2111 interface that include the target IP address. If no suitable 2112 local address is found we select the first local address 2113 we have on the outgoing interface or on all other interfaces, 2114 with the hope we will receive reply for our request and 2115 even sometimes no matter the source IP address we announce. 2116 2117 The max value from conf/{all,interface}/arp_announce is used. 2118 2119 Increasing the restriction level gives more chance for 2120 receiving answer from the resolved target while decreasing 2121 the level announces more valid sender's information. 2122 2123arp_ignore - INTEGER 2124 Define different modes for sending replies in response to 2125 received ARP requests that resolve local target IP addresses: 2126 2127 - 0 - (default): reply for any local target IP address, configured 2128 on any interface 2129 - 1 - reply only if the target IP address is local address 2130 configured on the incoming interface 2131 - 2 - reply only if the target IP address is local address 2132 configured on the incoming interface and both with the 2133 sender's IP address are part from same subnet on this interface 2134 - 3 - do not reply for local addresses configured with scope host, 2135 only resolutions for global and link addresses are replied 2136 - 4-7 - reserved 2137 - 8 - do not reply for all local addresses 2138 2139 The max value from conf/{all,interface}/arp_ignore is used 2140 when ARP request is received on the {interface} 2141 2142arp_notify - BOOLEAN 2143 Define mode for notification of address and device changes. 2144 2145 == ========================================================== 2146 0 (default): do nothing 2147 1 Generate gratuitous arp requests when device is brought up 2148 or hardware address changes. 2149 == ========================================================== 2150 2151arp_accept - INTEGER 2152 Define behavior for accepting gratuitous ARP (garp) frames from devices 2153 that are not already present in the ARP table: 2154 2155 - 0 - don't create new entries in the ARP table 2156 - 1 - create new entries in the ARP table 2157 - 2 - create new entries only if the source IP address is in the same 2158 subnet as an address configured on the interface that received the 2159 garp message. 2160 2161 Both replies and requests type gratuitous arp will trigger the 2162 ARP table to be updated, if this setting is on. 2163 2164 If the ARP table already contains the IP address of the 2165 gratuitous arp frame, the arp table will be updated regardless 2166 if this setting is on or off. 2167 2168arp_evict_nocarrier - BOOLEAN 2169 Clears the ARP cache on NOCARRIER events. This option is important for 2170 wireless devices where the ARP cache should not be cleared when roaming 2171 between access points on the same network. In most cases this should 2172 remain as the default (1). 2173 2174 Possible values: 2175 2176 - 0 (disabled) - Do not clear ARP cache on NOCARRIER events 2177 - 1 (enabled) - Clear the ARP cache on NOCARRIER events 2178 2179 Default: 1 (enabled) 2180 2181mcast_solicit - INTEGER 2182 The maximum number of multicast probes in INCOMPLETE state, 2183 when the associated hardware address is unknown. Defaults 2184 to 3. 2185 2186ucast_solicit - INTEGER 2187 The maximum number of unicast probes in PROBE state, when 2188 the hardware address is being reconfirmed. Defaults to 3. 2189 2190app_solicit - INTEGER 2191 The maximum number of probes to send to the user space ARP daemon 2192 via netlink before dropping back to multicast probes (see 2193 mcast_resolicit). Defaults to 0. 2194 2195mcast_resolicit - INTEGER 2196 The maximum number of multicast probes after unicast and 2197 app probes in PROBE state. Defaults to 0. 2198 2199disable_policy - BOOLEAN 2200 Disable IPSEC policy (SPD) for this interface 2201 2202 Possible values: 2203 2204 - 0 (disabled) 2205 - 1 (enabled) 2206 2207 Default: 0 (disabled) 2208 2209disable_xfrm - BOOLEAN 2210 Disable IPSEC encryption on this interface, whatever the policy 2211 2212 Possible values: 2213 2214 - 0 (disabled) 2215 - 1 (enabled) 2216 2217 Default: 0 (disabled) 2218 2219igmpv2_unsolicited_report_interval - INTEGER 2220 The interval in milliseconds in which the next unsolicited 2221 IGMPv1 or IGMPv2 report retransmit will take place. 2222 2223 Default: 10000 (10 seconds) 2224 2225igmpv3_unsolicited_report_interval - INTEGER 2226 The interval in milliseconds in which the next unsolicited 2227 IGMPv3 report retransmit will take place. 2228 2229 Default: 1000 (1 seconds) 2230 2231ignore_routes_with_linkdown - BOOLEAN 2232 Ignore routes whose link is down when performing a FIB lookup. 2233 2234 Possible values: 2235 2236 - 0 (disabled) 2237 - 1 (enabled) 2238 2239 Default: 0 (disabled) 2240 2241promote_secondaries - BOOLEAN 2242 When a primary IP address is removed from this interface 2243 promote a corresponding secondary IP address instead of 2244 removing all the corresponding secondary IP addresses. 2245 2246 Possible values: 2247 2248 - 0 (disabled) 2249 - 1 (enabled) 2250 2251 Default: 0 (disabled) 2252 2253drop_unicast_in_l2_multicast - BOOLEAN 2254 Drop any unicast IP packets that are received in link-layer 2255 multicast (or broadcast) frames. 2256 2257 This behavior (for multicast) is actually a SHOULD in RFC 2258 1122, but is disabled by default for compatibility reasons. 2259 2260 Possible values: 2261 2262 - 0 (disabled) 2263 - 1 (enabled) 2264 2265 Default: 0 (disabled) 2266 2267drop_gratuitous_arp - BOOLEAN 2268 Drop all gratuitous ARP frames, for example if there's a known 2269 good ARP proxy on the network and such frames need not be used 2270 (or in the case of 802.11, must not be used to prevent attacks.) 2271 2272 Possible values: 2273 2274 - 0 (disabled) 2275 - 1 (enabled) 2276 2277 Default: 0 (disabled) 2278 2279 2280tag - INTEGER 2281 Allows you to write a number, which can be used as required. 2282 2283 Default value is 0. 2284 2285xfrm4_gc_thresh - INTEGER 2286 (Obsolete since linux-4.14) 2287 The threshold at which we will start garbage collecting for IPv4 2288 destination cache entries. At twice this value the system will 2289 refuse new allocations. 2290 2291igmp_link_local_mcast_reports - BOOLEAN 2292 Enable IGMP reports for link local multicast groups in the 2293 224.0.0.X range. 2294 2295 Default TRUE 2296 2297Alexey Kuznetsov. 2298kuznet@ms2.inr.ac.ru 2299 2300Updated by: 2301 2302- Andi Kleen 2303 ak@muc.de 2304- Nicolas Delon 2305 delon.nicolas@wanadoo.fr 2306 2307 2308 2309 2310/proc/sys/net/ipv6/* Variables 2311============================== 2312 2313IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also 2314apply to IPv6 [XXX?]. 2315 2316bindv6only - BOOLEAN 2317 Default value for IPV6_V6ONLY socket option, 2318 which restricts use of the IPv6 socket to IPv6 communication 2319 only. 2320 2321 Possible values: 2322 2323 - 0 (disabled) - enable IPv4-mapped address feature 2324 - 1 (enabled) - disable IPv4-mapped address feature 2325 2326 Default: 0 (disabled) 2327 2328flowlabel_consistency - BOOLEAN 2329 Protect the consistency (and unicity) of flow label. 2330 You have to disable it to use IPV6_FL_F_REFLECT flag on the 2331 flow label manager. 