linux/Documentation/networking/ip-sysctl.txt History
<<
>>
Prefs
   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 64
  15
  16ip_no_pmtu_disc - BOOLEAN
  17        Disable Path MTU Discovery.
  18        default FALSE
  19
  20min_pmtu - INTEGER
  21        default 562 - minimum discovered Path MTU
  22
  23mtu_expires - INTEGER
  24        Time, in seconds, that cached PMTU information is kept.
  25
  26min_adv_mss - INTEGER
  27        The advertised MSS depends on the first hop route MTU, but will
  28        never be lower than this setting.
  29
  30rt_cache_rebuild_count - INTEGER
  31        The per net-namespace route cache emergency rebuild threshold.
  32        Any net-namespace having its route cache rebuilt due to
  33        a hash bucket chain being too long more than this many times
  34        will have its route caching disabled
  35
  36IP Fragmentation:
  37
  38ipfrag_high_thresh - INTEGER
  39        Maximum memory used to reassemble IP fragments. When
  40        ipfrag_high_thresh bytes of memory is allocated for this purpose,
  41        the fragment handler will toss packets until ipfrag_low_thresh
  42        is reached.
  43
  44ipfrag_low_thresh - INTEGER
  45        See ipfrag_high_thresh
  46
  47ipfrag_time - INTEGER
  48        Time in seconds to keep an IP fragment in memory.
  49
  50ipfrag_secret_interval - INTEGER
  51        Regeneration interval (in seconds) of the hash secret (or lifetime
  52        for the hash secret) for IP fragments.
  53        Default: 600
  54
  55ipfrag_max_dist - INTEGER
  56        ipfrag_max_dist is a non-negative integer value which defines the
  57        maximum "disorder" which is allowed among fragments which share a
  58        common IP source address. Note that reordering of packets is
  59        not unusual, but if a large number of fragments arrive from a source
  60        IP address while a particular fragment queue remains incomplete, it
  61        probably indicates that one or more fragments belonging to that queue
  62        have been lost. When ipfrag_max_dist is positive, an additional check
  63        is done on fragments before they are added to a reassembly queue - if
  64        ipfrag_max_dist (or more) fragments have arrived from a particular IP
  65        address between additions to any IP fragment queue using that source
  66        address, it's presumed that one or more fragments in the queue are
  67        lost. The existing fragment queue will be dropped, and a new one
  68        started. An ipfrag_max_dist value of zero disables this check.
  69
  70        Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
  71        result in unnecessarily dropping fragment queues when normal
  72        reordering of packets occurs, which could lead to poor application
  73        performance. Using a very large value, e.g. 50000, increases the
  74        likelihood of incorrectly reassembling IP fragments that originate
  75        from different IP datagrams, which could result in data corruption.
  76        Default: 64
  77
  78INET peer storage:
  79
  80inet_peer_threshold - INTEGER
  81        The approximate size of the storage.  Starting from this threshold
  82        entries will be thrown aggressively.  This threshold also determines
  83        entries' time-to-live and time intervals between garbage collection
  84        passes.  More entries, less time-to-live, less GC interval.
  85
  86inet_peer_minttl - INTEGER
  87        Minimum time-to-live of entries.  Should be enough to cover fragment
  88        time-to-live on the reassembling side.  This minimum time-to-live  is
  89        guaranteed if the pool size is less than inet_peer_threshold.
  90        Measured in seconds.
  91
  92inet_peer_maxttl - INTEGER
  93        Maximum time-to-live of entries.  Unused entries will expire after
  94        this period of time if there is no memory pressure on the pool (i.e.
  95        when the number of entries in the pool is very small).
  96        Measured in seconds.
  97
  98inet_peer_gc_mintime - INTEGER
  99        Minimum interval between garbage collection passes.  This interval is
 100        in effect under high memory pressure on the pool.
 101        Measured in seconds.
 102
 103inet_peer_gc_maxtime - INTEGER
 104        Minimum interval between garbage collection passes.  This interval is
 105        in effect under low (or absent) memory pressure on the pool.
 106        Measured in seconds.
 107
 108TCP variables:
 109
 110somaxconn - INTEGER
 111        Limit of socket listen() backlog, known in userspace as SOMAXCONN.
 112        Defaults to 128.  See also tcp_max_syn_backlog for additional tuning
 113        for TCP sockets.
 114
 115tcp_abc - INTEGER
 116        Controls Appropriate Byte Count (ABC) defined in RFC3465.
 117        ABC is a way of increasing congestion window (cwnd) more slowly
 118        in response to partial acknowledgments.
 119        Possible values are:
 120                0 increase cwnd once per acknowledgment (no ABC)
 121                1 increase cwnd once per acknowledgment of full sized segment
 122                2 allow increase cwnd by two if acknowledgment is
 123                  of two segments to compensate for delayed acknowledgments.
 124        Default: 0 (off)
 125
 126tcp_abort_on_overflow - BOOLEAN
 127        If listening service is too slow to accept new connections,
 128        reset them. Default state is FALSE. It means that if overflow
 129        occurred due to a burst, connection will recover. Enable this
 130        option _only_ if you are really sure that listening daemon
 131        cannot be tuned to accept connections faster. Enabling this
 132        option can harm clients of your server.
 133
 134tcp_adv_win_scale - INTEGER
 135        Count buffering overhead as bytes/2^tcp_adv_win_scale
 136        (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
 137        if it is <= 0.
 138        Default: 2
 139
 140tcp_allowed_congestion_control - STRING
 141        Show/set the congestion control choices available to non-privileged
 142        processes. The list is a subset of those listed in
 143        tcp_available_congestion_control.
 144        Default is "reno" and the default setting (tcp_congestion_control).
 145
 146tcp_app_win - INTEGER
 147        Reserve max(window/2^tcp_app_win, mss) of window for application
 148        buffer. Value 0 is special, it means that nothing is reserved.
 149        Default: 31
 150
 151tcp_available_congestion_control - STRING
 152        Shows the available congestion control choices that are registered.
 153        More congestion control algorithms may be available as modules,
 154        but not loaded.
 155
 156tcp_base_mss - INTEGER
 157        The initial value of search_low to be used by the packetization layer
 158        Path MTU discovery (MTU probing).  If MTU probing is enabled,
 159        this is the initial MSS used by the connection.
 160
 161tcp_congestion_control - STRING
 162        Set the congestion control algorithm to be used for new
 163        connections. The algorithm "reno" is always available, but
 164        additional choices may be available based on kernel configuration.
 165        Default is set as part of kernel configuration.
 166
 167tcp_cookie_size - INTEGER
 168        Default size of TCP Cookie Transactions (TCPCT) option, that may be
 169        overridden on a per socket basis by the TCPCT socket option.
 170        Values greater than the maximum (16) are interpreted as the maximum.
 171        Values greater than zero and less than the minimum (8) are interpreted
 172        as the minimum.  Odd values are interpreted as the next even value.
