ip_forward - BOOLEAN
0 - disabled (default)
- not 0 - enabled
+ not 0 - enabled
Forward Packets between interfaces.
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
+ 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
+ See ipfrag_high_thresh
ipfrag_time - INTEGER
- Time in seconds to keep an IP fragment in memory.
+ Time in seconds to keep an IP fragment in memory.
ipfrag_secret_interval - INTEGER
- Regeneration interval (in seconds) of the hash secret (or lifetime
+ 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
+ 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
+ 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
+ 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.
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 jiffies(1).
+ 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 jiffies(1).
+ 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 jiffies(1).
+ 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 jiffies(1).
+ Measured in seconds.
+
+TCP variables:
-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 defined in RFC3465. If set to
- 0 then does congestion avoid once per ack. 1 is conservative
- value, and 2 is more agressive.
+ 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_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_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_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_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_keepalive_time - INTEGER
- How often TCP sends out keepalive messages when keepalive is enabled.
- Default: 2hours.
+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_keepalive_probes - INTEGER
- How many keepalive probes TCP sends out, until it decides that the
- connection is broken. Default value: 9.
+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_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_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_retries1 - INTEGER
- How many times to retry before deciding that something is wrong
- and it is necessary to report this suspicion to network layer.
- Minimal RFC value is 3, it is default, which corresponds
- to ~3sec-8min depending on RTO.
+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_retries2 - INTEGER
- How may times to retry before killing alive TCP connection.
- RFC1122 says that the limit should be longer than 100 sec.
- It is too small number. Default value 15 corresponds to ~13-30min
- depending on RTO.
+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_orphan_retries - INTEGER
- How may times to retry before killing TCP connection, closed
- by our side. Default value 7 corresponds to ~50sec-16min
- depending on RTO. If you machine is loaded WEB server,
- you should think about lowering this value, such sockets
- may consume significant resources. Cf. tcp_max_orphans.
+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_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
because they eat maximum 1.5K of memory, but they tend
to live longer. Cf. tcp_max_orphans.
-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_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_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_keepalive_time - INTEGER
+ How often TCP sends out keepalive messages when keepalive is enabled.
+ Default: 2hours.
-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_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,
more aggressively. Let me to remind again: each orphan eats
up to ~64K of unswappable memory.
-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_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 synflood 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
- synflood warnings in logs not being really flooded, your server
- is seriously misconfigured.
-
-tcp_stdurg - BOOLEAN
- Use the Host requirements interpretation of the TCP urg 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_max_syn_backlog - INTEGER
Maximal number of remembered connection requests, which are
still did not receive an acknowledgment from connecting client.
and 128 for low memory machines. If server suffers of overload,
try to increase this number.
-tcp_window_scaling - BOOLEAN
- Enable window scaling as defined in RFC1323.
+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_timestamps - BOOLEAN
- Enable timestamps as defined in RFC1323.
+tcp_mem - vector of 3 INTEGERs: min, pressure, max
+ min: below this number of pages TCP is not bothered about its
+ memory appetite.
-tcp_sack - BOOLEAN
- Enable select acknowledgments (SACKS).
+ 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".
-tcp_fack - BOOLEAN
- Enable FACK congestion avoidance and fast retransmission.
- The value is not used, if tcp_sack is not enabled.
+ max: number of pages allowed for queueing by all TCP sockets.
-tcp_dsack - BOOLEAN
- Allows TCP to send "duplicate" SACKs.
+ Defaults are calculated at boot time from amount of available
+ memory.
-tcp_ecn - BOOLEAN
- Enable Explicit Congestion Notification in TCP.
+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
+ 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_wmem - vector of 3 INTEGERs: min, default, max
- min: Amount of memory reserved for send buffers for TCP socket.
- Each TCP socket has rights to use it due to fact of its birth.
- Default: 4K
+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.
- default: Amount of memory allowed for send buffers for TCP socket
- by default. This value overrides net.core.wmem_default used
- by other protocols, it is usually lower than net.core.wmem_default.
- Default: 16K
+ 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.
- max: Maximal amount of memory allowed for automatically selected
- send buffers for TCP socket. This value does not override
- net.core.wmem_max, "static" selection via SO_SNDBUF does not use this.
- Default: 128K
+ 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.
pressure.
Default: 8K
- default: default size of receive buffer used by TCP sockets.
+ 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
max: maximal size of receive buffer allowed for automatically
selected receiver buffers for TCP socket. This value does not override
- net.core.rmem_max, "static" selection via SO_RCVBUF does not use this.
- Default: 87380*2 bytes.
+ 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_mem - vector of 3 INTEGERs: min, pressure, max
- low: below this number of pages TCP is not bothered about its
- memory appetite.
+tcp_sack - BOOLEAN
+ Enable select acknowledgments (SACKS).
- 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 "low".
+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
- high: number of pages allowed for queueing by all TCP sockets.
+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
- Defaults are calculated at boot time from amount of available
- memory.
