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_ignore_broadcasts - BOOLEAN 1147 If set non-zero, then the kernel will ignore all ICMP ECHO and 1148 TIMESTAMP requests sent to it via broadcast/multicast. 1149 1150 Default: 1 1151 1152icmp_ratelimit - INTEGER 1153 Limit the maximal rates for sending ICMP packets whose type matches 1154 icmp_ratemask (see below) to specific targets. 1155 0 to disable any limiting, 1156 otherwise the minimal space between responses in milliseconds. 1157 Note that another sysctl, icmp_msgs_per_sec limits the number 1158 of ICMP packets sent on all targets. 1159 1160 Default: 1000 1161 1162icmp_msgs_per_sec - INTEGER 1163 Limit maximal number of ICMP packets sent per second from this host. 1164 Only messages whose type matches icmp_ratemask (see below) are 1165 controlled by this limit. For security reasons, the precise count 1166 of messages per second is randomized. 1167 1168 Default: 1000 1169 1170icmp_msgs_burst - INTEGER 1171 icmp_msgs_per_sec controls number of ICMP packets sent per second, 1172 while icmp_msgs_burst controls the burst size of these packets. 1173 For security reasons, the precise burst size is randomized. 1174 1175 Default: 50 1176 1177icmp_ratemask - INTEGER 1178 Mask made of ICMP types for which rates are being limited. 1179 1180 Significant bits: IHGFEDCBA9876543210 1181 1182 Default mask: 0000001100000011000 (6168) 1183 1184 Bit definitions (see include/linux/icmp.h): 1185 1186 = ========================= 1187 0 Echo Reply 1188 3 Destination Unreachable [1]_ 1189 4 Source Quench [1]_ 1190 5 Redirect 1191 8 Echo Request 1192 B Time Exceeded [1]_ 1193 C Parameter Problem [1]_ 1194 D Timestamp Request 1195 E Timestamp Reply 1196 F Info Request 1197 G Info Reply 1198 H Address Mask Request 1199 I Address Mask Reply 1200 = ========================= 1201 1202 .. [1] These are rate limited by default (see default mask above) 1203 1204icmp_ignore_bogus_error_responses - BOOLEAN 1205 Some routers violate RFC1122 by sending bogus responses to broadcast 1206 frames. Such violations are normally logged via a kernel warning. 1207 If this is set to TRUE, the kernel will not give such warnings, which 1208 will avoid log file clutter. 1209 1210 Default: 1 1211 1212icmp_errors_use_inbound_ifaddr - BOOLEAN 1213 1214 If zero, icmp error messages are sent with the primary address of 1215 the exiting interface. 1216 1217 If non-zero, the message will be sent with the primary address of 1218 the interface that received the packet that caused the icmp error. 1219 This is the behaviour many network administrators will expect from 1220 a router. And it can make debugging complicated network layouts 1221 much easier. 1222 1223 Note that if no primary address exists for the interface selected, 1224 then the primary address of the first non-loopback interface that 1225 has one will be used regardless of this setting. 1226 1227 Default: 0 1228 1229igmp_max_memberships - INTEGER 1230 Change the maximum number of multicast groups we can subscribe to. 1231 Default: 20 1232 1233 Theoretical maximum value is bounded by having to send a membership 1234 report in a single datagram (i.e. the report can't span multiple 1235 datagrams, or risk confusing the switch and leaving groups you don't 1236 intend to). 1237 1238 The number of supported groups 'M' is bounded by the number of group 1239 report entries you can fit into a single datagram of 65535 bytes. 1240 1241 M = 65536-sizeof (ip header)/(sizeof(Group record)) 1242 1243 Group records are variable length, with a minimum of 12 bytes. 1244 So net.ipv4.igmp_max_memberships should not be set higher than: 1245 1246 (65536-24) / 12 = 5459 1247 1248 The value 5459 assumes no IP header options, so in practice 1249 this number may be lower. 1250 1251igmp_max_msf - INTEGER 1252 Maximum number of addresses allowed in the source filter list for a 1253 multicast group. 1254 1255 Default: 10 1256 1257igmp_qrv - INTEGER 1258 Controls the IGMP query robustness variable (see RFC2236 8.1). 1259 1260 Default: 2 (as specified by RFC2236 8.1) 1261 1262 Minimum: 1 (as specified by RFC6636 4.5) 1263 1264force_igmp_version - INTEGER 1265 - 0 - (default) No enforcement of a IGMP version, IGMPv1/v2 fallback 1266 allowed. Will back to IGMPv3 mode again if all IGMPv1/v2 Querier 1267 Present timer expires. 1268 - 1 - Enforce to use IGMP version 1. Will also reply IGMPv1 report if 1269 receive IGMPv2/v3 query. 1270 - 2 - Enforce to use IGMP version 2. Will fallback to IGMPv1 if receive 1271 IGMPv1 query message. Will reply report if receive IGMPv3 query. 1272 - 3 - Enforce to use IGMP version 3. The same react with default 0. 1273 1274 .. note:: 1275 1276 this is not the same with force_mld_version because IGMPv3 RFC3376 1277 Security Considerations does not have clear description that we could 1278 ignore other version messages completely as MLDv2 RFC3810. So make 1279 this value as default 0 is recommended. 1280 1281``conf/interface/*`` 1282 changes special settings per interface (where 1283 interface" is the name of your network interface) 1284 1285``conf/all/*`` 1286 is special, changes the settings for all interfaces 1287 1288log_martians - BOOLEAN 1289 Log packets with impossible addresses to kernel log. 1290 log_martians for the interface will be enabled if at least one of 1291 conf/{all,interface}/log_martians is set to TRUE, 1292 it will be disabled otherwise 1293 1294accept_redirects - BOOLEAN 1295 Accept ICMP redirect messages. 1296 accept_redirects for the interface will be enabled if: 1297 1298 - both conf/{all,interface}/accept_redirects are TRUE in the case 1299 forwarding for the interface is enabled 1300 1301 or 1302 1303 - at least one of conf/{all,interface}/accept_redirects is TRUE in the 1304 case forwarding for the interface is disabled 1305 1306 accept_redirects for the interface will be disabled otherwise 1307 1308 default: 1309 1310 - TRUE (host) 1311 - FALSE (router) 1312 1313forwarding - BOOLEAN 1314 Enable IP forwarding on this interface. This controls whether packets 1315 received _on_ this interface can be forwarded. 1316 1317mc_forwarding - BOOLEAN 1318 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE 1319 and a multicast routing daemon is required. 1320 conf/all/mc_forwarding must also be set to TRUE to enable multicast 1321 routing for the interface 1322 1323medium_id - INTEGER 1324 Integer value used to differentiate the devices by the medium they 1325 are attached to. Two devices can have different id values when 1326 the broadcast packets are received only on one of them. 1327 The default value 0 means that the device is the only interface 1328 to its medium, value of -1 means that medium is not known. 1329 1330 Currently, it is used to change the proxy_arp behavior: 1331 the proxy_arp feature is enabled for packets forwarded between 1332 two devices attached to different media. 1333 1334proxy_arp - BOOLEAN 1335 Do proxy arp. 1336 1337 proxy_arp for the interface will be enabled if at least one of 1338 conf/{all,interface}/proxy_arp is set to TRUE, 1339 it will be disabled otherwise 1340 1341proxy_arp_pvlan - BOOLEAN 1342 Private VLAN proxy arp. 1343 1344 Basically allow proxy arp replies back to the same interface 1345 (from which the ARP request/solicitation was received). 