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 the smallest of the old MTU to 29 this destination and min_pmtu (see below). You will need 30 to raise min_pmtu to the smallest interface MTU on your system 31 manually if you want to avoid locally generated fragments. 32 33 In mode 2 incoming Path MTU Discovery messages will be 34 discarded. Outgoing frames are handled the same as in mode 1, 35 implicitly setting IP_PMTUDISC_DONT on every created socket. 36 37 Mode 3 is a hardened pmtu discover mode. The kernel will only 38 accept fragmentation-needed errors if the underlying protocol 39 can verify them besides a plain socket lookup. Current 40 protocols for which pmtu events will be honored are TCP, SCTP 41 and DCCP as they verify e.g. the sequence number or the 42 association. This mode should not be enabled globally but is 43 only intended to secure e.g. name servers in namespaces where 44 TCP path mtu must still work but path MTU information of other 45 protocols should be discarded. If enabled globally this mode 46 could break other protocols. 47 48 Possible values: 0-3 49 50 Default: FALSE 51 52min_pmtu - INTEGER 53 default 552 - minimum Path MTU. Unless this is changed manually, 54 each cached pmtu will never be lower than this setting. 55 56ip_forward_use_pmtu - BOOLEAN 57 By default we don't trust protocol path MTUs while forwarding 58 because they could be easily forged and can lead to unwanted 59 fragmentation by the router. 60 You only need to enable this if you have user-space software 61 which tries to discover path mtus by itself and depends on the 62 kernel honoring this information. This is normally not the 63 case. 64 65 Default: 0 (disabled) 66 67 Possible values: 68 69 - 0 - disabled 70 - 1 - enabled 71 72fwmark_reflect - BOOLEAN 73 Controls the fwmark of kernel-generated IPv4 reply packets that are not 74 associated with a socket for example, TCP RSTs or ICMP echo replies). 75 If unset, these packets have a fwmark of zero. If set, they have the 76 fwmark of the packet they are replying to. 77 78 Default: 0 79 80fib_multipath_use_neigh - BOOLEAN 81 Use status of existing neighbor entry when determining nexthop for 82 multipath routes. If disabled, neighbor information is not used and 83 packets could be directed to a failed nexthop. Only valid for kernels 84 built with CONFIG_IP_ROUTE_MULTIPATH enabled. 85 86 Default: 0 (disabled) 87 88 Possible values: 89 90 - 0 - disabled 91 - 1 - enabled 92 93fib_multipath_hash_policy - INTEGER 94 Controls which hash policy to use for multipath routes. Only valid 95 for kernels built with CONFIG_IP_ROUTE_MULTIPATH enabled. 96 97 Default: 0 (Layer 3) 98 99 Possible values: 100 101 - 0 - Layer 3 102 - 1 - Layer 4 103 - 2 - Layer 3 or inner Layer 3 if present 104 - 3 - Custom multipath hash. Fields used for multipath hash calculation 105 are determined by fib_multipath_hash_fields sysctl 106 107fib_multipath_hash_fields - UNSIGNED INTEGER 108 When fib_multipath_hash_policy is set to 3 (custom multipath hash), the 109 fields used for multipath hash calculation are determined by this 110 sysctl. 111 112 This value is a bitmask which enables various fields for multipath hash 113 calculation. 114 115 Possible fields are: 116 117 ====== ============================ 118 0x0001 Source IP address 119 0x0002 Destination IP address 120 0x0004 IP protocol 121 0x0008 Unused (Flow Label) 122 0x0010 Source port 123 0x0020 Destination port 124 0x0040 Inner source IP address 125 0x0080 Inner destination IP address 126 0x0100 Inner IP protocol 127 0x0200 Inner Flow Label 128 0x0400 Inner source port 129 0x0800 Inner destination port 130 ====== ============================ 131 132 Default: 0x0007 (source IP, destination IP and IP protocol) 133 134fib_sync_mem - UNSIGNED INTEGER 135 Amount of dirty memory from fib entries that can be backlogged before 136 synchronize_rcu is forced. 137 138 Default: 512kB Minimum: 64kB Maximum: 64MB 139 140ip_forward_update_priority - INTEGER 141 Whether to update SKB priority from "TOS" field in IPv4 header after it 142 is forwarded. The new SKB priority is mapped from TOS field value 143 according to an rt_tos2priority table (see e.g. man tc-prio). 144 145 Default: 1 (Update priority.) 146 147 Possible values: 148 149 - 0 - Do not update priority. 150 - 1 - Update priority. 151 152route/max_size - INTEGER 153 Maximum number of routes allowed in the kernel. Increase 154 this when using large numbers of interfaces and/or routes. 155 156 From linux kernel 3.6 onwards, this is deprecated for ipv4 157 as route cache is no longer used. 158 159 From linux kernel 6.3 onwards, this is deprecated for ipv6 160 as garbage collection manages cached route entries. 161 162neigh/default/gc_thresh1 - INTEGER 163 Minimum number of entries to keep. Garbage collector will not 164 purge entries if there are fewer than this number. 165 166 Default: 128 167 168neigh/default/gc_thresh2 - INTEGER 169 Threshold when garbage collector becomes more aggressive about 170 purging entries. Entries older than 5 seconds will be cleared 171 when over this number. 172 173 Default: 512 174 175neigh/default/gc_thresh3 - INTEGER 176 Maximum number of non-PERMANENT neighbor entries allowed. Increase 177 this when using large numbers of interfaces and when communicating 178 with large numbers of directly-connected peers. 179 180 Default: 1024 181 182neigh/default/unres_qlen_bytes - INTEGER 183 The maximum number of bytes which may be used by packets 184 queued for each unresolved address by other network layers. 185 (added in linux 3.3) 186 187 Setting negative value is meaningless and will return error. 188 189 Default: SK_WMEM_MAX, (same as net.core.wmem_default). 190 191 Exact value depends on architecture and kernel options, 192 but should be enough to allow queuing 256 packets 193 of medium size. 194 195neigh/default/unres_qlen - INTEGER 196 The maximum number of packets which may be queued for each 197 unresolved address by other network layers. 198 199 (deprecated in linux 3.3) : use unres_qlen_bytes instead. 200 201 Prior to linux 3.3, the default value is 3 which may cause 202 unexpected packet loss. The current default value is calculated 203 according to default value of unres_qlen_bytes and true size of 204 packet. 205 206 Default: 101 207 208neigh/default/interval_probe_time_ms - INTEGER 209 The probe interval for neighbor entries with NTF_MANAGED flag, 210 the min value is 1. 211 212 Default: 5000 213 214mtu_expires - INTEGER 215 Time, in seconds, that cached PMTU information is kept. 216 217min_adv_mss - INTEGER 218 The advertised MSS depends on the first hop route MTU, but will 219 never be lower than this setting. 220 221fib_notify_on_flag_change - INTEGER 222 Whether to emit RTM_NEWROUTE notifications whenever RTM_F_OFFLOAD/ 223 RTM_F_TRAP/RTM_F_OFFLOAD_FAILED flags are changed. 224 225 After installing a route to the kernel, user space receives an 226 acknowledgment, which means the route was installed in the kernel, 227 but not necessarily in hardware. 228 It is also possible for a route already installed in hardware to change 229 its action and therefore its flags. For example, a host route that is 230 trapping packets can be "promoted" to perform decapsulation following 231 the installation of an IPinIP/VXLAN tunnel. 232 The notifications will indicate to user-space the state of the route. 233 234 Default: 0 (Do not emit notifications.) 235 236 Possible values: 237 238 - 0 - Do not emit notifications. 239 - 1 - Emit notifications. 240 - 2 - Emit notifications only for RTM_F_OFFLOAD_FAILED flag change. 241 242IP Fragmentation: 243 244ipfrag_high_thresh - LONG INTEGER 245 Maximum memory used to reassemble IP fragments. 246 247ipfrag_low_thresh - LONG INTEGER 248 (Obsolete since linux-4.17) 249 Maximum memory used to reassemble IP fragments before the kernel 250 begins to remove incomplete fragment queues to free up resources. 251 The kernel still accepts new fragments for defragmentation. 252 253ipfrag_time - INTEGER 254 Time in seconds to keep an IP fragment in memory. 255 256ipfrag_max_dist - INTEGER 257 ipfrag_max_dist is a non-negative integer value which defines the 258 maximum "disorder" which is allowed among fragments which share a 259 common IP source address. Note that reordering of packets is 260 not unusual, but if a large number of fragments arrive from a source 261 IP address while a particular fragment queue remains incomplete, it 262 probably indicates that one or more fragments belonging to that queue 263 have been lost. When ipfrag_max_dist is positive, an additional check 264 is done on fragments before they are added to a reassembly queue - if 265 ipfrag_max_dist (or more) fragments have arrived from a particular IP 266 address between additions to any IP fragment queue using that source 267 address, it's presumed that one or more fragments in the queue are 268 lost. The existing fragment queue will be dropped, and a new one 269 started. An ipfrag_max_dist value of zero disables this check. 270 271 Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can 272 result in unnecessarily dropping fragment queues when normal 273 reordering of packets occurs, which could lead to poor application 274 performance. Using a very large value, e.g. 50000, increases the 275 likelihood of incorrectly reassembling IP fragments that originate 276 from different IP datagrams, which could result in data corruption. 277 Default: 64 278 279bc_forwarding - INTEGER 280 bc_forwarding enables the feature described in rfc1812#section-5.3.5.2 281 and rfc2644. It allows the router to forward directed broadcast. 282 To enable this feature, the 'all' entry and the input interface entry 283 should be set to 1. 284 Default: 0 285 286INET peer storage 287================= 288 289inet_peer_threshold - INTEGER 290 The approximate size of the storage. Starting from this threshold 291 entries will be thrown aggressively. This threshold also determines 292 entries' time-to-live and time intervals between garbage collection 293 passes. More entries, less time-to-live, less GC interval. 294 295inet_peer_minttl - INTEGER 296 Minimum time-to-live of entries. Should be enough to cover fragment 297 time-to-live on the reassembling side. This minimum time-to-live is 298 guaranteed if the pool size is less than inet_peer_threshold. 299 Measured in seconds. 300 301inet_peer_maxttl - INTEGER 302 Maximum time-to-live of entries. Unused entries will expire after 303 this period of time if there is no memory pressure on the pool (i.e. 304 when the number of entries in the pool is very small). 305 Measured in seconds. 306 307TCP variables 308============= 309 310somaxconn - INTEGER 311 Limit of socket listen() backlog, known in userspace as SOMAXCONN. 312 Defaults to 4096. (Was 128 before linux-5.4) 313 See also tcp_max_syn_backlog for additional tuning for TCP sockets. 314 315tcp_abort_on_overflow - BOOLEAN 316 If listening service is too slow to accept new connections, 317 reset them. Default state is FALSE. It means that if overflow 318 occurred due to a burst, connection will recover. Enable this 319 option _only_ if you are really sure that listening daemon 320 cannot be tuned to accept connections faster. Enabling this 321 option can harm clients of your server. 322 323tcp_adv_win_scale - INTEGER 324 Obsolete since linux-6.6 325 Count buffering overhead as bytes/2^tcp_adv_win_scale 326 (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale), 327 if it is <= 0. 328 329 Possible values are [-31, 31], inclusive. 330 331 Default: 1 332 333tcp_allowed_congestion_control - STRING 334 Show/set the congestion control choices available to non-privileged 335 processes. The list is a subset of those listed in 336 tcp_available_congestion_control. 337 338 Default is "reno" and the default setting (tcp_congestion_control). 339 340tcp_app_win - INTEGER 341 Reserve max(window/2^tcp_app_win, mss) of window for application 342 buffer. Value 0 is special, it means that nothing is reserved. 343 344 Possible values are [0, 31], inclusive. 345 346 Default: 31 347 348tcp_autocorking - BOOLEAN 349 Enable TCP auto corking : 350 When applications do consecutive small write()/sendmsg() system calls, 351 we try to coalesce these small writes as much as possible, to lower 352 total amount of sent packets. This is done if at least one prior 353 packet for the flow is waiting in Qdisc queues or device transmit 354 queue. Applications can still use TCP_CORK for optimal behavior 355 when they know how/when to uncork their sockets. 356 357 Default : 1 358 359tcp_available_congestion_control - STRING 360 Shows the available congestion control choices that are registered. 361 More congestion control algorithms may be available as modules, 362 but not loaded. 363 364tcp_base_mss - INTEGER 365 The initial value of search_low to be used by the packetization layer 366 Path MTU discovery (MTU probing). If MTU probing is enabled, 367 this is the initial MSS used by the connection. 368 369tcp_mtu_probe_floor - INTEGER 370 If MTU probing is enabled this caps the minimum MSS used for search_low 371 for the connection. 372 373 Default : 48 374 375tcp_min_snd_mss - INTEGER 376 TCP SYN and SYNACK messages usually advertise an ADVMSS option, 377 as described in RFC 1122 and RFC 6691. 378 379 If this ADVMSS option is smaller than tcp_min_snd_mss, 380 it is silently capped to tcp_min_snd_mss. 381 382 Default : 48 (at least 8 bytes of payload per segment) 383 384tcp_congestion_control - STRING 385 Set the congestion control algorithm to be used for new 386 connections. The algorithm "reno" is always available, but 387 additional choices may be available based on kernel configuration. 388 Default is set as part of kernel configuration. 389 For passive connections, the listener congestion control choice 390 is inherited. 391 392 [see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ] 393 394tcp_dsack - BOOLEAN 395 Allows TCP to send "duplicate" SACKs. 396 397tcp_early_retrans - INTEGER 398 Tail loss probe (TLP) converts RTOs occurring due to tail 399 losses into fast recovery (draft-ietf-tcpm-rack). Note that 400 TLP requires RACK to function properly (see tcp_recovery below) 401 402 Possible values: 403 404 - 0 disables TLP 405 - 3 or 4 enables TLP 406 407 Default: 3 408 409tcp_ecn - INTEGER 410 Control use of Explicit Congestion Notification (ECN) by TCP. 411 ECN is used only when both ends of the TCP connection indicate 412 support for it. This feature is useful in avoiding losses due 413 to congestion by allowing supporting routers to signal 414 congestion before having to drop packets. 415 416 Possible values are: 417 418 = ===================================================== 419 0 Disable ECN. Neither initiate nor accept ECN. 420 1 Enable ECN when requested by incoming connections and 421 also request ECN on outgoing connection attempts. 422 2 Enable ECN when requested by incoming connections 423 but do not request ECN on outgoing connections. 424 = ===================================================== 425 426 Default: 2 427 428tcp_ecn_fallback - BOOLEAN 429 If the kernel detects that ECN connection misbehaves, enable fall 430 back to non-ECN. Currently, this knob implements the fallback 431 from RFC3168, section 6.1.1.1., but we reserve that in future, 432 additional detection mechanisms could be implemented under this 433 knob. The value is not used, if tcp_ecn or per route (or congestion 434 control) ECN settings are disabled. 435 436 Default: 1 (fallback enabled) 437 438tcp_fack - BOOLEAN 439 This is a legacy option, it has no effect anymore. 440 441tcp_fin_timeout - INTEGER 442 The length of time an orphaned (no longer referenced by any 443 application) connection will remain in the FIN_WAIT_2 state 444 before it is aborted at the local end. While a perfectly 445 valid "receive only" state for an un-orphaned connection, an 446 orphaned connection in FIN_WAIT_2 state could otherwise wait 447 forever for the remote to close its end of the connection. 448 449 Cf. tcp_max_orphans 450 451 Default: 60 seconds 452 453tcp_frto - INTEGER 454 Enables Forward RTO-Recovery (F-RTO) defined in RFC5682. 455 F-RTO is an enhanced recovery algorithm for TCP retransmission 456 timeouts. It is particularly beneficial in networks where the 457 RTT fluctuates (e.g., wireless). F-RTO is sender-side only 458 modification. It does not require any support from the peer. 459 460 By default it's enabled with a non-zero value. 0 disables F-RTO. 461 462tcp_fwmark_accept - BOOLEAN 463 If set, incoming connections to listening sockets that do not have a 464 socket mark will set the mark of the accepting socket to the fwmark of 465 the incoming SYN packet. This will cause all packets on that connection 466 (starting from the first SYNACK) to be sent with that fwmark. The 467 listening socket's mark is unchanged. Listening sockets that already 468 have a fwmark set via setsockopt(SOL_SOCKET, SO_MARK, ...) are 469 unaffected. 470 471 Default: 0 472 473tcp_invalid_ratelimit - INTEGER 474 Limit the maximal rate for sending duplicate acknowledgments 475 in response to incoming TCP packets that are for an existing 476 connection but that are invalid due to any of these reasons: 477 478 (a) out-of-window sequence number, 479 (b) out-of-window acknowledgment number, or 480 (c) PAWS (Protection Against Wrapped Sequence numbers) check failure 481 482 This can help mitigate simple "ack loop" DoS attacks, wherein 483 a buggy or malicious middlebox or man-in-the-middle can 484 rewrite TCP header fields in manner that causes each endpoint 485 to think that the other is sending invalid TCP segments, thus 486 causing each side to send an unterminating stream of duplicate 487 acknowledgments for invalid segments. 488 489 Using 0 disables rate-limiting of dupacks in response to 490 invalid segments; otherwise this value specifies the minimal 491 space between sending such dupacks, in milliseconds. 492 493 Default: 500 (milliseconds). 494 495tcp_keepalive_time - INTEGER 496 How often TCP sends out keepalive messages when keepalive is enabled. 497 Default: 2hours. 498 499tcp_keepalive_probes - INTEGER 500 How many keepalive probes TCP sends out, until it decides that the 501 connection is broken. Default value: 9. 502 503tcp_keepalive_intvl - INTEGER 504 How frequently the probes are send out. Multiplied by 505 tcp_keepalive_probes it is time to kill not responding connection, 506 after probes started. Default value: 75sec i.e. connection 507 will be aborted after ~11 minutes of retries. 508 509tcp_l3mdev_accept - BOOLEAN 510 Enables child sockets to inherit the L3 master device index. 511 Enabling this option allows a "global" listen socket to work 512 across L3 master domains (e.g., VRFs) with connected sockets 513 derived from the listen socket to be bound to the L3 domain in 514 which the packets originated. Only valid when the kernel was 515 compiled with CONFIG_NET_L3_MASTER_DEV. 516 517 Default: 0 (disabled) 518 519tcp_low_latency - BOOLEAN 520 This is a legacy option, it has no effect anymore. 521 522tcp_max_orphans - INTEGER 523 Maximal number of TCP sockets not attached to any user file handle, 524 held by system. If this number is exceeded orphaned connections are 525 reset immediately and warning is printed. This limit exists 526 only to prevent simple DoS attacks, you _must_ not rely on this 527 or lower the limit artificially, but rather increase it 528 (probably, after increasing installed memory), 529 if network conditions require more than default value, 530 and tune network services to linger and kill such states 531 more aggressively. Let me to remind again: each orphan eats 532 up to ~64K of unswappable memory. 533 534tcp_max_syn_backlog - INTEGER 535 Maximal number of remembered connection requests (SYN_RECV), 536 which have not received an acknowledgment from connecting client. 537 538 This is a per-listener limit. 539 540 The minimal value is 128 for low memory machines, and it will 541 increase in proportion to the memory of machine. 542 543 If server suffers from overload, try increasing this number. 544 545 Remember to also check /proc/sys/net/core/somaxconn 546 A SYN_RECV request socket consumes about 304 bytes of memory. 547 548tcp_max_tw_buckets - INTEGER 549 Maximal number of timewait sockets held by system simultaneously. 550 If this number is exceeded time-wait socket is immediately destroyed 551 and warning is printed. This limit exists only to prevent 552 simple DoS attacks, you _must_ not lower the limit artificially, 553 but rather increase it (probably, after increasing installed memory), 554 if network conditions require more than default value. 555 556tcp_mem - vector of 3 INTEGERs: min, pressure, max 557 min: below this number of pages TCP is not bothered about its 558 memory appetite. 559 560 pressure: when amount of memory allocated by TCP exceeds this number 561 of pages, TCP moderates its memory consumption and enters memory 562 pressure mode, which is exited when memory consumption falls 563 under "min". 564 565 max: number of pages allowed for queueing by all TCP sockets. 566 567 Defaults are calculated at boot time from amount of available 568 memory. 569 570tcp_min_rtt_wlen - INTEGER 571 The window length of the windowed min filter to track the minimum RTT. 572 A shorter window lets a flow more quickly pick up new (higher) 573 minimum RTT when it is moved to a longer path (e.g., due to traffic 574 engineering). A longer window makes the filter more resistant to RTT 575 inflations such as transient congestion. The unit is seconds. 576 577 Possible values: 0 - 86400 (1 day) 578 579 Default: 300 580 581tcp_moderate_rcvbuf - BOOLEAN 582 If set, TCP performs receive buffer auto-tuning, attempting to 583 automatically size the buffer (no greater than tcp_rmem[2]) to 584 match the size required by the path for full throughput. Enabled by 585 default. 586 587tcp_mtu_probing - INTEGER 588 Controls TCP Packetization-Layer Path MTU Discovery. Takes three 589 values: 590 591 - 0 - Disabled 592 - 1 - Disabled by default, enabled when an ICMP black hole detected 593 - 2 - Always enabled, use initial MSS of tcp_base_mss. 594 595tcp_probe_interval - UNSIGNED INTEGER 596 Controls how often to start TCP Packetization-Layer Path MTU 597 Discovery reprobe. The default is reprobing every 10 minutes as 598 per RFC4821. 599 600tcp_probe_threshold - INTEGER 601 Controls when TCP Packetization-Layer Path MTU Discovery probing 602 will stop in respect to the width of search range in bytes. Default 603 is 8 bytes. 604 605tcp_no_metrics_save - BOOLEAN 606 By default, TCP saves various connection metrics in the route cache 607 when the connection closes, so that connections established in the 608 near future can use these to set initial conditions. Usually, this 609 increases overall performance, but may sometimes cause performance 610 degradation. If set, TCP will not cache metrics on closing 611 connections. 612 613tcp_no_ssthresh_metrics_save - BOOLEAN 614 Controls whether TCP saves ssthresh metrics in the route cache. 615 616 Default is 1, which disables ssthresh metrics. 617 618tcp_orphan_retries - INTEGER 619 This value influences the timeout of a locally closed TCP connection, 620 when RTO retransmissions remain unacknowledged. 621 See tcp_retries2 for more details. 622 623 The default value is 8. 624 625 If your machine is a loaded WEB server, 626 you should think about lowering this value, such sockets 627 may consume significant resources. Cf. tcp_max_orphans. 628 629tcp_recovery - INTEGER 630 This value is a bitmap to enable various experimental loss recovery 631 features. 632 633 ========= ============================================================= 634 RACK: 0x1 enables the RACK loss detection for fast detection of lost 635 retransmissions and tail drops. It also subsumes and disables 636 RFC6675 recovery for SACK connections. 637 638 RACK: 0x2 makes RACK's reordering window static (min_rtt/4). 639 640 RACK: 0x4 disables RACK's DUPACK threshold heuristic 641 ========= ============================================================= 642 643 Default: 0x1 644 645tcp_reflect_tos - BOOLEAN 646 For listening sockets, reuse the DSCP value of the initial SYN message 647 for outgoing packets. This allows to have both directions of a TCP 648 stream to use the same DSCP value, assuming DSCP remains unchanged for 649 the lifetime of the connection. 650 651 This options affects both IPv4 and IPv6. 652 653 Default: 0 (disabled) 654 655tcp_reordering - INTEGER 656 Initial reordering level of packets in a TCP stream. 657 TCP stack can then dynamically adjust flow reordering level 658 between this initial value and tcp_max_reordering 659 660 Default: 3 661 662tcp_max_reordering - INTEGER 663 Maximal reordering level of packets in a TCP stream. 664 300 is a fairly conservative value, but you might increase it 665 if paths are using per packet load balancing (like bonding rr mode) 666 667 Default: 300 668 669tcp_retrans_collapse - BOOLEAN 670 Bug-to-bug compatibility with some broken printers. 671 On retransmit try to send bigger packets to work around bugs in 672 certain TCP stacks. 673 674tcp_retries1 - INTEGER 675 This value influences the time, after which TCP decides, that 676 something is wrong due to unacknowledged RTO retransmissions, 677 and reports this suspicion to the network layer. 678 See tcp_retries2 for more details. 679 680 RFC 1122 recommends at least 3 retransmissions, which is the 681 default. 682 683tcp_retries2 - INTEGER 684 This value influences the timeout of an alive TCP connection, 685 when RTO retransmissions remain unacknowledged. 686 Given a value of N, a hypothetical TCP connection following 687 exponential backoff with an initial RTO of TCP_RTO_MIN would 688 retransmit N times before killing the connection at the (N+1)th RTO. 689 690 The default value of 15 yields a hypothetical timeout of 924.6 691 seconds and is a lower bound for the effective timeout. 692 TCP will effectively time out at the first RTO which exceeds the 693 hypothetical timeout. 694 695 RFC 1122 recommends at least 100 seconds for the timeout, 696 which corresponds to a value of at least 8. 697 698tcp_rfc1337 - BOOLEAN 699 If set, the TCP stack behaves conforming to RFC1337. If unset, 700 we are not conforming to RFC, but prevent TCP TIME_WAIT 701 assassination. 702 703 Default: 0 704 705tcp_rmem - vector of 3 INTEGERs: min, default, max 706 min: Minimal size of receive buffer used by TCP sockets. 707 It is guaranteed to each TCP socket, even under moderate memory 708 pressure. 709 710 Default: 4K 711 712 default: initial size of receive buffer used by TCP sockets. 713 This value overrides net.core.rmem_default used by other protocols. 714 Default: 131072 bytes. 715 This value results in initial window of 65535. 716 717 max: maximal size of receive buffer allowed for automatically 718 selected receiver buffers for TCP socket. This value does not override 719 net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables 720 automatic tuning of that socket's receive buffer size, in which 721 case this value is ignored. 722 Default: between 131072 and 6MB, depending on RAM size. 723 724tcp_sack - BOOLEAN 725 Enable select acknowledgments (SACKS). 726 727tcp_comp_sack_delay_ns - LONG INTEGER 728 TCP tries to reduce number of SACK sent, using a timer 729 based on 5% of SRTT, capped by this sysctl, in nano seconds. 730 The default is 1ms, based on TSO autosizing period. 731 732 Default : 1,000,000 ns (1 ms) 733 734tcp_comp_sack_slack_ns - LONG INTEGER 735 This sysctl control the slack used when arming the 736 timer used by SACK compression. This gives extra time 737 for small RTT flows, and reduces system overhead by allowing 738 opportunistic reduction of timer interrupts. 739 740 Default : 100,000 ns (100 us) 741 742tcp_comp_sack_nr - INTEGER 743 Max number of SACK that can be compressed. 744 Using 0 disables SACK compression. 745 746 Default : 44 747 748tcp_backlog_ack_defer - BOOLEAN 749 If set, user thread processing socket backlog tries sending 750 one ACK for the whole queue. This helps to avoid potential 751 long latencies at end of a TCP socket syscall. 752 753 Default : true 754 755tcp_slow_start_after_idle - BOOLEAN 756 If set, provide RFC2861 behavior and time out the congestion 757 window after an idle period. An idle period is defined at 758 the current RTO. If unset, the congestion window will not 759 be timed out after an idle period. 760 761 Default: 1 762 763tcp_stdurg - BOOLEAN 764 Use the Host requirements interpretation of the TCP urgent pointer field. 765 Most hosts use the older BSD interpretation, so if you turn this on 766 Linux might not communicate correctly with them. 767 768 Default: FALSE 769 770tcp_synack_retries - INTEGER 771 Number of times SYNACKs for a passive TCP connection attempt will 772 be retransmitted. Should not be higher than 255. Default value 773 is 5, which corresponds to 31seconds till the last retransmission 774 with the current initial RTO of 1second. With this the final timeout 775 for a passive TCP connection will happen after 63seconds. 776 777tcp_syncookies - INTEGER 778 Only valid when the kernel was compiled with CONFIG_SYN_COOKIES 779 Send out syncookies when the syn backlog queue of a socket 780 overflows. This is to prevent against the common 'SYN flood attack' 781 Default: 1 782 783 Note, that syncookies is fallback facility. 784 It MUST NOT be used to help highly loaded servers to stand 785 against legal connection rate. If you see SYN flood warnings 786 in your logs, but investigation shows that they occur 787 because of overload with legal connections, you should tune 788 another parameters until this warning disappear. 789 See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow. 790 791 syncookies seriously violate TCP protocol, do not allow 792 to use TCP extensions, can result in serious degradation 793 of some services (f.e. SMTP relaying), visible not by you, 794 but your clients and relays, contacting you. While you see 795 SYN flood warnings in logs not being really flooded, your server 796 is seriously misconfigured. 797 798 If you want to test which effects syncookies have to your 799 network connections you can set this knob to 2 to enable 800 unconditionally generation of syncookies. 801 802tcp_migrate_req - BOOLEAN 803 The incoming connection is tied to a specific listening socket when 804 the initial SYN packet is received during the three-way handshake. 805 When a listener is closed, in-flight request sockets during the 806 handshake and established sockets in the accept queue are aborted. 807 808 If the listener has SO_REUSEPORT enabled, other listeners on the 809 same port should have been able to accept such connections. This 810 option makes it possible to migrate such child sockets to another 811 listener after close() or shutdown(). 812 813 The BPF_SK_REUSEPORT_SELECT_OR_MIGRATE type of eBPF program should 814 usually be used to define the policy to pick an alive listener. 815 Otherwise, the kernel will randomly pick an alive listener only if 816 this option is enabled. 817 818 Note that migration between listeners with different settings may 819 crash applications. Let's say migration happens from listener A to 820 B, and only B has TCP_SAVE_SYN enabled. B cannot read SYN data from 821 the requests migrated from A. To avoid such a situation, cancel 822 migration by returning SK_DROP in the type of eBPF program, or 823 disable this option. 824 825 Default: 0 826 827tcp_fastopen - INTEGER 828 Enable TCP Fast Open (RFC7413) to send and accept data in the opening 829 SYN packet. 830 831 The client support is enabled by flag 0x1 (on by default). The client 832 then must use sendmsg() or sendto() with the MSG_FASTOPEN flag, 833 rather than connect() to send data in SYN. 834 835 The server support is enabled by flag 0x2 (off by default). Then 836 either enable for all listeners with another flag (0x400) or 837 enable individual listeners via TCP_FASTOPEN socket option with 838 the option value being the length of the syn-data backlog. 839 840 The values (bitmap) are 841 842 ===== ======== ====================================================== 843 0x1 (client) enables sending data in the opening SYN on the client. 844 0x2 (server) enables the server support, i.e., allowing data in 845 a SYN packet to be accepted and passed to the 846 application before 3-way handshake finishes. 847 0x4 (client) send data in the opening SYN regardless of cookie 848 availability and without a cookie option. 849 0x200 (server) accept data-in-SYN w/o any cookie option present. 850 0x400 (server) enable all listeners to support Fast Open by 851 default without explicit TCP_FASTOPEN socket option. 852 ===== ======== ====================================================== 853 854 Default: 0x1 855 856 Note that additional client or server features are only 857 effective if the basic support (0x1 and 0x2) are enabled respectively. 858 859tcp_fastopen_blackhole_timeout_sec - INTEGER 860 Initial time period in second to disable Fastopen on active TCP sockets 861 when a TFO firewall blackhole issue happens. 862 This time period will grow exponentially when more blackhole issues 863 get detected right after Fastopen is re-enabled and will reset to 864 initial value when the blackhole issue goes away. 865 0 to disable the blackhole detection. 866 867 By default, it is set to 0 (feature is disabled). 868 869tcp_fastopen_key - list of comma separated 32-digit hexadecimal INTEGERs 870 The list consists of a primary key and an optional backup key. The 871 primary key is used for both creating and validating cookies, while the 872 optional backup key is only used for validating cookies. The purpose of 873 the backup key is to maximize TFO validation when keys are rotated. 874 875 A randomly chosen primary key may be configured by the kernel if 876 the tcp_fastopen sysctl is set to 0x400 (see above), or if the 877 TCP_FASTOPEN setsockopt() optname is set and a key has not been 878 previously configured via sysctl. If keys are configured via 879 setsockopt() by using the TCP_FASTOPEN_KEY optname, then those 880 per-socket keys will be used instead of any keys that are specified via 881 sysctl. 882 883 A key is specified as 4 8-digit hexadecimal integers which are separated 884 by a '-' as: xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx. Leading zeros may be 885 omitted. A primary and a backup key may be specified by separating them 886 by a comma. If only one key is specified, it becomes the primary key and 887 any previously configured backup keys are removed. 888 889tcp_syn_retries - INTEGER 890 Number of times initial SYNs for an active TCP connection attempt 891 will be retransmitted. Should not be higher than 127. Default value 892 is 6, which corresponds to 67seconds (with tcp_syn_linear_timeouts = 4) 893 till the last retransmission with the current initial RTO of 1second. 894 With this the final timeout for an active TCP connection attempt 895 will happen after 131seconds. 896 897tcp_timestamps - INTEGER 898 Enable timestamps as defined in RFC1323. 899 900 - 0: Disabled. 901 - 1: Enable timestamps as defined in RFC1323 and use random offset for 902 each connection rather than only using the current time. 903 - 2: Like 1, but without random offsets. 904 905 Default: 1 906 907tcp_min_tso_segs - INTEGER 908 Minimal number of segments per TSO frame. 909 910 Since linux-3.12, TCP does an automatic sizing of TSO frames, 911 depending on flow rate, instead of filling 64Kbytes packets. 912 For specific usages, it's possible to force TCP to build big 913 TSO frames. Note that TCP stack might split too big TSO packets 914 if available window is too small. 915 916 Default: 2 917 918tcp_tso_rtt_log - INTEGER 919 Adjustment of TSO packet sizes based on min_rtt 920 921 Starting from linux-5.18, TCP autosizing can be tweaked 922 for flows having small RTT. 923 924 Old autosizing was splitting the pacing budget to send 1024 TSO 925 per second. 926 927 tso_packet_size = sk->sk_pacing_rate / 1024; 928 929 With the new mechanism, we increase this TSO sizing using: 930 931 distance = min_rtt_usec / (2^tcp_tso_rtt_log) 932 tso_packet_size += gso_max_size >> distance; 933 934 This means that flows between very close hosts can use bigger 935 TSO packets, reducing their cpu costs. 936 937 If you want to use the old autosizing, set this sysctl to 0. 938 939 Default: 9 (2^9 = 512 usec) 940 941tcp_pacing_ss_ratio - INTEGER 942 sk->sk_pacing_rate is set by TCP stack using a ratio applied 943 to current rate. (current_rate = cwnd * mss / srtt) 944 If TCP is in slow start, tcp_pacing_ss_ratio is applied 945 to let TCP probe for bigger speeds, assuming cwnd can be 946 doubled every other RTT. 947 948 Default: 200 949 950tcp_pacing_ca_ratio - INTEGER 951 sk->sk_pacing_rate is set by TCP stack using a ratio applied 952 to current rate. (current_rate = cwnd * mss / srtt) 953 If TCP is in congestion avoidance phase, tcp_pacing_ca_ratio 954 is applied to conservatively probe for bigger throughput. 955 956 Default: 120 957 958tcp_syn_linear_timeouts - INTEGER 959 The number of times for an active TCP connection to retransmit SYNs with 960 a linear backoff timeout before defaulting to an exponential backoff 961 timeout. This has no effect on SYNACK at the passive TCP side. 962 963 With an initial RTO of 1 and tcp_syn_linear_timeouts = 4 we would 964 expect SYN RTOs to be: 1, 1, 1, 1, 1, 2, 4, ... (4 linear timeouts, 965 and the first exponential backoff using 2^0 * initial_RTO). 966 Default: 4 967 968tcp_tso_win_divisor - INTEGER 969 This allows control over what percentage of the congestion window 970 can be consumed by a single TSO frame. 971 The setting of this parameter is a choice between burstiness and 972 building larger TSO frames. 973 974 Default: 3 975 976tcp_tw_reuse - INTEGER 977 Enable reuse of TIME-WAIT sockets for new connections when it is 978 safe from protocol viewpoint. 979 980 - 0 - disable 981 - 1 - global enable 982 - 2 - enable for loopback traffic only 983 984 It should not be changed without advice/request of technical 985 experts. 986 987 Default: 2 988 989tcp_window_scaling - BOOLEAN 990 Enable window scaling as defined in RFC1323. 991 992tcp_shrink_window - BOOLEAN 993 This changes how the TCP receive window is calculated. 994 995 RFC 7323, section 2.4, says there are instances when a retracted 996 window can be offered, and that TCP implementations MUST ensure 997 that they handle a shrinking window, as specified in RFC 1122. 998 999 - 0 - Disabled. The window is never shrunk. 1000 - 1 - Enabled. The window is shrunk when necessary to remain within 1001 the memory limit set by autotuning (sk_rcvbuf). 1002 This only occurs if a non-zero receive window 1003 scaling factor is also in effect. 1004 1005 Default: 0 1006 1007tcp_wmem - vector of 3 INTEGERs: min, default, max 1008 min: Amount of memory reserved for send buffers for TCP sockets. 1009 Each TCP socket has rights to use it due to fact of its birth. 1010 1011 Default: 4K 1012 1013 default: initial size of send buffer used by TCP sockets. This 1014 value overrides net.core.wmem_default used by other protocols. 1015 1016 It is usually lower than net.core.wmem_default. 1017 1018 Default: 16K 1019 1020 max: Maximal amount of memory allowed for automatically tuned 1021 send buffers for TCP sockets. This value does not override 1022 net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables 1023 automatic tuning of that socket's send buffer size, in which case 1024 this value is ignored. 1025 1026 Default: between 64K and 4MB, depending on RAM size. 1027 1028tcp_notsent_lowat - UNSIGNED INTEGER 1029 A TCP socket can control the amount of unsent bytes in its write queue, 1030 thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll() 1031 reports POLLOUT events if the amount of unsent bytes is below a per 1032 socket value, and if the write queue is not full. sendmsg() will 1033 also not add new buffers if the limit is hit. 1034 1035 This global variable controls the amount of unsent data for 1036 sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change 1037 to the global variable has immediate effect. 1038 1039 Default: UINT_MAX (0xFFFFFFFF) 1040 1041tcp_workaround_signed_windows - BOOLEAN 1042 If set, assume no receipt of a window scaling option means the 1043 remote TCP is broken and treats the window as a signed quantity. 1044 If unset, assume the remote TCP is not broken even if we do 1045 not receive a window scaling option from them. 1046 1047 Default: 0 1048 1049tcp_thin_linear_timeouts - BOOLEAN 1050 Enable dynamic triggering of linear timeouts for thin streams. 1051 If set, a check is performed upon retransmission by timeout to 1052 determine if the stream is thin (less than 4 packets in flight). 1053 As long as the stream is found to be thin, up to 6 linear 1054 timeouts may be performed before exponential backoff mode is 1055 initiated. This improves retransmission latency for 1056 non-aggressive thin streams, often found to be time-dependent. 1057 For more information on thin streams, see 1058 Documentation/networking/tcp-thin.rst 1059 1060 Default: 0 1061 1062tcp_limit_output_bytes - INTEGER 1063 Controls TCP Small Queue limit per tcp socket. 1064 TCP bulk sender tends to increase packets in flight until it 1065 gets losses notifications. With SNDBUF autotuning, this can 1066 result in a large amount of packets queued on the local machine 1067 (e.g.: qdiscs, CPU backlog, or device) hurting latency of other 1068 flows, for typical pfifo_fast qdiscs. tcp_limit_output_bytes 1069 limits the number of bytes on qdisc or device to reduce artificial 1070 RTT/cwnd and reduce bufferbloat. 1071 1072 Default: 1048576 (16 * 65536) 1073 1074tcp_challenge_ack_limit - INTEGER 1075 Limits number of Challenge ACK sent per second, as recommended 1076 in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks) 1077 Note that this per netns rate limit can allow some side channel 1078 attacks and probably should not be enabled. 1079 TCP stack implements per TCP socket limits anyway. 1080 Default: INT_MAX (unlimited) 1081 1082tcp_ehash_entries - INTEGER 1083 Show the number of hash buckets for TCP sockets in the current 1084 networking namespace. 1085 1086 A negative value means the networking namespace does not own its 1087 hash buckets and shares the initial networking namespace's one. 1088 1089tcp_child_ehash_entries - INTEGER 1090 Control the number of hash buckets for TCP sockets in the child 1091 networking namespace, which must be set before clone() or unshare(). 1092 1093 If the value is not 0, the kernel uses a value rounded up to 2^n 1094 as the actual hash bucket size. 0 is a special value, meaning 1095 the child networking namespace will share the initial networking 1096 namespace's hash buckets. 1097 1098 Note that the child will use the global one in case the kernel 1099 fails to allocate enough memory. In addition, the global hash 1100 buckets are spread over available NUMA nodes, but the allocation 1101 of the child hash table depends on the current process's NUMA 1102 policy, which could result in performance differences. 1103 1104 Note also that the default value of tcp_max_tw_buckets and 1105 tcp_max_syn_backlog depend on the hash bucket size. 1106 1107 Possible values: 0, 2^n (n: 0 - 24 (16Mi)) 1108 1109 Default: 0 1110 1111tcp_plb_enabled - BOOLEAN 1112 If set and the underlying congestion control (e.g. DCTCP) supports 1113 and enables PLB feature, TCP PLB (Protective Load Balancing) is 1114 enabled. PLB is described in the following paper: 1115 https://doi.org/10.1145/3544216.3544226. Based on PLB parameters, 1116 upon sensing sustained congestion, TCP triggers a change in 1117 flow label field for outgoing IPv6 packets. A change in flow label 1118 field potentially changes the path of outgoing packets for switches 1119 that use ECMP/WCMP for routing. 1120 1121 PLB changes socket txhash which results in a change in IPv6 Flow Label 1122 field, and currently no-op for IPv4 headers. It is possible 1123 to apply PLB for IPv4 with other network header fields (e.g. TCP 1124 or IPv4 options) or using encapsulation where outer header is used 1125 by switches to determine next hop. In either case, further host 1126 and switch side changes will be needed. 1127 1128 When set, PLB assumes that congestion signal (e.g. ECN) is made 1129 available and used by congestion control module to estimate a 1130 congestion measure (e.g. ce_ratio). PLB needs a congestion measure to 1131 make repathing decisions. 1132 1133 Default: FALSE 1134 1135tcp_plb_idle_rehash_rounds - INTEGER 1136 Number of consecutive congested rounds (RTT) seen after which 1137 a rehash can be performed, given there are no packets in flight. 1138 This is referred to as M in PLB paper: 1139 https://doi.org/10.1145/3544216.3544226. 1140 1141 Possible Values: 0 - 31 1142 1143 Default: 3 1144 1145tcp_plb_rehash_rounds - INTEGER 1146 Number of consecutive congested rounds (RTT) seen after which 1147 a forced rehash can be performed. Be careful when setting this 1148 parameter, as a small value increases the risk of retransmissions. 1149 This is referred to as N in PLB paper: 1150 https://doi.org/10.1145/3544216.3544226. 1151 1152 Possible Values: 0 - 31 1153 1154 Default: 12 1155 1156tcp_plb_suspend_rto_sec - INTEGER 1157 Time, in seconds, to suspend PLB in event of an RTO. In order to avoid 1158 having PLB repath onto a connectivity "black hole", after an RTO a TCP 1159 connection suspends PLB repathing for a random duration between 1x and 1160 2x of this parameter. Randomness is added to avoid concurrent rehashing 1161 of multiple TCP connections. This should be set corresponding to the 1162 amount of time it takes to repair a failed link. 1163 1164 Possible Values: 0 - 255 1165 1166 Default: 60 1167 1168tcp_plb_cong_thresh - INTEGER 1169 Fraction of packets marked with congestion over a round (RTT) to 1170 tag that round as congested. This is referred to as K in the PLB paper: 1171 https://doi.org/10.1145/3544216.3544226. 1172 1173 The 0-1 fraction range is mapped to 0-256 range to avoid floating 1174 point operations. For example, 128 means that if at least 50% of 1175 the packets in a round were marked as congested then the round 1176 will be tagged as congested. 1177 1178 Setting threshold to 0 means that PLB repaths every RTT regardless 1179 of congestion. This is not intended behavior for PLB and should be 1180 used only for experimentation purpose. 1181 1182 Possible Values: 0 - 256 1183 1184 Default: 128 1185 1186tcp_pingpong_thresh - INTEGER 1187 The number of estimated data replies sent for estimated incoming data 1188 requests that must happen before TCP considers that a connection is a 1189 "ping-pong" (request-response) connection for which delayed 1190 acknowledgments can provide benefits. 1191 1192 This threshold is 1 by default, but some applications may need a higher 1193 threshold for optimal performance. 1194 1195 Possible Values: 1 - 255 1196 1197 Default: 1 1198 1199UDP variables 1200============= 1201 1202udp_l3mdev_accept - BOOLEAN 1203 Enabling this option allows a "global" bound socket to work 1204 across L3 master domains (e.g., VRFs) with packets capable of 1205 being received regardless of the L3 domain in which they 1206 originated. Only valid when the kernel was compiled with 1207 CONFIG_NET_L3_MASTER_DEV. 1208 1209 Default: 0 (disabled) 1210 1211udp_mem - vector of 3 INTEGERs: min, pressure, max 1212 Number of pages allowed for queueing by all UDP sockets. 1213 1214 min: Number of pages allowed for queueing by all UDP sockets. 1215 1216 pressure: This value was introduced to follow format of tcp_mem. 1217 1218 max: This value was introduced to follow format of tcp_mem. 1219 1220 Default is calculated at boot time from amount of available memory. 1221 1222udp_rmem_min - INTEGER 1223 Minimal size of receive buffer used by UDP sockets in moderation. 1224 Each UDP socket is able to use the size for receiving data, even if 1225 total pages of UDP sockets exceed udp_mem pressure. The unit is byte. 1226 1227 Default: 4K 1228 1229udp_wmem_min - INTEGER 1230 UDP does not have tx memory accounting and this tunable has no effect. 1231 1232udp_hash_entries - INTEGER 1233 Show the number of hash buckets for UDP sockets in the current 1234 networking namespace. 1235 1236 A negative value means the networking namespace does not own its 1237 hash buckets and shares the initial networking namespace's one. 1238 1239udp_child_ehash_entries - INTEGER 1240 Control the number of hash buckets for UDP sockets in the child 1241 networking namespace, which must be set before clone() or unshare(). 1242 1243 If the value is not 0, the kernel uses a value rounded up to 2^n 1244 as the actual hash bucket size. 0 is a special value, meaning 1245 the child networking namespace will share the initial networking 1246 namespace's hash buckets. 1247 1248 Note that the child will use the global one in case the kernel 1249 fails to allocate enough memory. In addition, the global hash 1250 buckets are spread over available NUMA nodes, but the allocation 1251 of the child hash table depends on the current process's NUMA 1252 policy, which could result in performance differences. 1253 1254 Possible values: 0, 2^n (n: 7 (128) - 16 (64K)) 1255 1256 Default: 0 1257 1258 1259RAW variables 1260============= 1261 1262raw_l3mdev_accept - BOOLEAN 1263 Enabling this option allows a "global" bound socket to work 1264 across L3 master domains (e.g., VRFs) with packets capable of 1265 being received regardless of the L3 domain in which they 1266 originated. Only valid when the kernel was compiled with 1267 CONFIG_NET_L3_MASTER_DEV. 1268 1269 Default: 1 (enabled) 1270 1271CIPSOv4 Variables 1272================= 1273 1274cipso_cache_enable - BOOLEAN 1275 If set, enable additions to and lookups from the CIPSO label mapping 1276 cache. If unset, additions are ignored and lookups always result in a 1277 miss. However, regardless of the setting the cache is still 1278 invalidated when required when means you can safely toggle this on and 1279 off and the cache will always be "safe". 1280 1281 Default: 1 1282 1283cipso_cache_bucket_size - INTEGER 1284 The CIPSO label cache consists of a fixed size hash table with each 1285 hash bucket containing a number of cache entries. This variable limits 1286 the number of entries in each hash bucket; the larger the value is, the 1287 more CIPSO label mappings that can be cached. When the number of 1288 entries in a given hash bucket reaches this limit adding new entries 1289 causes the oldest entry in the bucket to be removed to make room. 1290 1291 Default: 10 1292 1293cipso_rbm_optfmt - BOOLEAN 1294 Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of 1295 the CIPSO draft specification (see Documentation/netlabel for details). 1296 This means that when set the CIPSO tag will be padded with empty 1297 categories in order to make the packet data 32-bit aligned. 1298 1299 Default: 0 1300 1301cipso_rbm_structvalid - BOOLEAN 1302 If set, do a very strict check of the CIPSO option when 1303 ip_options_compile() is called. If unset, relax the checks done during 1304 ip_options_compile(). Either way is "safe" as errors are caught else 1305 where in the CIPSO processing code but setting this to 0 (False) should 1306 result in less work (i.e. it should be faster) but could cause problems 1307 with other implementations that require strict checking. 1308 1309 Default: 0 1310 1311IP Variables 1312============ 1313 1314ip_local_port_range - 2 INTEGERS 1315 Defines the local port range that is used by TCP and UDP to 1316 choose the local port. The first number is the first, the 1317 second the last local port number. 1318 If possible, it is better these numbers have different parity 1319 (one even and one odd value). 1320 Must be greater than or equal to ip_unprivileged_port_start. 1321 The default values are 32768 and 60999 respectively. 1322 1323ip_local_reserved_ports - list of comma separated ranges 1324 Specify the ports which are reserved for known third-party 1325 applications. These ports will not be used by automatic port 1326 assignments (e.g. when calling connect() or bind() with port 1327 number 0). Explicit port allocation behavior is unchanged. 1328 1329 The format used for both input and output is a comma separated 1330 list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and 1331 10). Writing to the file will clear all previously reserved 1332 ports and update the current list with the one given in the 1333 input. 1334 1335 Note that ip_local_port_range and ip_local_reserved_ports 1336 settings are independent and both are considered by the kernel 1337 when determining which ports are available for automatic port 1338 assignments. 1339 1340 You can reserve ports which are not in the current 1341 ip_local_port_range, e.g.:: 1342 1343 $ cat /proc/sys/net/ipv4/ip_local_port_range 1344 32000 60999 1345 $ cat /proc/sys/net/ipv4/ip_local_reserved_ports 1346 8080,9148 1347 1348 although this is redundant. However such a setting is useful 1349 if later the port range is changed to a value that will 1350 include the reserved ports. Also keep in mind, that overlapping 1351 of these ranges may affect probability of selecting ephemeral 1352 ports which are right after block of reserved ports. 1353 1354 Default: Empty 1355 1356ip_unprivileged_port_start - INTEGER 1357 This is a per-namespace sysctl. It defines the first 1358 unprivileged port in the network namespace. Privileged ports 1359 require root or CAP_NET_BIND_SERVICE in order to bind to them. 1360 To disable all privileged ports, set this to 0. They must not 1361 overlap with the ip_local_port_range. 1362 1363 Default: 1024 1364 1365ip_nonlocal_bind - BOOLEAN 1366 If set, allows processes to bind() to non-local IP addresses, 1367 which can be quite useful - but may break some applications. 1368 1369 Default: 0 1370 1371ip_autobind_reuse - BOOLEAN 1372 By default, bind() does not select the ports automatically even if 1373 the new socket and all sockets bound to the port have SO_REUSEADDR. 1374 ip_autobind_reuse allows bind() to reuse the port and this is useful 1375 when you use bind()+connect(), but may break some applications. 1376 The preferred solution is to use IP_BIND_ADDRESS_NO_PORT and this 1377 option should only be set by experts. 1378 Default: 0 1379 1380ip_dynaddr - INTEGER 1381 If set non-zero, enables support for dynamic addresses. 1382 If set to a non-zero value larger than 1, a kernel log 1383 message will be printed when dynamic address rewriting 1384 occurs. 1385 1386 Default: 0 1387 1388ip_early_demux - BOOLEAN 1389 Optimize input packet processing down to one demux for 1390 certain kinds of local sockets. Currently we only do this 1391 for established TCP and connected UDP sockets. 1392 1393 It may add an additional cost for pure routing workloads that 1394 reduces overall throughput, in such case you should disable it. 1395 1396 Default: 1 1397 1398ping_group_range - 2 INTEGERS 1399 Restrict ICMP_PROTO datagram sockets to users in the group range. 1400 The default is "1 0", meaning, that nobody (not even root) may 1401 create ping sockets. Setting it to "100 100" would grant permissions 1402 to the single group. "0 4294967294" would enable it for the world, "100 1403 4294967294" would enable it for the users, but not daemons. 1404 1405tcp_early_demux - BOOLEAN 1406 Enable early demux for established TCP sockets. 1407 1408 Default: 1 1409 1410udp_early_demux - BOOLEAN 1411 Enable early demux for connected UDP sockets. Disable this if 1412 your system could experience more unconnected load. 1413 1414 Default: 1 1415 1416icmp_echo_ignore_all - BOOLEAN 1417 If set non-zero, then the kernel will ignore all ICMP ECHO 1418 requests sent to it. 1419 1420 Default: 0 1421 1422icmp_echo_enable_probe - BOOLEAN 1423 If set to one, then the kernel will respond to RFC 8335 PROBE 1424 requests sent to it. 1425 1426 Default: 0 1427 1428icmp_echo_ignore_broadcasts - BOOLEAN 1429 If set non-zero, then the kernel will ignore all ICMP ECHO and 1430 TIMESTAMP requests sent to it via broadcast/multicast. 1431 1432 Default: 1 1433 1434icmp_ratelimit - INTEGER 1435 Limit the maximal rates for sending ICMP packets whose type matches 1436 icmp_ratemask (see below) to specific targets. 1437 0 to disable any limiting, 1438 otherwise the minimal space between responses in milliseconds. 1439 Note that another sysctl, icmp_msgs_per_sec limits the number 1440 of ICMP packets sent on all targets. 1441 1442 Default: 1000 1443 1444icmp_msgs_per_sec - INTEGER 1445 Limit maximal number of ICMP packets sent per second from this host. 1446 Only messages whose type matches icmp_ratemask (see below) are 1447 controlled by this limit. For security reasons, the precise count 1448 of messages per second is randomized. 1449 1450 Default: 1000 1451 1452icmp_msgs_burst - INTEGER 1453 icmp_msgs_per_sec controls number of ICMP packets sent per second, 1454 while icmp_msgs_burst controls the burst size of these packets. 1455 For security reasons, the precise burst size is randomized. 1456 1457 Default: 50 1458 1459icmp_ratemask - INTEGER 1460 Mask made of ICMP types for which rates are being limited. 1461 1462 Significant bits: IHGFEDCBA9876543210 1463 1464 Default mask: 0000001100000011000 (6168) 1465 1466 Bit definitions (see include/linux/icmp.h): 1467 1468 = ========================= 1469 0 Echo Reply 1470 3 Destination Unreachable [1]_ 1471 4 Source Quench [1]_ 1472 5 Redirect 1473 8 Echo Request 1474 B Time Exceeded [1]_ 1475 C Parameter Problem [1]_ 1476 D Timestamp Request 1477 E Timestamp Reply 1478 F Info Request 1479 G Info Reply 1480 H Address Mask Request 1481 I Address Mask Reply 1482 = ========================= 1483 1484 .. [1] These are rate limited by default (see default mask above) 1485 1486icmp_ignore_bogus_error_responses - BOOLEAN 1487 Some routers violate RFC1122 by sending bogus responses to broadcast 1488 frames. Such violations are normally logged via a kernel warning. 1489 If this is set to TRUE, the kernel will not give such warnings, which 1490 will avoid log file clutter. 1491 1492 Default: 1 1493 1494icmp_errors_use_inbound_ifaddr - BOOLEAN 1495 1496 If zero, icmp error messages are sent with the primary address of 1497 the exiting interface. 1498 1499 If non-zero, the message will be sent with the primary address of 1500 the interface that received the packet that caused the icmp error. 1501 This is the behaviour many network administrators will expect from 1502 a router. And it can make debugging complicated network layouts 1503 much easier. 1504 1505 Note that if no primary address exists for the interface selected, 1506 then the primary address of the first non-loopback interface that 1507 has one will be used regardless of this setting. 1508 1509 Default: 0 1510 1511igmp_max_memberships - INTEGER 1512 Change the maximum number of multicast groups we can subscribe to. 1513 Default: 20 1514 1515 Theoretical maximum value is bounded by having to send a membership 1516 report in a single datagram (i.e. the report can't span multiple 1517 datagrams, or risk confusing the switch and leaving groups you don't 1518 intend to). 1519 1520 The number of supported groups 'M' is bounded by the number of group 1521 report entries you can fit into a single datagram of 65535 bytes. 1522 1523 M = 65536-sizeof (ip header)/(sizeof(Group record)) 1524 1525 Group records are variable length, with a minimum of 12 bytes. 1526 So net.ipv4.igmp_max_memberships should not be set higher than: 1527 1528 (65536-24) / 12 = 5459 1529 1530 The value 5459 assumes no IP header options, so in practice 1531 this number may be lower. 1532 1533igmp_max_msf - INTEGER 1534 Maximum number of addresses allowed in the source filter list for a 1535 multicast group. 1536 1537 Default: 10 1538 1539igmp_qrv - INTEGER 1540 Controls the IGMP query robustness variable (see RFC2236 8.1). 1541 1542 Default: 2 (as specified by RFC2236 8.1) 1543 1544 Minimum: 1 (as specified by RFC6636 4.5) 1545 1546force_igmp_version - INTEGER 1547 - 0 - (default) No enforcement of a IGMP version, IGMPv1/v2 fallback 1548 allowed. Will back to IGMPv3 mode again if all IGMPv1/v2 Querier 1549 Present timer expires. 1550 - 1 - Enforce to use IGMP version 1. Will also reply IGMPv1 report if 1551 receive IGMPv2/v3 query. 1552 - 2 - Enforce to use IGMP version 2. Will fallback to IGMPv1 if receive 1553 IGMPv1 query message. Will reply report if receive IGMPv3 query. 1554 - 3 - Enforce to use IGMP version 3. The same react with default 0. 1555 1556 .. note:: 1557 1558 this is not the same with force_mld_version because IGMPv3 RFC3376 1559 Security Considerations does not have clear description that we could 1560 ignore other version messages completely as MLDv2 RFC3810. So make 1561 this value as default 0 is recommended. 1562 1563``conf/interface/*`` 1564 changes special settings per interface (where 1565 interface" is the name of your network interface) 1566 1567``conf/all/*`` 1568 is special, changes the settings for all interfaces 1569 1570log_martians - BOOLEAN 1571 Log packets with impossible addresses to kernel log. 1572 log_martians for the interface will be enabled if at least one of 1573 conf/{all,interface}/log_martians is set to TRUE, 1574 it will be disabled otherwise 1575 1576accept_redirects - BOOLEAN 1577 Accept ICMP redirect messages. 