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 - 3 - Custom multipath hash. Fields used for multipath hash calculation 103 are determined by fib_multipath_hash_fields sysctl 104 105fib_multipath_hash_fields - UNSIGNED INTEGER 106 When fib_multipath_hash_policy is set to 3 (custom multipath hash), the 107 fields used for multipath hash calculation are determined by this 108 sysctl. 109 110 This value is a bitmask which enables various fields for multipath hash 111 calculation. 112 113 Possible fields are: 114 115 ====== ============================ 116 0x0001 Source IP address 117 0x0002 Destination IP address 118 0x0004 IP protocol 119 0x0008 Unused (Flow Label) 120 0x0010 Source port 121 0x0020 Destination port 122 0x0040 Inner source IP address 123 0x0080 Inner destination IP address 124 0x0100 Inner IP protocol 125 0x0200 Inner Flow Label 126 0x0400 Inner source port 127 0x0800 Inner destination port 128 ====== ============================ 129 130 Default: 0x0007 (source IP, destination IP and IP protocol) 131 132fib_sync_mem - UNSIGNED INTEGER 133 Amount of dirty memory from fib entries that can be backlogged before 134 synchronize_rcu is forced. 135 136 Default: 512kB Minimum: 64kB Maximum: 64MB 137 138ip_forward_update_priority - INTEGER 139 Whether to update SKB priority from "TOS" field in IPv4 header after it 140 is forwarded. The new SKB priority is mapped from TOS field value 141 according to an rt_tos2priority table (see e.g. man tc-prio). 142 143 Default: 1 (Update priority.) 144 145 Possible values: 146 147 - 0 - Do not update priority. 148 - 1 - Update priority. 149 150route/max_size - INTEGER 151 Maximum number of routes allowed in the kernel. Increase 152 this when using large numbers of interfaces and/or routes. 153 154 From linux kernel 3.6 onwards, this is deprecated for ipv4 155 as route cache is no longer used. 156 157neigh/default/gc_thresh1 - INTEGER 158 Minimum number of entries to keep. Garbage collector will not 159 purge entries if there are fewer than this number. 160 161 Default: 128 162 163neigh/default/gc_thresh2 - INTEGER 164 Threshold when garbage collector becomes more aggressive about 165 purging entries. Entries older than 5 seconds will be cleared 166 when over this number. 167 168 Default: 512 169 170neigh/default/gc_thresh3 - INTEGER 171 Maximum number of non-PERMANENT neighbor entries allowed. Increase 172 this when using large numbers of interfaces and when communicating 173 with large numbers of directly-connected peers. 174 175 Default: 1024 176 177neigh/default/unres_qlen_bytes - INTEGER 178 The maximum number of bytes which may be used by packets 179 queued for each unresolved address by other network layers. 180 (added in linux 3.3) 181 182 Setting negative value is meaningless and will return error. 183 184 Default: SK_WMEM_MAX, (same as net.core.wmem_default). 185 186 Exact value depends on architecture and kernel options, 187 but should be enough to allow queuing 256 packets 188 of medium size. 189 190neigh/default/unres_qlen - INTEGER 191 The maximum number of packets which may be queued for each 192 unresolved address by other network layers. 193 194 (deprecated in linux 3.3) : use unres_qlen_bytes instead. 195 196 Prior to linux 3.3, the default value is 3 which may cause 197 unexpected packet loss. The current default value is calculated 198 according to default value of unres_qlen_bytes and true size of 199 packet. 200 201 Default: 101 202 203mtu_expires - INTEGER 204 Time, in seconds, that cached PMTU information is kept. 205 206min_adv_mss - INTEGER 207 The advertised MSS depends on the first hop route MTU, but will 208 never be lower than this setting. 209 210fib_notify_on_flag_change - INTEGER 211 Whether to emit RTM_NEWROUTE notifications whenever RTM_F_OFFLOAD/ 212 RTM_F_TRAP/RTM_F_OFFLOAD_FAILED flags are changed. 213 214 After installing a route to the kernel, user space receives an 215 acknowledgment, which means the route was installed in the kernel, 216 but not necessarily in hardware. 217 It is also possible for a route already installed in hardware to change 218 its action and therefore its flags. For example, a host route that is 219 trapping packets can be "promoted" to perform decapsulation following 220 the installation of an IPinIP/VXLAN tunnel. 221 The notifications will indicate to user-space the state of the route. 222 223 Default: 0 (Do not emit notifications.) 224 225 Possible values: 226 227 - 0 - Do not emit notifications. 228 - 1 - Emit notifications. 229 - 2 - Emit notifications only for RTM_F_OFFLOAD_FAILED flag change. 230 231IP Fragmentation: 232 233ipfrag_high_thresh - LONG INTEGER 234 Maximum memory used to reassemble IP fragments. 235 236ipfrag_low_thresh - LONG INTEGER 237 (Obsolete since linux-4.17) 238 Maximum memory used to reassemble IP fragments before the kernel 239 begins to remove incomplete fragment queues to free up resources. 240 The kernel still accepts new fragments for defragmentation. 241 242ipfrag_time - INTEGER 243 Time in seconds to keep an IP fragment in memory. 244 245ipfrag_max_dist - INTEGER 246 ipfrag_max_dist is a non-negative integer value which defines the 247 maximum "disorder" which is allowed among fragments which share a 248 common IP source address. Note that reordering of packets is 249 not unusual, but if a large number of fragments arrive from a source 250 IP address while a particular fragment queue remains incomplete, it 251 probably indicates that one or more fragments belonging to that queue 252 have been lost. When ipfrag_max_dist is positive, an additional check 253 is done on fragments before they are added to a reassembly queue - if 254 ipfrag_max_dist (or more) fragments have arrived from a particular IP 255 address between additions to any IP fragment queue using that source 256 address, it's presumed that one or more fragments in the queue are 257 lost. The existing fragment queue will be dropped, and a new one 258 started. An ipfrag_max_dist value of zero disables this check. 259 260 Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can 261 result in unnecessarily dropping fragment queues when normal 262 reordering of packets occurs, which could lead to poor application 263 performance. Using a very large value, e.g. 50000, increases the 264 likelihood of incorrectly reassembling IP fragments that originate 265 from different IP datagrams, which could result in data corruption. 266 Default: 64 267 268INET peer storage 269================= 270 271inet_peer_threshold - INTEGER 272 The approximate size of the storage. Starting from this threshold 273 entries will be thrown aggressively. This threshold also determines 274 entries' time-to-live and time intervals between garbage collection 275 passes. More entries, less time-to-live, less GC interval. 276 277inet_peer_minttl - INTEGER 278 Minimum time-to-live of entries. Should be enough to cover fragment 279 time-to-live on the reassembling side. This minimum time-to-live is 280 guaranteed if the pool size is less than inet_peer_threshold. 281 Measured in seconds. 282 283inet_peer_maxttl - INTEGER 284 Maximum time-to-live of entries. Unused entries will expire after 285 this period of time if there is no memory pressure on the pool (i.e. 286 when the number of entries in the pool is very small). 287 Measured in seconds. 288 289TCP variables 290============= 291 292somaxconn - INTEGER 293 Limit of socket listen() backlog, known in userspace as SOMAXCONN. 294 Defaults to 4096. (Was 128 before linux-5.4) 295 See also tcp_max_syn_backlog for additional tuning for TCP sockets. 296 297tcp_abort_on_overflow - BOOLEAN 298 If listening service is too slow to accept new connections, 299 reset them. Default state is FALSE. It means that if overflow 300 occurred due to a burst, connection will recover. Enable this 301 option _only_ if you are really sure that listening daemon 302 cannot be tuned to accept connections faster. Enabling this 303 option can harm clients of your server. 304 305tcp_adv_win_scale - INTEGER 306 Count buffering overhead as bytes/2^tcp_adv_win_scale 307 (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale), 308 if it is <= 0. 309 310 Possible values are [-31, 31], inclusive. 311 312 Default: 1 313 314tcp_allowed_congestion_control - STRING 315 Show/set the congestion control choices available to non-privileged 316 processes. The list is a subset of those listed in 317 tcp_available_congestion_control. 318 319 Default is "reno" and the default setting (tcp_congestion_control). 320 321tcp_app_win - INTEGER 322 Reserve max(window/2^tcp_app_win, mss) of window for application 323 buffer. Value 0 is special, it means that nothing is reserved. 324 325 Default: 31 326 327tcp_autocorking - BOOLEAN 328 Enable TCP auto corking : 329 When applications do consecutive small write()/sendmsg() system calls, 330 we try to coalesce these small writes as much as possible, to lower 331 total amount of sent packets. This is done if at least one prior 332 packet for the flow is waiting in Qdisc queues or device transmit 333 queue. Applications can still use TCP_CORK for optimal behavior 334 when they know how/when to uncork their sockets. 335 336 Default : 1 337 338tcp_available_congestion_control - STRING 339 Shows the available congestion control choices that are registered. 340 More congestion control algorithms may be available as modules, 341 but not loaded. 342 343tcp_base_mss - INTEGER 344 The initial value of search_low to be used by the packetization layer 345 Path MTU discovery (MTU probing). If MTU probing is enabled, 346 this is the initial MSS used by the connection. 347 348tcp_mtu_probe_floor - INTEGER 349 If MTU probing is enabled this caps the minimum MSS used for search_low 350 for the connection. 351 352 Default : 48 353 354tcp_min_snd_mss - INTEGER 355 TCP SYN and SYNACK messages usually advertise an ADVMSS option, 356 as described in RFC 1122 and RFC 6691. 357 358 If this ADVMSS option is smaller than tcp_min_snd_mss, 359 it is silently capped to tcp_min_snd_mss. 360 361 Default : 48 (at least 8 bytes of payload per segment) 362 363tcp_congestion_control - STRING 364 Set the congestion control algorithm to be used for new 365 connections. The algorithm "reno" is always available, but 366 additional choices may be available based on kernel configuration. 367 Default is set as part of kernel configuration. 368 For passive connections, the listener congestion control choice 369 is inherited. 370 371 [see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ] 372 373tcp_dsack - BOOLEAN 374 Allows TCP to send "duplicate" SACKs. 375 376tcp_early_retrans - INTEGER 377 Tail loss probe (TLP) converts RTOs occurring due to tail 378 losses into fast recovery (draft-ietf-tcpm-rack). Note that 379 TLP requires RACK to function properly (see tcp_recovery below) 380 381 Possible values: 382 383 - 0 disables TLP 384 - 3 or 4 enables TLP 385 386 Default: 3 387 388tcp_ecn - INTEGER 389 Control use of Explicit Congestion Notification (ECN) by TCP. 390 ECN is used only when both ends of the TCP connection indicate 391 support for it. This feature is useful in avoiding losses due 392 to congestion by allowing supporting routers to signal 393 congestion before having to drop packets. 394 395 Possible values are: 396 397 = ===================================================== 398 0 Disable ECN. Neither initiate nor accept ECN. 399 1 Enable ECN when requested by incoming connections and 400 also request ECN on outgoing connection attempts. 401 2 Enable ECN when requested by incoming connections 402 but do not request ECN on outgoing connections. 403 = ===================================================== 404 405 Default: 2 406 407tcp_ecn_fallback - BOOLEAN 408 If the kernel detects that ECN connection misbehaves, enable fall 409 back to non-ECN. Currently, this knob implements the fallback 410 from RFC3168, section 6.1.1.1., but we reserve that in future, 411 additional detection mechanisms could be implemented under this 412 knob. The value is not used, if tcp_ecn or per route (or congestion 413 control) ECN settings are disabled. 414 415 Default: 1 (fallback enabled) 416 417tcp_fack - BOOLEAN 418 This is a legacy option, it has no effect anymore. 419 420tcp_fin_timeout - INTEGER 421 The length of time an orphaned (no longer referenced by any 422 application) connection will remain in the FIN_WAIT_2 state 423 before it is aborted at the local end. While a perfectly 424 valid "receive only" state for an un-orphaned connection, an 425 orphaned connection in FIN_WAIT_2 state could otherwise wait 426 forever for the remote to close its end of the connection. 427 428 Cf. tcp_max_orphans 429 430 Default: 60 seconds 431 432tcp_frto - INTEGER 433 Enables Forward RTO-Recovery (F-RTO) defined in RFC5682. 434 F-RTO is an enhanced recovery algorithm for TCP retransmission 435 timeouts. It is particularly beneficial in networks where the 436 RTT fluctuates (e.g., wireless). F-RTO is sender-side only 437 modification. It does not require any support from the peer. 438 439 By default it's enabled with a non-zero value. 