linux/Documentation/networking/ip-sysctl.txt
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   1/proc/sys/net/ipv4/* Variables:
   2
   3ip_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
  13ip_default_ttl - INTEGER
  14        Default value of TTL field (Time To Live) for outgoing (but not
  15        forwarded) IP packets. Should be between 1 and 255 inclusive.
  16        Default: 64 (as recommended by RFC1700)
  17
  18ip_no_pmtu_disc - BOOLEAN
  19        Disable Path MTU Discovery.
  20        default FALSE
  21
  22min_pmtu - INTEGER
  23        default 552 - minimum discovered Path MTU
  24
  25route/max_size - INTEGER
  26        Maximum number of routes allowed in the kernel.  Increase
  27        this when using large numbers of interfaces and/or routes.
  28
  29neigh/default/gc_thresh3 - INTEGER
  30        Maximum number of neighbor entries allowed.  Increase this
  31        when using large numbers of interfaces and when communicating
  32        with large numbers of directly-connected peers.
  33
  34mtu_expires - INTEGER
  35        Time, in seconds, that cached PMTU information is kept.
  36
  37min_adv_mss - INTEGER
  38        The advertised MSS depends on the first hop route MTU, but will
  39        never be lower than this setting.
  40
  41rt_cache_rebuild_count - INTEGER
  42        The per net-namespace route cache emergency rebuild threshold.
  43        Any net-namespace having its route cache rebuilt due to
  44        a hash bucket chain being too long more than this many times
  45        will have its route caching disabled
  46
  47IP Fragmentation:
  48
  49ipfrag_high_thresh - INTEGER
  50        Maximum memory used to reassemble IP fragments. When
  51        ipfrag_high_thresh bytes of memory is allocated for this purpose,
  52        the fragment handler will toss packets until ipfrag_low_thresh
  53        is reached.
  54
  55ipfrag_low_thresh - INTEGER
  56        See ipfrag_high_thresh
  57
  58ipfrag_time - INTEGER
  59        Time in seconds to keep an IP fragment in memory.
  60
  61ipfrag_secret_interval - INTEGER
  62        Regeneration interval (in seconds) of the hash secret (or lifetime
  63        for the hash secret) for IP fragments.
  64        Default: 600
  65
  66ipfrag_max_dist - INTEGER
  67        ipfrag_max_dist is a non-negative integer value which defines the
  68        maximum "disorder" which is allowed among fragments which share a
  69        common IP source address. Note that reordering of packets is
  70        not unusual, but if a large number of fragments arrive from a source
  71        IP address while a particular fragment queue remains incomplete, it
  72        probably indicates that one or more fragments belonging to that queue
  73        have been lost. When ipfrag_max_dist is positive, an additional check
  74        is done on fragments before they are added to a reassembly queue - if
  75        ipfrag_max_dist (or more) fragments have arrived from a particular IP
  76        address between additions to any IP fragment queue using that source
  77        address, it's presumed that one or more fragments in the queue are
  78        lost. The existing fragment queue will be dropped, and a new one
  79        started. An ipfrag_max_dist value of zero disables this check.
  80
  81        Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
  82        result in unnecessarily dropping fragment queues when normal
  83        reordering of packets occurs, which could lead to poor application
  84        performance. Using a very large value, e.g. 50000, increases the
  85        likelihood of incorrectly reassembling IP fragments that originate
  86        from different IP datagrams, which could result in data corruption.
  87        Default: 64
  88
  89INET peer storage:
  90
  91inet_peer_threshold - INTEGER
  92        The approximate size of the storage.  Starting from this threshold
  93        entries will be thrown aggressively.  This threshold also determines
  94        entries' time-to-live and time intervals between garbage collection
  95        passes.  More entries, less time-to-live, less GC interval.
  96
  97inet_peer_minttl - INTEGER
  98        Minimum time-to-live of entries.  Should be enough to cover fragment
  99        time-to-live on the reassembling side.  This minimum time-to-live  is
 100        guaranteed if the pool size is less than inet_peer_threshold.
 101        Measured in seconds.
 102
 103inet_peer_maxttl - INTEGER
 104        Maximum time-to-live of entries.  Unused entries will expire after
 105        this period of time if there is no memory pressure on the pool (i.e.
 106        when the number of entries in the pool is very small).
 107        Measured in seconds.
 108
 109TCP variables:
 110
 111somaxconn - INTEGER
 112        Limit of socket listen() backlog, known in userspace as SOMAXCONN.
 113        Defaults to 128.  See also tcp_max_syn_backlog for additional tuning
 114        for TCP sockets.
 115
 116tcp_abc - INTEGER
 117        Controls Appropriate Byte Count (ABC) defined in RFC3465.
 118        ABC is a way of increasing congestion window (cwnd) more slowly
 119        in response to partial acknowledgments.
 120        Possible values are:
 121                0 increase cwnd once per acknowledgment (no ABC)
 122                1 increase cwnd once per acknowledgment of full sized segment
 123                2 allow increase cwnd by two if acknowledgment is
 124                  of two segments to compensate for delayed acknowledgments.
 125        Default: 0 (off)
 126
 127tcp_abort_on_overflow - BOOLEAN
 128        If listening service is too slow to accept new connections,
 129        reset them. Default state is FALSE. It means that if overflow
 130        occurred due to a burst, connection will recover. Enable this
 131        option _only_ if you are really sure that listening daemon
 132        cannot be tuned to accept connections faster. Enabling this
 133        option can harm clients of your server.
 134
 135tcp_adv_win_scale - INTEGER
 136        Count buffering overhead as bytes/2^tcp_adv_win_scale
 137        (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
 138        if it is <= 0.
 139        Possible values are [-31, 31], inclusive.
 140        Default: 2
 141
 142tcp_allowed_congestion_control - STRING
 143        Show/set the congestion control choices available to non-privileged
 144        processes. The list is a subset of those listed in
 145        tcp_available_congestion_control.
 146        Default is "reno" and the default setting (tcp_congestion_control).
 147
 148tcp_app_win - INTEGER
 149        Reserve max(window/2^tcp_app_win, mss) of window for application
 150        buffer. Value 0 is special, it means that nothing is reserved.
 151        Default: 31
 152
 153tcp_available_congestion_control - STRING
 154        Shows the available congestion control choices that are registered.
 155        More congestion control algorithms may be available as modules,
 156        but not loaded.
 157
 158tcp_base_mss - INTEGER
 159        The initial value of search_low to be used by the packetization layer
 160        Path MTU discovery (MTU probing).  If MTU probing is enabled,
 161        this is the initial MSS used by the connection.
 162
 163tcp_congestion_control - STRING
 164        Set the congestion control algorithm to be used for new
 165        connections. The algorithm "reno" is always available, but
 166        additional choices may be available based on kernel configuration.
 167        Default is set as part of kernel configuration.
 168
 169tcp_cookie_size - INTEGER
 170        Default size of TCP Cookie Transactions (TCPCT) option, that may be
 171        overridden on a per socket basis by the TCPCT socket option.
 172        Values greater than the maximum (16) are interpreted as the maximum.
 173        Values greater than zero and less than the minimum (8) are interpreted
 174        as the minimum.  Odd values are interpreted as the next even value.