1578 accept_redirects for the interface will be enabled if: 1579 1580 - both conf/{all,interface}/accept_redirects are TRUE in the case 1581 forwarding for the interface is enabled 1582 1583 or 1584 1585 - at least one of conf/{all,interface}/accept_redirects is TRUE in the 1586 case forwarding for the interface is disabled 1587 1588 accept_redirects for the interface will be disabled otherwise 1589 1590 default: 1591 1592 - TRUE (host) 1593 - FALSE (router) 1594 1595forwarding - BOOLEAN 1596 Enable IP forwarding on this interface. This controls whether packets 1597 received _on_ this interface can be forwarded. 1598 1599mc_forwarding - BOOLEAN 1600 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE 1601 and a multicast routing daemon is required. 1602 conf/all/mc_forwarding must also be set to TRUE to enable multicast 1603 routing for the interface 1604 1605medium_id - INTEGER 1606 Integer value used to differentiate the devices by the medium they 1607 are attached to. Two devices can have different id values when 1608 the broadcast packets are received only on one of them. 1609 The default value 0 means that the device is the only interface 1610 to its medium, value of -1 means that medium is not known. 1611 1612 Currently, it is used to change the proxy_arp behavior: 1613 the proxy_arp feature is enabled for packets forwarded between 1614 two devices attached to different media. 1615 1616proxy_arp - BOOLEAN 1617 Do proxy arp. 1618 1619 proxy_arp for the interface will be enabled if at least one of 1620 conf/{all,interface}/proxy_arp is set to TRUE, 1621 it will be disabled otherwise 1622 1623proxy_arp_pvlan - BOOLEAN 1624 Private VLAN proxy arp. 1625 1626 Basically allow proxy arp replies back to the same interface 1627 (from which the ARP request/solicitation was received). 1628 1629 This is done to support (ethernet) switch features, like RFC 1630 3069, where the individual ports are NOT allowed to 1631 communicate with each other, but they are allowed to talk to 1632 the upstream router. As described in RFC 3069, it is possible 1633 to allow these hosts to communicate through the upstream 1634 router by proxy_arp'ing. Don't need to be used together with 1635 proxy_arp. 1636 1637 This technology is known by different names: 1638 1639 In RFC 3069 it is called VLAN Aggregation. 1640 Cisco and Allied Telesyn call it Private VLAN. 1641 Hewlett-Packard call it Source-Port filtering or port-isolation. 1642 Ericsson call it MAC-Forced Forwarding (RFC Draft). 1643 1644proxy_delay - INTEGER 1645 Delay proxy response. 1646 1647 Delay response to a neighbor solicitation when proxy_arp 1648 or proxy_ndp is enabled. A random value between [0, proxy_delay) 1649 will be chosen, setting to zero means reply with no delay. 1650 Value in jiffies. Defaults to 80. 1651 1652shared_media - BOOLEAN 1653 Send(router) or accept(host) RFC1620 shared media redirects. 1654 Overrides secure_redirects. 1655 1656 shared_media for the interface will be enabled if at least one of 1657 conf/{all,interface}/shared_media is set to TRUE, 1658 it will be disabled otherwise 1659 1660 default TRUE 1661 1662secure_redirects - BOOLEAN 1663 Accept ICMP redirect messages only to gateways listed in the 1664 interface's current gateway list. Even if disabled, RFC1122 redirect 1665 rules still apply. 1666 1667 Overridden by shared_media. 1668 1669 secure_redirects for the interface will be enabled if at least one of 1670 conf/{all,interface}/secure_redirects is set to TRUE, 1671 it will be disabled otherwise 1672 1673 default TRUE 1674 1675send_redirects - BOOLEAN 1676 Send redirects, if router. 1677 1678 send_redirects for the interface will be enabled if at least one of 1679 conf/{all,interface}/send_redirects is set to TRUE, 1680 it will be disabled otherwise 1681 1682 Default: TRUE 1683 1684bootp_relay - BOOLEAN 1685 Accept packets with source address 0.b.c.d destined 1686 not to this host as local ones. It is supposed, that 1687 BOOTP relay daemon will catch and forward such packets. 1688 conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay 1689 for the interface 1690 1691 default FALSE 1692 1693 Not Implemented Yet. 1694 1695accept_source_route - BOOLEAN 1696 Accept packets with SRR option. 1697 conf/all/accept_source_route must also be set to TRUE to accept packets 1698 with SRR option on the interface 1699 1700 default 1701 1702 - TRUE (router) 1703 - FALSE (host) 1704 1705accept_local - BOOLEAN 1706 Accept packets with local source addresses. In combination with 1707 suitable routing, this can be used to direct packets between two 1708 local interfaces over the wire and have them accepted properly. 1709 default FALSE 1710 1711route_localnet - BOOLEAN 1712 Do not consider loopback addresses as martian source or destination 1713 while routing. This enables the use of 127/8 for local routing purposes. 1714 1715 default FALSE 1716 1717rp_filter - INTEGER 1718 - 0 - No source validation. 1719 - 1 - Strict mode as defined in RFC3704 Strict Reverse Path 1720 Each incoming packet is tested against the FIB and if the interface 1721 is not the best reverse path the packet check will fail. 1722 By default failed packets are discarded. 1723 - 2 - Loose mode as defined in RFC3704 Loose Reverse Path 1724 Each incoming packet's source address is also tested against the FIB 1725 and if the source address is not reachable via any interface 1726 the packet check will fail. 1727 1728 Current recommended practice in RFC3704 is to enable strict mode 1729 to prevent IP spoofing from DDos attacks. If using asymmetric routing 1730 or other complicated routing, then loose mode is recommended. 1731 1732 The max value from conf/{all,interface}/rp_filter is used 1733 when doing source validation on the {interface}. 1734 1735 Default value is 0. Note that some distributions enable it 1736 in startup scripts. 1737 1738src_valid_mark - BOOLEAN 1739 - 0 - The fwmark of the packet is not included in reverse path 1740 route lookup. This allows for asymmetric routing configurations 1741 utilizing the fwmark in only one direction, e.g., transparent 1742 proxying. 1743 1744 - 1 - The fwmark of the packet is included in reverse path route 1745 lookup. This permits rp_filter to function when the fwmark is 1746 used for routing traffic in both directions. 1747 1748 This setting also affects the utilization of fmwark when 1749 performing source address selection for ICMP replies, or 1750 determining addresses stored for the IPOPT_TS_TSANDADDR and 1751 IPOPT_RR IP options. 1752 1753 The max value from conf/{all,interface}/src_valid_mark is used. 1754 1755 Default value is 0. 1756 1757arp_filter - BOOLEAN 1758 - 1 - Allows you to have multiple network interfaces on the same 1759 subnet, and have the ARPs for each interface be answered 1760 based on whether or not the kernel would route a packet from 1761 the ARP'd IP out that interface (therefore you must use source 1762 based routing for this to work). In other words it allows control 1763 of which cards (usually 1) will respond to an arp request. 1764 1765 - 0 - (default) The kernel can respond to arp requests with addresses 1766 from other interfaces. This may seem wrong but it usually makes 1767 sense, because it increases the chance of successful communication. 1768 IP addresses are owned by the complete host on Linux, not by 1769 particular interfaces. Only for more complex setups like load- 1770 balancing, does this behaviour cause problems. 1771 1772 arp_filter for the interface will be enabled if at least one of 1773 conf/{all,interface}/arp_filter is set to TRUE, 1774 it will be disabled otherwise 1775 1776arp_announce - INTEGER 1777 Define different restriction levels for announcing the local 1778 source IP address from IP packets in ARP requests sent on 1779 interface: 1780 1781 - 0 - (default) Use any local address, configured on any interface 1782 - 1 - Try to avoid local addresses that are not in the target's 1783 subnet for this interface. This mode is useful when target 1784 hosts reachable via this interface require the source IP 1785 address in ARP requests to be part of their logical network 1786 configured on the receiving interface. When we generate the 1787 request we will check all our subnets that include the 1788 target IP and will preserve the source address if it is from 1789 such subnet. If there is no such subnet we select source 1790 address according to the rules for level 2. 1791 - 2 - Always use the best local address for this target. 1792 In this mode we ignore the source address in the IP packet 1793 and try to select local address that we prefer for talks with 1794 the target host. Such local address is selected by looking 1795 for primary IP addresses on all our subnets on the outgoing 1796 interface that include the target IP address. If no suitable 1797 local address is found we select the first local address 1798 we have on the outgoing interface or on all other interfaces, 1799 with the hope we will receive reply for our request and 1800 even sometimes no matter the source IP address we announce. 1801 1802 The max value from conf/{all,interface}/arp_announce is used. 1803 1804 Increasing the restriction level gives more chance for 1805 receiving answer from the resolved target while decreasing 1806 the level announces more valid sender's information. 1807 1808arp_ignore - INTEGER 1809 Define different modes for sending replies in response to 1810 received ARP requests that resolve local target IP addresses: 1811 1812 - 0 - (default): reply for any local target IP address, configured 1813 on any interface 1814 - 1 - reply only if the target IP address is local address 1815 configured on the incoming interface 1816 - 2 - reply only if the target IP address is local address 1817 configured on the incoming interface and both with the 1818 sender's IP address are part from same subnet on this interface 1819 - 3 - do not reply for local addresses configured with scope host, 1820 only resolutions for global and link addresses are replied 1821 - 4-7 - reserved 1822 - 8 - do not reply for all local addresses 1823 1824 The max value from conf/{all,interface}/arp_ignore is used 1825 when ARP request is received on the {interface} 1826 1827arp_notify - BOOLEAN 1828 Define mode for notification of address and device changes. 1829 1830 == ========================================================== 1831 0 (default): do nothing 1832 1 Generate gratuitous arp requests when device is brought up 1833 or hardware address changes. 1834 == ========================================================== 1835 1836arp_accept - INTEGER 1837 Define behavior for accepting gratuitous ARP (garp) frames from devices 1838 that are not already present in the ARP table: 1839 1840 - 0 - don't create new entries in the ARP table 1841 - 1 - create new entries in the ARP table 1842 - 2 - create new entries only if the source IP address is in the same 1843 subnet as an address configured on the interface that received the 1844 garp message. 1845 1846 Both replies and requests type gratuitous arp will trigger the 1847 ARP table to be updated, if this setting is on. 1848 1849 If the ARP table already contains the IP address of the 1850 gratuitous arp frame, the arp table will be updated regardless 1851 if this setting is on or off. 1852 1853arp_evict_nocarrier - BOOLEAN 1854 Clears the ARP cache on NOCARRIER events. This option is important for 1855 wireless devices where the ARP cache should not be cleared when roaming 1856 between access points on the same network. In most cases this should 1857 remain as the default (1). 1858 1859 - 1 - (default): Clear the ARP cache on NOCARRIER events 1860 - 0 - Do not clear ARP cache on NOCARRIER events 1861 1862mcast_solicit - INTEGER 1863 The maximum number of multicast probes in INCOMPLETE state, 1864 when the associated hardware address is unknown. Defaults 1865 to 3. 1866 1867ucast_solicit - INTEGER 1868 The maximum number of unicast probes in PROBE state, when 1869 the hardware address is being reconfirmed. Defaults to 3. 1870 1871app_solicit - INTEGER 1872 The maximum number of probes to send to the user space ARP daemon 1873 via netlink before dropping back to multicast probes (see 1874 mcast_resolicit). Defaults to 0. 1875 1876mcast_resolicit - INTEGER 1877 The maximum number of multicast probes after unicast and 1878 app probes in PROBE state. Defaults to 0. 1879 1880disable_policy - BOOLEAN 1881 Disable IPSEC policy (SPD) for this interface 1882 1883disable_xfrm - BOOLEAN 1884 Disable IPSEC encryption on this interface, whatever the policy 1885 1886igmpv2_unsolicited_report_interval - INTEGER 1887 The interval in milliseconds in which the next unsolicited 1888 IGMPv1 or IGMPv2 report retransmit will take place. 1889 1890 Default: 10000 (10 seconds) 1891 1892igmpv3_unsolicited_report_interval - INTEGER 1893 The interval in milliseconds in which the next unsolicited 1894 IGMPv3 report retransmit will take place. 1895 1896 Default: 1000 (1 seconds) 1897 1898ignore_routes_with_linkdown - BOOLEAN 1899 Ignore routes whose link is down when performing a FIB lookup. 1900 1901promote_secondaries - BOOLEAN 1902 When a primary IP address is removed from this interface 1903 promote a corresponding secondary IP address instead of 1904 removing all the corresponding secondary IP addresses. 1905 1906drop_unicast_in_l2_multicast - BOOLEAN 1907 Drop any unicast IP packets that are received in link-layer 1908 multicast (or broadcast) frames. 1909 1910 This behavior (for multicast) is actually a SHOULD in RFC 1911 1122, but is disabled by default for compatibility reasons. 1912 1913 Default: off (0) 1914 1915drop_gratuitous_arp - BOOLEAN 1916 Drop all gratuitous ARP frames, for example if there's a known 1917 good ARP proxy on the network and such frames need not be used 1918 (or in the case of 802.11, must not be used to prevent attacks.) 1919 1920 Default: off (0) 1921 1922 1923tag - INTEGER 1924 Allows you to write a number, which can be used as required. 1925 1926 Default value is 0. 1927 1928xfrm4_gc_thresh - INTEGER 1929 (Obsolete since linux-4.14) 1930 The threshold at which we will start garbage collecting for IPv4 1931 destination cache entries. At twice this value the system will 1932 refuse new allocations. 1933 1934igmp_link_local_mcast_reports - BOOLEAN 1935 Enable IGMP reports for link local multicast groups in the 1936 224.0.0.X range. 1937 1938 Default TRUE 1939 1940Alexey Kuznetsov. 1941kuznet@ms2.inr.ac.ru 1942 1943Updated by: 1944 1945- Andi Kleen 1946 ak@muc.de 1947- Nicolas Delon 1948 delon.nicolas@wanadoo.fr 1949 1950 1951 1952 1953/proc/sys/net/ipv6/* Variables 1954============================== 1955 1956IPv6 has no global variables such as tcp_*. tcp_* settings under ipv4/ also 1957apply to IPv6 [XXX?]. 1958 1959bindv6only - BOOLEAN 1960 Default value for IPV6_V6ONLY socket option, 1961 which restricts use of the IPv6 socket to IPv6 communication 1962 only. 1963 1964 - TRUE: disable IPv4-mapped address feature 1965 - FALSE: enable IPv4-mapped address feature 1966 1967 Default: FALSE (as specified in RFC3493) 1968 1969flowlabel_consistency - BOOLEAN 1970 Protect the consistency (and unicity) of flow label. 1971 You have to disable it to use IPV6_FL_F_REFLECT flag on the 1972 flow label manager. 