2332 2333 Possible values: 2334 2335 - 0 (disabled) 2336 - 1 (enabled) 2337 2338 Default: 1 (enabled) 2339 2340auto_flowlabels - INTEGER 2341 Automatically generate flow labels based on a flow hash of the 2342 packet. This allows intermediate devices, such as routers, to 2343 identify packet flows for mechanisms like Equal Cost Multipath 2344 Routing (see RFC 6438). 2345 2346 = =========================================================== 2347 0 automatic flow labels are completely disabled 2348 1 automatic flow labels are enabled by default, they can be 2349 disabled on a per socket basis using the IPV6_AUTOFLOWLABEL 2350 socket option 2351 2 automatic flow labels are allowed, they may be enabled on a 2352 per socket basis using the IPV6_AUTOFLOWLABEL socket option 2353 3 automatic flow labels are enabled and enforced, they cannot 2354 be disabled by the socket option 2355 = =========================================================== 2356 2357 Default: 1 2358 2359flowlabel_state_ranges - BOOLEAN 2360 Split the flow label number space into two ranges. 0-0x7FFFF is 2361 reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF 2362 is reserved for stateless flow labels as described in RFC6437. 2363 2364 Possible values: 2365 2366 - 0 (disabled) 2367 - 1 (enabled) 2368 2369 Default: 1 (enabled) 2370 2371 2372flowlabel_reflect - INTEGER 2373 Control flow label reflection. Needed for Path MTU 2374 Discovery to work with Equal Cost Multipath Routing in anycast 2375 environments. See RFC 7690 and: 2376 https://tools.ietf.org/html/draft-wang-6man-flow-label-reflection-01 2377 2378 This is a bitmask. 2379 2380 - 1: enabled for established flows 2381 2382 Note that this prevents automatic flowlabel changes, as done 2383 in "tcp: change IPv6 flow-label upon receiving spurious retransmission" 2384 and "tcp: Change txhash on every SYN and RTO retransmit" 2385 2386 - 2: enabled for TCP RESET packets (no active listener) 2387 If set, a RST packet sent in response to a SYN packet on a closed 2388 port will reflect the incoming flow label. 2389 2390 - 4: enabled for ICMPv6 echo reply messages. 2391 2392 Default: 0 2393 2394fib_multipath_hash_policy - INTEGER 2395 Controls which hash policy to use for multipath routes. 2396 2397 Default: 0 (Layer 3) 2398 2399 Possible values: 2400 2401 - 0 - Layer 3 (source and destination addresses plus flow label) 2402 - 1 - Layer 4 (standard 5-tuple) 2403 - 2 - Layer 3 or inner Layer 3 if present 2404 - 3 - Custom multipath hash. Fields used for multipath hash calculation 2405 are determined by fib_multipath_hash_fields sysctl 2406 2407fib_multipath_hash_fields - UNSIGNED INTEGER 2408 When fib_multipath_hash_policy is set to 3 (custom multipath hash), the 2409 fields used for multipath hash calculation are determined by this 2410 sysctl. 2411 2412 This value is a bitmask which enables various fields for multipath hash 2413 calculation. 2414 2415 Possible fields are: 2416 2417 ====== ============================ 2418 0x0001 Source IP address 2419 0x0002 Destination IP address 2420 0x0004 IP protocol 2421 0x0008 Flow Label 2422 0x0010 Source port 2423 0x0020 Destination port 2424 0x0040 Inner source IP address 2425 0x0080 Inner destination IP address 2426 0x0100 Inner IP protocol 2427 0x0200 Inner Flow Label 2428 0x0400 Inner source port 2429 0x0800 Inner destination port 2430 ====== ============================ 2431 2432 Default: 0x0007 (source IP, destination IP and IP protocol) 2433 2434anycast_src_echo_reply - BOOLEAN 2435 Controls the use of anycast addresses as source addresses for ICMPv6 2436 echo reply 2437 2438 Possible values: 2439 2440 - 0 (disabled) 2441 - 1 (enabled) 2442 2443 Default: 0 (disabled) 2444 2445 2446idgen_delay - INTEGER 2447 Controls the delay in seconds after which time to retry 2448 privacy stable address generation if a DAD conflict is 2449 detected. 2450 2451 Default: 1 (as specified in RFC7217) 2452 2453idgen_retries - INTEGER 2454 Controls the number of retries to generate a stable privacy 2455 address if a DAD conflict is detected. 2456 2457 Default: 3 (as specified in RFC7217) 2458 2459mld_qrv - INTEGER 2460 Controls the MLD query robustness variable (see RFC3810 9.1). 2461 2462 Default: 2 (as specified by RFC3810 9.1) 2463 2464 Minimum: 1 (as specified by RFC6636 4.5) 2465 2466max_dst_opts_number - INTEGER 2467 Maximum number of non-padding TLVs allowed in a Destination 2468 options extension header. If this value is less than zero 2469 then unknown options are disallowed and the number of known 2470 TLVs allowed is the absolute value of this number. 2471 2472 Default: 8 2473 2474max_hbh_opts_number - INTEGER 2475 Maximum number of non-padding TLVs allowed in a Hop-by-Hop 2476 options extension header. If this value is less than zero 2477 then unknown options are disallowed and the number of known 2478 TLVs allowed is the absolute value of this number. 2479 2480 Default: 8 2481 2482max_dst_opts_length - INTEGER 2483 Maximum length allowed for a Destination options extension 2484 header. 2485 2486 Default: INT_MAX (unlimited) 2487 2488max_hbh_length - INTEGER 2489 Maximum length allowed for a Hop-by-Hop options extension 2490 header. 2491 2492 Default: INT_MAX (unlimited) 2493 2494skip_notify_on_dev_down - BOOLEAN 2495 Controls whether an RTM_DELROUTE message is generated for routes 2496 removed when a device is taken down or deleted. IPv4 does not 2497 generate this message; IPv6 does by default. Setting this sysctl 2498 to true skips the message, making IPv4 and IPv6 on par in relying 2499 on userspace caches to track link events and evict routes. 2500 2501 Possible values: 2502 2503 - 0 (disabled) - generate the message 2504 - 1 (enabled) - skip generating the message 2505 2506 Default: 0 (disabled) 2507 2508nexthop_compat_mode - BOOLEAN 2509 New nexthop API provides a means for managing nexthops independent of 2510 prefixes. Backwards compatibility with old route format is enabled by 2511 default which means route dumps and notifications contain the new 2512 nexthop attribute but also the full, expanded nexthop definition. 2513 Further, updates or deletes of a nexthop configuration generate route 2514 notifications for each fib entry using the nexthop. Once a system 2515 understands the new API, this sysctl can be disabled to achieve full 2516 performance benefits of the new API by disabling the nexthop expansion 2517 and extraneous notifications. 2518 2519 Note that as a backward-compatible mode, dumping of modern features 2520 might be incomplete or wrong. For example, resilient groups will not be 2521 shown as such, but rather as just a list of next hops. Also weights that 2522 do not fit into 8 bits will show incorrectly. 2523 2524 Default: true (backward compat mode) 2525 2526fib_notify_on_flag_change - INTEGER 2527 Whether to emit RTM_NEWROUTE notifications whenever RTM_F_OFFLOAD/ 2528 RTM_F_TRAP/RTM_F_OFFLOAD_FAILED flags are changed. 2529 2530 After installing a route to the kernel, user space receives an 2531 acknowledgment, which means the route was installed in the kernel, 2532 but not necessarily in hardware. 