 175        Default: 0 (off).
 176
 177tcp_dsack - BOOLEAN
 178        Allows TCP to send "duplicate" SACKs.
 179
 180tcp_ecn - INTEGER
 181        Enable Explicit Congestion Notification (ECN) in TCP. ECN is only
 182        used when both ends of the TCP flow support it. It is useful to
 183        avoid losses due to congestion (when the bottleneck router supports
 184        ECN).
 185        Possible values are:
 186                0 disable ECN
 187                1 ECN enabled
 188                2 Only server-side ECN enabled. If the other end does
 189                  not support ECN, behavior is like with ECN disabled.
 190        Default: 2
 191
 192tcp_fack - BOOLEAN
 193        Enable FACK congestion avoidance and fast retransmission.
 194        The value is not used, if tcp_sack is not enabled.
 195
 196tcp_fin_timeout - INTEGER
 197        Time to hold socket in state FIN-WAIT-2, if it was closed
 198        by our side. Peer can be broken and never close its side,
 199        or even died unexpectedly. Default value is 60sec.
 200        Usual value used in 2.2 was 180 seconds, you may restore
 201        it, but remember that if your machine is even underloaded WEB server,
 202        you risk to overflow memory with kilotons of dead sockets,
 203        FIN-WAIT-2 sockets are less dangerous than FIN-WAIT-1,
 204        because they eat maximum 1.5K of memory, but they tend
 205        to live longer. Cf. tcp_max_orphans.
 206
 207tcp_frto - INTEGER
 208        Enables Forward RTO-Recovery (F-RTO) defined in RFC4138.
 209        F-RTO is an enhanced recovery algorithm for TCP retransmission
 210        timeouts.  It is particularly beneficial in wireless environments
 211        where packet loss is typically due to random radio interference
 212        rather than intermediate router congestion.  F-RTO is sender-side
 213        only modification. Therefore it does not require any support from
 214        the peer.
 215
 216        If set to 1, basic version is enabled.  2 enables SACK enhanced
 217        F-RTO if flow uses SACK.  The basic version can be used also when
 218        SACK is in use though scenario(s) with it exists where F-RTO
 219        interacts badly with the packet counting of the SACK enabled TCP
 220        flow.
 221
 222tcp_frto_response - INTEGER
 223        When F-RTO has detected that a TCP retransmission timeout was
 224        spurious (i.e, the timeout would have been avoided had TCP set a
 225        longer retransmission timeout), TCP has several options what to do
 226        next. Possible values are:
 227                0 Rate halving based; a smooth and conservative response,
 228                  results in halved cwnd and ssthresh after one RTT
 229                1 Very conservative response; not recommended because even
 230                  though being valid, it interacts poorly with the rest of
 231                  Linux TCP, halves cwnd and ssthresh immediately
 232                2 Aggressive response; undoes congestion control measures
 233                  that are now known to be unnecessary (ignoring the
 234                  possibility of a lost retransmission that would require
 235                  TCP to be more cautious), cwnd and ssthresh are restored
 236                  to the values prior timeout
 237        Default: 0 (rate halving based)
 238
 239tcp_keepalive_time - INTEGER
 240        How often TCP sends out keepalive messages when keepalive is enabled.
 241        Default: 2hours.
 242
 243tcp_keepalive_probes - INTEGER
 244        How many keepalive probes TCP sends out, until it decides that the
 245        connection is broken. Default value: 9.
 246
 247tcp_keepalive_intvl - INTEGER
 248        How frequently the probes are send out. Multiplied by
 249        tcp_keepalive_probes it is time to kill not responding connection,
 250        after probes started. Default value: 75sec i.e. connection
 251        will be aborted after ~11 minutes of retries.
 252
 253tcp_low_latency - BOOLEAN
 254        If set, the TCP stack makes decisions that prefer lower
 255        latency as opposed to higher throughput.  By default, this
 256        option is not set meaning that higher throughput is preferred.
 257        An example of an application where this default should be
 258        changed would be a Beowulf compute cluster.
 259        Default: 0
 260
 261tcp_max_orphans - INTEGER
 262        Maximal number of TCP sockets not attached to any user file handle,
 263        held by system. If this number is exceeded orphaned connections are
 264        reset immediately and warning is printed. This limit exists
 265        only to prevent simple DoS attacks, you _must_ not rely on this
 266        or lower the limit artificially, but rather increase it
 267        (probably, after increasing installed memory),
 268        if network conditions require more than default value,
 269        and tune network services to linger and kill such states
 270        more aggressively. Let me to remind again: each orphan eats
 271        up to ~64K of unswappable memory.
 272
 273tcp_max_ssthresh - INTEGER
 274        Limited Slow-Start for TCP with large congestion windows (cwnd) defined in
 275        RFC3742. Limited slow-start is a mechanism to limit growth of the cwnd
 276        on the region where cwnd is larger than tcp_max_ssthresh. TCP increases cwnd
 277        by at most tcp_max_ssthresh segments, and by at least tcp_max_ssthresh/2
 278        segments per RTT when the cwnd is above tcp_max_ssthresh.
 279        If TCP connection increased cwnd to thousands (or tens of thousands) segments,
 280        and thousands of packets were being dropped during slow-start, you can set
 281        tcp_max_ssthresh to improve performance for new TCP connection.
 282        Default: 0 (off)
 283
 284tcp_max_syn_backlog - INTEGER
 285        Maximal number of remembered connection requests, which have not
 286        received an acknowledgment from connecting client.
 287        The minimal value is 128 for low memory machines, and it will
 288        increase in proportion to the memory of machine.
 289        If server suffers from overload, try increasing this number.
 290
 291tcp_max_tw_buckets - INTEGER
 292        Maximal number of timewait sockets held by system simultaneously.
 293        If this number is exceeded time-wait socket is immediately destroyed
 294        and warning is printed. This limit exists only to prevent
 295        simple DoS attacks, you _must_ not lower the limit artificially,
 296        but rather increase it (probably, after increasing installed memory),
 297        if network conditions require more than default value.
 298
 299tcp_mem - vector of 3 INTEGERs: min, pressure, max
 300        min: below this number of pages TCP is not bothered about its
 301        memory appetite.
 302
 303        pressure: when amount of memory allocated by TCP exceeds this number
 304        of pages, TCP moderates its memory consumption and enters memory
 305        pressure mode, which is exited when memory consumption falls
 306        under "min".
 307
 308        max: number of pages allowed for queueing by all TCP sockets.
 309
 310        Defaults are calculated at boot time from amount of available
 311        memory.
 312
 313tcp_moderate_rcvbuf - BOOLEAN
 314        If set, TCP performs receive buffer auto-tuning, attempting to
 315        automatically size the buffer (no greater than tcp_rmem[2]) to
 316        match the size required by the path for full throughput.  Enabled by
 317        default.
 318
 319tcp_mtu_probing - INTEGER
 320        Controls TCP Packetization-Layer Path MTU Discovery.  Takes three
 321        values:
 322          0 - Disabled
 323          1 - Disabled by default, enabled when an ICMP black hole detected
 324          2 - Always enabled, use initial MSS of tcp_base_mss.
 325
 326tcp_no_metrics_save - BOOLEAN
 327        By default, TCP saves various connection metrics in the route cache
 328        when the connection closes, so that connections established in the
 329        near future can use these to set initial conditions.  Usually, this
 330        increases overall performance, but may sometimes cause performance
 331        degradation.  If set, TCP will not cache metrics on closing
 332        connections.
 333
 334tcp_orphan_retries - INTEGER
 335        This value influences the timeout of a locally closed TCP connection,
 336        when RTO retransmissions remain unacknowledged.
