/proc/sys/net/ipv4/* Variables:

ip_forward - BOOLEAN
    0 - disabled (default)
    not 0 - enabled

    Forward Packets between interfaces.

    This variable is special, its change resets all configuration
    parameters to their default state (RFC1122 for hosts, RFC1812
    for routers)

ip_default_ttl - INTEGER
    default 64

ip_no_pmtu_disc - BOOLEAN
    Disable Path MTU Discovery.
    default FALSE

min_pmtu - INTEGER
    default 562 - minimum discovered Path MTU

mtu_expires - INTEGER
    Time, in seconds, that cached PMTU information is kept.

min_adv_mss - INTEGER
    The advertised MSS depends on the first hop route MTU, but will
    never be lower than this setting.

rt_cache_rebuild_count - INTEGER
    The per net-namespace route cache emergency rebuild threshold.
    Any net-namespace having its route cache rebuilt due to
    a hash bucket chain being too long more than this many times
    will have its route caching disabled

IP Fragmentation:

ipfrag_high_thresh - INTEGER
    Maximum memory used to reassemble IP fragments. When
    ipfrag_high_thresh bytes of memory is allocated for this purpose,
    the fragment handler will toss packets until ipfrag_low_thresh
    is reached.

ipfrag_low_thresh - INTEGER
    See ipfrag_high_thresh

ipfrag_time - INTEGER
    Time in seconds to keep an IP fragment in memory.

ipfrag_secret_interval - INTEGER
    Regeneration interval (in seconds) of the hash secret (or lifetime
    for the hash secret) for IP fragments.
    Default: 600

ipfrag_max_dist - INTEGER
    ipfrag_max_dist is a non-negative integer value which defines the
    maximum "disorder" which is allowed among fragments which share a
    common IP source address. Note that reordering of packets is
    not unusual, but if a large number of fragments arrive from a source
    IP address while a particular fragment queue remains incomplete, it
    probably indicates that one or more fragments belonging to that queue
    have been lost. When ipfrag_max_dist is positive, an additional check
    is done on fragments before they are added to a reassembly queue - if
    ipfrag_max_dist (or more) fragments have arrived from a particular IP
    address between additions to any IP fragment queue using that source
    address, it's presumed that one or more fragments in the queue are
    lost. The existing fragment queue will be dropped, and a new one
    started. An ipfrag_max_dist value of zero disables this check.

    Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
    result in unnecessarily dropping fragment queues when normal
    reordering of packets occurs, which could lead to poor application
    performance. Using a very large value, e.g. 50000, increases the
    likelihood of incorrectly reassembling IP fragments that originate
    from different IP datagrams, which could result in data corruption.
    Default: 64

INET peer storage:

inet_peer_threshold - INTEGER
    The approximate size of the storage.  Starting from this threshold
    entries will be thrown aggressively.  This threshold also determines
    entries' time-to-live and time intervals between garbage collection
    passes.  More entries, less time-to-live, less GC interval.

inet_peer_minttl - INTEGER
    Minimum time-to-live of entries.  Should be enough to cover fragment
    time-to-live on the reassembling side.  This minimum time-to-live  is
    guaranteed if the pool size is less than inet_peer_threshold.
    Measured in seconds.

inet_peer_maxttl - INTEGER
    Maximum time-to-live of entries.  Unused entries will expire after
    this period of time if there is no memory pressure on the pool (i.e.
    when the number of entries in the pool is very small).
    Measured in seconds.

inet_peer_gc_mintime - INTEGER
    Minimum interval between garbage collection passes.  This interval is
    in effect under high memory pressure on the pool.
    Measured in seconds.

inet_peer_gc_maxtime - INTEGER
    Minimum interval between garbage collection passes.  This interval is
    in effect under low (or absent) memory pressure on the pool.
    Measured in seconds.

TCP variables:

somaxconn - INTEGER
    Limit of socket listen() backlog, known in userspace as SOMAXCONN.
    Defaults to 128.  See also tcp_max_syn_backlog for additional tuning
    for TCP sockets.

tcp_abc - INTEGER
    Controls Appropriate Byte Count (ABC) defined in RFC3465.
    ABC is a way of increasing congestion window (cwnd) more slowly
    in response to partial acknowledgments.
    Possible values are:
        0 increase cwnd once per acknowledgment (no ABC)
        1 increase cwnd once per acknowledgment of full sized segment
        2 allow increase cwnd by two if acknowledgment is
          of two segments to compensate for delayed acknowledgments.
    Default: 0 (off)

tcp_abort_on_overflow - BOOLEAN
    If listening service is too slow to accept new connections,
    reset them. Default state is FALSE. It means that if overflow
    occurred due to a burst, connection will recover. Enable this
    option _only_ if you are really sure that listening daemon
    cannot be tuned to accept connections faster. Enabling this
    option can harm clients of your server.

tcp_adv_win_scale - INTEGER
    Count buffering overhead as bytes/2^tcp_adv_win_scale
    (if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
    if it is <= 0.
    Default: 2

tcp_allowed_congestion_control - STRING
    Show/set the congestion control choices available to non-privileged
    processes. The list is a subset of those listed in
    tcp_available_congestion_control.
    Default is "reno" and the default setting (tcp_congestion_control).

tcp_app_win - INTEGER
    Reserve max(window/2^tcp_app_win, mss) of window for application
    buffer. Value 0 is special, it means that nothing is reserved.
    Default: 31

tcp_available_congestion_control - STRING
    Shows the available congestion control choices that are registered.
    More congestion control algorithms may be available as modules,
    but not loaded.

tcp_base_mss - INTEGER
    The initial value of search_low to be used by the packetization layer
    Path MTU discovery (MTU probing).  If MTU probing is enabled,
    this is the initial MSS used by the connection.