+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_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_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
-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
+ 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.
-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
+ 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_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_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_frto - BOOLEAN
- Enables F-RTO, 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.
+ 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_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.
+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.
-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_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
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
+ 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
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 maximal rate in jiffies(1)
- Default: 100
+ 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.
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.
+ 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 regarldess of this setting.
+ has one will be used regardless of this setting.
Default: 0
Change the maximum number of multicast groups we can subscribe to.
Default: 20
-conf/interface/* changes special settings per interface (where "interface" is
+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
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
+ - 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
+ - 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)
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
+ 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
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.
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.
default TRUE (router)
FALSE (host)
-rp_filter - BOOLEAN
- 1 - do source validation by reversed path, as specified in RFC1812
- Recommended option for single homed hosts and stub network
- routers. Could cause troubles for complicated (not loop free)
- networks running a slow unreliable protocol (sort of RIP),
- or using static routes.
+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.
+ default FALSE
+rp_filter - INTEGER
0 - No source validation.
-
- conf/all/rp_filter must also be set to TRUE to do source validation
- on the interface
+ 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.
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
Allows you to write a number, which can be used as required.
Default value is 0.
-(1) Jiffie: internal timeunit for the kernel. On the i386 1/100s, on the
-Alpha 1/1024s. See the HZ define in /usr/include/asm/param.h for the exact
-value on your system.
-
Alexey Kuznetsov.
kuznet@ms2.inr.ac.ru
bindv6only - BOOLEAN
Default value for IPV6_V6ONLY socket option,
- which restricts use of the IPv6 socket to IPv6 communication
+ which restricts use of the IPv6 socket to IPv6 communication
only.
TRUE: disable IPv4-mapped address feature
FALSE: enable IPv4-mapped address feature
IPv6 Fragmentation:
ip6frag_high_thresh - INTEGER
- Maximum memory used to reassemble IPv6 fragments. When
+ 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
+ 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
+ Regeneration interval (in seconds) of the hash secret (or lifetime
for the hash secret) for IPv6 fragments.
Default: 600
conf/all/*:
- Change all the interface-specific settings.
+ Change all the interface-specific settings.
[XXX: Other special features than forwarding?]
conf/all/forwarding - BOOLEAN
- Enable global IPv6 forwarding between all interfaces.
+ Enable global IPv6 forwarding between all interfaces.
- IPv4 and IPv6 work differently here; e.g. netfilter must be used
+ 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
+ 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
+ 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.
disabled if accept_ra is disabled.
accept_ra_pinfo - BOOLEAN
- Learn Prefix Inforamtion in Router Advertisement.
+ Learn Prefix Information in Router Advertisement.
Functional default: enabled if accept_ra is enabled.
disabled if accept_ra is disabled.
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
+ Autoconfigure addresses using Prefix Information in Router
Advertisements.
Functional default: enabled if accept_ra_pinfo is enabled.
dad_transmits - INTEGER
The amount of Duplicate Address Detection probes to send.
Default: 1
-
+
forwarding - BOOLEAN
- Configure interface-specific Host/Router behaviour.
+ Configure interface-specific Host/Router behaviour.
- Note: It is recommended to have the same setting on all
+ Note: It is recommended to have the same setting on all
interfaces; mixed router/host scenarios are rather uncommon.
FALSE:
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
+ 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.
+ 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.
Default: 4
router_solicitations - INTEGER
- Number of Router Solicitations to send until assuming no
+ Number of Router Solicitations to send until assuming no
routers are present.
Default: 3
max_desync_factor - INTEGER
Maximum value for DESYNC_FACTOR, which is a random value
- that ensures that clients don't synchronize with each
+ 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.
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
+ 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.
+
+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."
+
icmp/*:
ratelimit - INTEGER
Limit the maximal rates for sending ICMPv6 packets.
- 0 to disable any limiting, otherwise the maximal rate in jiffies(1)
- Default: 100
+ 0 to disable any limiting,
+ otherwise the minimal space between responses in milliseconds.
+ Default: 1000
IPv6 Update by:
Default: 1
bridge-nf-filter-vlan-tagged - BOOLEAN
- 1 : pass bridged vlan-tagged ARP/IP traffic to arptables/iptables.
+ 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:
-dev_weight FIXME
-discovery_slots FIXME
-discovery_timeout FIXME
-fast_poll_increase FIXME
-ip6_queue_maxlen FIXME
-lap_keepalive_time FIXME
-lo_cong FIXME
-max_baud_rate FIXME
-max_dgram_qlen FIXME
-max_noreply_time FIXME
-max_tx_data_size FIXME
-max_tx_window FIXME
-min_tx_turn_time FIXME
-mod_cong FIXME
-no_cong FIXME
-no_cong_thresh FIXME
-slot_timeout FIXME
-warn_noreply_time FIXME
-
-$Id: ip-sysctl.txt,v 1.20 2001/12/13 09:00:18 davem Exp $
+/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
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff