Documentation/networking/ip-sysctl.txt

   1 /proc/sys/net/ipv4/* Variables:
   2
   3 ip_forward - BOOLEAN
   4         0 - disabled (default)
   5         not 0 - enabled
   6
   7         Forward Packets between interfaces.
   8
   9         This variable is special, its change resets all configuration
  10         parameters to their default state (RFC1122 for hosts, RFC1812
  11         for routers)
  12
  13 ip_default_ttl - INTEGER
  14         default 64
  15
  16 ip_no_pmtu_disc - BOOLEAN
  17         Disable Path MTU Discovery.
  18         default FALSE
  19
  20 min_pmtu - INTEGER
  21         default 562 - minimum discovered Path MTU
  22
  23 mtu_expires - INTEGER
  24         Time, in seconds, that cached PMTU information is kept.
  25
  26 min_adv_mss - INTEGER
  27         The advertised MSS depends on the first hop route MTU, but will
  28         never be lower than this setting.
  29
  30 IP Fragmentation:
  31
  32 ipfrag_high_thresh - INTEGER
  33         Maximum memory used to reassemble IP fragments. When
  34         ipfrag_high_thresh bytes of memory is allocated for this purpose,
  35         the fragment handler will toss packets until ipfrag_low_thresh
  36         is reached.
  37
  38 ipfrag_low_thresh - INTEGER
  39         See ipfrag_high_thresh
  40
  41 ipfrag_time - INTEGER
  42         Time in seconds to keep an IP fragment in memory.
  43
  44 ipfrag_secret_interval - INTEGER
  45         Regeneration interval (in seconds) of the hash secret (or lifetime
  46         for the hash secret) for IP fragments.
  47         Default: 600
  48
  49 ipfrag_max_dist - INTEGER
  50         ipfrag_max_dist is a non-negative integer value which defines the
  51         maximum "disorder" which is allowed among fragments which share a
  52         common IP source address. Note that reordering of packets is
  53         not unusual, but if a large number of fragments arrive from a source
  54         IP address while a particular fragment queue remains incomplete, it
  55         probably indicates that one or more fragments belonging to that queue
  56         have been lost. When ipfrag_max_dist is positive, an additional check
  57         is done on fragments before they are added to a reassembly queue - if
  58         ipfrag_max_dist (or more) fragments have arrived from a particular IP
  59         address between additions to any IP fragment queue using that source
  60         address, it's presumed that one or more fragments in the queue are
  61         lost. The existing fragment queue will be dropped, and a new one
  62         started. An ipfrag_max_dist value of zero disables this check.
  63
  64         Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
  65         result in unnecessarily dropping fragment queues when normal
  66         reordering of packets occurs, which could lead to poor application
  67         performance. Using a very large value, e.g. 50000, increases the
  68         likelihood of incorrectly reassembling IP fragments that originate
  69         from different IP datagrams, which could result in data corruption.
  70         Default: 64
  71
  72 INET peer storage:
  73
  74 inet_peer_threshold - INTEGER
  75         The approximate size of the storage.  Starting from this threshold
  76         entries will be thrown aggressively.  This threshold also determines
  77         entries' time-to-live and time intervals between garbage collection
  78         passes.  More entries, less time-to-live, less GC interval.
  79
  80 inet_peer_minttl - INTEGER
  81         Minimum time-to-live of entries.  Should be enough to cover fragment
  82         time-to-live on the reassembling side.  This minimum time-to-live  is
  83         guaranteed if the pool size is less than inet_peer_threshold.
  84         Measured in jiffies(1).
  85
  86 inet_peer_maxttl - INTEGER
  87         Maximum time-to-live of entries.  Unused entries will expire after
  88         this period of time if there is no memory pressure on the pool (i.e.
  89         when the number of entries in the pool is very small).
  90         Measured in jiffies(1).
  91
  92 inet_peer_gc_mintime - INTEGER
  93         Minimum interval between garbage collection passes.  This interval is
  94         in effect under high memory pressure on the pool.
  95         Measured in jiffies(1).
  96
  97 inet_peer_gc_maxtime - INTEGER
  98         Minimum interval between garbage collection passes.  This interval is
  99         in effect under low (or absent) memory pressure on the pool.
 100         Measured in jiffies(1).
 101
 102 TCP variables:
 103
 104 tcp_abc - INTEGER
 105         Controls Appropriate Byte Count defined in RFC3465. If set to
 106         0 then does congestion avoid once per ack. 1 is conservative
 107         value, and 2 is more agressive.
 108
 109 tcp_syn_retries - INTEGER
 110         Number of times initial SYNs for an active TCP connection attempt
 111         will be retransmitted. Should not be higher than 255. Default value
 112         is 5, which corresponds to ~180seconds.
 113
 114 tcp_synack_retries - INTEGER
 115         Number of times SYNACKs for a passive TCP connection attempt will
 116         be retransmitted. Should not be higher than 255. Default value
 117         is 5, which corresponds to ~180seconds.
 118
 119 tcp_keepalive_time - INTEGER
 120         How often TCP sends out keepalive messages when keepalive is enabled.
 121         Default: 2hours.
 122
 123 tcp_keepalive_probes - INTEGER
 124         How many keepalive probes TCP sends out, until it decides that the
 125         connection is broken. Default value: 9.
 126
 127 tcp_keepalive_intvl - INTEGER
 128         How frequently the probes are send out. Multiplied by
 129         tcp_keepalive_probes it is time to kill not responding connection,
 130         after probes started. Default value: 75sec i.e. connection
 131         will be aborted after ~11 minutes of retries.
 132
 133 tcp_retries1 - INTEGER
 134         How many times to retry before deciding that something is wrong
 135         and it is necessary to report this suspicion to network layer.
 136         Minimal RFC value is 3, it is default, which corresponds
 137         to ~3sec-8min depending on RTO.
 138
 139 tcp_retries2 - INTEGER
 140         How may times to retry before killing alive TCP connection.
 141         RFC1122 says that the limit should be longer than 100 sec.
 142         It is too small number. Default value 15 corresponds to ~13-30min
 143         depending on RTO.
 144
 145 tcp_orphan_retries - INTEGER
 146         How may times to retry before killing TCP connection, closed
 147         by our side. Default value 7 corresponds to ~50sec-16min
 148         depending on RTO. If you machine is loaded WEB server,
 149         you should think about lowering this value, such sockets
 150         may consume significant resources. Cf. tcp_max_orphans.
 151
 152 tcp_fin_timeout - INTEGER
 153         Time to hold socket in state FIN-WAIT-2, if it was closed
 154         by our side. Peer can be broken and never close its side,
 155         or even died unexpectedly. Default value is 60sec.
 156         Usual value used in 2.2 was 180 seconds, you may restore
 157         it, but remember that if your machine is even underloaded WEB server,
 158         you risk to overflow memory with kilotons of dead sockets,
 159         FIN-WAIT-2 sockets are less dangerous than FIN-WAIT-1,
 160         because they eat maximum 1.5K of memory, but they tend
 161         to live longer. Cf. tcp_max_orphans.
 162
 163 tcp_max_tw_buckets - INTEGER
 164         Maximal number of timewait sockets held by system simultaneously.
 165         If this number is exceeded time-wait socket is immediately destroyed
 166         and warning is printed. This limit exists only to prevent
 167         simple DoS attacks, you _must_ not lower the limit artificially,
 168         but rather increase it (probably, after increasing installed memory),
 169         if network conditions require more than default value.
 170
 171 tcp_tw_recycle - BOOLEAN
 172         Enable fast recycling TIME-WAIT sockets. Default value is 0.
 173         It should not be changed without advice/request of technical
 174         experts.
 175
 176 tcp_tw_reuse - BOOLEAN
 177         Allow to reuse TIME-WAIT sockets for new connections when it is
 178         safe from protocol viewpoint. Default value is 0.
 179         It should not be changed without advice/request of technical
 180         experts.
 181
 182 tcp_max_orphans - INTEGER
 183         Maximal number of TCP sockets not attached to any user file handle,
 184         held by system. If this number is exceeded orphaned connections are
 185         reset immediately and warning is printed. This limit exists
 186         only to prevent simple DoS attacks, you _must_ not rely on this
 187         or lower the limit artificially, but rather increase it
 188         (probably, after increasing installed memory),
 189         if network conditions require more than default value,
 190         and tune network services to linger and kill such states
 191         more aggressively. Let me to remind again: each orphan eats
 192         up to ~64K of unswappable memory.
 193
 194 tcp_abort_on_overflow - BOOLEAN
 195         If listening service is too slow to accept new connections,
 196         reset them. Default state is FALSE. It means that if overflow
 197         occurred due to a burst, connection will recover. Enable this
 198         option _only_ if you are really sure that listening daemon
 199         cannot be tuned to accept connections faster. Enabling this
 200         option can harm clients of your server.
 201
 202 tcp_syncookies - BOOLEAN
 203         Only valid when the kernel was compiled with CONFIG_SYNCOOKIES
 204         Send out syncookies when the syn backlog queue of a socket
 205         overflows. This is to prevent against the common 'syn flood attack'
 206         Default: FALSE
 207
 208         Note, that syncookies is fallback facility.
 209         It MUST NOT be used to help highly loaded servers to stand
 210         against legal connection rate. If you see synflood warnings
 211         in your logs, but investigation shows that they occur
 212         because of overload with legal connections, you should tune
 213         another parameters until this warning disappear.
 214         See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
 215
 216         syncookies seriously violate TCP protocol, do not allow
 217         to use TCP extensions, can result in serious degradation
 218         of some services (f.e. SMTP relaying), visible not by you,
 219         but your clients and relays, contacting you. While you see
 220         synflood warnings in logs not being really flooded, your server
 221         is seriously misconfigured.
 222
 223 tcp_stdurg - BOOLEAN
 224         Use the Host requirements interpretation of the TCP urg pointer field.
 225         Most hosts use the older BSD interpretation, so if you turn this on
 226         Linux might not communicate correctly with them.
 227         Default: FALSE
 228
 229 tcp_max_syn_backlog - INTEGER
 230         Maximal number of remembered connection requests, which are
 231         still did not receive an acknowledgment from connecting client.
 232         Default value is 1024 for systems with more than 128Mb of memory,
 233         and 128 for low memory machines. If server suffers of overload,
 234         try to increase this number.
 235
 236 tcp_window_scaling - BOOLEAN
 237         Enable window scaling as defined in RFC1323.
 238
 239 tcp_timestamps - BOOLEAN
 240         Enable timestamps as defined in RFC1323.
 241
 242 tcp_sack - BOOLEAN
 243         Enable select acknowledgments (SACKS).
 244
 245 tcp_fack - BOOLEAN
 246         Enable FACK congestion avoidance and fast retransmission.
 247         The value is not used, if tcp_sack is not enabled.
 248
 249 tcp_dsack - BOOLEAN
 250         Allows TCP to send "duplicate" SACKs.
 251
 252 tcp_ecn - BOOLEAN
 253         Enable Explicit Congestion Notification in TCP.
 254
 255 tcp_reordering - INTEGER
 256         Maximal reordering of packets in a TCP stream.
 257         Default: 3
 258
 259 tcp_retrans_collapse - BOOLEAN
 260         Bug-to-bug compatibility with some broken printers.
 261         On retransmit try to send bigger packets to work around bugs in
 262         certain TCP stacks.
 263
 264 tcp_wmem - vector of 3 INTEGERs: min, default, max
 265         min: Amount of memory reserved for send buffers for TCP socket.
 266         Each TCP socket has rights to use it due to fact of its birth.
 267         Default: 4K
 268
 269         default: Amount of memory allowed for send buffers for TCP socket
 270         by default. This value overrides net.core.wmem_default used
 271         by other protocols, it is usually lower than net.core.wmem_default.
 272         Default: 16K
 273
 274         max: Maximal amount of memory allowed for automatically selected
 275         send buffers for TCP socket. This value does not override
 276         net.core.wmem_max, "static" selection via SO_SNDBUF does not use this.
 277         Default: 128K
 278
 279 tcp_rmem - vector of 3 INTEGERs: min, default, max
 280         min: Minimal size of receive buffer used by TCP sockets.
 281         It is guaranteed to each TCP socket, even under moderate memory
 282         pressure.
 283         Default: 8K
 284
 285         default: default size of receive buffer used by TCP sockets.
 286         This value overrides net.core.rmem_default used by other protocols.
 287         Default: 87380 bytes. This value results in window of 65535 with
 288         default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
 289         less for default tcp_app_win. See below about these variables.
 290
 291         max: maximal size of receive buffer allowed for automatically
 292         selected receiver buffers for TCP socket. This value does not override
 293         net.core.rmem_max, "static" selection via SO_RCVBUF does not use this.
 294         Default: 87380*2 bytes.
 295
 296 tcp_mem - vector of 3 INTEGERs: min, pressure, max
 297         min: below this number of pages TCP is not bothered about its
 298         memory appetite.
 299
 300         pressure: when amount of memory allocated by TCP exceeds this number
 301         of pages, TCP moderates its memory consumption and enters memory
 302         pressure mode, which is exited when memory consumption falls
 303         under "min".
 304
 305         max: number of pages allowed for queueing by all TCP sockets.
 306
 307         Defaults are calculated at boot time from amount of available
 308         memory.
 309
 310 tcp_app_win - INTEGER
 311         Reserve max(window/2^tcp_app_win, mss) of window for application
 312         buffer. Value 0 is special, it means that nothing is reserved.
 313         Default: 31
 314
 315 tcp_adv_win_scale - INTEGER
 316         Count buffering overhead as bytes/2^tcp_adv_win_scale
 317         (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
 318         if it is <= 0.
 319         Default: 2
 320
 321 tcp_rfc1337 - BOOLEAN
 322         If set, the TCP stack behaves conforming to RFC1337. If unset,
 323         we are not conforming to RFC, but prevent TCP TIME_WAIT
 324         assassination.
 325         Default: 0
 326
 327 tcp_low_latency - BOOLEAN
 328         If set, the TCP stack makes decisions that prefer lower
 329         latency as opposed to higher throughput.  By default, this
 330         option is not set meaning that higher throughput is preferred.
 331         An example of an application where this default should be
 332         changed would be a Beowulf compute cluster.
 333         Default: 0
 334
 335 tcp_tso_win_divisor - INTEGER
 336        This allows control over what percentage of the congestion window
 337        can be consumed by a single TSO frame.
 338        The setting of this parameter is a choice between burstiness and
 339        building larger TSO frames.
 340        Default: 3
 341
 342 tcp_frto - BOOLEAN
 343         Enables F-RTO, an enhanced recovery algorithm for TCP retransmission
 344         timeouts.  It is particularly beneficial in wireless environments
 345         where packet loss is typically due to random radio interference
 346         rather than intermediate router congestion.
 347
 348 tcp_congestion_control - STRING
 349         Set the congestion control algorithm to be used for new
 350         connections. The algorithm "reno" is always available, but
 351         additional choices may be available based on kernel configuration.
 352
 353 somaxconn - INTEGER
 354         Limit of socket listen() backlog, known in userspace as SOMAXCONN.
 355         Defaults to 128.  See also tcp_max_syn_backlog for additional tuning
 356         for TCP sockets.
 357
 358 tcp_workaround_signed_windows - BOOLEAN
 359         If set, assume no receipt of a window scaling option means the
 360         remote TCP is broken and treats the window as a signed quantity.
 361         If unset, assume the remote TCP is not broken even if we do
 362         not receive a window scaling option from them.
 363         Default: 0
 364
 365 tcp_slow_start_after_idle - BOOLEAN
 366         If set, provide RFC2861 behavior and time out the congestion
 367         window after an idle period.  An idle period is defined at
 368         the current RTO.  If unset, the congestion window will not
 369         be timed out after an idle period.
 370         Default: 1
 371
 372 IP Variables:
 373
 374 ip_local_port_range - 2 INTEGERS
 375         Defines the local port range that is used by TCP and UDP to
 376         choose the local port. The first number is the first, the
 377         second the last local port number. Default value depends on
 378         amount of memory available on the system:
 379         > 128Mb 32768-61000
 380         < 128Mb 1024-4999 or even less.
 381         This number defines number of active connections, which this
 382         system can issue simultaneously to systems not supporting
 383         TCP extensions (timestamps). With tcp_tw_recycle enabled
 384         (i.e. by default) range 1024-4999 is enough to issue up to
 385         2000 connections per second to systems supporting timestamps.
 386
 387 ip_nonlocal_bind - BOOLEAN
 388         If set, allows processes to bind() to non-local IP addresses,
 389         which can be quite useful - but may break some applications.
 390         Default: 0
 391
 392 ip_dynaddr - BOOLEAN
 393         If set non-zero, enables support for dynamic addresses.
 394         If set to a non-zero value larger than 1, a kernel log
 395         message will be printed when dynamic address rewriting
 396         occurs.
 397         Default: 0
 398
 399 icmp_echo_ignore_all - BOOLEAN
 400         If set non-zero, then the kernel will ignore all ICMP ECHO
 401         requests sent to it.
 402         Default: 0
 403
 404 icmp_echo_ignore_broadcasts - BOOLEAN
 405         If set non-zero, then the kernel will ignore all ICMP ECHO and
 406         TIMESTAMP requests sent to it via broadcast/multicast.
 407         Default: 1
 408
 409 icmp_ratelimit - INTEGER
 410         Limit the maximal rates for sending ICMP packets whose type matches
 411         icmp_ratemask (see below) to specific targets.
 412         0 to disable any limiting, otherwise the maximal rate in jiffies(1)
 413         Default: 100
 414
 415 icmp_ratemask - INTEGER
 416         Mask made of ICMP types for which rates are being limited.
 417         Significant bits: IHGFEDCBA9876543210
 418         Default mask:     0000001100000011000 (6168)
 419
 420         Bit definitions (see include/linux/icmp.h):
 421                 0 Echo Reply
 422                 3 Destination Unreachable *
 423                 4 Source Quench *
 424                 5 Redirect
 425                 8 Echo Request
 426                 B Time Exceeded *
 427                 C Parameter Problem *
 428                 D Timestamp Request
 429                 E Timestamp Reply
 430                 F Info Request
 431                 G Info Reply
 432                 H Address Mask Request
 433                 I Address Mask Reply
 434
 435         * These are rate limited by default (see default mask above)
 436
 437 icmp_ignore_bogus_error_responses - BOOLEAN
 438         Some routers violate RFC1122 by sending bogus responses to broadcast
 439         frames.  Such violations are normally logged via a kernel warning.
