/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_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.

  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)
  
  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.

  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.

  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.

  	Possible values are [-31, 31], inclusive.

  	Default: 2

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

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

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

  tcp_base_mss - INTEGER

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

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

  	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_ecn - INTEGER

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

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

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

  tcp_frto - INTEGER

  	Enables Forward RTO-Recovery (F-RTO) defined in RFC4138.
  	F-RTO is an enhanced recovery algorithm for TCP retransmission

  	timeouts.  It is particularly beneficial in wireless environments
  	where packet loss is typically due to random radio interference

  	rather than intermediate router congestion.  F-RTO is sender-side

  	only modification. Therefore it does not require any support from
  	the peer.

  	If set to 1, basic version is enabled.  2 enables SACK enhanced
  	F-RTO if flow uses SACK.  The basic version can be used also when

  	SACK is in use though scenario(s) with it exists where F-RTO

  	interacts badly with the packet counting of the SACK enabled TCP
  	flow.

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

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

  tcp_keepalive_probes - INTEGER
  	How many keepalive probes TCP sends out, until it decides that the
  	connection is broken. Default value: 9.
  
  tcp_keepalive_intvl - INTEGER
  	How frequently the probes are send out. Multiplied by
  	tcp_keepalive_probes it is time to kill not responding connection,
  	after probes started. Default value: 75sec i.e. connection
  	will be aborted after ~11 minutes of retries.
  
  tcp_low_latency - BOOLEAN
  	If set, the TCP stack makes decisions that prefer lower
  	latency as opposed to higher throughput.  By default, this
  	option is not set meaning that higher throughput is preferred.
  	An example of an application where this default should be
  	changed would be a Beowulf compute cluster.
  	Default: 0

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

  tcp_max_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 4MB, depending on RAM size.

  tcp_sack - BOOLEAN
  	Enable select acknowledgments (SACKS).

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

  tcp_stdurg - BOOLEAN

  	Use the Host requirements interpretation of the TCP urgent pointer field.

  	Most hosts use the older BSD interpretation, so if you turn this on
  	Linux might not communicate correctly with them.
  	Default: FALSE

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

  tcp_syncookies - BOOLEAN
  	Only valid when the kernel was compiled with CONFIG_SYNCOOKIES
  	Send out syncookies when the syn backlog queue of a socket

  	overflows. This is to prevent against the common 'SYN flood attack'

  	Default: FALSE

  	Note, that syncookies is fallback facility.
  	It MUST NOT be used to help highly loaded servers to stand

  	against legal connection rate. If you see SYN flood warnings

  	in your logs, but investigation	shows that they occur
  	because of overload with legal connections, you should tune
  	another parameters until this warning disappear.
  	See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.

  	syncookies seriously violate TCP protocol, do not allow
  	to use TCP extensions, can result in serious degradation
  	of some services (f.e. SMTP relaying), visible not by you,
  	but your clients and relays, contacting you. While you see

  	SYN flood warnings in logs not being really flooded, your server

  	is seriously misconfigured.

  tcp_syn_retries - INTEGER
  	Number of times initial SYNs for an active TCP connection attempt
  	will be retransmitted. Should not be higher than 255. Default value
  	is 5, which corresponds to ~180seconds.
  
  tcp_timestamps - BOOLEAN
  	Enable timestamps as defined in RFC1323.

  tcp_tso_win_divisor - INTEGER

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

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

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

  tcp_window_scaling - BOOLEAN
  	Enable window scaling as defined in RFC1323.

  tcp_wmem - vector of 3 INTEGERs: min, default, max

  	min: Amount of memory reserved for send buffers for TCP sockets.

  	Each TCP socket has rights to use it due to fact of its birth.

  	Default: 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

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

  ip_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.
  	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."

  icmp/*:
  ratelimit - INTEGER
  	Limit the maximal rates for sending ICMPv6 packets.

  	0 to disable any limiting,
  	otherwise the minimal space between responses in milliseconds.
  	Default: 1000

  
  
  IPv6 Update by:
  Pekka Savola <pekkas@netcore.fi>
  YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
  
  
  /proc/sys/net/bridge/* Variables:
  
  bridge-nf-call-arptables - BOOLEAN
  	1 : pass bridged ARP traffic to arptables' FORWARD chain.
  	0 : disable this.
  	Default: 1
  
  bridge-nf-call-iptables - BOOLEAN
  	1 : pass bridged IPv4 traffic to iptables' chains.
  	0 : disable this.
  	Default: 1
  
  bridge-nf-call-ip6tables - BOOLEAN
  	1 : pass bridged IPv6 traffic to ip6tables' chains.
  	0 : disable this.
  	Default: 1
  
  bridge-nf-filter-vlan-tagged - BOOLEAN

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

  	0 : disable this.
  	Default: 1

  proc/sys/net/sctp/* Variables:
  
  addip_enable - BOOLEAN
  	Enable or disable extension of  Dynamic Address Reconfiguration
  	(ADD-IP) functionality specified in RFC5061.  This extension provides
  	the ability to dynamically add and remove new addresses for the SCTP
  	associations.
  
  	1: Enable extension.
  
  	0: Disable extension.
  
  	Default: 0
  
  addip_noauth_enable - BOOLEAN
  	Dynamic Address Reconfiguration (ADD-IP) requires the use of
  	authentication to protect the operations of adding or removing new
  	addresses.  This requirement is mandated so that unauthorized hosts
  	would not be able to hijack associations.  However, older
  	implementations may not have implemented this requirement while
  	allowing the ADD-IP extension.  For reasons of interoperability,
  	we provide this variable to control the enforcement of the
  	authentication requirement.
  