tcp_congestion_control - STRING
    Set the congestion control algorithm to be used for new
    connections. The algorithm "reno" is always available, but
    additional choices may be available based on kernel configuration.
    Default is set as part of kernel configuration.

tcp_dsack - BOOLEAN
    Allows TCP to send "duplicate" SACKs.

tcp_ecn - BOOLEAN
    Enable Explicit Congestion Notification (ECN) in TCP. ECN is only
    used when both ends of the TCP flow support it. It is useful to
    avoid losses due to congestion (when the bottleneck router supports
    ECN).
    Possible values are:
        0 disable ECN
        1 ECN enabled
        2 Only server-side ECN enabled. If the other end does
          not support ECN, behavior is like with ECN disabled.
    Default: 2

tcp_fack - BOOLEAN
    Enable FACK congestion avoidance and fast retransmission.
    The value is not used, if tcp_sack is not enabled.

tcp_fin_timeout - INTEGER
    Time to hold socket in state FIN-WAIT-2, if it was closed
    by our side. Peer can be broken and never close its side,
    or even died unexpectedly. Default value is 60sec.
    Usual value used in 2.2 was 180 seconds, you may restore
    it, but remember that if your machine is even underloaded WEB server,
    you risk to overflow memory with kilotons of dead sockets,
    FIN-WAIT-2 sockets are less dangerous than FIN-WAIT-1,
    because they eat maximum 1.5K of memory, but they tend
    to live longer.    Cf. tcp_max_orphans.

tcp_frto - INTEGER
    Enables Forward RTO-Recovery (F-RTO) defined in RFC4138.
    F-RTO is an enhanced recovery algorithm for TCP retransmission
    timeouts.  It is particularly beneficial in wireless environments
    where packet loss is typically due to random radio interference
    rather than intermediate router congestion.  F-RTO is sender-side
    only modification. Therefore it does not require any support from
    the peer.

    If set to 1, basic version is enabled.  2 enables SACK enhanced
    F-RTO if flow uses SACK.  The basic version can be used also when
    SACK is in use though scenario(s) with it exists where F-RTO
    interacts badly with the packet counting of the SACK enabled TCP
    flow.

tcp_frto_response - INTEGER
    When F-RTO has detected that a TCP retransmission timeout was
    spurious (i.e, the timeout would have been avoided had TCP set a
    longer retransmission timeout), TCP has several options what to do
    next. Possible values are:
        0 Rate halving based; a smooth and conservative response,
          results in halved cwnd and ssthresh after one RTT
        1 Very conservative response; not recommended because even
          though being valid, it interacts poorly with the rest of
          Linux TCP, halves cwnd and ssthresh immediately
        2 Aggressive response; undoes congestion control measures
          that are now known to be unnecessary (ignoring the
          possibility of a lost retransmission that would require
          TCP to be more cautious), cwnd and ssthresh are restored
          to the values prior timeout
    Default: 0 (rate halving based)

tcp_keepalive_time - INTEGER
    How often TCP sends out keepalive messages when keepalive is enabled.
    Default: 2hours.

tcp_keepalive_probes - INTEGER
    How many keepalive probes TCP sends out, until it decides that the
    connection is broken. Default value: 9.

tcp_keepalive_intvl - INTEGER
    How frequently the probes are send out. Multiplied by
    tcp_keepalive_probes it is time to kill not responding connection,
    after probes started. Default value: 75sec i.e. connection
    will be aborted after ~11 minutes of retries.

tcp_low_latency - BOOLEAN
    If set, the TCP stack makes decisions that prefer lower
    latency as opposed to higher throughput.  By default, this
    option is not set meaning that higher throughput is preferred.
    An example of an application where this default should be
    changed would be a Beowulf compute cluster.
    Default: 0

tcp_max_orphans - INTEGER
    Maximal number of TCP sockets not attached to any user file handle,
    held by system.    If this number is exceeded orphaned connections are
    reset immediately and warning is printed. This limit exists
    only to prevent simple DoS attacks, you _must_ not rely on this
    or lower the limit artificially, but rather increase it
    (probably, after increasing installed memory),
    if network conditions require more than default value,
    and tune network services to linger and kill such states
    more aggressively. Let me to remind again: each orphan eats
    up to ~64K of unswappable memory.

tcp_max_syn_backlog - INTEGER
    Maximal number of remembered connection requests, which are
    still did not receive an acknowledgment from connecting client.
    Default value is 1024 for systems with more than 128Mb of memory,
    and 128 for low memory machines. If server suffers of overload,
    try to increase this number.

tcp_max_tw_buckets - INTEGER
    Maximal number of timewait sockets held by system simultaneously.
    If this number is exceeded time-wait socket is immediately destroyed
    and warning is printed. This limit exists only to prevent
    simple DoS attacks, you _must_ not lower the limit artificially,
    but rather increase it (probably, after increasing installed memory),
    if network conditions require more than default value.

tcp_mem - vector of 3 INTEGERs: min, pressure, max
    min: below this number of pages TCP is not bothered about its
    memory appetite.

    pressure: when amount of memory allocated by TCP exceeds this number
    of pages, TCP moderates its memory consumption and enters memory
    pressure mode, which is exited when memory consumption falls
    under "min".

    max: number of pages allowed for queueing by all TCP sockets.