 173        Default: 0 (off).
 174
 175tcp_dsack - BOOLEAN
 176        Allows TCP to send "duplicate" SACKs.
 177
 178tcp_ecn - BOOLEAN
 179        Enable Explicit Congestion Notification (ECN) in TCP. ECN is only
 180        used when both ends of the TCP flow support it. It is useful to
 181        avoid losses due to congestion (when the bottleneck router supports
 182        ECN).
 183        Possible values are:
 184                0 disable ECN
 185                1 ECN enabled
 186                2 Only server-side ECN enabled. If the other end does
 187                  not support ECN, behavior is like with ECN disabled.
 188        Default: 2
 189
 190tcp_fack - BOOLEAN
 191        Enable FACK congestion avoidance and fast retransmission.
 192        The value is not used, if tcp_sack is not enabled.
 193
 194tcp_fin_timeout - INTEGER
 195        Time to hold socket in state FIN-WAIT-2, if it was closed
 196        by our side. Peer can be broken and never close its side,
 197        or even died unexpectedly. Default value is 60sec.
 198        Usual value used in 2.2 was 180 seconds, you may restore
 199        it, but remember that if your machine is even underloaded WEB server,
 200        you risk to overflow memory with kilotons of dead sockets,
 201        FIN-WAIT-2 sockets are less dangerous than FIN-WAIT-1,
 202        because they eat maximum 1.5K of memory, but they tend
 203        to live longer. Cf. tcp_max_orphans.
 204
 205tcp_frto - INTEGER
 206        Enables Forward RTO-Recovery (F-RTO) defined in RFC4138.
 207        F-RTO is an enhanced recovery algorithm for TCP retransmission
 208        timeouts.  It is particularly beneficial in wireless environments
 209        where packet loss is typically due to random radio interference
 210        rather than intermediate router congestion.  F-RTO is sender-side
 211        only modification. Therefore it does not require any support from
 212        the peer.
 213
 214        If set to 1, basic version is enabled.  2 enables SACK enhanced
 215        F-RTO if flow uses SACK.  The basic version can be used also when
 216        SACK is in use though scenario(s) with it exists where F-RTO
 217        interacts badly with the packet counting of the SACK enabled TCP
 218        flow.
 219
 220tcp_frto_response - INTEGER
 221        When F-RTO has detected that a TCP retransmission timeout was
 222        spurious (i.e, the timeout would have been avoided had TCP set a
 223        longer retransmission timeout), TCP has several options what to do
 224        next. Possible values are:
 225                0 Rate halving based; a smooth and conservative response,
 226                  results in halved cwnd and ssthresh after one RTT
 227                1 Very conservative response; not recommended because even
 228                  though being valid, it interacts poorly with the rest of
 229                  Linux TCP, halves cwnd and ssthresh immediately
 230                2 Aggressive response; undoes congestion control measures
 231                  that are now known to be unnecessary (ignoring the
 232                  possibility of a lost retransmission that would require
 233                  TCP to be more cautious), cwnd and ssthresh are restored
 234                  to the values prior timeout
 235        Default: 0 (rate halving based)
 236
 237tcp_keepalive_time - INTEGER
 238        How often TCP sends out keepalive messages when keepalive is enabled.
 239        Default: 2hours.
 240
 241tcp_keepalive_probes - INTEGER
 242        How many keepalive probes TCP sends out, until it decides that the
 243        connection is broken. Default value: 9.
 244
 245tcp_keepalive_intvl - INTEGER
 246        How frequently the probes are send out. Multiplied by
 247        tcp_keepalive_probes it is time to kill not responding connection,
 248        after probes started. Default value: 75sec i.e. connection
 249        will be aborted after ~11 minutes of retries.
 250
 251tcp_low_latency - BOOLEAN
 252        If set, the TCP stack makes decisions that prefer lower
 253        latency as opposed to higher throughput.  By default, this
 254        option is not set meaning that higher throughput is preferred.
 255        An example of an application where this default should be
 256        changed would be a Beowulf compute cluster.
 257        Default: 0
 258
 259tcp_max_orphans - INTEGER
 260        Maximal number of TCP sockets not attached to any user file handle,
 261        held by system. If this number is exceeded orphaned connections are
 262        reset immediately and warning is printed. This limit exists
 263        only to prevent simple DoS attacks, you _must_ not rely on this
 264        or lower the limit artificially, but rather increase it
 265        (probably, after increasing installed memory),
 266        if network conditions require more than default value,
 267        and tune network services to linger and kill such states
 268        more aggressively. Let me to remind again: each orphan eats
 269        up to ~64K of unswappable memory.
 270
 271tcp_max_syn_backlog - INTEGER
 272        Maximal number of remembered connection requests, which are
 273        still did not receive an acknowledgment from connecting client.
 274        Default value is 1024 for systems with more than 128Mb of memory,
 275        and 128 for low memory machines. If server suffers of overload,
 276        try to increase this number.
 277
 278tcp_max_tw_buckets - INTEGER
 279        Maximal number of timewait sockets held by system simultaneously.
 280        If this number is exceeded time-wait socket is immediately destroyed
 281        and warning is printed. This limit exists only to prevent
 282        simple DoS attacks, you _must_ not lower the limit artificially,
 283        but rather increase it (probably, after increasing installed memory),
 284        if network conditions require more than default value.
 285
 286tcp_mem - vector of 3 INTEGERs: min, pressure, max
 287        min: below this number of pages TCP is not bothered about its
 288        memory appetite.
 289
 290        pressure: when amount of memory allocated by TCP exceeds this number
 291        of pages, TCP moderates its memory consumption and enters memory
 292        pressure mode, which is exited when memory consumption falls
 293        under "min".
 294
 295        max: number of pages allowed for queueing by all TCP sockets.
 296
 297        Defaults are calculated at boot time from amount of available
 298        memory.
 299
 300tcp_moderate_rcvbuf - BOOLEAN
 301        If set, TCP performs receive buffer auto-tuning, attempting to
 302        automatically size the buffer (no greater than tcp_rmem[2]) to
 303        match the size required by the path for full throughput.  Enabled by
 304        default.
 305
 306tcp_mtu_probing - INTEGER
 307        Controls TCP Packetization-Layer Path MTU Discovery.  Takes three
 308        values:
 309          0 - Disabled
 310          1 - Disabled by default, enabled when an ICMP black hole detected
 311          2 - Always enabled, use initial MSS of tcp_base_mss.
 312
 313tcp_no_metrics_save - BOOLEAN
 314        By default, TCP saves various connection metrics in the route cache
 315        when the connection closes, so that connections established in the
 316        near future can use these to set initial conditions.  Usually, this
 317        increases overall performance, but may sometimes cause performance
 318        degradation.  If set, TCP will not cache metrics on closing
 319        connections.
 320
 321tcp_orphan_retries - INTEGER
 322        This value influences the timeout of a locally closed TCP connection,
 323        when RTO retransmissions remain unacknowledged.
 324        See tcp_retries2 for more details.
 325
 326        The default value is 7.
 327        If your machine is a loaded WEB server,
 328        you should think about lowering this value, such sockets
 329        may consume significant resources. Cf. tcp_max_orphans.
