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+/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 value of TTL field (Time To Live) for outgoing (but not
+ forwarded) IP packets. Should be between 1 and 255 inclusive.
+ Default: 64 (as recommended by RFC1700)
+
+ip_no_pmtu_disc - BOOLEAN
+ Disable Path MTU Discovery.
+ default FALSE
+
+min_pmtu - INTEGER
+ default 552 - minimum discovered Path MTU
+
+route/max_size - INTEGER
+ Maximum number of routes allowed in the kernel. Increase
+ this when using large numbers of interfaces and/or routes.
+
+neigh/default/gc_thresh1 - INTEGER
+ Minimum number of entries to keep. Garbage collector will not
+ purge entries if there are fewer than this number.
+ Default: 256
+
+neigh/default/gc_thresh3 - INTEGER
+ Maximum number of neighbor entries allowed. Increase this
+ when using large numbers of interfaces and when communicating
+ with large numbers of directly-connected peers.
+ Default: 1024
+
+neigh/default/unres_qlen_bytes - INTEGER
+ The maximum number of bytes which may be used by packets
+ queued for each unresolved address by other network layers.
+ (added in linux 3.3)
+ Setting negative value is meaningless and will return error.
+ Default: 65536 Bytes(64KB)
+
+neigh/default/unres_qlen - INTEGER
+ The maximum number of packets which may be queued for each
+ unresolved address by other network layers.
+ (deprecated in linux 3.3) : use unres_qlen_bytes instead.
+ Prior to linux 3.3, the default value is 3 which may cause
+ unexpected packet loss. The current default value is calculated
+ according to default value of unres_qlen_bytes and true size of
+ packet.
+ Default: 31
+
+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.
+
+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.
+
+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_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.
+ Possible values are [-31, 31], inclusive.
+ Default: 1
+
+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.
+ For passive connections, the listener congestion control choice
+ is inherited.
+ [see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ]
+
+tcp_cookie_size - INTEGER
+ Default size of TCP Cookie Transactions (TCPCT) option, that may be
+ overridden on a per socket basis by the TCPCT socket option.
+ Values greater than the maximum (16) are interpreted as the maximum.
+ Values greater than zero and less than the minimum (8) are interpreted
+ as the minimum. Odd values are interpreted as the next even value.
+ Default: 0 (off).
+
+tcp_dsack - BOOLEAN
+ Allows TCP to send "duplicate" SACKs.
+
+tcp_early_retrans - INTEGER
+ Enable Early Retransmit (ER), per RFC 5827. ER lowers the threshold
+ for triggering fast retransmit when the amount of outstanding data is
+ small and when no previously unsent data can be transmitted (such
+ that limited transmit could be used).
+ Possible values:
+ 0 disables ER
+ 1 enables ER
+ 2 enables ER but delays fast recovery and fast retransmit
+ by a fourth of RTT. This mitigates connection falsely
+ recovers when network has a small degree of reordering
+ (less than 3 packets).
+ Default: 2
+
+tcp_ecn - INTEGER
+ Control use of Explicit Congestion Notification (ECN) by TCP.
+ ECN is used only when both ends of the TCP connection indicate
+ support for it. This feature is useful in avoiding losses due
+ to congestion by allowing supporting routers to signal
+ congestion before having to drop packets.
+ Possible values are:
+ 0 Disable ECN. Neither initiate nor accept ECN.
+ 1 Enable ECN when requested by incoming connections and
+ also request ECN on outgoing connection attempts.
+ 2 Enable ECN when requested by incoming connections
+ but do not request ECN on outgoing connections.
+ 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
+ The length of time an orphaned (no longer referenced by any
+ application) connection will remain in the FIN_WAIT_2 state
+ before it is aborted at the local end. While a perfectly
+ valid "receive only" state for an un-orphaned connection, an
+ orphaned connection in FIN_WAIT_2 state could otherwise wait
+ forever for the remote to close its end of the connection.
+ Cf. tcp_max_orphans
+ Default: 60 seconds
+
+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_ssthresh - INTEGER
+ Limited Slow-Start for TCP with large congestion windows (cwnd) defined in
+ RFC3742. Limited slow-start is a mechanism to limit growth of the cwnd
+ on the region where cwnd is larger than tcp_max_ssthresh. TCP increases cwnd
+ by at most tcp_max_ssthresh segments, and by at least tcp_max_ssthresh/2
+ segments per RTT when the cwnd is above tcp_max_ssthresh.