    Defaults are calculated at boot time from amount of available
    memory.

tcp_moderate_rcvbuf - BOOLEAN
    If set, TCP performs receive buffer auto-tuning, attempting to
    automatically size the buffer (no greater than tcp_rmem[2]) to
    match the size required by the path for full throughput.  Enabled by
    default.

tcp_mtu_probing - INTEGER
    Controls TCP Packetization-Layer Path MTU Discovery.  Takes three
    values:
      0 - Disabled
      1 - Disabled by default, enabled when an ICMP black hole detected
      2 - Always enabled, use initial MSS of tcp_base_mss.

tcp_no_metrics_save - BOOLEAN
    By default, TCP saves various connection metrics in the route cache
    when the connection closes, so that connections established in the
    near future can use these to set initial conditions.  Usually, this
    increases overall performance, but may sometimes cause performance
    degradation.  If set, TCP will not cache metrics on closing
    connections.

tcp_orphan_retries - INTEGER
    This value influences the timeout of a locally closed TCP connection,
    when RTO retransmissions remain unacknowledged.
    See tcp_retries2 for more details.

    The default value is 7.
    If your machine is a loaded WEB server,
    you should think about lowering this value, such sockets
    may consume significant resources. Cf. tcp_max_orphans.

tcp_reordering - INTEGER
    Maximal reordering of packets in a TCP stream.
    Default: 3

tcp_retrans_collapse - BOOLEAN
    Bug-to-bug compatibility with some broken printers.
    On retransmit try to send bigger packets to work around bugs in
    certain TCP stacks.

tcp_retries1 - INTEGER
    This value influences the time, after which TCP decides, that
    something is wrong due to unacknowledged RTO retransmissions,
    and reports this suspicion to the network layer.
    See tcp_retries2 for more details.

    RFC 1122 recommends at least 3 retransmissions, which is the
    default.

tcp_retries2 - INTEGER
    This value influences the timeout of an alive TCP connection,
    when RTO retransmissions remain unacknowledged.
    Given a value of N, a hypothetical TCP connection following
    exponential backoff with an initial RTO of TCP_RTO_MIN would
    retransmit N times before killing the connection at the (N+1)th RTO.

    The default value of 15 yields a hypothetical timeout of 924.6
    seconds and is a lower bound for the effective timeout.
    TCP will effectively time out at the first RTO which exceeds the
    hypothetical timeout.

    RFC 1122 recommends at least 100 seconds for the timeout,
    which corresponds to a value of at least 8.

tcp_rfc1337 - BOOLEAN
    If set, the TCP stack behaves conforming to RFC1337. If unset,
    we are not conforming to RFC, but prevent TCP TIME_WAIT
    assassination.
    Default: 0

tcp_rmem - vector of 3 INTEGERs: min, default, max
    min: Minimal size of receive buffer used by TCP sockets.
    It is guaranteed to each TCP socket, even under moderate memory
    pressure.
    Default: 8K

    default: initial size of receive buffer used by TCP sockets.
    This value overrides net.core.rmem_default used by other protocols.
    Default: 87380 bytes. This value results in window of 65535 with
    default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
    less for default tcp_app_win. See below about these variables.

    max: maximal size of receive buffer allowed for automatically
    selected receiver buffers for TCP socket. This value does not override
    net.core.rmem_max.  Calling setsockopt() with SO_RCVBUF disables
    automatic tuning of that socket's receive buffer size, in which
    case this value is ignored.
    Default: between 87380B and 4MB, depending on RAM size.

tcp_sack - BOOLEAN
    Enable select acknowledgments (SACKS).

tcp_slow_start_after_idle - BOOLEAN
    If set, provide RFC2861 behavior and time out the congestion
    window after an idle period.  An idle period is defined at
    the current RTO.  If unset, the congestion window will not
    be timed out after an idle period.
    Default: 1

tcp_stdurg - BOOLEAN
    Use the Host requirements interpretation of the TCP urgent pointer field.
    Most hosts use the older BSD interpretation, so if you turn this on
    Linux might not communicate correctly with them.
    Default: FALSE

tcp_synack_retries - INTEGER
    Number of times SYNACKs for a passive TCP connection attempt will
    be retransmitted. Should not be higher than 255. Default value
    is 5, which corresponds to ~180seconds.

tcp_syncookies - BOOLEAN
    Only valid when the kernel was compiled with CONFIG_SYNCOOKIES
    Send out syncookies when the syn backlog queue of a socket
    overflows. This is to prevent against the common 'SYN flood attack'
    Default: FALSE

    Note, that syncookies is fallback facility.
    It MUST NOT be used to help highly loaded servers to stand
    against legal connection rate. If you see SYN flood warnings
    in your logs, but investigation    shows that they occur
    because of overload with legal connections, you should tune
    another parameters until this warning disappear.
    See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.

    syncookies seriously violate TCP protocol, do not allow
    to use TCP extensions, can result in serious degradation
    of some services (f.e. SMTP relaying), visible not by you,
    but your clients and relays, contacting you. While you see
    SYN flood warnings in logs not being really flooded, your server
    is seriously misconfigured.

tcp_syn_retries - INTEGER
    Number of times initial SYNs for an active TCP connection attempt
    will be retransmitted. Should not be higher than 255. Default value
    is 5, which corresponds to ~180seconds.

tcp_timestamps - BOOLEAN
    Enable timestamps as defined in RFC1323.

tcp_tso_win_divisor - INTEGER
    This allows control over what percentage of the congestion window
    can be consumed by a single TSO frame.
    The setting of this parameter is a choice between burstiness and
    building larger TSO frames.
    Default: 3

tcp_tw_recycle - BOOLEAN
    Enable fast recycling TIME-WAIT sockets. Default value is 0.
    It should not be changed without advice/request of technical
    experts.

tcp_tw_reuse - BOOLEAN
    Allow to reuse TIME-WAIT sockets for new connections when it is
    safe from protocol viewpoint. Default value is 0.
    It should not be changed without advice/request of technical
    experts.