2533 It is also possible for a route already installed in hardware to change 2534 its action and therefore its flags. For example, a host route that is 2535 trapping packets can be "promoted" to perform decapsulation following 2536 the installation of an IPinIP/VXLAN tunnel. 2537 The notifications will indicate to user-space the state of the route. 2538 2539 Default: 0 (Do not emit notifications.) 2540 2541 Possible values: 2542 2543 - 0 - Do not emit notifications. 2544 - 1 - Emit notifications. 2545 - 2 - Emit notifications only for RTM_F_OFFLOAD_FAILED flag change. 2546 2547ioam6_id - INTEGER 2548 Define the IOAM id of this node. Uses only 24 bits out of 32 in total. 2549 2550 Possible value range: 2551 2552 - Min: 0 2553 - Max: 0xFFFFFF 2554 2555 Default: 0xFFFFFF 2556 2557ioam6_id_wide - LONG INTEGER 2558 Define the wide IOAM id of this node. Uses only 56 bits out of 64 in 2559 total. Can be different from ioam6_id. 2560 2561 Possible value range: 2562 2563 - Min: 0 2564 - Max: 0xFFFFFFFFFFFFFF 2565 2566 Default: 0xFFFFFFFFFFFFFF 2567 2568IPv6 Fragmentation: 2569 2570ip6frag_high_thresh - INTEGER 2571 Maximum memory used to reassemble IPv6 fragments. When 2572 ip6frag_high_thresh bytes of memory is allocated for this purpose, 2573 the fragment handler will toss packets until ip6frag_low_thresh 2574 is reached. 2575 2576ip6frag_low_thresh - INTEGER 2577 See ip6frag_high_thresh 2578 2579ip6frag_time - INTEGER 2580 Time in seconds to keep an IPv6 fragment in memory. 2581 2582``conf/default/*``: 2583 Change the interface-specific default settings. 2584 2585 These settings would be used during creating new interfaces. 2586 2587 2588``conf/all/*``: 2589 Change all the interface-specific settings. 2590 2591 [XXX: Other special features than forwarding?] 2592 2593conf/all/disable_ipv6 - BOOLEAN 2594 Changing this value is same as changing ``conf/default/disable_ipv6`` 2595 setting and also all per-interface ``disable_ipv6`` settings to the same 2596 value. 2597 2598 Reading this value does not have any particular meaning. It does not say 2599 whether IPv6 support is enabled or disabled. Returned value can be 1 2600 also in the case when some interface has ``disable_ipv6`` set to 0 and 2601 has configured IPv6 addresses. 2602 2603conf/all/forwarding - BOOLEAN 2604 Enable global IPv6 forwarding between all interfaces. 2605 2606 IPv4 and IPv6 work differently here; the ``force_forwarding`` flag must 2607 be used to control which interfaces may forward packets. 2608 2609 This also sets all interfaces' Host/Router setting 2610 'forwarding' to the specified value. See below for details. 2611 2612 This referred to as global forwarding. 2613 2614proxy_ndp - BOOLEAN 2615 Do proxy ndp. 2616 2617 Possible values: 2618 2619 - 0 (disabled) 2620 - 1 (enabled) 2621 2622 Default: 0 (disabled) 2623 2624force_forwarding - BOOLEAN 2625 Enable forwarding on this interface only -- regardless of the setting on 2626 ``conf/all/forwarding``. When setting ``conf.all.forwarding`` to 0, 2627 the ``force_forwarding`` flag will be reset on all interfaces. 2628 2629fwmark_reflect - BOOLEAN 2630 Controls the fwmark of kernel-generated IPv6 reply packets that are not 2631 associated with a socket for example, TCP RSTs or ICMPv6 echo replies). 2632 If disabled, these packets have a fwmark of zero. If enabled, they have the 2633 fwmark of the packet they are replying to. 2634 2635 Possible values: 2636 2637 - 0 (disabled) 2638 - 1 (enabled) 2639 2640 Default: 0 (disabled) 2641 2642``conf/interface/*``: 2643 Change special settings per interface. 2644 2645 The functional behaviour for certain settings is different 2646 depending on whether local forwarding is enabled or not. 2647 2648accept_ra - INTEGER 2649 Accept Router Advertisements; autoconfigure using them. 2650 2651 It also determines whether or not to transmit Router 2652 Solicitations. If and only if the functional setting is to 2653 accept Router Advertisements, Router Solicitations will be 2654 transmitted. 2655 2656 Possible values are: 2657 2658 == =========================================================== 2659 0 Do not accept Router Advertisements. 2660 1 Accept Router Advertisements if forwarding is disabled. 2661 2 Overrule forwarding behaviour. Accept Router Advertisements 2662 even if forwarding is enabled. 2663 == =========================================================== 2664 2665 Functional default: 2666 2667 - enabled if local forwarding is disabled. 2668 - disabled if local forwarding is enabled. 2669 2670accept_ra_defrtr - BOOLEAN 2671 Learn default router in Router Advertisement. 2672 2673 Functional default: 2674 2675 - enabled if accept_ra is enabled. 2676 - disabled if accept_ra is disabled. 2677 2678ra_defrtr_metric - UNSIGNED INTEGER 2679 Route metric for default route learned in Router Advertisement. This value 2680 will be assigned as metric for the default route learned via IPv6 Router 2681 Advertisement. Takes affect only if accept_ra_defrtr is enabled. 2682 2683 Possible values: 2684 1 to 0xFFFFFFFF 2685 2686 Default: IP6_RT_PRIO_USER i.e. 1024. 2687 2688accept_ra_from_local - BOOLEAN 2689 Accept RA with source-address that is found on local machine 2690 if the RA is otherwise proper and able to be accepted. 2691 2692 Default is to NOT accept these as it may be an un-intended 2693 network loop. 2694 2695 Functional default: 2696 2697 - enabled if accept_ra_from_local is enabled 2698 on a specific interface. 2699 - disabled if accept_ra_from_local is disabled 2700 on a specific interface. 2701 2702accept_ra_min_hop_limit - INTEGER 2703 Minimum hop limit Information in Router Advertisement. 2704 2705 Hop limit Information in Router Advertisement less than this 2706 variable shall be ignored. 2707 2708 Default: 1 2709 2710accept_ra_min_lft - INTEGER 2711 Minimum acceptable lifetime value in Router Advertisement. 2712 2713 RA sections with a lifetime less than this value shall be 2714 ignored. Zero lifetimes stay unaffected. 2715 2716 Default: 0 2717 2718accept_ra_pinfo - BOOLEAN 2719 Learn Prefix Information in Router Advertisement. 2720 2721 Functional default: 2722 2723 - enabled if accept_ra is enabled. 2724 - disabled if accept_ra is disabled. 2725 2726ra_honor_pio_life - BOOLEAN 2727 Whether to use RFC4862 Section 5.5.3e to determine the valid 2728 lifetime of an address matching a prefix sent in a Router 2729 Advertisement Prefix Information Option. 2730 2731 Possible values: 2732 2733 - 0 (disabled) - RFC4862 section 5.5.3e is used to determine 2734 the valid lifetime of the address. 2735 - 1 (enabled) - the PIO valid lifetime will always be honored. 2736 2737 Default: 0 (disabled) 2738 2739ra_honor_pio_pflag - BOOLEAN 2740 The Prefix Information Option P-flag indicates the network can 2741 allocate a unique IPv6 prefix per client using DHCPv6-PD. 2742 This sysctl can be enabled when a userspace DHCPv6-PD client 2743 is running to cause the P-flag to take effect: i.e. the 2744 P-flag suppresses any effects of the A-flag within the same 2745 PIO. For a given PIO, P=1 and A=1 is treated as A=0. 2746 2747 Possible values: 2748 2749 - 0 (disabled) - the P-flag is ignored. 2750 - 1 (enabled) - the P-flag will disable SLAAC autoconfiguration 2751 for the given Prefix Information Option. 