1.. SPDX-License-Identifier: GPL-2.0 2 3========= 4IP Sysctl 5========= 6 7/proc/sys/net/ipv4/* Variables 8============================== 9 10ip_forward - BOOLEAN 11 - 0 - disabled (default) 12 - not 0 - enabled 13 14 Forward Packets between interfaces. 15 16 This variable is special, its change resets all configuration 17 parameters to their default state (RFC1122 for hosts, RFC1812 18 for routers) 19 20ip_default_ttl - INTEGER 21 Default value of TTL field (Time To Live) for outgoing (but not 22 forwarded) IP packets. Should be between 1 and 255 inclusive. 23 Default: 64 (as recommended by RFC1700) 24 25ip_no_pmtu_disc - INTEGER 26 Disable Path MTU Discovery. If enabled in mode 1 and a 27 fragmentation-required ICMP is received, the PMTU to this 28 destination will be set to min_pmtu (see below). You will need 29 to raise min_pmtu to the smallest interface MTU on your system 30 manually if you want to avoid locally generated fragments. 31 32 In mode 2 incoming Path MTU Discovery messages will be 33 discarded. Outgoing frames are handled the same as in mode 1, 34 implicitly setting IP_PMTUDISC_DONT on every created socket. 35 36 Mode 3 is a hardened pmtu discover mode. The kernel will only 37 accept fragmentation-needed errors if the underlying protocol 38 can verify them besides a plain socket lookup. Current 39 protocols for which pmtu events will be honored are TCP, SCTP 40 and DCCP as they verify e.g. the sequence number or the 41 association. This mode should not be enabled globally but is 42 only intended to secure e.g. name servers in namespaces where 43 TCP path mtu must still work but path MTU information of other 44 protocols should be discarded. If enabled globally this mode 45 could break other protocols. 46 47 Possible values: 0-3 48 49 Default: FALSE 50 51min_pmtu - INTEGER 52 default 552 - minimum discovered Path MTU 53 54ip_forward_use_pmtu - BOOLEAN 55 By default we don't trust protocol path MTUs while forwarding 56 because they could be easily forged and can lead to unwanted 57 fragmentation by the router. 58 You only need to enable this if you have user-space software 59 which tries to discover path mtus by itself and depends on the 60 kernel honoring this information. This is normally not the 61 case. 62 63 Default: 0 (disabled) 64 65 Possible values: 66 67 - 0 - disabled 68 - 1 - enabled 69 70fwmark_reflect - BOOLEAN 71 Controls the fwmark of kernel-generated IPv4 reply packets that are not 72 associated with a socket for example, TCP RSTs or ICMP echo replies). 73 If unset, these packets have a fwmark of zero. If set, they have the 74 fwmark of the packet they are replying to. 75 76 Default: 0 77 78fib_multipath_use_neigh - BOOLEAN 79 Use status of existing neighbor entry when determining nexthop for 80 multipath routes. If disabled, neighbor information is not used and 81 packets could be directed to a failed nexthop. Only valid for kernels 82 built with CONFIG_IP_ROUTE_MULTIPATH enabled. 83 84 Default: 0 (disabled) 85 86 Possible values: 87 88 - 0 - disabled 89 - 1 - enabled 90 91fib_multipath_hash_policy - INTEGER 92 Controls which hash policy to use for multipath routes. Only valid 93 for kernels built with CONFIG_IP_ROUTE_MULTIPATH enabled. 94 95 Default: 0 (Layer 3) 96 97 Possible values: 98 99 - 0 - Layer 3 100 - 1 - Layer 4 101 - 2 - Layer 3 or inner Layer 3 if present 102 103fib_sync_mem - UNSIGNED INTEGER 104 Amount of dirty memory from fib entries that can be backlogged before 105 synchronize_rcu is forced. 106 107 Default: 512kB Minimum: 64kB Maximum: 64MB 108 109ip_forward_update_priority - INTEGER 110 Whether to update SKB priority from "TOS" field in IPv4 header after it 111 is forwarded. The new SKB priority is mapped from TOS field value 112 according to an rt_tos2priority table (see e.g. man tc-prio). 113 114 Default: 1 (Update priority.) 115 116 Possible values: 117 118 - 0 - Do not update priority. 119 - 1 - Update priority. 120 121route/max_size - INTEGER 122 Maximum number of routes allowed in the kernel. Increase 123 this when using large numbers of interfaces and/or routes. 124 125 From linux kernel 3.6 onwards, this is deprecated for ipv4 126 as route cache is no longer used. 127 128neigh/default/gc_thresh1 - INTEGER 129 Minimum number of entries to keep. Garbage collector will not 130 purge entries if there are fewer than this number. 131 132 Default: 128 133 134neigh/default/gc_thresh2 - INTEGER 135 Threshold when garbage collector becomes more aggressive about 136 purging entries. Entries older than 5 seconds will be cleared 137 when over this number. 138 139 Default: 512 140 141neigh/default/gc_thresh3 - INTEGER 142 Maximum number of non-PERMANENT neighbor entries allowed. Increase 143 this when using large numbers of interfaces and when communicating 144 with large numbers of directly-connected peers. 145 146 Default: 1024 147 148neigh/default/unres_qlen_bytes - INTEGER 149 The maximum number of bytes which may be used by packets 150 queued for each unresolved address by other network layers. 151 (added in linux 3.3) 152 153 Setting negative value is meaningless and will return error. 154 155 Default: SK_WMEM_MAX, (same as net.core.wmem_default). 156 157 Exact value depends on architecture and kernel options, 158 but should be enough to allow queuing 256 packets 159 of medium size. 160 161neigh/default/unres_qlen - INTEGER 162 The maximum number of packets which may be queued for each 163 unresolved address by other network layers. 164 165 (deprecated in linux 3.3) : use unres_qlen_bytes instead. 166 167 Prior to linux 3.3, the default value is 3 which may cause 168 unexpected packet loss. The current default value is calculated 169 according to default value of unres_qlen_bytes and true size of 170 packet. 171 172 Default: 101 173 174mtu_expires - INTEGER 175 Time, in seconds, that cached PMTU information is kept. 176 177min_adv_mss - INTEGER 178 The advertised MSS depends on the first hop route MTU, but will 179 never be lower than this setting. 180 181fib_notify_on_flag_change - INTEGER 182 Whether to emit RTM_NEWROUTE notifications whenever RTM_F_OFFLOAD/ 183 RTM_F_TRAP/RTM_F_OFFLOAD_FAILED flags are changed. 184 185 After installing a route to the kernel, user space receives an 186 acknowledgment, which means the route was installed in the kernel, 187 but not necessarily in hardware. 188 It is also possible for a route already installed in hardware to change 189 its action and therefore its flags. For example, a host route that is 190 trapping packets can be "promoted" to perform decapsulation following 191 the installation of an IPinIP/VXLAN tunnel. 192 The notifications will indicate to user-space the state of the route. 193 194 Default: 0 (Do not emit notifications.) 195 196 Possible values: 197 198 - 0 - Do not emit notifications. 199 - 1 - Emit notifications. 200 - 2 - Emit notifications only for RTM_F_OFFLOAD_FAILED flag change. 201 202IP Fragmentation: 203 204ipfrag_high_thresh - LONG INTEGER 205 Maximum memory used to reassemble IP fragments. 206 207ipfrag_low_thresh - LONG INTEGER 208 (Obsolete since linux-4.17) 209 Maximum memory used to reassemble IP fragments before the kernel 210 begins to remove incomplete fragment queues to free up resources. 211 The kernel still accepts new fragments for defragmentation. 212 213ipfrag_time - INTEGER 214 Time in seconds to keep an IP fragment in memory. 215 216ipfrag_max_dist - INTEGER 217 ipfrag_max_dist is a non-negative integer value which defines the 218 maximum "disorder" which is allowed among fragments which share a 219 common IP source address. Note that reordering of packets is 220 not unusual, but if a large number of fragments arrive from a source 221 IP address while a particular fragment queue remains incomplete, it 222 probably indicates that one or more fragments belonging to that queue 223 have been lost. When ipfrag_max_dist is positive, an additional check 224 is done on fragments before they are added to a reassembly queue - if 225 ipfrag_max_dist (or more) fragments have arrived from a particular IP 226 address between additions to any IP fragment queue using that source 227 address, it's presumed that one or more fragments in the queue are 228 lost. The existing fragment queue will be dropped, and a new one 229 started. An ipfrag_max_dist value of zero disables this check. 230 231 Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can 232 result in unnecessarily dropping fragment queues when normal 233 reordering of packets occurs, which could lead to poor application 234 performance. Using a very large value, e.g. 50000, increases the 235 likelihood of incorrectly reassembling IP fragments that originate 236 from different IP datagrams, which could result in data corruption. 237 Default: 64 238 239INET peer storage 240================= 241 242inet_peer_threshold - INTEGER 243 The approximate size of the storage. Starting from this threshold 244 entries will be thrown aggressively. This threshold also determines 245 entries' time-to-live and time intervals between garbage collection 246 passes. More entries, less time-to-live, less GC interval. 247 248inet_peer_minttl - INTEGER 249 Minimum time-to-live of entries. Should be enough to cover fragment 250 time-to-live on the reassembling side. This minimum time-to-live is 251 guaranteed if the pool size is less than inet_peer_threshold. 252 Measured in seconds. 253 254inet_peer_maxttl - INTEGER 255 Maximum time-to-live of entries. Unused entries will expire after 256 this period of time if there is no memory pressure on the pool (i.e. 257 when the number of entries in the pool is very small). 258 Measured in seconds. 259 260TCP variables 261============= 262 263somaxconn - INTEGER 264 Limit of socket listen() backlog, known in userspace as SOMAXCONN. 265 Defaults to 4096. (Was 128 before linux-5.4) 266 See also tcp_max_syn_backlog for additional tuning for TCP sockets. 267 268tcp_abort_on_overflow - BOOLEAN 269 If listening service is too slow to accept new connections, 270 reset them. Default state is FALSE. It means that if overflow 271 occurred due to a burst, connection will recover. Enable this 272 option _only_ if you are really sure that listening daemon 273 cannot be tuned to accept connections faster. Enabling this 274 option can harm clients of your server. 275 276tcp_adv_win_scale - INTEGER 277 Count buffering overhead as bytes/2^tcp_adv_win_scale 278 (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale), 279 if it is <= 0. 280 281 Possible values are [-31, 31], inclusive. 282 283 Default: 1 284 285tcp_allowed_congestion_control - STRING 286 Show/set the congestion control choices available to non-privileged 287 processes. The list is a subset of those listed in 288 tcp_available_congestion_control. 289 290 Default is "reno" and the default setting (tcp_congestion_control). 291 292tcp_app_win - INTEGER 293 Reserve max(window/2^tcp_app_win, mss) of window for application 294 buffer. Value 0 is special, it means that nothing is reserved. 295 296 Default: 31 297 298tcp_autocorking - BOOLEAN 299 Enable TCP auto corking : 300 When applications do consecutive small write()/sendmsg() system calls, 301 we try to coalesce these small writes as much as possible, to lower 302 total amount of sent packets. This is done if at least one prior 303 packet for the flow is waiting in Qdisc queues or device transmit 304 queue. Applications can still use TCP_CORK for optimal behavior 305 when they know how/when to uncork their sockets. 306 307 Default : 1 308 309tcp_available_congestion_control - STRING 310 Shows the available congestion control choices that are registered. 311 More congestion control algorithms may be available as modules, 312 but not loaded. 313 314tcp_base_mss - INTEGER 315 The initial value of search_low to be used by the packetization layer 316 Path MTU discovery (MTU probing). If MTU probing is enabled, 317 this is the initial MSS used by the connection. 318 319tcp_mtu_probe_floor - INTEGER 320 If MTU probing is enabled this caps the minimum MSS used for search_low 321 for the connection. 322 323 Default : 48 324 325tcp_min_snd_mss - INTEGER 326 TCP SYN and SYNACK messages usually advertise an ADVMSS option, 327 as described in RFC 1122 and RFC 6691. 328 329 If this ADVMSS option is smaller than tcp_min_snd_mss, 330 it is silently capped to tcp_min_snd_mss. 331 332 Default : 48 (at least 8 bytes of payload per segment) 333 334tcp_congestion_control - STRING 335 Set the congestion control algorithm to be used for new 336 connections. The algorithm "reno" is always available, but 337 additional choices may be available based on kernel configuration. 338 Default is set as part of kernel configuration. 339 For passive connections, the listener congestion control choice 340 is inherited. 341 342 [see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ] 343 344tcp_dsack - BOOLEAN 345 Allows TCP to send "duplicate" SACKs. 