 337        See tcp_retries2 for more details.
 338
 339        The default value is 8.
 340        If your machine is a loaded WEB server,
 341        you should think about lowering this value, such sockets
 342        may consume significant resources. Cf. tcp_max_orphans.
 343
 344tcp_reordering - INTEGER
 345        Maximal reordering of packets in a TCP stream.
 346        Default: 3
 347
 348tcp_retrans_collapse - BOOLEAN
 349        Bug-to-bug compatibility with some broken printers.
 350        On retransmit try to send bigger packets to work around bugs in
 351        certain TCP stacks.
 352
 353tcp_retries1 - INTEGER
 354        This value influences the time, after which TCP decides, that
 355        something is wrong due to unacknowledged RTO retransmissions,
 356        and reports this suspicion to the network layer.
 357        See tcp_retries2 for more details.
 358
 359        RFC 1122 recommends at least 3 retransmissions, which is the
 360        default.
 361
 362tcp_retries2 - INTEGER
 363        This value influences the timeout of an alive TCP connection,
 364        when RTO retransmissions remain unacknowledged.
 365        Given a value of N, a hypothetical TCP connection following
 366        exponential backoff with an initial RTO of TCP_RTO_MIN would
 367        retransmit N times before killing the connection at the (N+1)th RTO.
 368
 369        The default value of 15 yields a hypothetical timeout of 924.6
 370        seconds and is a lower bound for the effective timeout.
 371        TCP will effectively time out at the first RTO which exceeds the
 372        hypothetical timeout.
 373
 374        RFC 1122 recommends at least 100 seconds for the timeout,
 375        which corresponds to a value of at least 8.
 376
 377tcp_rfc1337 - BOOLEAN
 378        If set, the TCP stack behaves conforming to RFC1337. If unset,
 379        we are not conforming to RFC, but prevent TCP TIME_WAIT
 380        assassination.
 381        Default: 0
 382
 383tcp_rmem - vector of 3 INTEGERs: min, default, max
 384        min: Minimal size of receive buffer used by TCP sockets.
 385        It is guaranteed to each TCP socket, even under moderate memory
 386        pressure.
 387        Default: 1 page
 388
 389        default: initial size of receive buffer used by TCP sockets.
 390        This value overrides net.core.rmem_default used by other protocols.
 391        Default: 87380 bytes. This value results in window of 65535 with
 392        default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
 393        less for default tcp_app_win. See below about these variables.
 394
 395        max: maximal size of receive buffer allowed for automatically
 396        selected receiver buffers for TCP socket. This value does not override
 397        net.core.rmem_max.  Calling setsockopt() with SO_RCVBUF disables
 398        automatic tuning of that socket's receive buffer size, in which
 399        case this value is ignored.
 400        Default: between 87380B and 4MB, depending on RAM size.
 401
 402tcp_sack - BOOLEAN
 403        Enable select acknowledgments (SACKS).
 404
 405tcp_slow_start_after_idle - BOOLEAN
 406        If set, provide RFC2861 behavior and time out the congestion
 407        window after an idle period.  An idle period is defined at
 408        the current RTO.  If unset, the congestion window will not
 409        be timed out after an idle period.
 410        Default: 1
 411
 412tcp_stdurg - BOOLEAN
 413        Use the Host requirements interpretation of the TCP urgent pointer field.
 414        Most hosts use the older BSD interpretation, so if you turn this on
 415        Linux might not communicate correctly with them.
 416        Default: FALSE
 417
 418tcp_synack_retries - INTEGER
 419        Number of times SYNACKs for a passive TCP connection attempt will
 420        be retransmitted. Should not be higher than 255. Default value
 421        is 5, which corresponds to ~180seconds.
 422
 423tcp_syncookies - BOOLEAN
 424        Only valid when the kernel was compiled with CONFIG_SYNCOOKIES
 425        Send out syncookies when the syn backlog queue of a socket
 426        overflows. This is to prevent against the common 'SYN flood attack'
 427        Default: FALSE
 428
 429        Note, that syncookies is fallback facility.
 430        It MUST NOT be used to help highly loaded servers to stand
 431        against legal connection rate. If you see SYN flood warnings
 432        in your logs, but investigation shows that they occur
 433        because of overload with legal connections, you should tune
 434        another parameters until this warning disappear.
 435        See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
 436
 437        syncookies seriously violate TCP protocol, do not allow
 438        to use TCP extensions, can result in serious degradation
 439        of some services (f.e. SMTP relaying), visible not by you,
 440        but your clients and relays, contacting you. While you see
 441        SYN flood warnings in logs not being really flooded, your server
 442        is seriously misconfigured.
 443
 444tcp_syn_retries - INTEGER
 445        Number of times initial SYNs for an active TCP connection attempt
 446        will be retransmitted. Should not be higher than 255. Default value
 447        is 5, which corresponds to ~180seconds.
 448
 449tcp_timestamps - BOOLEAN
 450        Enable timestamps as defined in RFC1323.
 451
 452tcp_tso_win_divisor - INTEGER
 453        This allows control over what percentage of the congestion window
 454        can be consumed by a single TSO frame.
 455        The setting of this parameter is a choice between burstiness and
 456        building larger TSO frames.
 457        Default: 3
 458
 459tcp_tw_recycle - BOOLEAN
 460        Enable fast recycling TIME-WAIT sockets. Default value is 0.
 461        It should not be changed without advice/request of technical
 462        experts.
 463
 464tcp_tw_reuse - BOOLEAN
 465        Allow to reuse TIME-WAIT sockets for new connections when it is
 466        safe from protocol viewpoint. Default value is 0.
 467        It should not be changed without advice/request of technical
 468        experts.
 469
 470tcp_window_scaling - BOOLEAN
 471        Enable window scaling as defined in RFC1323.
 472
 473tcp_wmem - vector of 3 INTEGERs: min, default, max
 474        min: Amount of memory reserved for send buffers for TCP sockets.
 475        Each TCP socket has rights to use it due to fact of its birth.
 476        Default: 1 page
 477
 478        default: initial size of send buffer used by TCP sockets.  This
 479        value overrides net.core.wmem_default used by other protocols.
 480        It is usually lower than net.core.wmem_default.
 481        Default: 16K
 482
 483        max: Maximal amount of memory allowed for automatically tuned
 484        send buffers for TCP sockets. This value does not override
 485        net.core.wmem_max.  Calling setsockopt() with SO_SNDBUF disables
 486        automatic tuning of that socket's send buffer size, in which case
 487        this value is ignored.
 488        Default: between 64K and 4MB, depending on RAM size.
 489
 490tcp_workaround_signed_windows - BOOLEAN
 491        If set, assume no receipt of a window scaling option means the
 492        remote TCP is broken and treats the window as a signed quantity.
 493        If unset, assume the remote TCP is not broken even if we do
 494        not receive a window scaling option from them.
 495        Default: 0
 496
 497tcp_dma_copybreak - INTEGER
 498        Lower limit, in bytes, of the size of socket reads that will be
 499        offloaded to a DMA copy engine, if one is present in the system
 500        and CONFIG_NET_DMA is enabled.
 501        Default: 4096
 502
 503tcp_thin_linear_timeouts - BOOLEAN
 504        Enable dynamic triggering of linear timeouts for thin streams.
 505        If set, a check is performed upon retransmission by timeout to
 506        determine if the stream is thin (less than 4 packets in flight).
 507        As long as the stream is found to be thin, up to 6 linear
 508        timeouts may be performed before exponential backoff mode is
 509        initiated. This improves retransmission latency for
 510        non-aggressive thin streams, often found to be time-dependent.