2752 2753 Default: 0 (disabled) 2754 2755accept_ra_rt_info_min_plen - INTEGER 2756 Minimum prefix length of Route Information in RA. 2757 2758 Route Information w/ prefix smaller than this variable shall 2759 be ignored. 2760 2761 Functional default: 2762 2763 * 0 if accept_ra_rtr_pref is enabled. 2764 * -1 if accept_ra_rtr_pref is disabled. 2765 2766accept_ra_rt_info_max_plen - INTEGER 2767 Maximum prefix length of Route Information in RA. 2768 2769 Route Information w/ prefix larger than this variable shall 2770 be ignored. 2771 2772 Functional default: 2773 2774 * 0 if accept_ra_rtr_pref is enabled. 2775 * -1 if accept_ra_rtr_pref is disabled. 2776 2777accept_ra_rtr_pref - BOOLEAN 2778 Accept Router Preference in RA. 2779 2780 Functional default: 2781 2782 - enabled if accept_ra is enabled. 2783 - disabled if accept_ra is disabled. 2784 2785accept_ra_mtu - BOOLEAN 2786 Apply the MTU value specified in RA option 5 (RFC4861). If 2787 disabled, the MTU specified in the RA will be ignored. 2788 2789 Functional default: 2790 2791 - enabled if accept_ra is enabled. 2792 - disabled if accept_ra is disabled. 2793 2794accept_redirects - BOOLEAN 2795 Accept Redirects. 2796 2797 Functional default: 2798 2799 - enabled if local forwarding is disabled. 2800 - disabled if local forwarding is enabled. 2801 2802accept_source_route - INTEGER 2803 Accept source routing (routing extension header). 2804 2805 - >= 0: Accept only routing header type 2. 2806 - < 0: Do not accept routing header. 2807 2808 Default: 0 2809 2810autoconf - BOOLEAN 2811 Autoconfigure addresses using Prefix Information in Router 2812 Advertisements. 2813 2814 Functional default: 2815 2816 - enabled if accept_ra_pinfo is enabled. 2817 - disabled if accept_ra_pinfo is disabled. 2818 2819dad_transmits - INTEGER 2820 The amount of Duplicate Address Detection probes to send. 2821 2822 Default: 1 2823 2824forwarding - INTEGER 2825 Configure interface-specific Host/Router behaviour. 2826 2827 .. note:: 2828 2829 It is recommended to have the same setting on all 2830 interfaces; mixed router/host scenarios are rather uncommon. 2831 2832 Possible values are: 2833 2834 - 0 Forwarding disabled 2835 - 1 Forwarding enabled 2836 2837 **FALSE (0)**: 2838 2839 By default, Host behaviour is assumed. This means: 2840 2841 1. IsRouter flag is not set in Neighbour Advertisements. 2842 2. If accept_ra is TRUE (default), transmit Router 2843 Solicitations. 2844 3. If accept_ra is TRUE (default), accept Router 2845 Advertisements (and do autoconfiguration). 2846 4. If accept_redirects is TRUE (default), accept Redirects. 2847 2848 **TRUE (1)**: 2849 2850 If local forwarding is enabled, Router behaviour is assumed. 2851 This means exactly the reverse from the above: 2852 2853 1. IsRouter flag is set in Neighbour Advertisements. 2854 2. Router Solicitations are not sent unless accept_ra is 2. 2855 3. Router Advertisements are ignored unless accept_ra is 2. 2856 4. Redirects are ignored. 2857 2858 Default: 0 (disabled) if global forwarding is disabled (default), 2859 otherwise 1 (enabled). 2860 2861hop_limit - INTEGER 2862 Default Hop Limit to set. 2863 2864 Default: 64 2865 2866mtu - INTEGER 2867 Default Maximum Transfer Unit 2868 2869 Default: 1280 (IPv6 required minimum) 2870 2871ip_nonlocal_bind - BOOLEAN 2872 If enabled, allows processes to bind() to non-local IPv6 addresses, 2873 which can be quite useful - but may break some applications. 2874 2875 Possible values: 2876 2877 - 0 (disabled) 2878 - 1 (enabled) 2879 2880 Default: 0 (disabled) 2881 2882router_probe_interval - INTEGER 2883 Minimum interval (in seconds) between Router Probing described 2884 in RFC4191. 2885 2886 Default: 60 2887 2888router_solicitation_delay - INTEGER 2889 Number of seconds to wait after interface is brought up 2890 before sending Router Solicitations. 2891 2892 Default: 1 2893 2894router_solicitation_interval - INTEGER 2895 Number of seconds to wait between Router Solicitations. 2896 2897 Default: 4 2898 2899router_solicitations - INTEGER 2900 Number of Router Solicitations to send until assuming no 2901 routers are present. 2902 2903 Default: 3 2904 2905use_oif_addrs_only - BOOLEAN 2906 When enabled, the candidate source addresses for destinations 2907 routed via this interface are restricted to the set of addresses 2908 configured on this interface (vis. RFC 6724, section 4). 2909 2910 Possible values: 2911 2912 - 0 (disabled) 2913 - 1 (enabled) 2914 2915 Default: 0 (disabled) 2916 2917use_tempaddr - INTEGER 2918 Preference for Privacy Extensions (RFC3041). 2919 2920 * <= 0 : disable Privacy Extensions 2921 * == 1 : enable Privacy Extensions, but prefer public 2922 addresses over temporary addresses. 2923 * > 1 : enable Privacy Extensions and prefer temporary 2924 addresses over public addresses. 2925 2926 Default: 2927 2928 * 0 (for most devices) 2929 * -1 (for point-to-point devices and loopback devices) 2930 2931temp_valid_lft - INTEGER 2932 valid lifetime (in seconds) for temporary addresses. If less than the 2933 minimum required lifetime (typically 5-7 seconds), temporary addresses 2934 will not be created. 2935 2936 Default: 172800 (2 days) 2937 2938temp_prefered_lft - INTEGER 2939 Preferred lifetime (in seconds) for temporary addresses. If 2940 temp_prefered_lft is less than the minimum required lifetime (typically 2941 5-7 seconds), the preferred lifetime is the minimum required. If 2942 temp_prefered_lft is greater than temp_valid_lft, the preferred lifetime 2943 is temp_valid_lft. 2944 2945 Default: 86400 (1 day) 2946 2947keep_addr_on_down - INTEGER 2948 Keep all IPv6 addresses on an interface down event. If set static 2949 global addresses with no expiration time are not flushed. 2950 2951 * >0 : enabled 2952 * 0 : system default 2953 * <0 : disabled 2954 2955 Default: 0 (addresses are removed) 2956 2957max_desync_factor - INTEGER 2958 Maximum value for DESYNC_FACTOR, which is a random value 2959 that ensures that clients don't synchronize with each 2960 other and generate new addresses at exactly the same time. 2961 value is in seconds. 2962 2963 Default: 600 2964 2965regen_min_advance - INTEGER 2966 How far in advance (in seconds), at minimum, to create a new temporary 2967 address before the current one is deprecated. This value is added to 2968 the amount of time that may be required for duplicate address detection 2969 to determine when to create a new address. Linux permits setting this 2970 value to less than the default of 2 seconds, but a value less than 2 2971 does not conform to RFC 8981. 2972 2973 Default: 2 2974 2975regen_max_retry - INTEGER 2976 Number of attempts before give up attempting to generate 2977 valid temporary addresses. 2978 2979 Default: 5 2980 2981max_addresses - INTEGER 2982 Maximum number of autoconfigured addresses per interface. Setting 2983 to zero disables the limitation. It is not recommended to set this 2984 value too large (or to zero) because it would be an easy way to 2985 crash the kernel by allowing too many addresses to be created. 2986 2987 Default: 16 2988 2989disable_ipv6 - BOOLEAN 2990 Disable IPv6 operation. If accept_dad is set to 2, this value 2991 will be dynamically set to TRUE if DAD fails for the link-local 2992 address. 