346 347tcp_early_retrans - INTEGER 348 Tail loss probe (TLP) converts RTOs occurring due to tail 349 losses into fast recovery (draft-ietf-tcpm-rack). Note that 350 TLP requires RACK to function properly (see tcp_recovery below) 351 352 Possible values: 353 354 - 0 disables TLP 355 - 3 or 4 enables TLP 356 357 Default: 3 358 359tcp_ecn - INTEGER 360 Control use of Explicit Congestion Notification (ECN) by TCP. 361 ECN is used only when both ends of the TCP connection indicate 362 support for it. This feature is useful in avoiding losses due 363 to congestion by allowing supporting routers to signal 364 congestion before having to drop packets. 365 366 Possible values are: 367 368 = ===================================================== 369 0 Disable ECN. Neither initiate nor accept ECN. 370 1 Enable ECN when requested by incoming connections and 371 also request ECN on outgoing connection attempts. 372 2 Enable ECN when requested by incoming connections 373 but do not request ECN on outgoing connections. 374 = ===================================================== 375 376 Default: 2 377 378tcp_ecn_fallback - BOOLEAN 379 If the kernel detects that ECN connection misbehaves, enable fall 380 back to non-ECN. Currently, this knob implements the fallback 381 from RFC3168, section 6.1.1.1., but we reserve that in future, 382 additional detection mechanisms could be implemented under this 383 knob. The value is not used, if tcp_ecn or per route (or congestion 384 control) ECN settings are disabled. 385 386 Default: 1 (fallback enabled) 387 388tcp_fack - BOOLEAN 389 This is a legacy option, it has no effect anymore. 390 391tcp_fin_timeout - INTEGER 392 The length of time an orphaned (no longer referenced by any 393 application) connection will remain in the FIN_WAIT_2 state 394 before it is aborted at the local end. While a perfectly 395 valid "receive only" state for an un-orphaned connection, an 396 orphaned connection in FIN_WAIT_2 state could otherwise wait 397 forever for the remote to close its end of the connection. 398 399 Cf. tcp_max_orphans 400 401 Default: 60 seconds 402 403tcp_frto - INTEGER 404 Enables Forward RTO-Recovery (F-RTO) defined in RFC5682. 405 F-RTO is an enhanced recovery algorithm for TCP retransmission 406 timeouts. It is particularly beneficial in networks where the 407 RTT fluctuates (e.g., wireless). F-RTO is sender-side only 408 modification. It does not require any support from the peer. 409 410 By default it's enabled with a non-zero value. 0 disables F-RTO. 411 412tcp_fwmark_accept - BOOLEAN 413 If set, incoming connections to listening sockets that do not have a 414 socket mark will set the mark of the accepting socket to the fwmark of 415 the incoming SYN packet. This will cause all packets on that connection 416 (starting from the first SYNACK) to be sent with that fwmark. The 417 listening socket's mark is unchanged. Listening sockets that already 418 have a fwmark set via setsockopt(SOL_SOCKET, SO_MARK, ...) are 419 unaffected. 420 421 Default: 0 422 423tcp_invalid_ratelimit - INTEGER 424 Limit the maximal rate for sending duplicate acknowledgments 425 in response to incoming TCP packets that are for an existing 426 connection but that are invalid due to any of these reasons: 427 428 (a) out-of-window sequence number, 429 (b) out-of-window acknowledgment number, or 430 (c) PAWS (Protection Against Wrapped Sequence numbers) check failure 431 432 This can help mitigate simple "ack loop" DoS attacks, wherein 433 a buggy or malicious middlebox or man-in-the-middle can 434 rewrite TCP header fields in manner that causes each endpoint 435 to think that the other is sending invalid TCP segments, thus 436 causing each side to send an unterminating stream of duplicate 437 acknowledgments for invalid segments. 438 439 Using 0 disables rate-limiting of dupacks in response to 440 invalid segments; otherwise this value specifies the minimal 441 space between sending such dupacks, in milliseconds. 442 443 Default: 500 (milliseconds). 444 445tcp_keepalive_time - INTEGER 446 How often TCP sends out keepalive messages when keepalive is enabled. 447 Default: 2hours. 448 449tcp_keepalive_probes - INTEGER 450 How many keepalive probes TCP sends out, until it decides that the 451 connection is broken. Default value: 9. 452 453tcp_keepalive_intvl - INTEGER 454 How frequently the probes are send out. Multiplied by 455 tcp_keepalive_probes it is time to kill not responding connection, 456 after probes started. Default value: 75sec i.e. connection 457 will be aborted after ~11 minutes of retries. 458 459tcp_l3mdev_accept - BOOLEAN 460 Enables child sockets to inherit the L3 master device index. 461 Enabling this option allows a "global" listen socket to work 462 across L3 master domains (e.g., VRFs) with connected sockets 463 derived from the listen socket to be bound to the L3 domain in 464 which the packets originated. Only valid when the kernel was 465 compiled with CONFIG_NET_L3_MASTER_DEV. 466 467 Default: 0 (disabled) 468 469tcp_low_latency - BOOLEAN 470 This is a legacy option, it has no effect anymore. 471 472tcp_max_orphans - INTEGER 473 Maximal number of TCP sockets not attached to any user file handle, 474 held by system. If this number is exceeded orphaned connections are 475 reset immediately and warning is printed. This limit exists 476 only to prevent simple DoS attacks, you _must_ not rely on this 477 or lower the limit artificially, but rather increase it 478 (probably, after increasing installed memory), 479 if network conditions require more than default value, 480 and tune network services to linger and kill such states 481 more aggressively. Let me to remind again: each orphan eats 482 up to ~64K of unswappable memory. 483 484tcp_max_syn_backlog - INTEGER 485 Maximal number of remembered connection requests (SYN_RECV), 486 which have not received an acknowledgment from connecting client. 487 488 This is a per-listener limit. 489 490 The minimal value is 128 for low memory machines, and it will 491 increase in proportion to the memory of machine. 492 493 If server suffers from overload, try increasing this number. 494 495 Remember to also check /proc/sys/net/core/somaxconn 496 A SYN_RECV request socket consumes about 304 bytes of memory. 497 498tcp_max_tw_buckets - INTEGER 499 Maximal number of timewait sockets held by system simultaneously. 500 If this number is exceeded time-wait socket is immediately destroyed 501 and warning is printed. This limit exists only to prevent 502 simple DoS attacks, you _must_ not lower the limit artificially, 503 but rather increase it (probably, after increasing installed memory), 504 if network conditions require more than default value. 505 506tcp_mem - vector of 3 INTEGERs: min, pressure, max 507 min: below this number of pages TCP is not bothered about its 508 memory appetite. 509 510 pressure: when amount of memory allocated by TCP exceeds this number 511 of pages, TCP moderates its memory consumption and enters memory 512 pressure mode, which is exited when memory consumption falls 513 under "min". 514 515 max: number of pages allowed for queueing by all TCP sockets. 516 517 Defaults are calculated at boot time from amount of available 518 memory. 519 520tcp_min_rtt_wlen - INTEGER 521 The window length of the windowed min filter to track the minimum RTT. 522 A shorter window lets a flow more quickly pick up new (higher) 523 minimum RTT when it is moved to a longer path (e.g., due to traffic 524 engineering). A longer window makes the filter more resistant to RTT 525 inflations such as transient congestion. The unit is seconds. 526 527 Possible values: 0 - 86400 (1 day) 528 529 Default: 300 530 531tcp_moderate_rcvbuf - BOOLEAN 532 If set, TCP performs receive buffer auto-tuning, attempting to 533 automatically size the buffer (no greater than tcp_rmem[2]) to 534 match the size required by the path for full throughput. Enabled by 535 default. 536 537tcp_mtu_probing - INTEGER 538 Controls TCP Packetization-Layer Path MTU Discovery. Takes three 539 values: 540 541 - 0 - Disabled 542 - 1 - Disabled by default, enabled when an ICMP black hole detected 543 - 2 - Always enabled, use initial MSS of tcp_base_mss. 544 545tcp_probe_interval - UNSIGNED INTEGER 546 Controls how often to start TCP Packetization-Layer Path MTU 547 Discovery reprobe. The default is reprobing every 10 minutes as 548 per RFC4821. 549 550tcp_probe_threshold - INTEGER 551 Controls when TCP Packetization-Layer Path MTU Discovery probing 552 will stop in respect to the width of search range in bytes. Default 553 is 8 bytes. 554 555tcp_no_metrics_save - BOOLEAN 556 By default, TCP saves various connection metrics in the route cache 557 when the connection closes, so that connections established in the 558 near future can use these to set initial conditions. Usually, this 559 increases overall performance, but may sometimes cause performance 560 degradation. If set, TCP will not cache metrics on closing 561 connections. 562 563tcp_no_ssthresh_metrics_save - BOOLEAN 564 Controls whether TCP saves ssthresh metrics in the route cache. 565 566 Default is 1, which disables ssthresh metrics. 567 568tcp_orphan_retries - INTEGER 569 This value influences the timeout of a locally closed TCP connection, 570 when RTO retransmissions remain unacknowledged. 571 See tcp_retries2 for more details. 572 573 The default value is 8. 574 575 If your machine is a loaded WEB server, 576 you should think about lowering this value, such sockets 577 may consume significant resources. Cf. tcp_max_orphans. 578 579tcp_recovery - INTEGER 580 This value is a bitmap to enable various experimental loss recovery 581 features. 582 583 ========= ============================================================= 584 RACK: 0x1 enables the RACK loss detection for fast detection of lost 585 retransmissions and tail drops. It also subsumes and disables 586 RFC6675 recovery for SACK connections. 587 588 RACK: 0x2 makes RACK's reordering window static (min_rtt/4). 589 590 RACK: 0x4 disables RACK's DUPACK threshold heuristic 591 ========= ============================================================= 592 593 Default: 0x1 594 595tcp_reordering - INTEGER 596 Initial reordering level of packets in a TCP stream. 597 TCP stack can then dynamically adjust flow reordering level 598 between this initial value and tcp_max_reordering 599 600 Default: 3 601 602tcp_max_reordering - INTEGER 603 Maximal reordering level of packets in a TCP stream. 604 300 is a fairly conservative value, but you might increase it 605 if paths are using per packet load balancing (like bonding rr mode) 606 607 Default: 300 608 609tcp_retrans_collapse - BOOLEAN 610 Bug-to-bug compatibility with some broken printers. 611 On retransmit try to send bigger packets to work around bugs in 612 certain TCP stacks. 613 614tcp_retries1 - INTEGER 615 This value influences the time, after which TCP decides, that 616 something is wrong due to unacknowledged RTO retransmissions, 617 and reports this suspicion to the network layer. 618 See tcp_retries2 for more details. 619 620 RFC 1122 recommends at least 3 retransmissions, which is the 621 default. 622 623tcp_retries2 - INTEGER 624 This value influences the timeout of an alive TCP connection, 625 when RTO retransmissions remain unacknowledged. 626 Given a value of N, a hypothetical TCP connection following 627 exponential backoff with an initial RTO of TCP_RTO_MIN would 628 retransmit N times before killing the connection at the (N+1)th RTO. 629 630 The default value of 15 yields a hypothetical timeout of 924.6 631 seconds and is a lower bound for the effective timeout. 632 TCP will effectively time out at the first RTO which exceeds the 633 hypothetical timeout. 634 635 RFC 1122 recommends at least 100 seconds for the timeout, 636 which corresponds to a value of at least 8. 637 638tcp_rfc1337 - BOOLEAN 639 If set, the TCP stack behaves conforming to RFC1337. If unset, 640 we are not conforming to RFC, but prevent TCP TIME_WAIT 641 assassination. 642 643 Default: 0 644 645tcp_rmem - vector of 3 INTEGERs: min, default, max 646 min: Minimal size of receive buffer used by TCP sockets. 647 It is guaranteed to each TCP socket, even under moderate memory 648 pressure. 649 650 Default: 4K 651 652 default: initial size of receive buffer used by TCP sockets. 653 This value overrides net.core.rmem_default used by other protocols. 654 Default: 131072 bytes. 655 This value results in initial window of 65535. 656 657 max: maximal size of receive buffer allowed for automatically 658 selected receiver buffers for TCP socket. This value does not override 659 net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables 660 automatic tuning of that socket's receive buffer size, in which 661 case this value is ignored. 662 Default: between 131072 and 6MB, depending on RAM size. 663 664tcp_sack - BOOLEAN 665 Enable select acknowledgments (SACKS). 666 667tcp_comp_sack_delay_ns - LONG INTEGER 668 TCP tries to reduce number of SACK sent, using a timer 669 based on 5% of SRTT, capped by this sysctl, in nano seconds. 670 The default is 1ms, based on TSO autosizing period. 