tcp_window_scaling - BOOLEAN
    Enable window scaling as defined in RFC1323.

tcp_wmem - vector of 3 INTEGERs: min, default, max
    min: Amount of memory reserved for send buffers for TCP sockets.
    Each TCP socket has rights to use it due to fact of its birth.
    Default: 4K

    default: initial size of send buffer used by TCP sockets.  This
    value overrides net.core.wmem_default used by other protocols.
    It is usually lower than net.core.wmem_default.
    Default: 16K

    max: Maximal amount of memory allowed for automatically tuned
    send buffers for TCP sockets. This value does not override
    net.core.wmem_max.  Calling setsockopt() with SO_SNDBUF disables
    automatic tuning of that socket's send buffer size, in which case
    this value is ignored.
    Default: between 64K and 4MB, depending on RAM size.

tcp_workaround_signed_windows - BOOLEAN
    If set, assume no receipt of a window scaling option means the
    remote TCP is broken and treats the window as a signed quantity.
    If unset, assume the remote TCP is not broken even if we do
    not receive a window scaling option from them.
    Default: 0

tcp_dma_copybreak - INTEGER
    Lower limit, in bytes, of the size of socket reads that will be
    offloaded to a DMA copy engine, if one is present in the system
    and CONFIG_NET_DMA is enabled.
    Default: 4096

UDP variables:

udp_mem - vector of 3 INTEGERs: min, pressure, max
    Number of pages allowed for queueing by all UDP sockets.

    min: Below this number of pages UDP is not bothered about its
    memory appetite. When amount of memory allocated by UDP exceeds
    this number, UDP starts to moderate memory usage.

    pressure: This value was introduced to follow format of tcp_mem.

    max: Number of pages allowed for queueing by all UDP sockets.

    Default is calculated at boot time from amount of available memory.

udp_rmem_min - INTEGER
    Minimal size of receive buffer used by UDP sockets in moderation.
    Each UDP socket is able to use the size for receiving data, even if
    total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
    Default: 4096

udp_wmem_min - INTEGER
    Minimal size of send buffer used by UDP sockets in moderation.
    Each UDP socket is able to use the size for sending data, even if
    total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
    Default: 4096

CIPSOv4 Variables:

cipso_cache_enable - BOOLEAN
    If set, enable additions to and lookups from the CIPSO label mapping
    cache.  If unset, additions are ignored and lookups always result in a
    miss.  However, regardless of the setting the cache is still
    invalidated when required when means you can safely toggle this on and
    off and the cache will always be "safe".
    Default: 1

cipso_cache_bucket_size - INTEGER
    The CIPSO label cache consists of a fixed size hash table with each
    hash bucket containing a number of cache entries.  This variable limits
    the number of entries in each hash bucket; the larger the value the
    more CIPSO label mappings that can be cached.  When the number of
    entries in a given hash bucket reaches this limit adding new entries
    causes the oldest entry in the bucket to be removed to make room.
    Default: 10

cipso_rbm_optfmt - BOOLEAN
    Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
    the CIPSO draft specification (see Documentation/netlabel for details).
    This means that when set the CIPSO tag will be padded with empty
    categories in order to make the packet data 32-bit aligned.
    Default: 0

cipso_rbm_structvalid - BOOLEAN
    If set, do a very strict check of the CIPSO option when
    ip_options_compile() is called.  If unset, relax the checks done during
    ip_options_compile().  Either way is "safe" as errors are caught else
    where in the CIPSO processing code but setting this to 0 (False) should
    result in less work (i.e. it should be faster) but could cause problems
    with other implementations that require strict checking.
    Default: 0

IP Variables:

ip_local_port_range - 2 INTEGERS
    Defines the local port range that is used by TCP and UDP to
    choose the local port. The first number is the first, the
    second the last local port number. Default value depends on
    amount of memory available on the system:
    > 128Mb 32768-61000
    < 128Mb 1024-4999 or even less.
    This number defines number of active connections, which this
    system can issue simultaneously to systems not supporting
    TCP extensions (timestamps). With tcp_tw_recycle enabled
    (i.e. by default) range 1024-4999 is enough to issue up to
    2000 connections per second to systems supporting timestamps.

ip_nonlocal_bind - BOOLEAN
    If set, allows processes to bind() to non-local IP addresses,
    which can be quite useful - but may break some applications.
    Default: 0

ip_dynaddr - BOOLEAN
    If set non-zero, enables support for dynamic addresses.
    If set to a non-zero value larger than 1, a kernel log
    message will be printed when dynamic address rewriting
    occurs.
    Default: 0

icmp_echo_ignore_all - BOOLEAN
    If set non-zero, then the kernel will ignore all ICMP ECHO
    requests sent to it.
    Default: 0

icmp_echo_ignore_broadcasts - BOOLEAN
    If set non-zero, then the kernel will ignore all ICMP ECHO and
    TIMESTAMP requests sent to it via broadcast/multicast.
    Default: 1

icmp_ratelimit - INTEGER
    Limit the maximal rates for sending ICMP packets whose type matches
    icmp_ratemask (see below) to specific targets.
    0 to disable any limiting,
    otherwise the minimal space between responses in milliseconds.
    Default: 1000

icmp_ratemask - INTEGER
    Mask made of ICMP types for which rates are being limited.
    Significant bits: IHGFEDCBA9876543210
    Default mask:     0000001100000011000 (6168)

    Bit definitions (see include/linux/icmp.h):
        0 Echo Reply
        3 Destination Unreachable *
        4 Source Quench *
        5 Redirect
        8 Echo Request
        B Time Exceeded *
        C Parameter Problem *
        D Timestamp Request
        E Timestamp Reply
        F Info Request
        G Info Reply
        H Address Mask Request
        I Address Mask Reply

    * These are rate limited by default (see default mask above)

icmp_ignore_bogus_error_responses - BOOLEAN
    Some routers violate RFC1122 by sending bogus responses to broadcast
    frames.  Such violations are normally logged via a kernel warning.
    If this is set to TRUE, the kernel will not give such warnings, which
    will avoid log file clutter.
    Default: FALSE

icmp_errors_use_inbound_ifaddr - BOOLEAN

    If zero, icmp error messages are sent with the primary address of
    the exiting interface.