2993 2994 Default: FALSE (enable IPv6 operation) 2995 2996 When this value is changed from 1 to 0 (IPv6 is being enabled), 2997 it will dynamically create a link-local address on the given 2998 interface and start Duplicate Address Detection, if necessary. 2999 3000 When this value is changed from 0 to 1 (IPv6 is being disabled), 3001 it will dynamically delete all addresses and routes on the given 3002 interface. From now on it will not possible to add addresses/routes 3003 to the selected interface. 3004 3005accept_dad - INTEGER 3006 Whether to accept DAD (Duplicate Address Detection). 3007 3008 == ============================================================== 3009 0 Disable DAD 3010 1 Enable DAD (default) 3011 2 Enable DAD, and disable IPv6 operation if MAC-based duplicate 3012 link-local address has been found. 3013 == ============================================================== 3014 3015 DAD operation and mode on a given interface will be selected according 3016 to the maximum value of conf/{all,interface}/accept_dad. 3017 3018force_tllao - BOOLEAN 3019 Enable sending the target link-layer address option even when 3020 responding to a unicast neighbor solicitation. 3021 3022 Default: FALSE 3023 3024 Quoting from RFC 2461, section 4.4, Target link-layer address: 3025 3026 "The option MUST be included for multicast solicitations in order to 3027 avoid infinite Neighbor Solicitation "recursion" when the peer node 3028 does not have a cache entry to return a Neighbor Advertisements 3029 message. When responding to unicast solicitations, the option can be 3030 omitted since the sender of the solicitation has the correct link- 3031 layer address; otherwise it would not have be able to send the unicast 3032 solicitation in the first place. However, including the link-layer 3033 address in this case adds little overhead and eliminates a potential 3034 race condition where the sender deletes the cached link-layer address 3035 prior to receiving a response to a previous solicitation." 3036 3037ndisc_notify - BOOLEAN 3038 Define mode for notification of address and device changes. 3039 3040 Possible values: 3041 3042 - 0 (disabled) - do nothing 3043 - 1 (enabled) - Generate unsolicited neighbour advertisements when device is brought 3044 up or hardware address changes. 3045 3046 Default: 0 (disabled) 3047 3048ndisc_tclass - INTEGER 3049 The IPv6 Traffic Class to use by default when sending IPv6 Neighbor 3050 Discovery (Router Solicitation, Router Advertisement, Neighbor 3051 Solicitation, Neighbor Advertisement, Redirect) messages. 3052 These 8 bits can be interpreted as 6 high order bits holding the DSCP 3053 value and 2 low order bits representing ECN (which you probably want 3054 to leave cleared). 3055 3056 * 0 - (default) 3057 3058ndisc_evict_nocarrier - BOOLEAN 3059 Clears the neighbor discovery table on NOCARRIER events. This option is 3060 important for wireless devices where the neighbor discovery cache should 3061 not be cleared when roaming between access points on the same network. 3062 In most cases this should remain as the default (1). 3063 3064 Possible values: 3065 3066 - 0 (disabled) - Do not clear neighbor discovery cache on NOCARRIER events. 3067 - 1 (enabled) - Clear neighbor discover cache on NOCARRIER events. 3068 3069 Default: 1 (enabled) 3070 3071mldv1_unsolicited_report_interval - INTEGER 3072 The interval in milliseconds in which the next unsolicited 3073 MLDv1 report retransmit will take place. 3074 3075 Default: 10000 (10 seconds) 3076 3077mldv2_unsolicited_report_interval - INTEGER 3078 The interval in milliseconds in which the next unsolicited 3079 MLDv2 report retransmit will take place. 3080 3081 Default: 1000 (1 second) 3082 3083force_mld_version - INTEGER 3084 * 0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed 3085 * 1 - Enforce to use MLD version 1 3086 * 2 - Enforce to use MLD version 2 3087 3088suppress_frag_ndisc - INTEGER 3089 Control RFC 6980 (Security Implications of IPv6 Fragmentation 3090 with IPv6 Neighbor Discovery) behavior: 3091 3092 * 1 - (default) discard fragmented neighbor discovery packets 3093 * 0 - allow fragmented neighbor discovery packets 3094 3095optimistic_dad - BOOLEAN 3096 Whether to perform Optimistic Duplicate Address Detection (RFC 4429). 3097 3098 Optimistic Duplicate Address Detection for the interface will be enabled 3099 if at least one of conf/{all,interface}/optimistic_dad is set to 1, 3100 it will be disabled otherwise. 3101 3102 Possible values: 3103 3104 - 0 (disabled) 3105 - 1 (enabled) 3106 3107 Default: 0 (disabled) 3108 3109 3110use_optimistic - BOOLEAN 3111 If enabled, do not classify optimistic addresses as deprecated during 3112 source address selection. Preferred addresses will still be chosen 3113 before optimistic addresses, subject to other ranking in the source 3114 address selection algorithm. 3115 3116 This will be enabled if at least one of 3117 conf/{all,interface}/use_optimistic is set to 1, disabled otherwise. 3118 3119 Possible values: 3120 3121 - 0 (disabled) 3122 - 1 (enabled) 3123 3124 Default: 0 (disabled) 3125 3126stable_secret - IPv6 address 3127 This IPv6 address will be used as a secret to generate IPv6 3128 addresses for link-local addresses and autoconfigured 3129 ones. All addresses generated after setting this secret will 3130 be stable privacy ones by default. This can be changed via the 3131 addrgenmode ip-link. conf/default/stable_secret is used as the 3132 secret for the namespace, the interface specific ones can 3133 overwrite that. Writes to conf/all/stable_secret are refused. 3134 3135 It is recommended to generate this secret during installation 3136 of a system and keep it stable after that. 3137 3138 By default the stable secret is unset. 3139 3140addr_gen_mode - INTEGER 3141 Defines how link-local and autoconf addresses are generated. 3142 3143 = ================================================================= 3144 0 generate address based on EUI64 (default) 3145 1 do no generate a link-local address, use EUI64 for addresses 3146 generated from autoconf 3147 2 generate stable privacy addresses, using the secret from 3148 stable_secret (RFC7217) 3149 3 generate stable privacy addresses, using a random secret if unset 3150 = ================================================================= 3151 3152drop_unicast_in_l2_multicast - BOOLEAN 3153 Drop any unicast IPv6 packets that are received in link-layer 3154 multicast (or broadcast) frames. 3155 3156 Possible values: 3157 3158 - 0 (disabled) 3159 - 1 (enabled) 3160 3161 Default: 0 (disabled) 3162 3163drop_unsolicited_na - BOOLEAN 3164 Drop all unsolicited neighbor advertisements, for example if there's 3165 a known good NA proxy on the network and such frames need not be used 3166 (or in the case of 802.11, must not be used to prevent attacks.) 3167 3168 Possible values: 3169 3170 - 0 (disabled) 3171 - 1 (enabled) 3172 3173 Default: 0 (disabled). 3174 3175accept_untracked_na - INTEGER 3176 Define behavior for accepting neighbor advertisements from devices that 3177 are absent in the neighbor cache: 3178 3179 - 0 - (default) Do not accept unsolicited and untracked neighbor 3180 advertisements. 