 511        For more information on thin streams, see
 512        Documentation/networking/tcp-thin.txt
 513        Default: 0
 514
 515tcp_thin_dupack - BOOLEAN
 516        Enable dynamic triggering of retransmissions after one dupACK
 517        for thin streams. If set, a check is performed upon reception
 518        of a dupACK to determine if the stream is thin (less than 4
 519        packets in flight). As long as the stream is found to be thin,
 520        data is retransmitted on the first received dupACK. This
 521        improves retransmission latency for non-aggressive thin
 522        streams, often found to be time-dependent.
 523        For more information on thin streams, see
 524        Documentation/networking/tcp-thin.txt
 525        Default: 0
 526
 527UDP variables:
 528
 529udp_mem - vector of 3 INTEGERs: min, pressure, max
 530        Number of pages allowed for queueing by all UDP sockets.
 531
 532        min: Below this number of pages UDP is not bothered about its
 533        memory appetite. When amount of memory allocated by UDP exceeds
 534        this number, UDP starts to moderate memory usage.
 535
 536        pressure: This value was introduced to follow format of tcp_mem.
 537
 538        max: Number of pages allowed for queueing by all UDP sockets.
 539
 540        Default is calculated at boot time from amount of available memory.
 541
 542udp_rmem_min - INTEGER
 543        Minimal size of receive buffer used by UDP sockets in moderation.
 544        Each UDP socket is able to use the size for receiving data, even if
 545        total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
 546        Default: 1 page
 547
 548udp_wmem_min - INTEGER
 549        Minimal size of send buffer used by UDP sockets in moderation.
 550        Each UDP socket is able to use the size for sending data, even if
 551        total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
 552        Default: 1 page
 553
 554CIPSOv4 Variables:
 555
 556cipso_cache_enable - BOOLEAN
 557        If set, enable additions to and lookups from the CIPSO label mapping
 558        cache.  If unset, additions are ignored and lookups always result in a
 559        miss.  However, regardless of the setting the cache is still
 560        invalidated when required when means you can safely toggle this on and
 561        off and the cache will always be "safe".
 562        Default: 1
 563
 564cipso_cache_bucket_size - INTEGER
 565        The CIPSO label cache consists of a fixed size hash table with each
 566        hash bucket containing a number of cache entries.  This variable limits
 567        the number of entries in each hash bucket; the larger the value the
 568        more CIPSO label mappings that can be cached.  When the number of
 569        entries in a given hash bucket reaches this limit adding new entries
 570        causes the oldest entry in the bucket to be removed to make room.
 571        Default: 10
 572
 573cipso_rbm_optfmt - BOOLEAN
 574        Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
 575        the CIPSO draft specification (see Documentation/netlabel for details).
 576        This means that when set the CIPSO tag will be padded with empty
 577        categories in order to make the packet data 32-bit aligned.
 578        Default: 0
 579
 580cipso_rbm_structvalid - BOOLEAN
 581        If set, do a very strict check of the CIPSO option when
 582        ip_options_compile() is called.  If unset, relax the checks done during
 583        ip_options_compile().  Either way is "safe" as errors are caught else
 584        where in the CIPSO processing code but setting this to 0 (False) should
 585        result in less work (i.e. it should be faster) but could cause problems
 586        with other implementations that require strict checking.
 587        Default: 0
 588
 589IP Variables:
 590
 591ip_local_port_range - 2 INTEGERS
 592        Defines the local port range that is used by TCP and UDP to
 593        choose the local port. The first number is the first, the
 594        second the last local port number. Default value depends on
 595        amount of memory available on the system:
 596        > 128Mb 32768-61000
 597        < 128Mb 1024-4999 or even less.
 598        This number defines number of active connections, which this
 599        system can issue simultaneously to systems not supporting
 600        TCP extensions (timestamps). With tcp_tw_recycle enabled
 601        (i.e. by default) range 1024-4999 is enough to issue up to
 602        2000 connections per second to systems supporting timestamps.
 603
 604ip_local_reserved_ports - list of comma separated ranges
 605        Specify the ports which are reserved for known third-party
 606        applications. These ports will not be used by automatic port
 607        assignments (e.g. when calling connect() or bind() with port
 608        number 0). Explicit port allocation behavior is unchanged.
 609
 610        The format used for both input and output is a comma separated
 611        list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and
 612        10). Writing to the file will clear all previously reserved
 613        ports and update the current list with the one given in the
 614        input.
 615
 616        Note that ip_local_port_range and ip_local_reserved_ports
 617        settings are independent and both are considered by the kernel
 618        when determining which ports are available for automatic port
 619        assignments.
 620
 621        You can reserve ports which are not in the current
 622        ip_local_port_range, e.g.:
 623
 624        $ cat /proc/sys/net/ipv4/ip_local_port_range
 625        32000   61000
 626        $ cat /proc/sys/net/ipv4/ip_local_reserved_ports
 627        8080,9148
 628
 629        although this is redundant. However such a setting is useful
 630        if later the port range is changed to a value that will
 631        include the reserved ports.
 632
 633        Default: Empty
 634
 635ip_nonlocal_bind - BOOLEAN
 636        If set, allows processes to bind() to non-local IP addresses,
 637        which can be quite useful - but may break some applications.
 638        Default: 0
 639
 640ip_dynaddr - BOOLEAN
 641        If set non-zero, enables support for dynamic addresses.
 642        If set to a non-zero value larger than 1, a kernel log
 643        message will be printed when dynamic address rewriting
 644        occurs.
 645        Default: 0
 646
 647icmp_echo_ignore_all - BOOLEAN
 648        If set non-zero, then the kernel will ignore all ICMP ECHO
 649        requests sent to it.
 650        Default: 0
 651
 652icmp_echo_ignore_broadcasts - BOOLEAN
 653        If set non-zero, then the kernel will ignore all ICMP ECHO and
 654        TIMESTAMP requests sent to it via broadcast/multicast.
 655        Default: 1
 656
 657icmp_ratelimit - INTEGER
 658        Limit the maximal rates for sending ICMP packets whose type matches
 659        icmp_ratemask (see below) to specific targets.
 660        0 to disable any limiting,
 661        otherwise the minimal space between responses in milliseconds.
 662        Default: 1000
 663
 664icmp_ratemask - INTEGER
 665        Mask made of ICMP types for which rates are being limited.
 666        Significant bits: IHGFEDCBA9876543210
 667        Default mask:     0000001100000011000 (6168)
 668
 669        Bit definitions (see include/linux/icmp.h):
 670                0 Echo Reply
 671                3 Destination Unreachable *
 672                4 Source Quench *
 673                5 Redirect
 674                8 Echo Request
 675                B Time Exceeded *
 676                C Parameter Problem *
 677                D Timestamp Request
 678                E Timestamp Reply
 679                F Info Request
 680                G Info Reply
 681                H Address Mask Request
 682                I Address Mask Reply
 683
 684        * These are rate limited by default (see default mask above)
 685
 686icmp_ignore_bogus_error_responses - BOOLEAN
 687        Some routers violate RFC1122 by sending bogus responses to broadcast
 688        frames.  Such violations are normally logged via a kernel warning.
 689        If this is set to TRUE, the kernel will not give such warnings, which
 690        will avoid log file clutter.
 691        Default: FALSE
 692
 693icmp_errors_use_inbound_ifaddr - BOOLEAN
 694
 695        If zero, icmp error messages are sent with the primary address of
 696        the exiting interface.
