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+/proc/sys/net/ipv4/* Variables:
+
+ip_forward - BOOLEAN
+	0 - disabled (default)
+	not 0 - enabled
+
+	Forward Packets between interfaces.
+
+	This variable is special, its change resets all configuration
+	parameters to their default state (RFC1122 for hosts, RFC1812
+	for routers)
+
+ip_default_ttl - INTEGER
+	Default value of TTL field (Time To Live) for outgoing (but not
+	forwarded) IP packets. Should be between 1 and 255 inclusive.
+	Default: 64 (as recommended by RFC1700)
+
+ip_no_pmtu_disc - INTEGER
+	Disable Path MTU Discovery. If enabled in mode 1 and a
+	fragmentation-required ICMP is received, the PMTU to this
+	destination will be set to min_pmtu (see below). You will need
+	to raise min_pmtu to the smallest interface MTU on your system
+	manually if you want to avoid locally generated fragments.
+
+	In mode 2 incoming Path MTU Discovery messages will be
+	discarded. Outgoing frames are handled the same as in mode 1,
+	implicitly setting IP_PMTUDISC_DONT on every created socket.
+
+	Mode 3 is a hardend pmtu discover mode. The kernel will only
+	accept fragmentation-needed errors if the underlying protocol
+	can verify them besides a plain socket lookup. Current
+	protocols for which pmtu events will be honored are TCP, SCTP
+	and DCCP as they verify e.g. the sequence number or the
+	association. This mode should not be enabled globally but is
+	only intended to secure e.g. name servers in namespaces where
+	TCP path mtu must still work but path MTU information of other
+	protocols should be discarded. If enabled globally this mode
+	could break other protocols.
+
+	Possible values: 0-3
+	Default: FALSE
+
+min_pmtu - INTEGER
+	default 552 - minimum discovered Path MTU
+
+ip_forward_use_pmtu - BOOLEAN
+	By default we don't trust protocol path MTUs while forwarding
+	because they could be easily forged and can lead to unwanted
+	fragmentation by the router.
+	You only need to enable this if you have user-space software
+	which tries to discover path mtus by itself and depends on the
+	kernel honoring this information. This is normally not the
+	case.
+	Default: 0 (disabled)
+	Possible values:
+	0 - disabled
+	1 - enabled
+
+fwmark_reflect - BOOLEAN
+	Controls the fwmark of kernel-generated IPv4 reply packets that are not
+	associated with a socket for example, TCP RSTs or ICMP echo replies).
+	If unset, these packets have a fwmark of zero. If set, they have the
+	fwmark of the packet they are replying to.
+	Default: 0
+
+route/max_size - INTEGER
+	Maximum number of routes allowed in the kernel.  Increase
+	this when using large numbers of interfaces and/or routes.
+	From linux kernel 3.6 onwards, this is deprecated for ipv4
+	as route cache is no longer used.
+
+neigh/default/gc_thresh1 - INTEGER
+	Minimum number of entries to keep.  Garbage collector will not
+	purge entries if there are fewer than this number.
+	Default: 128
+
+neigh/default/gc_thresh2 - INTEGER
+	Threshold when garbage collector becomes more aggressive about
+	purging entries. Entries older than 5 seconds will be cleared
+	when over this number.
+	Default: 512
+
+neigh/default/gc_thresh3 - INTEGER
+	Maximum number of neighbor entries allowed.  Increase this
+	when using large numbers of interfaces and when communicating
+	with large numbers of directly-connected peers.
+	Default: 1024
+
+neigh/default/unres_qlen_bytes - INTEGER
+	The maximum number of bytes which may be used by packets
+	queued for each	unresolved address by other network layers.
+	(added in linux 3.3)
+	Setting negative value is meaningless and will return error.
+	Default: 65536 Bytes(64KB)
+
+neigh/default/unres_qlen - INTEGER
+	The maximum number of packets which may be queued for each
+	unresolved address by other network layers.
+	(deprecated in linux 3.3) : use unres_qlen_bytes instead.
+	Prior to linux 3.3, the default value is 3 which may cause
+	unexpected packet loss. The current default value is calculated
+	according to default value of unres_qlen_bytes and true size of
+	packet.
+	Default: 31
+
+mtu_expires - INTEGER
+	Time, in seconds, that cached PMTU information is kept.
+
+min_adv_mss - INTEGER
+	The advertised MSS depends on the first hop route MTU, but will
+	never be lower than this setting.
+
+IP Fragmentation:
+
+ipfrag_high_thresh - INTEGER
+	Maximum memory used to reassemble IP fragments. When
+	ipfrag_high_thresh bytes of memory is allocated for this purpose,
+	the fragment handler will toss packets until ipfrag_low_thresh
+	is reached. This also serves as a maximum limit to namespaces
+	different from the initial one.
+
+ipfrag_low_thresh - INTEGER
+	Maximum memory used to reassemble IP fragments before the kernel
+	begins to remove incomplete fragment queues to free up resources.
+	The kernel still accepts new fragments for defragmentation.
+
+ipfrag_time - INTEGER
+	Time in seconds to keep an IP fragment in memory.
+
+ipfrag_max_dist - INTEGER
+	ipfrag_max_dist is a non-negative integer value which defines the
+	maximum "disorder" which is allowed among fragments which share a
+	common IP source address. Note that reordering of packets is
+	not unusual, but if a large number of fragments arrive from a source
+	IP address while a particular fragment queue remains incomplete, it
+	probably indicates that one or more fragments belonging to that queue
+	have been lost. When ipfrag_max_dist is positive, an additional check
+	is done on fragments before they are added to a reassembly queue - if
+	ipfrag_max_dist (or more) fragments have arrived from a particular IP
+	address between additions to any IP fragment queue using that source
+	address, it's presumed that one or more fragments in the queue are
+	lost. The existing fragment queue will be dropped, and a new one
+	started. An ipfrag_max_dist value of zero disables this check.
+
+	Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
+	result in unnecessarily dropping fragment queues when normal
+	reordering of packets occurs, which could lead to poor application
+	performance. Using a very large value, e.g. 50000, increases the
+	likelihood of incorrectly reassembling IP fragments that originate
+	from different IP datagrams, which could result in data corruption.
+	Default: 64
+
+INET peer storage:
+
+inet_peer_threshold - INTEGER
+	The approximate size of the storage.  Starting from this threshold
+	entries will be thrown aggressively.  This threshold also determines
+	entries' time-to-live and time intervals between garbage collection
+	passes.  More entries, less time-to-live, less GC interval.