1973 1974 - TRUE: enabled 1975 - FALSE: disabled 1976 1977 Default: TRUE 1978 1979auto_flowlabels - INTEGER 1980 Automatically generate flow labels based on a flow hash of the 1981 packet. This allows intermediate devices, such as routers, to 1982 identify packet flows for mechanisms like Equal Cost Multipath 1983 Routing (see RFC 6438). 1984 1985 = =========================================================== 1986 0 automatic flow labels are completely disabled 1987 1 automatic flow labels are enabled by default, they can be 1988 disabled on a per socket basis using the IPV6_AUTOFLOWLABEL 1989 socket option 1990 2 automatic flow labels are allowed, they may be enabled on a 1991 per socket basis using the IPV6_AUTOFLOWLABEL socket option 1992 3 automatic flow labels are enabled and enforced, they cannot 1993 be disabled by the socket option 1994 = =========================================================== 1995 1996 Default: 1 1997 1998flowlabel_state_ranges - BOOLEAN 1999 Split the flow label number space into two ranges. 0-0x7FFFF is 2000 reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF 2001 is reserved for stateless flow labels as described in RFC6437. 2002 2003 - TRUE: enabled 2004 - FALSE: disabled 2005 2006 Default: true 2007 2008flowlabel_reflect - INTEGER 2009 Control flow label reflection. Needed for Path MTU 2010 Discovery to work with Equal Cost Multipath Routing in anycast 2011 environments. See RFC 7690 and: 2012 https://tools.ietf.org/html/draft-wang-6man-flow-label-reflection-01 2013 2014 This is a bitmask. 2015 2016 - 1: enabled for established flows 2017 2018 Note that this prevents automatic flowlabel changes, as done 2019 in "tcp: change IPv6 flow-label upon receiving spurious retransmission" 2020 and "tcp: Change txhash on every SYN and RTO retransmit" 2021 2022 - 2: enabled for TCP RESET packets (no active listener) 2023 If set, a RST packet sent in response to a SYN packet on a closed 2024 port will reflect the incoming flow label. 2025 2026 - 4: enabled for ICMPv6 echo reply messages. 2027 2028 Default: 0 2029 2030fib_multipath_hash_policy - INTEGER 2031 Controls which hash policy to use for multipath routes. 2032 2033 Default: 0 (Layer 3) 2034 2035 Possible values: 2036 2037 - 0 - Layer 3 (source and destination addresses plus flow label) 2038 - 1 - Layer 4 (standard 5-tuple) 2039 - 2 - Layer 3 or inner Layer 3 if present 2040 - 3 - Custom multipath hash. Fields used for multipath hash calculation 2041 are determined by fib_multipath_hash_fields sysctl 2042 2043fib_multipath_hash_fields - UNSIGNED INTEGER 2044 When fib_multipath_hash_policy is set to 3 (custom multipath hash), the 2045 fields used for multipath hash calculation are determined by this 2046 sysctl. 2047 2048 This value is a bitmask which enables various fields for multipath hash 2049 calculation. 2050 2051 Possible fields are: 2052 2053 ====== ============================ 2054 0x0001 Source IP address 2055 0x0002 Destination IP address 2056 0x0004 IP protocol 2057 0x0008 Flow Label 2058 0x0010 Source port 2059 0x0020 Destination port 2060 0x0040 Inner source IP address 2061 0x0080 Inner destination IP address 2062 0x0100 Inner IP protocol 2063 0x0200 Inner Flow Label 2064 0x0400 Inner source port 2065 0x0800 Inner destination port 2066 ====== ============================ 2067 2068 Default: 0x0007 (source IP, destination IP and IP protocol) 2069 2070anycast_src_echo_reply - BOOLEAN 2071 Controls the use of anycast addresses as source addresses for ICMPv6 2072 echo reply 2073 2074 - TRUE: enabled 2075 - FALSE: disabled 2076 2077 Default: FALSE 2078 2079idgen_delay - INTEGER 2080 Controls the delay in seconds after which time to retry 2081 privacy stable address generation if a DAD conflict is 2082 detected. 2083 2084 Default: 1 (as specified in RFC7217) 2085 2086idgen_retries - INTEGER 2087 Controls the number of retries to generate a stable privacy 2088 address if a DAD conflict is detected. 2089 2090 Default: 3 (as specified in RFC7217) 2091 2092mld_qrv - INTEGER 2093 Controls the MLD query robustness variable (see RFC3810 9.1). 2094 2095 Default: 2 (as specified by RFC3810 9.1) 2096 2097 Minimum: 1 (as specified by RFC6636 4.5) 2098 2099max_dst_opts_number - INTEGER 2100 Maximum number of non-padding TLVs allowed in a Destination 2101 options extension header. If this value is less than zero 2102 then unknown options are disallowed and the number of known 2103 TLVs allowed is the absolute value of this number. 2104 2105 Default: 8 2106 2107max_hbh_opts_number - INTEGER 2108 Maximum number of non-padding TLVs allowed in a Hop-by-Hop 2109 options extension header. If this value is less than zero 2110 then unknown options are disallowed and the number of known 2111 TLVs allowed is the absolute value of this number. 2112 2113 Default: 8 2114 2115max_dst_opts_length - INTEGER 2116 Maximum length allowed for a Destination options extension 2117 header. 2118 2119 Default: INT_MAX (unlimited) 2120 2121max_hbh_length - INTEGER 2122 Maximum length allowed for a Hop-by-Hop options extension 2123 header. 2124 2125 Default: INT_MAX (unlimited) 2126 2127skip_notify_on_dev_down - BOOLEAN 2128 Controls whether an RTM_DELROUTE message is generated for routes 2129 removed when a device is taken down or deleted. IPv4 does not 2130 generate this message; IPv6 does by default. Setting this sysctl 2131 to true skips the message, making IPv4 and IPv6 on par in relying 2132 on userspace caches to track link events and evict routes. 2133 2134 Default: false (generate message) 2135 2136nexthop_compat_mode - BOOLEAN 2137 New nexthop API provides a means for managing nexthops independent of 2138 prefixes. Backwards compatibility with old route format is enabled by 2139 default which means route dumps and notifications contain the new 2140 nexthop attribute but also the full, expanded nexthop definition. 2141 Further, updates or deletes of a nexthop configuration generate route 2142 notifications for each fib entry using the nexthop. Once a system 2143 understands the new API, this sysctl can be disabled to achieve full 2144 performance benefits of the new API by disabling the nexthop expansion 2145 and extraneous notifications. 2146 Default: true (backward compat mode) 2147 2148fib_notify_on_flag_change - INTEGER 2149 Whether to emit RTM_NEWROUTE notifications whenever RTM_F_OFFLOAD/ 2150 RTM_F_TRAP/RTM_F_OFFLOAD_FAILED flags are changed. 2151 2152 After installing a route to the kernel, user space receives an 2153 acknowledgment, which means the route was installed in the kernel, 2154 but not necessarily in hardware. 2155 It is also possible for a route already installed in hardware to change 2156 its action and therefore its flags. For example, a host route that is 2157 trapping packets can be "promoted" to perform decapsulation following 2158 the installation of an IPinIP/VXLAN tunnel. 2159 The notifications will indicate to user-space the state of the route. 2160 2161 Default: 0 (Do not emit notifications.) 2162 2163 Possible values: 2164 2165 - 0 - Do not emit notifications. 2166 - 1 - Emit notifications. 2167 - 2 - Emit notifications only for RTM_F_OFFLOAD_FAILED flag change. 2168 2169ioam6_id - INTEGER 2170 Define the IOAM id of this node. Uses only 24 bits out of 32 in total. 2171 2172 Min: 0 2173 Max: 0xFFFFFF 2174 2175 Default: 0xFFFFFF 2176 2177ioam6_id_wide - LONG INTEGER 2178 Define the wide IOAM id of this node. Uses only 56 bits out of 64 in 2179 total. Can be different from ioam6_id. 2180 2181 Min: 0 2182 Max: 0xFFFFFFFFFFFFFF 2183 2184 Default: 0xFFFFFFFFFFFFFF 2185 2186IPv6 Fragmentation: 2187 2188ip6frag_high_thresh - INTEGER 2189 Maximum memory used to reassemble IPv6 fragments. When 2190 ip6frag_high_thresh bytes of memory is allocated for this purpose, 2191 the fragment handler will toss packets until ip6frag_low_thresh 2192 is reached. 2193 2194ip6frag_low_thresh - INTEGER 2195 See ip6frag_high_thresh 2196 2197ip6frag_time - INTEGER 2198 Time in seconds to keep an IPv6 fragment in memory. 2199 2200``conf/default/*``: 2201 Change the interface-specific default settings. 2202 2203 These settings would be used during creating new interfaces. 2204 2205 2206``conf/all/*``: 2207 Change all the interface-specific settings. 2208 2209 [XXX: Other special features than forwarding?] 2210 2211conf/all/disable_ipv6 - BOOLEAN 2212 Changing this value is same as changing ``conf/default/disable_ipv6`` 2213 setting and also all per-interface ``disable_ipv6`` settings to the same 2214 value. 2215 2216 Reading this value does not have any particular meaning. It does not say 2217 whether IPv6 support is enabled or disabled. Returned value can be 1 2218 also in the case when some interface has ``disable_ipv6`` set to 0 and 2219 has configured IPv6 addresses. 2220 2221conf/all/forwarding - BOOLEAN 2222 Enable global IPv6 forwarding between all interfaces. 2223 2224 IPv4 and IPv6 work differently here; e.g. netfilter must be used 2225 to control which interfaces may forward packets and which not. 2226 2227 This also sets all interfaces' Host/Router setting 2228 'forwarding' to the specified value. See below for details. 2229 2230 This referred to as global forwarding. 2231 2232proxy_ndp - BOOLEAN 2233 Do proxy ndp. 2234 2235fwmark_reflect - BOOLEAN 2236 Controls the fwmark of kernel-generated IPv6 reply packets that are not 2237 associated with a socket for example, TCP RSTs or ICMPv6 echo replies). 2238 If unset, these packets have a fwmark of zero. If set, they have the 2239 fwmark of the packet they are replying to. 2240 2241 Default: 0 2242 2243``conf/interface/*``: 2244 Change special settings per interface. 2245 2246 The functional behaviour for certain settings is different 2247 depending on whether local forwarding is enabled or not. 2248 2249accept_ra - INTEGER 2250 Accept Router Advertisements; autoconfigure using them. 2251 2252 It also determines whether or not to transmit Router 2253 Solicitations. If and only if the functional setting is to 2254 accept Router Advertisements, Router Solicitations will be 2255 transmitted. 2256 2257 Possible values are: 2258 2259 == =========================================================== 2260 0 Do not accept Router Advertisements. 2261 1 Accept Router Advertisements if forwarding is disabled. 2262 2 Overrule forwarding behaviour. Accept Router Advertisements 2263 even if forwarding is enabled. 2264 == =========================================================== 2265 2266 Functional default: 2267 2268 - enabled if local forwarding is disabled. 2269 - disabled if local forwarding is enabled. 2270 2271accept_ra_defrtr - BOOLEAN 2272 Learn default router in Router Advertisement. 2273 2274 Functional default: 2275 2276 - enabled if accept_ra is enabled. 2277 - disabled if accept_ra is disabled. 2278 2279ra_defrtr_metric - UNSIGNED INTEGER 2280 Route metric for default route learned in Router Advertisement. This value 2281 will be assigned as metric for the default route learned via IPv6 Router 2282 Advertisement. Takes affect only if accept_ra_defrtr is enabled. 2283 2284 Possible values: 2285 1 to 0xFFFFFFFF 2286 2287 Default: IP6_RT_PRIO_USER i.e. 1024. 2288 2289accept_ra_from_local - BOOLEAN 2290 Accept RA with source-address that is found on local machine 2291 if the RA is otherwise proper and able to be accepted. 2292 2293 Default is to NOT accept these as it may be an un-intended 2294 network loop. 2295 2296 Functional default: 2297 2298 - enabled if accept_ra_from_local is enabled 2299 on a specific interface. 2300 - disabled if accept_ra_from_local is disabled 2301 on a specific interface. 2302 2303accept_ra_min_hop_limit - INTEGER 2304 Minimum hop limit Information in Router Advertisement. 2305 2306 Hop limit Information in Router Advertisement less than this 2307 variable shall be ignored. 2308 2309 Default: 1 2310 2311accept_ra_min_lft - INTEGER 2312 Minimum acceptable lifetime value in Router Advertisement. 2313 2314 RA sections with a lifetime less than this value shall be 2315 ignored. Zero lifetimes stay unaffected. 2316 2317 Default: 0 2318 2319accept_ra_pinfo - BOOLEAN 2320 Learn Prefix Information in Router Advertisement. 2321 2322 Functional default: 2323 2324 - enabled if accept_ra is enabled. 2325 - disabled if accept_ra is disabled. 2326 2327ra_honor_pio_life - BOOLEAN 2328 Whether to use RFC4862 Section 5.5.3e to determine the valid 2329 lifetime of an address matching a prefix sent in a Router 2330 Advertisement Prefix Information Option. 2331 2332 - If enabled, the PIO valid lifetime will always be honored. 2333 - If disabled, RFC4862 section 5.5.3e is used to determine 2334 the valid lifetime of the address. 2335 2336 Default: 0 (disabled) 2337 2338accept_ra_rt_info_min_plen - INTEGER 2339 Minimum prefix length of Route Information in RA. 2340 2341 Route Information w/ prefix smaller than this variable shall 2342 be ignored. 2343 2344 Functional default: 2345 2346 * 0 if accept_ra_rtr_pref is enabled. 2347 * -1 if accept_ra_rtr_pref is disabled. 2348 2349accept_ra_rt_info_max_plen - INTEGER 2350 Maximum prefix length of Route Information in RA. 2351 2352 Route Information w/ prefix larger than this variable shall 2353 be ignored. 2354 2355 Functional default: 2356 2357 * 0 if accept_ra_rtr_pref is enabled. 2358 * -1 if accept_ra_rtr_pref is disabled. 2359 2360accept_ra_rtr_pref - BOOLEAN 2361 Accept Router Preference in RA. 2362 2363 Functional default: 2364 2365 - enabled if accept_ra is enabled. 2366 - disabled if accept_ra is disabled. 2367 2368accept_ra_mtu - BOOLEAN 2369 Apply the MTU value specified in RA option 5 (RFC4861). If 2370 disabled, the MTU specified in the RA will be ignored. 2371 2372 Functional default: 2373 2374 - enabled if accept_ra is enabled. 2375 - disabled if accept_ra is disabled. 2376 2377accept_redirects - BOOLEAN 2378 Accept Redirects. 2379 2380 Functional default: 2381 2382 - enabled if local forwarding is disabled. 2383 - disabled if local forwarding is enabled. 2384 2385accept_source_route - INTEGER 2386 Accept source routing (routing extension header). 2387 2388 - >= 0: Accept only routing header type 2. 2389 - < 0: Do not accept routing header. 2390 2391 Default: 0 2392 2393autoconf - BOOLEAN 2394 Autoconfigure addresses using Prefix Information in Router 2395 Advertisements. 2396 2397 Functional default: 2398 2399 - enabled if accept_ra_pinfo is enabled. 2400 - disabled if accept_ra_pinfo is disabled. 2401 2402dad_transmits - INTEGER 2403 The amount of Duplicate Address Detection probes to send. 2404 2405 Default: 1 2406 2407forwarding - INTEGER 2408 Configure interface-specific Host/Router behaviour. 2409 2410 .. note:: 2411 2412 It is recommended to have the same setting on all 2413 interfaces; mixed router/host scenarios are rather uncommon. 2414 2415 Possible values are: 2416 2417 - 0 Forwarding disabled 2418 - 1 Forwarding enabled 2419 2420 **FALSE (0)**: 2421 2422 By default, Host behaviour is assumed. This means: 2423 2424 1. IsRouter flag is not set in Neighbour Advertisements. 2425 2. If accept_ra is TRUE (default), transmit Router 2426 Solicitations. 2427 3. If accept_ra is TRUE (default), accept Router 2428 Advertisements (and do autoconfiguration). 2429 4. If accept_redirects is TRUE (default), accept Redirects. 2430 2431 **TRUE (1)**: 2432 2433 If local forwarding is enabled, Router behaviour is assumed. 