 697
 698        If non-zero, the message will be sent with the primary address of
 699        the interface that received the packet that caused the icmp error.
 700        This is the behaviour network many administrators will expect from
 701        a router. And it can make debugging complicated network layouts
 702        much easier.
 703
 704        Note that if no primary address exists for the interface selected,
 705        then the primary address of the first non-loopback interface that
 706        has one will be used regardless of this setting.
 707
 708        Default: 0
 709
 710igmp_max_memberships - INTEGER
 711        Change the maximum number of multicast groups we can subscribe to.
 712        Default: 20
 713
 714        Theoretical maximum value is bounded by having to send a membership
 715        report in a single datagram (i.e. the report can't span multiple
 716        datagrams, or risk confusing the switch and leaving groups you don't
 717        intend to).
 718
 719        The number of supported groups 'M' is bounded by the number of group
 720        report entries you can fit into a single datagram of 65535 bytes.
 721
 722        M = 65536-sizeof (ip header)/(sizeof(Group record))
 723
 724        Group records are variable length, with a minimum of 12 bytes.
 725        So net.ipv4.igmp_max_memberships should not be set higher than:
 726
 727        (65536-24) / 12 = 5459
 728
 729        The value 5459 assumes no IP header options, so in practice
 730        this number may be lower.
 731
 732        conf/interface/*  changes special settings per interface (where
 733        "interface" is the name of your network interface)
 734
 735        conf/all/*        is special, changes the settings for all interfaces
 736
 737log_martians - BOOLEAN
 738        Log packets with impossible addresses to kernel log.
 739        log_martians for the interface will be enabled if at least one of
 740        conf/{all,interface}/log_martians is set to TRUE,
 741        it will be disabled otherwise
 742
 743accept_redirects - BOOLEAN
 744        Accept ICMP redirect messages.
 745        accept_redirects for the interface will be enabled if:
 746        - both conf/{all,interface}/accept_redirects are TRUE in the case
 747          forwarding for the interface is enabled
 748        or
 749        - at least one of conf/{all,interface}/accept_redirects is TRUE in the
 750          case forwarding for the interface is disabled
 751        accept_redirects for the interface will be disabled otherwise
 752        default TRUE (host)
 753                FALSE (router)
 754
 755forwarding - BOOLEAN
 756        Enable IP forwarding on this interface.
 757
 758mc_forwarding - BOOLEAN
 759        Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
 760        and a multicast routing daemon is required.
 761        conf/all/mc_forwarding must also be set to TRUE to enable multicast
 762        routing for the interface
 763
 764medium_id - INTEGER
 765        Integer value used to differentiate the devices by the medium they
 766        are attached to. Two devices can have different id values when
 767        the broadcast packets are received only on one of them.
 768        The default value 0 means that the device is the only interface
 769        to its medium, value of -1 means that medium is not known.
 770
 771        Currently, it is used to change the proxy_arp behavior:
 772        the proxy_arp feature is enabled for packets forwarded between
 773        two devices attached to different media.
 774
 775proxy_arp - BOOLEAN
 776        Do proxy arp.
 777        proxy_arp for the interface will be enabled if at least one of
 778        conf/{all,interface}/proxy_arp is set to TRUE,
 779        it will be disabled otherwise
 780
 781proxy_arp_pvlan - BOOLEAN
 782        Private VLAN proxy arp.
 783        Basically allow proxy arp replies back to the same interface
 784        (from which the ARP request/solicitation was received).
 785
 786        This is done to support (ethernet) switch features, like RFC
 787        3069, where the individual ports are NOT allowed to
 788        communicate with each other, but they are allowed to talk to
 789        the upstream router.  As described in RFC 3069, it is possible
 790        to allow these hosts to communicate through the upstream
 791        router by proxy_arp'ing. Don't need to be used together with
 792        proxy_arp.
 793
 794        This technology is known by different names:
 795          In RFC 3069 it is called VLAN Aggregation.
 796          Cisco and Allied Telesyn call it Private VLAN.
 797          Hewlett-Packard call it Source-Port filtering or port-isolation.
 798          Ericsson call it MAC-Forced Forwarding (RFC Draft).
 799
 800shared_media - BOOLEAN
 801        Send(router) or accept(host) RFC1620 shared media redirects.
 802        Overrides ip_secure_redirects.
 803        shared_media for the interface will be enabled if at least one of
 804        conf/{all,interface}/shared_media is set to TRUE,
 805        it will be disabled otherwise
 806        default TRUE
 807
 808secure_redirects - BOOLEAN
 809        Accept ICMP redirect messages only for gateways,
 810        listed in default gateway list.
 811        secure_redirects for the interface will be enabled if at least one of
 812        conf/{all,interface}/secure_redirects is set to TRUE,
 813        it will be disabled otherwise
 814        default TRUE
 815
 816send_redirects - BOOLEAN
 817        Send redirects, if router.
 818        send_redirects for the interface will be enabled if at least one of
 819        conf/{all,interface}/send_redirects is set to TRUE,
 820        it will be disabled otherwise
 821        Default: TRUE
 822
 823bootp_relay - BOOLEAN
 824        Accept packets with source address 0.b.c.d destined
 825        not to this host as local ones. It is supposed, that
 826        BOOTP relay daemon will catch and forward such packets.
 827        conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
 828        for the interface
 829        default FALSE
 830        Not Implemented Yet.
 831
 832accept_source_route - BOOLEAN
 833        Accept packets with SRR option.
 834        conf/all/accept_source_route must also be set to TRUE to accept packets
 835        with SRR option on the interface
 836        default TRUE (router)
 837                FALSE (host)
 838
 839accept_local - BOOLEAN
 840        Accept packets with local source addresses. In combination with
 841        suitable routing, this can be used to direct packets between two
 842        local interfaces over the wire and have them accepted properly.
 843        default FALSE
 844
 845rp_filter - INTEGER
 846        0 - No source validation.
 847        1 - Strict mode as defined in RFC3704 Strict Reverse Path
 848            Each incoming packet is tested against the FIB and if the interface
 849            is not the best reverse path the packet check will fail.
 850            By default failed packets are discarded.
 851        2 - Loose mode as defined in RFC3704 Loose Reverse Path
 852            Each incoming packet's source address is also tested against the FIB
 853            and if the source address is not reachable via any interface
 854            the packet check will fail.
 855
 856        Current recommended practice in RFC3704 is to enable strict mode
 857        to prevent IP spoofing from DDos attacks. If using asymmetric routing
 858        or other complicated routing, then loose mode is recommended.
 859
 860        The max value from conf/{all,interface}/rp_filter is used
 861        when doing source validation on the {interface}.
 862
 863        Default value is 0. Note that some distributions enable it
 864        in startup scripts.
 865
 866arp_filter - BOOLEAN
 867        1 - Allows you to have multiple network interfaces on the same
 868        subnet, and have the ARPs for each interface be answered
 869        based on whether or not the kernel would route a packet from
 870        the ARP'd IP out that interface (therefore you must use source
 871        based routing for this to work). In other words it allows control
 872        of which cards (usually 1) will respond to an arp request.
 873
 874        0 - (default) The kernel can respond to arp requests with addresses
 875        from other interfaces. This may seem wrong but it usually makes
 876        sense, because it increases the chance of successful communication.
 877        IP addresses are owned by the complete host on Linux, not by
 878        particular interfaces. Only for more complex setups like load-
 879        balancing, does this behaviour cause problems.