 330
 331tcp_reordering - INTEGER
 332        Maximal reordering of packets in a TCP stream.
 333        Default: 3
 334
 335tcp_retrans_collapse - BOOLEAN
 336        Bug-to-bug compatibility with some broken printers.
 337        On retransmit try to send bigger packets to work around bugs in
 338        certain TCP stacks.
 339
 340tcp_retries1 - INTEGER
 341        This value influences the time, after which TCP decides, that
 342        something is wrong due to unacknowledged RTO retransmissions,
 343        and reports this suspicion to the network layer.
 344        See tcp_retries2 for more details.
 345
 346        RFC 1122 recommends at least 3 retransmissions, which is the
 347        default.
 348
 349tcp_retries2 - INTEGER
 350        This value influences the timeout of an alive TCP connection,
 351        when RTO retransmissions remain unacknowledged.
 352        Given a value of N, a hypothetical TCP connection following
 353        exponential backoff with an initial RTO of TCP_RTO_MIN would
 354        retransmit N times before killing the connection at the (N+1)th RTO.
 355
 356        The default value of 15 yields a hypothetical timeout of 924.6
 357        seconds and is a lower bound for the effective timeout.
 358        TCP will effectively time out at the first RTO which exceeds the
 359        hypothetical timeout.
 360
 361        RFC 1122 recommends at least 100 seconds for the timeout,
 362        which corresponds to a value of at least 8.
 363
 364tcp_rfc1337 - BOOLEAN
 365        If set, the TCP stack behaves conforming to RFC1337. If unset,
 366        we are not conforming to RFC, but prevent TCP TIME_WAIT
 367        assassination.
 368        Default: 0
 369
 370tcp_rmem - vector of 3 INTEGERs: min, default, max
 371        min: Minimal size of receive buffer used by TCP sockets.
 372        It is guaranteed to each TCP socket, even under moderate memory
 373        pressure.
 374        Default: 8K
 375
 376        default: initial size of receive buffer used by TCP sockets.
 377        This value overrides net.core.rmem_default used by other protocols.
 378        Default: 87380 bytes. This value results in window of 65535 with
 379        default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
 380        less for default tcp_app_win. See below about these variables.
 381
 382        max: maximal size of receive buffer allowed for automatically
 383        selected receiver buffers for TCP socket. This value does not override
 384        net.core.rmem_max.  Calling setsockopt() with SO_RCVBUF disables
 385        automatic tuning of that socket's receive buffer size, in which
 386        case this value is ignored.
 387        Default: between 87380B and 4MB, depending on RAM size.
 388
 389tcp_sack - BOOLEAN
 390        Enable select acknowledgments (SACKS).
 391
 392tcp_slow_start_after_idle - BOOLEAN
 393        If set, provide RFC2861 behavior and time out the congestion
 394        window after an idle period.  An idle period is defined at
 395        the current RTO.  If unset, the congestion window will not
 396        be timed out after an idle period.
 397        Default: 1
 398
 399tcp_stdurg - BOOLEAN
 400        Use the Host requirements interpretation of the TCP urgent pointer field.
 401        Most hosts use the older BSD interpretation, so if you turn this on
 402        Linux might not communicate correctly with them.
 403        Default: FALSE
 404
 405tcp_synack_retries - INTEGER
 406        Number of times SYNACKs for a passive TCP connection attempt will
 407        be retransmitted. Should not be higher than 255. Default value
 408        is 5, which corresponds to ~180seconds.
 409
 410tcp_syncookies - BOOLEAN
 411        Only valid when the kernel was compiled with CONFIG_SYNCOOKIES
 412        Send out syncookies when the syn backlog queue of a socket
 413        overflows. This is to prevent against the common 'SYN flood attack'
 414        Default: FALSE
 415
 416        Note, that syncookies is fallback facility.
 417        It MUST NOT be used to help highly loaded servers to stand
 418        against legal connection rate. If you see SYN flood warnings
 419        in your logs, but investigation shows that they occur
 420        because of overload with legal connections, you should tune
 421        another parameters until this warning disappear.
 422        See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
 423
 424        syncookies seriously violate TCP protocol, do not allow
 425        to use TCP extensions, can result in serious degradation
 426        of some services (f.e. SMTP relaying), visible not by you,
 427        but your clients and relays, contacting you. While you see
 428        SYN flood warnings in logs not being really flooded, your server
 429        is seriously misconfigured.
 430
 431tcp_syn_retries - INTEGER
 432        Number of times initial SYNs for an active TCP connection attempt
 433        will be retransmitted. Should not be higher than 255. Default value
 434        is 5, which corresponds to ~180seconds.
 435
 436tcp_timestamps - BOOLEAN
 437        Enable timestamps as defined in RFC1323.
 438
 439tcp_tso_win_divisor - INTEGER
 440        This allows control over what percentage of the congestion window
 441        can be consumed by a single TSO frame.
 442        The setting of this parameter is a choice between burstiness and
 443        building larger TSO frames.
 444        Default: 3
 445
 446tcp_tw_recycle - BOOLEAN
 447        Enable fast recycling TIME-WAIT sockets. Default value is 0.
 448        It should not be changed without advice/request of technical
 449        experts.
 450
 451tcp_tw_reuse - BOOLEAN
 452        Allow to reuse TIME-WAIT sockets for new connections when it is
 453        safe from protocol viewpoint. Default value is 0.
 454        It should not be changed without advice/request of technical
 455        experts.
 456
 457tcp_window_scaling - BOOLEAN
 458        Enable window scaling as defined in RFC1323.
 459
 460tcp_wmem - vector of 3 INTEGERs: min, default, max
 461        min: Amount of memory reserved for send buffers for TCP sockets.
 462        Each TCP socket has rights to use it due to fact of its birth.
 463        Default: 4K
 464
 465        default: initial size of send buffer used by TCP sockets.  This
 466        value overrides net.core.wmem_default used by other protocols.
 467        It is usually lower than net.core.wmem_default.
 468        Default: 16K
 469
 470        max: Maximal amount of memory allowed for automatically tuned
 471        send buffers for TCP sockets. This value does not override
 472        net.core.wmem_max.  Calling setsockopt() with SO_SNDBUF disables
 473        automatic tuning of that socket's send buffer size, in which case
 474        this value is ignored.
 475        Default: between 64K and 4MB, depending on RAM size.
 476
 477tcp_workaround_signed_windows - BOOLEAN
 478        If set, assume no receipt of a window scaling option means the
 479        remote TCP is broken and treats the window as a signed quantity.
 480        If unset, assume the remote TCP is not broken even if we do
 481        not receive a window scaling option from them.
 482        Default: 0
 483
 484tcp_dma_copybreak - INTEGER
 485        Lower limit, in bytes, of the size of socket reads that will be
 486        offloaded to a DMA copy engine, if one is present in the system
 487        and CONFIG_NET_DMA is enabled.