1346 1347 This is done to support (ethernet) switch features, like RFC 1348 3069, where the individual ports are NOT allowed to 1349 communicate with each other, but they are allowed to talk to 1350 the upstream router. As described in RFC 3069, it is possible 1351 to allow these hosts to communicate through the upstream 1352 router by proxy_arp'ing. Don't need to be used together with 1353 proxy_arp. 1354 1355 This technology is known by different names: 1356 1357 In RFC 3069 it is called VLAN Aggregation. 1358 Cisco and Allied Telesyn call it Private VLAN. 1359 Hewlett-Packard call it Source-Port filtering or port-isolation. 1360 Ericsson call it MAC-Forced Forwarding (RFC Draft). 1361 1362shared_media - BOOLEAN 1363 Send(router) or accept(host) RFC1620 shared media redirects. 1364 Overrides secure_redirects. 1365 1366 shared_media for the interface will be enabled if at least one of 1367 conf/{all,interface}/shared_media is set to TRUE, 1368 it will be disabled otherwise 1369 1370 default TRUE 1371 1372secure_redirects - BOOLEAN 1373 Accept ICMP redirect messages only to gateways listed in the 1374 interface's current gateway list. Even if disabled, RFC1122 redirect 1375 rules still apply. 1376 1377 Overridden by shared_media. 1378 1379 secure_redirects for the interface will be enabled if at least one of 1380 conf/{all,interface}/secure_redirects is set to TRUE, 1381 it will be disabled otherwise 1382 1383 default TRUE 1384 1385send_redirects - BOOLEAN 1386 Send redirects, if router. 1387 1388 send_redirects for the interface will be enabled if at least one of 1389 conf/{all,interface}/send_redirects is set to TRUE, 1390 it will be disabled otherwise 1391 1392 Default: TRUE 1393 1394bootp_relay - BOOLEAN 1395 Accept packets with source address 0.b.c.d destined 1396 not to this host as local ones. It is supposed, that 1397 BOOTP relay daemon will catch and forward such packets. 1398 conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay 1399 for the interface 1400 1401 default FALSE 1402 1403 Not Implemented Yet. 1404 1405accept_source_route - BOOLEAN 1406 Accept packets with SRR option. 1407 conf/all/accept_source_route must also be set to TRUE to accept packets 1408 with SRR option on the interface 1409 1410 default 1411 1412 - TRUE (router) 1413 - FALSE (host) 1414 1415accept_local - BOOLEAN 1416 Accept packets with local source addresses. In combination with 1417 suitable routing, this can be used to direct packets between two 1418 local interfaces over the wire and have them accepted properly. 1419 default FALSE 1420 1421route_localnet - BOOLEAN 1422 Do not consider loopback addresses as martian source or destination 1423 while routing. This enables the use of 127/8 for local routing purposes. 1424 1425 default FALSE 1426 1427rp_filter - INTEGER 1428 - 0 - No source validation. 1429 - 1 - Strict mode as defined in RFC3704 Strict Reverse Path 1430 Each incoming packet is tested against the FIB and if the interface 1431 is not the best reverse path the packet check will fail. 1432 By default failed packets are discarded. 1433 - 2 - Loose mode as defined in RFC3704 Loose Reverse Path 1434 Each incoming packet's source address is also tested against the FIB 1435 and if the source address is not reachable via any interface 1436 the packet check will fail. 1437 1438 Current recommended practice in RFC3704 is to enable strict mode 1439 to prevent IP spoofing from DDos attacks. If using asymmetric routing 1440 or other complicated routing, then loose mode is recommended. 1441 1442 The max value from conf/{all,interface}/rp_filter is used 1443 when doing source validation on the {interface}. 1444 1445 Default value is 0. Note that some distributions enable it 1446 in startup scripts. 1447 1448src_valid_mark - BOOLEAN 1449 - 0 - The fwmark of the packet is not included in reverse path 1450 route lookup. This allows for asymmetric routing configurations 1451 utilizing the fwmark in only one direction, e.g., transparent 1452 proxying. 1453 1454 - 1 - The fwmark of the packet is included in reverse path route 1455 lookup. This permits rp_filter to function when the fwmark is 1456 used for routing traffic in both directions. 1457 1458 This setting also affects the utilization of fmwark when 1459 performing source address selection for ICMP replies, or 1460 determining addresses stored for the IPOPT_TS_TSANDADDR and 1461 IPOPT_RR IP options. 1462 1463 The max value from conf/{all,interface}/src_valid_mark is used. 1464 1465 Default value is 0. 1466 1467arp_filter - BOOLEAN 1468 - 1 - Allows you to have multiple network interfaces on the same 1469 subnet, and have the ARPs for each interface be answered 1470 based on whether or not the kernel would route a packet from 1471 the ARP'd IP out that interface (therefore you must use source 1472 based routing for this to work). In other words it allows control 1473 of which cards (usually 1) will respond to an arp request. 1474 1475 - 0 - (default) The kernel can respond to arp requests with addresses 1476 from other interfaces. This may seem wrong but it usually makes 1477 sense, because it increases the chance of successful communication. 1478 IP addresses are owned by the complete host on Linux, not by 1479 particular interfaces. Only for more complex setups like load- 1480 balancing, does this behaviour cause problems. 1481 1482 arp_filter for the interface will be enabled if at least one of 1483 conf/{all,interface}/arp_filter is set to TRUE, 1484 it will be disabled otherwise 1485 1486arp_announce - INTEGER 1487 Define different restriction levels for announcing the local 1488 source IP address from IP packets in ARP requests sent on 1489 interface: 1490 1491 - 0 - (default) Use any local address, configured on any interface 1492 - 1 - Try to avoid local addresses that are not in the target's 1493 subnet for this interface. This mode is useful when target 1494 hosts reachable via this interface require the source IP 1495 address in ARP requests to be part of their logical network 1496 configured on the receiving interface. When we generate the 1497 request we will check all our subnets that include the 1498 target IP and will preserve the source address if it is from 1499 such subnet. If there is no such subnet we select source 1500 address according to the rules for level 2. 1501 - 2 - Always use the best local address for this target. 1502 In this mode we ignore the source address in the IP packet 1503 and try to select local address that we prefer for talks with 1504 the target host. Such local address is selected by looking 1505 for primary IP addresses on all our subnets on the outgoing 1506 interface that include the target IP address. If no suitable 1507 local address is found we select the first local address 1508 we have on the outgoing interface or on all other interfaces, 1509 with the hope we will receive reply for our request and 1510 even sometimes no matter the source IP address we announce. 1511 1512 The max value from conf/{all,interface}/arp_announce is used. 1513 1514 Increasing the restriction level gives more chance for 1515 receiving answer from the resolved target while decreasing 1516 the level announces more valid sender's information. 