671 672 Default : 1,000,000 ns (1 ms) 673 674tcp_comp_sack_slack_ns - LONG INTEGER 675 This sysctl control the slack used when arming the 676 timer used by SACK compression. This gives extra time 677 for small RTT flows, and reduces system overhead by allowing 678 opportunistic reduction of timer interrupts. 679 680 Default : 100,000 ns (100 us) 681 682tcp_comp_sack_nr - INTEGER 683 Max number of SACK that can be compressed. 684 Using 0 disables SACK compression. 685 686 Default : 44 687 688tcp_slow_start_after_idle - BOOLEAN 689 If set, provide RFC2861 behavior and time out the congestion 690 window after an idle period. An idle period is defined at 691 the current RTO. If unset, the congestion window will not 692 be timed out after an idle period. 693 694 Default: 1 695 696tcp_stdurg - BOOLEAN 697 Use the Host requirements interpretation of the TCP urgent pointer field. 698 Most hosts use the older BSD interpretation, so if you turn this on 699 Linux might not communicate correctly with them. 700 701 Default: FALSE 702 703tcp_synack_retries - INTEGER 704 Number of times SYNACKs for a passive TCP connection attempt will 705 be retransmitted. Should not be higher than 255. Default value 706 is 5, which corresponds to 31seconds till the last retransmission 707 with the current initial RTO of 1second. With this the final timeout 708 for a passive TCP connection will happen after 63seconds. 709 710tcp_syncookies - INTEGER 711 Only valid when the kernel was compiled with CONFIG_SYN_COOKIES 712 Send out syncookies when the syn backlog queue of a socket 713 overflows. This is to prevent against the common 'SYN flood attack' 714 Default: 1 715 716 Note, that syncookies is fallback facility. 717 It MUST NOT be used to help highly loaded servers to stand 718 against legal connection rate. If you see SYN flood warnings 719 in your logs, but investigation shows that they occur 720 because of overload with legal connections, you should tune 721 another parameters until this warning disappear. 722 See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow. 723 724 syncookies seriously violate TCP protocol, do not allow 725 to use TCP extensions, can result in serious degradation 726 of some services (f.e. SMTP relaying), visible not by you, 727 but your clients and relays, contacting you. While you see 728 SYN flood warnings in logs not being really flooded, your server 729 is seriously misconfigured. 730 731 If you want to test which effects syncookies have to your 732 network connections you can set this knob to 2 to enable 733 unconditionally generation of syncookies. 734 735tcp_fastopen - INTEGER 736 Enable TCP Fast Open (RFC7413) to send and accept data in the opening 737 SYN packet. 738 739 The client support is enabled by flag 0x1 (on by default). The client 740 then must use sendmsg() or sendto() with the MSG_FASTOPEN flag, 741 rather than connect() to send data in SYN. 742 743 The server support is enabled by flag 0x2 (off by default). Then 744 either enable for all listeners with another flag (0x400) or 745 enable individual listeners via TCP_FASTOPEN socket option with 746 the option value being the length of the syn-data backlog. 747 748 The values (bitmap) are 749 750 ===== ======== ====================================================== 751 0x1 (client) enables sending data in the opening SYN on the client. 752 0x2 (server) enables the server support, i.e., allowing data in 753 a SYN packet to be accepted and passed to the 754 application before 3-way handshake finishes. 755 0x4 (client) send data in the opening SYN regardless of cookie 756 availability and without a cookie option. 757 0x200 (server) accept data-in-SYN w/o any cookie option present. 758 0x400 (server) enable all listeners to support Fast Open by 759 default without explicit TCP_FASTOPEN socket option. 760 ===== ======== ====================================================== 761 762 Default: 0x1 763 764 Note that additional client or server features are only 765 effective if the basic support (0x1 and 0x2) are enabled respectively. 766 767tcp_fastopen_blackhole_timeout_sec - INTEGER 768 Initial time period in second to disable Fastopen on active TCP sockets 769 when a TFO firewall blackhole issue happens. 770 This time period will grow exponentially when more blackhole issues 771 get detected right after Fastopen is re-enabled and will reset to 772 initial value when the blackhole issue goes away. 773 0 to disable the blackhole detection. 774 775 By default, it is set to 1hr. 776 777tcp_fastopen_key - list of comma separated 32-digit hexadecimal INTEGERs 778 The list consists of a primary key and an optional backup key. The 779 primary key is used for both creating and validating cookies, while the 780 optional backup key is only used for validating cookies. The purpose of 781 the backup key is to maximize TFO validation when keys are rotated. 782 783 A randomly chosen primary key may be configured by the kernel if 784 the tcp_fastopen sysctl is set to 0x400 (see above), or if the 785 TCP_FASTOPEN setsockopt() optname is set and a key has not been 786 previously configured via sysctl. If keys are configured via 787 setsockopt() by using the TCP_FASTOPEN_KEY optname, then those 788 per-socket keys will be used instead of any keys that are specified via 789 sysctl. 790 791 A key is specified as 4 8-digit hexadecimal integers which are separated 792 by a '-' as: xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx. Leading zeros may be 793 omitted. A primary and a backup key may be specified by separating them 794 by a comma. If only one key is specified, it becomes the primary key and 795 any previously configured backup keys are removed. 796 797tcp_syn_retries - INTEGER 798 Number of times initial SYNs for an active TCP connection attempt 799 will be retransmitted. Should not be higher than 127. Default value 800 is 6, which corresponds to 63seconds till the last retransmission 801 with the current initial RTO of 1second. With this the final timeout 802 for an active TCP connection attempt will happen after 127seconds. 803 804tcp_timestamps - INTEGER 805 Enable timestamps as defined in RFC1323. 806 807 - 0: Disabled. 808 - 1: Enable timestamps as defined in RFC1323 and use random offset for 809 each connection rather than only using the current time. 810 - 2: Like 1, but without random offsets. 811 812 Default: 1 813 814tcp_min_tso_segs - INTEGER 815 Minimal number of segments per TSO frame. 816 817 Since linux-3.12, TCP does an automatic sizing of TSO frames, 818 depending on flow rate, instead of filling 64Kbytes packets. 819 For specific usages, it's possible to force TCP to build big 820 TSO frames. Note that TCP stack might split too big TSO packets 821 if available window is too small. 822 823 Default: 2 824 825tcp_pacing_ss_ratio - INTEGER 826 sk->sk_pacing_rate is set by TCP stack using a ratio applied 827 to current rate. (current_rate = cwnd * mss / srtt) 828 If TCP is in slow start, tcp_pacing_ss_ratio is applied 829 to let TCP probe for bigger speeds, assuming cwnd can be 830 doubled every other RTT. 831 832 Default: 200 833 834tcp_pacing_ca_ratio - INTEGER 835 sk->sk_pacing_rate is set by TCP stack using a ratio applied 836 to current rate. (current_rate = cwnd * mss / srtt) 837 If TCP is in congestion avoidance phase, tcp_pacing_ca_ratio 838 is applied to conservatively probe for bigger throughput. 839 840 Default: 120 841 842tcp_tso_win_divisor - INTEGER 843 This allows control over what percentage of the congestion window 844 can be consumed by a single TSO frame. 845 The setting of this parameter is a choice between burstiness and 846 building larger TSO frames. 847 848 Default: 3 849 850tcp_tw_reuse - INTEGER 851 Enable reuse of TIME-WAIT sockets for new connections when it is 852 safe from protocol viewpoint. 853 854 - 0 - disable 855 - 1 - global enable 856 - 2 - enable for loopback traffic only 857 858 It should not be changed without advice/request of technical 859 experts. 860 861 Default: 2 862 863tcp_window_scaling - BOOLEAN 864 Enable window scaling as defined in RFC1323. 865 866tcp_wmem - vector of 3 INTEGERs: min, default, max 867 min: Amount of memory reserved for send buffers for TCP sockets. 868 Each TCP socket has rights to use it due to fact of its birth. 869 870 Default: 4K 871 872 default: initial size of send buffer used by TCP sockets. This 873 value overrides net.core.wmem_default used by other protocols. 874 875 It is usually lower than net.core.wmem_default. 876 877 Default: 16K 878 879 max: Maximal amount of memory allowed for automatically tuned 880 send buffers for TCP sockets. This value does not override 881 net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables 882 automatic tuning of that socket's send buffer size, in which case 883 this value is ignored. 884 885 Default: between 64K and 4MB, depending on RAM size. 886 887tcp_notsent_lowat - UNSIGNED INTEGER 888 A TCP socket can control the amount of unsent bytes in its write queue, 889 thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll() 890 reports POLLOUT events if the amount of unsent bytes is below a per 891 socket value, and if the write queue is not full. sendmsg() will 892 also not add new buffers if the limit is hit. 893 894 This global variable controls the amount of unsent data for 895 sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change 896 to the global variable has immediate effect. 897 898 Default: UINT_MAX (0xFFFFFFFF) 899 900tcp_workaround_signed_windows - BOOLEAN 901 If set, assume no receipt of a window scaling option means the 902 remote TCP is broken and treats the window as a signed quantity. 903 If unset, assume the remote TCP is not broken even if we do 904 not receive a window scaling option from them. 905 906 Default: 0 907 908tcp_thin_linear_timeouts - BOOLEAN 909 Enable dynamic triggering of linear timeouts for thin streams. 910 If set, a check is performed upon retransmission by timeout to 911 determine if the stream is thin (less than 4 packets in flight). 912 As long as the stream is found to be thin, up to 6 linear 913 timeouts may be performed before exponential backoff mode is 914 initiated. This improves retransmission latency for 915 non-aggressive thin streams, often found to be time-dependent. 916 For more information on thin streams, see 917 Documentation/networking/tcp-thin.rst 918 919 Default: 0 920 921tcp_limit_output_bytes - INTEGER 922 Controls TCP Small Queue limit per tcp socket. 923 TCP bulk sender tends to increase packets in flight until it 924 gets losses notifications. With SNDBUF autotuning, this can 925 result in a large amount of packets queued on the local machine 926 (e.g.: qdiscs, CPU backlog, or device) hurting latency of other 927 flows, for typical pfifo_fast qdiscs. tcp_limit_output_bytes 928 limits the number of bytes on qdisc or device to reduce artificial 929 RTT/cwnd and reduce bufferbloat. 930 931 Default: 1048576 (16 * 65536) 932 933tcp_challenge_ack_limit - INTEGER 934 Limits number of Challenge ACK sent per second, as recommended 935 in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks) 936 Default: 1000 937 938tcp_rx_skb_cache - BOOLEAN 939 Controls a per TCP socket cache of one skb, that might help 940 performance of some workloads. This might be dangerous 941 on systems with a lot of TCP sockets, since it increases 942 memory usage. 943 944 Default: 0 (disabled) 945 946UDP variables 947============= 948 949udp_l3mdev_accept - BOOLEAN 950 Enabling this option allows a "global" bound socket to work 951 across L3 master domains (e.g., VRFs) with packets capable of 952 being received regardless of the L3 domain in which they 953 originated. Only valid when the kernel was compiled with 954 CONFIG_NET_L3_MASTER_DEV. 955 956 Default: 0 (disabled) 957 958udp_mem - vector of 3 INTEGERs: min, pressure, max 959 Number of pages allowed for queueing by all UDP sockets. 960 961 min: Below this number of pages UDP is not bothered about its 962 memory appetite. When amount of memory allocated by UDP exceeds 963 this number, UDP starts to moderate memory usage. 964 965 pressure: This value was introduced to follow format of tcp_mem. 966 967 max: Number of pages allowed for queueing by all UDP sockets. 968 969 Default is calculated at boot time from amount of available memory. 970 971udp_rmem_min - INTEGER 972 Minimal size of receive buffer used by UDP sockets in moderation. 973 Each UDP socket is able to use the size for receiving data, even if 974 total pages of UDP sockets exceed udp_mem pressure. The unit is byte. 975 976 Default: 4K 977 978udp_wmem_min - INTEGER 979 Minimal size of send buffer used by UDP sockets in moderation. 980 Each UDP socket is able to use the size for sending data, even if 981 total pages of UDP sockets exceed udp_mem pressure. The unit is byte. 982 983 Default: 4K 984 985RAW variables 986============= 987 988raw_l3mdev_accept - BOOLEAN 989 Enabling this option allows a "global" bound socket to work 990 across L3 master domains (e.g., VRFs) with packets capable of 991 being received regardless of the L3 domain in which they 992 originated. Only valid when the kernel was compiled with 993 CONFIG_NET_L3_MASTER_DEV. 994 995 Default: 1 (enabled) 996 997CIPSOv4 Variables 998================= 999 1000cipso_cache_enable - BOOLEAN 1001 If set, enable additions to and lookups from the CIPSO label mapping 1002 cache. If unset, additions are ignored and lookups always result in a 1003 miss. However, regardless of the setting the cache is still 1004 invalidated when required when means you can safely toggle this on and 1005 off and the cache will always be "safe". 