+
+inet_peer_minttl - INTEGER
+	Minimum time-to-live of entries.  Should be enough to cover fragment
+	time-to-live on the reassembling side.  This minimum time-to-live  is
+	guaranteed if the pool size is less than inet_peer_threshold.
+	Measured in seconds.
+
+inet_peer_maxttl - INTEGER
+	Maximum time-to-live of entries.  Unused entries will expire after
+	this period of time if there is no memory pressure on the pool (i.e.
+	when the number of entries in the pool is very small).
+	Measured in seconds.
+
+TCP variables:
+
+somaxconn - INTEGER
+	Limit of socket listen() backlog, known in userspace as SOMAXCONN.
+	Defaults to 128.  See also tcp_max_syn_backlog for additional tuning
+	for TCP sockets.
+
+tcp_abort_on_overflow - BOOLEAN
+	If listening service is too slow to accept new connections,
+	reset them. Default state is FALSE. It means that if overflow
+	occurred due to a burst, connection will recover. Enable this
+	option _only_ if you are really sure that listening daemon
+	cannot be tuned to accept connections faster. Enabling this
+	option can harm clients of your server.
+
+tcp_adv_win_scale - INTEGER
+	Count buffering overhead as bytes/2^tcp_adv_win_scale
+	(if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
+	if it is <= 0.
+	Possible values are [-31, 31], inclusive.
+	Default: 1
+
+tcp_allowed_congestion_control - STRING
+	Show/set the congestion control choices available to non-privileged
+	processes. The list is a subset of those listed in
+	tcp_available_congestion_control.
+	Default is "reno" and the default setting (tcp_congestion_control).
+
+tcp_app_win - INTEGER
+	Reserve max(window/2^tcp_app_win, mss) of window for application
+	buffer. Value 0 is special, it means that nothing is reserved.
+	Default: 31
+
+tcp_autocorking - BOOLEAN
+	Enable TCP auto corking :
+	When applications do consecutive small write()/sendmsg() system calls,
+	we try to coalesce these small writes as much as possible, to lower
+	total amount of sent packets. This is done if at least one prior
+	packet for the flow is waiting in Qdisc queues or device transmit
+	queue. Applications can still use TCP_CORK for optimal behavior
+	when they know how/when to uncork their sockets.
+	Default : 1
+
+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_dsack - BOOLEAN
+	Allows TCP to send "duplicate" SACKs.
+
+tcp_early_retrans - INTEGER
+	Enable Early Retransmit (ER), per RFC 5827. ER lowers the threshold
+	for triggering fast retransmit when the amount of outstanding data is
+	small and when no previously unsent data can be transmitted (such
+	that limited transmit could be used). Also controls the use of
+	Tail loss probe (TLP) that converts RTOs occurring due to tail
+	losses into fast recovery (draft-dukkipati-tcpm-tcp-loss-probe-01).
+	Possible values:
+		0 disables ER
+		1 enables ER
+		2 enables ER but delays fast recovery and fast retransmit
+		  by a fourth of RTT. This mitigates connection falsely
+		  recovers when network has a small degree of reordering
+		  (less than 3 packets).
+		3 enables delayed ER and TLP.
+		4 enables TLP only.
+	Default: 3
+
+tcp_ecn - INTEGER
+	Control use of Explicit Congestion Notification (ECN) by TCP.
+	ECN is used only when both ends of the TCP connection indicate
+	support for it.  This feature is useful in avoiding losses due
+	to congestion by allowing supporting routers to signal
+	congestion before having to drop packets.
+	Possible values are:
+		0 Disable ECN.  Neither initiate nor accept ECN.
+		1 Enable ECN when requested by incoming connections and
+		  also request ECN on outgoing connection attempts.
+		2 Enable ECN when requested by incoming connections
+		  but do not request ECN on outgoing connections.
+	Default: 2
+
+tcp_fack - BOOLEAN
+	Enable FACK congestion avoidance and fast retransmission.
+	The value is not used, if tcp_sack is not enabled.
+
+tcp_fin_timeout - INTEGER
+	The length of time an orphaned (no longer referenced by any
+	application) connection will remain in the FIN_WAIT_2 state
+	before it is aborted at the local end.  While a perfectly
+	valid "receive only" state for an un-orphaned connection, an
+	orphaned connection in FIN_WAIT_2 state could otherwise wait
+	forever for the remote to close its end of the connection.
+	Cf. tcp_max_orphans
+	Default: 60 seconds
+
+tcp_frto - INTEGER
+	Enables Forward RTO-Recovery (F-RTO) defined in RFC5682.
+	F-RTO is an enhanced recovery algorithm for TCP retransmission
+	timeouts.  It is particularly beneficial in networks where the
+	RTT fluctuates (e.g., wireless). F-RTO is sender-side only
+	modification. It does not require any support from the peer.
+
+	By default it's enabled with a non-zero value. 0 disables F-RTO.
+
+tcp_invalid_ratelimit - INTEGER
+	Limit the maximal rate for sending duplicate acknowledgments
+	in response to incoming TCP packets that are for an existing
+	connection but that are invalid due to any of these reasons:
+
+	  (a) out-of-window sequence number,
+	  (b) out-of-window acknowledgment number, or
+	  (c) PAWS (Protection Against Wrapped Sequence numbers) check failure
+
+	This can help mitigate simple "ack loop" DoS attacks, wherein
+	a buggy or malicious middlebox or man-in-the-middle can
+	rewrite TCP header fields in manner that causes each endpoint
+	to think that the other is sending invalid TCP segments, thus
+	causing each side to send an unterminating stream of duplicate
+	acknowledgments for invalid segments.
+
+	Using 0 disables rate-limiting of dupacks in response to
+	invalid segments; otherwise this value specifies the minimal
+	space between sending such dupacks, in milliseconds.
+
+	Default: 500 (milliseconds).
+
+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_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_probe_interval - INTEGER
+	Controls how often to start TCP Packetization-Layer Path MTU
+	Discovery reprobe. The default is reprobing every 10 minutes as
+	per RFC4821.
+
+tcp_probe_threshold - INTEGER
+	Controls when TCP Packetization-Layer Path MTU Discovery probing
+	will stop in respect to the width of search range in bytes. Default
+	is 8 bytes.