    If non-zero, the message will be sent with the primary address of
    the interface that received the packet that caused the icmp error.
    This is the behaviour network many administrators will expect from
    a router. And it can make debugging complicated network layouts
    much easier.

    Note that if no primary address exists for the interface selected,
    then the primary address of the first non-loopback interface that
    has one will be used regardless of this setting.

    Default: 0

igmp_max_memberships - INTEGER
    Change the maximum number of multicast groups we can subscribe to.
    Default: 20

conf/interface/*  changes special settings per interface (where "interface" is
          the name of your network interface)
conf/all/*      is special, changes the settings for all interfaces


log_martians - BOOLEAN
    Log packets with impossible addresses to kernel log.
    log_martians for the interface will be enabled if at least one of
    conf/{all,interface}/log_martians is set to TRUE,
    it will be disabled otherwise

accept_redirects - BOOLEAN
    Accept ICMP redirect messages.
    accept_redirects for the interface will be enabled if:
    - both conf/{all,interface}/accept_redirects are TRUE in the case
      forwarding for the interface is enabled
    or
    - at least one of conf/{all,interface}/accept_redirects is TRUE in the
      case forwarding for the interface is disabled
    accept_redirects for the interface will be disabled otherwise
    default TRUE (host)
        FALSE (router)

forwarding - BOOLEAN
    Enable IP forwarding on this interface.

mc_forwarding - BOOLEAN
    Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
    and a multicast routing daemon is required.
    conf/all/mc_forwarding must also be set to TRUE to enable multicast
    routing    for the interface

medium_id - INTEGER
    Integer value used to differentiate the devices by the medium they
    are attached to. Two devices can have different id values when
    the broadcast packets are received only on one of them.
    The default value 0 means that the device is the only interface
    to its medium, value of -1 means that medium is not known.

    Currently, it is used to change the proxy_arp behavior:
    the proxy_arp feature is enabled for packets forwarded between
    two devices attached to different media.

proxy_arp - BOOLEAN
    Do proxy arp.
    proxy_arp for the interface will be enabled if at least one of
    conf/{all,interface}/proxy_arp is set to TRUE,
    it will be disabled otherwise

shared_media - BOOLEAN
    Send(router) or accept(host) RFC1620 shared media redirects.
    Overrides ip_secure_redirects.
    shared_media for the interface will be enabled if at least one of
    conf/{all,interface}/shared_media is set to TRUE,
    it will be disabled otherwise
    default TRUE

secure_redirects - BOOLEAN
    Accept ICMP redirect messages only for gateways,
    listed in default gateway list.
    secure_redirects for the interface will be enabled if at least one of
    conf/{all,interface}/secure_redirects is set to TRUE,
    it will be disabled otherwise
    default TRUE

send_redirects - BOOLEAN
    Send redirects, if router.
    send_redirects for the interface will be enabled if at least one of
    conf/{all,interface}/send_redirects is set to TRUE,
    it will be disabled otherwise
    Default: TRUE

bootp_relay - BOOLEAN
    Accept packets with source address 0.b.c.d destined
    not to this host as local ones. It is supposed, that
    BOOTP relay daemon will catch and forward such packets.
    conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
    for the interface
    default FALSE
    Not Implemented Yet.

accept_source_route - BOOLEAN
    Accept packets with SRR option.
    conf/all/accept_source_route must also be set to TRUE to accept packets
    with SRR option on the interface
    default TRUE (router)
        FALSE (host)

rp_filter - INTEGER
    0 - No source validation.
    1 - Strict mode as defined in RFC3704 Strict Reverse Path
        Each incoming packet is tested against the FIB and if the interface
        is not the best reverse path the packet check will fail.
        By default failed packets are discarded.
    2 - Loose mode as defined in RFC3704 Loose Reverse Path
        Each incoming packet's source address is also tested against the FIB
        and if the source address is not reachable via any interface
        the packet check will fail.

    Current recommended practice in RFC3704 is to enable strict mode
    to prevent IP spoofing from DDos attacks. If using asymmetric routing
    or other complicated routing, then loose mode is recommended.

    conf/all/rp_filter must also be set to non-zero to do source validation
    on the interface

    Default value is 0. Note that some distributions enable it
    in startup scripts.

arp_filter - BOOLEAN
    1 - Allows you to have multiple network interfaces on the same
    subnet, and have the ARPs for each interface be answered
    based on whether or not the kernel would route a packet from
    the ARP'd IP out that interface (therefore you must use source
    based routing for this to work). In other words it allows control
    of which cards (usually 1) will respond to an arp request.