 880
 881        arp_filter for the interface will be enabled if at least one of
 882        conf/{all,interface}/arp_filter is set to TRUE,
 883        it will be disabled otherwise
 884
 885arp_announce - INTEGER
 886        Define different restriction levels for announcing the local
 887        source IP address from IP packets in ARP requests sent on
 888        interface:
 889        0 - (default) Use any local address, configured on any interface
 890        1 - Try to avoid local addresses that are not in the target's
 891        subnet for this interface. This mode is useful when target
 892        hosts reachable via this interface require the source IP
 893        address in ARP requests to be part of their logical network
 894        configured on the receiving interface. When we generate the
 895        request we will check all our subnets that include the
 896        target IP and will preserve the source address if it is from
 897        such subnet. If there is no such subnet we select source
 898        address according to the rules for level 2.
 899        2 - Always use the best local address for this target.
 900        In this mode we ignore the source address in the IP packet
 901        and try to select local address that we prefer for talks with
 902        the target host. Such local address is selected by looking
 903        for primary IP addresses on all our subnets on the outgoing
 904        interface that include the target IP address. If no suitable
 905        local address is found we select the first local address
 906        we have on the outgoing interface or on all other interfaces,
 907        with the hope we will receive reply for our request and
 908        even sometimes no matter the source IP address we announce.
 909
 910        The max value from conf/{all,interface}/arp_announce is used.
 911
 912        Increasing the restriction level gives more chance for
 913        receiving answer from the resolved target while decreasing
 914        the level announces more valid sender's information.
 915
 916arp_ignore - INTEGER
 917        Define different modes for sending replies in response to
 918        received ARP requests that resolve local target IP addresses:
 919        0 - (default): reply for any local target IP address, configured
 920        on any interface
 921        1 - reply only if the target IP address is local address
 922        configured on the incoming interface
 923        2 - reply only if the target IP address is local address
 924        configured on the incoming interface and both with the
 925        sender's IP address are part from same subnet on this interface
 926        3 - do not reply for local addresses configured with scope host,
 927        only resolutions for global and link addresses are replied
 928        4-7 - reserved
 929        8 - do not reply for all local addresses
 930
 931        The max value from conf/{all,interface}/arp_ignore is used
 932        when ARP request is received on the {interface}
 933
 934arp_notify - BOOLEAN
 935        Define mode for notification of address and device changes.
 936        0 - (default): do nothing
 937        1 - Generate gratuitous arp requests when device is brought up
 938            or hardware address changes.
 939
 940arp_accept - BOOLEAN
 941        Define behavior for gratuitous ARP frames who's IP is not
 942        already present in the ARP table:
 943        0 - don't create new entries in the ARP table
 944        1 - create new entries in the ARP table
 945
 946        Both replies and requests type gratuitous arp will trigger the
 947        ARP table to be updated, if this setting is on.
 948
 949        If the ARP table already contains the IP address of the
 950        gratuitous arp frame, the arp table will be updated regardless
 951        if this setting is on or off.
 952
 953
 954app_solicit - INTEGER
 955        The maximum number of probes to send to the user space ARP daemon
 956        via netlink before dropping back to multicast probes (see
 957        mcast_solicit).  Defaults to 0.
 958
 959disable_policy - BOOLEAN
 960        Disable IPSEC policy (SPD) for this interface
 961
 962disable_xfrm - BOOLEAN
 963        Disable IPSEC encryption on this interface, whatever the policy
 964
 965
 966
 967tag - INTEGER
 968        Allows you to write a number, which can be used as required.
 969        Default value is 0.
 970
 971Alexey Kuznetsov.
 972kuznet@ms2.inr.ac.ru
 973
 974Updated by:
 975Andi Kleen
 976ak@muc.de
 977Nicolas Delon
 978delon.nicolas@wanadoo.fr
 979
 980
 981
 982
 983/proc/sys/net/ipv6/* Variables:
 984
 985IPv6 has no global variables such as tcp_*.  tcp_* settings under ipv4/ also
 986apply to IPv6 [XXX?].
 987
 988bindv6only - BOOLEAN
 989        Default value for IPV6_V6ONLY socket option,
 990        which restricts use of the IPv6 socket to IPv6 communication
 991        only.
 992                TRUE: disable IPv4-mapped address feature
 993                FALSE: enable IPv4-mapped address feature
 994
 995        Default: FALSE (as specified in RFC3493)
 996
 997IPv6 Fragmentation:
 998
 999ip6frag_high_thresh - INTEGER
1000        Maximum memory used to reassemble IPv6 fragments. When
1001        ip6frag_high_thresh bytes of memory is allocated for this purpose,
1002        the fragment handler will toss packets until ip6frag_low_thresh
1003        is reached.
1004
1005ip6frag_low_thresh - INTEGER
1006        See ip6frag_high_thresh
1007
1008ip6frag_time - INTEGER
1009        Time in seconds to keep an IPv6 fragment in memory.
1010
1011ip6frag_secret_interval - INTEGER
1012        Regeneration interval (in seconds) of the hash secret (or lifetime
1013        for the hash secret) for IPv6 fragments.
1014        Default: 600
1015
1016conf/default/*:
1017        Change the interface-specific default settings.
1018
1019
1020conf/all/*:
1021        Change all the interface-specific settings.
1022
1023        [XXX:  Other special features than forwarding?]
1024
1025conf/all/forwarding - BOOLEAN
1026        Enable global IPv6 forwarding between all interfaces.
1027
1028        IPv4 and IPv6 work differently here; e.g. netfilter must be used
1029        to control which interfaces may forward packets and which not.
1030
1031        This also sets all interfaces' Host/Router setting
1032        'forwarding' to the specified value.  See below for details.
1033
1034        This referred to as global forwarding.
1035
1036proxy_ndp - BOOLEAN
1037        Do proxy ndp.
1038
1039conf/interface/*:
1040        Change special settings per interface.
1041
1042        The functional behaviour for certain settings is different
1043        depending on whether local forwarding is enabled or not.
1044
1045accept_ra - INTEGER
1046        Accept Router Advertisements; autoconfigure using them.
1047
1048        It also determines whether or not to transmit Router
1049        Solicitations. If and only if the functional setting is to
1050        accept Router Advertisements, Router Solicitations will be
1051        transmitted.
1052
1053        Possible values are:
1054                0 Do not accept Router Advertisements.
1055                1 Accept Router Advertisements if forwarding is disabled.
1056                2 Overrule forwarding behaviour. Accept Router Advertisements
1057                  even if forwarding is enabled.
1058
1059        Functional default: enabled if local forwarding is disabled.
1060                            disabled if local forwarding is enabled.
1061
1062accept_ra_defrtr - BOOLEAN
1063        Learn default router in Router Advertisement.
1064
1065        Functional default: enabled if accept_ra is enabled.
1066                            disabled if accept_ra is disabled.
1067
1068accept_ra_pinfo - BOOLEAN
1069        Learn Prefix Information in Router Advertisement.
1070
1071        Functional default: enabled if accept_ra is enabled.
1072                            disabled if accept_ra is disabled.
1073
1074accept_ra_rt_info_max_plen - INTEGER
1075        Maximum prefix length of Route Information in RA.
1076
1077        Route Information w/ prefix larger than or equal to this
1078        variable shall be ignored.
1079
1080        Functional default: 0 if accept_ra_rtr_pref is enabled.
1081                            -1 if accept_ra_rtr_pref is disabled.