+ If TCP connection increased cwnd to thousands (or tens of thousands) segments,
+ and thousands of packets were being dropped during slow-start, you can set
+ tcp_max_ssthresh to improve performance for new TCP connection.
+ Default: 0 (off)
+
+tcp_max_syn_backlog - INTEGER
+ Maximal number of remembered connection requests, which have not
+ received an acknowledgment from connecting client.
+ The minimal value is 128 for low memory machines, and it will
+ increase in proportion to the memory of machine.
+ If server suffers from overload, try increasing 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 8.
+ 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: 1 page
+
+ 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 6MB, 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 31seconds till the last retransmission
+ with the current initial RTO of 1second. With this the final timeout
+ for a passive TCP connection will happen after 63seconds.
+
+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_fastopen - INTEGER
+ Enable TCP Fast Open feature (draft-ietf-tcpm-fastopen) to send data
+ in the opening SYN packet. To use this feature, the client application
+ must use sendmsg() or sendto() with MSG_FASTOPEN flag rather than
+ connect() to perform a TCP handshake automatically.
+
+ The values (bitmap) are
+ 1: Enables sending data in the opening SYN on the client.
+ 2: Enables TCP Fast Open on the server side, i.e., allowing data in
+ a SYN packet to be accepted and passed to the application before
+ 3-way hand shake finishes.
+ 4: Send data in the opening SYN regardless of cookie availability and
+ without a cookie option.
+ 0x100: Accept SYN data w/o validating the cookie.
+ 0x200: Accept data-in-SYN w/o any cookie option present.
+ 0x400/0x800: Enable Fast Open on all listeners regardless of the
+ TCP_FASTOPEN socket option. The two different flags designate two
+ different ways of setting max_qlen without the TCP_FASTOPEN socket
+ option.
+
+ Default: 0
+
+ Note that the client & server side Fast Open flags (1 and 2
+ respectively) must be also enabled before the rest of flags can take
+ effect.
+
+ See include/net/tcp.h and the code for more details.
+
+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 6, which corresponds to 63seconds till the last retransmission
+ with the current initial RTO of 1second. With this the final timeout
+ for an active TCP connection attempt will happen after 127seconds.
+
+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: 1 page
+
+ 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
+
+tcp_thin_linear_timeouts - BOOLEAN
+ Enable dynamic triggering of linear timeouts for thin streams.
+ If set, a check is performed upon retransmission by timeout to
+ determine if the stream is thin (less than 4 packets in flight).
+ As long as the stream is found to be thin, up to 6 linear
+ timeouts may be performed before exponential backoff mode is
+ initiated. This improves retransmission latency for
+ non-aggressive thin streams, often found to be time-dependent.
+ For more information on thin streams, see
+ Documentation/networking/tcp-thin.txt
+ Default: 0
+
+tcp_thin_dupack - BOOLEAN
+ Enable dynamic triggering of retransmissions after one dupACK
+ for thin streams. If set, a check is performed upon reception
+ of a dupACK to determine if the stream is thin (less than 4
+ packets in flight). As long as the stream is found to be thin,
+ data is retransmitted on the first received dupACK. This
+ improves retransmission latency for non-aggressive thin
+ streams, often found to be time-dependent.
+ For more information on thin streams, see
+ Documentation/networking/tcp-thin.txt
+ Default: 0
+
+tcp_limit_output_bytes - INTEGER
+ Controls TCP Small Queue limit per tcp socket.
+ TCP bulk sender tends to increase packets in flight until it
+ gets losses notifications. With SNDBUF autotuning, this can
+ result in a large amount of packets queued in qdisc/device
+ on the local machine, hurting latency of other flows, for
+ typical pfifo_fast qdiscs.
+ tcp_limit_output_bytes limits the number of bytes on qdisc
+ or device to reduce artificial RTT/cwnd and reduce bufferbloat.
+ Note: For GSO/TSO enabled flows, we try to have at least two
+ packets in flight. Reducing tcp_limit_output_bytes might also
+ reduce the size of individual GSO packet (64KB being the max)
+ Default: 131072
+
+tcp_challenge_ack_limit - INTEGER
+ Limits number of Challenge ACK sent per second, as recommended
+ in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
+ Default: 100
+
+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: 1 page
+
+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: 1 page
+
+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. The default values are
+ 32768 and 61000 respectively.