    0 - (default) The kernel can respond to arp requests with addresses
    from other interfaces. This may seem wrong but it usually makes
    sense, because it increases the chance of successful communication.
    IP addresses are owned by the complete host on Linux, not by
    particular interfaces. Only for more complex setups like load-
    balancing, does this behaviour cause problems.

    arp_filter for the interface will be enabled if at least one of
    conf/{all,interface}/arp_filter is set to TRUE,
    it will be disabled otherwise

arp_announce - INTEGER
    Define different restriction levels for announcing the local
    source IP address from IP packets in ARP requests sent on
    interface:
    0 - (default) Use any local address, configured on any interface
    1 - Try to avoid local addresses that are not in the target's
    subnet for this interface. This mode is useful when target
    hosts reachable via this interface require the source IP
    address in ARP requests to be part of their logical network
    configured on the receiving interface. When we generate the
    request we will check all our subnets that include the
    target IP and will preserve the source address if it is from
    such subnet. If there is no such subnet we select source
    address according to the rules for level 2.
    2 - Always use the best local address for this target.
    In this mode we ignore the source address in the IP packet
    and try to select local address that we prefer for talks with
    the target host. Such local address is selected by looking
    for primary IP addresses on all our subnets on the outgoing
    interface that include the target IP address. If no suitable
    local address is found we select the first local address
    we have on the outgoing interface or on all other interfaces,
    with the hope we will receive reply for our request and
    even sometimes no matter the source IP address we announce.

    The max value from conf/{all,interface}/arp_announce is used.

    Increasing the restriction level gives more chance for
    receiving answer from the resolved target while decreasing
    the level announces more valid sender's information.

arp_ignore - INTEGER
    Define different modes for sending replies in response to
    received ARP requests that resolve local target IP addresses:
    0 - (default): reply for any local target IP address, configured
    on any interface
    1 - reply only if the target IP address is local address
    configured on the incoming interface
    2 - reply only if the target IP address is local address
    configured on the incoming interface and both with the
    sender's IP address are part from same subnet on this interface
    3 - do not reply for local addresses configured with scope host,
    only resolutions for global and link addresses are replied
    4-7 - reserved
    8 - do not reply for all local addresses

    The max value from conf/{all,interface}/arp_ignore is used
    when ARP request is received on the {interface}

arp_notify - BOOLEAN
    Define mode for notification of address and device changes.
    0 - (default): do nothing
    1 - Generate gratuitous arp replies when device is brought up
        or hardware address changes.

arp_accept - BOOLEAN
    Define behavior when gratuitous arp replies are received:
    0 - drop gratuitous arp frames
    1 - accept gratuitous arp frames

app_solicit - INTEGER
    The maximum number of probes to send to the user space ARP daemon
    via netlink before dropping back to multicast probes (see
    mcast_solicit).  Defaults to 0.

disable_policy - BOOLEAN
    Disable IPSEC policy (SPD) for this interface

disable_xfrm - BOOLEAN
    Disable IPSEC encryption on this interface, whatever the policy



tag - INTEGER
    Allows you to write a number, which can be used as required.
    Default value is 0.

Alexey Kuznetsov.
kuznet@ms2.inr.ac.ru

Updated by:
Andi Kleen
ak@muc.de
Nicolas Delon
delon.nicolas@wanadoo.fr




/proc/sys/net/ipv6/* Variables:

IPv6 has no global variables such as tcp_*.  tcp_* settings under ipv4/ also
apply to IPv6 [XXX?].

bindv6only - BOOLEAN
    Default value for IPV6_V6ONLY socket option,
    which restricts use of the IPv6 socket to IPv6 communication
    only.
        TRUE: disable IPv4-mapped address feature
        FALSE: enable IPv4-mapped address feature

    Default: FALSE (as specified in RFC2553bis)

IPv6 Fragmentation:

ip6frag_high_thresh - INTEGER
    Maximum memory used to reassemble IPv6 fragments. When
    ip6frag_high_thresh bytes of memory is allocated for this purpose,
    the fragment handler will toss packets until ip6frag_low_thresh
    is reached.

ip6frag_low_thresh - INTEGER
    See ip6frag_high_thresh

ip6frag_time - INTEGER
    Time in seconds to keep an IPv6 fragment in memory.

ip6frag_secret_interval - INTEGER
    Regeneration interval (in seconds) of the hash secret (or lifetime
    for the hash secret) for IPv6 fragments.
    Default: 600

conf/default/*:
    Change the interface-specific default settings.


conf/all/*:
    Change all the interface-specific settings.

    [XXX:  Other special features than forwarding?]

conf/all/forwarding - BOOLEAN
    Enable global IPv6 forwarding between all interfaces.

    IPv4 and IPv6 work differently here; e.g. netfilter must be used
    to control which interfaces may forward packets and which not.

    This also sets all interfaces' Host/Router setting
    'forwarding' to the specified value.  See below for details.

    This referred to as global forwarding.

proxy_ndp - BOOLEAN
    Do proxy ndp.

conf/interface/*:
    Change special settings per interface.

    The functional behaviour for certain settings is different
    depending on whether local forwarding is enabled or not.

accept_ra - BOOLEAN
    Accept Router Advertisements; autoconfigure using them.

    Functional default: enabled if local forwarding is disabled.
                disabled if local forwarding is enabled.

accept_ra_defrtr - BOOLEAN
    Learn default router in Router Advertisement.

    Functional default: enabled if accept_ra is enabled.
                disabled if accept_ra is disabled.

accept_ra_pinfo - BOOLEAN
    Learn Prefix Information in Router Advertisement.

    Functional default: enabled if accept_ra is enabled.
                disabled if accept_ra is disabled.

accept_ra_rt_info_max_plen - INTEGER
    Maximum prefix length of Route Information in RA.

    Route Information w/ prefix larger than or equal to this
    variable shall be ignored.

    Functional default: 0 if accept_ra_rtr_pref is enabled.
                -1 if accept_ra_rtr_pref is disabled.

accept_ra_rtr_pref - BOOLEAN
    Accept Router Preference in RA.

    Functional default: enabled if accept_ra is enabled.
                disabled if accept_ra is disabled.

accept_redirects - BOOLEAN
    Accept Redirects.