+
+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
+	Initial reordering level of packets in a TCP stream.
+	TCP stack can then dynamically adjust flow reordering level
+	between this initial value and tcp_max_reordering
+	Default: 3
+
+tcp_max_reordering - INTEGER
+	Maximal reordering level of packets in a TCP stream.
+	300 is a fairly conservative value, but you might increase it
+	if paths are using per packet load balancing (like bonding rr mode)
+	Default: 300
+
+tcp_retrans_collapse - BOOLEAN
+	Bug-to-bug compatibility with some broken printers.
+	On retransmit try to send bigger packets to work around bugs in
+	certain TCP stacks.
+
+tcp_retries1 - INTEGER
+	This value influences the time, after which TCP decides, that
+	something is wrong due to unacknowledged RTO retransmissions,
+	and reports this suspicion to the network layer.
+	See tcp_retries2 for more details.
+
+	RFC 1122 recommends at least 3 retransmissions, which is the
+	default.
+
+tcp_retries2 - INTEGER
+	This value influences the timeout of an alive TCP connection,
+	when RTO retransmissions remain unacknowledged.
+	Given a value of N, a hypothetical TCP connection following
+	exponential backoff with an initial RTO of TCP_RTO_MIN would
+	retransmit N times before killing the connection at the (N+1)th RTO.
+
+	The default value of 15 yields a hypothetical timeout of 924.6
+	seconds and is a lower bound for the effective timeout.
+	TCP will effectively time out at the first RTO which exceeds the
+	hypothetical timeout.
+
+	RFC 1122 recommends at least 100 seconds for the timeout,
+	which corresponds to a value of at least 8.
+
+tcp_rfc1337 - BOOLEAN
+	If set, the TCP stack behaves conforming to RFC1337. If unset,
+	we are not conforming to RFC, but prevent TCP TIME_WAIT
+	assassination.
+	Default: 0
+
+tcp_rmem - vector of 3 INTEGERs: min, default, max
+	min: Minimal size of receive buffer used by TCP sockets.
+	It is guaranteed to each TCP socket, even under moderate memory
+	pressure.
+	Default: 1 page
+
+	default: initial size of receive buffer used by TCP sockets.
+	This value overrides net.core.rmem_default used by other protocols.
+	Default: 87380 bytes. This value results in window of 65535 with
+	default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
+	less for default tcp_app_win. See below about these variables.
+
+	max: maximal size of receive buffer allowed for automatically
+	selected receiver buffers for TCP socket. This value does not override
+	net.core.rmem_max.  Calling setsockopt() with SO_RCVBUF disables
+	automatic tuning of that socket's receive buffer size, in which
+	case this value is ignored.
+	Default: between 87380B and 6MB, depending on RAM size.
+
+tcp_sack - BOOLEAN
+	Enable select acknowledgments (SACKS).
+
+tcp_slow_start_after_idle - BOOLEAN
+	If set, provide RFC2861 behavior and time out the congestion
+	window after an idle period.  An idle period is defined at
+	the current RTO.  If unset, the congestion window will not
+	be timed out after an idle period.
+	Default: 1
+
+tcp_stdurg - BOOLEAN
+	Use the Host requirements interpretation of the TCP urgent pointer field.
+	Most hosts use the older BSD interpretation, so if you turn this on
+	Linux might not communicate correctly with them.
+	Default: FALSE
+
+tcp_synack_retries - INTEGER
+	Number of times SYNACKs for a passive TCP connection attempt will
+	be retransmitted. Should not be higher than 255. Default value
+	is 5, which corresponds to 31seconds till the last retransmission
+	with the current initial RTO of 1second. With this the final timeout
+	for a passive TCP connection will happen after 63seconds.
+
+tcp_syncookies - BOOLEAN
+	Only valid when the kernel was compiled with CONFIG_SYN_COOKIES
+	Send out syncookies when the syn backlog queue of a socket
+	overflows. This is to prevent against the common 'SYN flood attack'
+	Default: 1
+
+	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.
+
+	If you want to test which effects syncookies have to your
+	network connections you can set this knob to 2 to enable
+	unconditionally generation of syncookies.
+
+tcp_fastopen - INTEGER
+	Enable TCP Fast Open feature (draft-ietf-tcpm-fastopen) to send data
+	in the opening SYN packet. To use this feature, the client application
+	must use sendmsg() or sendto() with MSG_FASTOPEN flag rather than
+	connect() to perform a TCP handshake automatically.
+
+	The values (bitmap) are
+	1: Enables sending data in the opening SYN on the client w/ MSG_FASTOPEN.
+	2: Enables TCP Fast Open on the server side, i.e., allowing data in
+	   a SYN packet to be accepted and passed to the application before
+	   3-way hand shake finishes.
+	4: Send data in the opening SYN regardless of cookie availability and
+	   without a cookie option.
+	0x100: Accept SYN data w/o validating the cookie.
+	0x200: Accept data-in-SYN w/o any cookie option present.
+	0x400/0x800: Enable Fast Open on all listeners regardless of the
+	   TCP_FASTOPEN socket option. The two different flags designate two
+	   different ways of setting max_qlen without the TCP_FASTOPEN socket
+	   option.
+
+	Default: 1
+
+	Note that the client & server side Fast Open flags (1 and 2
+	respectively) must be also enabled before the rest of flags can take
+	effect.
+
+	See include/net/tcp.h and the code for more details.
+
+tcp_syn_retries - INTEGER
+	Number of times initial SYNs for an active TCP connection attempt
+	will be retransmitted. Should not be higher than 255. Default value
+	is 6, which corresponds to 63seconds till the last retransmission
+	with the current initial RTO of 1second. With this the final timeout
+	for an active TCP connection attempt will happen after 127seconds.
+
+tcp_timestamps - BOOLEAN
+	Enable timestamps as defined in RFC1323.
+
+tcp_min_tso_segs - INTEGER
+	Minimal number of segments per TSO frame.
+	Since linux-3.12, TCP does an automatic sizing of TSO frames,
+	depending on flow rate, instead of filling 64Kbytes packets.
+	For specific usages, it's possible to force TCP to build big
+	TSO frames. Note that TCP stack might split too big TSO packets
+	if available window is too small.
+	Default: 2
+
+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_notsent_lowat - UNSIGNED INTEGER
+	A TCP socket can control the amount of unsent bytes in its write queue,
+	thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll()
+	reports POLLOUT events if the amount of unsent bytes is below a per
+	socket value, and if the write queue is not full. sendmsg() will
+	also not add new buffers if the limit is hit.