+
+ip_local_reserved_ports - list of comma separated ranges
+ Specify the ports which are reserved for known third-party
+ applications. These ports will not be used by automatic port
+ assignments (e.g. when calling connect() or bind() with port
+ number 0). Explicit port allocation behavior is unchanged.
+
+ The format used for both input and output is a comma separated
+ list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and
+ 10). Writing to the file will clear all previously reserved
+ ports and update the current list with the one given in the
+ input.
+
+ Note that ip_local_port_range and ip_local_reserved_ports
+ settings are independent and both are considered by the kernel
+ when determining which ports are available for automatic port
+ assignments.
+
+ You can reserve ports which are not in the current
+ ip_local_port_range, e.g.:
+
+ $ cat /proc/sys/net/ipv4/ip_local_port_range
+ 32000 61000
+ $ cat /proc/sys/net/ipv4/ip_local_reserved_ports
+ 8080,9148
+
+ although this is redundant. However such a setting is useful
+ if later the port range is changed to a value that will
+ include the reserved ports.
+
+ Default: Empty
+
+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
+
+ Theoretical maximum value is bounded by having to send a membership
+ report in a single datagram (i.e. the report can't span multiple
+ datagrams, or risk confusing the switch and leaving groups you don't
+ intend to).
+
+ The number of supported groups 'M' is bounded by the number of group
+ report entries you can fit into a single datagram of 65535 bytes.
+
+ M = 65536-sizeof (ip header)/(sizeof(Group record))
+
+ Group records are variable length, with a minimum of 12 bytes.
+ So net.ipv4.igmp_max_memberships should not be set higher than:
+
+ (65536-24) / 12 = 5459
+
+ The value 5459 assumes no IP header options, so in practice
+ this number may be lower.
+
+ 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
+
+proxy_arp_pvlan - BOOLEAN
+ Private VLAN proxy arp.
+ Basically allow proxy arp replies back to the same interface
+ (from which the ARP request/solicitation was received).
+
+ This is done to support (ethernet) switch features, like RFC
+ 3069, where the individual ports are NOT allowed to
+ communicate with each other, but they are allowed to talk to
+ the upstream router. As described in RFC 3069, it is possible
+ to allow these hosts to communicate through the upstream
+ router by proxy_arp'ing. Don't need to be used together with
+ proxy_arp.
+
+ This technology is known by different names:
+ In RFC 3069 it is called VLAN Aggregation.
+ Cisco and Allied Telesyn call it Private VLAN.
+ Hewlett-Packard call it Source-Port filtering or port-isolation.
+ Ericsson call it MAC-Forced Forwarding (RFC Draft).
+
+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)
+
+accept_local - BOOLEAN
+ Accept packets with local source addresses. In combination
+ with suitable routing, this can be used to direct packets
+ between two local interfaces over the wire and have them
+ accepted properly.
+
+ rp_filter must be set to a non-zero value in order for
+ accept_local to have an effect.
+
+ default FALSE
+
+route_localnet - BOOLEAN
+ Do not consider loopback addresses as martian source or destination
+ while routing. This enables the use of 127/8 for local routing purposes.
+ default FALSE
+
+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.
+
+ The max value from conf/{all,interface}/rp_filter is used
+ when doing 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 requests when device is brought up
+ or hardware address changes.
+
+arp_accept - BOOLEAN
+ Define behavior for gratuitous ARP frames who's IP is not
+ already present in the ARP table:
+ 0 - don't create new entries in the ARP table
+ 1 - create new entries in the ARP table
+
+ Both replies and requests type gratuitous arp will trigger the
+ ARP table to be updated, if this setting is on.
+
+ If the ARP table already contains the IP address of the
+ gratuitous arp frame, the arp table will be updated regardless
+ if this setting is on or off.
+
+
+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 RFC3493)
+
+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 - INTEGER
+ Accept Router Advertisements; autoconfigure using them.
+
+ It also determines whether or not to transmit Router
+ Solicitations. If and only if the functional setting is to
+ accept Router Advertisements, Router Solicitations will be
+ transmitted.
+
+ Possible values are:
+ 0 Do not accept Router Advertisements.
+ 1 Accept Router Advertisements if forwarding is disabled.
+ 2 Overrule forwarding behaviour. Accept Router Advertisements
+ even if forwarding is enabled.
+
+ 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 - INTEGER
+ 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.