1082
1083accept_ra_rtr_pref - BOOLEAN
1084        Accept Router Preference in RA.
1085
1086        Functional default: enabled if accept_ra is enabled.
1087                            disabled if accept_ra is disabled.
1088
1089accept_redirects - BOOLEAN
1090        Accept Redirects.
1091
1092        Functional default: enabled if local forwarding is disabled.
1093                            disabled if local forwarding is enabled.
1094
1095accept_source_route - INTEGER
1096        Accept source routing (routing extension header).
1097
1098        >= 0: Accept only routing header type 2.
1099        < 0: Do not accept routing header.
1100
1101        Default: 0
1102
1103autoconf - BOOLEAN
1104        Autoconfigure addresses using Prefix Information in Router
1105        Advertisements.
1106
1107        Functional default: enabled if accept_ra_pinfo is enabled.
1108                            disabled if accept_ra_pinfo is disabled.
1109
1110dad_transmits - INTEGER
1111        The amount of Duplicate Address Detection probes to send.
1112        Default: 1
1113
1114forwarding - INTEGER
1115        Configure interface-specific Host/Router behaviour.
1116
1117        Note: It is recommended to have the same setting on all
1118        interfaces; mixed router/host scenarios are rather uncommon.
1119
1120        Possible values are:
1121                0 Forwarding disabled
1122                1 Forwarding enabled
1123
1124        FALSE (0):
1125
1126        By default, Host behaviour is assumed.  This means:
1127
1128        1. IsRouter flag is not set in Neighbour Advertisements.
1129        2. If accept_ra is TRUE (default), transmit Router
1130           Solicitations.
1131        3. If accept_ra is TRUE (default), accept Router
1132           Advertisements (and do autoconfiguration).
1133        4. If accept_redirects is TRUE (default), accept Redirects.
1134
1135        TRUE (1):
1136
1137        If local forwarding is enabled, Router behaviour is assumed.
1138        This means exactly the reverse from the above:
1139
1140        1. IsRouter flag is set in Neighbour Advertisements.
1141        2. Router Solicitations are not sent unless accept_ra is 2.
1142        3. Router Advertisements are ignored unless accept_ra is 2.
1143        4. Redirects are ignored.
1144
1145        Default: 0 (disabled) if global forwarding is disabled (default),
1146                 otherwise 1 (enabled).
1147
1148hop_limit - INTEGER
1149        Default Hop Limit to set.
1150        Default: 64
1151
1152mtu - INTEGER
1153        Default Maximum Transfer Unit
1154        Default: 1280 (IPv6 required minimum)
1155
1156router_probe_interval - INTEGER
1157        Minimum interval (in seconds) between Router Probing described
1158        in RFC4191.
1159
1160        Default: 60
1161
1162router_solicitation_delay - INTEGER
1163        Number of seconds to wait after interface is brought up
1164        before sending Router Solicitations.
1165        Default: 1
1166
1167router_solicitation_interval - INTEGER
1168        Number of seconds to wait between Router Solicitations.
1169        Default: 4
1170
1171router_solicitations - INTEGER
1172        Number of Router Solicitations to send until assuming no
1173        routers are present.
1174        Default: 3
1175
1176use_tempaddr - INTEGER
1177        Preference for Privacy Extensions (RFC3041).
1178          <= 0 : disable Privacy Extensions
1179          == 1 : enable Privacy Extensions, but prefer public
1180                 addresses over temporary addresses.
1181          >  1 : enable Privacy Extensions and prefer temporary
1182                 addresses over public addresses.
1183        Default:  0 (for most devices)
1184                 -1 (for point-to-point devices and loopback devices)
1185
1186temp_valid_lft - INTEGER
1187        valid lifetime (in seconds) for temporary addresses.
1188        Default: 604800 (7 days)
1189
1190temp_prefered_lft - INTEGER
1191        Preferred lifetime (in seconds) for temporary addresses.
1192        Default: 86400 (1 day)
1193
1194max_desync_factor - INTEGER
1195        Maximum value for DESYNC_FACTOR, which is a random value
1196        that ensures that clients don't synchronize with each
1197        other and generate new addresses at exactly the same time.
1198        value is in seconds.
1199        Default: 600
1200
1201regen_max_retry - INTEGER
1202        Number of attempts before give up attempting to generate
1203        valid temporary addresses.
1204        Default: 5
1205
1206max_addresses - INTEGER
1207        Maximum number of autoconfigured addresses per interface.  Setting
1208        to zero disables the limitation.  It is not recommended to set this
1209        value too large (or to zero) because it would be an easy way to
1210        crash the kernel by allowing too many addresses to be created.
1211        Default: 16
1212
1213disable_ipv6 - BOOLEAN
1214        Disable IPv6 operation.  If accept_dad is set to 2, this value
1215        will be dynamically set to TRUE if DAD fails for the link-local
1216        address.
1217        Default: FALSE (enable IPv6 operation)
1218
1219        When this value is changed from 1 to 0 (IPv6 is being enabled),
1220        it will dynamically create a link-local address on the given
1221        interface and start Duplicate Address Detection, if necessary.
1222
1223        When this value is changed from 0 to 1 (IPv6 is being disabled),
1224        it will dynamically delete all address on the given interface.
1225
1226accept_dad - INTEGER
1227        Whether to accept DAD (Duplicate Address Detection).
1228        0: Disable DAD
1229        1: Enable DAD (default)
1230        2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
1231           link-local address has been found.
1232
1233force_tllao - BOOLEAN
1234        Enable sending the target link-layer address option even when
1235        responding to a unicast neighbor solicitation.
1236        Default: FALSE
1237
1238        Quoting from RFC 2461, section 4.4, Target link-layer address:
1239
1240        "The option MUST be included for multicast solicitations in order to
1241        avoid infinite Neighbor Solicitation "recursion" when the peer node
1242        does not have a cache entry to return a Neighbor Advertisements
1243        message.  When responding to unicast solicitations, the option can be
1244        omitted since the sender of the solicitation has the correct link-
1245        layer address; otherwise it would not have be able to send the unicast
1246        solicitation in the first place. However, including the link-layer
1247        address in this case adds little overhead and eliminates a potential
1248        race condition where the sender deletes the cached link-layer address
1249        prior to receiving a response to a previous solicitation."
1250
1251icmp/*:
1252ratelimit - INTEGER
1253        Limit the maximal rates for sending ICMPv6 packets.
1254        0 to disable any limiting,
1255        otherwise the minimal space between responses in milliseconds.
1256        Default: 1000
1257
1258
1259IPv6 Update by:
1260Pekka Savola <pekkas@netcore.fi>
1261YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
1262
1263
1264/proc/sys/net/bridge/* Variables:
1265
1266bridge-nf-call-arptables - BOOLEAN
1267        1 : pass bridged ARP traffic to arptables' FORWARD chain.
1268        0 : disable this.
1269        Default: 1
1270
1271bridge-nf-call-iptables - BOOLEAN
1272        1 : pass bridged IPv4 traffic to iptables' chains.
1273        0 : disable this.
1274        Default: 1
1275
1276bridge-nf-call-ip6tables - BOOLEAN
1277        1 : pass bridged IPv6 traffic to ip6tables' chains.
1278        0 : disable this.
1279        Default: 1
1280
1281bridge-nf-filter-vlan-tagged - BOOLEAN
1282        1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
1283        0 : disable this.