+
+	This global variable controls the amount of unsent data for
+	sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change
+	to the global variable has immediate effect.
+
+	Default: UINT_MAX (0xFFFFFFFF)
+
+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_thin_linear_timeouts - BOOLEAN
+	Enable dynamic triggering of linear timeouts for thin streams.
+	If set, a check is performed upon retransmission by timeout to
+	determine if the stream is thin (less than 4 packets in flight).
+	As long as the stream is found to be thin, up to 6 linear
+	timeouts may be performed before exponential backoff mode is
+	initiated. This improves retransmission latency for
+	non-aggressive thin streams, often found to be time-dependent.
+	For more information on thin streams, see
+	Documentation/networking/tcp-thin.txt
+	Default: 0
+
+tcp_thin_dupack - BOOLEAN
+	Enable dynamic triggering of retransmissions after one dupACK
+	for thin streams. If set, a check is performed upon reception
+	of a dupACK to determine if the stream is thin (less than 4
+	packets in flight). As long as the stream is found to be thin,
+	data is retransmitted on the first received dupACK. This
+	improves retransmission latency for non-aggressive thin
+	streams, often found to be time-dependent.
+	For more information on thin streams, see
+	Documentation/networking/tcp-thin.txt
+	Default: 0
+
+tcp_limit_output_bytes - INTEGER
+	Controls TCP Small Queue limit per tcp socket.
+	TCP bulk sender tends to increase packets in flight until it
+	gets losses notifications. With SNDBUF autotuning, this can
+	result in a large amount of packets queued in qdisc/device
+	on the local machine, hurting latency of other flows, for
+	typical pfifo_fast qdiscs.
+	tcp_limit_output_bytes limits the number of bytes on qdisc
+	or device to reduce artificial RTT/cwnd and reduce bufferbloat.
+	Default: 131072
+
+tcp_challenge_ack_limit - INTEGER
+	Limits number of Challenge ACK sent per second, as recommended
+	in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
+	Default: 100
+
+UDP variables:
+
+udp_mem - vector of 3 INTEGERs: min, pressure, max
+	Number of pages allowed for queueing by all UDP sockets.
+
+	min: Below this number of pages UDP is not bothered about its
+	memory appetite. When amount of memory allocated by UDP exceeds
+	this number, UDP starts to moderate memory usage.
+
+	pressure: This value was introduced to follow format of tcp_mem.
+
+	max: Number of pages allowed for queueing by all UDP sockets.
+
+	Default is calculated at boot time from amount of available memory.
+
+udp_rmem_min - INTEGER
+	Minimal size of receive buffer used by UDP sockets in moderation.
+	Each UDP socket is able to use the size for receiving data, even if
+	total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
+	Default: 1 page
+
+udp_wmem_min - INTEGER
+	Minimal size of send buffer used by UDP sockets in moderation.
+	Each UDP socket is able to use the size for sending data, even if
+	total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
+	Default: 1 page
+
+CIPSOv4 Variables:
+
+cipso_cache_enable - BOOLEAN
+	If set, enable additions to and lookups from the CIPSO label mapping
+	cache.  If unset, additions are ignored and lookups always result in a
+	miss.  However, regardless of the setting the cache is still
+	invalidated when required when means you can safely toggle this on and
+	off and the cache will always be "safe".
+	Default: 1
+
+cipso_cache_bucket_size - INTEGER
+	The CIPSO label cache consists of a fixed size hash table with each
+	hash bucket containing a number of cache entries.  This variable limits
+	the number of entries in each hash bucket; the larger the value the
+	more CIPSO label mappings that can be cached.  When the number of
+	entries in a given hash bucket reaches this limit adding new entries
+	causes the oldest entry in the bucket to be removed to make room.
+	Default: 10
+
+cipso_rbm_optfmt - BOOLEAN
+	Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
+	the CIPSO draft specification (see Documentation/netlabel for details).
+	This means that when set the CIPSO tag will be padded with empty
+	categories in order to make the packet data 32-bit aligned.
+	Default: 0
+
+cipso_rbm_structvalid - BOOLEAN
+	If set, do a very strict check of the CIPSO option when
+	ip_options_compile() is called.  If unset, relax the checks done during
+	ip_options_compile().  Either way is "safe" as errors are caught else
+	where in the CIPSO processing code but setting this to 0 (False) should
+	result in less work (i.e. it should be faster) but could cause problems
+	with other implementations that require strict checking.
+	Default: 0
+
+IP Variables:
+
+ip_local_port_range - 2 INTEGERS
+	Defines the local port range that is used by TCP and UDP to
+	choose the local port. The first number is the first, the
+	second the last local port number. The default values are
+	32768 and 61000 respectively.
+
+ip_local_reserved_ports - list of comma separated ranges
+	Specify the ports which are reserved for known third-party
+	applications. These ports will not be used by automatic port
+	assignments (e.g. when calling connect() or bind() with port
+	number 0). Explicit port allocation behavior is unchanged.
+
+	The format used for both input and output is a comma separated
+	list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and
+	10). Writing to the file will clear all previously reserved
+	ports and update the current list with the one given in the
+	input.
+
+	Note that ip_local_port_range and ip_local_reserved_ports
+	settings are independent and both are considered by the kernel
+	when determining which ports are available for automatic port
+	assignments.
+
+	You can reserve ports which are not in the current
+	ip_local_port_range, e.g.:
+
+	$ cat /proc/sys/net/ipv4/ip_local_port_range
+	32000	61000
+	$ cat /proc/sys/net/ipv4/ip_local_reserved_ports
+	8080,9148
+
+	although this is redundant. However such a setting is useful
+	if later the port range is changed to a value that will
+	include the reserved ports.
+
+	Default: Empty
+
+ip_nonlocal_bind - BOOLEAN
+	If set, allows processes to bind() to non-local IP addresses,
+	which can be quite useful - but may break some applications.
+	Default: 0
+
+ip_dynaddr - BOOLEAN
+	If set non-zero, enables support for dynamic addresses.
+	If set to a non-zero value larger than 1, a kernel log
+	message will be printed when dynamic address rewriting
+	occurs.
+	Default: 0
+
+ip_early_demux - BOOLEAN
+	Optimize input packet processing down to one demux for
+	certain kinds of local sockets.  Currently we only do this
+	for established TCP sockets.