2434 This means exactly the reverse from the above: 2435 2436 1. IsRouter flag is set in Neighbour Advertisements. 2437 2. Router Solicitations are not sent unless accept_ra is 2. 2438 3. Router Advertisements are ignored unless accept_ra is 2. 2439 4. Redirects are ignored. 2440 2441 Default: 0 (disabled) if global forwarding is disabled (default), 2442 otherwise 1 (enabled). 2443 2444hop_limit - INTEGER 2445 Default Hop Limit to set. 2446 2447 Default: 64 2448 2449mtu - INTEGER 2450 Default Maximum Transfer Unit 2451 2452 Default: 1280 (IPv6 required minimum) 2453 2454ip_nonlocal_bind - BOOLEAN 2455 If set, allows processes to bind() to non-local IPv6 addresses, 2456 which can be quite useful - but may break some applications. 2457 2458 Default: 0 2459 2460router_probe_interval - INTEGER 2461 Minimum interval (in seconds) between Router Probing described 2462 in RFC4191. 2463 2464 Default: 60 2465 2466router_solicitation_delay - INTEGER 2467 Number of seconds to wait after interface is brought up 2468 before sending Router Solicitations. 2469 2470 Default: 1 2471 2472router_solicitation_interval - INTEGER 2473 Number of seconds to wait between Router Solicitations. 2474 2475 Default: 4 2476 2477router_solicitations - INTEGER 2478 Number of Router Solicitations to send until assuming no 2479 routers are present. 2480 2481 Default: 3 2482 2483use_oif_addrs_only - BOOLEAN 2484 When enabled, the candidate source addresses for destinations 2485 routed via this interface are restricted to the set of addresses 2486 configured on this interface (vis. RFC 6724, section 4). 2487 2488 Default: false 2489 2490use_tempaddr - INTEGER 2491 Preference for Privacy Extensions (RFC3041). 2492 2493 * <= 0 : disable Privacy Extensions 2494 * == 1 : enable Privacy Extensions, but prefer public 2495 addresses over temporary addresses. 2496 * > 1 : enable Privacy Extensions and prefer temporary 2497 addresses over public addresses. 2498 2499 Default: 2500 2501 * 0 (for most devices) 2502 * -1 (for point-to-point devices and loopback devices) 2503 2504temp_valid_lft - INTEGER 2505 valid lifetime (in seconds) for temporary addresses. If less than the 2506 minimum required lifetime (typically 5 seconds), temporary addresses 2507 will not be created. 2508 2509 Default: 172800 (2 days) 2510 2511temp_prefered_lft - INTEGER 2512 Preferred lifetime (in seconds) for temporary addresses. If 2513 temp_prefered_lft is less than the minimum required lifetime (typically 2514 5 seconds), the preferred lifetime is the minimum required. If 2515 temp_prefered_lft is greater than temp_valid_lft, the preferred lifetime 2516 is temp_valid_lft. 2517 2518 Default: 86400 (1 day) 2519 2520keep_addr_on_down - INTEGER 2521 Keep all IPv6 addresses on an interface down event. If set static 2522 global addresses with no expiration time are not flushed. 2523 2524 * >0 : enabled 2525 * 0 : system default 2526 * <0 : disabled 2527 2528 Default: 0 (addresses are removed) 2529 2530max_desync_factor - INTEGER 2531 Maximum value for DESYNC_FACTOR, which is a random value 2532 that ensures that clients don't synchronize with each 2533 other and generate new addresses at exactly the same time. 2534 value is in seconds. 2535 2536 Default: 600 2537 2538regen_max_retry - INTEGER 2539 Number of attempts before give up attempting to generate 2540 valid temporary addresses. 2541 2542 Default: 5 2543 2544max_addresses - INTEGER 2545 Maximum number of autoconfigured addresses per interface. Setting 2546 to zero disables the limitation. It is not recommended to set this 2547 value too large (or to zero) because it would be an easy way to 2548 crash the kernel by allowing too many addresses to be created. 2549 2550 Default: 16 2551 2552disable_ipv6 - BOOLEAN 2553 Disable IPv6 operation. If accept_dad is set to 2, this value 2554 will be dynamically set to TRUE if DAD fails for the link-local 2555 address. 2556 2557 Default: FALSE (enable IPv6 operation) 2558 2559 When this value is changed from 1 to 0 (IPv6 is being enabled), 2560 it will dynamically create a link-local address on the given 2561 interface and start Duplicate Address Detection, if necessary. 2562 2563 When this value is changed from 0 to 1 (IPv6 is being disabled), 2564 it will dynamically delete all addresses and routes on the given 2565 interface. From now on it will not possible to add addresses/routes 2566 to the selected interface. 2567 2568accept_dad - INTEGER 2569 Whether to accept DAD (Duplicate Address Detection). 2570 2571 == ============================================================== 2572 0 Disable DAD 2573 1 Enable DAD (default) 2574 2 Enable DAD, and disable IPv6 operation if MAC-based duplicate 2575 link-local address has been found. 2576 == ============================================================== 2577 2578 DAD operation and mode on a given interface will be selected according 2579 to the maximum value of conf/{all,interface}/accept_dad. 2580 2581force_tllao - BOOLEAN 2582 Enable sending the target link-layer address option even when 2583 responding to a unicast neighbor solicitation. 2584 2585 Default: FALSE 2586 2587 Quoting from RFC 2461, section 4.4, Target link-layer address: 2588 2589 "The option MUST be included for multicast solicitations in order to 2590 avoid infinite Neighbor Solicitation "recursion" when the peer node 2591 does not have a cache entry to return a Neighbor Advertisements 2592 message. When responding to unicast solicitations, the option can be 2593 omitted since the sender of the solicitation has the correct link- 2594 layer address; otherwise it would not have be able to send the unicast 2595 solicitation in the first place. However, including the link-layer 2596 address in this case adds little overhead and eliminates a potential 2597 race condition where the sender deletes the cached link-layer address 2598 prior to receiving a response to a previous solicitation." 2599 2600ndisc_notify - BOOLEAN 2601 Define mode for notification of address and device changes. 2602 2603 * 0 - (default): do nothing 2604 * 1 - Generate unsolicited neighbour advertisements when device is brought 2605 up or hardware address changes. 2606 2607ndisc_tclass - INTEGER 2608 The IPv6 Traffic Class to use by default when sending IPv6 Neighbor 2609 Discovery (Router Solicitation, Router Advertisement, Neighbor 2610 Solicitation, Neighbor Advertisement, Redirect) messages. 2611 These 8 bits can be interpreted as 6 high order bits holding the DSCP 2612 value and 2 low order bits representing ECN (which you probably want 2613 to leave cleared). 2614 2615 * 0 - (default) 2616 2617ndisc_evict_nocarrier - BOOLEAN 2618 Clears the neighbor discovery table on NOCARRIER events. This option is 2619 important for wireless devices where the neighbor discovery cache should 2620 not be cleared when roaming between access points on the same network. 2621 In most cases this should remain as the default (1). 2622 2623 - 1 - (default): Clear neighbor discover cache on NOCARRIER events. 2624 - 0 - Do not clear neighbor discovery cache on NOCARRIER events. 2625 2626mldv1_unsolicited_report_interval - INTEGER 2627 The interval in milliseconds in which the next unsolicited 2628 MLDv1 report retransmit will take place. 2629 2630 Default: 10000 (10 seconds) 2631 2632mldv2_unsolicited_report_interval - INTEGER 2633 The interval in milliseconds in which the next unsolicited 2634 MLDv2 report retransmit will take place. 2635 2636 Default: 1000 (1 second) 2637 2638force_mld_version - INTEGER 2639 * 0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed 2640 * 1 - Enforce to use MLD version 1 2641 * 2 - Enforce to use MLD version 2 2642 2643suppress_frag_ndisc - INTEGER 2644 Control RFC 6980 (Security Implications of IPv6 Fragmentation 2645 with IPv6 Neighbor Discovery) behavior: 2646 2647 * 1 - (default) discard fragmented neighbor discovery packets 2648 * 0 - allow fragmented neighbor discovery packets 2649 2650optimistic_dad - BOOLEAN 2651 Whether to perform Optimistic Duplicate Address Detection (RFC 4429). 2652 2653 * 0: disabled (default) 2654 * 1: enabled 2655 2656 Optimistic Duplicate Address Detection for the interface will be enabled 2657 if at least one of conf/{all,interface}/optimistic_dad is set to 1, 2658 it will be disabled otherwise. 2659 2660use_optimistic - BOOLEAN 2661 If enabled, do not classify optimistic addresses as deprecated during 2662 source address selection. Preferred addresses will still be chosen 2663 before optimistic addresses, subject to other ranking in the source 2664 address selection algorithm. 2665 2666 * 0: disabled (default) 2667 * 1: enabled 2668 2669 This will be enabled if at least one of 2670 conf/{all,interface}/use_optimistic is set to 1, disabled otherwise. 2671 2672stable_secret - IPv6 address 2673 This IPv6 address will be used as a secret to generate IPv6 2674 addresses for link-local addresses and autoconfigured 2675 ones. All addresses generated after setting this secret will 2676 be stable privacy ones by default. This can be changed via the 2677 addrgenmode ip-link. conf/default/stable_secret is used as the 2678 secret for the namespace, the interface specific ones can 2679 overwrite that. Writes to conf/all/stable_secret are refused. 2680 2681 It is recommended to generate this secret during installation 2682 of a system and keep it stable after that. 2683 2684 By default the stable secret is unset. 2685 2686addr_gen_mode - INTEGER 2687 Defines how link-local and autoconf addresses are generated. 2688 2689 = ================================================================= 2690 0 generate address based on EUI64 (default) 2691 1 do no generate a link-local address, use EUI64 for addresses 2692 generated from autoconf 2693 2 generate stable privacy addresses, using the secret from 2694 stable_secret (RFC7217) 2695 3 generate stable privacy addresses, using a random secret if unset 2696 = ================================================================= 2697 2698drop_unicast_in_l2_multicast - BOOLEAN 2699 Drop any unicast IPv6 packets that are received in link-layer 2700 multicast (or broadcast) frames. 2701 2702 By default this is turned off. 2703 2704drop_unsolicited_na - BOOLEAN 2705 Drop all unsolicited neighbor advertisements, for example if there's 2706 a known good NA proxy on the network and such frames need not be used 2707 (or in the case of 802.11, must not be used to prevent attacks.) 2708 2709 By default this is turned off. 2710 2711accept_untracked_na - INTEGER 2712 Define behavior for accepting neighbor advertisements from devices that 2713 are absent in the neighbor cache: 2714 2715 - 0 - (default) Do not accept unsolicited and untracked neighbor 2716 advertisements. 2717 2718 - 1 - Add a new neighbor cache entry in STALE state for routers on 2719 receiving a neighbor advertisement (either solicited or unsolicited) 2720 with target link-layer address option specified if no neighbor entry 2721 is already present for the advertised IPv6 address. Without this knob, 2722 NAs received for untracked addresses (absent in neighbor cache) are 2723 silently ignored. 2724 2725 This is as per router-side behavior documented in RFC9131. 2726 2727 This has lower precedence than drop_unsolicited_na. 2728 2729 This will optimize the return path for the initial off-link 2730 communication that is initiated by a directly connected host, by 2731 ensuring that the first-hop router which turns on this setting doesn't 2732 have to buffer the initial return packets to do neighbor-solicitation. 2733 The prerequisite is that the host is configured to send unsolicited 2734 neighbor advertisements on interface bringup. This setting should be 2735 used in conjunction with the ndisc_notify setting on the host to 2736 satisfy this prerequisite. 2737 2738 - 2 - Extend option (1) to add a new neighbor cache entry only if the 2739 source IP address is in the same subnet as an address configured on 2740 the interface that received the neighbor advertisement. 2741 2742enhanced_dad - BOOLEAN 2743 Include a nonce option in the IPv6 neighbor solicitation messages used for 2744 duplicate address detection per RFC7527. A received DAD NS will only signal 2745 a duplicate address if the nonce is different. This avoids any false 2746 detection of duplicates due to loopback of the NS messages that we send. 2747 The nonce option will be sent on an interface unless both of 2748 conf/{all,interface}/enhanced_dad are set to FALSE. 2749 2750 Default: TRUE 2751 2752``icmp/*``: 2753=========== 2754 2755ratelimit - INTEGER 2756 Limit the maximal rates for sending ICMPv6 messages. 2757 2758 0 to disable any limiting, 2759 otherwise the minimal space between responses in milliseconds. 2760 2761 Default: 1000 2762 2763ratemask - list of comma separated ranges 2764 For ICMPv6 message types matching the ranges in the ratemask, limit 2765 the sending of the message according to ratelimit parameter. 2766 2767 The format used for both input and output is a comma separated 2768 list of ranges (e.g. "0-127,129" for ICMPv6 message type 0 to 127 and 2769 129). Writing to the file will clear all previous ranges of ICMPv6 2770 message types and update the current list with the input. 2771 2772 Refer to: https://www.iana.org/assignments/icmpv6-parameters/icmpv6-parameters.xhtml 2773 for numerical values of ICMPv6 message types, e.g. echo request is 128 2774 and echo reply is 129. 2775 2776 Default: 0-1,3-127 (rate limit ICMPv6 errors except Packet Too Big) 2777 2778echo_ignore_all - BOOLEAN 2779 If set non-zero, then the kernel will ignore all ICMP ECHO 2780 requests sent to it over the IPv6 protocol. 2781 2782 Default: 0 2783 2784echo_ignore_multicast - BOOLEAN 2785 If set non-zero, then the kernel will ignore all ICMP ECHO 2786 requests sent to it over the IPv6 protocol via multicast. 2787 2788 Default: 0 2789 2790echo_ignore_anycast - BOOLEAN 2791 If set non-zero, then the kernel will ignore all ICMP ECHO 2792 requests sent to it over the IPv6 protocol destined to anycast address. 2793 2794 Default: 0 2795 2796error_anycast_as_unicast - BOOLEAN 2797 If set to 1, then the kernel will respond with ICMP Errors 2798 resulting from requests sent to it over the IPv6 protocol destined 2799 to anycast address essentially treating anycast as unicast. 2800 2801 Default: 0 2802 2803xfrm6_gc_thresh - INTEGER 2804 (Obsolete since linux-4.14) 2805 The threshold at which we will start garbage collecting for IPv6 2806 destination cache entries. At twice this value the system will 2807 refuse new allocations. 2808 2809 2810IPv6 Update by: 2811Pekka Savola <pekkas@netcore.fi> 2812YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org> 2813 2814 2815/proc/sys/net/bridge/* Variables: 2816================================= 2817 2818bridge-nf-call-arptables - BOOLEAN 2819 - 1 : pass bridged ARP traffic to arptables' FORWARD chain. 2820 - 0 : disable this. 2821 2822 Default: 1 2823 2824bridge-nf-call-iptables - BOOLEAN 2825 - 1 : pass bridged IPv4 traffic to iptables' chains. 2826 - 0 : disable this. 2827 2828 Default: 1 2829 2830bridge-nf-call-ip6tables - BOOLEAN 2831 - 1 : pass bridged IPv6 traffic to ip6tables' chains. 2832 - 0 : disable this. 2833 2834 Default: 1 2835 2836bridge-nf-filter-vlan-tagged - BOOLEAN 2837 - 1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables. 