 488        Default: 4096
 489
 490tcp_thin_linear_timeouts - BOOLEAN
 491        Enable dynamic triggering of linear timeouts for thin streams.
 492        If set, a check is performed upon retransmission by timeout to
 493        determine if the stream is thin (less than 4 packets in flight).
 494        As long as the stream is found to be thin, up to 6 linear
 495        timeouts may be performed before exponential backoff mode is
 496        initiated. This improves retransmission latency for
 497        non-aggressive thin streams, often found to be time-dependent.
 498        For more information on thin streams, see
 499        Documentation/networking/tcp-thin.txt
 500        Default: 0
 501
 502tcp_thin_dupack - BOOLEAN
 503        Enable dynamic triggering of retransmissions after one dupACK
 504        for thin streams. If set, a check is performed upon reception
 505        of a dupACK to determine if the stream is thin (less than 4
 506        packets in flight). As long as the stream is found to be thin,
 507        data is retransmitted on the first received dupACK. This
 508        improves retransmission latency for non-aggressive thin
 509        streams, often found to be time-dependent.
 510        For more information on thin streams, see
 511        Documentation/networking/tcp-thin.txt
 512        Default: 0
 513
 514UDP variables:
 515
 516udp_mem - vector of 3 INTEGERs: min, pressure, max
 517        Number of pages allowed for queueing by all UDP sockets.
 518
 519        min: Below this number of pages UDP is not bothered about its
 520        memory appetite. When amount of memory allocated by UDP exceeds
 521        this number, UDP starts to moderate memory usage.
 522
 523        pressure: This value was introduced to follow format of tcp_mem.
 524
 525        max: Number of pages allowed for queueing by all UDP sockets.
 526
 527        Default is calculated at boot time from amount of available memory.
 528
 529udp_rmem_min - INTEGER
 530        Minimal size of receive buffer used by UDP sockets in moderation.
 531        Each UDP socket is able to use the size for receiving data, even if
 532        total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
 533        Default: 4096
 534
 535udp_wmem_min - INTEGER
 536        Minimal size of send buffer used by UDP sockets in moderation.
 537        Each UDP socket is able to use the size for sending data, even if
 538        total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
 539        Default: 4096
 540
 541CIPSOv4 Variables:
 542
 543cipso_cache_enable - BOOLEAN
 544        If set, enable additions to and lookups from the CIPSO label mapping
 545        cache.  If unset, additions are ignored and lookups always result in a
 546        miss.  However, regardless of the setting the cache is still
 547        invalidated when required when means you can safely toggle this on and
 548        off and the cache will always be "safe".
 549        Default: 1
 550
 551cipso_cache_bucket_size - INTEGER
 552        The CIPSO label cache consists of a fixed size hash table with each
 553        hash bucket containing a number of cache entries.  This variable limits
 554        the number of entries in each hash bucket; the larger the value the
 555        more CIPSO label mappings that can be cached.  When the number of
 556        entries in a given hash bucket reaches this limit adding new entries
 557        causes the oldest entry in the bucket to be removed to make room.
 558        Default: 10
 559
 560cipso_rbm_optfmt - BOOLEAN
 561        Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
 562        the CIPSO draft specification (see Documentation/netlabel for details).
 563        This means that when set the CIPSO tag will be padded with empty
 564        categories in order to make the packet data 32-bit aligned.
 565        Default: 0
 566
 567cipso_rbm_structvalid - BOOLEAN
 568        If set, do a very strict check of the CIPSO option when
 569        ip_options_compile() is called.  If unset, relax the checks done during
 570        ip_options_compile().  Either way is "safe" as errors are caught else
 571        where in the CIPSO processing code but setting this to 0 (False) should
 572        result in less work (i.e. it should be faster) but could cause problems
 573        with other implementations that require strict checking.
 574        Default: 0
 575
 576IP Variables:
 577
 578ip_local_port_range - 2 INTEGERS
 579        Defines the local port range that is used by TCP and UDP to
 580        choose the local port. The first number is the first, the
 581        second the last local port number. Default value depends on
 582        amount of memory available on the system:
 583        > 128Mb 32768-61000
 584        < 128Mb 1024-4999 or even less.
 585        This number defines number of active connections, which this
 586        system can issue simultaneously to systems not supporting
 587        TCP extensions (timestamps). With tcp_tw_recycle enabled
 588        (i.e. by default) range 1024-4999 is enough to issue up to
 589        2000 connections per second to systems supporting timestamps.
 590
 591ip_nonlocal_bind - BOOLEAN
 592        If set, allows processes to bind() to non-local IP addresses,
 593        which can be quite useful - but may break some applications.
 594        Default: 0
 595
 596ip_dynaddr - BOOLEAN
 597        If set non-zero, enables support for dynamic addresses.
 598        If set to a non-zero value larger than 1, a kernel log
 599        message will be printed when dynamic address rewriting
 600        occurs.
 601        Default: 0
 602
 603icmp_echo_ignore_all - BOOLEAN
 604        If set non-zero, then the kernel will ignore all ICMP ECHO
 605        requests sent to it.
 606        Default: 0
 607
 608icmp_echo_ignore_broadcasts - BOOLEAN
 609        If set non-zero, then the kernel will ignore all ICMP ECHO and
 610        TIMESTAMP requests sent to it via broadcast/multicast.
 611        Default: 1
 612
 613icmp_ratelimit - INTEGER
 614        Limit the maximal rates for sending ICMP packets whose type matches
 615        icmp_ratemask (see below) to specific targets.
 616        0 to disable any limiting,
 617        otherwise the minimal space between responses in milliseconds.
 618        Default: 1000
 619
 620icmp_ratemask - INTEGER
 621        Mask made of ICMP types for which rates are being limited.
 622        Significant bits: IHGFEDCBA9876543210
 623        Default mask:     0000001100000011000 (6168)
 624
 625        Bit definitions (see include/linux/icmp.h):
 626                0 Echo Reply
 627                3 Destination Unreachable *
 628                4 Source Quench *
 629                5 Redirect
 630                8 Echo Request
 631                B Time Exceeded *
 632                C Parameter Problem *
 633                D Timestamp Request
 634                E Timestamp Reply
 635                F Info Request
 636                G Info Reply
 637                H Address Mask Request
 638                I Address Mask Reply
 639
 640        * These are rate limited by default (see default mask above)
 641
 642icmp_ignore_bogus_error_responses - BOOLEAN
 643        Some routers violate RFC1122 by sending bogus responses to broadcast
 644        frames.  Such violations are normally logged via a kernel warning.
 645        If this is set to TRUE, the kernel will not give such warnings, which
 646        will avoid log file clutter.
 647        Default: FALSE
 648
 649icmp_errors_use_inbound_ifaddr - BOOLEAN
 650
 651        If zero, icmp error messages are sent with the primary address of
 652        the exiting interface.
 653
 654        If non-zero, the message will be sent with the primary address of
 655        the interface that received the packet that caused the icmp error.
 656        This is the behaviour network many administrators will expect from
 657        a router. And it can make debugging complicated network layouts
 658        much easier.