3181 3182 - 1 - Add a new neighbor cache entry in STALE state for routers on 3183 receiving a neighbor advertisement (either solicited or unsolicited) 3184 with target link-layer address option specified if no neighbor entry 3185 is already present for the advertised IPv6 address. Without this knob, 3186 NAs received for untracked addresses (absent in neighbor cache) are 3187 silently ignored. 3188 3189 This is as per router-side behavior documented in RFC9131. 3190 3191 This has lower precedence than drop_unsolicited_na. 3192 3193 This will optimize the return path for the initial off-link 3194 communication that is initiated by a directly connected host, by 3195 ensuring that the first-hop router which turns on this setting doesn't 3196 have to buffer the initial return packets to do neighbor-solicitation. 3197 The prerequisite is that the host is configured to send unsolicited 3198 neighbor advertisements on interface bringup. This setting should be 3199 used in conjunction with the ndisc_notify setting on the host to 3200 satisfy this prerequisite. 3201 3202 - 2 - Extend option (1) to add a new neighbor cache entry only if the 3203 source IP address is in the same subnet as an address configured on 3204 the interface that received the neighbor advertisement. 3205 3206enhanced_dad - BOOLEAN 3207 Include a nonce option in the IPv6 neighbor solicitation messages used for 3208 duplicate address detection per RFC7527. A received DAD NS will only signal 3209 a duplicate address if the nonce is different. This avoids any false 3210 detection of duplicates due to loopback of the NS messages that we send. 3211 The nonce option will be sent on an interface unless both of 3212 conf/{all,interface}/enhanced_dad are set to FALSE. 3213 3214 Possible values: 3215 3216 - 0 (disabled) 3217 - 1 (enabled) 3218 3219 Default: 1 (enabled) 3220 3221``icmp/*``: 3222=========== 3223 3224ratelimit - INTEGER 3225 Limit the maximal rates for sending ICMPv6 messages. 3226 3227 0 to disable any limiting, 3228 otherwise the minimal space between responses in milliseconds. 3229 3230 Default: 1000 3231 3232ratemask - list of comma separated ranges 3233 For ICMPv6 message types matching the ranges in the ratemask, limit 3234 the sending of the message according to ratelimit parameter. 3235 3236 The format used for both input and output is a comma separated 3237 list of ranges (e.g. "0-127,129" for ICMPv6 message type 0 to 127 and 3238 129). Writing to the file will clear all previous ranges of ICMPv6 3239 message types and update the current list with the input. 3240 3241 Refer to: https://www.iana.org/assignments/icmpv6-parameters/icmpv6-parameters.xhtml 3242 for numerical values of ICMPv6 message types, e.g. echo request is 128 3243 and echo reply is 129. 3244 3245 Default: 0-1,3-127 (rate limit ICMPv6 errors except Packet Too Big) 3246 3247echo_ignore_all - BOOLEAN 3248 If enabled, then the kernel will ignore all ICMP ECHO 3249 requests sent to it over the IPv6 protocol. 3250 3251 Possible values: 3252 3253 - 0 (disabled) 3254 - 1 (enabled) 3255 3256 Default: 0 (disabled) 3257 3258echo_ignore_multicast - BOOLEAN 3259 If enabled, then the kernel will ignore all ICMP ECHO 3260 requests sent to it over the IPv6 protocol via multicast. 3261 3262 Possible values: 3263 3264 - 0 (disabled) 3265 - 1 (enabled) 3266 3267 Default: 0 (disabled) 3268 3269echo_ignore_anycast - BOOLEAN 3270 If enabled, then the kernel will ignore all ICMP ECHO 3271 requests sent to it over the IPv6 protocol destined to anycast address. 3272 3273 Possible values: 3274 3275 - 0 (disabled) 3276 - 1 (enabled) 3277 3278 Default: 0 (disabled) 3279 3280error_anycast_as_unicast - BOOLEAN 3281 If enabled, then the kernel will respond with ICMP Errors 3282 resulting from requests sent to it over the IPv6 protocol destined 3283 to anycast address essentially treating anycast as unicast. 3284 3285 Possible values: 3286 3287 - 0 (disabled) 3288 - 1 (enabled) 3289 3290 Default: 0 (disabled) 3291 3292errors_extension_mask - UNSIGNED INTEGER 3293 Bitmask of ICMP extensions to append to ICMPv6 error messages 3294 ("Destination Unreachable" and "Time Exceeded"). The original datagram 3295 is trimmed / padded to 128 bytes in order to be compatible with 3296 applications that do not comply with RFC 4884. 3297 3298 Possible extensions are: 3299 3300 ==== ============================================================== 3301 0x01 Incoming IP interface information according to RFC 5837. 3302 Extension will include the index, IPv6 address (if present), 3303 name and MTU of the IP interface that received the datagram 3304 which elicited the ICMP error. 3305 ==== ============================================================== 3306 3307 Default: 0x00 (no extensions) 3308 3309xfrm6_gc_thresh - INTEGER 3310 (Obsolete since linux-4.14) 3311 The threshold at which we will start garbage collecting for IPv6 3312 destination cache entries. At twice this value the system will 3313 refuse new allocations. 3314 3315 3316IPv6 Update by: 3317Pekka Savola <pekkas@netcore.fi> 3318YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org> 3319 3320 3321/proc/sys/net/bridge/* Variables: 3322================================= 3323 3324bridge-nf-call-arptables - BOOLEAN 3325 3326 Possible values: 3327 3328 - 0 (disabled) - disable this. 3329 - 1 (enabled) - pass bridged ARP traffic to arptables' FORWARD chain. 3330 3331 Default: 1 (enabled) 3332 3333bridge-nf-call-iptables - BOOLEAN 3334 3335 Possible values: 3336 3337 - 0 (disabled) - disable this. 3338 - 1 (enabled) - pass bridged IPv4 traffic to iptables' chains. 3339 3340 Default: 1 (enabled) 3341 3342bridge-nf-call-ip6tables - BOOLEAN 3343 3344 Possible values: 3345 3346 - 0 (disabled) - disable this. 3347 - 1 (enabled) - pass bridged IPv6 traffic to ip6tables' chains. 3348 3349 Default: 1 (enabled) 3350 3351bridge-nf-filter-vlan-tagged - BOOLEAN 3352 3353 Possible values: 3354 3355 - 0 (disabled) - disable this. 3356 - 1 (enabled) - pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables 3357 3358 Default: 0 (disabled) 3359 3360bridge-nf-filter-pppoe-tagged - BOOLEAN 3361 3362 Possible values: 3363 3364 - 0 (disabled) - disable this. 3365 - 1 (enabled) - pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables. 3366 3367 Default: 0 (disabled) 3368 3369bridge-nf-pass-vlan-input-dev - BOOLEAN 3370 - 1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan 3371 interface on the bridge and set the netfilter input device to the 3372 vlan. This allows use of e.g. "iptables -i br0.1" and makes the 3373 REDIRECT target work with vlan-on-top-of-bridge interfaces. When no 3374 matching vlan interface is found, or this switch is off, the input 3375 device is set to the bridge interface. 3376 3377 - 0: disable bridge netfilter vlan interface lookup. 3378 3379 Default: 0 3380 3381``proc/sys/net/sctp/*`` Variables: 3382================================== 3383 3384addip_enable - BOOLEAN 3385 Enable or disable extension of Dynamic Address Reconfiguration 3386 (ADD-IP) functionality specified in RFC5061. This extension provides 3387 the ability to dynamically add and remove new addresses for the SCTP 3388 associations. 