 440         If this is set to TRUE, the kernel will not give such warnings, which
 441         will avoid log file clutter.
 442         Default: FALSE
 443
 444 icmp_errors_use_inbound_ifaddr - BOOLEAN
 445
 446         If zero, icmp error messages are sent with the primary address of
 447         the exiting interface.
 448
 449         If non-zero, the message will be sent with the primary address of
 450         the interface that received the packet that caused the icmp error.
 451         This is the behaviour network many administrators will expect from
 452         a router. And it can make debugging complicated network layouts
 453         much easier.
 454
 455         Note that if no primary address exists for the interface selected,
 456         then the primary address of the first non-loopback interface that
 457         has one will be used regarldess of this setting.
 458
 459         Default: 0
 460
 461 igmp_max_memberships - INTEGER
 462         Change the maximum number of multicast groups we can subscribe to.
 463         Default: 20
 464
 465 conf/interface/*  changes special settings per interface (where "interface" is
 466                   the name of your network interface)
 467 conf/all/*        is special, changes the settings for all interfaces
 468
 469
 470 log_martians - BOOLEAN
 471         Log packets with impossible addresses to kernel log.
 472         log_martians for the interface will be enabled if at least one of
 473         conf/{all,interface}/log_martians is set to TRUE,
 474         it will be disabled otherwise
 475
 476 accept_redirects - BOOLEAN
 477         Accept ICMP redirect messages.
 478         accept_redirects for the interface will be enabled if:
 479         - both conf/{all,interface}/accept_redirects are TRUE in the case forwarding
 480           for the interface is enabled
 481         or
 482         - at least one of conf/{all,interface}/accept_redirects is TRUE in the case
 483           forwarding for the interface is disabled
 484         accept_redirects for the interface will be disabled otherwise
 485         default TRUE (host)
 486                 FALSE (router)
 487
 488 forwarding - BOOLEAN
 489         Enable IP forwarding on this interface.
 490
 491 mc_forwarding - BOOLEAN
 492         Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
 493         and a multicast routing daemon is required.
 494         conf/all/mc_forwarding must also be set to TRUE to enable multicast routing
 495         for the interface
 496
 497 medium_id - INTEGER
 498         Integer value used to differentiate the devices by the medium they
 499         are attached to. Two devices can have different id values when
 500         the broadcast packets are received only on one of them.
 501         The default value 0 means that the device is the only interface
 502         to its medium, value of -1 means that medium is not known.
 503
 504         Currently, it is used to change the proxy_arp behavior:
 505         the proxy_arp feature is enabled for packets forwarded between
 506         two devices attached to different media.
 507
 508 proxy_arp - BOOLEAN
 509         Do proxy arp.
 510         proxy_arp for the interface will be enabled if at least one of
 511         conf/{all,interface}/proxy_arp is set to TRUE,
 512         it will be disabled otherwise
 513
 514 shared_media - BOOLEAN
 515         Send(router) or accept(host) RFC1620 shared media redirects.
 516         Overrides ip_secure_redirects.
 517         shared_media for the interface will be enabled if at least one of
 518         conf/{all,interface}/shared_media is set to TRUE,
 519         it will be disabled otherwise
 520         default TRUE
 521
 522 secure_redirects - BOOLEAN
 523         Accept ICMP redirect messages only for gateways,
 524         listed in default gateway list.
 525         secure_redirects for the interface will be enabled if at least one of
 526         conf/{all,interface}/secure_redirects is set to TRUE,
 527         it will be disabled otherwise
 528         default TRUE
 529
 530 send_redirects - BOOLEAN
 531         Send redirects, if router.
 532         send_redirects for the interface will be enabled if at least one of
 533         conf/{all,interface}/send_redirects is set to TRUE,
 534         it will be disabled otherwise
 535         Default: TRUE
 536
 537 bootp_relay - BOOLEAN
 538         Accept packets with source address 0.b.c.d destined
 539         not to this host as local ones. It is supposed, that
 540         BOOTP relay daemon will catch and forward such packets.
 541         conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
 542         for the interface
 543         default FALSE
 544         Not Implemented Yet.
 545
 546 accept_source_route - BOOLEAN
 547         Accept packets with SRR option.
 548         conf/all/accept_source_route must also be set to TRUE to accept packets
 549         with SRR option on the interface
 550         default TRUE (router)
 551                 FALSE (host)
 552
 553 rp_filter - BOOLEAN
 554         1 - do source validation by reversed path, as specified in RFC1812
 555             Recommended option for single homed hosts and stub network
 556             routers. Could cause troubles for complicated (not loop free)
 557             networks running a slow unreliable protocol (sort of RIP),
 558             or using static routes.