1006 1007 Default: 1 1008 1009cipso_cache_bucket_size - INTEGER 1010 The CIPSO label cache consists of a fixed size hash table with each 1011 hash bucket containing a number of cache entries. This variable limits 1012 the number of entries in each hash bucket; the larger the value the 1013 more CIPSO label mappings that can be cached. When the number of 1014 entries in a given hash bucket reaches this limit adding new entries 1015 causes the oldest entry in the bucket to be removed to make room. 1016 1017 Default: 10 1018 1019cipso_rbm_optfmt - BOOLEAN 1020 Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of 1021 the CIPSO draft specification (see Documentation/netlabel for details). 1022 This means that when set the CIPSO tag will be padded with empty 1023 categories in order to make the packet data 32-bit aligned. 1024 1025 Default: 0 1026 1027cipso_rbm_structvalid - BOOLEAN 1028 If set, do a very strict check of the CIPSO option when 1029 ip_options_compile() is called. If unset, relax the checks done during 1030 ip_options_compile(). Either way is "safe" as errors are caught else 1031 where in the CIPSO processing code but setting this to 0 (False) should 1032 result in less work (i.e. it should be faster) but could cause problems 1033 with other implementations that require strict checking. 1034 1035 Default: 0 1036 1037IP Variables 1038============ 1039 1040ip_local_port_range - 2 INTEGERS 1041 Defines the local port range that is used by TCP and UDP to 1042 choose the local port. The first number is the first, the 1043 second the last local port number. 1044 If possible, it is better these numbers have different parity 1045 (one even and one odd value). 1046 Must be greater than or equal to ip_unprivileged_port_start. 1047 The default values are 32768 and 60999 respectively. 1048 1049ip_local_reserved_ports - list of comma separated ranges 1050 Specify the ports which are reserved for known third-party 1051 applications. These ports will not be used by automatic port 1052 assignments (e.g. when calling connect() or bind() with port 1053 number 0). Explicit port allocation behavior is unchanged. 1054 1055 The format used for both input and output is a comma separated 1056 list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and 1057 10). Writing to the file will clear all previously reserved 1058 ports and update the current list with the one given in the 1059 input. 1060 1061 Note that ip_local_port_range and ip_local_reserved_ports 1062 settings are independent and both are considered by the kernel 1063 when determining which ports are available for automatic port 1064 assignments. 1065 1066 You can reserve ports which are not in the current 1067 ip_local_port_range, e.g.:: 1068 1069 $ cat /proc/sys/net/ipv4/ip_local_port_range 1070 32000 60999 1071 $ cat /proc/sys/net/ipv4/ip_local_reserved_ports 1072 8080,9148 1073 1074 although this is redundant. However such a setting is useful 1075 if later the port range is changed to a value that will 1076 include the reserved ports. 1077 1078 Default: Empty 1079 1080ip_unprivileged_port_start - INTEGER 1081 This is a per-namespace sysctl. It defines the first 1082 unprivileged port in the network namespace. Privileged ports 1083 require root or CAP_NET_BIND_SERVICE in order to bind to them. 1084 To disable all privileged ports, set this to 0. They must not 1085 overlap with the ip_local_port_range. 1086 1087 Default: 1024 1088 1089ip_nonlocal_bind - BOOLEAN 1090 If set, allows processes to bind() to non-local IP addresses, 1091 which can be quite useful - but may break some applications. 1092 1093 Default: 0 1094 1095ip_autobind_reuse - BOOLEAN 1096 By default, bind() does not select the ports automatically even if 1097 the new socket and all sockets bound to the port have SO_REUSEADDR. 1098 ip_autobind_reuse allows bind() to reuse the port and this is useful 1099 when you use bind()+connect(), but may break some applications. 1100 The preferred solution is to use IP_BIND_ADDRESS_NO_PORT and this 1101 option should only be set by experts. 1102 Default: 0 1103 1104ip_dynaddr - BOOLEAN 1105 If set non-zero, enables support for dynamic addresses. 1106 If set to a non-zero value larger than 1, a kernel log 1107 message will be printed when dynamic address rewriting 1108 occurs. 1109 1110 Default: 0 1111 1112ip_early_demux - BOOLEAN 1113 Optimize input packet processing down to one demux for 1114 certain kinds of local sockets. Currently we only do this 1115 for established TCP and connected UDP sockets. 1116 1117 It may add an additional cost for pure routing workloads that 1118 reduces overall throughput, in such case you should disable it. 1119 1120 Default: 1 1121 1122ping_group_range - 2 INTEGERS 1123 Restrict ICMP_PROTO datagram sockets to users in the group range. 1124 The default is "1 0", meaning, that nobody (not even root) may 1125 create ping sockets. Setting it to "100 100" would grant permissions 1126 to the single group. "0 4294967295" would enable it for the world, "100 1127 4294967295" would enable it for the users, but not daemons. 1128 1129tcp_early_demux - BOOLEAN 1130 Enable early demux for established TCP sockets. 1131 1132 Default: 1 1133 1134udp_early_demux - BOOLEAN 1135 Enable early demux for connected UDP sockets. Disable this if 1136 your system could experience more unconnected load. 1137 1138 Default: 1 1139 1140icmp_echo_ignore_all - BOOLEAN 1141 If set non-zero, then the kernel will ignore all ICMP ECHO 1142 requests sent to it. 1143 1144 Default: 0 1145 1146icmp_echo_enable_probe - BOOLEAN 1147 If set to one, then the kernel will respond to RFC 8335 PROBE 1148 requests sent to it. 1149 1150 Default: 0 1151 1152icmp_echo_ignore_broadcasts - BOOLEAN 1153 If set non-zero, then the kernel will ignore all ICMP ECHO and 1154 TIMESTAMP requests sent to it via broadcast/multicast. 1155 1156 Default: 1 1157 1158icmp_ratelimit - INTEGER 1159 Limit the maximal rates for sending ICMP packets whose type matches 1160 icmp_ratemask (see below) to specific targets. 1161 0 to disable any limiting, 1162 otherwise the minimal space between responses in milliseconds. 1163 Note that another sysctl, icmp_msgs_per_sec limits the number 1164 of ICMP packets sent on all targets. 1165 1166 Default: 1000 1167 1168icmp_msgs_per_sec - INTEGER 1169 Limit maximal number of ICMP packets sent per second from this host. 1170 Only messages whose type matches icmp_ratemask (see below) are 1171 controlled by this limit. For security reasons, the precise count 1172 of messages per second is randomized. 1173 1174 Default: 1000 1175 1176icmp_msgs_burst - INTEGER 1177 icmp_msgs_per_sec controls number of ICMP packets sent per second, 1178 while icmp_msgs_burst controls the burst size of these packets. 1179 For security reasons, the precise burst size is randomized. 1180 1181 Default: 50 1182 1183icmp_ratemask - INTEGER 1184 Mask made of ICMP types for which rates are being limited. 1185 1186 Significant bits: IHGFEDCBA9876543210 1187 1188 Default mask: 0000001100000011000 (6168) 1189 1190 Bit definitions (see include/linux/icmp.h): 1191 1192 = ========================= 1193 0 Echo Reply 1194 3 Destination Unreachable [1]_ 1195 4 Source Quench [1]_ 1196 5 Redirect 1197 8 Echo Request 1198 B Time Exceeded [1]_ 1199 C Parameter Problem [1]_ 1200 D Timestamp Request 1201 E Timestamp Reply 1202 F Info Request 1203 G Info Reply 1204 H Address Mask Request 1205 I Address Mask Reply 1206 = ========================= 1207 1208 .. [1] These are rate limited by default (see default mask above) 1209 1210icmp_ignore_bogus_error_responses - BOOLEAN 1211 Some routers violate RFC1122 by sending bogus responses to broadcast 1212 frames. Such violations are normally logged via a kernel warning. 1213 If this is set to TRUE, the kernel will not give such warnings, which 1214 will avoid log file clutter. 1215 1216 Default: 1 1217 1218icmp_errors_use_inbound_ifaddr - BOOLEAN 1219 1220 If zero, icmp error messages are sent with the primary address of 1221 the exiting interface. 1222 1223 If non-zero, the message will be sent with the primary address of 1224 the interface that received the packet that caused the icmp error. 1225 This is the behaviour many network administrators will expect from 1226 a router. And it can make debugging complicated network layouts 1227 much easier. 1228 1229 Note that if no primary address exists for the interface selected, 1230 then the primary address of the first non-loopback interface that 1231 has one will be used regardless of this setting. 1232 1233 Default: 0 1234 1235igmp_max_memberships - INTEGER 1236 Change the maximum number of multicast groups we can subscribe to. 1237 Default: 20 1238 1239 Theoretical maximum value is bounded by having to send a membership 1240 report in a single datagram (i.e. the report can't span multiple 1241 datagrams, or risk confusing the switch and leaving groups you don't 1242 intend to). 1243 1244 The number of supported groups 'M' is bounded by the number of group 1245 report entries you can fit into a single datagram of 65535 bytes. 1246 1247 M = 65536-sizeof (ip header)/(sizeof(Group record)) 1248 1249 Group records are variable length, with a minimum of 12 bytes. 1250 So net.ipv4.igmp_max_memberships should not be set higher than: 1251 1252 (65536-24) / 12 = 5459 1253 1254 The value 5459 assumes no IP header options, so in practice 1255 this number may be lower. 1256 1257igmp_max_msf - INTEGER 1258 Maximum number of addresses allowed in the source filter list for a 1259 multicast group. 1260 1261 Default: 10 1262 1263igmp_qrv - INTEGER 1264 Controls the IGMP query robustness variable (see RFC2236 8.1). 1265 1266 Default: 2 (as specified by RFC2236 8.1) 1267 1268 Minimum: 1 (as specified by RFC6636 4.5) 1269 1270force_igmp_version - INTEGER 1271 - 0 - (default) No enforcement of a IGMP version, IGMPv1/v2 fallback 1272 allowed. Will back to IGMPv3 mode again if all IGMPv1/v2 Querier 1273 Present timer expires. 1274 - 1 - Enforce to use IGMP version 1. Will also reply IGMPv1 report if 1275 receive IGMPv2/v3 query. 1276 - 2 - Enforce to use IGMP version 2. Will fallback to IGMPv1 if receive 1277 IGMPv1 query message. Will reply report if receive IGMPv3 query. 1278 - 3 - Enforce to use IGMP version 3. The same react with default 0. 1279 1280 .. note:: 1281 1282 this is not the same with force_mld_version because IGMPv3 RFC3376 1283 Security Considerations does not have clear description that we could 1284 ignore other version messages completely as MLDv2 RFC3810. So make 1285 this value as default 0 is recommended. 1286 1287``conf/interface/*`` 1288 changes special settings per interface (where 1289 interface" is the name of your network interface) 1290 1291``conf/all/*`` 1292 is special, changes the settings for all interfaces 1293 1294log_martians - BOOLEAN 1295 Log packets with impossible addresses to kernel log. 1296 log_martians for the interface will be enabled if at least one of 1297 conf/{all,interface}/log_martians is set to TRUE, 1298 it will be disabled otherwise 1299 1300accept_redirects - BOOLEAN 1301 Accept ICMP redirect messages. 1302 accept_redirects for the interface will be enabled if: 1303 1304 - both conf/{all,interface}/accept_redirects are TRUE in the case 1305 forwarding for the interface is enabled 1306 1307 or 1308 1309 - at least one of conf/{all,interface}/accept_redirects is TRUE in the 1310 case forwarding for the interface is disabled 1311 1312 accept_redirects for the interface will be disabled otherwise 1313 1314 default: 1315 1316 - TRUE (host) 1317 - FALSE (router) 1318 1319forwarding - BOOLEAN 1320 Enable IP forwarding on this interface. This controls whether packets 1321 received _on_ this interface can be forwarded. 1322 1323mc_forwarding - BOOLEAN 1324 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE 1325 and a multicast routing daemon is required. 1326 conf/all/mc_forwarding must also be set to TRUE to enable multicast 1327 routing for the interface 1328 1329medium_id - INTEGER 1330 Integer value used to differentiate the devices by the medium they 1331 are attached to. Two devices can have different id values when 1332 the broadcast packets are received only on one of them. 1333 The default value 0 means that the device is the only interface 1334 to its medium, value of -1 means that medium is not known. 1335 1336 Currently, it is used to change the proxy_arp behavior: 1337 the proxy_arp feature is enabled for packets forwarded between 1338 two devices attached to different media. 