1517 1518arp_ignore - INTEGER 1519 Define different modes for sending replies in response to 1520 received ARP requests that resolve local target IP addresses: 1521 1522 - 0 - (default): reply for any local target IP address, configured 1523 on any interface 1524 - 1 - reply only if the target IP address is local address 1525 configured on the incoming interface 1526 - 2 - reply only if the target IP address is local address 1527 configured on the incoming interface and both with the 1528 sender's IP address are part from same subnet on this interface 1529 - 3 - do not reply for local addresses configured with scope host, 1530 only resolutions for global and link addresses are replied 1531 - 4-7 - reserved 1532 - 8 - do not reply for all local addresses 1533 1534 The max value from conf/{all,interface}/arp_ignore is used 1535 when ARP request is received on the {interface} 1536 1537arp_notify - BOOLEAN 1538 Define mode for notification of address and device changes. 1539 1540 == ========================================================== 1541 0 (default): do nothing 1542 1 Generate gratuitous arp requests when device is brought up 1543 or hardware address changes. 1544 == ========================================================== 1545 1546arp_accept - BOOLEAN 1547 Define behavior for gratuitous ARP frames who's IP is not 1548 already present in the ARP table: 1549 1550 - 0 - don't create new entries in the ARP table 1551 - 1 - create new entries in the ARP table 1552 1553 Both replies and requests type gratuitous arp will trigger the 1554 ARP table to be updated, if this setting is on. 1555 1556 If the ARP table already contains the IP address of the 1557 gratuitous arp frame, the arp table will be updated regardless 1558 if this setting is on or off. 1559 1560mcast_solicit - INTEGER 1561 The maximum number of multicast probes in INCOMPLETE state, 1562 when the associated hardware address is unknown. Defaults 1563 to 3. 1564 1565ucast_solicit - INTEGER 1566 The maximum number of unicast probes in PROBE state, when 1567 the hardware address is being reconfirmed. Defaults to 3. 1568 1569app_solicit - INTEGER 1570 The maximum number of probes to send to the user space ARP daemon 1571 via netlink before dropping back to multicast probes (see 1572 mcast_resolicit). Defaults to 0. 1573 1574mcast_resolicit - INTEGER 1575 The maximum number of multicast probes after unicast and 1576 app probes in PROBE state. Defaults to 0. 1577 1578disable_policy - BOOLEAN 1579 Disable IPSEC policy (SPD) for this interface 1580 1581disable_xfrm - BOOLEAN 1582 Disable IPSEC encryption on this interface, whatever the policy 1583 1584igmpv2_unsolicited_report_interval - INTEGER 1585 The interval in milliseconds in which the next unsolicited 1586 IGMPv1 or IGMPv2 report retransmit will take place. 1587 1588 Default: 10000 (10 seconds) 1589 1590igmpv3_unsolicited_report_interval - INTEGER 1591 The interval in milliseconds in which the next unsolicited 1592 IGMPv3 report retransmit will take place. 1593 1594 Default: 1000 (1 seconds) 1595 1596ignore_routes_with_linkdown - BOOLEAN 1597 Ignore routes whose link is down when performing a FIB lookup. 1598 1599promote_secondaries - BOOLEAN 1600 When a primary IP address is removed from this interface 1601 promote a corresponding secondary IP address instead of 1602 removing all the corresponding secondary IP addresses. 1603 1604drop_unicast_in_l2_multicast - BOOLEAN 1605 Drop any unicast IP packets that are received in link-layer 1606 multicast (or broadcast) frames. 1607 1608 This behavior (for multicast) is actually a SHOULD in RFC 1609 1122, but is disabled by default for compatibility reasons. 1610 1611 Default: off (0) 1612 1613drop_gratuitous_arp - BOOLEAN 1614 Drop all gratuitous ARP frames, for example if there's a known 1615 good ARP proxy on the network and such frames need not be used 1616 (or in the case of 802.11, must not be used to prevent attacks.) 1617 1618 Default: off (0) 1619 1620 1621tag - INTEGER 1622 Allows you to write a number, which can be used as required. 1623 1624 Default value is 0. 1625 1626xfrm4_gc_thresh - INTEGER 1627 (Obsolete since linux-4.14) 1628 The threshold at which we will start garbage collecting for IPv4 1629 destination cache entries. At twice this value the system will 1630 refuse new allocations. 1631 1632igmp_link_local_mcast_reports - BOOLEAN 1633 Enable IGMP reports for link local multicast groups in the 1634 224.0.0.X range. 1635 1636 Default TRUE 1637 1638Alexey Kuznetsov. 1639kuznet@ms2.inr.ac.ru 1640 1641Updated by: 1642 1643- Andi Kleen 1644 ak@muc.de 1645- Nicolas Delon 1646 delon.nicolas@wanadoo.fr 1647 1648 1649 1650 1651/proc/sys/net/ipv6/* Variables 1652============================== 1653 1654IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also 1655apply to IPv6 [XXX?]. 1656 1657bindv6only - BOOLEAN 1658 Default value for IPV6_V6ONLY socket option, 1659 which restricts use of the IPv6 socket to IPv6 communication 1660 only. 1661 1662 - TRUE: disable IPv4-mapped address feature 1663 - FALSE: enable IPv4-mapped address feature 1664 1665 Default: FALSE (as specified in RFC3493) 1666 1667flowlabel_consistency - BOOLEAN 1668 Protect the consistency (and unicity) of flow label. 1669 You have to disable it to use IPV6_FL_F_REFLECT flag on the 1670 flow label manager. 1671 1672 - TRUE: enabled 1673 - FALSE: disabled 1674 1675 Default: TRUE 1676 1677auto_flowlabels - INTEGER 1678 Automatically generate flow labels based on a flow hash of the 1679 packet. This allows intermediate devices, such as routers, to 1680 identify packet flows for mechanisms like Equal Cost Multipath 1681 Routing (see RFC 6438). 1682 1683 = =========================================================== 1684 0 automatic flow labels are completely disabled 1685 1 automatic flow labels are enabled by default, they can be 1686 disabled on a per socket basis using the IPV6_AUTOFLOWLABEL 1687 socket option 1688 2 automatic flow labels are allowed, they may be enabled on a 1689 per socket basis using the IPV6_AUTOFLOWLABEL socket option 1690 3 automatic flow labels are enabled and enforced, they cannot 1691 be disabled by the socket option 1692 = =========================================================== 1693 1694 Default: 1 1695 1696flowlabel_state_ranges - BOOLEAN 1697 Split the flow label number space into two ranges. 0-0x7FFFF is 1698 reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF 1699 is reserved for stateless flow labels as described in RFC6437. 1700 1701 - TRUE: enabled 1702 - FALSE: disabled 1703 1704 Default: true 1705 1706flowlabel_reflect - INTEGER 1707 Control flow label reflection. Needed for Path MTU 1708 Discovery to work with Equal Cost Multipath Routing in anycast 1709 environments. See RFC 7690 and: 1710 https://tools.ietf.org/html/draft-wang-6man-flow-label-reflection-01 1711 1712 This is a bitmask. 1713 1714 - 1: enabled for established flows 1715 1716 Note that this prevents automatic flowlabel changes, as done 1717 in "tcp: change IPv6 flow-label upon receiving spurious retransmission" 1718 and "tcp: Change txhash on every SYN and RTO retransmit" 1719 1720 - 2: enabled for TCP RESET packets (no active listener) 1721 If set, a RST packet sent in response to a SYN packet on a closed 1722 port will reflect the incoming flow label. 1723 1724 - 4: enabled for ICMPv6 echo reply messages. 1725 1726 Default: 0 1727 1728fib_multipath_hash_policy - INTEGER 1729 Controls which hash policy to use for multipath routes. 