0 disables F-RTO. 440 441tcp_fwmark_accept - BOOLEAN 442 If set, incoming connections to listening sockets that do not have a 443 socket mark will set the mark of the accepting socket to the fwmark of 444 the incoming SYN packet. This will cause all packets on that connection 445 (starting from the first SYNACK) to be sent with that fwmark. The 446 listening socket's mark is unchanged. Listening sockets that already 447 have a fwmark set via setsockopt(SOL_SOCKET, SO_MARK, ...) are 448 unaffected. 449 450 Default: 0 451 452tcp_invalid_ratelimit - INTEGER 453 Limit the maximal rate for sending duplicate acknowledgments 454 in response to incoming TCP packets that are for an existing 455 connection but that are invalid due to any of these reasons: 456 457 (a) out-of-window sequence number, 458 (b) out-of-window acknowledgment number, or 459 (c) PAWS (Protection Against Wrapped Sequence numbers) check failure 460 461 This can help mitigate simple "ack loop" DoS attacks, wherein 462 a buggy or malicious middlebox or man-in-the-middle can 463 rewrite TCP header fields in manner that causes each endpoint 464 to think that the other is sending invalid TCP segments, thus 465 causing each side to send an unterminating stream of duplicate 466 acknowledgments for invalid segments. 467 468 Using 0 disables rate-limiting of dupacks in response to 469 invalid segments; otherwise this value specifies the minimal 470 space between sending such dupacks, in milliseconds. 471 472 Default: 500 (milliseconds). 473 474tcp_keepalive_time - INTEGER 475 How often TCP sends out keepalive messages when keepalive is enabled. 476 Default: 2hours. 477 478tcp_keepalive_probes - INTEGER 479 How many keepalive probes TCP sends out, until it decides that the 480 connection is broken. Default value: 9. 481 482tcp_keepalive_intvl - INTEGER 483 How frequently the probes are send out. Multiplied by 484 tcp_keepalive_probes it is time to kill not responding connection, 485 after probes started. Default value: 75sec i.e. connection 486 will be aborted after ~11 minutes of retries. 487 488tcp_l3mdev_accept - BOOLEAN 489 Enables child sockets to inherit the L3 master device index. 490 Enabling this option allows a "global" listen socket to work 491 across L3 master domains (e.g., VRFs) with connected sockets 492 derived from the listen socket to be bound to the L3 domain in 493 which the packets originated. Only valid when the kernel was 494 compiled with CONFIG_NET_L3_MASTER_DEV. 495 496 Default: 0 (disabled) 497 498tcp_low_latency - BOOLEAN 499 This is a legacy option, it has no effect anymore. 500 501tcp_max_orphans - INTEGER 502 Maximal number of TCP sockets not attached to any user file handle, 503 held by system. If this number is exceeded orphaned connections are 504 reset immediately and warning is printed. This limit exists 505 only to prevent simple DoS attacks, you _must_ not rely on this 506 or lower the limit artificially, but rather increase it 507 (probably, after increasing installed memory), 508 if network conditions require more than default value, 509 and tune network services to linger and kill such states 510 more aggressively. Let me to remind again: each orphan eats 511 up to ~64K of unswappable memory. 512 513tcp_max_syn_backlog - INTEGER 514 Maximal number of remembered connection requests (SYN_RECV), 515 which have not received an acknowledgment from connecting client. 516 517 This is a per-listener limit. 518 519 The minimal value is 128 for low memory machines, and it will 520 increase in proportion to the memory of machine. 521 522 If server suffers from overload, try increasing this number. 523 524 Remember to also check /proc/sys/net/core/somaxconn 525 A SYN_RECV request socket consumes about 304 bytes of memory. 526 527tcp_max_tw_buckets - INTEGER 528 Maximal number of timewait sockets held by system simultaneously. 529 If this number is exceeded time-wait socket is immediately destroyed 530 and warning is printed. This limit exists only to prevent 531 simple DoS attacks, you _must_ not lower the limit artificially, 532 but rather increase it (probably, after increasing installed memory), 533 if network conditions require more than default value. 534 535tcp_mem - vector of 3 INTEGERs: min, pressure, max 536 min: below this number of pages TCP is not bothered about its 537 memory appetite. 538 539 pressure: when amount of memory allocated by TCP exceeds this number 540 of pages, TCP moderates its memory consumption and enters memory 541 pressure mode, which is exited when memory consumption falls 542 under "min". 543 544 max: number of pages allowed for queueing by all TCP sockets. 545 546 Defaults are calculated at boot time from amount of available 547 memory. 548 549tcp_min_rtt_wlen - INTEGER 550 The window length of the windowed min filter to track the minimum RTT. 551 A shorter window lets a flow more quickly pick up new (higher) 552 minimum RTT when it is moved to a longer path (e.g., due to traffic 553 engineering). A longer window makes the filter more resistant to RTT 554 inflations such as transient congestion. The unit is seconds. 555 556 Possible values: 0 - 86400 (1 day) 557 558 Default: 300 559 560tcp_moderate_rcvbuf - BOOLEAN 561 If set, TCP performs receive buffer auto-tuning, attempting to 562 automatically size the buffer (no greater than tcp_rmem[2]) to 563 match the size required by the path for full throughput. Enabled by 564 default. 565 566tcp_mtu_probing - INTEGER 567 Controls TCP Packetization-Layer Path MTU Discovery. Takes three 568 values: 569 570 - 0 - Disabled 571 - 1 - Disabled by default, enabled when an ICMP black hole detected 572 - 2 - Always enabled, use initial MSS of tcp_base_mss. 573 574tcp_probe_interval - UNSIGNED INTEGER 575 Controls how often to start TCP Packetization-Layer Path MTU 576 Discovery reprobe. The default is reprobing every 10 minutes as 577 per RFC4821. 578 579tcp_probe_threshold - INTEGER 580 Controls when TCP Packetization-Layer Path MTU Discovery probing 581 will stop in respect to the width of search range in bytes. Default 582 is 8 bytes. 583 584tcp_no_metrics_save - BOOLEAN 585 By default, TCP saves various connection metrics in the route cache 586 when the connection closes, so that connections established in the 587 near future can use these to set initial conditions. Usually, this 588 increases overall performance, but may sometimes cause performance 589 degradation. If set, TCP will not cache metrics on closing 590 connections. 591 592tcp_no_ssthresh_metrics_save - BOOLEAN 593 Controls whether TCP saves ssthresh metrics in the route cache. 594 595 Default is 1, which disables ssthresh metrics. 596 597tcp_orphan_retries - INTEGER 598 This value influences the timeout of a locally closed TCP connection, 599 when RTO retransmissions remain unacknowledged. 600 See tcp_retries2 for more details. 601 602 The default value is 8. 603 604 If your machine is a loaded WEB server, 605 you should think about lowering this value, such sockets 606 may consume significant resources. Cf. tcp_max_orphans. 607 608tcp_recovery - INTEGER 609 This value is a bitmap to enable various experimental loss recovery 610 features. 611 612 ========= ============================================================= 613 RACK: 0x1 enables the RACK loss detection for fast detection of lost 614 retransmissions and tail drops. It also subsumes and disables 615 RFC6675 recovery for SACK connections. 616 617 RACK: 0x2 makes RACK's reordering window static (min_rtt/4). 618 619 RACK: 0x4 disables RACK's DUPACK threshold heuristic 620 ========= ============================================================= 621 622 Default: 0x1 623 624tcp_reordering - INTEGER 625 Initial reordering level of packets in a TCP stream. 626 TCP stack can then dynamically adjust flow reordering level 627 between this initial value and tcp_max_reordering 628 629 Default: 3 630 631tcp_max_reordering - INTEGER 632 Maximal reordering level of packets in a TCP stream. 633 300 is a fairly conservative value, but you might increase it 634 if paths are using per packet load balancing (like bonding rr mode) 635 636 Default: 300 637 638tcp_retrans_collapse - BOOLEAN 639 Bug-to-bug compatibility with some broken printers. 640 On retransmit try to send bigger packets to work around bugs in 641 certain TCP stacks. 642 643tcp_retries1 - INTEGER 644 This value influences the time, after which TCP decides, that 645 something is wrong due to unacknowledged RTO retransmissions, 646 and reports this suspicion to the network layer. 647 See tcp_retries2 for more details. 648 649 RFC 1122 recommends at least 3 retransmissions, which is the 650 default. 651 652tcp_retries2 - INTEGER 653 This value influences the timeout of an alive TCP connection, 654 when RTO retransmissions remain unacknowledged. 655 Given a value of N, a hypothetical TCP connection following 656 exponential backoff with an initial RTO of TCP_RTO_MIN would 657 retransmit N times before killing the connection at the (N+1)th RTO. 658 659 The default value of 15 yields a hypothetical timeout of 924.6 660 seconds and is a lower bound for the effective timeout. 661 TCP will effectively time out at the first RTO which exceeds the 662 hypothetical timeout. 663 664 RFC 1122 recommends at least 100 seconds for the timeout, 665 which corresponds to a value of at least 8. 666 667tcp_rfc1337 - BOOLEAN 668 If set, the TCP stack behaves conforming to RFC1337. If unset, 669 we are not conforming to RFC, but prevent TCP TIME_WAIT 670 assassination. 671 672 Default: 0 673 674tcp_rmem - vector of 3 INTEGERs: min, default, max 675 min: Minimal size of receive buffer used by TCP sockets. 676 It is guaranteed to each TCP socket, even under moderate memory 677 pressure. 678 679 Default: 4K 680 681 default: initial size of receive buffer used by TCP sockets. 682 This value overrides net.core.rmem_default used by other protocols. 683 Default: 131072 bytes. 684 This value results in initial window of 65535. 685 686 max: maximal size of receive buffer allowed for automatically 687 selected receiver buffers for TCP socket. This value does not override 688 net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables 689 automatic tuning of that socket's receive buffer size, in which 690 case this value is ignored. 691 Default: between 131072 and 6MB, depending on RAM size. 692 693tcp_sack - BOOLEAN 694 Enable select acknowledgments (SACKS). 695 696tcp_comp_sack_delay_ns - LONG INTEGER 697 TCP tries to reduce number of SACK sent, using a timer 698 based on 5% of SRTT, capped by this sysctl, in nano seconds. 699 The default is 1ms, based on TSO autosizing period. 700 701 Default : 1,000,000 ns (1 ms) 702 703tcp_comp_sack_slack_ns - LONG INTEGER 704 This sysctl control the slack used when arming the 705 timer used by SACK compression. This gives extra time 706 for small RTT flows, and reduces system overhead by allowing 707 opportunistic reduction of timer interrupts. 708 709 Default : 100,000 ns (100 us) 710 711tcp_comp_sack_nr - INTEGER 712 Max number of SACK that can be compressed. 713 Using 0 disables SACK compression. 714 715 Default : 44 716 717tcp_slow_start_after_idle - BOOLEAN 718 If set, provide RFC2861 behavior and time out the congestion 719 window after an idle period. An idle period is defined at 720 the current RTO. If unset, the congestion window will not 721 be timed out after an idle period. 722 723 Default: 1 724 725tcp_stdurg - BOOLEAN 726 Use the Host requirements interpretation of the TCP urgent pointer field. 727 Most hosts use the older BSD interpretation, so if you turn this on 728 Linux might not communicate correctly with them. 729 730 Default: FALSE 731 732tcp_synack_retries - INTEGER 733 Number of times SYNACKs for a passive TCP connection attempt will 734 be retransmitted. Should not be higher than 255. Default value 735 is 5, which corresponds to 31seconds till the last retransmission 736 with the current initial RTO of 1second. With this the final timeout 737 for a passive TCP connection will happen after 63seconds. 738 739tcp_syncookies - INTEGER 740 Only valid when the kernel was compiled with CONFIG_SYN_COOKIES 741 Send out syncookies when the syn backlog queue of a socket 742 overflows. This is to prevent against the common 'SYN flood attack' 743 Default: 1 744 745 Note, that syncookies is fallback facility. 746 It MUST NOT be used to help highly loaded servers to stand 747 against legal connection rate. If you see SYN flood warnings 748 in your logs, but investigation shows that they occur 749 because of overload with legal connections, you should tune 750 another parameters until this warning disappear. 751 See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow. 752 753 syncookies seriously violate TCP protocol, do not allow 754 to use TCP extensions, can result in serious degradation 755 of some services (f.e. SMTP relaying), visible not by you, 756 but your clients and relays, contacting you. While you see 757 SYN flood warnings in logs not being really flooded, your server 758 is seriously misconfigured. 759 760 If you want to test which effects syncookies have to your 761 network connections you can set this knob to 2 to enable 762 unconditionally generation of syncookies. 