  	1: Allow ADD-IP extension to be used without authentication.  This
  	   should only be set in a closed environment for interoperability
  	   with older implementations.
  
  	0: Enforce the authentication requirement
  
  	Default: 0
  
  auth_enable - BOOLEAN
  	Enable or disable Authenticated Chunks extension.  This extension
  	provides the ability to send and receive authenticated chunks and is
  	required for secure operation of Dynamic Address Reconfiguration
  	(ADD-IP) extension.
  
  	1: Enable this extension.
  	0: Disable this extension.
  
  	Default: 0
  
  prsctp_enable - BOOLEAN
  	Enable or disable the Partial Reliability extension (RFC3758) which
  	is used to notify peers that a given DATA should no longer be expected.
  
  	1: Enable extension
  	0: Disable
  
  	Default: 1
  
  max_burst - INTEGER
  	The limit of the number of new packets that can be initially sent.  It
  	controls how bursty the generated traffic can be.
  
  	Default: 4
  
  association_max_retrans - INTEGER
  	Set the maximum number for retransmissions that an association can
  	attempt deciding that the remote end is unreachable.  If this value
  	is exceeded, the association is terminated.
  
  	Default: 10
  
  max_init_retransmits - INTEGER
  	The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
  	that an association will attempt before declaring the destination
  	unreachable and terminating.
  
  	Default: 8
  
  path_max_retrans - INTEGER
  	The maximum number of retransmissions that will be attempted on a given
  	path.  Once this threshold is exceeded, the path is considered
  	unreachable, and new traffic will use a different path when the
  	association is multihomed.
  
  	Default: 5
  
  rto_initial - INTEGER
  	The initial round trip timeout value in milliseconds that will be used
  	in calculating round trip times.  This is the initial time interval
  	for retransmissions.
  
  	Default: 3000

  rto_max - INTEGER
  	The maximum value (in milliseconds) of the round trip timeout.  This
  	is the largest time interval that can elapse between retransmissions.
  
  	Default: 60000
  
  rto_min - INTEGER
  	The minimum value (in milliseconds) of the round trip timeout.  This
  	is the smallest time interval the can elapse between retransmissions.
  
  	Default: 1000
  
  hb_interval - INTEGER
  	The interval (in milliseconds) between HEARTBEAT chunks.  These chunks
  	are sent at the specified interval on idle paths to probe the state of
  	a given path between 2 associations.
  
  	Default: 30000
  
  sack_timeout - INTEGER
  	The amount of time (in milliseconds) that the implementation will wait
  	to send a SACK.
  
  	Default: 200
  
  valid_cookie_life - INTEGER
  	The default lifetime of the SCTP cookie (in milliseconds).  The cookie
  	is used during association establishment.
  
  	Default: 60000
  
  cookie_preserve_enable - BOOLEAN
  	Enable or disable the ability to extend the lifetime of the SCTP cookie
  	that is used during the establishment phase of SCTP association
  
  	1: Enable cookie lifetime extension.
  	0: Disable
  
  	Default: 1
  
  rcvbuf_policy - INTEGER
  	Determines if the receive buffer is attributed to the socket or to
  	association.   SCTP supports the capability to create multiple
  	associations on a single socket.  When using this capability, it is
  	possible that a single stalled association that's buffering a lot
  	of data may block other associations from delivering their data by
  	consuming all of the receive buffer space.  To work around this,
  	the rcvbuf_policy could be set to attribute the receiver buffer space
  	to each association instead of the socket.  This prevents the described
  	blocking.
  
  	1: rcvbuf space is per association
  	0: recbuf space is per socket
  
  	Default: 0
  
  sndbuf_policy - INTEGER
  	Similar to rcvbuf_policy above, this applies to send buffer space.
  
  	1: Send buffer is tracked per association
  	0: Send buffer is tracked per socket.
  
  	Default: 0
  
  sctp_mem - vector of 3 INTEGERs: min, pressure, max
  	Number of pages allowed for queueing by all SCTP sockets.
  
  	min: Below this number of pages SCTP is not bothered about its
  	memory appetite. When amount of memory allocated by SCTP exceeds
  	this number, SCTP starts to moderate memory usage.
  
  	pressure: This value was introduced to follow format of tcp_mem.
  
  	max: Number of pages allowed for queueing by all SCTP sockets.
  
  	Default is calculated at boot time from amount of available memory.
  
  sctp_rmem - vector of 3 INTEGERs: min, default, max

  	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/*

  dev_weight - INTEGER
  	The maximum number of packets that kernel can handle on a NAPI
  	interrupt, it's a Per-CPU variable.
  
  	Default: 64

  
  /proc/sys/net/unix/*

  max_dgram_qlen - INTEGER
  	The maximum length of dgram socket receive queue
  
  	Default: 10
  
  
  UNDOCUMENTED:

  
  /proc/sys/net/irda/*
  	fast_poll_increase FIXME
  	warn_noreply_time FIXME
  	discovery_slots FIXME
  	slot_timeout FIXME
  	max_baud_rate FIXME
  	discovery_timeout FIXME
  	lap_keepalive_time FIXME
  	max_noreply_time FIXME
  	max_tx_data_size FIXME
  	max_tx_window FIXME
  	min_tx_turn_time FIXME