1730 1731 Default: 0 (Layer 3) 1732 1733 Possible values: 1734 1735 - 0 - Layer 3 (source and destination addresses plus flow label) 1736 - 1 - Layer 4 (standard 5-tuple) 1737 - 2 - Layer 3 or inner Layer 3 if present 1738 1739anycast_src_echo_reply - BOOLEAN 1740 Controls the use of anycast addresses as source addresses for ICMPv6 1741 echo reply 1742 1743 - TRUE: enabled 1744 - FALSE: disabled 1745 1746 Default: FALSE 1747 1748idgen_delay - INTEGER 1749 Controls the delay in seconds after which time to retry 1750 privacy stable address generation if a DAD conflict is 1751 detected. 1752 1753 Default: 1 (as specified in RFC7217) 1754 1755idgen_retries - INTEGER 1756 Controls the number of retries to generate a stable privacy 1757 address if a DAD conflict is detected. 1758 1759 Default: 3 (as specified in RFC7217) 1760 1761mld_qrv - INTEGER 1762 Controls the MLD query robustness variable (see RFC3810 9.1). 1763 1764 Default: 2 (as specified by RFC3810 9.1) 1765 1766 Minimum: 1 (as specified by RFC6636 4.5) 1767 1768max_dst_opts_number - INTEGER 1769 Maximum number of non-padding TLVs allowed in a Destination 1770 options extension header. If this value is less than zero 1771 then unknown options are disallowed and the number of known 1772 TLVs allowed is the absolute value of this number. 1773 1774 Default: 8 1775 1776max_hbh_opts_number - INTEGER 1777 Maximum number of non-padding TLVs allowed in a Hop-by-Hop 1778 options extension header. If this value is less than zero 1779 then unknown options are disallowed and the number of known 1780 TLVs allowed is the absolute value of this number. 1781 1782 Default: 8 1783 1784max_dst_opts_length - INTEGER 1785 Maximum length allowed for a Destination options extension 1786 header. 1787 1788 Default: INT_MAX (unlimited) 1789 1790max_hbh_length - INTEGER 1791 Maximum length allowed for a Hop-by-Hop options extension 1792 header. 1793 1794 Default: INT_MAX (unlimited) 1795 1796skip_notify_on_dev_down - BOOLEAN 1797 Controls whether an RTM_DELROUTE message is generated for routes 1798 removed when a device is taken down or deleted. IPv4 does not 1799 generate this message; IPv6 does by default. Setting this sysctl 1800 to true skips the message, making IPv4 and IPv6 on par in relying 1801 on userspace caches to track link events and evict routes. 1802 1803 Default: false (generate message) 1804 1805nexthop_compat_mode - BOOLEAN 1806 New nexthop API provides a means for managing nexthops independent of 1807 prefixes. Backwards compatibilty with old route format is enabled by 1808 default which means route dumps and notifications contain the new 1809 nexthop attribute but also the full, expanded nexthop definition. 1810 Further, updates or deletes of a nexthop configuration generate route 1811 notifications for each fib entry using the nexthop. Once a system 1812 understands the new API, this sysctl can be disabled to achieve full 1813 performance benefits of the new API by disabling the nexthop expansion 1814 and extraneous notifications. 1815 Default: true (backward compat mode) 1816 1817fib_notify_on_flag_change - INTEGER 1818 Whether to emit RTM_NEWROUTE notifications whenever RTM_F_OFFLOAD/ 1819 RTM_F_TRAP/RTM_F_OFFLOAD_FAILED flags are changed. 1820 1821 After installing a route to the kernel, user space receives an 1822 acknowledgment, which means the route was installed in the kernel, 1823 but not necessarily in hardware. 1824 It is also possible for a route already installed in hardware to change 1825 its action and therefore its flags. For example, a host route that is 1826 trapping packets can be "promoted" to perform decapsulation following 1827 the installation of an IPinIP/VXLAN tunnel. 1828 The notifications will indicate to user-space the state of the route. 1829 1830 Default: 0 (Do not emit notifications.) 1831 1832 Possible values: 1833 1834 - 0 - Do not emit notifications. 1835 - 1 - Emit notifications. 1836 - 2 - Emit notifications only for RTM_F_OFFLOAD_FAILED flag change. 1837 1838IPv6 Fragmentation: 1839 1840ip6frag_high_thresh - INTEGER 1841 Maximum memory used to reassemble IPv6 fragments. When 1842 ip6frag_high_thresh bytes of memory is allocated for this purpose, 1843 the fragment handler will toss packets until ip6frag_low_thresh 1844 is reached. 1845 1846ip6frag_low_thresh - INTEGER 1847 See ip6frag_high_thresh 1848 1849ip6frag_time - INTEGER 1850 Time in seconds to keep an IPv6 fragment in memory. 1851 1852IPv6 Segment Routing: 1853 1854seg6_flowlabel - INTEGER 1855 Controls the behaviour of computing the flowlabel of outer 1856 IPv6 header in case of SR T.encaps 1857 1858 == ======================================================= 1859 -1 set flowlabel to zero. 1860 0 copy flowlabel from Inner packet in case of Inner IPv6 1861 (Set flowlabel to 0 in case IPv4/L2) 1862 1 Compute the flowlabel using seg6_make_flowlabel() 1863 == ======================================================= 1864 1865 Default is 0. 1866 1867``conf/default/*``: 1868 Change the interface-specific default settings. 1869 1870 These settings would be used during creating new interfaces. 1871 1872 1873``conf/all/*``: 1874 Change all the interface-specific settings. 1875 1876 [XXX: Other special features than forwarding?] 1877 1878conf/all/disable_ipv6 - BOOLEAN 1879 Changing this value is same as changing ``conf/default/disable_ipv6`` 1880 setting and also all per-interface ``disable_ipv6`` settings to the same 1881 value. 1882 1883 Reading this value does not have any particular meaning. It does not say 1884 whether IPv6 support is enabled or disabled. Returned value can be 1 1885 also in the case when some interface has ``disable_ipv6`` set to 0 and 1886 has configured IPv6 addresses. 1887 1888conf/all/forwarding - BOOLEAN 1889 Enable global IPv6 forwarding between all interfaces. 1890 1891 IPv4 and IPv6 work differently here; e.g. netfilter must be used 1892 to control which interfaces may forward packets and which not. 1893 1894 This also sets all interfaces' Host/Router setting 1895 'forwarding' to the specified value. See below for details. 1896 1897 This referred to as global forwarding. 1898 1899proxy_ndp - BOOLEAN 1900 Do proxy ndp. 1901 1902fwmark_reflect - BOOLEAN 1903 Controls the fwmark of kernel-generated IPv6 reply packets that are not 1904 associated with a socket for example, TCP RSTs or ICMPv6 echo replies). 1905 If unset, these packets have a fwmark of zero. If set, they have the 1906 fwmark of the packet they are replying to. 1907 1908 Default: 0 1909 1910``conf/interface/*``: 1911 Change special settings per interface. 1912 1913 The functional behaviour for certain settings is different 1914 depending on whether local forwarding is enabled or not. 1915 1916accept_ra - INTEGER 1917 Accept Router Advertisements; autoconfigure using them. 1918 1919 It also determines whether or not to transmit Router 1920 Solicitations. If and only if the functional setting is to 1921 accept Router Advertisements, Router Solicitations will be 1922 transmitted. 1923 1924 Possible values are: 1925 1926 == =========================================================== 1927 0 Do not accept Router Advertisements. 1928 1 Accept Router Advertisements if forwarding is disabled. 1929 2 Overrule forwarding behaviour. Accept Router Advertisements 1930 even if forwarding is enabled. 1931 == =========================================================== 1932 1933 Functional default: 1934 1935 - enabled if local forwarding is disabled. 1936 - disabled if local forwarding is enabled. 1937 1938accept_ra_defrtr - BOOLEAN 1939 Learn default router in Router Advertisement. 