 559
 560         0 - No source validation.
 561
 562         conf/all/rp_filter must also be set to TRUE to do source validation
 563         on the interface
 564
 565         Default value is 0. Note that some distributions enable it
 566         in startup scripts.
 567
 568 arp_filter - BOOLEAN
 569         1 - Allows you to have multiple network interfaces on the same
 570         subnet, and have the ARPs for each interface be answered
 571         based on whether or not the kernel would route a packet from
 572         the ARP'd IP out that interface (therefore you must use source
 573         based routing for this to work). In other words it allows control
 574         of which cards (usually 1) will respond to an arp request.
 575
 576         0 - (default) The kernel can respond to arp requests with addresses
 577         from other interfaces. This may seem wrong but it usually makes
 578         sense, because it increases the chance of successful communication.
 579         IP addresses are owned by the complete host on Linux, not by
 580         particular interfaces. Only for more complex setups like load-
 581         balancing, does this behaviour cause problems.
 582
 583         arp_filter for the interface will be enabled if at least one of
 584         conf/{all,interface}/arp_filter is set to TRUE,
 585         it will be disabled otherwise
 586
 587 arp_announce - INTEGER
 588         Define different restriction levels for announcing the local
 589         source IP address from IP packets in ARP requests sent on
 590         interface:
 591         0 - (default) Use any local address, configured on any interface
 592         1 - Try to avoid local addresses that are not in the target's
 593         subnet for this interface. This mode is useful when target
 594         hosts reachable via this interface require the source IP
 595         address in ARP requests to be part of their logical network
 596         configured on the receiving interface. When we generate the
 597         request we will check all our subnets that include the
 598         target IP and will preserve the source address if it is from
 599         such subnet. If there is no such subnet we select source
 600         address according to the rules for level 2.
 601         2 - Always use the best local address for this target.
 602         In this mode we ignore the source address in the IP packet
 603         and try to select local address that we prefer for talks with
 604         the target host. Such local address is selected by looking
 605         for primary IP addresses on all our subnets on the outgoing
 606         interface that include the target IP address. If no suitable
 607         local address is found we select the first local address
 608         we have on the outgoing interface or on all other interfaces,
 609         with the hope we will receive reply for our request and
 610         even sometimes no matter the source IP address we announce.
 611
 612         The max value from conf/{all,interface}/arp_announce is used.
 613
 614         Increasing the restriction level gives more chance for
 615         receiving answer from the resolved target while decreasing
 616         the level announces more valid sender's information.
 617
 618 arp_ignore - INTEGER
 619         Define different modes for sending replies in response to
 620         received ARP requests that resolve local target IP addresses:
 621         0 - (default): reply for any local target IP address, configured
 622         on any interface
 623         1 - reply only if the target IP address is local address
 624         configured on the incoming interface
 625         2 - reply only if the target IP address is local address
 626         configured on the incoming interface and both with the
 627         sender's IP address are part from same subnet on this interface
 628         3 - do not reply for local addresses configured with scope host,
 629         only resolutions for global and link addresses are replied
 630         4-7 - reserved
 631         8 - do not reply for all local addresses
 632
 633         The max value from conf/{all,interface}/arp_ignore is used
 634         when ARP request is received on the {interface}
 635
 636 arp_accept - BOOLEAN
 637         Define behavior when gratuitous arp replies are received:
 638         0 - drop gratuitous arp frames
 639         1 - accept gratuitous arp frames
 640
 641 app_solicit - INTEGER
 642         The maximum number of probes to send to the user space ARP daemon
 643         via netlink before dropping back to multicast probes (see
 644         mcast_solicit).  Defaults to 0.
 645
 646 disable_policy - BOOLEAN
 647         Disable IPSEC policy (SPD) for this interface
 648
 649 disable_xfrm - BOOLEAN
 650         Disable IPSEC encryption on this interface, whatever the policy
 651
 652
 653
 654 tag - INTEGER
 655         Allows you to write a number, which can be used as required.
 656         Default value is 0.
 657
 658 (1) Jiffie: internal timeunit for the kernel. On the i386 1/100s, on the
 659 Alpha 1/1024s. See the HZ define in /usr/include/asm/param.h for the exact
 660 value on your system.
 661
 662 Alexey Kuznetsov.
 663 kuznet@ms2.inr.ac.ru
 664
 665 Updated by:
 666 Andi Kleen
 667 ak@muc.de
 668 Nicolas Delon
 669 delon.nicolas@wanadoo.fr
 670
 671
 672
 673
 674 /proc/sys/net/ipv6/* Variables:
 675
 676 IPv6 has no global variables such as tcp_*.  tcp_* settings under ipv4/ also
 677 apply to IPv6 [XXX?].