1339 1340proxy_arp - BOOLEAN 1341 Do proxy arp. 1342 1343 proxy_arp for the interface will be enabled if at least one of 1344 conf/{all,interface}/proxy_arp is set to TRUE, 1345 it will be disabled otherwise 1346 1347proxy_arp_pvlan - BOOLEAN 1348 Private VLAN proxy arp. 1349 1350 Basically allow proxy arp replies back to the same interface 1351 (from which the ARP request/solicitation was received). 1352 1353 This is done to support (ethernet) switch features, like RFC 1354 3069, where the individual ports are NOT allowed to 1355 communicate with each other, but they are allowed to talk to 1356 the upstream router. As described in RFC 3069, it is possible 1357 to allow these hosts to communicate through the upstream 1358 router by proxy_arp'ing. Don't need to be used together with 1359 proxy_arp. 1360 1361 This technology is known by different names: 1362 1363 In RFC 3069 it is called VLAN Aggregation. 1364 Cisco and Allied Telesyn call it Private VLAN. 1365 Hewlett-Packard call it Source-Port filtering or port-isolation. 1366 Ericsson call it MAC-Forced Forwarding (RFC Draft). 1367 1368shared_media - BOOLEAN 1369 Send(router) or accept(host) RFC1620 shared media redirects. 1370 Overrides secure_redirects. 1371 1372 shared_media for the interface will be enabled if at least one of 1373 conf/{all,interface}/shared_media is set to TRUE, 1374 it will be disabled otherwise 1375 1376 default TRUE 1377 1378secure_redirects - BOOLEAN 1379 Accept ICMP redirect messages only to gateways listed in the 1380 interface's current gateway list. Even if disabled, RFC1122 redirect 1381 rules still apply. 1382 1383 Overridden by shared_media. 1384 1385 secure_redirects for the interface will be enabled if at least one of 1386 conf/{all,interface}/secure_redirects is set to TRUE, 1387 it will be disabled otherwise 1388 1389 default TRUE 1390 1391send_redirects - BOOLEAN 1392 Send redirects, if router. 1393 1394 send_redirects for the interface will be enabled if at least one of 1395 conf/{all,interface}/send_redirects is set to TRUE, 1396 it will be disabled otherwise 1397 1398 Default: TRUE 1399 1400bootp_relay - BOOLEAN 1401 Accept packets with source address 0.b.c.d destined 1402 not to this host as local ones. It is supposed, that 1403 BOOTP relay daemon will catch and forward such packets. 1404 conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay 1405 for the interface 1406 1407 default FALSE 1408 1409 Not Implemented Yet. 1410 1411accept_source_route - BOOLEAN 1412 Accept packets with SRR option. 1413 conf/all/accept_source_route must also be set to TRUE to accept packets 1414 with SRR option on the interface 1415 1416 default 1417 1418 - TRUE (router) 1419 - FALSE (host) 1420 1421accept_local - BOOLEAN 1422 Accept packets with local source addresses. In combination with 1423 suitable routing, this can be used to direct packets between two 1424 local interfaces over the wire and have them accepted properly. 1425 default FALSE 1426 1427route_localnet - BOOLEAN 1428 Do not consider loopback addresses as martian source or destination 1429 while routing. This enables the use of 127/8 for local routing purposes. 1430 1431 default FALSE 1432 1433rp_filter - INTEGER 1434 - 0 - No source validation. 1435 - 1 - Strict mode as defined in RFC3704 Strict Reverse Path 1436 Each incoming packet is tested against the FIB and if the interface 1437 is not the best reverse path the packet check will fail. 1438 By default failed packets are discarded. 1439 - 2 - Loose mode as defined in RFC3704 Loose Reverse Path 1440 Each incoming packet's source address is also tested against the FIB 1441 and if the source address is not reachable via any interface 1442 the packet check will fail. 1443 1444 Current recommended practice in RFC3704 is to enable strict mode 1445 to prevent IP spoofing from DDos attacks. If using asymmetric routing 1446 or other complicated routing, then loose mode is recommended. 1447 1448 The max value from conf/{all,interface}/rp_filter is used 1449 when doing source validation on the {interface}. 1450 1451 Default value is 0. Note that some distributions enable it 1452 in startup scripts. 1453 1454src_valid_mark - BOOLEAN 1455 - 0 - The fwmark of the packet is not included in reverse path 1456 route lookup. This allows for asymmetric routing configurations 1457 utilizing the fwmark in only one direction, e.g., transparent 1458 proxying. 1459 1460 - 1 - The fwmark of the packet is included in reverse path route 1461 lookup. This permits rp_filter to function when the fwmark is 1462 used for routing traffic in both directions. 1463 1464 This setting also affects the utilization of fmwark when 1465 performing source address selection for ICMP replies, or 1466 determining addresses stored for the IPOPT_TS_TSANDADDR and 1467 IPOPT_RR IP options. 1468 1469 The max value from conf/{all,interface}/src_valid_mark is used. 1470 1471 Default value is 0. 1472 1473arp_filter - BOOLEAN 1474 - 1 - Allows you to have multiple network interfaces on the same 1475 subnet, and have the ARPs for each interface be answered 1476 based on whether or not the kernel would route a packet from 1477 the ARP'd IP out that interface (therefore you must use source 1478 based routing for this to work). In other words it allows control 1479 of which cards (usually 1) will respond to an arp request. 1480 1481 - 0 - (default) The kernel can respond to arp requests with addresses 1482 from other interfaces. This may seem wrong but it usually makes 1483 sense, because it increases the chance of successful communication. 1484 IP addresses are owned by the complete host on Linux, not by 1485 particular interfaces. Only for more complex setups like load- 1486 balancing, does this behaviour cause problems. 1487 1488 arp_filter for the interface will be enabled if at least one of 1489 conf/{all,interface}/arp_filter is set to TRUE, 1490 it will be disabled otherwise 1491 1492arp_announce - INTEGER 1493 Define different restriction levels for announcing the local 1494 source IP address from IP packets in ARP requests sent on 1495 interface: 1496 1497 - 0 - (default) Use any local address, configured on any interface 1498 - 1 - Try to avoid local addresses that are not in the target's 1499 subnet for this interface. This mode is useful when target 1500 hosts reachable via this interface require the source IP 1501 address in ARP requests to be part of their logical network 1502 configured on the receiving interface. When we generate the 1503 request we will check all our subnets that include the 1504 target IP and will preserve the source address if it is from 1505 such subnet. If there is no such subnet we select source 1506 address according to the rules for level 2. 1507 - 2 - Always use the best local address for this target. 1508 In this mode we ignore the source address in the IP packet 1509 and try to select local address that we prefer for talks with 1510 the target host. Such local address is selected by looking 1511 for primary IP addresses on all our subnets on the outgoing 1512 interface that include the target IP address. If no suitable 1513 local address is found we select the first local address 1514 we have on the outgoing interface or on all other interfaces, 1515 with the hope we will receive reply for our request and 1516 even sometimes no matter the source IP address we announce. 1517 1518 The max value from conf/{all,interface}/arp_announce is used. 1519 1520 Increasing the restriction level gives more chance for 1521 receiving answer from the resolved target while decreasing 1522 the level announces more valid sender's information. 1523 1524arp_ignore - INTEGER 1525 Define different modes for sending replies in response to 1526 received ARP requests that resolve local target IP addresses: 1527 1528 - 0 - (default): reply for any local target IP address, configured 1529 on any interface 1530 - 1 - reply only if the target IP address is local address 1531 configured on the incoming interface 1532 - 2 - reply only if the target IP address is local address 1533 configured on the incoming interface and both with the 1534 sender's IP address are part from same subnet on this interface 1535 - 3 - do not reply for local addresses configured with scope host, 1536 only resolutions for global and link addresses are replied 1537 - 4-7 - reserved 1538 - 8 - do not reply for all local addresses 1539 1540 The max value from conf/{all,interface}/arp_ignore is used 1541 when ARP request is received on the {interface} 1542 1543arp_notify - BOOLEAN 1544 Define mode for notification of address and device changes. 1545 1546 == ========================================================== 1547 0 (default): do nothing 1548 1 Generate gratuitous arp requests when device is brought up 1549 or hardware address changes. 1550 == ========================================================== 1551 1552arp_accept - BOOLEAN 1553 Define behavior for gratuitous ARP frames who's IP is not 1554 already present in the ARP table: 1555 1556 - 0 - don't create new entries in the ARP table 1557 - 1 - create new entries in the ARP table 1558 1559 Both replies and requests type gratuitous arp will trigger the 1560 ARP table to be updated, if this setting is on. 1561 1562 If the ARP table already contains the IP address of the 1563 gratuitous arp frame, the arp table will be updated regardless 1564 if this setting is on or off. 1565 1566mcast_solicit - INTEGER 1567 The maximum number of multicast probes in INCOMPLETE state, 1568 when the associated hardware address is unknown. Defaults 1569 to 3. 1570 1571ucast_solicit - INTEGER 1572 The maximum number of unicast probes in PROBE state, when 1573 the hardware address is being reconfirmed. Defaults to 3. 1574 1575app_solicit - INTEGER 1576 The maximum number of probes to send to the user space ARP daemon 1577 via netlink before dropping back to multicast probes (see 1578 mcast_resolicit). Defaults to 0. 1579 1580mcast_resolicit - INTEGER 1581 The maximum number of multicast probes after unicast and 1582 app probes in PROBE state. Defaults to 0. 1583 1584disable_policy - BOOLEAN 1585 Disable IPSEC policy (SPD) for this interface 1586 1587disable_xfrm - BOOLEAN 1588 Disable IPSEC encryption on this interface, whatever the policy 1589 1590igmpv2_unsolicited_report_interval - INTEGER 1591 The interval in milliseconds in which the next unsolicited 1592 IGMPv1 or IGMPv2 report retransmit will take place. 1593 1594 Default: 10000 (10 seconds) 1595 1596igmpv3_unsolicited_report_interval - INTEGER 1597 The interval in milliseconds in which the next unsolicited 1598 IGMPv3 report retransmit will take place. 1599 1600 Default: 1000 (1 seconds) 1601 1602ignore_routes_with_linkdown - BOOLEAN 1603 Ignore routes whose link is down when performing a FIB lookup. 1604 1605promote_secondaries - BOOLEAN 1606 When a primary IP address is removed from this interface 1607 promote a corresponding secondary IP address instead of 1608 removing all the corresponding secondary IP addresses. 1609 1610drop_unicast_in_l2_multicast - BOOLEAN 1611 Drop any unicast IP packets that are received in link-layer 1612 multicast (or broadcast) frames. 1613 1614 This behavior (for multicast) is actually a SHOULD in RFC 1615 1122, but is disabled by default for compatibility reasons. 1616 1617 Default: off (0) 1618 1619drop_gratuitous_arp - BOOLEAN 1620 Drop all gratuitous ARP frames, for example if there's a known 1621 good ARP proxy on the network and such frames need not be used 1622 (or in the case of 802.11, must not be used to prevent attacks.) 1623 1624 Default: off (0) 1625 1626 1627tag - INTEGER 1628 Allows you to write a number, which can be used as required. 1629 1630 Default value is 0. 1631 1632xfrm4_gc_thresh - INTEGER 1633 (Obsolete since linux-4.14) 1634 The threshold at which we will start garbage collecting for IPv4 1635 destination cache entries. At twice this value the system will 1636 refuse new allocations. 1637 1638igmp_link_local_mcast_reports - BOOLEAN 1639 Enable IGMP reports for link local multicast groups in the 1640 224.0.0.X range. 1641 1642 Default TRUE 1643 1644Alexey Kuznetsov. 1645kuznet@ms2.inr.ac.ru 1646 1647Updated by: 1648 1649- Andi Kleen 1650 ak@muc.de 1651- Nicolas Delon 1652 delon.nicolas@wanadoo.fr 1653 1654 1655 1656 1657/proc/sys/net/ipv6/* Variables 1658============================== 1659 1660IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also 1661apply to IPv6 [XXX?]. 1662 1663bindv6only - BOOLEAN 1664 Default value for IPV6_V6ONLY socket option, 1665 which restricts use of the IPv6 socket to IPv6 communication 1666 only. 1667 1668 - TRUE: disable IPv4-mapped address feature 1669 - FALSE: enable IPv4-mapped address feature 1670 1671 Default: FALSE (as specified in RFC3493) 1672 1673flowlabel_consistency - BOOLEAN 1674 Protect the consistency (and unicity) of flow label. 1675 You have to disable it to use IPV6_FL_F_REFLECT flag on the 1676 flow label manager. 1677 1678 - TRUE: enabled 1679 - FALSE: disabled 1680 1681 Default: TRUE 1682 1683auto_flowlabels - INTEGER 1684 Automatically generate flow labels based on a flow hash of the 1685 packet. This allows intermediate devices, such as routers, to 1686 identify packet flows for mechanisms like Equal Cost Multipath 1687 Routing (see RFC 6438). 