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