1940 1941 Functional default: 1942 1943 - enabled if accept_ra is enabled. 1944 - disabled if accept_ra is disabled. 1945 1946ra_defrtr_metric - UNSIGNED INTEGER 1947 Route metric for default route learned in Router Advertisement. This value 1948 will be assigned as metric for the default route learned via IPv6 Router 1949 Advertisement. Takes affect only if accept_ra_defrtr is enabled. 1950 1951 Possible values: 1952 1 to 0xFFFFFFFF 1953 1954 Default: IP6_RT_PRIO_USER i.e. 1024. 1955 1956accept_ra_from_local - BOOLEAN 1957 Accept RA with source-address that is found on local machine 1958 if the RA is otherwise proper and able to be accepted. 1959 1960 Default is to NOT accept these as it may be an un-intended 1961 network loop. 1962 1963 Functional default: 1964 1965 - enabled if accept_ra_from_local is enabled 1966 on a specific interface. 1967 - disabled if accept_ra_from_local is disabled 1968 on a specific interface. 1969 1970accept_ra_min_hop_limit - INTEGER 1971 Minimum hop limit Information in Router Advertisement. 1972 1973 Hop limit Information in Router Advertisement less than this 1974 variable shall be ignored. 1975 1976 Default: 1 1977 1978accept_ra_pinfo - BOOLEAN 1979 Learn Prefix Information in Router Advertisement. 1980 1981 Functional default: 1982 1983 - enabled if accept_ra is enabled. 1984 - disabled if accept_ra is disabled. 1985 1986accept_ra_rt_info_min_plen - INTEGER 1987 Minimum prefix length of Route Information in RA. 1988 1989 Route Information w/ prefix smaller than this variable shall 1990 be ignored. 1991 1992 Functional default: 1993 1994 * 0 if accept_ra_rtr_pref is enabled. 1995 * -1 if accept_ra_rtr_pref is disabled. 1996 1997accept_ra_rt_info_max_plen - INTEGER 1998 Maximum prefix length of Route Information in RA. 1999 2000 Route Information w/ prefix larger than this variable shall 2001 be ignored. 2002 2003 Functional default: 2004 2005 * 0 if accept_ra_rtr_pref is enabled. 2006 * -1 if accept_ra_rtr_pref is disabled. 2007 2008accept_ra_rtr_pref - BOOLEAN 2009 Accept Router Preference in RA. 2010 2011 Functional default: 2012 2013 - enabled if accept_ra is enabled. 2014 - disabled if accept_ra is disabled. 2015 2016accept_ra_mtu - BOOLEAN 2017 Apply the MTU value specified in RA option 5 (RFC4861). If 2018 disabled, the MTU specified in the RA will be ignored. 2019 2020 Functional default: 2021 2022 - enabled if accept_ra is enabled. 2023 - disabled if accept_ra is disabled. 2024 2025accept_redirects - BOOLEAN 2026 Accept Redirects. 2027 2028 Functional default: 2029 2030 - enabled if local forwarding is disabled. 2031 - disabled if local forwarding is enabled. 2032 2033accept_source_route - INTEGER 2034 Accept source routing (routing extension header). 2035 2036 - >= 0: Accept only routing header type 2. 2037 - < 0: Do not accept routing header. 2038 2039 Default: 0 2040 2041autoconf - BOOLEAN 2042 Autoconfigure addresses using Prefix Information in Router 2043 Advertisements. 2044 2045 Functional default: 2046 2047 - enabled if accept_ra_pinfo is enabled. 2048 - disabled if accept_ra_pinfo is disabled. 2049 2050dad_transmits - INTEGER 2051 The amount of Duplicate Address Detection probes to send. 2052 2053 Default: 1 2054 2055forwarding - INTEGER 2056 Configure interface-specific Host/Router behaviour. 2057 2058 .. note:: 2059 2060 It is recommended to have the same setting on all 2061 interfaces; mixed router/host scenarios are rather uncommon. 2062 2063 Possible values are: 2064 2065 - 0 Forwarding disabled 2066 - 1 Forwarding enabled 2067 2068 **FALSE (0)**: 2069 2070 By default, Host behaviour is assumed. This means: 2071 2072 1. IsRouter flag is not set in Neighbour Advertisements. 2073 2. If accept_ra is TRUE (default), transmit Router 2074 Solicitations. 2075 3. If accept_ra is TRUE (default), accept Router 2076 Advertisements (and do autoconfiguration). 2077 4. If accept_redirects is TRUE (default), accept Redirects. 2078 2079 **TRUE (1)**: 2080 2081 If local forwarding is enabled, Router behaviour is assumed. 2082 This means exactly the reverse from the above: 2083 2084 1. IsRouter flag is set in Neighbour Advertisements. 2085 2. Router Solicitations are not sent unless accept_ra is 2. 2086 3. Router Advertisements are ignored unless accept_ra is 2. 2087 4. Redirects are ignored. 2088 2089 Default: 0 (disabled) if global forwarding is disabled (default), 2090 otherwise 1 (enabled). 2091 2092hop_limit - INTEGER 2093 Default Hop Limit to set. 2094 2095 Default: 64 2096 2097mtu - INTEGER 2098 Default Maximum Transfer Unit 2099 2100 Default: 1280 (IPv6 required minimum) 2101 2102ip_nonlocal_bind - BOOLEAN 2103 If set, allows processes to bind() to non-local IPv6 addresses, 2104 which can be quite useful - but may break some applications. 2105 2106 Default: 0 2107 2108router_probe_interval - INTEGER 2109 Minimum interval (in seconds) between Router Probing described 2110 in RFC4191. 2111 2112 Default: 60 2113 2114router_solicitation_delay - INTEGER 2115 Number of seconds to wait after interface is brought up 2116 before sending Router Solicitations. 2117 2118 Default: 1 2119 2120router_solicitation_interval - INTEGER 2121 Number of seconds to wait between Router Solicitations. 2122 2123 Default: 4 2124 2125router_solicitations - INTEGER 2126 Number of Router Solicitations to send until assuming no 2127 routers are present. 2128 2129 Default: 3 2130 2131use_oif_addrs_only - BOOLEAN 2132 When enabled, the candidate source addresses for destinations 2133 routed via this interface are restricted to the set of addresses 2134 configured on this interface (vis. RFC 6724, section 4). 2135 2136 Default: false 2137 2138use_tempaddr - INTEGER 2139 Preference for Privacy Extensions (RFC3041). 2140 2141 * <= 0 : disable Privacy Extensions 2142 * == 1 : enable Privacy Extensions, but prefer public 2143 addresses over temporary addresses. 2144 * > 1 : enable Privacy Extensions and prefer temporary 2145 addresses over public addresses. 2146 2147 Default: 2148 2149 * 0 (for most devices) 2150 * -1 (for point-to-point devices and loopback devices) 2151 2152temp_valid_lft - INTEGER 2153 valid lifetime (in seconds) for temporary addresses. 2154 2155 Default: 172800 (2 days) 2156 2157temp_prefered_lft - INTEGER 2158 Preferred lifetime (in seconds) for temporary addresses. 2159 2160 Default: 86400 (1 day) 2161 2162keep_addr_on_down - INTEGER 2163 Keep all IPv6 addresses on an interface down event. If set static 2164 global addresses with no expiration time are not flushed. 2165 2166 * >0 : enabled 2167 * 0 : system default 2168 * <0 : disabled 2169 2170 Default: 0 (addresses are removed) 2171 2172max_desync_factor - INTEGER 2173 Maximum value for DESYNC_FACTOR, which is a random value 2174 that ensures that clients don't synchronize with each 2175 other and generate new addresses at exactly the same time. 2176 value is in seconds. 2177 2178 Default: 600 2179 2180regen_max_retry - INTEGER 2181 Number of attempts before give up attempting to generate 2182 valid temporary addresses. 2183 2184 Default: 5 2185 2186max_addresses - INTEGER 2187 Maximum number of autoconfigured addresses per interface. Setting 2188 to zero disables the limitation. It is not recommended to set this 2189 value too large (or to zero) because it would be an easy way to 2190 crash the kernel by allowing too many addresses to be created. 