+
+	It may add an additional cost for pure routing workloads that
+	reduces overall throughput, in such case you should disable it.
+	Default: 1
+
+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.
+	Note that another sysctl, icmp_msgs_per_sec limits the number
+	of ICMP packets	sent on all targets.
+	Default: 1000
+
+icmp_msgs_per_sec - INTEGER
+	Limit maximal number of ICMP packets sent per second from this host.
+	Only messages whose type matches icmp_ratemask (see below) are
+	controlled by this limit.
+	Default: 1000
+
+icmp_msgs_burst - INTEGER
+	icmp_msgs_per_sec controls number of ICMP packets sent per second,
+	while icmp_msgs_burst controls the burst size of these packets.
+	Default: 50
+
+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: 1
+
+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
+
+igmp_qrv - INTEGER
+	 Controls the IGMP query robustness variable (see RFC2236 8.1).
+	 Default: 2 (as specified by RFC2236 8.1)
+	 Minimum: 1 (as specified by RFC6636 4.5)
+
+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
+
+route_localnet - BOOLEAN
+	Do not consider loopback addresses as martian source or destination
+	while routing. This enables the use of 127/8 for local routing purposes.
+	default FALSE
+
+rp_filter - INTEGER
+	0 - No source validation.
+	1 - Strict mode as defined in RFC3704 Strict Reverse Path
+	    Each incoming packet is tested against the FIB and if the interface
+	    is not the best reverse path the packet check will fail.
+	    By default failed packets are discarded.
+	2 - Loose mode as defined in RFC3704 Loose Reverse Path
+	    Each incoming packet's source address is also tested against the FIB
+	    and if the source address is not reachable via any interface
+	    the packet check will fail.
+
+	Current recommended practice in RFC3704 is to enable strict mode
+	to prevent IP spoofing from DDos attacks. If using asymmetric routing
+	or other complicated routing, then loose mode is recommended.
+
+	The max value from conf/{all,interface}/rp_filter is used
+	when doing source validation on the {interface}.
+
+	Default value is 0. Note that some distributions enable it
+	in startup scripts.
+
+arp_filter - BOOLEAN
+	1 - Allows you to have multiple network interfaces on the same
+	subnet, and have the ARPs for each interface be answered
+	based on whether or not the kernel would route a packet from
+	the ARP'd IP out that interface (therefore you must use source
+	based routing for this to work). In other words it allows control
+	of which cards (usually 1) will respond to an arp request.
+
+	0 - (default) The kernel can respond to arp requests with addresses
+	from other interfaces. This may seem wrong but it usually makes
+	sense, because it increases the chance of successful communication.
+	IP addresses are owned by the complete host on Linux, not by
+	particular interfaces. Only for more complex setups like load-
+	balancing, does this behaviour cause problems.
+
+	arp_filter for the interface will be enabled if at least one of
+	conf/{all,interface}/arp_filter is set to TRUE,
+	it will be disabled otherwise
+
+arp_announce - INTEGER
+	Define different restriction levels for announcing the local
+	source IP address from IP packets in ARP requests sent on
+	interface:
+	0 - (default) Use any local address, configured on any interface
+	1 - Try to avoid local addresses that are not in the target's
+	subnet for this interface. This mode is useful when target
+	hosts reachable via this interface require the source IP
+	address in ARP requests to be part of their logical network
+	configured on the receiving interface. When we generate the
+	request we will check all our subnets that include the
+	target IP and will preserve the source address if it is from
+	such subnet. If there is no such subnet we select source
+	address according to the rules for level 2.
+	2 - Always use the best local address for this target.
+	In this mode we ignore the source address in the IP packet
+	and try to select local address that we prefer for talks with
+	the target host. Such local address is selected by looking
+	for primary IP addresses on all our subnets on the outgoing
+	interface that include the target IP address. If no suitable
+	local address is found we select the first local address
+	we have on the outgoing interface or on all other interfaces,
+	with the hope we will receive reply for our request and
+	even sometimes no matter the source IP address we announce.
+
+	The max value from conf/{all,interface}/arp_announce is used.
+
+	Increasing the restriction level gives more chance for
+	receiving answer from the resolved target while decreasing
+	the level announces more valid sender's information.
+
+arp_ignore - INTEGER
+	Define different modes for sending replies in response to
+	received ARP requests that resolve local target IP addresses:
+	0 - (default): reply for any local target IP address, configured
+	on any interface
+	1 - reply only if the target IP address is local address
+	configured on the incoming interface
+	2 - reply only if the target IP address is local address
+	configured on the incoming interface and both with the
+	sender's IP address are part from same subnet on this interface
+	3 - do not reply for local addresses configured with scope host,
+	only resolutions for global and link addresses are replied
+	4-7 - reserved
+	8 - do not reply for all local addresses
+
+	The max value from conf/{all,interface}/arp_ignore is used
+	when ARP request is received on the {interface}
+
+arp_notify - BOOLEAN
+	Define mode for notification of address and device changes.
+	0 - (default): do nothing
+	1 - Generate gratuitous arp requests when device is brought up
+	    or hardware address changes.
+
+arp_accept - BOOLEAN
+	Define behavior for gratuitous ARP frames who's IP is not
+	already present in the ARP table:
+	0 - don't create new entries in the ARP table
+	1 - create new entries in the ARP table
+
+	Both replies and requests type gratuitous arp will trigger the
+	ARP table to be updated, if this setting is on.
+
+	If the ARP table already contains the IP address of the
+	gratuitous arp frame, the arp table will be updated regardless
+	if this setting is on or off.
+
+mcast_solicit - INTEGER
+	The maximum number of multicast probes in INCOMPLETE state,
+	when the associated hardware address is unknown.  Defaults
+	to 3.
+
+ucast_solicit - INTEGER
+	The maximum number of unicast probes in PROBE state, when
+	the hardware address is being reconfirmed.  Defaults to 3.
+
+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_resolicit).  Defaults to 0.
+
+mcast_resolicit - INTEGER
+	The maximum number of multicast probes after unicast and
+	app probes in PROBE state.  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
+
+igmpv2_unsolicited_report_interval - INTEGER
+	The interval in milliseconds in which the next unsolicited
+	IGMPv1 or IGMPv2 report retransmit will take place.
+	Default: 10000 (10 seconds)
+
+igmpv3_unsolicited_report_interval - INTEGER
+	The interval in milliseconds in which the next unsolicited
+	IGMPv3 report retransmit will take place.