 659
 660        Note that if no primary address exists for the interface selected,
 661        then the primary address of the first non-loopback interface that
 662        has one will be used regardless of this setting.
 663
 664        Default: 0
 665
 666igmp_max_memberships - INTEGER
 667        Change the maximum number of multicast groups we can subscribe to.
 668        Default: 20
 669
 670conf/interface/*  changes special settings per interface (where "interface" is
 671                  the name of your network interface)
 672conf/all/*        is special, changes the settings for all interfaces
 673
 674
 675log_martians - BOOLEAN
 676        Log packets with impossible addresses to kernel log.
 677        log_martians for the interface will be enabled if at least one of
 678        conf/{all,interface}/log_martians is set to TRUE,
 679        it will be disabled otherwise
 680
 681accept_redirects - BOOLEAN
 682        Accept ICMP redirect messages.
 683        accept_redirects for the interface will be enabled if:
 684        - both conf/{all,interface}/accept_redirects are TRUE in the case
 685          forwarding for the interface is enabled
 686        or
 687        - at least one of conf/{all,interface}/accept_redirects is TRUE in the
 688          case forwarding for the interface is disabled
 689        accept_redirects for the interface will be disabled otherwise
 690        default TRUE (host)
 691                FALSE (router)
 692
 693forwarding - BOOLEAN
 694        Enable IP forwarding on this interface.
 695
 696mc_forwarding - BOOLEAN
 697        Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
 698        and a multicast routing daemon is required.
 699        conf/all/mc_forwarding must also be set to TRUE to enable multicast
 700        routing for the interface
 701
 702medium_id - INTEGER
 703        Integer value used to differentiate the devices by the medium they
 704        are attached to. Two devices can have different id values when
 705        the broadcast packets are received only on one of them.
 706        The default value 0 means that the device is the only interface
 707        to its medium, value of -1 means that medium is not known.
 708
 709        Currently, it is used to change the proxy_arp behavior:
 710        the proxy_arp feature is enabled for packets forwarded between
 711        two devices attached to different media.
 712
 713proxy_arp - BOOLEAN
 714        Do proxy arp.
 715        proxy_arp for the interface will be enabled if at least one of
 716        conf/{all,interface}/proxy_arp is set to TRUE,
 717        it will be disabled otherwise
 718
 719proxy_arp_pvlan - BOOLEAN
 720        Private VLAN proxy arp.
 721        Basically allow proxy arp replies back to the same interface
 722        (from which the ARP request/solicitation was received).
 723
 724        This is done to support (ethernet) switch features, like RFC
 725        3069, where the individual ports are NOT allowed to
 726        communicate with each other, but they are allowed to talk to
 727        the upstream router.  As described in RFC 3069, it is possible
 728        to allow these hosts to communicate through the upstream
 729        router by proxy_arp'ing. Don't need to be used together with
 730        proxy_arp.
 731
 732        This technology is known by different names:
 733          In RFC 3069 it is called VLAN Aggregation.
 734          Cisco and Allied Telesyn call it Private VLAN.
 735          Hewlett-Packard call it Source-Port filtering or port-isolation.
 736          Ericsson call it MAC-Forced Forwarding (RFC Draft).
 737
 738shared_media - BOOLEAN
 739        Send(router) or accept(host) RFC1620 shared media redirects.
 740        Overrides ip_secure_redirects.
 741        shared_media for the interface will be enabled if at least one of
 742        conf/{all,interface}/shared_media is set to TRUE,
 743        it will be disabled otherwise
 744        default TRUE
 745
 746secure_redirects - BOOLEAN
 747        Accept ICMP redirect messages only for gateways,
 748        listed in default gateway list.
 749        secure_redirects for the interface will be enabled if at least one of
 750        conf/{all,interface}/secure_redirects is set to TRUE,
 751        it will be disabled otherwise
 752        default TRUE
 753
 754send_redirects - BOOLEAN
 755        Send redirects, if router.
 756        send_redirects for the interface will be enabled if at least one of
 757        conf/{all,interface}/send_redirects is set to TRUE,
 758        it will be disabled otherwise
 759        Default: TRUE
 760
 761bootp_relay - BOOLEAN
 762        Accept packets with source address 0.b.c.d destined
 763        not to this host as local ones. It is supposed, that
 764        BOOTP relay daemon will catch and forward such packets.
 765        conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
 766        for the interface
 767        default FALSE
 768        Not Implemented Yet.
 769
 770accept_source_route - BOOLEAN
 771        Accept packets with SRR option.
 772        conf/all/accept_source_route must also be set to TRUE to accept packets
 773        with SRR option on the interface
 774        default TRUE (router)
 775                FALSE (host)
 776
 777accept_local - BOOLEAN
 778        Accept packets with local source addresses. In combination with
 779        suitable routing, this can be used to direct packets between two
 780        local interfaces over the wire and have them accepted properly.
 781        default FALSE
 782
 783rp_filter - INTEGER
 784        0 - No source validation.
 785        1 - Strict mode as defined in RFC3704 Strict Reverse Path
 786            Each incoming packet is tested against the FIB and if the interface
 787            is not the best reverse path the packet check will fail.
 788            By default failed packets are discarded.
 789        2 - Loose mode as defined in RFC3704 Loose Reverse Path
 790            Each incoming packet's source address is also tested against the FIB
 791            and if the source address is not reachable via any interface
 792            the packet check will fail.
 793
 794        Current recommended practice in RFC3704 is to enable strict mode
 795        to prevent IP spoofing from DDos attacks. If using asymmetric routing
 796        or other complicated routing, then loose mode is recommended.
 797
 798        The max value from conf/{all,interface}/rp_filter is used
 799        when doing source validation on the {interface}.
 800
 801        Default value is 0. Note that some distributions enable it
 802        in startup scripts.
 803
 804arp_filter - BOOLEAN
 805        1 - Allows you to have multiple network interfaces on the same
 806        subnet, and have the ARPs for each interface be answered
 807        based on whether or not the kernel would route a packet from
 808        the ARP'd IP out that interface (therefore you must use source
 809        based routing for this to work). In other words it allows control
 810        of which cards (usually 1) will respond to an arp request.
 811
 812        0 - (default) The kernel can respond to arp requests with addresses
 813        from other interfaces. This may seem wrong but it usually makes
 814        sense, because it increases the chance of successful communication.
 815        IP addresses are owned by the complete host on Linux, not by
 816        particular interfaces. Only for more complex setups like load-
 817        balancing, does this behaviour cause problems.
 818
 819        arp_filter for the interface will be enabled if at least one of
 820        conf/{all,interface}/arp_filter is set to TRUE,
 821        it will be disabled otherwise
 822
 823arp_announce - INTEGER
 824        Define different restriction levels for announcing the local
 825        source IP address from IP packets in ARP requests sent on
 826        interface:
 827        0 - (default) Use any local address, configured on any interface
 828        1 - Try to avoid local addresses that are not in the target's
 829        subnet for this interface. This mode is useful when target
 830        hosts reachable via this interface require the source IP
 831        address in ARP requests to be part of their logical network
 832        configured on the receiving interface. When we generate the
 833        request we will check all our subnets that include the
 834        target IP and will preserve the source address if it is from
 835        such subnet. If there is no such subnet we select source
 836        address according to the rules for level 2.