 678
 679 bindv6only - BOOLEAN
 680         Default value for IPV6_V6ONLY socket option,
 681         which restricts use of the IPv6 socket to IPv6 communication
 682         only.
 683                 TRUE: disable IPv4-mapped address feature
 684                 FALSE: enable IPv4-mapped address feature
 685
 686         Default: FALSE (as specified in RFC2553bis)
 687
 688 IPv6 Fragmentation:
 689
 690 ip6frag_high_thresh - INTEGER
 691         Maximum memory used to reassemble IPv6 fragments. When
 692         ip6frag_high_thresh bytes of memory is allocated for this purpose,
 693         the fragment handler will toss packets until ip6frag_low_thresh
 694         is reached.
 695
 696 ip6frag_low_thresh - INTEGER
 697         See ip6frag_high_thresh
 698
 699 ip6frag_time - INTEGER
 700         Time in seconds to keep an IPv6 fragment in memory.
 701
 702 ip6frag_secret_interval - INTEGER
 703         Regeneration interval (in seconds) of the hash secret (or lifetime
 704         for the hash secret) for IPv6 fragments.
 705         Default: 600
 706
 707 conf/default/*:
 708         Change the interface-specific default settings.
 709
 710
 711 conf/all/*:
 712         Change all the interface-specific settings.
 713
 714         [XXX:  Other special features than forwarding?]
 715
 716 conf/all/forwarding - BOOLEAN
 717         Enable global IPv6 forwarding between all interfaces.
 718
 719         IPv4 and IPv6 work differently here; e.g. netfilter must be used
 720         to control which interfaces may forward packets and which not.
 721
 722         This also sets all interfaces' Host/Router setting
 723         'forwarding' to the specified value.  See below for details.
 724
 725         This referred to as global forwarding.
 726
 727 conf/interface/*:
 728         Change special settings per interface.
 729
 730         The functional behaviour for certain settings is different
 731         depending on whether local forwarding is enabled or not.
 732
 733 accept_ra - BOOLEAN
 734         Accept Router Advertisements; autoconfigure using them.
 735
 736         Functional default: enabled if local forwarding is disabled.
 737                             disabled if local forwarding is enabled.
 738
 739 accept_ra_defrtr - BOOLEAN
 740         Learn default router in Router Advertisement.
 741
 742         Functional default: enabled if accept_ra is enabled.
 743                             disabled if accept_ra is disabled.
 744
 745 accept_ra_pinfo - BOOLEAN
 746         Learn Prefix Inforamtion in Router Advertisement.
 747
 748         Functional default: enabled if accept_ra is enabled.
 749                             disabled if accept_ra is disabled.
 750
 751 accept_ra_rt_info_max_plen - INTEGER
 752         Maximum prefix length of Route Information in RA.
 753
 754         Route Information w/ prefix larger than or equal to this
 755         variable shall be ignored.
 756
 757         Functional default: 0 if accept_ra_rtr_pref is enabled.
 758                             -1 if accept_ra_rtr_pref is disabled.
 759
 760 accept_ra_rtr_pref - BOOLEAN
 761         Accept Router Preference in RA.
 762
 763         Functional default: enabled if accept_ra is enabled.
 764                             disabled if accept_ra is disabled.
 765
 766 accept_redirects - BOOLEAN
 767         Accept Redirects.
 768
 769         Functional default: enabled if local forwarding is disabled.
 770                             disabled if local forwarding is enabled.
 771
 772 autoconf - BOOLEAN
 773         Autoconfigure addresses using Prefix Information in Router
 774         Advertisements.
 775
 776         Functional default: enabled if accept_ra_pinfo is enabled.
 777                             disabled if accept_ra_pinfo is disabled.
 778
 779 dad_transmits - INTEGER
 780         The amount of Duplicate Address Detection probes to send.
 781         Default: 1
 782
 783 forwarding - BOOLEAN
 784         Configure interface-specific Host/Router behaviour.
 785
 786         Note: It is recommended to have the same setting on all
 787         interfaces; mixed router/host scenarios are rather uncommon.
 788
 789         FALSE:
 790
 791         By default, Host behaviour is assumed.  This means:
 792
 793         1. IsRouter flag is not set in Neighbour Advertisements.
 794         2. Router Solicitations are being sent when necessary.
 795         3. If accept_ra is TRUE (default), accept Router
 796            Advertisements (and do autoconfiguration).
 797         4. If accept_redirects is TRUE (default), accept Redirects.
 798
 799         TRUE:
 800
 801         If local forwarding is enabled, Router behaviour is assumed.
 802         This means exactly the reverse from the above:
 803
 804         1. IsRouter flag is set in Neighbour Advertisements.