763 764tcp_migrate_req - BOOLEAN 765 The incoming connection is tied to a specific listening socket when 766 the initial SYN packet is received during the three-way handshake. 767 When a listener is closed, in-flight request sockets during the 768 handshake and established sockets in the accept queue are aborted. 769 770 If the listener has SO_REUSEPORT enabled, other listeners on the 771 same port should have been able to accept such connections. This 772 option makes it possible to migrate such child sockets to another 773 listener after close() or shutdown(). 774 775 The BPF_SK_REUSEPORT_SELECT_OR_MIGRATE type of eBPF program should 776 usually be used to define the policy to pick an alive listener. 777 Otherwise, the kernel will randomly pick an alive listener only if 778 this option is enabled. 779 780 Note that migration between listeners with different settings may 781 crash applications. Let's say migration happens from listener A to 782 B, and only B has TCP_SAVE_SYN enabled. B cannot read SYN data from 783 the requests migrated from A. To avoid such a situation, cancel 784 migration by returning SK_DROP in the type of eBPF program, or 785 disable this option. 786 787 Default: 0 788 789tcp_fastopen - INTEGER 790 Enable TCP Fast Open (RFC7413) to send and accept data in the opening 791 SYN packet. 792 793 The client support is enabled by flag 0x1 (on by default). The client 794 then must use sendmsg() or sendto() with the MSG_FASTOPEN flag, 795 rather than connect() to send data in SYN. 796 797 The server support is enabled by flag 0x2 (off by default). Then 798 either enable for all listeners with another flag (0x400) or 799 enable individual listeners via TCP_FASTOPEN socket option with 800 the option value being the length of the syn-data backlog. 801 802 The values (bitmap) are 803 804 ===== ======== ====================================================== 805 0x1 (client) enables sending data in the opening SYN on the client. 806 0x2 (server) enables the server support, i.e., allowing data in 807 a SYN packet to be accepted and passed to the 808 application before 3-way handshake finishes. 809 0x4 (client) send data in the opening SYN regardless of cookie 810 availability and without a cookie option. 811 0x200 (server) accept data-in-SYN w/o any cookie option present. 812 0x400 (server) enable all listeners to support Fast Open by 813 default without explicit TCP_FASTOPEN socket option. 814 ===== ======== ====================================================== 815 816 Default: 0x1 817 818 Note that additional client or server features are only 819 effective if the basic support (0x1 and 0x2) are enabled respectively. 820 821tcp_fastopen_blackhole_timeout_sec - INTEGER 822 Initial time period in second to disable Fastopen on active TCP sockets 823 when a TFO firewall blackhole issue happens. 824 This time period will grow exponentially when more blackhole issues 825 get detected right after Fastopen is re-enabled and will reset to 826 initial value when the blackhole issue goes away. 827 0 to disable the blackhole detection. 828 829 By default, it is set to 0 (feature is disabled). 830 831tcp_fastopen_key - list of comma separated 32-digit hexadecimal INTEGERs 832 The list consists of a primary key and an optional backup key. The 833 primary key is used for both creating and validating cookies, while the 834 optional backup key is only used for validating cookies. The purpose of 835 the backup key is to maximize TFO validation when keys are rotated. 836 837 A randomly chosen primary key may be configured by the kernel if 838 the tcp_fastopen sysctl is set to 0x400 (see above), or if the 839 TCP_FASTOPEN setsockopt() optname is set and a key has not been 840 previously configured via sysctl. If keys are configured via 841 setsockopt() by using the TCP_FASTOPEN_KEY optname, then those 842 per-socket keys will be used instead of any keys that are specified via 843 sysctl. 844 845 A key is specified as 4 8-digit hexadecimal integers which are separated 846 by a '-' as: xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx. Leading zeros may be 847 omitted. A primary and a backup key may be specified by separating them 848 by a comma. If only one key is specified, it becomes the primary key and 849 any previously configured backup keys are removed. 850 851tcp_syn_retries - INTEGER 852 Number of times initial SYNs for an active TCP connection attempt 853 will be retransmitted. Should not be higher than 127. Default value 854 is 6, which corresponds to 63seconds till the last retransmission 855 with the current initial RTO of 1second. With this the final timeout 856 for an active TCP connection attempt will happen after 127seconds. 857 858tcp_timestamps - INTEGER 859 Enable timestamps as defined in RFC1323. 860 861 - 0: Disabled. 862 - 1: Enable timestamps as defined in RFC1323 and use random offset for 863 each connection rather than only using the current time. 864 - 2: Like 1, but without random offsets. 865 866 Default: 1 867 868tcp_min_tso_segs - INTEGER 869 Minimal number of segments per TSO frame. 870 871 Since linux-3.12, TCP does an automatic sizing of TSO frames, 872 depending on flow rate, instead of filling 64Kbytes packets. 873 For specific usages, it's possible to force TCP to build big 874 TSO frames. Note that TCP stack might split too big TSO packets 875 if available window is too small. 876 877 Default: 2 878 879tcp_pacing_ss_ratio - INTEGER 880 sk->sk_pacing_rate is set by TCP stack using a ratio applied 881 to current rate. (current_rate = cwnd * mss / srtt) 882 If TCP is in slow start, tcp_pacing_ss_ratio is applied 883 to let TCP probe for bigger speeds, assuming cwnd can be 884 doubled every other RTT. 885 886 Default: 200 887 888tcp_pacing_ca_ratio - INTEGER 889 sk->sk_pacing_rate is set by TCP stack using a ratio applied 890 to current rate. (current_rate = cwnd * mss / srtt) 891 If TCP is in congestion avoidance phase, tcp_pacing_ca_ratio 892 is applied to conservatively probe for bigger throughput. 893 894 Default: 120 895 896tcp_tso_win_divisor - INTEGER 897 This allows control over what percentage of the congestion window 898 can be consumed by a single TSO frame. 899 The setting of this parameter is a choice between burstiness and 900 building larger TSO frames. 901 902 Default: 3 903 904tcp_tw_reuse - INTEGER 905 Enable reuse of TIME-WAIT sockets for new connections when it is 906 safe from protocol viewpoint. 907 908 - 0 - disable 909 - 1 - global enable 910 - 2 - enable for loopback traffic only 911 912 It should not be changed without advice/request of technical 913 experts. 914 915 Default: 2 916 917tcp_window_scaling - BOOLEAN 918 Enable window scaling as defined in RFC1323. 919 920tcp_wmem - vector of 3 INTEGERs: min, default, max 921 min: Amount of memory reserved for send buffers for TCP sockets. 922 Each TCP socket has rights to use it due to fact of its birth. 923 924 Default: 4K 925 926 default: initial size of send buffer used by TCP sockets. This 927 value overrides net.core.wmem_default used by other protocols. 928 929 It is usually lower than net.core.wmem_default. 930 931 Default: 16K 932 933 max: Maximal amount of memory allowed for automatically tuned 934 send buffers for TCP sockets. This value does not override 935 net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables 936 automatic tuning of that socket's send buffer size, in which case 937 this value is ignored. 938 939 Default: between 64K and 4MB, depending on RAM size. 940 941tcp_notsent_lowat - UNSIGNED INTEGER 942 A TCP socket can control the amount of unsent bytes in its write queue, 943 thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll() 944 reports POLLOUT events if the amount of unsent bytes is below a per 945 socket value, and if the write queue is not full. sendmsg() will 946 also not add new buffers if the limit is hit. 947 948 This global variable controls the amount of unsent data for 949 sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change 950 to the global variable has immediate effect. 951 952 Default: UINT_MAX (0xFFFFFFFF) 953 954tcp_workaround_signed_windows - BOOLEAN 955 If set, assume no receipt of a window scaling option means the 956 remote TCP is broken and treats the window as a signed quantity. 957 If unset, assume the remote TCP is not broken even if we do 958 not receive a window scaling option from them. 959 960 Default: 0 961 962tcp_thin_linear_timeouts - BOOLEAN 963 Enable dynamic triggering of linear timeouts for thin streams. 964 If set, a check is performed upon retransmission by timeout to 965 determine if the stream is thin (less than 4 packets in flight). 966 As long as the stream is found to be thin, up to 6 linear 967 timeouts may be performed before exponential backoff mode is 968 initiated. This improves retransmission latency for 969 non-aggressive thin streams, often found to be time-dependent. 970 For more information on thin streams, see 971 Documentation/networking/tcp-thin.rst 972 973 Default: 0 974 975tcp_limit_output_bytes - INTEGER 976 Controls TCP Small Queue limit per tcp socket. 977 TCP bulk sender tends to increase packets in flight until it 978 gets losses notifications. With SNDBUF autotuning, this can 979 result in a large amount of packets queued on the local machine 980 (e.g.: qdiscs, CPU backlog, or device) hurting latency of other 981 flows, for typical pfifo_fast qdiscs. tcp_limit_output_bytes 982 limits the number of bytes on qdisc or device to reduce artificial 983 RTT/cwnd and reduce bufferbloat. 984 985 Default: 1048576 (16 * 65536) 986 987tcp_challenge_ack_limit - INTEGER 988 Limits number of Challenge ACK sent per second, as recommended 989 in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks) 990 Default: 1000 991 992UDP variables 993============= 994 995udp_l3mdev_accept - BOOLEAN 996 Enabling this option allows a "global" bound socket to work 997 across L3 master domains (e.g., VRFs) with packets capable of 998 being received regardless of the L3 domain in which they 999 originated. Only valid when the kernel was compiled with 1000 CONFIG_NET_L3_MASTER_DEV. 1001 1002 Default: 0 (disabled) 1003 1004udp_mem - vector of 3 INTEGERs: min, pressure, max 1005 Number of pages allowed for queueing by all UDP sockets. 1006 1007 min: Below this number of pages UDP is not bothered about its 1008 memory appetite. When amount of memory allocated by UDP exceeds 1009 this number, UDP starts to moderate memory usage. 1010 1011 pressure: This value was introduced to follow format of tcp_mem. 1012 1013 max: Number of pages allowed for queueing by all UDP sockets. 1014 1015 Default is calculated at boot time from amount of available memory. 1016 1017udp_rmem_min - INTEGER 1018 Minimal size of receive buffer used by UDP sockets in moderation. 1019 Each UDP socket is able to use the size for receiving data, even if 1020 total pages of UDP sockets exceed udp_mem pressure. The unit is byte. 1021 1022 Default: 4K 1023 1024udp_wmem_min - INTEGER 1025 Minimal size of send buffer used by UDP sockets in moderation. 1026 Each UDP socket is able to use the size for sending data, even if 1027 total pages of UDP sockets exceed udp_mem pressure. The unit is byte. 1028 1029 Default: 4K 1030 1031RAW variables 1032============= 1033 1034raw_l3mdev_accept - BOOLEAN 1035 Enabling this option allows a "global" bound socket to work 1036 across L3 master domains (e.g., VRFs) with packets capable of 1037 being received regardless of the L3 domain in which they 1038 originated. Only valid when the kernel was compiled with 1039 CONFIG_NET_L3_MASTER_DEV. 1040 1041 Default: 1 (enabled) 1042 1043CIPSOv4 Variables 1044================= 1045 1046cipso_cache_enable - BOOLEAN 1047 If set, enable additions to and lookups from the CIPSO label mapping 1048 cache. If unset, additions are ignored and lookups always result in a 1049 miss. However, regardless of the setting the cache is still 1050 invalidated when required when means you can safely toggle this on and 1051 off and the cache will always be "safe". 1052 1053 Default: 1 1054 1055cipso_cache_bucket_size - INTEGER 1056 The CIPSO label cache consists of a fixed size hash table with each 1057 hash bucket containing a number of cache entries. This variable limits 1058 the number of entries in each hash bucket; the larger the value the 1059 more CIPSO label mappings that can be cached. When the number of 1060 entries in a given hash bucket reaches this limit adding new entries 1061 causes the oldest entry in the bucket to be removed to make room. 1062 1063 Default: 10 1064 1065cipso_rbm_optfmt - BOOLEAN 1066 Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of 1067 the CIPSO draft specification (see Documentation/netlabel for details). 1068 This means that when set the CIPSO tag will be padded with empty 1069 categories in order to make the packet data 32-bit aligned. 1070 1071 Default: 0 1072 1073cipso_rbm_structvalid - BOOLEAN 1074 If set, do a very strict check of the CIPSO option when 1075 ip_options_compile() is called. If unset, relax the checks done during 1076 ip_options_compile(). Either way is "safe" as errors are caught else 1077 where in the CIPSO processing code but setting this to 0 (False) should 1078 result in less work (i.e. it should be faster) but could cause problems 1079 with other implementations that require strict checking. 