+	Default: 1000 (1 seconds)
+
+promote_secondaries - BOOLEAN
+	When a primary IP address is removed from this interface
+	promote a corresponding secondary IP address instead of
+	removing all the corresponding secondary IP addresses.
+
+
+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)
+
+flowlabel_consistency - BOOLEAN
+	Protect the consistency (and unicity) of flow label.
+	You have to disable it to use IPV6_FL_F_REFLECT flag on the
+	flow label manager.
+	TRUE: enabled
+	FALSE: disabled
+	Default: TRUE
+
+auto_flowlabels - BOOLEAN
+	Automatically generate flow labels based based on a flow hash
+	of the packet. This allows intermediate devices, such as routers,
+	to idenfify packet flows for mechanisms like Equal Cost Multipath
+	Routing (see RFC 6438).
+	TRUE: enabled
+	FALSE: disabled
+	Default: false
+
+anycast_src_echo_reply - BOOLEAN
+	Controls the use of anycast addresses as source addresses for ICMPv6
+	echo reply
+	TRUE:  enabled
+	FALSE: disabled
+	Default: FALSE
+
+idgen_delay - INTEGER
+	Controls the delay in seconds after which time to retry
+	privacy stable address generation if a DAD conflict is
+	detected.
+	Default: 1 (as specified in RFC7217)
+
+idgen_retries - INTEGER
+	Controls the number of retries to generate a stable privacy
+	address if a DAD conflict is detected.
+	Default: 3 (as specified in RFC7217)
+
+mld_qrv - INTEGER
+	Controls the MLD query robustness variable (see RFC3810 9.1).
+	Default: 2 (as specified by RFC3810 9.1)
+	Minimum: 1 (as specified by RFC6636 4.5)
+
+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.
+
+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.
+
+fwmark_reflect - BOOLEAN
+	Controls the fwmark of kernel-generated IPv6 reply packets that are not
+	associated with a socket for example, TCP RSTs or ICMPv6 echo replies).
+	If unset, these packets have a fwmark of zero. If set, they have the
+	fwmark of the packet they are replying to.
+	Default: 0
+
+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_from_local - BOOLEAN
+	Accept RA with source-address that is found on local machine
+        if the RA is otherwise proper and able to be accepted.
+        Default is to NOT accept these as it may be an un-intended
+        network loop.
+
+	Functional default:
+           enabled if accept_ra_from_local is enabled
+               on a specific interface.
+	   disabled if accept_ra_from_local is disabled
+               on a specific interface.
+
+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_ra_mtu - BOOLEAN
+	Apply the MTU value specified in RA option 5 (RFC4861). If
+	disabled, the MTU specified in the RA will be ignored.
+
+	Functional default: enabled if accept_ra is enabled.
+			    disabled if accept_ra is disabled.
+
+accept_redirects - BOOLEAN
+	Accept Redirects.
+
+	Functional default: enabled if local forwarding is disabled.
+			    disabled if local forwarding is enabled.
+
+accept_source_route - INTEGER
+	Accept source routing (routing extension header).
+
+	>= 0: Accept only routing header type 2.
+	< 0: Do not accept routing header.
+
+	Default: 0
+
+autoconf - BOOLEAN
+	Autoconfigure addresses using Prefix Information in Router
+	Advertisements.
+
+	Functional default: enabled if accept_ra_pinfo is enabled.
+			    disabled if accept_ra_pinfo is disabled.
+
+dad_transmits - INTEGER
+	The amount of Duplicate Address Detection probes to send.
+	Default: 1
+
+forwarding - INTEGER
+	Configure interface-specific Host/Router behaviour.
+
+	Note: It is recommended to have the same setting on all
+	interfaces; mixed router/host scenarios are rather uncommon.
+
+	Possible values are:
+		0 Forwarding disabled
+		1 Forwarding enabled
+
+	FALSE (0):
+
+	By default, Host behaviour is assumed.  This means:
+
+	1. IsRouter flag is not set in Neighbour Advertisements.
+	2. If accept_ra is TRUE (default), transmit Router
+	   Solicitations.
+	3. If accept_ra is TRUE (default), accept Router
+	   Advertisements (and do autoconfiguration).
+	4. If accept_redirects is TRUE (default), accept Redirects.
+
+	TRUE (1):
+
+	If local forwarding is enabled, Router behaviour is assumed.
+	This means exactly the reverse from the above:
+
+	1. IsRouter flag is set in Neighbour Advertisements.
+	2. Router Solicitations are not sent unless accept_ra is 2.
+	3. Router Advertisements are ignored unless accept_ra is 2.
+	4. Redirects are ignored.
+
+	Default: 0 (disabled) if global forwarding is disabled (default),
+		 otherwise 1 (enabled).
+
+hop_limit - INTEGER
+	Default Hop Limit to set.
+	Default: 64
+
+mtu - INTEGER
+	Default Maximum Transfer Unit
+	Default: 1280 (IPv6 required minimum)
+
+router_probe_interval - INTEGER
+	Minimum interval (in seconds) between Router Probing described
+	in RFC4191.
+
+	Default: 60
+
+router_solicitation_delay - INTEGER
+	Number of seconds to wait after interface is brought up
+	before sending Router Solicitations.
+	Default: 1
+
+router_solicitation_interval - INTEGER
+	Number of seconds to wait between Router Solicitations.
+	Default: 4
+
+router_solicitations - INTEGER
+	Number of Router Solicitations to send until assuming no
+	routers are present.
+	Default: 3
+
+use_tempaddr - INTEGER
+	Preference for Privacy Extensions (RFC3041).
+	  <= 0 : disable Privacy Extensions
+	  == 1 : enable Privacy Extensions, but prefer public
+	         addresses over temporary addresses.
+	  >  1 : enable Privacy Extensions and prefer temporary
+	         addresses over public addresses.
+	Default:  0 (for most devices)
+		 -1 (for point-to-point devices and loopback devices)
+
+temp_valid_lft - INTEGER
+	valid lifetime (in seconds) for temporary addresses.
+	Default: 604800 (7 days)
+
+temp_prefered_lft - INTEGER
+	Preferred lifetime (in seconds) for temporary addresses.
+	Default: 86400 (1 day)
+
+max_desync_factor - INTEGER
+	Maximum value for DESYNC_FACTOR, which is a random value
+	that ensures that clients don't synchronize with each
+	other and generate new addresses at exactly the same time.