1688 1689 = =========================================================== 1690 0 automatic flow labels are completely disabled 1691 1 automatic flow labels are enabled by default, they can be 1692 disabled on a per socket basis using the IPV6_AUTOFLOWLABEL 1693 socket option 1694 2 automatic flow labels are allowed, they may be enabled on a 1695 per socket basis using the IPV6_AUTOFLOWLABEL socket option 1696 3 automatic flow labels are enabled and enforced, they cannot 1697 be disabled by the socket option 1698 = =========================================================== 1699 1700 Default: 1 1701 1702flowlabel_state_ranges - BOOLEAN 1703 Split the flow label number space into two ranges. 0-0x7FFFF is 1704 reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF 1705 is reserved for stateless flow labels as described in RFC6437. 1706 1707 - TRUE: enabled 1708 - FALSE: disabled 1709 1710 Default: true 1711 1712flowlabel_reflect - INTEGER 1713 Control flow label reflection. Needed for Path MTU 1714 Discovery to work with Equal Cost Multipath Routing in anycast 1715 environments. See RFC 7690 and: 1716 https://tools.ietf.org/html/draft-wang-6man-flow-label-reflection-01 1717 1718 This is a bitmask. 1719 1720 - 1: enabled for established flows 1721 1722 Note that this prevents automatic flowlabel changes, as done 1723 in "tcp: change IPv6 flow-label upon receiving spurious retransmission" 1724 and "tcp: Change txhash on every SYN and RTO retransmit" 1725 1726 - 2: enabled for TCP RESET packets (no active listener) 1727 If set, a RST packet sent in response to a SYN packet on a closed 1728 port will reflect the incoming flow label. 1729 1730 - 4: enabled for ICMPv6 echo reply messages. 1731 1732 Default: 0 1733 1734fib_multipath_hash_policy - INTEGER 1735 Controls which hash policy to use for multipath routes. 1736 1737 Default: 0 (Layer 3) 1738 1739 Possible values: 1740 1741 - 0 - Layer 3 (source and destination addresses plus flow label) 1742 - 1 - Layer 4 (standard 5-tuple) 1743 - 2 - Layer 3 or inner Layer 3 if present 1744 1745anycast_src_echo_reply - BOOLEAN 1746 Controls the use of anycast addresses as source addresses for ICMPv6 1747 echo reply 1748 1749 - TRUE: enabled 1750 - FALSE: disabled 1751 1752 Default: FALSE 1753 1754idgen_delay - INTEGER 1755 Controls the delay in seconds after which time to retry 1756 privacy stable address generation if a DAD conflict is 1757 detected. 1758 1759 Default: 1 (as specified in RFC7217) 1760 1761idgen_retries - INTEGER 1762 Controls the number of retries to generate a stable privacy 1763 address if a DAD conflict is detected. 1764 1765 Default: 3 (as specified in RFC7217) 1766 1767mld_qrv - INTEGER 1768 Controls the MLD query robustness variable (see RFC3810 9.1). 1769 1770 Default: 2 (as specified by RFC3810 9.1) 1771 1772 Minimum: 1 (as specified by RFC6636 4.5) 1773 1774max_dst_opts_number - INTEGER 1775 Maximum number of non-padding TLVs allowed in a Destination 1776 options extension header. If this value is less than zero 1777 then unknown options are disallowed and the number of known 1778 TLVs allowed is the absolute value of this number. 1779 1780 Default: 8 1781 1782max_hbh_opts_number - INTEGER 1783 Maximum number of non-padding TLVs allowed in a Hop-by-Hop 1784 options extension header. If this value is less than zero 1785 then unknown options are disallowed and the number of known 1786 TLVs allowed is the absolute value of this number. 1787 1788 Default: 8 1789 1790max_dst_opts_length - INTEGER 1791 Maximum length allowed for a Destination options extension 1792 header. 1793 1794 Default: INT_MAX (unlimited) 1795 1796max_hbh_length - INTEGER 1797 Maximum length allowed for a Hop-by-Hop options extension 1798 header. 1799 1800 Default: INT_MAX (unlimited) 1801 1802skip_notify_on_dev_down - BOOLEAN 1803 Controls whether an RTM_DELROUTE message is generated for routes 1804 removed when a device is taken down or deleted. IPv4 does not 1805 generate this message; IPv6 does by default. Setting this sysctl 1806 to true skips the message, making IPv4 and IPv6 on par in relying 1807 on userspace caches to track link events and evict routes. 1808 1809 Default: false (generate message) 1810 1811nexthop_compat_mode - BOOLEAN 1812 New nexthop API provides a means for managing nexthops independent of 1813 prefixes. Backwards compatibilty with old route format is enabled by 1814 default which means route dumps and notifications contain the new 1815 nexthop attribute but also the full, expanded nexthop definition. 1816 Further, updates or deletes of a nexthop configuration generate route 1817 notifications for each fib entry using the nexthop. Once a system 1818 understands the new API, this sysctl can be disabled to achieve full 1819 performance benefits of the new API by disabling the nexthop expansion 1820 and extraneous notifications. 1821 Default: true (backward compat mode) 1822 1823fib_notify_on_flag_change - INTEGER 1824 Whether to emit RTM_NEWROUTE notifications whenever RTM_F_OFFLOAD/ 1825 RTM_F_TRAP/RTM_F_OFFLOAD_FAILED flags are changed. 1826 1827 After installing a route to the kernel, user space receives an 1828 acknowledgment, which means the route was installed in the kernel, 1829 but not necessarily in hardware. 1830 It is also possible for a route already installed in hardware to change 1831 its action and therefore its flags. For example, a host route that is 1832 trapping packets can be "promoted" to perform decapsulation following 1833 the installation of an IPinIP/VXLAN tunnel. 1834 The notifications will indicate to user-space the state of the route. 1835 1836 Default: 0 (Do not emit notifications.) 1837 1838 Possible values: 1839 1840 - 0 - Do not emit notifications. 1841 - 1 - Emit notifications. 1842 - 2 - Emit notifications only for RTM_F_OFFLOAD_FAILED flag change. 1843 1844IPv6 Fragmentation: 1845 1846ip6frag_high_thresh - INTEGER 1847 Maximum memory used to reassemble IPv6 fragments. When 1848 ip6frag_high_thresh bytes of memory is allocated for this purpose, 1849 the fragment handler will toss packets until ip6frag_low_thresh 1850 is reached. 1851 1852ip6frag_low_thresh - INTEGER 1853 See ip6frag_high_thresh 1854 1855ip6frag_time - INTEGER 1856 Time in seconds to keep an IPv6 fragment in memory. 1857 1858IPv6 Segment Routing: 1859 1860seg6_flowlabel - INTEGER 1861 Controls the behaviour of computing the flowlabel of outer 1862 IPv6 header in case of SR T.encaps 1863 1864 == ======================================================= 1865 -1 set flowlabel to zero. 1866 0 copy flowlabel from Inner packet in case of Inner IPv6 1867 (Set flowlabel to 0 in case IPv4/L2) 1868 1 Compute the flowlabel using seg6_make_flowlabel() 1869 == ======================================================= 1870 1871 Default is 0. 1872 1873``conf/default/*``: 1874 Change the interface-specific default settings. 1875 1876 These settings would be used during creating new interfaces. 1877 1878 1879``conf/all/*``: 1880 Change all the interface-specific settings. 1881 1882 [XXX: Other special features than forwarding?] 1883 1884conf/all/disable_ipv6 - BOOLEAN 1885 Changing this value is same as changing ``conf/default/disable_ipv6`` 1886 setting and also all per-interface ``disable_ipv6`` settings to the same 1887 value. 1888 1889 Reading this value does not have any particular meaning. It does not say 1890 whether IPv6 support is enabled or disabled. Returned value can be 1 1891 also in the case when some interface has ``disable_ipv6`` set to 0 and 1892 has configured IPv6 addresses. 1893 1894conf/all/forwarding - BOOLEAN 1895 Enable global IPv6 forwarding between all interfaces. 1896 1897 IPv4 and IPv6 work differently here; e.g. netfilter must be used 1898 to control which interfaces may forward packets and which not. 1899 1900 This also sets all interfaces' Host/Router setting 1901 'forwarding' to the specified value. See below for details. 1902 1903 This referred to as global forwarding. 1904 1905proxy_ndp - BOOLEAN 1906 Do proxy ndp. 1907 1908fwmark_reflect - BOOLEAN 1909 Controls the fwmark of kernel-generated IPv6 reply packets that are not 1910 associated with a socket for example, TCP RSTs or ICMPv6 echo replies). 1911 If unset, these packets have a fwmark of zero. If set, they have the 1912 fwmark of the packet they are replying to. 1913 1914 Default: 0 1915 1916``conf/interface/*``: 1917 Change special settings per interface. 1918 1919 The functional behaviour for certain settings is different 1920 depending on whether local forwarding is enabled or not. 1921 1922accept_ra - INTEGER 1923 Accept Router Advertisements; autoconfigure using them. 1924 1925 It also determines whether or not to transmit Router 1926 Solicitations. If and only if the functional setting is to 1927 accept Router Advertisements, Router Solicitations will be 1928 transmitted. 1929 1930 Possible values are: 1931 1932 == =========================================================== 1933 0 Do not accept Router Advertisements. 1934 1 Accept Router Advertisements if forwarding is disabled. 1935 2 Overrule forwarding behaviour. Accept Router Advertisements 1936 even if forwarding is enabled. 1937 == =========================================================== 1938 1939 Functional default: 1940 1941 - enabled if local forwarding is disabled. 1942 - disabled if local forwarding is enabled. 1943 1944accept_ra_defrtr - BOOLEAN 1945 Learn default router in Router Advertisement. 1946 1947 Functional default: 1948 1949 - enabled if accept_ra is enabled. 1950 - disabled if accept_ra is disabled. 1951 1952ra_defrtr_metric - UNSIGNED INTEGER 1953 Route metric for default route learned in Router Advertisement. This value 1954 will be assigned as metric for the default route learned via IPv6 Router 1955 Advertisement. Takes affect only if accept_ra_defrtr is enabled. 1956 1957 Possible values: 1958 1 to 0xFFFFFFFF 1959 1960 Default: IP6_RT_PRIO_USER i.e. 1024. 1961 1962accept_ra_from_local - BOOLEAN 1963 Accept RA with source-address that is found on local machine 1964 if the RA is otherwise proper and able to be accepted. 1965 1966 Default is to NOT accept these as it may be an un-intended 1967 network loop. 1968 1969 Functional default: 1970 1971 - enabled if accept_ra_from_local is enabled 1972 on a specific interface. 1973 - disabled if accept_ra_from_local is disabled 1974 on a specific interface. 1975 1976accept_ra_min_hop_limit - INTEGER 1977 Minimum hop limit Information in Router Advertisement. 1978 1979 Hop limit Information in Router Advertisement less than this 1980 variable shall be ignored. 1981 1982 Default: 1 1983 1984accept_ra_pinfo - BOOLEAN 1985 Learn Prefix Information in Router Advertisement. 1986 1987 Functional default: 1988 1989 - enabled if accept_ra is enabled. 1990 - disabled if accept_ra is disabled. 1991 1992accept_ra_rt_info_min_plen - INTEGER 1993 Minimum prefix length of Route Information in RA. 1994 1995 Route Information w/ prefix smaller than this variable shall 1996 be ignored. 1997 1998 Functional default: 1999 2000 * 0 if accept_ra_rtr_pref is enabled. 2001 * -1 if accept_ra_rtr_pref is disabled. 2002 2003accept_ra_rt_info_max_plen - INTEGER 2004 Maximum prefix length of Route Information in RA. 2005 2006 Route Information w/ prefix larger than this variable shall 2007 be ignored. 2008 2009 Functional default: 2010 2011 * 0 if accept_ra_rtr_pref is enabled. 2012 * -1 if accept_ra_rtr_pref is disabled. 2013 2014accept_ra_rtr_pref - BOOLEAN 2015 Accept Router Preference in RA. 2016 2017 Functional default: 2018 2019 - enabled if accept_ra is enabled. 2020 - disabled if accept_ra is disabled. 2021 2022accept_ra_mtu - BOOLEAN 2023 Apply the MTU value specified in RA option 5 (RFC4861). If 2024 disabled, the MTU specified in the RA will be ignored. 2025 2026 Functional default: 2027 2028 - enabled if accept_ra is enabled. 2029 - disabled if accept_ra is disabled. 2030 2031accept_redirects - BOOLEAN 2032 Accept Redirects. 2033 2034 Functional default: 2035 2036 - enabled if local forwarding is disabled. 2037 - disabled if local forwarding is enabled. 2038 2039accept_source_route - INTEGER 2040 Accept source routing (routing extension header). 2041 2042 - >= 0: Accept only routing header type 2. 2043 - < 0: Do not accept routing header. 2044 2045 Default: 0 2046 2047autoconf - BOOLEAN 2048 Autoconfigure addresses using Prefix Information in Router 2049 Advertisements. 2050 2051 Functional default: 2052 2053 - enabled if accept_ra_pinfo is enabled. 2054 - disabled if accept_ra_pinfo is disabled. 2055 2056dad_transmits - INTEGER 2057 The amount of Duplicate Address Detection probes to send. 2058 2059 Default: 1 2060 2061forwarding - INTEGER 2062 Configure interface-specific Host/Router behaviour. 2063 2064 .. note:: 2065 2066 It is recommended to have the same setting on all 2067 interfaces; mixed router/host scenarios are rather uncommon. 