1080 1081 Default: 0 1082 1083IP Variables 1084============ 1085 1086ip_local_port_range - 2 INTEGERS 1087 Defines the local port range that is used by TCP and UDP to 1088 choose the local port. The first number is the first, the 1089 second the last local port number. 1090 If possible, it is better these numbers have different parity 1091 (one even and one odd value). 1092 Must be greater than or equal to ip_unprivileged_port_start. 1093 The default values are 32768 and 60999 respectively. 1094 1095ip_local_reserved_ports - list of comma separated ranges 1096 Specify the ports which are reserved for known third-party 1097 applications. These ports will not be used by automatic port 1098 assignments (e.g. when calling connect() or bind() with port 1099 number 0). Explicit port allocation behavior is unchanged. 1100 1101 The format used for both input and output is a comma separated 1102 list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and 1103 10). Writing to the file will clear all previously reserved 1104 ports and update the current list with the one given in the 1105 input. 1106 1107 Note that ip_local_port_range and ip_local_reserved_ports 1108 settings are independent and both are considered by the kernel 1109 when determining which ports are available for automatic port 1110 assignments. 1111 1112 You can reserve ports which are not in the current 1113 ip_local_port_range, e.g.:: 1114 1115 $ cat /proc/sys/net/ipv4/ip_local_port_range 1116 32000 60999 1117 $ cat /proc/sys/net/ipv4/ip_local_reserved_ports 1118 8080,9148 1119 1120 although this is redundant. However such a setting is useful 1121 if later the port range is changed to a value that will 1122 include the reserved ports. Also keep in mind, that overlapping 1123 of these ranges may affect probability of selecting ephemeral 1124 ports which are right after block of reserved ports. 1125 1126 Default: Empty 1127 1128ip_unprivileged_port_start - INTEGER 1129 This is a per-namespace sysctl. It defines the first 1130 unprivileged port in the network namespace. Privileged ports 1131 require root or CAP_NET_BIND_SERVICE in order to bind to them. 1132 To disable all privileged ports, set this to 0. They must not 1133 overlap with the ip_local_port_range. 1134 1135 Default: 1024 1136 1137ip_nonlocal_bind - BOOLEAN 1138 If set, allows processes to bind() to non-local IP addresses, 1139 which can be quite useful - but may break some applications. 1140 1141 Default: 0 1142 1143ip_autobind_reuse - BOOLEAN 1144 By default, bind() does not select the ports automatically even if 1145 the new socket and all sockets bound to the port have SO_REUSEADDR. 1146 ip_autobind_reuse allows bind() to reuse the port and this is useful 1147 when you use bind()+connect(), but may break some applications. 1148 The preferred solution is to use IP_BIND_ADDRESS_NO_PORT and this 1149 option should only be set by experts. 1150 Default: 0 1151 1152ip_dynaddr - BOOLEAN 1153 If set non-zero, enables support for dynamic addresses. 1154 If set to a non-zero value larger than 1, a kernel log 1155 message will be printed when dynamic address rewriting 1156 occurs. 1157 1158 Default: 0 1159 1160ip_early_demux - BOOLEAN 1161 Optimize input packet processing down to one demux for 1162 certain kinds of local sockets. Currently we only do this 1163 for established TCP and connected UDP sockets. 1164 1165 It may add an additional cost for pure routing workloads that 1166 reduces overall throughput, in such case you should disable it. 1167 1168 Default: 1 1169 1170ping_group_range - 2 INTEGERS 1171 Restrict ICMP_PROTO datagram sockets to users in the group range. 1172 The default is "1 0", meaning, that nobody (not even root) may 1173 create ping sockets. Setting it to "100 100" would grant permissions 1174 to the single group. "0 4294967295" would enable it for the world, "100 1175 4294967295" would enable it for the users, but not daemons. 1176 1177tcp_early_demux - BOOLEAN 1178 Enable early demux for established TCP sockets. 1179 1180 Default: 1 1181 1182udp_early_demux - BOOLEAN 1183 Enable early demux for connected UDP sockets. Disable this if 1184 your system could experience more unconnected load. 1185 1186 Default: 1 1187 1188icmp_echo_ignore_all - BOOLEAN 1189 If set non-zero, then the kernel will ignore all ICMP ECHO 1190 requests sent to it. 1191 1192 Default: 0 1193 1194icmp_echo_enable_probe - BOOLEAN 1195 If set to one, then the kernel will respond to RFC 8335 PROBE 1196 requests sent to it. 1197 1198 Default: 0 1199 1200icmp_echo_ignore_broadcasts - BOOLEAN 1201 If set non-zero, then the kernel will ignore all ICMP ECHO and 1202 TIMESTAMP requests sent to it via broadcast/multicast. 1203 1204 Default: 1 1205 1206icmp_ratelimit - INTEGER 1207 Limit the maximal rates for sending ICMP packets whose type matches 1208 icmp_ratemask (see below) to specific targets. 1209 0 to disable any limiting, 1210 otherwise the minimal space between responses in milliseconds. 1211 Note that another sysctl, icmp_msgs_per_sec limits the number 1212 of ICMP packets sent on all targets. 1213 1214 Default: 1000 1215 1216icmp_msgs_per_sec - INTEGER 1217 Limit maximal number of ICMP packets sent per second from this host. 1218 Only messages whose type matches icmp_ratemask (see below) are 1219 controlled by this limit. For security reasons, the precise count 1220 of messages per second is randomized. 1221 1222 Default: 1000 1223 1224icmp_msgs_burst - INTEGER 1225 icmp_msgs_per_sec controls number of ICMP packets sent per second, 1226 while icmp_msgs_burst controls the burst size of these packets. 1227 For security reasons, the precise burst size is randomized. 1228 1229 Default: 50 1230 1231icmp_ratemask - INTEGER 1232 Mask made of ICMP types for which rates are being limited. 1233 1234 Significant bits: IHGFEDCBA9876543210 1235 1236 Default mask: 0000001100000011000 (6168) 1237 1238 Bit definitions (see include/linux/icmp.h): 1239 1240 = ========================= 1241 0 Echo Reply 1242 3 Destination Unreachable [1]_ 1243 4 Source Quench [1]_ 1244 5 Redirect 1245 8 Echo Request 1246 B Time Exceeded [1]_ 1247 C Parameter Problem [1]_ 1248 D Timestamp Request 1249 E Timestamp Reply 1250 F Info Request 1251 G Info Reply 1252 H Address Mask Request 1253 I Address Mask Reply 1254 = ========================= 1255 1256 .. [1] These are rate limited by default (see default mask above) 1257 1258icmp_ignore_bogus_error_responses - BOOLEAN 1259 Some routers violate RFC1122 by sending bogus responses to broadcast 1260 frames. Such violations are normally logged via a kernel warning. 1261 If this is set to TRUE, the kernel will not give such warnings, which 1262 will avoid log file clutter. 1263 1264 Default: 1 1265 1266icmp_errors_use_inbound_ifaddr - BOOLEAN 1267 1268 If zero, icmp error messages are sent with the primary address of 1269 the exiting interface. 1270 1271 If non-zero, the message will be sent with the primary address of 1272 the interface that received the packet that caused the icmp error. 1273 This is the behaviour many network administrators will expect from 1274 a router. And it can make debugging complicated network layouts 1275 much easier. 1276 1277 Note that if no primary address exists for the interface selected, 1278 then the primary address of the first non-loopback interface that 1279 has one will be used regardless of this setting. 1280 1281 Default: 0 1282 1283igmp_max_memberships - INTEGER 1284 Change the maximum number of multicast groups we can subscribe to. 1285 Default: 20 1286 1287 Theoretical maximum value is bounded by having to send a membership 1288 report in a single datagram (i.e. the report can't span multiple 1289 datagrams, or risk confusing the switch and leaving groups you don't 1290 intend to). 1291 1292 The number of supported groups 'M' is bounded by the number of group 1293 report entries you can fit into a single datagram of 65535 bytes. 1294 1295 M = 65536-sizeof (ip header)/(sizeof(Group record)) 1296 1297 Group records are variable length, with a minimum of 12 bytes. 1298 So net.ipv4.igmp_max_memberships should not be set higher than: 1299 1300 (65536-24) / 12 = 5459 1301 1302 The value 5459 assumes no IP header options, so in practice 1303 this number may be lower. 1304 1305igmp_max_msf - INTEGER 1306 Maximum number of addresses allowed in the source filter list for a 1307 multicast group. 1308 1309 Default: 10 1310 1311igmp_qrv - INTEGER 1312 Controls the IGMP query robustness variable (see RFC2236 8.1). 1313 1314 Default: 2 (as specified by RFC2236 8.1) 1315 1316 Minimum: 1 (as specified by RFC6636 4.5) 1317 1318force_igmp_version - INTEGER 1319 - 0 - (default) No enforcement of a IGMP version, IGMPv1/v2 fallback 1320 allowed. Will back to IGMPv3 mode again if all IGMPv1/v2 Querier 1321 Present timer expires. 1322 - 1 - Enforce to use IGMP version 1. Will also reply IGMPv1 report if 1323 receive IGMPv2/v3 query. 1324 - 2 - Enforce to use IGMP version 2. Will fallback to IGMPv1 if receive 1325 IGMPv1 query message. Will reply report if receive IGMPv3 query. 1326 - 3 - Enforce to use IGMP version 3. The same react with default 0. 1327 1328 .. note:: 1329 1330 this is not the same with force_mld_version because IGMPv3 RFC3376 1331 Security Considerations does not have clear description that we could 1332 ignore other version messages completely as MLDv2 RFC3810. So make 1333 this value as default 0 is recommended. 1334 1335``conf/interface/*`` 1336 changes special settings per interface (where 1337 interface" is the name of your network interface) 1338 1339``conf/all/*`` 1340 is special, changes the settings for all interfaces 1341 1342log_martians - BOOLEAN 1343 Log packets with impossible addresses to kernel log. 1344 log_martians for the interface will be enabled if at least one of 1345 conf/{all,interface}/log_martians is set to TRUE, 1346 it will be disabled otherwise 1347 1348accept_redirects - BOOLEAN 1349 Accept ICMP redirect messages. 1350 accept_redirects for the interface will be enabled if: 1351 1352 - both conf/{all,interface}/accept_redirects are TRUE in the case 1353 forwarding for the interface is enabled 1354 1355 or 1356 1357 - at least one of conf/{all,interface}/accept_redirects is TRUE in the 1358 case forwarding for the interface is disabled 1359 1360 accept_redirects for the interface will be disabled otherwise 1361 1362 default: 1363 1364 - TRUE (host) 1365 - FALSE (router) 1366 1367forwarding - BOOLEAN 1368 Enable IP forwarding on this interface. This controls whether packets 1369 received _on_ this interface can be forwarded. 1370 1371mc_forwarding - BOOLEAN 1372 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE 1373 and a multicast routing daemon is required. 1374 conf/all/mc_forwarding must also be set to TRUE to enable multicast 1375 routing for the interface 1376 1377medium_id - INTEGER 1378 Integer value used to differentiate the devices by the medium they 1379 are attached to. Two devices can have different id values when 1380 the broadcast packets are received only on one of them. 1381 The default value 0 means that the device is the only interface 1382 to its medium, value of -1 means that medium is not known. 1383 1384 Currently, it is used to change the proxy_arp behavior: 1385 the proxy_arp feature is enabled for packets forwarded between 1386 two devices attached to different media. 1387 1388proxy_arp - BOOLEAN 1389 Do proxy arp. 1390 1391 proxy_arp for the interface will be enabled if at least one of 1392 conf/{all,interface}/proxy_arp is set to TRUE, 1393 it will be disabled otherwise 1394 1395proxy_arp_pvlan - BOOLEAN 1396 Private VLAN proxy arp. 1397 1398 Basically allow proxy arp replies back to the same interface 1399 (from which the ARP request/solicitation was received). 1400 1401 This is done to support (ethernet) switch features, like RFC 1402 3069, where the individual ports are NOT allowed to 1403 communicate with each other, but they are allowed to talk to 1404 the upstream router. As described in RFC 3069, it is possible 1405 to allow these hosts to communicate through the upstream 1406 router by proxy_arp'ing. Don't need to be used together with 1407 proxy_arp. 1408 1409 This technology is known by different names: 1410 1411 In RFC 3069 it is called VLAN Aggregation. 1412 Cisco and Allied Telesyn call it Private VLAN. 1413 Hewlett-Packard call it Source-Port filtering or port-isolation. 1414 Ericsson call it MAC-Forced Forwarding (RFC Draft). 1415 1416shared_media - BOOLEAN 1417 Send(router) or accept(host) RFC1620 shared media redirects. 1418 Overrides secure_redirects. 1419 1420 shared_media for the interface will be enabled if at least one of 1421 conf/{all,interface}/shared_media is set to TRUE, 1422 it will be disabled otherwise 1423 1424 default TRUE 1425 1426secure_redirects - BOOLEAN 1427 Accept ICMP redirect messages only to gateways listed in the 1428 interface's current gateway list. Even if disabled, RFC1122 redirect 1429 rules still apply. 1430 1431 Overridden by shared_media. 