+	value is in seconds.
+	Default: 600
+
+regen_max_retry - INTEGER
+	Number of attempts before give up attempting to generate
+	valid temporary addresses.
+	Default: 5
+
+max_addresses - INTEGER
+	Maximum number of autoconfigured addresses per interface.  Setting
+	to zero disables the limitation.  It is not recommended to set this
+	value too large (or to zero) because it would be an easy way to
+	crash the kernel by allowing too many addresses to be created.
+	Default: 16
+
+disable_ipv6 - BOOLEAN
+	Disable IPv6 operation.  If accept_dad is set to 2, this value
+	will be dynamically set to TRUE if DAD fails for the link-local
+	address.
+	Default: FALSE (enable IPv6 operation)
+
+	When this value is changed from 1 to 0 (IPv6 is being enabled),
+	it will dynamically create a link-local address on the given
+	interface and start Duplicate Address Detection, if necessary.
+
+	When this value is changed from 0 to 1 (IPv6 is being disabled),
+	it will dynamically delete all address on the given interface.
+
+accept_dad - INTEGER
+	Whether to accept DAD (Duplicate Address Detection).
+	0: Disable DAD
+	1: Enable DAD (default)
+	2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
+	   link-local address has been found.
+
+force_tllao - BOOLEAN
+	Enable sending the target link-layer address option even when
+	responding to a unicast neighbor solicitation.
+	Default: FALSE
+
+	Quoting from RFC 2461, section 4.4, Target link-layer address:
+
+	"The option MUST be included for multicast solicitations in order to
+	avoid infinite Neighbor Solicitation "recursion" when the peer node
+	does not have a cache entry to return a Neighbor Advertisements
+	message.  When responding to unicast solicitations, the option can be
+	omitted since the sender of the solicitation has the correct link-
+	layer address; otherwise it would not have be able to send the unicast
+	solicitation in the first place. However, including the link-layer
+	address in this case adds little overhead and eliminates a potential
+	race condition where the sender deletes the cached link-layer address
+	prior to receiving a response to a previous solicitation."
+
+ndisc_notify - BOOLEAN
+	Define mode for notification of address and device changes.
+	0 - (default): do nothing
+	1 - Generate unsolicited neighbour advertisements when device is brought
+	    up or hardware address changes.
+
+mldv1_unsolicited_report_interval - INTEGER
+	The interval in milliseconds in which the next unsolicited
+	MLDv1 report retransmit will take place.
+	Default: 10000 (10 seconds)
+
+mldv2_unsolicited_report_interval - INTEGER
+	The interval in milliseconds in which the next unsolicited
+	MLDv2 report retransmit will take place.
+	Default: 1000 (1 second)
+
+force_mld_version - INTEGER
+	0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed
+	1 - Enforce to use MLD version 1
+	2 - Enforce to use MLD version 2
+
+suppress_frag_ndisc - INTEGER
+	Control RFC 6980 (Security Implications of IPv6 Fragmentation
+	with IPv6 Neighbor Discovery) behavior:
+	1 - (default) discard fragmented neighbor discovery packets
+	0 - allow fragmented neighbor discovery packets
+
+optimistic_dad - BOOLEAN
+	Whether to perform Optimistic Duplicate Address Detection (RFC 4429).
+		0: disabled (default)
+		1: enabled
+
+use_optimistic - BOOLEAN
+	If enabled, do not classify optimistic addresses as deprecated during
+	source address selection.  Preferred addresses will still be chosen
+	before optimistic addresses, subject to other ranking in the source
+	address selection algorithm.
+		0: disabled (default)
+		1: enabled
+
+stable_secret - IPv6 address
+	This IPv6 address will be used as a secret to generate IPv6
+	addresses for link-local addresses and autoconfigured
+	ones. All addresses generated after setting this secret will
+	be stable privacy ones by default. This can be changed via the
+	addrgenmode ip-link. conf/default/stable_secret is used as the
+	secret for the namespace, the interface specific ones can
+	overwrite that. Writes to conf/all/stable_secret are refused.
+
+	It is recommended to generate this secret during installation
+	of a system and keep it stable after that.
+
+	By default the stable secret is unset.
+
+icmp/*:
+ratelimit - INTEGER
+	Limit the maximal rates for sending ICMPv6 packets.
+	0 to disable any limiting,
+	otherwise the minimal space between responses in milliseconds.
+	Default: 1000
+
+
+IPv6 Update by:
+Pekka Savola <pekkas@netcore.fi>
+YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
+
+
+/proc/sys/net/bridge/* Variables:
+
+bridge-nf-call-arptables - BOOLEAN
+	1 : pass bridged ARP traffic to arptables' FORWARD chain.
+	0 : disable this.
+	Default: 1
+
+bridge-nf-call-iptables - BOOLEAN
+	1 : pass bridged IPv4 traffic to iptables' chains.
+	0 : disable this.
+	Default: 1
+
+bridge-nf-call-ip6tables - BOOLEAN
+	1 : pass bridged IPv6 traffic to ip6tables' chains.
+	0 : disable this.
+	Default: 1
+
+bridge-nf-filter-vlan-tagged - BOOLEAN
+	1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
+	0 : disable this.
+	Default: 0
+
+bridge-nf-filter-pppoe-tagged - BOOLEAN
+	1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
+	0 : disable this.
+	Default: 0
+
+bridge-nf-pass-vlan-input-dev - BOOLEAN
+	1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan
+	interface on the bridge and set the netfilter input device to the vlan.
+	This allows use of e.g. "iptables -i br0.1" and makes the REDIRECT
+	target work with vlan-on-top-of-bridge interfaces.  When no matching
+	vlan interface is found, or this switch is off, the input device is
+	set to the bridge interface.
+	0: disable bridge netfilter vlan interface lookup.
+	Default: 0
+
+proc/sys/net/sctp/* Variables:
+
+addip_enable - BOOLEAN
+	Enable or disable extension of  Dynamic Address Reconfiguration
+	(ADD-IP) functionality specified in RFC5061.  This extension provides
+	the ability to dynamically add and remove new addresses for the SCTP
+	associations.
+
+	1: Enable extension.
+
+	0: Disable extension.