    Functional default: enabled if local forwarding is disabled.
                disabled if local forwarding is enabled.

accept_source_route - INTEGER
    Accept source routing (routing extension header).

    >= 0: Accept only routing header type 2.
    < 0: Do not accept routing header.

    Default: 0

autoconf - BOOLEAN
    Autoconfigure addresses using Prefix Information in Router
    Advertisements.

    Functional default: enabled if accept_ra_pinfo is enabled.
                disabled if accept_ra_pinfo is disabled.

dad_transmits - INTEGER
    The amount of Duplicate Address Detection probes to send.
    Default: 1

forwarding - BOOLEAN
    Configure interface-specific Host/Router behaviour.

    Note: It is recommended to have the same setting on all
    interfaces; mixed router/host scenarios are rather uncommon.

    FALSE:

    By default, Host behaviour is assumed.  This means:

    1. IsRouter flag is not set in Neighbour Advertisements.
    2. Router Solicitations are being sent when necessary.
    3. If accept_ra is TRUE (default), accept Router
       Advertisements (and do autoconfiguration).
    4. If accept_redirects is TRUE (default), accept Redirects.

    TRUE:

    If local forwarding is enabled, Router behaviour is assumed.
    This means exactly the reverse from the above:

    1. IsRouter flag is set in Neighbour Advertisements.
    2. Router Solicitations are not sent.
    3. Router Advertisements are ignored.
    4. Redirects are ignored.

    Default: FALSE if global forwarding is disabled (default),
         otherwise TRUE.

hop_limit - INTEGER
    Default Hop Limit to set.
    Default: 64

mtu - INTEGER
    Default Maximum Transfer Unit
    Default: 1280 (IPv6 required minimum)

router_probe_interval - INTEGER
    Minimum interval (in seconds) between Router Probing described
    in RFC4191.

    Default: 60

router_solicitation_delay - INTEGER
    Number of seconds to wait after interface is brought up
    before sending Router Solicitations.
    Default: 1

router_solicitation_interval - INTEGER
    Number of seconds to wait between Router Solicitations.
    Default: 4

router_solicitations - INTEGER
    Number of Router Solicitations to send until assuming no
    routers are present.
    Default: 3

use_tempaddr - INTEGER
    Preference for Privacy Extensions (RFC3041).
      <= 0 : disable Privacy Extensions
      == 1 : enable Privacy Extensions, but prefer public
             addresses over temporary addresses.
      >  1 : enable Privacy Extensions and prefer temporary
             addresses over public addresses.
    Default:  0 (for most devices)
         -1 (for point-to-point devices and loopback devices)

temp_valid_lft - INTEGER
    valid lifetime (in seconds) for temporary addresses.
    Default: 604800 (7 days)

temp_prefered_lft - INTEGER
    Preferred lifetime (in seconds) for temporary addresses.
    Default: 86400 (1 day)

max_desync_factor - INTEGER
    Maximum value for DESYNC_FACTOR, which is a random value
    that ensures that clients don't synchronize with each
    other and generate new addresses at exactly the same time.
    value is in seconds.
    Default: 600

regen_max_retry - INTEGER
    Number of attempts before give up attempting to generate
    valid temporary addresses.
    Default: 5

max_addresses - INTEGER
    Number of maximum addresses per interface.  0 disables limitation.
    It is recommended not set too large value (or 0) because it would
    be too easy way to crash kernel to allow to create too much of
    autoconfigured addresses.
    Default: 16

disable_ipv6 - BOOLEAN
    Disable IPv6 operation.  If accept_dad is set to 2, this value
    will be dynamically set to TRUE if DAD fails for the link-local
    address.
    Default: FALSE (enable IPv6 operation)

    When this value is changed from 1 to 0 (IPv6 is being enabled),
    it will dynamically create a link-local address on the given
    interface and start Duplicate Address Detection, if necessary.

    When this value is changed from 0 to 1 (IPv6 is being disabled),
    it will dynamically delete all address on the given interface.

accept_dad - INTEGER
    Whether to accept DAD (Duplicate Address Detection).
    0: Disable DAD
    1: Enable DAD (default)
    2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
       link-local address has been found.

icmp/*:
ratelimit - INTEGER
    Limit the maximal rates for sending ICMPv6 packets.
    0 to disable any limiting,
    otherwise the minimal space between responses in milliseconds.
    Default: 1000


IPv6 Update by:
Pekka Savola <pekkas@netcore.fi>
YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>


/proc/sys/net/bridge/* Variables:

bridge-nf-call-arptables - BOOLEAN
    1 : pass bridged ARP traffic to arptables' FORWARD chain.
    0 : disable this.
    Default: 1

bridge-nf-call-iptables - BOOLEAN
    1 : pass bridged IPv4 traffic to iptables' chains.
    0 : disable this.
    Default: 1

bridge-nf-call-ip6tables - BOOLEAN
    1 : pass bridged IPv6 traffic to ip6tables' chains.
    0 : disable this.
    Default: 1

bridge-nf-filter-vlan-tagged - BOOLEAN
    1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
    0 : disable this.
    Default: 1

bridge-nf-filter-pppoe-tagged - BOOLEAN
    1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
    0 : disable this.
    Default: 1


proc/sys/net/sctp/* Variables:

addip_enable - BOOLEAN
    Enable or disable extension of  Dynamic Address Reconfiguration
    (ADD-IP) functionality specified in RFC5061.  This extension provides
    the ability to dynamically add and remove new addresses for the SCTP
    associations.

    1: Enable extension.

    0: Disable extension.