1432 1433 secure_redirects for the interface will be enabled if at least one of 1434 conf/{all,interface}/secure_redirects is set to TRUE, 1435 it will be disabled otherwise 1436 1437 default TRUE 1438 1439send_redirects - BOOLEAN 1440 Send redirects, if router. 1441 1442 send_redirects for the interface will be enabled if at least one of 1443 conf/{all,interface}/send_redirects is set to TRUE, 1444 it will be disabled otherwise 1445 1446 Default: TRUE 1447 1448bootp_relay - BOOLEAN 1449 Accept packets with source address 0.b.c.d destined 1450 not to this host as local ones. It is supposed, that 1451 BOOTP relay daemon will catch and forward such packets. 1452 conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay 1453 for the interface 1454 1455 default FALSE 1456 1457 Not Implemented Yet. 1458 1459accept_source_route - BOOLEAN 1460 Accept packets with SRR option. 1461 conf/all/accept_source_route must also be set to TRUE to accept packets 1462 with SRR option on the interface 1463 1464 default 1465 1466 - TRUE (router) 1467 - FALSE (host) 1468 1469accept_local - BOOLEAN 1470 Accept packets with local source addresses. In combination with 1471 suitable routing, this can be used to direct packets between two 1472 local interfaces over the wire and have them accepted properly. 1473 default FALSE 1474 1475route_localnet - BOOLEAN 1476 Do not consider loopback addresses as martian source or destination 1477 while routing. This enables the use of 127/8 for local routing purposes. 1478 1479 default FALSE 1480 1481rp_filter - INTEGER 1482 - 0 - No source validation. 1483 - 1 - Strict mode as defined in RFC3704 Strict Reverse Path 1484 Each incoming packet is tested against the FIB and if the interface 1485 is not the best reverse path the packet check will fail. 1486 By default failed packets are discarded. 1487 - 2 - Loose mode as defined in RFC3704 Loose Reverse Path 1488 Each incoming packet's source address is also tested against the FIB 1489 and if the source address is not reachable via any interface 1490 the packet check will fail. 1491 1492 Current recommended practice in RFC3704 is to enable strict mode 1493 to prevent IP spoofing from DDos attacks. If using asymmetric routing 1494 or other complicated routing, then loose mode is recommended. 1495 1496 The max value from conf/{all,interface}/rp_filter is used 1497 when doing source validation on the {interface}. 1498 1499 Default value is 0. Note that some distributions enable it 1500 in startup scripts. 1501 1502src_valid_mark - BOOLEAN 1503 - 0 - The fwmark of the packet is not included in reverse path 1504 route lookup. This allows for asymmetric routing configurations 1505 utilizing the fwmark in only one direction, e.g., transparent 1506 proxying. 1507 1508 - 1 - The fwmark of the packet is included in reverse path route 1509 lookup. This permits rp_filter to function when the fwmark is 1510 used for routing traffic in both directions. 1511 1512 This setting also affects the utilization of fmwark when 1513 performing source address selection for ICMP replies, or 1514 determining addresses stored for the IPOPT_TS_TSANDADDR and 1515 IPOPT_RR IP options. 1516 1517 The max value from conf/{all,interface}/src_valid_mark is used. 1518 1519 Default value is 0. 1520 1521arp_filter - BOOLEAN 1522 - 1 - Allows you to have multiple network interfaces on the same 1523 subnet, and have the ARPs for each interface be answered 1524 based on whether or not the kernel would route a packet from 1525 the ARP'd IP out that interface (therefore you must use source 1526 based routing for this to work). In other words it allows control 1527 of which cards (usually 1) will respond to an arp request. 1528 1529 - 0 - (default) The kernel can respond to arp requests with addresses 1530 from other interfaces. This may seem wrong but it usually makes 1531 sense, because it increases the chance of successful communication. 1532 IP addresses are owned by the complete host on Linux, not by 1533 particular interfaces. Only for more complex setups like load- 1534 balancing, does this behaviour cause problems. 1535 1536 arp_filter for the interface will be enabled if at least one of 1537 conf/{all,interface}/arp_filter is set to TRUE, 1538 it will be disabled otherwise 1539 1540arp_announce - INTEGER 1541 Define different restriction levels for announcing the local 1542 source IP address from IP packets in ARP requests sent on 1543 interface: 1544 1545 - 0 - (default) Use any local address, configured on any interface 1546 - 1 - Try to avoid local addresses that are not in the target's 1547 subnet for this interface. This mode is useful when target 1548 hosts reachable via this interface require the source IP 1549 address in ARP requests to be part of their logical network 1550 configured on the receiving interface. When we generate the 1551 request we will check all our subnets that include the 1552 target IP and will preserve the source address if it is from 1553 such subnet. If there is no such subnet we select source 1554 address according to the rules for level 2. 1555 - 2 - Always use the best local address for this target. 1556 In this mode we ignore the source address in the IP packet 1557 and try to select local address that we prefer for talks with 1558 the target host. Such local address is selected by looking 1559 for primary IP addresses on all our subnets on the outgoing 1560 interface that include the target IP address. If no suitable 1561 local address is found we select the first local address 1562 we have on the outgoing interface or on all other interfaces, 1563 with the hope we will receive reply for our request and 1564 even sometimes no matter the source IP address we announce. 1565 1566 The max value from conf/{all,interface}/arp_announce is used. 1567 1568 Increasing the restriction level gives more chance for 1569 receiving answer from the resolved target while decreasing 1570 the level announces more valid sender's information. 1571 1572arp_ignore - INTEGER 1573 Define different modes for sending replies in response to 1574 received ARP requests that resolve local target IP addresses: 1575 1576 - 0 - (default): reply for any local target IP address, configured 1577 on any interface 1578 - 1 - reply only if the target IP address is local address 1579 configured on the incoming interface 1580 - 2 - reply only if the target IP address is local address 1581 configured on the incoming interface and both with the 1582 sender's IP address are part from same subnet on this interface 1583 - 3 - do not reply for local addresses configured with scope host, 1584 only resolutions for global and link addresses are replied 1585 - 4-7 - reserved 1586 - 8 - do not reply for all local addresses 1587 1588 The max value from conf/{all,interface}/arp_ignore is used 1589 when ARP request is received on the {interface} 1590 1591arp_notify - BOOLEAN 1592 Define mode for notification of address and device changes. 1593 1594 == ========================================================== 1595 0 (default): do nothing 1596 1 Generate gratuitous arp requests when device is brought up 1597 or hardware address changes. 1598 == ========================================================== 1599 1600arp_accept - BOOLEAN 1601 Define behavior for gratuitous ARP frames who's IP is not 1602 already present in the ARP table: 1603 1604 - 0 - don't create new entries in the ARP table 1605 - 1 - create new entries in the ARP table 1606 1607 Both replies and requests type gratuitous arp will trigger the 1608 ARP table to be updated, if this setting is on. 1609 1610 If the ARP table already contains the IP address of the 1611 gratuitous arp frame, the arp table will be updated regardless 1612 if this setting is on or off. 1613 1614arp_evict_nocarrier - BOOLEAN 1615 Clears the ARP cache on NOCARRIER events. This option is important for 1616 wireless devices where the ARP cache should not be cleared when roaming 1617 between access points on the same network. In most cases this should 1618 remain as the default (1). 1619 1620 - 1 - (default): Clear the ARP cache on NOCARRIER events 1621 - 0 - Do not clear ARP cache on NOCARRIER events 1622 1623mcast_solicit - INTEGER 1624 The maximum number of multicast probes in INCOMPLETE state, 1625 when the associated hardware address is unknown. Defaults 1626 to 3. 1627 1628ucast_solicit - INTEGER 1629 The maximum number of unicast probes in PROBE state, when 1630 the hardware address is being reconfirmed. Defaults to 3. 1631 1632app_solicit - INTEGER 1633 The maximum number of probes to send to the user space ARP daemon 1634 via netlink before dropping back to multicast probes (see 1635 mcast_resolicit). Defaults to 0. 1636 1637mcast_resolicit - INTEGER 1638 The maximum number of multicast probes after unicast and 1639 app probes in PROBE state. Defaults to 0. 1640 1641disable_policy - BOOLEAN 1642 Disable IPSEC policy (SPD) for this interface 1643 1644disable_xfrm - BOOLEAN 1645 Disable IPSEC encryption on this interface, whatever the policy 1646 1647igmpv2_unsolicited_report_interval - INTEGER 1648 The interval in milliseconds in which the next unsolicited 1649 IGMPv1 or IGMPv2 report retransmit will take place. 1650 1651 Default: 10000 (10 seconds) 1652 1653igmpv3_unsolicited_report_interval - INTEGER 1654 The interval in milliseconds in which the next unsolicited 1655 IGMPv3 report retransmit will take place. 1656 1657 Default: 1000 (1 seconds) 1658 1659ignore_routes_with_linkdown - BOOLEAN 1660 Ignore routes whose link is down when performing a FIB lookup. 1661 1662promote_secondaries - BOOLEAN 1663 When a primary IP address is removed from this interface 1664 promote a corresponding secondary IP address instead of 1665 removing all the corresponding secondary IP addresses. 1666 1667drop_unicast_in_l2_multicast - BOOLEAN 1668 Drop any unicast IP packets that are received in link-layer 1669 multicast (or broadcast) frames. 1670 1671 This behavior (for multicast) is actually a SHOULD in RFC 1672 1122, but is disabled by default for compatibility reasons. 1673 1674 Default: off (0) 1675 1676drop_gratuitous_arp - BOOLEAN 1677 Drop all gratuitous ARP frames, for example if there's a known 1678 good ARP proxy on the network and such frames need not be used 1679 (or in the case of 802.11, must not be used to prevent attacks.) 1680 1681 Default: off (0) 1682 1683 1684tag - INTEGER 1685 Allows you to write a number, which can be used as required. 1686 1687 Default value is 0. 1688 1689xfrm4_gc_thresh - INTEGER 1690 (Obsolete since linux-4.14) 1691 The threshold at which we will start garbage collecting for IPv4 1692 destination cache entries. At twice this value the system will 1693 refuse new allocations. 1694 1695igmp_link_local_mcast_reports - BOOLEAN 1696 Enable IGMP reports for link local multicast groups in the 1697 224.0.0.X range. 1698 1699 Default TRUE 1700 1701Alexey Kuznetsov. 1702kuznet@ms2.inr.ac.ru 1703 1704Updated by: 1705 1706- Andi Kleen 1707 ak@muc.de 1708- Nicolas Delon 1709 delon.nicolas@wanadoo.fr 1710 1711 1712 1713 1714/proc/sys/net/ipv6/* Variables 1715============================== 1716 1717IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also 1718apply to IPv6 [XXX?]. 1719 1720bindv6only - BOOLEAN 1721 Default value for IPV6_V6ONLY socket option, 1722 which restricts use of the IPv6 socket to IPv6 communication 1723 only. 1724 1725 - TRUE: disable IPv4-mapped address feature 1726 - FALSE: enable IPv4-mapped address feature 1727 1728 Default: FALSE (as specified in RFC3493) 1729 1730flowlabel_consistency - BOOLEAN 1731 Protect the consistency (and unicity) of flow label. 1732 You have to disable it to use IPV6_FL_F_REFLECT flag on the 1733 flow label manager. 1734 1735 - TRUE: enabled 1736 - FALSE: disabled 1737 1738 Default: TRUE 1739 1740auto_flowlabels - INTEGER 1741 Automatically generate flow labels based on a flow hash of the 1742 packet. This allows intermediate devices, such as routers, to 1743 identify packet flows for mechanisms like Equal Cost Multipath 1744 Routing (see RFC 6438). 1745 1746 = =========================================================== 1747 0 automatic flow labels are completely disabled 1748 1 automatic flow labels are enabled by default, they can be 1749 disabled on a per socket basis using the IPV6_AUTOFLOWLABEL 1750 socket option 1751 2 automatic flow labels are allowed, they may be enabled on a 1752 per socket basis using the IPV6_AUTOFLOWLABEL socket option 1753 3 automatic flow labels are enabled and enforced, they cannot 1754 be disabled by the socket option 1755 = =========================================================== 1756 1757 Default: 1 1758 1759flowlabel_state_ranges - BOOLEAN 1760 Split the flow label number space into two ranges. 0-0x7FFFF is 1761 reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF 1762 is reserved for stateless flow labels as described in RFC6437. 1763 1764 - TRUE: enabled 1765 - FALSE: disabled 1766 1767 Default: true 1768 1769flowlabel_reflect - INTEGER 1770 Control flow label reflection. Needed for Path MTU 1771 Discovery to work with Equal Cost Multipath Routing in anycast 1772 environments. See RFC 7690 and: 1773 https://tools.ietf.org/html/draft-wang-6man-flow-label-reflection-01 1774 1775 This is a bitmask. 