 837        2 - Always use the best local address for this target.
 838        In this mode we ignore the source address in the IP packet
 839        and try to select local address that we prefer for talks with
 840        the target host. Such local address is selected by looking
 841        for primary IP addresses on all our subnets on the outgoing
 842        interface that include the target IP address. If no suitable
 843        local address is found we select the first local address
 844        we have on the outgoing interface or on all other interfaces,
 845        with the hope we will receive reply for our request and
 846        even sometimes no matter the source IP address we announce.
 847
 848        The max value from conf/{all,interface}/arp_announce is used.
 849
 850        Increasing the restriction level gives more chance for
 851        receiving answer from the resolved target while decreasing
 852        the level announces more valid sender's information.
 853
 854arp_ignore - INTEGER
 855        Define different modes for sending replies in response to
 856        received ARP requests that resolve local target IP addresses:
 857        0 - (default): reply for any local target IP address, configured
 858        on any interface
 859        1 - reply only if the target IP address is local address
 860        configured on the incoming interface
 861        2 - reply only if the target IP address is local address
 862        configured on the incoming interface and both with the
 863        sender's IP address are part from same subnet on this interface
 864        3 - do not reply for local addresses configured with scope host,
 865        only resolutions for global and link addresses are replied
 866        4-7 - reserved
 867        8 - do not reply for all local addresses
 868
 869        The max value from conf/{all,interface}/arp_ignore is used
 870        when ARP request is received on the {interface}
 871
 872arp_notify - BOOLEAN
 873        Define mode for notification of address and device changes.
 874        0 - (default): do nothing
 875        1 - Generate gratuitous arp replies when device is brought up
 876            or hardware address changes.
 877
 878arp_accept - BOOLEAN
 879        Define behavior for gratuitous ARP frames who's IP is not
 880        already present in the ARP table:
 881        0 - don't create new entries in the ARP table
 882        1 - create new entries in the ARP table
 883
 884        Both replies and requests type gratuitous arp will trigger the
 885        ARP table to be updated, if this setting is on.
 886
 887        If the ARP table already contains the IP address of the
 888        gratuitous arp frame, the arp table will be updated regardless
 889        if this setting is on or off.
 890
 891
 892app_solicit - INTEGER
 893        The maximum number of probes to send to the user space ARP daemon
 894        via netlink before dropping back to multicast probes (see
 895        mcast_solicit).  Defaults to 0.
 896
 897disable_policy - BOOLEAN
 898        Disable IPSEC policy (SPD) for this interface
 899
 900disable_xfrm - BOOLEAN
 901        Disable IPSEC encryption on this interface, whatever the policy
 902
 903
 904
 905tag - INTEGER
 906        Allows you to write a number, which can be used as required.
 907        Default value is 0.
 908
 909Alexey Kuznetsov.
 910kuznet@ms2.inr.ac.ru
 911
 912Updated by:
 913Andi Kleen
 914ak@muc.de
 915Nicolas Delon
 916delon.nicolas@wanadoo.fr
 917
 918
 919
 920
 921/proc/sys/net/ipv6/* Variables:
 922
 923IPv6 has no global variables such as tcp_*.  tcp_* settings under ipv4/ also
 924apply to IPv6 [XXX?].
 925
 926bindv6only - BOOLEAN
 927        Default value for IPV6_V6ONLY socket option,
 928        which restricts use of the IPv6 socket to IPv6 communication
 929        only.
 930                TRUE: disable IPv4-mapped address feature
 931                FALSE: enable IPv4-mapped address feature
 932
 933        Default: FALSE (as specified in RFC2553bis)
 934
 935IPv6 Fragmentation:
 936
 937ip6frag_high_thresh - INTEGER
 938        Maximum memory used to reassemble IPv6 fragments. When
 939        ip6frag_high_thresh bytes of memory is allocated for this purpose,
 940        the fragment handler will toss packets until ip6frag_low_thresh
 941        is reached.
 942
 943ip6frag_low_thresh - INTEGER
 944        See ip6frag_high_thresh
 945
 946ip6frag_time - INTEGER
 947        Time in seconds to keep an IPv6 fragment in memory.
 948
 949ip6frag_secret_interval - INTEGER
 950        Regeneration interval (in seconds) of the hash secret (or lifetime
 951        for the hash secret) for IPv6 fragments.
 952        Default: 600
 953
 954conf/default/*:
 955        Change the interface-specific default settings.
 956
 957
 958conf/all/*:
 959        Change all the interface-specific settings.
 960
 961        [XXX:  Other special features than forwarding?]
 962
 963conf/all/forwarding - BOOLEAN
 964        Enable global IPv6 forwarding between all interfaces.
 965
 966        IPv4 and IPv6 work differently here; e.g. netfilter must be used
 967        to control which interfaces may forward packets and which not.
 968
 969        This also sets all interfaces' Host/Router setting
 970        'forwarding' to the specified value.  See below for details.
 971
 972        This referred to as global forwarding.
 973
 974proxy_ndp - BOOLEAN
 975        Do proxy ndp.
 976
 977conf/interface/*:
 978        Change special settings per interface.
 979
 980        The functional behaviour for certain settings is different
 981        depending on whether local forwarding is enabled or not.
 982
 983accept_ra - BOOLEAN
 984        Accept Router Advertisements; autoconfigure using them.
 985
 986        Functional default: enabled if local forwarding is disabled.
 987                            disabled if local forwarding is enabled.
 988
 989accept_ra_defrtr - BOOLEAN
 990        Learn default router in Router Advertisement.
 991
 992        Functional default: enabled if accept_ra is enabled.
 993                            disabled if accept_ra is disabled.
 994
 995accept_ra_pinfo - BOOLEAN
 996        Learn Prefix Information in Router Advertisement.
 997
 998        Functional default: enabled if accept_ra is enabled.
 999                            disabled if accept_ra is disabled.
1000
1001accept_ra_rt_info_max_plen - INTEGER
1002        Maximum prefix length of Route Information in RA.
1003
1004        Route Information w/ prefix larger than or equal to this
1005        variable shall be ignored.
1006
1007        Functional default: 0 if accept_ra_rtr_pref is enabled.
1008                            -1 if accept_ra_rtr_pref is disabled.
1009
1010accept_ra_rtr_pref - BOOLEAN
1011        Accept Router Preference in RA.
1012
1013        Functional default: enabled if accept_ra is enabled.
1014                            disabled if accept_ra is disabled.
1015
1016accept_redirects - BOOLEAN
1017        Accept Redirects.
1018
1019        Functional default: enabled if local forwarding is disabled.
1020                            disabled if local forwarding is enabled.