    Default: 0

addip_noauth_enable - BOOLEAN
    Dynamic Address Reconfiguration (ADD-IP) requires the use of
    authentication to protect the operations of adding or removing new
    addresses.  This requirement is mandated so that unauthorized hosts
    would not be able to hijack associations.  However, older
    implementations may not have implemented this requirement while
    allowing the ADD-IP extension.  For reasons of interoperability,
    we provide this variable to control the enforcement of the
    authentication requirement.

    1: Allow ADD-IP extension to be used without authentication.  This
       should only be set in a closed environment for interoperability
       with older implementations.

    0: Enforce the authentication requirement

    Default: 0

auth_enable - BOOLEAN
    Enable or disable Authenticated Chunks extension.  This extension
    provides the ability to send and receive authenticated chunks and is
    required for secure operation of Dynamic Address Reconfiguration
    (ADD-IP) extension.

    1: Enable this extension.
    0: Disable this extension.

    Default: 0

prsctp_enable - BOOLEAN
    Enable or disable the Partial Reliability extension (RFC3758) which
    is used to notify peers that a given DATA should no longer be expected.

    1: Enable extension
    0: Disable

    Default: 1

max_burst - INTEGER
    The limit of the number of new packets that can be initially sent.  It
    controls how bursty the generated traffic can be.

    Default: 4

association_max_retrans - INTEGER
    Set the maximum number for retransmissions that an association can
    attempt deciding that the remote end is unreachable.  If this value
    is exceeded, the association is terminated.

    Default: 10

max_init_retransmits - INTEGER
    The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
    that an association will attempt before declaring the destination
    unreachable and terminating.

    Default: 8

path_max_retrans - INTEGER
    The maximum number of retransmissions that will be attempted on a given
    path.  Once this threshold is exceeded, the path is considered
    unreachable, and new traffic will use a different path when the
    association is multihomed.

    Default: 5

rto_initial - INTEGER
    The initial round trip timeout value in milliseconds that will be used
    in calculating round trip times.  This is the initial time interval
    for retransmissions.

    Default: 3000

rto_max - INTEGER
    The maximum value (in milliseconds) of the round trip timeout.  This
    is the largest time interval that can elapse between retransmissions.

    Default: 60000

rto_min - INTEGER
    The minimum value (in milliseconds) of the round trip timeout.  This
    is the smallest time interval the can elapse between retransmissions.

    Default: 1000

hb_interval - INTEGER
    The interval (in milliseconds) between HEARTBEAT chunks.  These chunks
    are sent at the specified interval on idle paths to probe the state of
    a given path between 2 associations.

    Default: 30000

sack_timeout - INTEGER
    The amount of time (in milliseconds) that the implementation will wait
    to send a SACK.

    Default: 200

valid_cookie_life - INTEGER
    The default lifetime of the SCTP cookie (in milliseconds).  The cookie
    is used during association establishment.

    Default: 60000

cookie_preserve_enable - BOOLEAN
    Enable or disable the ability to extend the lifetime of the SCTP cookie
    that is used during the establishment phase of SCTP association

    1: Enable cookie lifetime extension.
    0: Disable

    Default: 1

rcvbuf_policy - INTEGER
    Determines if the receive buffer is attributed to the socket or to
    association.   SCTP supports the capability to create multiple
    associations on a single socket.  When using this capability, it is
    possible that a single stalled association that's buffering a lot
    of data may block other associations from delivering their data by
    consuming all of the receive buffer space.  To work around this,
    the rcvbuf_policy could be set to attribute the receiver buffer space
    to each association instead of the socket.  This prevents the described
    blocking.

    1: rcvbuf space is per association
    0: recbuf space is per socket

    Default: 0

sndbuf_policy - INTEGER
    Similar to rcvbuf_policy above, this applies to send buffer space.

    1: Send buffer is tracked per association
    0: Send buffer is tracked per socket.

    Default: 0

sctp_mem - vector of 3 INTEGERs: min, pressure, max
    Number of pages allowed for queueing by all SCTP sockets.

    min: Below this number of pages SCTP is not bothered about its
    memory appetite. When amount of memory allocated by SCTP exceeds
    this number, SCTP starts to moderate memory usage.

    pressure: This value was introduced to follow format of tcp_mem.

    max: Number of pages allowed for queueing by all SCTP sockets.

    Default is calculated at boot time from amount of available memory.

sctp_rmem - vector of 3 INTEGERs: min, default, max
    See tcp_rmem for a description.

sctp_wmem  - vector of 3 INTEGERs: min, default, max
    See tcp_wmem for a description.

addr_scope_policy - INTEGER
    Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00

    0   - Disable IPv4 address scoping
    1   - Enable IPv4 address scoping
    2   - Follow draft but allow IPv4 private addresses
    3   - Follow draft but allow IPv4 link local addresses

    Default: 1


/proc/sys/net/core/*
dev_weight - INTEGER
    The maximum number of packets that kernel can handle on a NAPI
    interrupt, it's a Per-CPU variable.

    Default: 64

/proc/sys/net/unix/*
max_dgram_qlen - INTEGER
    The maximum length of dgram socket receive queue

    Default: 10


UNDOCUMENTED:

/proc/sys/net/irda/*
    fast_poll_increase FIXME
    warn_noreply_time FIXME
    discovery_slots FIXME
    slot_timeout FIXME
    max_baud_rate FIXME
    discovery_timeout FIXME
    lap_keepalive_time FIXME
    max_noreply_time FIXME
    max_tx_data_size FIXME
    max_tx_window FIXME
    min_tx_turn_time FIXME
Copyright © opschina.org 2017 with zzlyzq@gmail.com all right reserved,powered by Gitbook该文件修订时间: 2017-07-11 11:32:48

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