TCP variables:
+somaxconn - INTEGER
+ Limit of socket listen() backlog, known in userspace as SOMAXCONN.
+ Defaults to 128. See also tcp_max_syn_backlog for additional tuning
+ for TCP sockets.
+
tcp_abc - INTEGER
Controls Appropriate Byte Count (ABC) defined in RFC3465.
ABC is a way of increasing congestion window (cwnd) more slowly
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_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_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_dsack - BOOLEAN
+ Allows TCP to send "duplicate" SACKs.
-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_ecn - BOOLEAN
+ Enable Explicit Congestion Notification in TCP.
+
+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 - 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.
-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_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_reordering - INTEGER
Maximal reordering of packets in a TCP stream.
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
+ 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.
- 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
+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.
- 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
+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.
net.core.rmem_max, "static" selection via SO_RCVBUF does not use this.
Default: 87380*2 bytes.
-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_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
- max: number of pages allowed for queueing by all TCP sockets.
+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
- 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 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.
-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
+ synflood 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
+ 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.
+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_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_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_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_window_scaling - BOOLEAN
+ Enable window scaling as defined in RFC1323.
-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_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
-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.
+ 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
+
+ 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
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_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
-
CIPSOv4 Variables:
cipso_cache_enable - BOOLEAN
slot_timeout FIXME
warn_noreply_time FIXME
-$Id: ip-sysctl.txt,v 1.20 2001/12/13 09:00:18 davem Exp $
projects / linux-2.6-omap-h63xx.git / commitdiff