2191 2192 Default: 16 2193 2194disable_ipv6 - BOOLEAN 2195 Disable IPv6 operation. If accept_dad is set to 2, this value 2196 will be dynamically set to TRUE if DAD fails for the link-local 2197 address. 2198 2199 Default: FALSE (enable IPv6 operation) 2200 2201 When this value is changed from 1 to 0 (IPv6 is being enabled), 2202 it will dynamically create a link-local address on the given 2203 interface and start Duplicate Address Detection, if necessary. 2204 2205 When this value is changed from 0 to 1 (IPv6 is being disabled), 2206 it will dynamically delete all addresses and routes on the given 2207 interface. From now on it will not possible to add addresses/routes 2208 to the selected interface. 2209 2210accept_dad - INTEGER 2211 Whether to accept DAD (Duplicate Address Detection). 2212 2213 == ============================================================== 2214 0 Disable DAD 2215 1 Enable DAD (default) 2216 2 Enable DAD, and disable IPv6 operation if MAC-based duplicate 2217 link-local address has been found. 2218 == ============================================================== 2219 2220 DAD operation and mode on a given interface will be selected according 2221 to the maximum value of conf/{all,interface}/accept_dad. 2222 2223force_tllao - BOOLEAN 2224 Enable sending the target link-layer address option even when 2225 responding to a unicast neighbor solicitation. 2226 2227 Default: FALSE 2228 2229 Quoting from RFC 2461, section 4.4, Target link-layer address: 2230 2231 "The option MUST be included for multicast solicitations in order to 2232 avoid infinite Neighbor Solicitation "recursion" when the peer node 2233 does not have a cache entry to return a Neighbor Advertisements 2234 message. When responding to unicast solicitations, the option can be 2235 omitted since the sender of the solicitation has the correct link- 2236 layer address; otherwise it would not have be able to send the unicast 2237 solicitation in the first place. However, including the link-layer 2238 address in this case adds little overhead and eliminates a potential 2239 race condition where the sender deletes the cached link-layer address 2240 prior to receiving a response to a previous solicitation." 2241 2242ndisc_notify - BOOLEAN 2243 Define mode for notification of address and device changes. 2244 2245 * 0 - (default): do nothing 2246 * 1 - Generate unsolicited neighbour advertisements when device is brought 2247 up or hardware address changes. 2248 2249ndisc_tclass - INTEGER 2250 The IPv6 Traffic Class to use by default when sending IPv6 Neighbor 2251 Discovery (Router Solicitation, Router Advertisement, Neighbor 2252 Solicitation, Neighbor Advertisement, Redirect) messages. 2253 These 8 bits can be interpreted as 6 high order bits holding the DSCP 2254 value and 2 low order bits representing ECN (which you probably want 2255 to leave cleared). 2256 2257 * 0 - (default) 2258 2259mldv1_unsolicited_report_interval - INTEGER 2260 The interval in milliseconds in which the next unsolicited 2261 MLDv1 report retransmit will take place. 2262 2263 Default: 10000 (10 seconds) 2264 2265mldv2_unsolicited_report_interval - INTEGER 2266 The interval in milliseconds in which the next unsolicited 2267 MLDv2 report retransmit will take place. 2268 2269 Default: 1000 (1 second) 2270 2271force_mld_version - INTEGER 2272 * 0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed 2273 * 1 - Enforce to use MLD version 1 2274 * 2 - Enforce to use MLD version 2 2275 2276suppress_frag_ndisc - INTEGER 2277 Control RFC 6980 (Security Implications of IPv6 Fragmentation 2278 with IPv6 Neighbor Discovery) behavior: 2279 2280 * 1 - (default) discard fragmented neighbor discovery packets 2281 * 0 - allow fragmented neighbor discovery packets 2282 2283optimistic_dad - BOOLEAN 2284 Whether to perform Optimistic Duplicate Address Detection (RFC 4429). 2285 2286 * 0: disabled (default) 2287 * 1: enabled 2288 2289 Optimistic Duplicate Address Detection for the interface will be enabled 2290 if at least one of conf/{all,interface}/optimistic_dad is set to 1, 2291 it will be disabled otherwise. 2292 2293use_optimistic - BOOLEAN 2294 If enabled, do not classify optimistic addresses as deprecated during 2295 source address selection. Preferred addresses will still be chosen 2296 before optimistic addresses, subject to other ranking in the source 2297 address selection algorithm. 2298 2299 * 0: disabled (default) 2300 * 1: enabled 2301 2302 This will be enabled if at least one of 2303 conf/{all,interface}/use_optimistic is set to 1, disabled otherwise. 2304 2305stable_secret - IPv6 address 2306 This IPv6 address will be used as a secret to generate IPv6 2307 addresses for link-local addresses and autoconfigured 2308 ones. All addresses generated after setting this secret will 2309 be stable privacy ones by default. This can be changed via the 2310 addrgenmode ip-link. conf/default/stable_secret is used as the 2311 secret for the namespace, the interface specific ones can 2312 overwrite that. Writes to conf/all/stable_secret are refused. 2313 2314 It is recommended to generate this secret during installation 2315 of a system and keep it stable after that. 2316 2317 By default the stable secret is unset. 2318 2319addr_gen_mode - INTEGER 2320 Defines how link-local and autoconf addresses are generated. 2321 2322 = ================================================================= 2323 0 generate address based on EUI64 (default) 2324 1 do no generate a link-local address, use EUI64 for addresses 2325 generated from autoconf 2326 2 generate stable privacy addresses, using the secret from 2327 stable_secret (RFC7217) 2328 3 generate stable privacy addresses, using a random secret if unset 2329 = ================================================================= 2330 2331drop_unicast_in_l2_multicast - BOOLEAN 2332 Drop any unicast IPv6 packets that are received in link-layer 2333 multicast (or broadcast) frames. 2334 2335 By default this is turned off. 2336 2337drop_unsolicited_na - BOOLEAN 2338 Drop all unsolicited neighbor advertisements, for example if there's 2339 a known good NA proxy on the network and such frames need not be used 2340 (or in the case of 802.11, must not be used to prevent attacks.) 2341 2342 By default this is turned off. 2343 2344enhanced_dad - BOOLEAN 2345 Include a nonce option in the IPv6 neighbor solicitation messages used for 2346 duplicate address detection per RFC7527. A received DAD NS will only signal 2347 a duplicate address if the nonce is different. This avoids any false 2348 detection of duplicates due to loopback of the NS messages that we send. 2349 The nonce option will be sent on an interface unless both of 2350 conf/{all,interface}/enhanced_dad are set to FALSE. 2351 2352 Default: TRUE 2353 2354``icmp/*``: 2355=========== 2356 2357ratelimit - INTEGER 2358 Limit the maximal rates for sending ICMPv6 messages. 2359 2360 0 to disable any limiting, 2361 otherwise the minimal space between responses in milliseconds. 2362 2363 Default: 1000 2364 2365ratemask - list of comma separated ranges 2366 For ICMPv6 message types matching the ranges in the ratemask, limit 2367 the sending of the message according to ratelimit parameter. 2368 2369 The format used for both input and output is a comma separated 2370 list of ranges (e.g. "0-127,129" for ICMPv6 message type 0 to 127 and 2371 129). Writing to the file will clear all previous ranges of ICMPv6 2372 message types and update the current list with the input. 