2068 2069 Possible values are: 2070 2071 - 0 Forwarding disabled 2072 - 1 Forwarding enabled 2073 2074 **FALSE (0)**: 2075 2076 By default, Host behaviour is assumed. This means: 2077 2078 1. IsRouter flag is not set in Neighbour Advertisements. 2079 2. If accept_ra is TRUE (default), transmit Router 2080 Solicitations. 2081 3. If accept_ra is TRUE (default), accept Router 2082 Advertisements (and do autoconfiguration). 2083 4. If accept_redirects is TRUE (default), accept Redirects. 2084 2085 **TRUE (1)**: 2086 2087 If local forwarding is enabled, Router behaviour is assumed. 2088 This means exactly the reverse from the above: 2089 2090 1. IsRouter flag is set in Neighbour Advertisements. 2091 2. Router Solicitations are not sent unless accept_ra is 2. 2092 3. Router Advertisements are ignored unless accept_ra is 2. 2093 4. Redirects are ignored. 2094 2095 Default: 0 (disabled) if global forwarding is disabled (default), 2096 otherwise 1 (enabled). 2097 2098hop_limit - INTEGER 2099 Default Hop Limit to set. 2100 2101 Default: 64 2102 2103mtu - INTEGER 2104 Default Maximum Transfer Unit 2105 2106 Default: 1280 (IPv6 required minimum) 2107 2108ip_nonlocal_bind - BOOLEAN 2109 If set, allows processes to bind() to non-local IPv6 addresses, 2110 which can be quite useful - but may break some applications. 2111 2112 Default: 0 2113 2114router_probe_interval - INTEGER 2115 Minimum interval (in seconds) between Router Probing described 2116 in RFC4191. 2117 2118 Default: 60 2119 2120router_solicitation_delay - INTEGER 2121 Number of seconds to wait after interface is brought up 2122 before sending Router Solicitations. 2123 2124 Default: 1 2125 2126router_solicitation_interval - INTEGER 2127 Number of seconds to wait between Router Solicitations. 2128 2129 Default: 4 2130 2131router_solicitations - INTEGER 2132 Number of Router Solicitations to send until assuming no 2133 routers are present. 2134 2135 Default: 3 2136 2137use_oif_addrs_only - BOOLEAN 2138 When enabled, the candidate source addresses for destinations 2139 routed via this interface are restricted to the set of addresses 2140 configured on this interface (vis. RFC 6724, section 4). 2141 2142 Default: false 2143 2144use_tempaddr - INTEGER 2145 Preference for Privacy Extensions (RFC3041). 2146 2147 * <= 0 : disable Privacy Extensions 2148 * == 1 : enable Privacy Extensions, but prefer public 2149 addresses over temporary addresses. 2150 * > 1 : enable Privacy Extensions and prefer temporary 2151 addresses over public addresses. 2152 2153 Default: 2154 2155 * 0 (for most devices) 2156 * -1 (for point-to-point devices and loopback devices) 2157 2158temp_valid_lft - INTEGER 2159 valid lifetime (in seconds) for temporary addresses. 2160 2161 Default: 172800 (2 days) 2162 2163temp_prefered_lft - INTEGER 2164 Preferred lifetime (in seconds) for temporary addresses. 2165 2166 Default: 86400 (1 day) 2167 2168keep_addr_on_down - INTEGER 2169 Keep all IPv6 addresses on an interface down event. If set static 2170 global addresses with no expiration time are not flushed. 2171 2172 * >0 : enabled 2173 * 0 : system default 2174 * <0 : disabled 2175 2176 Default: 0 (addresses are removed) 2177 2178max_desync_factor - INTEGER 2179 Maximum value for DESYNC_FACTOR, which is a random value 2180 that ensures that clients don't synchronize with each 2181 other and generate new addresses at exactly the same time. 2182 value is in seconds. 2183 2184 Default: 600 2185 2186regen_max_retry - INTEGER 2187 Number of attempts before give up attempting to generate 2188 valid temporary addresses. 2189 2190 Default: 5 2191 2192max_addresses - INTEGER 2193 Maximum number of autoconfigured addresses per interface. Setting 2194 to zero disables the limitation. It is not recommended to set this 2195 value too large (or to zero) because it would be an easy way to 2196 crash the kernel by allowing too many addresses to be created. 2197 2198 Default: 16 2199 2200disable_ipv6 - BOOLEAN 2201 Disable IPv6 operation. If accept_dad is set to 2, this value 2202 will be dynamically set to TRUE if DAD fails for the link-local 2203 address. 2204 2205 Default: FALSE (enable IPv6 operation) 2206 2207 When this value is changed from 1 to 0 (IPv6 is being enabled), 2208 it will dynamically create a link-local address on the given 2209 interface and start Duplicate Address Detection, if necessary. 2210 2211 When this value is changed from 0 to 1 (IPv6 is being disabled), 2212 it will dynamically delete all addresses and routes on the given 2213 interface. From now on it will not possible to add addresses/routes 2214 to the selected interface. 2215 2216accept_dad - INTEGER 2217 Whether to accept DAD (Duplicate Address Detection). 2218 2219 == ============================================================== 2220 0 Disable DAD 2221 1 Enable DAD (default) 2222 2 Enable DAD, and disable IPv6 operation if MAC-based duplicate 2223 link-local address has been found. 2224 == ============================================================== 2225 2226 DAD operation and mode on a given interface will be selected according 2227 to the maximum value of conf/{all,interface}/accept_dad. 2228 2229force_tllao - BOOLEAN 2230 Enable sending the target link-layer address option even when 2231 responding to a unicast neighbor solicitation. 2232 2233 Default: FALSE 2234 2235 Quoting from RFC 2461, section 4.4, Target link-layer address: 2236 2237 "The option MUST be included for multicast solicitations in order to 2238 avoid infinite Neighbor Solicitation "recursion" when the peer node 2239 does not have a cache entry to return a Neighbor Advertisements 2240 message. When responding to unicast solicitations, the option can be 2241 omitted since the sender of the solicitation has the correct link- 2242 layer address; otherwise it would not have be able to send the unicast 2243 solicitation in the first place. However, including the link-layer 2244 address in this case adds little overhead and eliminates a potential 2245 race condition where the sender deletes the cached link-layer address 2246 prior to receiving a response to a previous solicitation." 2247 2248ndisc_notify - BOOLEAN 2249 Define mode for notification of address and device changes. 2250 2251 * 0 - (default): do nothing 2252 * 1 - Generate unsolicited neighbour advertisements when device is brought 2253 up or hardware address changes. 2254 2255ndisc_tclass - INTEGER 2256 The IPv6 Traffic Class to use by default when sending IPv6 Neighbor 2257 Discovery (Router Solicitation, Router Advertisement, Neighbor 2258 Solicitation, Neighbor Advertisement, Redirect) messages. 2259 These 8 bits can be interpreted as 6 high order bits holding the DSCP 2260 value and 2 low order bits representing ECN (which you probably want 2261 to leave cleared). 2262 2263 * 0 - (default) 2264 2265mldv1_unsolicited_report_interval - INTEGER 2266 The interval in milliseconds in which the next unsolicited 2267 MLDv1 report retransmit will take place. 2268 2269 Default: 10000 (10 seconds) 2270 2271mldv2_unsolicited_report_interval - INTEGER 2272 The interval in milliseconds in which the next unsolicited 2273 MLDv2 report retransmit will take place. 2274 2275 Default: 1000 (1 second) 2276 2277force_mld_version - INTEGER 2278 * 0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed 2279 * 1 - Enforce to use MLD version 1 2280 * 2 - Enforce to use MLD version 2 2281 2282suppress_frag_ndisc - INTEGER 2283 Control RFC 6980 (Security Implications of IPv6 Fragmentation 2284 with IPv6 Neighbor Discovery) behavior: 2285 2286 * 1 - (default) discard fragmented neighbor discovery packets 2287 * 0 - allow fragmented neighbor discovery packets 2288 2289optimistic_dad - BOOLEAN 2290 Whether to perform Optimistic Duplicate Address Detection (RFC 4429). 2291 2292 * 0: disabled (default) 2293 * 1: enabled 2294 2295 Optimistic Duplicate Address Detection for the interface will be enabled 2296 if at least one of conf/{all,interface}/optimistic_dad is set to 1, 2297 it will be disabled otherwise. 2298 2299use_optimistic - BOOLEAN 2300 If enabled, do not classify optimistic addresses as deprecated during 2301 source address selection. Preferred addresses will still be chosen 2302 before optimistic addresses, subject to other ranking in the source 2303 address selection algorithm. 2304 2305 * 0: disabled (default) 2306 * 1: enabled 2307 2308 This will be enabled if at least one of 2309 conf/{all,interface}/use_optimistic is set to 1, disabled otherwise. 2310 2311stable_secret - IPv6 address 2312 This IPv6 address will be used as a secret to generate IPv6 2313 addresses for link-local addresses and autoconfigured 2314 ones. All addresses generated after setting this secret will 2315 be stable privacy ones by default. This can be changed via the 2316 addrgenmode ip-link. conf/default/stable_secret is used as the 2317 secret for the namespace, the interface specific ones can 2318 overwrite that. Writes to conf/all/stable_secret are refused. 2319 2320 It is recommended to generate this secret during installation 2321 of a system and keep it stable after that. 2322 2323 By default the stable secret is unset. 2324 2325addr_gen_mode - INTEGER 2326 Defines how link-local and autoconf addresses are generated. 2327 2328 = ================================================================= 2329 0 generate address based on EUI64 (default) 2330 1 do no generate a link-local address, use EUI64 for addresses 2331 generated from autoconf 2332 2 generate stable privacy addresses, using the secret from 2333 stable_secret (RFC7217) 2334 3 generate stable privacy addresses, using a random secret if unset 2335 = ================================================================= 2336 2337drop_unicast_in_l2_multicast - BOOLEAN 2338 Drop any unicast IPv6 packets that are received in link-layer 2339 multicast (or broadcast) frames. 2340 2341 By default this is turned off. 2342 2343drop_unsolicited_na - BOOLEAN 2344 Drop all unsolicited neighbor advertisements, for example if there's 2345 a known good NA proxy on the network and such frames need not be used 2346 (or in the case of 802.11, must not be used to prevent attacks.) 2347 2348 By default this is turned off. 2349 2350enhanced_dad - BOOLEAN 2351 Include a nonce option in the IPv6 neighbor solicitation messages used for 2352 duplicate address detection per RFC7527. A received DAD NS will only signal 2353 a duplicate address if the nonce is different. This avoids any false 2354 detection of duplicates due to loopback of the NS messages that we send. 2355 The nonce option will be sent on an interface unless both of 2356 conf/{all,interface}/enhanced_dad are set to FALSE. 2357 2358 Default: TRUE 2359 2360``icmp/*``: 2361=========== 2362 2363ratelimit - INTEGER 2364 Limit the maximal rates for sending ICMPv6 messages. 2365 2366 0 to disable any limiting, 2367 otherwise the minimal space between responses in milliseconds. 2368 2369 Default: 1000 2370 2371ratemask - list of comma separated ranges 2372 For ICMPv6 message types matching the ranges in the ratemask, limit 2373 the sending of the message according to ratelimit parameter. 2374 2375 The format used for both input and output is a comma separated 2376 list of ranges (e.g. "0-127,129" for ICMPv6 message type 0 to 127 and 2377 129). Writing to the file will clear all previous ranges of ICMPv6 2378 message types and update the current list with the input. 2379 2380 Refer to: https://www.iana.org/assignments/icmpv6-parameters/icmpv6-parameters.xhtml 2381 for numerical values of ICMPv6 message types, e.g. echo request is 128 2382 and echo reply is 129. 2383 2384 Default: 0-1,3-127 (rate limit ICMPv6 errors except Packet Too Big) 2385 2386echo_ignore_all - BOOLEAN 2387 If set non-zero, then the kernel will ignore all ICMP ECHO 2388 requests sent to it over the IPv6 protocol. 2389 2390 Default: 0 2391 2392echo_ignore_multicast - BOOLEAN 2393 If set non-zero, then the kernel will ignore all ICMP ECHO 2394 requests sent to it over the IPv6 protocol via multicast. 2395 2396 Default: 0 2397 2398echo_ignore_anycast - BOOLEAN 2399 If set non-zero, then the kernel will ignore all ICMP ECHO 2400 requests sent to it over the IPv6 protocol destined to anycast address. 2401 2402 Default: 0 2403 2404xfrm6_gc_thresh - INTEGER 2405 (Obsolete since linux-4.14) 2406 The threshold at which we will start garbage collecting for IPv6 2407 destination cache entries. At twice this value the system will 2408 refuse new allocations. 2409 2410 2411IPv6 Update by: 2412Pekka Savola <pekkas@netcore.fi> 2413YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org> 2414 2415 2416/proc/sys/net/bridge/* Variables: 2417================================= 2418 2419bridge-nf-call-arptables - BOOLEAN 2420 - 1 : pass bridged ARP traffic to arptables' FORWARD chain. 2421 - 0 : disable this. 2422 2423 Default: 1 2424 2425bridge-nf-call-iptables - BOOLEAN 2426 - 1 : pass bridged IPv4 traffic to iptables' chains. 2427 - 0 : disable this. 2428 2429 Default: 1 2430 2431bridge-nf-call-ip6tables - BOOLEAN 2432 - 1 : pass bridged IPv6 traffic to ip6tables' chains. 