1776 1777 - 1: enabled for established flows 1778 1779 Note that this prevents automatic flowlabel changes, as done 1780 in "tcp: change IPv6 flow-label upon receiving spurious retransmission" 1781 and "tcp: Change txhash on every SYN and RTO retransmit" 1782 1783 - 2: enabled for TCP RESET packets (no active listener) 1784 If set, a RST packet sent in response to a SYN packet on a closed 1785 port will reflect the incoming flow label. 1786 1787 - 4: enabled for ICMPv6 echo reply messages. 1788 1789 Default: 0 1790 1791fib_multipath_hash_policy - INTEGER 1792 Controls which hash policy to use for multipath routes. 1793 1794 Default: 0 (Layer 3) 1795 1796 Possible values: 1797 1798 - 0 - Layer 3 (source and destination addresses plus flow label) 1799 - 1 - Layer 4 (standard 5-tuple) 1800 - 2 - Layer 3 or inner Layer 3 if present 1801 - 3 - Custom multipath hash. Fields used for multipath hash calculation 1802 are determined by fib_multipath_hash_fields sysctl 1803 1804fib_multipath_hash_fields - UNSIGNED INTEGER 1805 When fib_multipath_hash_policy is set to 3 (custom multipath hash), the 1806 fields used for multipath hash calculation are determined by this 1807 sysctl. 1808 1809 This value is a bitmask which enables various fields for multipath hash 1810 calculation. 1811 1812 Possible fields are: 1813 1814 ====== ============================ 1815 0x0001 Source IP address 1816 0x0002 Destination IP address 1817 0x0004 IP protocol 1818 0x0008 Flow Label 1819 0x0010 Source port 1820 0x0020 Destination port 1821 0x0040 Inner source IP address 1822 0x0080 Inner destination IP address 1823 0x0100 Inner IP protocol 1824 0x0200 Inner Flow Label 1825 0x0400 Inner source port 1826 0x0800 Inner destination port 1827 ====== ============================ 1828 1829 Default: 0x0007 (source IP, destination IP and IP protocol) 1830 1831anycast_src_echo_reply - BOOLEAN 1832 Controls the use of anycast addresses as source addresses for ICMPv6 1833 echo reply 1834 1835 - TRUE: enabled 1836 - FALSE: disabled 1837 1838 Default: FALSE 1839 1840idgen_delay - INTEGER 1841 Controls the delay in seconds after which time to retry 1842 privacy stable address generation if a DAD conflict is 1843 detected. 1844 1845 Default: 1 (as specified in RFC7217) 1846 1847idgen_retries - INTEGER 1848 Controls the number of retries to generate a stable privacy 1849 address if a DAD conflict is detected. 1850 1851 Default: 3 (as specified in RFC7217) 1852 1853mld_qrv - INTEGER 1854 Controls the MLD query robustness variable (see RFC3810 9.1). 1855 1856 Default: 2 (as specified by RFC3810 9.1) 1857 1858 Minimum: 1 (as specified by RFC6636 4.5) 1859 1860max_dst_opts_number - INTEGER 1861 Maximum number of non-padding TLVs allowed in a Destination 1862 options extension header. If this value is less than zero 1863 then unknown options are disallowed and the number of known 1864 TLVs allowed is the absolute value of this number. 1865 1866 Default: 8 1867 1868max_hbh_opts_number - INTEGER 1869 Maximum number of non-padding TLVs allowed in a Hop-by-Hop 1870 options extension header. If this value is less than zero 1871 then unknown options are disallowed and the number of known 1872 TLVs allowed is the absolute value of this number. 1873 1874 Default: 8 1875 1876max_dst_opts_length - INTEGER 1877 Maximum length allowed for a Destination options extension 1878 header. 1879 1880 Default: INT_MAX (unlimited) 1881 1882max_hbh_length - INTEGER 1883 Maximum length allowed for a Hop-by-Hop options extension 1884 header. 1885 1886 Default: INT_MAX (unlimited) 1887 1888skip_notify_on_dev_down - BOOLEAN 1889 Controls whether an RTM_DELROUTE message is generated for routes 1890 removed when a device is taken down or deleted. IPv4 does not 1891 generate this message; IPv6 does by default. Setting this sysctl 1892 to true skips the message, making IPv4 and IPv6 on par in relying 1893 on userspace caches to track link events and evict routes. 1894 1895 Default: false (generate message) 1896 1897nexthop_compat_mode - BOOLEAN 1898 New nexthop API provides a means for managing nexthops independent of 1899 prefixes. Backwards compatibilty with old route format is enabled by 1900 default which means route dumps and notifications contain the new 1901 nexthop attribute but also the full, expanded nexthop definition. 1902 Further, updates or deletes of a nexthop configuration generate route 1903 notifications for each fib entry using the nexthop. Once a system 1904 understands the new API, this sysctl can be disabled to achieve full 1905 performance benefits of the new API by disabling the nexthop expansion 1906 and extraneous notifications. 1907 Default: true (backward compat mode) 1908 1909fib_notify_on_flag_change - INTEGER 1910 Whether to emit RTM_NEWROUTE notifications whenever RTM_F_OFFLOAD/ 1911 RTM_F_TRAP/RTM_F_OFFLOAD_FAILED flags are changed. 1912 1913 After installing a route to the kernel, user space receives an 1914 acknowledgment, which means the route was installed in the kernel, 1915 but not necessarily in hardware. 1916 It is also possible for a route already installed in hardware to change 1917 its action and therefore its flags. For example, a host route that is 1918 trapping packets can be "promoted" to perform decapsulation following 1919 the installation of an IPinIP/VXLAN tunnel. 1920 The notifications will indicate to user-space the state of the route. 1921 1922 Default: 0 (Do not emit notifications.) 1923 1924 Possible values: 1925 1926 - 0 - Do not emit notifications. 1927 - 1 - Emit notifications. 1928 - 2 - Emit notifications only for RTM_F_OFFLOAD_FAILED flag change. 1929 1930ioam6_id - INTEGER 1931 Define the IOAM id of this node. Uses only 24 bits out of 32 in total. 1932 1933 Min: 0 1934 Max: 0xFFFFFF 1935 1936 Default: 0xFFFFFF 1937 1938ioam6_id_wide - LONG INTEGER 1939 Define the wide IOAM id of this node. Uses only 56 bits out of 64 in 1940 total. Can be different from ioam6_id. 1941 1942 Min: 0 1943 Max: 0xFFFFFFFFFFFFFF 1944 1945 Default: 0xFFFFFFFFFFFFFF 1946 1947IPv6 Fragmentation: 1948 1949ip6frag_high_thresh - INTEGER 1950 Maximum memory used to reassemble IPv6 fragments. When 1951 ip6frag_high_thresh bytes of memory is allocated for this purpose, 1952 the fragment handler will toss packets until ip6frag_low_thresh 1953 is reached. 1954 1955ip6frag_low_thresh - INTEGER 1956 See ip6frag_high_thresh 1957 1958ip6frag_time - INTEGER 1959 Time in seconds to keep an IPv6 fragment in memory. 1960 1961``conf/default/*``: 1962 Change the interface-specific default settings. 1963 1964 These settings would be used during creating new interfaces. 1965 1966 1967``conf/all/*``: 1968 Change all the interface-specific settings. 1969 1970 [XXX: Other special features than forwarding?] 1971 1972conf/all/disable_ipv6 - BOOLEAN 1973 Changing this value is same as changing ``conf/default/disable_ipv6`` 1974 setting and also all per-interface ``disable_ipv6`` settings to the same 1975 value. 1976 1977 Reading this value does not have any particular meaning. It does not say 1978 whether IPv6 support is enabled or disabled. Returned value can be 1 1979 also in the case when some interface has ``disable_ipv6`` set to 0 and 1980 has configured IPv6 addresses. 1981 1982conf/all/forwarding - BOOLEAN 1983 Enable global IPv6 forwarding between all interfaces. 1984 1985 IPv4 and IPv6 work differently here; e.g. netfilter must be used 1986 to control which interfaces may forward packets and which not. 1987 1988 This also sets all interfaces' Host/Router setting 1989 'forwarding' to the specified value. See below for details. 1990 1991 This referred to as global forwarding. 1992 1993proxy_ndp - BOOLEAN 1994 Do proxy ndp. 1995 1996fwmark_reflect - BOOLEAN 1997 Controls the fwmark of kernel-generated IPv6 reply packets that are not 1998 associated with a socket for example, TCP RSTs or ICMPv6 echo replies). 1999 If unset, these packets have a fwmark of zero. If set, they have the 2000 fwmark of the packet they are replying to. 2001 2002 Default: 0 2003 2004``conf/interface/*``: 2005 Change special settings per interface. 2006 2007 The functional behaviour for certain settings is different 2008 depending on whether local forwarding is enabled or not. 2009 2010accept_ra - INTEGER 2011 Accept Router Advertisements; autoconfigure using them. 2012 2013 It also determines whether or not to transmit Router 2014 Solicitations. If and only if the functional setting is to 2015 accept Router Advertisements, Router Solicitations will be 2016 transmitted. 2017 2018 Possible values are: 2019 2020 == =========================================================== 2021 0 Do not accept Router Advertisements. 2022 1 Accept Router Advertisements if forwarding is disabled. 2023 2 Overrule forwarding behaviour. Accept Router Advertisements 2024 even if forwarding is enabled. 2025 == =========================================================== 2026 2027 Functional default: 2028 2029 - enabled if local forwarding is disabled. 2030 - disabled if local forwarding is enabled. 2031 2032accept_ra_defrtr - BOOLEAN 2033 Learn default router in Router Advertisement. 2034 2035 Functional default: 2036 2037 - enabled if accept_ra is enabled. 2038 - disabled if accept_ra is disabled. 2039 2040ra_defrtr_metric - UNSIGNED INTEGER 2041 Route metric for default route learned in Router Advertisement. This value 2042 will be assigned as metric for the default route learned via IPv6 Router 2043 Advertisement. Takes affect only if accept_ra_defrtr is enabled. 2044 2045 Possible values: 2046 1 to 0xFFFFFFFF 2047 2048 Default: IP6_RT_PRIO_USER i.e. 1024. 2049 2050accept_ra_from_local - BOOLEAN 2051 Accept RA with source-address that is found on local machine 2052 if the RA is otherwise proper and able to be accepted. 2053 2054 Default is to NOT accept these as it may be an un-intended 2055 network loop. 2056 2057 Functional default: 2058 2059 - enabled if accept_ra_from_local is enabled 2060 on a specific interface. 2061 - disabled if accept_ra_from_local is disabled 2062 on a specific interface. 2063 2064accept_ra_min_hop_limit - INTEGER 2065 Minimum hop limit Information in Router Advertisement. 2066 2067 Hop limit Information in Router Advertisement less than this 2068 variable shall be ignored. 2069 2070 Default: 1 2071 2072accept_ra_pinfo - BOOLEAN 2073 Learn Prefix Information in Router Advertisement. 2074 2075 Functional default: 2076 2077 - enabled if accept_ra is enabled. 2078 - disabled if accept_ra is disabled. 2079 2080accept_ra_rt_info_min_plen - INTEGER 2081 Minimum prefix length of Route Information in RA. 2082 2083 Route Information w/ prefix smaller than this variable shall 2084 be ignored. 2085 2086 Functional default: 2087 2088 * 0 if accept_ra_rtr_pref is enabled. 2089 * -1 if accept_ra_rtr_pref is disabled. 2090 2091accept_ra_rt_info_max_plen - INTEGER 2092 Maximum prefix length of Route Information in RA. 2093 2094 Route Information w/ prefix larger than this variable shall 2095 be ignored. 2096 2097 Functional default: 2098 2099 * 0 if accept_ra_rtr_pref is enabled. 2100 * -1 if accept_ra_rtr_pref is disabled. 2101 2102accept_ra_rtr_pref - BOOLEAN 2103 Accept Router Preference in RA. 2104 2105 Functional default: 2106 2107 - enabled if accept_ra is enabled. 2108 - disabled if accept_ra is disabled. 2109 2110accept_ra_mtu - BOOLEAN 2111 Apply the MTU value specified in RA option 5 (RFC4861). If 2112 disabled, the MTU specified in the RA will be ignored. 2113 2114 Functional default: 2115 2116 - enabled if accept_ra is enabled. 2117 - disabled if accept_ra is disabled. 2118 2119accept_redirects - BOOLEAN 2120 Accept Redirects. 2121 2122 Functional default: 2123 2124 - enabled if local forwarding is disabled. 2125 - disabled if local forwarding is enabled. 2126 2127accept_source_route - INTEGER 2128 Accept source routing (routing extension header). 2129 2130 - >= 0: Accept only routing header type 2. 2131 - < 0: Do not accept routing header. 2132 2133 Default: 0 2134 2135autoconf - BOOLEAN 2136 Autoconfigure addresses using Prefix Information in Router 2137 Advertisements. 2138 2139 Functional default: 2140 2141 - enabled if accept_ra_pinfo is enabled. 2142 - disabled if accept_ra_pinfo is disabled. 2143 2144dad_transmits - INTEGER 2145 The amount of Duplicate Address Detection probes to send. 2146 2147 Default: 1 2148 2149forwarding - INTEGER 2150 Configure interface-specific Host/Router behaviour. 2151 2152 .. note:: 2153 2154 It is recommended to have the same setting on all 2155 interfaces; mixed router/host scenarios are rather uncommon. 2156 2157 Possible values are: 2158 2159 - 0 Forwarding disabled 2160 - 1 Forwarding enabled 2161 2162 **FALSE (0)**: 2163 2164 By default, Host behaviour is assumed. This means: 2165 2166 1. IsRouter flag is not set in Neighbour Advertisements. 2167 2. If accept_ra is TRUE (default), transmit Router 2168 Solicitations. 2169 3. If accept_ra is TRUE (default), accept Router 2170 Advertisements (and do autoconfiguration). 2171 4. If accept_redirects is TRUE (default), accept Redirects. 2172 2173 **TRUE (1)**: 2174 2175 If local forwarding is enabled, Router behaviour is assumed. 2176 This means exactly the reverse from the above: 2177 2178 1. IsRouter flag is set in Neighbour Advertisements. 