2373 2374 Refer to: https://www.iana.org/assignments/icmpv6-parameters/icmpv6-parameters.xhtml 2375 for numerical values of ICMPv6 message types, e.g. echo request is 128 2376 and echo reply is 129. 2377 2378 Default: 0-1,3-127 (rate limit ICMPv6 errors except Packet Too Big) 2379 2380echo_ignore_all - BOOLEAN 2381 If set non-zero, then the kernel will ignore all ICMP ECHO 2382 requests sent to it over the IPv6 protocol. 2383 2384 Default: 0 2385 2386echo_ignore_multicast - BOOLEAN 2387 If set non-zero, then the kernel will ignore all ICMP ECHO 2388 requests sent to it over the IPv6 protocol via multicast. 2389 2390 Default: 0 2391 2392echo_ignore_anycast - BOOLEAN 2393 If set non-zero, then the kernel will ignore all ICMP ECHO 2394 requests sent to it over the IPv6 protocol destined to anycast address. 2395 2396 Default: 0 2397 2398xfrm6_gc_thresh - INTEGER 2399 (Obsolete since linux-4.14) 2400 The threshold at which we will start garbage collecting for IPv6 2401 destination cache entries. At twice this value the system will 2402 refuse new allocations. 2403 2404 2405IPv6 Update by: 2406Pekka Savola <pekkas@netcore.fi> 2407YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org> 2408 2409 2410/proc/sys/net/bridge/* Variables: 2411================================= 2412 2413bridge-nf-call-arptables - BOOLEAN 2414 - 1 : pass bridged ARP traffic to arptables' FORWARD chain. 2415 - 0 : disable this. 2416 2417 Default: 1 2418 2419bridge-nf-call-iptables - BOOLEAN 2420 - 1 : pass bridged IPv4 traffic to iptables' chains. 2421 - 0 : disable this. 2422 2423 Default: 1 2424 2425bridge-nf-call-ip6tables - BOOLEAN 2426 - 1 : pass bridged IPv6 traffic to ip6tables' chains. 2427 - 0 : disable this. 2428 2429 Default: 1 2430 2431bridge-nf-filter-vlan-tagged - BOOLEAN 2432 - 1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables. 2433 - 0 : disable this. 2434 2435 Default: 0 2436 2437bridge-nf-filter-pppoe-tagged - BOOLEAN 2438 - 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables. 2439 - 0 : disable this. 2440 2441 Default: 0 2442 2443bridge-nf-pass-vlan-input-dev - BOOLEAN 2444 - 1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan 2445 interface on the bridge and set the netfilter input device to the 2446 vlan. This allows use of e.g. "iptables -i br0.1" and makes the 2447 REDIRECT target work with vlan-on-top-of-bridge interfaces. When no 2448 matching vlan interface is found, or this switch is off, the input 2449 device is set to the bridge interface. 2450 2451 - 0: disable bridge netfilter vlan interface lookup. 2452 2453 Default: 0 2454 2455``proc/sys/net/sctp/*`` Variables: 2456================================== 2457 2458addip_enable - BOOLEAN 2459 Enable or disable extension of Dynamic Address Reconfiguration 2460 (ADD-IP) functionality specified in RFC5061. This extension provides 2461 the ability to dynamically add and remove new addresses for the SCTP 2462 associations. 2463 2464 1: Enable extension. 2465 2466 0: Disable extension. 2467 2468 Default: 0 2469 2470pf_enable - INTEGER 2471 Enable or disable pf (pf is short for potentially failed) state. A value 2472 of pf_retrans > path_max_retrans also disables pf state. That is, one of 2473 both pf_enable and pf_retrans > path_max_retrans can disable pf state. 2474 Since pf_retrans and path_max_retrans can be changed by userspace 2475 application, sometimes user expects to disable pf state by the value of 2476 pf_retrans > path_max_retrans, but occasionally the value of pf_retrans 2477 or path_max_retrans is changed by the user application, this pf state is 2478 enabled. As such, it is necessary to add this to dynamically enable 2479 and disable pf state. See: 2480 https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover for 2481 details. 2482 2483 1: Enable pf. 2484 2485 0: Disable pf. 2486 2487 Default: 1 2488 2489pf_expose - INTEGER 2490 Unset or enable/disable pf (pf is short for potentially failed) state 2491 exposure. Applications can control the exposure of the PF path state 2492 in the SCTP_PEER_ADDR_CHANGE event and the SCTP_GET_PEER_ADDR_INFO 2493 sockopt. When it's unset, no SCTP_PEER_ADDR_CHANGE event with 2494 SCTP_ADDR_PF state will be sent and a SCTP_PF-state transport info 2495 can be got via SCTP_GET_PEER_ADDR_INFO sockopt; When it's enabled, 2496 a SCTP_PEER_ADDR_CHANGE event will be sent for a transport becoming 2497 SCTP_PF state and a SCTP_PF-state transport info can be got via 2498 SCTP_GET_PEER_ADDR_INFO sockopt; When it's diabled, no 2499 SCTP_PEER_ADDR_CHANGE event will be sent and it returns -EACCES when 2500 trying to get a SCTP_PF-state transport info via SCTP_GET_PEER_ADDR_INFO 2501 sockopt. 2502 2503 0: Unset pf state exposure, Compatible with old applications. 2504 2505 1: Disable pf state exposure. 2506 2507 2: Enable pf state exposure. 2508 2509 Default: 0 2510 2511addip_noauth_enable - BOOLEAN 2512 Dynamic Address Reconfiguration (ADD-IP) requires the use of 2513 authentication to protect the operations of adding or removing new 2514 addresses. This requirement is mandated so that unauthorized hosts 2515 would not be able to hijack associations. However, older 2516 implementations may not have implemented this requirement while 2517 allowing the ADD-IP extension. For reasons of interoperability, 2518 we provide this variable to control the enforcement of the 2519 authentication requirement. 2520 2521 == =============================================================== 2522 1 Allow ADD-IP extension to be used without authentication. This 2523 should only be set in a closed environment for interoperability 2524 with older implementations. 2525 2526 0 Enforce the authentication requirement 2527 == =============================================================== 2528 2529 Default: 0 2530 2531auth_enable - BOOLEAN 2532 Enable or disable Authenticated Chunks extension. This extension 2533 provides the ability to send and receive authenticated chunks and is 2534 required for secure operation of Dynamic Address Reconfiguration 2535 (ADD-IP) extension. 2536 2537 - 1: Enable this extension. 2538 - 0: Disable this extension. 2539 2540 Default: 0 2541 2542prsctp_enable - BOOLEAN 2543 Enable or disable the Partial Reliability extension (RFC3758) which 2544 is used to notify peers that a given DATA should no longer be expected. 2545 2546 - 1: Enable extension 2547 - 0: Disable 2548 2549 Default: 1 2550 2551max_burst - INTEGER 2552 The limit of the number of new packets that can be initially sent. It 2553 controls how bursty the generated traffic can be. 2554 2555 Default: 4 2556 2557association_max_retrans - INTEGER 2558 Set the maximum number for retransmissions that an association can 2559 attempt deciding that the remote end is unreachable. If this value 2560 is exceeded, the association is terminated. 2561 2562 Default: 10 2563 2564max_init_retransmits - INTEGER 2565 The maximum number of retransmissions of INIT and COOKIE-ECHO chunks 2566 that an association will attempt before declaring the destination 2567 unreachable and terminating. 2568 2569 Default: 8 2570 2571path_max_retrans - INTEGER 2572 The maximum number of retransmissions that will be attempted on a given 2573 path. Once this threshold is exceeded, the path is considered 2574 unreachable, and new traffic will use a different path when the 2575 association is multihomed. 