2433 - 0 : disable this. 2434 2435 Default: 1 2436 2437bridge-nf-filter-vlan-tagged - BOOLEAN 2438 - 1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables. 2439 - 0 : disable this. 2440 2441 Default: 0 2442 2443bridge-nf-filter-pppoe-tagged - BOOLEAN 2444 - 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables. 2445 - 0 : disable this. 2446 2447 Default: 0 2448 2449bridge-nf-pass-vlan-input-dev - BOOLEAN 2450 - 1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan 2451 interface on the bridge and set the netfilter input device to the 2452 vlan. This allows use of e.g. "iptables -i br0.1" and makes the 2453 REDIRECT target work with vlan-on-top-of-bridge interfaces. When no 2454 matching vlan interface is found, or this switch is off, the input 2455 device is set to the bridge interface. 2456 2457 - 0: disable bridge netfilter vlan interface lookup. 2458 2459 Default: 0 2460 2461``proc/sys/net/sctp/*`` Variables: 2462================================== 2463 2464addip_enable - BOOLEAN 2465 Enable or disable extension of Dynamic Address Reconfiguration 2466 (ADD-IP) functionality specified in RFC5061. This extension provides 2467 the ability to dynamically add and remove new addresses for the SCTP 2468 associations. 2469 2470 1: Enable extension. 2471 2472 0: Disable extension. 2473 2474 Default: 0 2475 2476pf_enable - INTEGER 2477 Enable or disable pf (pf is short for potentially failed) state. A value 2478 of pf_retrans > path_max_retrans also disables pf state. That is, one of 2479 both pf_enable and pf_retrans > path_max_retrans can disable pf state. 2480 Since pf_retrans and path_max_retrans can be changed by userspace 2481 application, sometimes user expects to disable pf state by the value of 2482 pf_retrans > path_max_retrans, but occasionally the value of pf_retrans 2483 or path_max_retrans is changed by the user application, this pf state is 2484 enabled. As such, it is necessary to add this to dynamically enable 2485 and disable pf state. See: 2486 https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover for 2487 details. 2488 2489 1: Enable pf. 2490 2491 0: Disable pf. 2492 2493 Default: 1 2494 2495pf_expose - INTEGER 2496 Unset or enable/disable pf (pf is short for potentially failed) state 2497 exposure. Applications can control the exposure of the PF path state 2498 in the SCTP_PEER_ADDR_CHANGE event and the SCTP_GET_PEER_ADDR_INFO 2499 sockopt. When it's unset, no SCTP_PEER_ADDR_CHANGE event with 2500 SCTP_ADDR_PF state will be sent and a SCTP_PF-state transport info 2501 can be got via SCTP_GET_PEER_ADDR_INFO sockopt; When it's enabled, 2502 a SCTP_PEER_ADDR_CHANGE event will be sent for a transport becoming 2503 SCTP_PF state and a SCTP_PF-state transport info can be got via 2504 SCTP_GET_PEER_ADDR_INFO sockopt; When it's diabled, no 2505 SCTP_PEER_ADDR_CHANGE event will be sent and it returns -EACCES when 2506 trying to get a SCTP_PF-state transport info via SCTP_GET_PEER_ADDR_INFO 2507 sockopt. 2508 2509 0: Unset pf state exposure, Compatible with old applications. 2510 2511 1: Disable pf state exposure. 2512 2513 2: Enable pf state exposure. 2514 2515 Default: 0 2516 2517addip_noauth_enable - BOOLEAN 2518 Dynamic Address Reconfiguration (ADD-IP) requires the use of 2519 authentication to protect the operations of adding or removing new 2520 addresses. This requirement is mandated so that unauthorized hosts 2521 would not be able to hijack associations. However, older 2522 implementations may not have implemented this requirement while 2523 allowing the ADD-IP extension. For reasons of interoperability, 2524 we provide this variable to control the enforcement of the 2525 authentication requirement. 2526 2527 == =============================================================== 2528 1 Allow ADD-IP extension to be used without authentication. This 2529 should only be set in a closed environment for interoperability 2530 with older implementations. 2531 2532 0 Enforce the authentication requirement 2533 == =============================================================== 2534 2535 Default: 0 2536 2537auth_enable - BOOLEAN 2538 Enable or disable Authenticated Chunks extension. This extension 2539 provides the ability to send and receive authenticated chunks and is 2540 required for secure operation of Dynamic Address Reconfiguration 2541 (ADD-IP) extension. 2542 2543 - 1: Enable this extension. 2544 - 0: Disable this extension. 2545 2546 Default: 0 2547 2548prsctp_enable - BOOLEAN 2549 Enable or disable the Partial Reliability extension (RFC3758) which 2550 is used to notify peers that a given DATA should no longer be expected. 2551 2552 - 1: Enable extension 2553 - 0: Disable 2554 2555 Default: 1 2556 2557max_burst - INTEGER 2558 The limit of the number of new packets that can be initially sent. It 2559 controls how bursty the generated traffic can be. 2560 2561 Default: 4 2562 2563association_max_retrans - INTEGER 2564 Set the maximum number for retransmissions that an association can 2565 attempt deciding that the remote end is unreachable. If this value 2566 is exceeded, the association is terminated. 2567 2568 Default: 10 2569 2570max_init_retransmits - INTEGER 2571 The maximum number of retransmissions of INIT and COOKIE-ECHO chunks 2572 that an association will attempt before declaring the destination 2573 unreachable and terminating. 2574 2575 Default: 8 2576 2577path_max_retrans - INTEGER 2578 The maximum number of retransmissions that will be attempted on a given 2579 path. Once this threshold is exceeded, the path is considered 2580 unreachable, and new traffic will use a different path when the 2581 association is multihomed. 2582 2583 Default: 5 2584 2585pf_retrans - INTEGER 2586 The number of retransmissions that will be attempted on a given path 2587 before traffic is redirected to an alternate transport (should one 2588 exist). Note this is distinct from path_max_retrans, as a path that 2589 passes the pf_retrans threshold can still be used. Its only 2590 deprioritized when a transmission path is selected by the stack. This 2591 setting is primarily used to enable fast failover mechanisms without 2592 having to reduce path_max_retrans to a very low value. See: 2593 http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt 2594 for details. Note also that a value of pf_retrans > path_max_retrans 2595 disables this feature. Since both pf_retrans and path_max_retrans can 2596 be changed by userspace application, a variable pf_enable is used to 2597 disable pf state. 2598 2599 Default: 0 2600 2601ps_retrans - INTEGER 2602 Primary.Switchover.Max.Retrans (PSMR), it's a tunable parameter coming 2603 from section-5 "Primary Path Switchover" in rfc7829. The primary path 2604 will be changed to another active path when the path error counter on 2605 the old primary path exceeds PSMR, so that "the SCTP sender is allowed 2606 to continue data transmission on a new working path even when the old 2607 primary destination address becomes active again". Note this feature 2608 is disabled by initializing 'ps_retrans' per netns as 0xffff by default, 2609 and its value can't be less than 'pf_retrans' when changing by sysctl. 2610 2611 Default: 0xffff 2612 2613rto_initial - INTEGER 2614 The initial round trip timeout value in milliseconds that will be used 2615 in calculating round trip times. This is the initial time interval 2616 for retransmissions. 2617 2618 Default: 3000 2619 2620rto_max - INTEGER 2621 The maximum value (in milliseconds) of the round trip timeout. This 2622 is the largest time interval that can elapse between retransmissions. 2623 2624 Default: 60000 2625 2626rto_min - INTEGER 2627 The minimum value (in milliseconds) of the round trip timeout. This 2628 is the smallest time interval the can elapse between retransmissions. 2629 2630 Default: 1000 2631 2632hb_interval - INTEGER 2633 The interval (in milliseconds) between HEARTBEAT chunks. These chunks 2634 are sent at the specified interval on idle paths to probe the state of 2635 a given path between 2 associations. 2636 2637 Default: 30000 2638 2639sack_timeout - INTEGER 2640 The amount of time (in milliseconds) that the implementation will wait 2641 to send a SACK. 2642 2643 Default: 200 2644 2645valid_cookie_life - INTEGER 2646 The default lifetime of the SCTP cookie (in milliseconds). The cookie 2647 is used during association establishment. 2648 2649 Default: 60000 2650 2651cookie_preserve_enable - BOOLEAN 2652 Enable or disable the ability to extend the lifetime of the SCTP cookie 2653 that is used during the establishment phase of SCTP association 2654 2655 - 1: Enable cookie lifetime extension. 2656 - 0: Disable 2657 2658 Default: 1 2659 2660cookie_hmac_alg - STRING 2661 Select the hmac algorithm used when generating the cookie value sent by 2662 a listening sctp socket to a connecting client in the INIT-ACK chunk. 2663 Valid values are: 2664 2665 * md5 2666 * sha1 2667 * none 2668 2669 Ability to assign md5 or sha1 as the selected alg is predicated on the 2670 configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and 2671 CONFIG_CRYPTO_SHA1). 2672 2673 Default: Dependent on configuration. MD5 if available, else SHA1 if 2674 available, else none. 2675 2676rcvbuf_policy - INTEGER 2677 Determines if the receive buffer is attributed to the socket or to 2678 association. SCTP supports the capability to create multiple 2679 associations on a single socket. When using this capability, it is 2680 possible that a single stalled association that's buffering a lot 2681 of data may block other associations from delivering their data by 2682 consuming all of the receive buffer space. To work around this, 2683 the rcvbuf_policy could be set to attribute the receiver buffer space 2684 to each association instead of the socket. This prevents the described 2685 blocking. 2686 2687 - 1: rcvbuf space is per association 2688 - 0: rcvbuf space is per socket 2689 2690 Default: 0 2691 2692sndbuf_policy - INTEGER 2693 Similar to rcvbuf_policy above, this applies to send buffer space. 2694 2695 - 1: Send buffer is tracked per association 2696 - 0: Send buffer is tracked per socket. 2697 2698 Default: 0 2699 2700sctp_mem - vector of 3 INTEGERs: min, pressure, max 2701 Number of pages allowed for queueing by all SCTP sockets. 2702 2703 min: Below this number of pages SCTP is not bothered about its 2704 memory appetite. When amount of memory allocated by SCTP exceeds 2705 this number, SCTP starts to moderate memory usage. 2706 2707 pressure: This value was introduced to follow format of tcp_mem. 2708 2709 max: Number of pages allowed for queueing by all SCTP sockets. 2710 2711 Default is calculated at boot time from amount of available memory. 2712 2713sctp_rmem - vector of 3 INTEGERs: min, default, max 2714 Only the first value ("min") is used, "default" and "max" are 2715 ignored. 2716 2717 min: Minimal size of receive buffer used by SCTP socket. 2718 It is guaranteed to each SCTP socket (but not association) even 2719 under moderate memory pressure. 2720 2721 Default: 4K 2722 2723sctp_wmem - vector of 3 INTEGERs: min, default, max 2724 Currently this tunable has no effect. 2725 2726addr_scope_policy - INTEGER 2727 Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00 2728 2729 - 0 - Disable IPv4 address scoping 2730 - 1 - Enable IPv4 address scoping 2731 - 2 - Follow draft but allow IPv4 private addresses 2732 - 3 - Follow draft but allow IPv4 link local addresses 2733 2734 Default: 1 2735 2736udp_port - INTEGER 2737 The listening port for the local UDP tunneling sock. Normally it's 2738 using the IANA-assigned UDP port number 9899 (sctp-tunneling). 2739 2740 This UDP sock is used for processing the incoming UDP-encapsulated 2741 SCTP packets (from RFC6951), and shared by all applications in the 2742 same net namespace. This UDP sock will be closed when the value is 2743 set to 0. 2744 2745 The value will also be used to set the src port of the UDP header 2746 for the outgoing UDP-encapsulated SCTP packets. For the dest port, 2747 please refer to 'encap_port' below. 2748 2749 Default: 0 2750 2751encap_port - INTEGER 2752 The default remote UDP encapsulation port. 2753 2754 This value is used to set the dest port of the UDP header for the 2755 outgoing UDP-encapsulated SCTP packets by default. Users can also 2756 change the value for each sock/asoc/transport by using setsockopt. 2757 For further information, please refer to RFC6951. 2758 2759 Note that when connecting to a remote server, the client should set 2760 this to the port that the UDP tunneling sock on the peer server is 2761 listening to and the local UDP tunneling sock on the client also 2762 must be started. On the server, it would get the encap_port from 2763 the incoming packet's source port. 2764 2765 Default: 0 2766 2767 2768``/proc/sys/net/core/*`` 2769======================== 2770 2771 Please see: Documentation/admin-guide/sysctl/net.rst for descriptions of these entries. 2772 2773 2774``/proc/sys/net/unix/*`` 2775======================== 2776 2777max_dgram_qlen - INTEGER 2778 The maximum length of dgram socket receive queue 2779 2780 Default: 10 2781 2782