path: root/Documentation/networking/ip-sysctl.txt

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

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

	Forward Packets between interfaces.

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

ip_default_ttl - INTEGER
	default 64

ip_no_pmtu_disc - BOOLEAN
	Disable Path MTU Discovery.
	default FALSE

min_pmtu - INTEGER
	default 562 - minimum discovered Path MTU

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

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

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

IP Fragmentation:

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

ipfrag_low_thresh - INTEGER
	See ipfrag_high_thresh

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

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

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

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

INET peer storage:

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

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

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

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

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

TCP variables:

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

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

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

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

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

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

tcp_available_congesti