+
+ Possible values are:
+ 0 Forwarding disabled
+ 1 Forwarding enabled
+
+ FALSE (0):
+
+ By default, Host behaviour is assumed. This means:
+
+ 1. IsRouter flag is not set in Neighbour Advertisements.
+ 2. If accept_ra is TRUE (default), transmit Router
+ Solicitations.
+ 3. If accept_ra is TRUE (default), accept Router
+ Advertisements (and do autoconfiguration).
+ 4. If accept_redirects is TRUE (default), accept Redirects.
+
+ TRUE (1):
+
+ 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 unless accept_ra is 2.
+ 3. Router Advertisements are ignored unless accept_ra is 2.
+ 4. Redirects are ignored.
+
+ Default: 0 (disabled) if global forwarding is disabled (default),
+ otherwise 1 (enabled).
+
+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
+ Maximum number of autoconfigured addresses per interface. Setting
+ to zero disables the limitation. It is not recommended to set this
+ value too large (or to zero) because it would be an easy way to
+ crash the kernel by allowing too many addresses to be created.
+ 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.
+
+force_tllao - BOOLEAN
+ Enable sending the target link-layer address option even when
+ responding to a unicast neighbor solicitation.
+ Default: FALSE
+
+ Quoting from RFC 2461, section 4.4, Target link-layer address:
+
+ "The option MUST be included for multicast solicitations in order to
+ avoid infinite Neighbor Solicitation "recursion" when the peer node
+ does not have a cache entry to return a Neighbor Advertisements
+ message. When responding to unicast solicitations, the option can be
+ omitted since the sender of the solicitation has the correct link-
+ layer address; otherwise it would not have be able to send the unicast
+ solicitation in the first place. However, including the link-layer
+ address in this case adds little overhead and eliminates a potential
+ race condition where the sender deletes the cached link-layer address
+ prior to receiving a response to a previous solicitation."
+
+ndisc_notify - BOOLEAN
+ Define mode for notification of address and device changes.
+ 0 - (default): do nothing
+ 1 - Generate unsolicited neighbour advertisements when device is brought
+ up or hardware address changes.
+
+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: 0
+
+bridge-nf-filter-pppoe-tagged - BOOLEAN
+ 1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
+ 0 : disable this.
+ Default: 0
+
+bridge-nf-pass-vlan-input-dev - BOOLEAN
+ 1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan
+ interface on the bridge and set the netfilter input device to the vlan.
+ This allows use of e.g. "iptables -i br0.1" and makes the REDIRECT
+ target work with vlan-on-top-of-bridge interfaces. When no matching
+ vlan interface is found, or this switch is off, the input device is
+ set to the bridge interface.
+ 0: disable bridge netfilter vlan interface lookup.
+ Default: 0
+
+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
+
+pf_retrans - INTEGER
+ The number of retransmissions that will be attempted on a given path
+ before traffic is redirected to an alternate transport (should one
+ exist). Note this is distinct from path_max_retrans, as a path that
+ passes the pf_retrans threshold can still be used. Its only
+ deprioritized when a transmission path is selected by the stack. This
+ setting is primarily used to enable fast failover mechanisms without
+ having to reduce path_max_retrans to a very low value. See:
+ http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt
+ for details. Note also that a value of pf_retrans > path_max_retrans
+ disables this feature
+
+ Default: 0
+
+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
+
+cookie_hmac_alg - STRING
+ Select the hmac algorithm used when generating the cookie value sent by
+ a listening sctp socket to a connecting client in the INIT-ACK chunk.
+ Valid values are:
+ * md5
+ * sha1
+ * none
+ Ability to assign md5 or sha1 as the selected alg is predicated on the
+ configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and
+ CONFIG_CRYPTO_SHA1).
+
+ Default: Dependent on configuration. MD5 if available, else SHA1 if
+ available, else none.
+
+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: rcvbuf 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
+ Only the first value ("min") is used, "default" and "max" are
+ ignored.
+
+ min: Minimal size of receive buffer used by SCTP socket.
+ It is guaranteed to each SCTP socket (but not association) even
+ under moderate memory pressure.
+
+ Default: 1 page
+
+sctp_wmem - vector of 3 INTEGERs: min, default, max
+ Currently this tunable has no effect.
+
+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/*
+ Please see: Documentation/sysctl/net.txt for descriptions of these entries.
+
+
+/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