3389 3390 Possible values: 3391 3392 - 0 (disabled) - disable extension. 3393 - 1 (enabled) - enable extension 3394 3395 Default: 0 (disabled) 3396 3397pf_enable - INTEGER 3398 Enable or disable pf (pf is short for potentially failed) state. A value 3399 of pf_retrans > path_max_retrans also disables pf state. That is, one of 3400 both pf_enable and pf_retrans > path_max_retrans can disable pf state. 3401 Since pf_retrans and path_max_retrans can be changed by userspace 3402 application, sometimes user expects to disable pf state by the value of 3403 pf_retrans > path_max_retrans, but occasionally the value of pf_retrans 3404 or path_max_retrans is changed by the user application, this pf state is 3405 enabled. As such, it is necessary to add this to dynamically enable 3406 and disable pf state. See: 3407 https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover for 3408 details. 3409 3410 Possible values: 3411 3412 - 1: Enable pf. 3413 - 0: Disable pf. 3414 3415 Default: 1 3416 3417pf_expose - INTEGER 3418 Unset or enable/disable pf (pf is short for potentially failed) state 3419 exposure. Applications can control the exposure of the PF path state 3420 in the SCTP_PEER_ADDR_CHANGE event and access of SCTP_PF-state 3421 transport info via SCTP_GET_PEER_ADDR_INFO sockopt. 3422 3423 Possible values: 3424 3425 - 0: Unset pf state exposure (compatible with old applications). No 3426 event will be sent but the transport info can be queried. 3427 - 1: Disable pf state exposure. No event will be sent and trying to 3428 obtain transport info will return -EACCESS. 3429 - 2: Enable pf state exposure. The event will be sent for a transport 3430 becoming SCTP_PF state and transport info can be obtained. 3431 3432 Default: 0 3433 3434addip_noauth_enable - BOOLEAN 3435 Dynamic Address Reconfiguration (ADD-IP) requires the use of 3436 authentication to protect the operations of adding or removing new 3437 addresses. This requirement is mandated so that unauthorized hosts 3438 would not be able to hijack associations. However, older 3439 implementations may not have implemented this requirement while 3440 allowing the ADD-IP extension. For reasons of interoperability, 3441 we provide this variable to control the enforcement of the 3442 authentication requirement. 3443 3444 == =============================================================== 3445 1 Allow ADD-IP extension to be used without authentication. This 3446 should only be set in a closed environment for interoperability 3447 with older implementations. 3448 3449 0 Enforce the authentication requirement 3450 == =============================================================== 3451 3452 Default: 0 3453 3454auth_enable - BOOLEAN 3455 Enable or disable Authenticated Chunks extension. This extension 3456 provides the ability to send and receive authenticated chunks and is 3457 required for secure operation of Dynamic Address Reconfiguration 3458 (ADD-IP) extension. 3459 3460 Possible values: 3461 3462 - 0 (disabled) - disable extension. 3463 - 1 (enabled) - enable extension 3464 3465 Default: 0 (disabled) 3466 3467prsctp_enable - BOOLEAN 3468 Enable or disable the Partial Reliability extension (RFC3758) which 3469 is used to notify peers that a given DATA should no longer be expected. 3470 3471 Possible values: 3472 3473 - 0 (disabled) - disable extension. 3474 - 1 (enabled) - enable extension 3475 3476 Default: 1 (enabled) 3477 3478max_burst - INTEGER 3479 The limit of the number of new packets that can be initially sent. It 3480 controls how bursty the generated traffic can be. 3481 3482 Default: 4 3483 3484association_max_retrans - INTEGER 3485 Set the maximum number for retransmissions that an association can 3486 attempt deciding that the remote end is unreachable. If this value 3487 is exceeded, the association is terminated. 3488 3489 Default: 10 3490 3491max_init_retransmits - INTEGER 3492 The maximum number of retransmissions of INIT and COOKIE-ECHO chunks 3493 that an association will attempt before declaring the destination 3494 unreachable and terminating. 3495 3496 Default: 8 3497 3498path_max_retrans - INTEGER 3499 The maximum number of retransmissions that will be attempted on a given 3500 path. Once this threshold is exceeded, the path is considered 3501 unreachable, and new traffic will use a different path when the 3502 association is multihomed. 3503 3504 Default: 5 3505 3506pf_retrans - INTEGER 3507 The number of retransmissions that will be attempted on a given path 3508 before traffic is redirected to an alternate transport (should one 3509 exist). Note this is distinct from path_max_retrans, as a path that 3510 passes the pf_retrans threshold can still be used. Its only 3511 deprioritized when a transmission path is selected by the stack. This 3512 setting is primarily used to enable fast failover mechanisms without 3513 having to reduce path_max_retrans to a very low value. See: 3514 http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt 3515 for details. Note also that a value of pf_retrans > path_max_retrans 3516 disables this feature. Since both pf_retrans and path_max_retrans can 3517 be changed by userspace application, a variable pf_enable is used to 3518 disable pf state. 3519 3520 Default: 0 3521 3522ps_retrans - INTEGER 3523 Primary.Switchover.Max.Retrans (PSMR), it's a tunable parameter coming 3524 from section-5 "Primary Path Switchover" in rfc7829. The primary path 3525 will be changed to another active path when the path error counter on 3526 the old primary path exceeds PSMR, so that "the SCTP sender is allowed 3527 to continue data transmission on a new working path even when the old 3528 primary destination address becomes active again". Note this feature 3529 is disabled by initializing 'ps_retrans' per netns as 0xffff by default, 3530 and its value can't be less than 'pf_retrans' when changing by sysctl. 3531 3532 Default: 0xffff 3533 3534rto_initial - INTEGER 3535 The initial round trip timeout value in milliseconds that will be used 3536 in calculating round trip times. This is the initial time interval 3537 for retransmissions. 3538 3539 Default: 3000 3540 3541rto_max - INTEGER 3542 The maximum value (in milliseconds) of the round trip timeout. This 3543 is the largest time interval that can elapse between retransmissions. 3544 3545 Default: 60000 3546 3547rto_min - INTEGER 3548 The minimum value (in milliseconds) of the round trip timeout. This 3549 is the smallest time interval the can elapse between retransmissions. 3550 3551 Default: 1000 3552 3553hb_interval - INTEGER 3554 The interval (in milliseconds) between HEARTBEAT chunks. These chunks 3555 are sent at the specified interval on idle paths to probe the state of 3556 a given path between 2 associations. 3557 3558 Default: 30000 3559 3560sack_timeout - INTEGER 3561 The amount of time (in milliseconds) that the implementation will wait 3562 to send a SACK. 3563 3564 Default: 200 3565 3566valid_cookie_life - INTEGER 3567 The default lifetime of the SCTP cookie (in milliseconds). The cookie 3568 is used during association establishment. 