2179 2. Router Solicitations are not sent unless accept_ra is 2. 2180 3. Router Advertisements are ignored unless accept_ra is 2. 2181 4. Redirects are ignored. 2182 2183 Default: 0 (disabled) if global forwarding is disabled (default), 2184 otherwise 1 (enabled). 2185 2186hop_limit - INTEGER 2187 Default Hop Limit to set. 2188 2189 Default: 64 2190 2191mtu - INTEGER 2192 Default Maximum Transfer Unit 2193 2194 Default: 1280 (IPv6 required minimum) 2195 2196ip_nonlocal_bind - BOOLEAN 2197 If set, allows processes to bind() to non-local IPv6 addresses, 2198 which can be quite useful - but may break some applications. 2199 2200 Default: 0 2201 2202router_probe_interval - INTEGER 2203 Minimum interval (in seconds) between Router Probing described 2204 in RFC4191. 2205 2206 Default: 60 2207 2208router_solicitation_delay - INTEGER 2209 Number of seconds to wait after interface is brought up 2210 before sending Router Solicitations. 2211 2212 Default: 1 2213 2214router_solicitation_interval - INTEGER 2215 Number of seconds to wait between Router Solicitations. 2216 2217 Default: 4 2218 2219router_solicitations - INTEGER 2220 Number of Router Solicitations to send until assuming no 2221 routers are present. 2222 2223 Default: 3 2224 2225use_oif_addrs_only - BOOLEAN 2226 When enabled, the candidate source addresses for destinations 2227 routed via this interface are restricted to the set of addresses 2228 configured on this interface (vis. RFC 6724, section 4). 2229 2230 Default: false 2231 2232use_tempaddr - INTEGER 2233 Preference for Privacy Extensions (RFC3041). 2234 2235 * <= 0 : disable Privacy Extensions 2236 * == 1 : enable Privacy Extensions, but prefer public 2237 addresses over temporary addresses. 2238 * > 1 : enable Privacy Extensions and prefer temporary 2239 addresses over public addresses. 2240 2241 Default: 2242 2243 * 0 (for most devices) 2244 * -1 (for point-to-point devices and loopback devices) 2245 2246temp_valid_lft - INTEGER 2247 valid lifetime (in seconds) for temporary addresses. 2248 2249 Default: 172800 (2 days) 2250 2251temp_prefered_lft - INTEGER 2252 Preferred lifetime (in seconds) for temporary addresses. 2253 2254 Default: 86400 (1 day) 2255 2256keep_addr_on_down - INTEGER 2257 Keep all IPv6 addresses on an interface down event. If set static 2258 global addresses with no expiration time are not flushed. 2259 2260 * >0 : enabled 2261 * 0 : system default 2262 * <0 : disabled 2263 2264 Default: 0 (addresses are removed) 2265 2266max_desync_factor - INTEGER 2267 Maximum value for DESYNC_FACTOR, which is a random value 2268 that ensures that clients don't synchronize with each 2269 other and generate new addresses at exactly the same time. 2270 value is in seconds. 2271 2272 Default: 600 2273 2274regen_max_retry - INTEGER 2275 Number of attempts before give up attempting to generate 2276 valid temporary addresses. 2277 2278 Default: 5 2279 2280max_addresses - INTEGER 2281 Maximum number of autoconfigured addresses per interface. Setting 2282 to zero disables the limitation. It is not recommended to set this 2283 value too large (or to zero) because it would be an easy way to 2284 crash the kernel by allowing too many addresses to be created. 2285 2286 Default: 16 2287 2288disable_ipv6 - BOOLEAN 2289 Disable IPv6 operation. If accept_dad is set to 2, this value 2290 will be dynamically set to TRUE if DAD fails for the link-local 2291 address. 2292 2293 Default: FALSE (enable IPv6 operation) 2294 2295 When this value is changed from 1 to 0 (IPv6 is being enabled), 2296 it will dynamically create a link-local address on the given 2297 interface and start Duplicate Address Detection, if necessary. 2298 2299 When this value is changed from 0 to 1 (IPv6 is being disabled), 2300 it will dynamically delete all addresses and routes on the given 2301 interface. From now on it will not possible to add addresses/routes 2302 to the selected interface. 2303 2304accept_dad - INTEGER 2305 Whether to accept DAD (Duplicate Address Detection). 2306 2307 == ============================================================== 2308 0 Disable DAD 2309 1 Enable DAD (default) 2310 2 Enable DAD, and disable IPv6 operation if MAC-based duplicate 2311 link-local address has been found. 2312 == ============================================================== 2313 2314 DAD operation and mode on a given interface will be selected according 2315 to the maximum value of conf/{all,interface}/accept_dad. 2316 2317force_tllao - BOOLEAN 2318 Enable sending the target link-layer address option even when 2319 responding to a unicast neighbor solicitation. 2320 2321 Default: FALSE 2322 2323 Quoting from RFC 2461, section 4.4, Target link-layer address: 2324 2325 "The option MUST be included for multicast solicitations in order to 2326 avoid infinite Neighbor Solicitation "recursion" when the peer node 2327 does not have a cache entry to return a Neighbor Advertisements 2328 message. When responding to unicast solicitations, the option can be 2329 omitted since the sender of the solicitation has the correct link- 2330 layer address; otherwise it would not have be able to send the unicast 2331 solicitation in the first place. However, including the link-layer 2332 address in this case adds little overhead and eliminates a potential 2333 race condition where the sender deletes the cached link-layer address 2334 prior to receiving a response to a previous solicitation." 2335 2336ndisc_notify - BOOLEAN 2337 Define mode for notification of address and device changes. 2338 2339 * 0 - (default): do nothing 2340 * 1 - Generate unsolicited neighbour advertisements when device is brought 2341 up or hardware address changes. 2342 2343ndisc_tclass - INTEGER 2344 The IPv6 Traffic Class to use by default when sending IPv6 Neighbor 2345 Discovery (Router Solicitation, Router Advertisement, Neighbor 2346 Solicitation, Neighbor Advertisement, Redirect) messages. 2347 These 8 bits can be interpreted as 6 high order bits holding the DSCP 2348 value and 2 low order bits representing ECN (which you probably want 2349 to leave cleared). 2350 2351 * 0 - (default) 2352 2353ndisc_evict_nocarrier - BOOLEAN 2354 Clears the neighbor discovery table on NOCARRIER events. This option is 2355 important for wireless devices where the neighbor discovery cache should 2356 not be cleared when roaming between access points on the same network. 2357 In most cases this should remain as the default (1). 2358 2359 - 1 - (default): Clear neighbor discover cache on NOCARRIER events. 2360 - 0 - Do not clear neighbor discovery cache on NOCARRIER events. 2361 2362mldv1_unsolicited_report_interval - INTEGER 2363 The interval in milliseconds in which the next unsolicited 2364 MLDv1 report retransmit will take place. 2365 2366 Default: 10000 (10 seconds) 2367 2368mldv2_unsolicited_report_interval - INTEGER 2369 The interval in milliseconds in which the next unsolicited 2370 MLDv2 report retransmit will take place. 2371 2372 Default: 1000 (1 second) 2373 2374force_mld_version - INTEGER 2375 * 0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed 2376 * 1 - Enforce to use MLD version 1 2377 * 2 - Enforce to use MLD version 2 2378 2379suppress_frag_ndisc - INTEGER 2380 Control RFC 6980 (Security Implications of IPv6 Fragmentation 2381 with IPv6 Neighbor Discovery) behavior: 2382 2383 * 1 - (default) discard fragmented neighbor discovery packets 2384 * 0 - allow fragmented neighbor discovery packets 2385 2386optimistic_dad - BOOLEAN 2387 Whether to perform Optimistic Duplicate Address Detection (RFC 4429). 2388 2389 * 0: disabled (default) 2390 * 1: enabled 2391 2392 Optimistic Duplicate Address Detection for the interface will be enabled 2393 if at least one of conf/{all,interface}/optimistic_dad is set to 1, 2394 it will be disabled otherwise. 2395 2396use_optimistic - BOOLEAN 2397 If enabled, do not classify optimistic addresses as deprecated during 2398 source address selection. Preferred addresses will still be chosen 2399 before optimistic addresses, subject to other ranking in the source 2400 address selection algorithm. 2401 2402 * 0: disabled (default) 2403 * 1: enabled 2404 2405 This will be enabled if at least one of 2406 conf/{all,interface}/use_optimistic is set to 1, disabled otherwise. 2407 2408stable_secret - IPv6 address 2409 This IPv6 address will be used as a secret to generate IPv6 2410 addresses for link-local addresses and autoconfigured 2411 ones. All addresses generated after setting this secret will 2412 be stable privacy ones by default. This can be changed via the 2413 addrgenmode ip-link. conf/default/stable_secret is used as the 2414 secret for the namespace, the interface specific ones can 2415 overwrite that. Writes to conf/all/stable_secret are refused. 2416 2417 It is recommended to generate this secret during installation 2418 of a system and keep it stable after that. 2419 2420 By default the stable secret is unset. 2421 2422addr_gen_mode - INTEGER 2423 Defines how link-local and autoconf addresses are generated. 2424 2425 = ================================================================= 2426 0 generate address based on EUI64 (default) 2427 1 do no generate a link-local address, use EUI64 for addresses 2428 generated from autoconf 2429 2 generate stable privacy addresses, using the secret from 2430 stable_secret (RFC7217) 2431 3 generate stable privacy addresses, using a random secret if unset 2432 = ================================================================= 2433 2434drop_unicast_in_l2_multicast - BOOLEAN 2435 Drop any unicast IPv6 packets that are received in link-layer 2436 multicast (or broadcast) frames. 2437 2438 By default this is turned off. 2439 2440drop_unsolicited_na - BOOLEAN 2441 Drop all unsolicited neighbor advertisements, for example if there's 2442 a known good NA proxy on the network and such frames need not be used 2443 (or in the case of 802.11, must not be used to prevent attacks.) 2444 2445 By default this is turned off. 2446 2447enhanced_dad - BOOLEAN 2448 Include a nonce option in the IPv6 neighbor solicitation messages used for 2449 duplicate address detection per RFC7527. A received DAD NS will only signal 2450 a duplicate address if the nonce is different. This avoids any false 2451 detection of duplicates due to loopback of the NS messages that we send. 2452 The nonce option will be sent on an interface unless both of 2453 conf/{all,interface}/enhanced_dad are set to FALSE. 2454 2455 Default: TRUE 2456 2457``icmp/*``: 2458=========== 2459 2460ratelimit - INTEGER 2461 Limit the maximal rates for sending ICMPv6 messages. 2462 2463 0 to disable any limiting, 2464 otherwise the minimal space between responses in milliseconds. 2465 2466 Default: 1000 2467 2468ratemask - list of comma separated ranges 2469 For ICMPv6 message types matching the ranges in the ratemask, limit 2470 the sending of the message according to ratelimit parameter. 2471 2472 The format used for both input and output is a comma separated 2473 list of ranges (e.g. "0-127,129" for ICMPv6 message type 0 to 127 and 2474 129). Writing to the file will clear all previous ranges of ICMPv6 2475 message types and update the current list with the input. 2476 2477 Refer to: https://www.iana.org/assignments/icmpv6-parameters/icmpv6-parameters.xhtml 2478 for numerical values of ICMPv6 message types, e.g. echo request is 128 2479 and echo reply is 129. 2480 2481 Default: 0-1,3-127 (rate limit ICMPv6 errors except Packet Too Big) 2482 2483echo_ignore_all - BOOLEAN 2484 If set non-zero, then the kernel will ignore all ICMP ECHO 2485 requests sent to it over the IPv6 protocol. 2486 2487 Default: 0 2488 2489echo_ignore_multicast - BOOLEAN 2490 If set non-zero, then the kernel will ignore all ICMP ECHO 2491 requests sent to it over the IPv6 protocol via multicast. 2492 2493 Default: 0 2494 2495echo_ignore_anycast - BOOLEAN 2496 If set non-zero, then the kernel will ignore all ICMP ECHO 2497 requests sent to it over the IPv6 protocol destined to anycast address. 2498 2499 Default: 0 2500 2501xfrm6_gc_thresh - INTEGER 2502 (Obsolete since linux-4.14) 2503 The threshold at which we will start garbage collecting for IPv6 2504 destination cache entries. At twice this value the system will 2505 refuse new allocations. 2506 2507 2508IPv6 Update by: 2509Pekka Savola <pekkas@netcore.fi> 2510YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org> 2511 2512 2513/proc/sys/net/bridge/* Variables: 2514================================= 2515 2516bridge-nf-call-arptables - BOOLEAN 2517 - 1 : pass bridged ARP traffic to arptables' FORWARD chain. 2518 - 0 : disable this. 2519 2520 Default: 1 2521 2522bridge-nf-call-iptables - BOOLEAN 2523 - 1 : pass bridged IPv4 traffic to iptables' chains. 2524 - 0 : disable this. 2525 2526 Default: 1 2527 2528bridge-nf-call-ip6tables - BOOLEAN 2529 - 1 : pass bridged IPv6 traffic to ip6tables' chains. 2530 - 0 : disable this. 2531 2532 Default: 1 2533 2534bridge-nf-filter-vlan-tagged - BOOLEAN 2535 - 1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables. 2536 - 0 : disable this. 2537 2538 Default: 0 2539 2540bridge-nf-filter-pppoe-tagged - BOOLEAN 2541 - 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables. 