1021
1022accept_source_route - INTEGER
1023        Accept source routing (routing extension header).
1024
1025        >= 0: Accept only routing header type 2.
1026        < 0: Do not accept routing header.
1027
1028        Default: 0
1029
1030autoconf - BOOLEAN
1031        Autoconfigure addresses using Prefix Information in Router
1032        Advertisements.
1033
1034        Functional default: enabled if accept_ra_pinfo is enabled.
1035                            disabled if accept_ra_pinfo is disabled.
1036
1037dad_transmits - INTEGER
1038        The amount of Duplicate Address Detection probes to send.
1039        Default: 1
1040
1041forwarding - BOOLEAN
1042        Configure interface-specific Host/Router behaviour.
1043
1044        Note: It is recommended to have the same setting on all
1045        interfaces; mixed router/host scenarios are rather uncommon.
1046
1047        FALSE:
1048
1049        By default, Host behaviour is assumed.  This means:
1050
1051        1. IsRouter flag is not set in Neighbour Advertisements.
1052        2. Router Solicitations are being sent when necessary.
1053        3. If accept_ra is TRUE (default), accept Router
1054           Advertisements (and do autoconfiguration).
1055        4. If accept_redirects is TRUE (default), accept Redirects.
1056
1057        TRUE:
1058
1059        If local forwarding is enabled, Router behaviour is assumed.
1060        This means exactly the reverse from the above:
1061
1062        1. IsRouter flag is set in Neighbour Advertisements.
1063        2. Router Solicitations are not sent.
1064        3. Router Advertisements are ignored.
1065        4. Redirects are ignored.
1066
1067        Default: FALSE if global forwarding is disabled (default),
1068                 otherwise TRUE.
1069
1070hop_limit - INTEGER
1071        Default Hop Limit to set.
1072        Default: 64
1073
1074mtu - INTEGER
1075        Default Maximum Transfer Unit
1076        Default: 1280 (IPv6 required minimum)
1077
1078router_probe_interval - INTEGER
1079        Minimum interval (in seconds) between Router Probing described
1080        in RFC4191.
1081
1082        Default: 60
1083
1084router_solicitation_delay - INTEGER
1085        Number of seconds to wait after interface is brought up
1086        before sending Router Solicitations.
1087        Default: 1
1088
1089router_solicitation_interval - INTEGER
1090        Number of seconds to wait between Router Solicitations.
1091        Default: 4
1092
1093router_solicitations - INTEGER
1094        Number of Router Solicitations to send until assuming no
1095        routers are present.
1096        Default: 3
1097
1098use_tempaddr - INTEGER
1099        Preference for Privacy Extensions (RFC3041).
1100          <= 0 : disable Privacy Extensions
1101          == 1 : enable Privacy Extensions, but prefer public
1102                 addresses over temporary addresses.
1103          >  1 : enable Privacy Extensions and prefer temporary
1104                 addresses over public addresses.
1105        Default:  0 (for most devices)
1106                 -1 (for point-to-point devices and loopback devices)
1107
1108temp_valid_lft - INTEGER
1109        valid lifetime (in seconds) for temporary addresses.
1110        Default: 604800 (7 days)
1111
1112temp_prefered_lft - INTEGER
1113        Preferred lifetime (in seconds) for temporary addresses.
1114        Default: 86400 (1 day)
1115
1116max_desync_factor - INTEGER
1117        Maximum value for DESYNC_FACTOR, which is a random value
1118        that ensures that clients don't synchronize with each
1119        other and generate new addresses at exactly the same time.
1120        value is in seconds.
1121        Default: 600
1122
1123regen_max_retry - INTEGER
1124        Number of attempts before give up attempting to generate
1125        valid temporary addresses.
1126        Default: 5
1127
1128max_addresses - INTEGER
1129        Maximum number of autoconfigured addresses per interface.  Setting
1130        to zero disables the limitation.  It is not recommended to set this
1131        value too large (or to zero) because it would be an easy way to
1132        crash the kernel by allowing too many addresses to be created.
1133        Default: 16
1134
1135disable_ipv6 - BOOLEAN
1136        Disable IPv6 operation.  If accept_dad is set to 2, this value
1137        will be dynamically set to TRUE if DAD fails for the link-local
1138        address.
1139        Default: FALSE (enable IPv6 operation)
1140
1141        When this value is changed from 1 to 0 (IPv6 is being enabled),
1142        it will dynamically create a link-local address on the given
1143        interface and start Duplicate Address Detection, if necessary.
1144
1145        When this value is changed from 0 to 1 (IPv6 is being disabled),
1146        it will dynamically delete all address on the given interface.
1147
1148accept_dad - INTEGER
1149        Whether to accept DAD (Duplicate Address Detection).
1150        0: Disable DAD
1151        1: Enable DAD (default)
1152        2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
1153           link-local address has been found.
1154
1155force_tllao - BOOLEAN
1156        Enable sending the target link-layer address option even when
1157        responding to a unicast neighbor solicitation.
1158        Default: FALSE
1159
1160        Quoting from RFC 2461, section 4.4, Target link-layer address:
1161
1162        "The option MUST be included for multicast solicitations in order to
1163        avoid infinite Neighbor Solicitation "recursion" when the peer node
1164        does not have a cache entry to return a Neighbor Advertisements
1165        message.  When responding to unicast solicitations, the option can be
1166        omitted since the sender of the solicitation has the correct link-
1167        layer address; otherwise it would not have be able to send the unicast
1168        solicitation in the first place. However, including the link-layer
1169        address in this case adds little overhead and eliminates a potential
1170        race condition where the sender deletes the cached link-layer address
1171        prior to receiving a response to a previous solicitation."
1172
1173icmp/*:
1174ratelimit - INTEGER
1175        Limit the maximal rates for sending ICMPv6 packets.
1176        0 to disable any limiting,
1177        otherwise the minimal space between responses in milliseconds.
1178        Default: 1000
1179
1180
1181IPv6 Update by:
1182Pekka Savola <pekkas@netcore.fi>
1183YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
1184
1185
1186/proc/sys/net/bridge/* Variables:
1187
1188bridge-nf-call-arptables - BOOLEAN
1189        1 : pass bridged ARP traffic to arptables' FORWARD chain.
1190        0 : disable this.
1191        Default: 1
1192
1193bridge-nf-call-iptables - BOOLEAN
1194        1 : pass bridged IPv4 traffic to iptables' chains.
1195        0 : disable this.
1196        Default: 1
1197
1198bridge-nf-call-ip6tables - BOOLEAN
1199        1 : pass bridged IPv6 traffic to ip6tables' chains.
1200        0 : disable this.
1201        Default: 1
1202
1203bridge-nf-filter-vlan-tagged - BOOLEAN
1204        1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
1205        0 : disable this.
1206        Default: 1
1207
1208bridge-nf-filter-pppoe-tagged - BOOLEAN
1209        1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
1210        0 : disable this.