2838 - 0 : disable this. 2839 2840 Default: 0 2841 2842bridge-nf-filter-pppoe-tagged - BOOLEAN 2843 - 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables. 2844 - 0 : disable this. 2845 2846 Default: 0 2847 2848bridge-nf-pass-vlan-input-dev - BOOLEAN 2849 - 1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan 2850 interface on the bridge and set the netfilter input device to the 2851 vlan. This allows use of e.g. "iptables -i br0.1" and makes the 2852 REDIRECT target work with vlan-on-top-of-bridge interfaces. When no 2853 matching vlan interface is found, or this switch is off, the input 2854 device is set to the bridge interface. 2855 2856 - 0: disable bridge netfilter vlan interface lookup. 2857 2858 Default: 0 2859 2860``proc/sys/net/sctp/*`` Variables: 2861================================== 2862 2863addip_enable - BOOLEAN 2864 Enable or disable extension of Dynamic Address Reconfiguration 2865 (ADD-IP) functionality specified in RFC5061. This extension provides 2866 the ability to dynamically add and remove new addresses for the SCTP 2867 associations. 2868 2869 1: Enable extension. 2870 2871 0: Disable extension. 2872 2873 Default: 0 2874 2875pf_enable - INTEGER 2876 Enable or disable pf (pf is short for potentially failed) state. A value 2877 of pf_retrans > path_max_retrans also disables pf state. That is, one of 2878 both pf_enable and pf_retrans > path_max_retrans can disable pf state. 2879 Since pf_retrans and path_max_retrans can be changed by userspace 2880 application, sometimes user expects to disable pf state by the value of 2881 pf_retrans > path_max_retrans, but occasionally the value of pf_retrans 2882 or path_max_retrans is changed by the user application, this pf state is 2883 enabled. As such, it is necessary to add this to dynamically enable 2884 and disable pf state. See: 2885 https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover for 2886 details. 2887 2888 1: Enable pf. 2889 2890 0: Disable pf. 2891 2892 Default: 1 2893 2894pf_expose - INTEGER 2895 Unset or enable/disable pf (pf is short for potentially failed) state 2896 exposure. Applications can control the exposure of the PF path state 2897 in the SCTP_PEER_ADDR_CHANGE event and the SCTP_GET_PEER_ADDR_INFO 2898 sockopt. When it's unset, no SCTP_PEER_ADDR_CHANGE event with 2899 SCTP_ADDR_PF state will be sent and a SCTP_PF-state transport info 2900 can be got via SCTP_GET_PEER_ADDR_INFO sockopt; When it's enabled, 2901 a SCTP_PEER_ADDR_CHANGE event will be sent for a transport becoming 2902 SCTP_PF state and a SCTP_PF-state transport info can be got via 2903 SCTP_GET_PEER_ADDR_INFO sockopt; When it's disabled, no 2904 SCTP_PEER_ADDR_CHANGE event will be sent and it returns -EACCES when 2905 trying to get a SCTP_PF-state transport info via SCTP_GET_PEER_ADDR_INFO 2906 sockopt. 2907 2908 0: Unset pf state exposure, Compatible with old applications. 2909 2910 1: Disable pf state exposure. 2911 2912 2: Enable pf state exposure. 2913 2914 Default: 0 2915 2916addip_noauth_enable - BOOLEAN 2917 Dynamic Address Reconfiguration (ADD-IP) requires the use of 2918 authentication to protect the operations of adding or removing new 2919 addresses. This requirement is mandated so that unauthorized hosts 2920 would not be able to hijack associations. However, older 2921 implementations may not have implemented this requirement while 2922 allowing the ADD-IP extension. For reasons of interoperability, 2923 we provide this variable to control the enforcement of the 2924 authentication requirement. 2925 2926 == =============================================================== 2927 1 Allow ADD-IP extension to be used without authentication. This 2928 should only be set in a closed environment for interoperability 2929 with older implementations. 2930 2931 0 Enforce the authentication requirement 2932 == =============================================================== 2933 2934 Default: 0 2935 2936auth_enable - BOOLEAN 2937 Enable or disable Authenticated Chunks extension. This extension 2938 provides the ability to send and receive authenticated chunks and is 2939 required for secure operation of Dynamic Address Reconfiguration 2940 (ADD-IP) extension. 2941 2942 - 1: Enable this extension. 2943 - 0: Disable this extension. 2944 2945 Default: 0 2946 2947prsctp_enable - BOOLEAN 2948 Enable or disable the Partial Reliability extension (RFC3758) which 2949 is used to notify peers that a given DATA should no longer be expected. 2950 2951 - 1: Enable extension 2952 - 0: Disable 2953 2954 Default: 1 2955 2956max_burst - INTEGER 2957 The limit of the number of new packets that can be initially sent. It 2958 controls how bursty the generated traffic can be. 2959 2960 Default: 4 2961 2962association_max_retrans - INTEGER 2963 Set the maximum number for retransmissions that an association can 2964 attempt deciding that the remote end is unreachable. If this value 2965 is exceeded, the association is terminated. 2966 2967 Default: 10 2968 2969max_init_retransmits - INTEGER 2970 The maximum number of retransmissions of INIT and COOKIE-ECHO chunks 2971 that an association will attempt before declaring the destination 2972 unreachable and terminating. 2973 2974 Default: 8 2975 2976path_max_retrans - INTEGER 2977 The maximum number of retransmissions that will be attempted on a given 2978 path. Once this threshold is exceeded, the path is considered 2979 unreachable, and new traffic will use a different path when the 2980 association is multihomed. 2981 2982 Default: 5 2983 2984pf_retrans - INTEGER 2985 The number of retransmissions that will be attempted on a given path 2986 before traffic is redirected to an alternate transport (should one 2987 exist). Note this is distinct from path_max_retrans, as a path that 2988 passes the pf_retrans threshold can still be used. Its only 2989 deprioritized when a transmission path is selected by the stack. This 2990 setting is primarily used to enable fast failover mechanisms without 2991 having to reduce path_max_retrans to a very low value. See: 2992 http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt 2993 for details. Note also that a value of pf_retrans > path_max_retrans 2994 disables this feature. Since both pf_retrans and path_max_retrans can 2995 be changed by userspace application, a variable pf_enable is used to 2996 disable pf state. 2997 2998 Default: 0 2999 3000ps_retrans - INTEGER 3001 Primary.Switchover.Max.Retrans (PSMR), it's a tunable parameter coming 3002 from section-5 "Primary Path Switchover" in rfc7829. The primary path 3003 will be changed to another active path when the path error counter on 3004 the old primary path exceeds PSMR, so that "the SCTP sender is allowed 3005 to continue data transmission on a new working path even when the old 3006 primary destination address becomes active again". Note this feature 3007 is disabled by initializing 'ps_retrans' per netns as 0xffff by default, 3008 and its value can't be less than 'pf_retrans' when changing by sysctl. 3009 3010 Default: 0xffff 3011 3012rto_initial - INTEGER 3013 The initial round trip timeout value in milliseconds that will be used 3014 in calculating round trip times. This is the initial time interval 3015 for retransmissions. 3016 3017 Default: 3000 3018 3019rto_max - INTEGER 3020 The maximum value (in milliseconds) of the round trip timeout. This 3021 is the largest time interval that can elapse between retransmissions. 3022 3023 Default: 60000 3024 3025rto_min - INTEGER 3026 The minimum value (in milliseconds) of the round trip timeout. This 3027 is the smallest time interval the can elapse between retransmissions. 3028 3029 Default: 1000 3030 3031hb_interval - INTEGER 3032 The interval (in milliseconds) between HEARTBEAT chunks. These chunks 3033 are sent at the specified interval on idle paths to probe the state of 3034 a given path between 2 associations. 3035 3036 Default: 30000 3037 3038sack_timeout - INTEGER 3039 The amount of time (in milliseconds) that the implementation will wait 3040 to send a SACK. 3041 3042 Default: 200 3043 3044valid_cookie_life - INTEGER 3045 The default lifetime of the SCTP cookie (in milliseconds). The cookie 3046 is used during association establishment. 3047 3048 Default: 60000 3049 3050cookie_preserve_enable - BOOLEAN 3051 Enable or disable the ability to extend the lifetime of the SCTP cookie 3052 that is used during the establishment phase of SCTP association 3053 3054 - 1: Enable cookie lifetime extension. 3055 - 0: Disable 3056 3057 Default: 1 3058 3059cookie_hmac_alg - STRING 3060 Select the hmac algorithm used when generating the cookie value sent by 3061 a listening sctp socket to a connecting client in the INIT-ACK chunk. 3062 Valid values are: 3063 3064 * md5 3065 * sha1 3066 * none 3067 3068 Ability to assign md5 or sha1 as the selected alg is predicated on the 3069 configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and 3070 CONFIG_CRYPTO_SHA1). 3071 3072 Default: Dependent on configuration. MD5 if available, else SHA1 if 3073 available, else none. 3074 3075rcvbuf_policy - INTEGER 3076 Determines if the receive buffer is attributed to the socket or to 3077 association. SCTP supports the capability to create multiple 3078 associations on a single socket. When using this capability, it is 3079 possible that a single stalled association that's buffering a lot 3080 of data may block other associations from delivering their data by 3081 consuming all of the receive buffer space. To work around this, 3082 the rcvbuf_policy could be set to attribute the receiver buffer space 3083 to each association instead of the socket. This prevents the described 3084 blocking. 3085 3086 - 1: rcvbuf space is per association 3087 - 0: rcvbuf space is per socket 3088 3089 Default: 0 3090 3091sndbuf_policy - INTEGER 3092 Similar to rcvbuf_policy above, this applies to send buffer space. 3093 3094 - 1: Send buffer is tracked per association 3095 - 0: Send buffer is tracked per socket. 3096 3097 Default: 0 3098 3099sctp_mem - vector of 3 INTEGERs: min, pressure, max 3100 Number of pages allowed for queueing by all SCTP sockets. 3101 3102 min: Below this number of pages SCTP is not bothered about its 3103 memory appetite. When amount of memory allocated by SCTP exceeds 3104 this number, SCTP starts to moderate memory usage. 3105 3106 pressure: This value was introduced to follow format of tcp_mem. 3107 3108 max: Number of pages allowed for queueing by all SCTP sockets. 3109 3110 Default is calculated at boot time from amount of available memory. 3111 3112sctp_rmem - vector of 3 INTEGERs: min, default, max 3113 Only the first value ("min") is used, "default" and "max" are 3114 ignored. 3115 3116 min: Minimal size of receive buffer used by SCTP socket. 3117 It is guaranteed to each SCTP socket (but not association) even 3118 under moderate memory pressure. 3119 3120 Default: 4K 3121 3122sctp_wmem - vector of 3 INTEGERs: min, default, max 3123 Only the first value ("min") is used, "default" and "max" are 3124 ignored. 3125 3126 min: Minimum size of send buffer that can be used by SCTP sockets. 3127 It is guaranteed to each SCTP socket (but not association) even 3128 under moderate memory pressure. 3129 3130 Default: 4K 3131 3132addr_scope_policy - INTEGER 3133 Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00 3134 3135 - 0 - Disable IPv4 address scoping 3136 - 1 - Enable IPv4 address scoping 3137 - 2 - Follow draft but allow IPv4 private addresses 3138 - 3 - Follow draft but allow IPv4 link local addresses 3139 3140 Default: 1 3141 3142udp_port - INTEGER 3143 The listening port for the local UDP tunneling sock. Normally it's 3144 using the IANA-assigned UDP port number 9899 (sctp-tunneling). 3145 3146 This UDP sock is used for processing the incoming UDP-encapsulated 3147 SCTP packets (from RFC6951), and shared by all applications in the 3148 same net namespace. This UDP sock will be closed when the value is 3149 set to 0. 3150 3151 The value will also be used to set the src port of the UDP header 3152 for the outgoing UDP-encapsulated SCTP packets. For the dest port, 3153 please refer to 'encap_port' below. 3154 3155 Default: 0 3156 3157encap_port - INTEGER 3158 The default remote UDP encapsulation port. 3159 3160 This value is used to set the dest port of the UDP header for the 3161 outgoing UDP-encapsulated SCTP packets by default. Users can also 3162 change the value for each sock/asoc/transport by using setsockopt. 3163 For further information, please refer to RFC6951. 3164 3165 Note that when connecting to a remote server, the client should set 3166 this to the port that the UDP tunneling sock on the peer server is 3167 listening to and the local UDP tunneling sock on the client also 3168 must be started. On the server, it would get the encap_port from 3169 the incoming packet's source port. 3170 3171 Default: 0 3172 3173plpmtud_probe_interval - INTEGER 3174 The time interval (in milliseconds) for the PLPMTUD probe timer, 3175 which is configured to expire after this period to receive an 3176 acknowledgment to a probe packet. This is also the time interval 3177 between the probes for the current pmtu when the probe search 3178 is done. 3179 3180 PLPMTUD will be disabled when 0 is set, and other values for it 3181 must be >= 5000. 3182 3183 Default: 0 3184 3185reconf_enable - BOOLEAN 3186 Enable or disable extension of Stream Reconfiguration functionality 3187 specified in RFC6525. This extension provides the ability to "reset" 3188 a stream, and it includes the Parameters of "Outgoing/Incoming SSN 3189 Reset", "SSN/TSN Reset" and "Add Outgoing/Incoming Streams". 3190 3191 - 1: Enable extension. 3192 - 0: Disable extension. 3193 3194 Default: 0 3195 3196intl_enable - BOOLEAN 3197 Enable or disable extension of User Message Interleaving functionality 3198 specified in RFC8260. This extension allows the interleaving of user 3199 messages sent on different streams. With this feature enabled, I-DATA 3200 chunk will replace DATA chunk to carry user messages if also supported 3201 by the peer. Note that to use this feature, one needs to set this option 3202 to 1 and also needs to set socket options SCTP_FRAGMENT_INTERLEAVE to 2 3203 and SCTP_INTERLEAVING_SUPPORTED to 1. 3204 3205 - 1: Enable extension. 3206 - 0: Disable extension. 3207 3208 Default: 0 3209 3210ecn_enable - BOOLEAN 3211 Control use of Explicit Congestion Notification (ECN) by SCTP. 3212 Like in TCP, ECN is used only when both ends of the SCTP connection 3213 indicate support for it. This feature is useful in avoiding losses 3214 due to congestion by allowing supporting routers to signal congestion 3215 before having to drop packets. 3216 3217 1: Enable ecn. 3218 0: Disable ecn. 3219 3220 Default: 1 3221 3222l3mdev_accept - BOOLEAN 3223 Enabling this option allows a "global" bound socket to work 3224 across L3 master domains (e.g., VRFs) with packets capable of 3225 being received regardless of the L3 domain in which they 3226 originated. Only valid when the kernel was compiled with 3227 CONFIG_NET_L3_MASTER_DEV. 3228 3229 Default: 1 (enabled) 3230 3231 3232``/proc/sys/net/core/*`` 3233======================== 3234 3235 Please see: Documentation/admin-guide/sysctl/net.rst for descriptions of these entries. 3236 3237 3238``/proc/sys/net/unix/*`` 3239======================== 3240 3241max_dgram_qlen - INTEGER 3242 The maximum length of dgram socket receive queue 3243 3244 Default: 10 3245 3246