 805         2. Router Solicitations are not sent.
 806         3. Router Advertisements are ignored.
 807         4. Redirects are ignored.
 808
 809         Default: FALSE if global forwarding is disabled (default),
 810                  otherwise TRUE.
 811
 812 hop_limit - INTEGER
 813         Default Hop Limit to set.
 814         Default: 64
 815
 816 mtu - INTEGER
 817         Default Maximum Transfer Unit
 818         Default: 1280 (IPv6 required minimum)
 819
 820 router_probe_interval - INTEGER
 821         Minimum interval (in seconds) between Router Probing described
 822         in RFC4191.
 823
 824         Default: 60
 825
 826 router_solicitation_delay - INTEGER
 827         Number of seconds to wait after interface is brought up
 828         before sending Router Solicitations.
 829         Default: 1
 830
 831 router_solicitation_interval - INTEGER
 832         Number of seconds to wait between Router Solicitations.
 833         Default: 4
 834
 835 router_solicitations - INTEGER
 836         Number of Router Solicitations to send until assuming no
 837         routers are present.
 838         Default: 3
 839
 840 use_tempaddr - INTEGER
 841         Preference for Privacy Extensions (RFC3041).
 842           <= 0 : disable Privacy Extensions
 843           == 1 : enable Privacy Extensions, but prefer public
 844                  addresses over temporary addresses.
 845           >  1 : enable Privacy Extensions and prefer temporary
 846                  addresses over public addresses.
 847         Default:  0 (for most devices)
 848                  -1 (for point-to-point devices and loopback devices)
 849
 850 temp_valid_lft - INTEGER
 851         valid lifetime (in seconds) for temporary addresses.
 852         Default: 604800 (7 days)
 853
 854 temp_prefered_lft - INTEGER
 855         Preferred lifetime (in seconds) for temporary addresses.
 856         Default: 86400 (1 day)
 857
 858 max_desync_factor - INTEGER
 859         Maximum value for DESYNC_FACTOR, which is a random value
 860         that ensures that clients don't synchronize with each
 861         other and generate new addresses at exactly the same time.
 862         value is in seconds.
 863         Default: 600
 864
 865 regen_max_retry - INTEGER
 866         Number of attempts before give up attempting to generate
 867         valid temporary addresses.
 868         Default: 5
 869
 870 max_addresses - INTEGER
 871         Number of maximum addresses per interface.  0 disables limitation.
 872         It is recommended not set too large value (or 0) because it would
 873         be too easy way to crash kernel to allow to create too much of
 874         autoconfigured addresses.
 875         Default: 16
 876
 877 icmp/*:
 878 ratelimit - INTEGER
 879         Limit the maximal rates for sending ICMPv6 packets.
 880         0 to disable any limiting, otherwise the maximal rate in jiffies(1)
 881         Default: 100
 882
 883
 884 IPv6 Update by:
 885 Pekka Savola <pekkas@netcore.fi>
 886 YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
 887
 888
 889 /proc/sys/net/bridge/* Variables:
 890
 891 bridge-nf-call-arptables - BOOLEAN
 892         1 : pass bridged ARP traffic to arptables' FORWARD chain.
 893         0 : disable this.
 894         Default: 1
 895
 896 bridge-nf-call-iptables - BOOLEAN
 897         1 : pass bridged IPv4 traffic to iptables' chains.
 898         0 : disable this.
 899         Default: 1
 900
 901 bridge-nf-call-ip6tables - BOOLEAN
 902         1 : pass bridged IPv6 traffic to ip6tables' chains.
 903         0 : disable this.
 904         Default: 1
 905
 906 bridge-nf-filter-vlan-tagged - BOOLEAN
 907         1 : pass bridged vlan-tagged ARP/IP traffic to arptables/iptables.
 908         0 : disable this.
 909         Default: 1
 910
 911
 912 UNDOCUMENTED:
 913
 914 dev_weight FIXME
 915 discovery_slots FIXME
 916 discovery_timeout FIXME
 917 fast_poll_increase FIXME
 918 ip6_queue_maxlen FIXME
 919 lap_keepalive_time FIXME
 920 lo_cong FIXME
 921 max_baud_rate FIXME
 922 max_dgram_qlen FIXME
 923 max_noreply_time FIXME
 924 max_tx_data_size FIXME
 925 max_tx_window FIXME
 926 min_tx_turn_time FIXME
 927 mod_cong FIXME
 928 no_cong FIXME
 929 no_cong_thresh FIXME
 930 slot_timeout FIXME
 931 warn_noreply_time FIXME
 932
 933 $Id: ip-sysctl.txt,v 1.20 2001/12/13 09:00:18 davem Exp $