2576 2577 Default: 5 2578 2579pf_retrans - INTEGER 2580 The number of retransmissions that will be attempted on a given path 2581 before traffic is redirected to an alternate transport (should one 2582 exist). Note this is distinct from path_max_retrans, as a path that 2583 passes the pf_retrans threshold can still be used. Its only 2584 deprioritized when a transmission path is selected by the stack. This 2585 setting is primarily used to enable fast failover mechanisms without 2586 having to reduce path_max_retrans to a very low value. See: 2587 http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt 2588 for details. Note also that a value of pf_retrans > path_max_retrans 2589 disables this feature. Since both pf_retrans and path_max_retrans can 2590 be changed by userspace application, a variable pf_enable is used to 2591 disable pf state. 2592 2593 Default: 0 2594 2595ps_retrans - INTEGER 2596 Primary.Switchover.Max.Retrans (PSMR), it's a tunable parameter coming 2597 from section-5 "Primary Path Switchover" in rfc7829. The primary path 2598 will be changed to another active path when the path error counter on 2599 the old primary path exceeds PSMR, so that "the SCTP sender is allowed 2600 to continue data transmission on a new working path even when the old 2601 primary destination address becomes active again". Note this feature 2602 is disabled by initializing 'ps_retrans' per netns as 0xffff by default, 2603 and its value can't be less than 'pf_retrans' when changing by sysctl. 2604 2605 Default: 0xffff 2606 2607rto_initial - INTEGER 2608 The initial round trip timeout value in milliseconds that will be used 2609 in calculating round trip times. This is the initial time interval 2610 for retransmissions. 2611 2612 Default: 3000 2613 2614rto_max - INTEGER 2615 The maximum value (in milliseconds) of the round trip timeout. This 2616 is the largest time interval that can elapse between retransmissions. 2617 2618 Default: 60000 2619 2620rto_min - INTEGER 2621 The minimum value (in milliseconds) of the round trip timeout. This 2622 is the smallest time interval the can elapse between retransmissions. 2623 2624 Default: 1000 2625 2626hb_interval - INTEGER 2627 The interval (in milliseconds) between HEARTBEAT chunks. These chunks 2628 are sent at the specified interval on idle paths to probe the state of 2629 a given path between 2 associations. 2630 2631 Default: 30000 2632 2633sack_timeout - INTEGER 2634 The amount of time (in milliseconds) that the implementation will wait 2635 to send a SACK. 2636 2637 Default: 200 2638 2639valid_cookie_life - INTEGER 2640 The default lifetime of the SCTP cookie (in milliseconds). The cookie 2641 is used during association establishment. 2642 2643 Default: 60000 2644 2645cookie_preserve_enable - BOOLEAN 2646 Enable or disable the ability to extend the lifetime of the SCTP cookie 2647 that is used during the establishment phase of SCTP association 2648 2649 - 1: Enable cookie lifetime extension. 2650 - 0: Disable 2651 2652 Default: 1 2653 2654cookie_hmac_alg - STRING 2655 Select the hmac algorithm used when generating the cookie value sent by 2656 a listening sctp socket to a connecting client in the INIT-ACK chunk. 2657 Valid values are: 2658 2659 * md5 2660 * sha1 2661 * none 2662 2663 Ability to assign md5 or sha1 as the selected alg is predicated on the 2664 configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and 2665 CONFIG_CRYPTO_SHA1). 2666 2667 Default: Dependent on configuration. MD5 if available, else SHA1 if 2668 available, else none. 2669 2670rcvbuf_policy - INTEGER 2671 Determines if the receive buffer is attributed to the socket or to 2672 association. SCTP supports the capability to create multiple 2673 associations on a single socket. When using this capability, it is 2674 possible that a single stalled association that's buffering a lot 2675 of data may block other associations from delivering their data by 2676 consuming all of the receive buffer space. To work around this, 2677 the rcvbuf_policy could be set to attribute the receiver buffer space 2678 to each association instead of the socket. This prevents the described 2679 blocking. 2680 2681 - 1: rcvbuf space is per association 2682 - 0: rcvbuf space is per socket 2683 2684 Default: 0 2685 2686sndbuf_policy - INTEGER 2687 Similar to rcvbuf_policy above, this applies to send buffer space. 2688 2689 - 1: Send buffer is tracked per association 2690 - 0: Send buffer is tracked per socket. 2691 2692 Default: 0 2693 2694sctp_mem - vector of 3 INTEGERs: min, pressure, max 2695 Number of pages allowed for queueing by all SCTP sockets. 2696 2697 min: Below this number of pages SCTP is not bothered about its 2698 memory appetite. When amount of memory allocated by SCTP exceeds 2699 this number, SCTP starts to moderate memory usage. 2700 2701 pressure: This value was introduced to follow format of tcp_mem. 2702 2703 max: Number of pages allowed for queueing by all SCTP sockets. 2704 2705 Default is calculated at boot time from amount of available memory. 2706 2707sctp_rmem - vector of 3 INTEGERs: min, default, max 2708 Only the first value ("min") is used, "default" and "max" are 2709 ignored. 2710 2711 min: Minimal size of receive buffer used by SCTP socket. 2712 It is guaranteed to each SCTP socket (but not association) even 2713 under moderate memory pressure. 2714 2715 Default: 4K 2716 2717sctp_wmem - vector of 3 INTEGERs: min, default, max 2718 Currently this tunable has no effect. 2719 2720addr_scope_policy - INTEGER 2721 Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00 2722 2723 - 0 - Disable IPv4 address scoping 2724 - 1 - Enable IPv4 address scoping 2725 - 2 - Follow draft but allow IPv4 private addresses 2726 - 3 - Follow draft but allow IPv4 link local addresses 2727 2728 Default: 1 2729 2730udp_port - INTEGER 2731 The listening port for the local UDP tunneling sock. Normally it's 2732 using the IANA-assigned UDP port number 9899 (sctp-tunneling). 2733 2734 This UDP sock is used for processing the incoming UDP-encapsulated 2735 SCTP packets (from RFC6951), and shared by all applications in the 2736 same net namespace. This UDP sock will be closed when the value is 2737 set to 0. 2738 2739 The value will also be used to set the src port of the UDP header 2740 for the outgoing UDP-encapsulated SCTP packets. For the dest port, 2741 please refer to 'encap_port' below. 2742 2743 Default: 0 2744 2745encap_port - INTEGER 2746 The default remote UDP encapsulation port. 2747 2748 This value is used to set the dest port of the UDP header for the 2749 outgoing UDP-encapsulated SCTP packets by default. Users can also 2750 change the value for each sock/asoc/transport by using setsockopt. 2751 For further information, please refer to RFC6951. 2752 2753 Note that when connecting to a remote server, the client should set 2754 this to the port that the UDP tunneling sock on the peer server is 2755 listening to and the local UDP tunneling sock on the client also 2756 must be started. On the server, it would get the encap_port from 2757 the incoming packet's source port. 2758 2759 Default: 0 2760 2761 2762``/proc/sys/net/core/*`` 2763======================== 2764 2765 Please see: Documentation/admin-guide/sysctl/net.rst for descriptions of these entries. 2766 2767 2768``/proc/sys/net/unix/*`` 2769======================== 2770 2771max_dgram_qlen - INTEGER 2772 The maximum length of dgram socket receive queue 2773 2774 Default: 10 2775 2776