1284        Default: 1
1285
1286bridge-nf-filter-pppoe-tagged - BOOLEAN
1287        1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
1288        0 : disable this.
1289        Default: 1
1290
1291
1292proc/sys/net/sctp/* Variables:
1293
1294addip_enable - BOOLEAN
1295        Enable or disable extension of  Dynamic Address Reconfiguration
1296        (ADD-IP) functionality specified in RFC5061.  This extension provides
1297        the ability to dynamically add and remove new addresses for the SCTP
1298        associations.
1299
1300        1: Enable extension.
1301
1302        0: Disable extension.
1303
1304        Default: 0
1305
1306addip_noauth_enable - BOOLEAN
1307        Dynamic Address Reconfiguration (ADD-IP) requires the use of
1308        authentication to protect the operations of adding or removing new
1309        addresses.  This requirement is mandated so that unauthorized hosts
1310        would not be able to hijack associations.  However, older
1311        implementations may not have implemented this requirement while
1312        allowing the ADD-IP extension.  For reasons of interoperability,
1313        we provide this variable to control the enforcement of the
1314        authentication requirement.
1315
1316        1: Allow ADD-IP extension to be used without authentication.  This
1317           should only be set in a closed environment for interoperability
1318           with older implementations.
1319
1320        0: Enforce the authentication requirement
1321
1322        Default: 0
1323
1324auth_enable - BOOLEAN
1325        Enable or disable Authenticated Chunks extension.  This extension
1326        provides the ability to send and receive authenticated chunks and is
1327        required for secure operation of Dynamic Address Reconfiguration
1328        (ADD-IP) extension.
1329
1330        1: Enable this extension.
1331        0: Disable this extension.
1332
1333        Default: 0
1334
1335prsctp_enable - BOOLEAN
1336        Enable or disable the Partial Reliability extension (RFC3758) which
1337        is used to notify peers that a given DATA should no longer be expected.
1338
1339        1: Enable extension
1340        0: Disable
1341
1342        Default: 1
1343
1344max_burst - INTEGER
1345        The limit of the number of new packets that can be initially sent.  It
1346        controls how bursty the generated traffic can be.
1347
1348        Default: 4
1349
1350association_max_retrans - INTEGER
1351        Set the maximum number for retransmissions that an association can
1352        attempt deciding that the remote end is unreachable.  If this value
1353        is exceeded, the association is terminated.
1354
1355        Default: 10
1356
1357max_init_retransmits - INTEGER
1358        The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
1359        that an association will attempt before declaring the destination
1360        unreachable and terminating.
1361
1362        Default: 8
1363
1364path_max_retrans - INTEGER
1365        The maximum number of retransmissions that will be attempted on a given
1366        path.  Once this threshold is exceeded, the path is considered
1367        unreachable, and new traffic will use a different path when the
1368        association is multihomed.
1369
1370        Default: 5
1371
1372rto_initial - INTEGER
1373        The initial round trip timeout value in milliseconds that will be used
1374        in calculating round trip times.  This is the initial time interval
1375        for retransmissions.
1376
1377        Default: 3000
1378
1379rto_max - INTEGER
1380        The maximum value (in milliseconds) of the round trip timeout.  This
1381        is the largest time interval that can elapse between retransmissions.
1382
1383        Default: 60000
1384
1385rto_min - INTEGER
1386        The minimum value (in milliseconds) of the round trip timeout.  This
1387        is the smallest time interval the can elapse between retransmissions.
1388
1389        Default: 1000
1390
1391hb_interval - INTEGER
1392        The interval (in milliseconds) between HEARTBEAT chunks.  These chunks
1393        are sent at the specified interval on idle paths to probe the state of
1394        a given path between 2 associations.
1395
1396        Default: 30000
1397
1398sack_timeout - INTEGER
1399        The amount of time (in milliseconds) that the implementation will wait
1400        to send a SACK.
1401
1402        Default: 200
1403
1404valid_cookie_life - INTEGER
1405        The default lifetime of the SCTP cookie (in milliseconds).  The cookie
1406        is used during association establishment.
1407
1408        Default: 60000
1409
1410cookie_preserve_enable - BOOLEAN
1411        Enable or disable the ability to extend the lifetime of the SCTP cookie
1412        that is used during the establishment phase of SCTP association
1413
1414        1: Enable cookie lifetime extension.
1415        0: Disable
1416
1417        Default: 1
1418
1419rcvbuf_policy - INTEGER
1420        Determines if the receive buffer is attributed to the socket or to
1421        association.   SCTP supports the capability to create multiple
1422        associations on a single socket.  When using this capability, it is
1423        possible that a single stalled association that's buffering a lot
1424        of data may block other associations from delivering their data by
1425        consuming all of the receive buffer space.  To work around this,
1426        the rcvbuf_policy could be set to attribute the receiver buffer space
1427        to each association instead of the socket.  This prevents the described
1428        blocking.
1429
1430        1: rcvbuf space is per association
1431        0: recbuf space is per socket
1432
1433        Default: 0
1434
1435sndbuf_policy - INTEGER
1436        Similar to rcvbuf_policy above, this applies to send buffer space.
1437
1438        1: Send buffer is tracked per association
1439        0: Send buffer is tracked per socket.
1440
1441        Default: 0
1442
1443sctp_mem - vector of 3 INTEGERs: min, pressure, max
1444        Number of pages allowed for queueing by all SCTP sockets.
1445
1446        min: Below this number of pages SCTP is not bothered about its
1447        memory appetite. When amount of memory allocated by SCTP exceeds
1448        this number, SCTP starts to moderate memory usage.
1449
1450        pressure: This value was introduced to follow format of tcp_mem.
1451
1452        max: Number of pages allowed for queueing by all SCTP sockets.
1453
1454        Default is calculated at boot time from amount of available memory.
1455
1456sctp_rmem - vector of 3 INTEGERs: min, default, max
1457        Only the first value ("min") is used, "default" and "max" are
1458        ignored.
1459
1460        min: Minimal size of receive buffer used by SCTP socket.
1461        It is guaranteed to each SCTP socket (but not association) even
1462        under moderate memory pressure.
1463
1464        Default: 1 page
1465
1466sctp_wmem  - vector of 3 INTEGERs: min, default, max
1467        Currently this tunable has no effect.
1468
1469addr_scope_policy - INTEGER
1470        Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00
1471
1472        0   - Disable IPv4 address scoping
1473        1   - Enable IPv4 address scoping
1474        2   - Follow draft but allow IPv4 private addresses
1475        3   - Follow draft but allow IPv4 link local addresses
1476
1477        Default: 1
1478
1479
1480/proc/sys/net/core/*
1481dev_weight - INTEGER
1482        The maximum number of packets that kernel can handle on a NAPI
1483        interrupt, it's a Per-CPU variable.
1484
1485        Default: 64
1486
1487/proc/sys/net/unix/*
1488max_dgram_qlen - INTEGER
1489        The maximum length of dgram socket receive queue
1490
1491        Default: 10
1492
1493
1494UNDOCUMENTED:
1495
1496/proc/sys/net/irda/*
1497        fast_poll_increase FIXME
1498        warn_noreply_time FIXME
1499        discovery_slots FIXME
1500        slot_timeout FIXME
1501        max_baud_rate FIXME
1502        discovery_timeout FIXME
1503        lap_keepalive_time FIXME
1504        max_noreply_time FIXME
1505        max_tx_data_size FIXME
1506        max_tx_window FIXME
1507        min_tx_turn_time FIXME
1508
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