3569 3570 Default: 60000 3571 3572cookie_preserve_enable - BOOLEAN 3573 Enable or disable the ability to extend the lifetime of the SCTP cookie 3574 that is used during the establishment phase of SCTP association 3575 3576 Possible values: 3577 3578 - 0 (disabled) - disable. 3579 - 1 (enabled) - enable cookie lifetime extension. 3580 3581 Default: 1 (enabled) 3582 3583cookie_hmac_alg - STRING 3584 Select the hmac algorithm used when generating the cookie value sent by 3585 a listening sctp socket to a connecting client in the INIT-ACK chunk. 3586 Valid values are: 3587 3588 * sha256 3589 * none 3590 3591 Default: sha256 3592 3593rcvbuf_policy - INTEGER 3594 Determines if the receive buffer is attributed to the socket or to 3595 association. SCTP supports the capability to create multiple 3596 associations on a single socket. When using this capability, it is 3597 possible that a single stalled association that's buffering a lot 3598 of data may block other associations from delivering their data by 3599 consuming all of the receive buffer space. To work around this, 3600 the rcvbuf_policy could be set to attribute the receiver buffer space 3601 to each association instead of the socket. This prevents the described 3602 blocking. 3603 3604 - 1: rcvbuf space is per association 3605 - 0: rcvbuf space is per socket 3606 3607 Default: 0 3608 3609sndbuf_policy - INTEGER 3610 Similar to rcvbuf_policy above, this applies to send buffer space. 3611 3612 - 1: Send buffer is tracked per association 3613 - 0: Send buffer is tracked per socket. 3614 3615 Default: 0 3616 3617sctp_mem - vector of 3 INTEGERs: min, pressure, max 3618 Number of pages allowed for queueing by all SCTP sockets. 3619 3620 * min: Below this number of pages SCTP is not bothered about its 3621 memory usage. When amount of memory allocated by SCTP exceeds 3622 this number, SCTP starts to moderate memory usage. 3623 * pressure: This value was introduced to follow format of tcp_mem. 3624 * max: Maximum number of allowed pages. 3625 3626 Default is calculated at boot time from amount of available memory. 3627 3628sctp_rmem - vector of 3 INTEGERs: min, default, max 3629 Only the first value ("min") is used, "default" and "max" are 3630 ignored. 3631 3632 * min: Minimal size of receive buffer used by SCTP socket. 3633 It is guaranteed to each SCTP socket (but not association) even 3634 under moderate memory pressure. 3635 3636 Default: 4K 3637 3638sctp_wmem - vector of 3 INTEGERs: min, default, max 3639 Only the first value ("min") is used, "default" and "max" are 3640 ignored. 3641 3642 * min: Minimum size of send buffer that can be used by SCTP sockets. 3643 It is guaranteed to each SCTP socket (but not association) even 3644 under moderate memory pressure. 3645 3646 Default: 4K 3647 3648addr_scope_policy - INTEGER 3649 Control IPv4 address scoping (see 3650 https://datatracker.ietf.org/doc/draft-stewart-tsvwg-sctp-ipv4/00/ 3651 for details). 3652 3653 - 0 - Disable IPv4 address scoping 3654 - 1 - Enable IPv4 address scoping 3655 - 2 - Follow draft but allow IPv4 private addresses 3656 - 3 - Follow draft but allow IPv4 link local addresses 3657 3658 Default: 1 3659 3660udp_port - INTEGER 3661 The listening port for the local UDP tunneling sock. Normally it's 3662 using the IANA-assigned UDP port number 9899 (sctp-tunneling). 3663 3664 This UDP sock is used for processing the incoming UDP-encapsulated 3665 SCTP packets (from RFC6951), and shared by all applications in the 3666 same net namespace. This UDP sock will be closed when the value is 3667 set to 0. 3668 3669 The value will also be used to set the src port of the UDP header 3670 for the outgoing UDP-encapsulated SCTP packets. For the dest port, 3671 please refer to 'encap_port' below. 3672 3673 Default: 0 3674 3675encap_port - INTEGER 3676 The default remote UDP encapsulation port. 3677 3678 This value is used to set the dest port of the UDP header for the 3679 outgoing UDP-encapsulated SCTP packets by default. Users can also 3680 change the value for each sock/asoc/transport by using setsockopt. 3681 For further information, please refer to RFC6951. 3682 3683 Note that when connecting to a remote server, the client should set 3684 this to the port that the UDP tunneling sock on the peer server is 3685 listening to and the local UDP tunneling sock on the client also 3686 must be started. On the server, it would get the encap_port from 3687 the incoming packet's source port. 3688 3689 Default: 0 3690 3691plpmtud_probe_interval - INTEGER 3692 The time interval (in milliseconds) for the PLPMTUD probe timer, 3693 which is configured to expire after this period to receive an 3694 acknowledgment to a probe packet. This is also the time interval 3695 between the probes for the current pmtu when the probe search 3696 is done. 3697 3698 PLPMTUD will be disabled when 0 is set, and other values for it 3699 must be >= 5000. 3700 3701 Default: 0 3702 3703reconf_enable - BOOLEAN 3704 Enable or disable extension of Stream Reconfiguration functionality 3705 specified in RFC6525. This extension provides the ability to "reset" 3706 a stream, and it includes the Parameters of "Outgoing/Incoming SSN 3707 Reset", "SSN/TSN Reset" and "Add Outgoing/Incoming Streams". 3708 3709 Possible values: 3710 3711 - 0 (disabled) - Disable extension. 3712 - 1 (enabled) - Enable extension. 3713 3714 Default: 0 (disabled) 3715 3716intl_enable - BOOLEAN 3717 Enable or disable extension of User Message Interleaving functionality 3718 specified in RFC8260. This extension allows the interleaving of user 3719 messages sent on different streams. With this feature enabled, I-DATA 3720 chunk will replace DATA chunk to carry user messages if also supported 3721 by the peer. Note that to use this feature, one needs to set this option 3722 to 1 and also needs to set socket options SCTP_FRAGMENT_INTERLEAVE to 2 3723 and SCTP_INTERLEAVING_SUPPORTED to 1. 3724 3725 Possible values: 3726 3727 - 0 (disabled) - Disable extension. 3728 - 1 (enabled) - Enable extension. 3729 3730 Default: 0 (disabled) 3731 3732ecn_enable - BOOLEAN 3733 Control use of Explicit Congestion Notification (ECN) by SCTP. 3734 Like in TCP, ECN is used only when both ends of the SCTP connection 3735 indicate support for it. This feature is useful in avoiding losses 3736 due to congestion by allowing supporting routers to signal congestion 3737 before having to drop packets. 3738 3739 Possible values: 3740 3741 - 0 (disabled) - Disable ecn. 3742 - 1 (enabled) - Enable ecn. 3743 3744 Default: 1 (enabled) 3745 3746l3mdev_accept - BOOLEAN 3747 Enabling this option allows a "global" bound socket to work 3748 across L3 master domains (e.g., VRFs) with packets capable of 3749 being received regardless of the L3 domain in which they 3750 originated. Only valid when the kernel was compiled with 3751 CONFIG_NET_L3_MASTER_DEV. 3752 3753 Possible values: 3754 3755 - 0 (disabled) 3756 - 1 (enabled) 3757 3758 Default: 1 (enabled) 3759 3760 3761``/proc/sys/net/core/*`` 3762======================== 3763 3764 Please see: Documentation/admin-guide/sysctl/net.rst for descriptions of these entries. 3765 3766 3767``/proc/sys/net/unix/*`` 3768======================== 3769 3770max_dgram_qlen - INTEGER 3771 The maximum length of dgram socket receive queue 3772 3773 Default: 10 3774 3775