1211        Default: 1
1212
1213
1214proc/sys/net/sctp/* Variables:
1215
1216addip_enable - BOOLEAN
1217        Enable or disable extension of  Dynamic Address Reconfiguration
1218        (ADD-IP) functionality specified in RFC5061.  This extension provides
1219        the ability to dynamically add and remove new addresses for the SCTP
1220        associations.
1221
1222        1: Enable extension.
1223
1224        0: Disable extension.
1225
1226        Default: 0
1227
1228addip_noauth_enable - BOOLEAN
1229        Dynamic Address Reconfiguration (ADD-IP) requires the use of
1230        authentication to protect the operations of adding or removing new
1231        addresses.  This requirement is mandated so that unauthorized hosts
1232        would not be able to hijack associations.  However, older
1233        implementations may not have implemented this requirement while
1234        allowing the ADD-IP extension.  For reasons of interoperability,
1235        we provide this variable to control the enforcement of the
1236        authentication requirement.
1237
1238        1: Allow ADD-IP extension to be used without authentication.  This
1239           should only be set in a closed environment for interoperability
1240           with older implementations.
1241
1242        0: Enforce the authentication requirement
1243
1244        Default: 0
1245
1246auth_enable - BOOLEAN
1247        Enable or disable Authenticated Chunks extension.  This extension
1248        provides the ability to send and receive authenticated chunks and is
1249        required for secure operation of Dynamic Address Reconfiguration
1250        (ADD-IP) extension.
1251
1252        1: Enable this extension.
1253        0: Disable this extension.
1254
1255        Default: 0
1256
1257prsctp_enable - BOOLEAN
1258        Enable or disable the Partial Reliability extension (RFC3758) which
1259        is used to notify peers that a given DATA should no longer be expected.
1260
1261        1: Enable extension
1262        0: Disable
1263
1264        Default: 1
1265
1266max_burst - INTEGER
1267        The limit of the number of new packets that can be initially sent.  It
1268        controls how bursty the generated traffic can be.
1269
1270        Default: 4
1271
1272association_max_retrans - INTEGER
1273        Set the maximum number for retransmissions that an association can
1274        attempt deciding that the remote end is unreachable.  If this value
1275        is exceeded, the association is terminated.
1276
1277        Default: 10
1278
1279max_init_retransmits - INTEGER
1280        The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
1281        that an association will attempt before declaring the destination
1282        unreachable and terminating.
1283
1284        Default: 8
1285
1286path_max_retrans - INTEGER
1287        The maximum number of retransmissions that will be attempted on a given
1288        path.  Once this threshold is exceeded, the path is considered
1289        unreachable, and new traffic will use a different path when the
1290        association is multihomed.
1291
1292        Default: 5
1293
1294rto_initial - INTEGER
1295        The initial round trip timeout value in milliseconds that will be used
1296        in calculating round trip times.  This is the initial time interval
1297        for retransmissions.
1298
1299        Default: 3000
1300
1301rto_max - INTEGER
1302        The maximum value (in milliseconds) of the round trip timeout.  This
1303        is the largest time interval that can elapse between retransmissions.
1304
1305        Default: 60000
1306
1307rto_min - INTEGER
1308        The minimum value (in milliseconds) of the round trip timeout.  This
1309        is the smallest time interval the can elapse between retransmissions.
1310
1311        Default: 1000
1312
1313hb_interval - INTEGER
1314        The interval (in milliseconds) between HEARTBEAT chunks.  These chunks
1315        are sent at the specified interval on idle paths to probe the state of
1316        a given path between 2 associations.
1317
1318        Default: 30000
1319
1320sack_timeout - INTEGER
1321        The amount of time (in milliseconds) that the implementation will wait
1322        to send a SACK.
1323
1324        Default: 200
1325
1326valid_cookie_life - INTEGER
1327        The default lifetime of the SCTP cookie (in milliseconds).  The cookie
1328        is used during association establishment.
1329
1330        Default: 60000
1331
1332cookie_preserve_enable - BOOLEAN
1333        Enable or disable the ability to extend the lifetime of the SCTP cookie
1334        that is used during the establishment phase of SCTP association
1335
1336        1: Enable cookie lifetime extension.
1337        0: Disable
1338
1339        Default: 1
1340
1341rcvbuf_policy - INTEGER
1342        Determines if the receive buffer is attributed to the socket or to
1343        association.   SCTP supports the capability to create multiple
1344        associations on a single socket.  When using this capability, it is
1345        possible that a single stalled association that's buffering a lot
1346        of data may block other associations from delivering their data by
1347        consuming all of the receive buffer space.  To work around this,
1348        the rcvbuf_policy could be set to attribute the receiver buffer space
1349        to each association instead of the socket.  This prevents the described
1350        blocking.
1351
1352        1: rcvbuf space is per association
1353        0: recbuf space is per socket
1354
1355        Default: 0
1356
1357sndbuf_policy - INTEGER
1358        Similar to rcvbuf_policy above, this applies to send buffer space.
1359
1360        1: Send buffer is tracked per association
1361        0: Send buffer is tracked per socket.
1362
1363        Default: 0
1364
1365sctp_mem - vector of 3 INTEGERs: min, pressure, max
1366        Number of pages allowed for queueing by all SCTP sockets.
1367
1368        min: Below this number of pages SCTP is not bothered about its
1369        memory appetite. When amount of memory allocated by SCTP exceeds
1370        this number, SCTP starts to moderate memory usage.
1371
1372        pressure: This value was introduced to follow format of tcp_mem.
1373
1374        max: Number of pages allowed for queueing by all SCTP sockets.
1375
1376        Default is calculated at boot time from amount of available memory.
1377
1378sctp_rmem - vector of 3 INTEGERs: min, default, max
1379        See tcp_rmem for a description.
1380
1381sctp_wmem  - vector of 3 INTEGERs: min, default, max
1382        See tcp_wmem for a description.
1383
1384addr_scope_policy - INTEGER
1385        Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00
1386
1387        0   - Disable IPv4 address scoping
1388        1   - Enable IPv4 address scoping
1389        2   - Follow draft but allow IPv4 private addresses
1390        3   - Follow draft but allow IPv4 link local addresses
1391
1392        Default: 1
1393
1394
1395/proc/sys/net/core/*
1396dev_weight - INTEGER
1397        The maximum number of packets that kernel can handle on a NAPI
1398        interrupt, it's a Per-CPU variable.
1399
1400        Default: 64
1401
1402/proc/sys/net/unix/*
1403max_dgram_qlen - INTEGER
1404        The maximum length of dgram socket receive queue
1405
1406        Default: 10
1407
1408
1409UNDOCUMENTED:
1410
1411/proc/sys/net/irda/*
1412        fast_poll_increase FIXME
1413        warn_noreply_time FIXME
1414        discovery_slots FIXME
1415        slot_timeout FIXME
1416        max_baud_rate FIXME
1417        discovery_timeout FIXME
1418        lap_keepalive_time FIXME
1419        max_noreply_time FIXME
1420        max_tx_data_size FIXME
1421        max_tx_window FIXME
1422        min_tx_turn_time FIXME
1423
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.