2542 - 0 : disable this. 2543 2544 Default: 0 2545 2546bridge-nf-pass-vlan-input-dev - BOOLEAN 2547 - 1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan 2548 interface on the bridge and set the netfilter input device to the 2549 vlan. This allows use of e.g. "iptables -i br0.1" and makes the 2550 REDIRECT target work with vlan-on-top-of-bridge interfaces. When no 2551 matching vlan interface is found, or this switch is off, the input 2552 device is set to the bridge interface. 2553 2554 - 0: disable bridge netfilter vlan interface lookup. 2555 2556 Default: 0 2557 2558``proc/sys/net/sctp/*`` Variables: 2559================================== 2560 2561addip_enable - BOOLEAN 2562 Enable or disable extension of Dynamic Address Reconfiguration 2563 (ADD-IP) functionality specified in RFC5061. This extension provides 2564 the ability to dynamically add and remove new addresses for the SCTP 2565 associations. 2566 2567 1: Enable extension. 2568 2569 0: Disable extension. 2570 2571 Default: 0 2572 2573pf_enable - INTEGER 2574 Enable or disable pf (pf is short for potentially failed) state. A value 2575 of pf_retrans > path_max_retrans also disables pf state. That is, one of 2576 both pf_enable and pf_retrans > path_max_retrans can disable pf state. 2577 Since pf_retrans and path_max_retrans can be changed by userspace 2578 application, sometimes user expects to disable pf state by the value of 2579 pf_retrans > path_max_retrans, but occasionally the value of pf_retrans 2580 or path_max_retrans is changed by the user application, this pf state is 2581 enabled. As such, it is necessary to add this to dynamically enable 2582 and disable pf state. See: 2583 https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover for 2584 details. 2585 2586 1: Enable pf. 2587 2588 0: Disable pf. 2589 2590 Default: 1 2591 2592pf_expose - INTEGER 2593 Unset or enable/disable pf (pf is short for potentially failed) state 2594 exposure. Applications can control the exposure of the PF path state 2595 in the SCTP_PEER_ADDR_CHANGE event and the SCTP_GET_PEER_ADDR_INFO 2596 sockopt. When it's unset, no SCTP_PEER_ADDR_CHANGE event with 2597 SCTP_ADDR_PF state will be sent and a SCTP_PF-state transport info 2598 can be got via SCTP_GET_PEER_ADDR_INFO sockopt; When it's enabled, 2599 a SCTP_PEER_ADDR_CHANGE event will be sent for a transport becoming 2600 SCTP_PF state and a SCTP_PF-state transport info can be got via 2601 SCTP_GET_PEER_ADDR_INFO sockopt; When it's diabled, no 2602 SCTP_PEER_ADDR_CHANGE event will be sent and it returns -EACCES when 2603 trying to get a SCTP_PF-state transport info via SCTP_GET_PEER_ADDR_INFO 2604 sockopt. 2605 2606 0: Unset pf state exposure, Compatible with old applications. 2607 2608 1: Disable pf state exposure. 2609 2610 2: Enable pf state exposure. 2611 2612 Default: 0 2613 2614addip_noauth_enable - BOOLEAN 2615 Dynamic Address Reconfiguration (ADD-IP) requires the use of 2616 authentication to protect the operations of adding or removing new 2617 addresses. This requirement is mandated so that unauthorized hosts 2618 would not be able to hijack associations. However, older 2619 implementations may not have implemented this requirement while 2620 allowing the ADD-IP extension. For reasons of interoperability, 2621 we provide this variable to control the enforcement of the 2622 authentication requirement. 2623 2624 == =============================================================== 2625 1 Allow ADD-IP extension to be used without authentication. This 2626 should only be set in a closed environment for interoperability 2627 with older implementations. 2628 2629 0 Enforce the authentication requirement 2630 == =============================================================== 2631 2632 Default: 0 2633 2634auth_enable - BOOLEAN 2635 Enable or disable Authenticated Chunks extension. This extension 2636 provides the ability to send and receive authenticated chunks and is 2637 required for secure operation of Dynamic Address Reconfiguration 2638 (ADD-IP) extension. 2639 2640 - 1: Enable this extension. 2641 - 0: Disable this extension. 2642 2643 Default: 0 2644 2645prsctp_enable - BOOLEAN 2646 Enable or disable the Partial Reliability extension (RFC3758) which 2647 is used to notify peers that a given DATA should no longer be expected. 2648 2649 - 1: Enable extension 2650 - 0: Disable 2651 2652 Default: 1 2653 2654max_burst - INTEGER 2655 The limit of the number of new packets that can be initially sent. It 2656 controls how bursty the generated traffic can be. 2657 2658 Default: 4 2659 2660association_max_retrans - INTEGER 2661 Set the maximum number for retransmissions that an association can 2662 attempt deciding that the remote end is unreachable. If this value 2663 is exceeded, the association is terminated. 2664 2665 Default: 10 2666 2667max_init_retransmits - INTEGER 2668 The maximum number of retransmissions of INIT and COOKIE-ECHO chunks 2669 that an association will attempt before declaring the destination 2670 unreachable and terminating. 2671 2672 Default: 8 2673 2674path_max_retrans - INTEGER 2675 The maximum number of retransmissions that will be attempted on a given 2676 path. Once this threshold is exceeded, the path is considered 2677 unreachable, and new traffic will use a different path when the 2678 association is multihomed. 2679 2680 Default: 5 2681 2682pf_retrans - INTEGER 2683 The number of retransmissions that will be attempted on a given path 2684 before traffic is redirected to an alternate transport (should one 2685 exist). Note this is distinct from path_max_retrans, as a path that 2686 passes the pf_retrans threshold can still be used. Its only 2687 deprioritized when a transmission path is selected by the stack. This 2688 setting is primarily used to enable fast failover mechanisms without 2689 having to reduce path_max_retrans to a very low value. See: 2690 http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt 2691 for details. Note also that a value of pf_retrans > path_max_retrans 2692 disables this feature. Since both pf_retrans and path_max_retrans can 2693 be changed by userspace application, a variable pf_enable is used to 2694 disable pf state. 2695 2696 Default: 0 2697 2698ps_retrans - INTEGER 2699 Primary.Switchover.Max.Retrans (PSMR), it's a tunable parameter coming 2700 from section-5 "Primary Path Switchover" in rfc7829. The primary path 2701 will be changed to another active path when the path error counter on 2702 the old primary path exceeds PSMR, so that "the SCTP sender is allowed 2703 to continue data transmission on a new working path even when the old 2704 primary destination address becomes active again". Note this feature 2705 is disabled by initializing 'ps_retrans' per netns as 0xffff by default, 2706 and its value can't be less than 'pf_retrans' when changing by sysctl. 2707 2708 Default: 0xffff 2709 2710rto_initial - INTEGER 2711 The initial round trip timeout value in milliseconds that will be used 2712 in calculating round trip times. This is the initial time interval 2713 for retransmissions. 2714 2715 Default: 3000 2716 2717rto_max - INTEGER 2718 The maximum value (in milliseconds) of the round trip timeout. This 2719 is the largest time interval that can elapse between retransmissions. 2720 2721 Default: 60000 2722 2723rto_min - INTEGER 2724 The minimum value (in milliseconds) of the round trip timeout. This 2725 is the smallest time interval the can elapse between retransmissions. 2726 2727 Default: 1000 2728 2729hb_interval - INTEGER 2730 The interval (in milliseconds) between HEARTBEAT chunks. These chunks 2731 are sent at the specified interval on idle paths to probe the state of 2732 a given path between 2 associations. 2733 2734 Default: 30000 2735 2736sack_timeout - INTEGER 2737 The amount of time (in milliseconds) that the implementation will wait 2738 to send a SACK. 2739 2740 Default: 200 2741 2742valid_cookie_life - INTEGER 2743 The default lifetime of the SCTP cookie (in milliseconds). The cookie 2744 is used during association establishment. 2745 2746 Default: 60000 2747 2748cookie_preserve_enable - BOOLEAN 2749 Enable or disable the ability to extend the lifetime of the SCTP cookie 2750 that is used during the establishment phase of SCTP association 2751 2752 - 1: Enable cookie lifetime extension. 2753 - 0: Disable 2754 2755 Default: 1 2756 2757cookie_hmac_alg - STRING 2758 Select the hmac algorithm used when generating the cookie value sent by 2759 a listening sctp socket to a connecting client in the INIT-ACK chunk. 2760 Valid values are: 2761 2762 * md5 2763 * sha1 2764 * none 2765 2766 Ability to assign md5 or sha1 as the selected alg is predicated on the 2767 configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and 2768 CONFIG_CRYPTO_SHA1). 2769 2770 Default: Dependent on configuration. MD5 if available, else SHA1 if 2771 available, else none. 2772 2773rcvbuf_policy - INTEGER 2774 Determines if the receive buffer is attributed to the socket or to 2775 association. SCTP supports the capability to create multiple 2776 associations on a single socket. When using this capability, it is 2777 possible that a single stalled association that's buffering a lot 2778 of data may block other associations from delivering their data by 2779 consuming all of the receive buffer space. To work around this, 2780 the rcvbuf_policy could be set to attribute the receiver buffer space 2781 to each association instead of the socket. This prevents the described 2782 blocking. 2783 2784 - 1: rcvbuf space is per association 2785 - 0: rcvbuf space is per socket 2786 2787 Default: 0 2788 2789sndbuf_policy - INTEGER 2790 Similar to rcvbuf_policy above, this applies to send buffer space. 2791 2792 - 1: Send buffer is tracked per association 2793 - 0: Send buffer is tracked per socket. 2794 2795 Default: 0 2796 2797sctp_mem - vector of 3 INTEGERs: min, pressure, max 2798 Number of pages allowed for queueing by all SCTP sockets. 2799 2800 min: Below this number of pages SCTP is not bothered about its 2801 memory appetite. When amount of memory allocated by SCTP exceeds 2802 this number, SCTP starts to moderate memory usage. 2803 2804 pressure: This value was introduced to follow format of tcp_mem. 2805 2806 max: Number of pages allowed for queueing by all SCTP sockets. 2807 2808 Default is calculated at boot time from amount of available memory. 2809 2810sctp_rmem - vector of 3 INTEGERs: min, default, max 2811 Only the first value ("min") is used, "default" and "max" are 2812 ignored. 2813 2814 min: Minimal size of receive buffer used by SCTP socket. 2815 It is guaranteed to each SCTP socket (but not association) even 2816 under moderate memory pressure. 2817 2818 Default: 4K 2819 2820sctp_wmem - vector of 3 INTEGERs: min, default, max 2821 Currently this tunable has no effect. 2822 2823addr_scope_policy - INTEGER 2824 Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00 2825 2826 - 0 - Disable IPv4 address scoping 2827 - 1 - Enable IPv4 address scoping 2828 - 2 - Follow draft but allow IPv4 private addresses 2829 - 3 - Follow draft but allow IPv4 link local addresses 2830 2831 Default: 1 2832 2833udp_port - INTEGER 2834 The listening port for the local UDP tunneling sock. Normally it's 2835 using the IANA-assigned UDP port number 9899 (sctp-tunneling). 2836 2837 This UDP sock is used for processing the incoming UDP-encapsulated 2838 SCTP packets (from RFC6951), and shared by all applications in the 2839 same net namespace. This UDP sock will be closed when the value is 2840 set to 0. 2841 2842 The value will also be used to set the src port of the UDP header 2843 for the outgoing UDP-encapsulated SCTP packets. For the dest port, 2844 please refer to 'encap_port' below. 2845 2846 Default: 0 2847 2848encap_port - INTEGER 2849 The default remote UDP encapsulation port. 2850 2851 This value is used to set the dest port of the UDP header for the 2852 outgoing UDP-encapsulated SCTP packets by default. Users can also 2853 change the value for each sock/asoc/transport by using setsockopt. 2854 For further information, please refer to RFC6951. 2855 2856 Note that when connecting to a remote server, the client should set 2857 this to the port that the UDP tunneling sock on the peer server is 2858 listening to and the local UDP tunneling sock on the client also 2859 must be started. On the server, it would get the encap_port from 2860 the incoming packet's source port. 2861 2862 Default: 0 2863 2864plpmtud_probe_interval - INTEGER 2865 The time interval (in milliseconds) for the PLPMTUD probe timer, 2866 which is configured to expire after this period to receive an 2867 acknowledgment to a probe packet. This is also the time interval 2868 between the probes for the current pmtu when the probe search 2869 is done. 2870 2871 PLPMTUD will be disabled when 0 is set, and other values for it 2872 must be >= 5000. 2873 2874 Default: 0 2875 2876 2877``/proc/sys/net/core/*`` 2878======================== 2879 2880 Please see: Documentation/admin-guide/sysctl/net.rst for descriptions of these entries. 2881 2882 2883``/proc/sys/net/unix/*`` 2884======================== 2885 2886max_dgram_qlen - INTEGER 2887 The maximum length of dgram socket receive queue 2888 2889 Default: 10 2890 2891