+
+	Default: 0
+
+addip_noauth_enable - BOOLEAN
+	Dynamic Address Reconfiguration (ADD-IP) requires the use of
+	authentication to protect the operations of adding or removing new
+	addresses.  This requirement is mandated so that unauthorized hosts
+	would not be able to hijack associations.  However, older
+	implementations may not have implemented this requirement while
+	allowing the ADD-IP extension.  For reasons of interoperability,
+	we provide this variable to control the enforcement of the
+	authentication requirement.
+
+	1: Allow ADD-IP extension to be used without authentication.  This
+	   should only be set in a closed environment for interoperability
+	   with older implementations.
+
+	0: Enforce the authentication requirement
+
+	Default: 0
+
+auth_enable - BOOLEAN
+	Enable or disable Authenticated Chunks extension.  This extension
+	provides the ability to send and receive authenticated chunks and is
+	required for secure operation of Dynamic Address Reconfiguration
+	(ADD-IP) extension.
+
+	1: Enable this extension.
+	0: Disable this extension.
+
+	Default: 0
+
+prsctp_enable - BOOLEAN
+	Enable or disable the Partial Reliability extension (RFC3758) which
+	is used to notify peers that a given DATA should no longer be expected.
+
+	1: Enable extension
+	0: Disable
+
+	Default: 1
+
+max_burst - INTEGER
+	The limit of the number of new packets that can be initially sent.  It
+	controls how bursty the generated traffic can be.
+
+	Default: 4
+
+association_max_retrans - INTEGER
+	Set the maximum number for retransmissions that an association can
+	attempt deciding that the remote end is unreachable.  If this value
+	is exceeded, the association is terminated.
+
+	Default: 10
+
+max_init_retransmits - INTEGER
+	The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
+	that an association will attempt before declaring the destination
+	unreachable and terminating.
+
+	Default: 8
+
+path_max_retrans - INTEGER
+	The maximum number of retransmissions that will be attempted on a given
+	path.  Once this threshold is exceeded, the path is considered
+	unreachable, and new traffic will use a different path when the
+	association is multihomed.
+
+	Default: 5
+
+pf_retrans - INTEGER
+	The number of retransmissions that will be attempted on a given path
+	before traffic is redirected to an alternate transport (should one
+	exist).  Note this is distinct from path_max_retrans, as a path that
+	passes the pf_retrans threshold can still be used.  Its only
+	deprioritized when a transmission path is selected by the stack.  This
+	setting is primarily used to enable fast failover mechanisms without
+	having to reduce path_max_retrans to a very low value.  See:
+	http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt
+	for details.  Note also that a value of pf_retrans > path_max_retrans
+	disables this feature
+
+	Default: 0
+
+rto_initial - INTEGER
+	The initial round trip timeout value in milliseconds that will be used
+	in calculating round trip times.  This is the initial time interval
+	for retransmissions.
+
+	Default: 3000
+
+rto_max - INTEGER
+	The maximum value (in milliseconds) of the round trip timeout.  This
+	is the largest time interval that can elapse between retransmissions.
+
+	Default: 60000
+
+rto_min - INTEGER
+	The minimum value (in milliseconds) of the round trip timeout.  This
+	is the smallest time interval the can elapse between retransmissions.
+
+	Default: 1000
+
+hb_interval - INTEGER
+	The interval (in milliseconds) between HEARTBEAT chunks.  These chunks
+	are sent at the specified interval on idle paths to probe the state of
+	a given path between 2 associations.
+
+	Default: 30000
+
+sack_timeout - INTEGER
+	The amount of time (in milliseconds) that the implementation will wait
+	to send a SACK.
+
+	Default: 200
+
+valid_cookie_life - INTEGER
+	The default lifetime of the SCTP cookie (in milliseconds).  The cookie
+	is used during association establishment.
+
+	Default: 60000
+
+cookie_preserve_enable - BOOLEAN
+	Enable or disable the ability to extend the lifetime of the SCTP cookie
+	that is used during the establishment phase of SCTP association
+
+	1: Enable cookie lifetime extension.
+	0: Disable
+
+	Default: 1
+
+cookie_hmac_alg - STRING
+	Select the hmac algorithm used when generating the cookie value sent by
+	a listening sctp socket to a connecting client in the INIT-ACK chunk.
+	Valid values are:
+	* md5
+	* sha1
+	* none
+	Ability to assign md5 or sha1 as the selected alg is predicated on the
+	configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and
+	CONFIG_CRYPTO_SHA1).
+
+	Default: Dependent on configuration.  MD5 if available, else SHA1 if
+	available, else none.
+
+rcvbuf_policy - INTEGER
+	Determines if the receive buffer is attributed to the socket or to
+	association.   SCTP supports the capability to create multiple
+	associations on a single socket.  When using this capability, it is
+	possible that a single stalled association that's buffering a lot
+	of data may block other associations from delivering their data by
+	consuming all of the receive buffer space.  To work around this,
+	the rcvbuf_policy could be set to attribute the receiver buffer space
+	to each association instead of the socket.  This prevents the described
+	blocking.
+
+	1: rcvbuf space is per association
+	0: rcvbuf space is per socket
+
+	Default: 0
+
+sndbuf_policy - INTEGER
+	Similar to rcvbuf_policy above, this applies to send buffer space.
+
+	1: Send buffer is tracked per association
+	0: Send buffer is tracked per socket.
+
+	Default: 0
+
+sctp_mem - vector of 3 INTEGERs: min, pressure, max
+	Number of pages allowed for queueing by all SCTP sockets.
+
+	min: Below this number of pages SCTP is not bothered about its
+	memory appetite. When amount of memory allocated by SCTP exceeds
+	this number, SCTP starts to moderate memory usage.
+
+	pressure: This value was introduced to follow format of tcp_mem.
+
+	max: Number of pages allowed for queueing by all SCTP sockets.
+
+	Default is calculated at boot time from amount of available memory.
+
+sctp_rmem - vector of 3 INTEGERs: min, default, max
+	Only the first value ("min") is used, "default" and "max" are
+	ignored.
+
+	min: Minimal size of receive buffer used by SCTP socket.
+	It is guaranteed to each SCTP socket (but not association) even
+	under moderate memory pressure.
+
+	Default: 1 page
+
+sctp_wmem  - vector of 3 INTEGERs: min, default, max
+	Currently this tunable has no effect.
+
+addr_scope_policy - INTEGER
+	Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00
+
+	0   - Disable IPv4 address scoping
+	1   - Enable IPv4 address scoping
+	2   - Follow draft but allow IPv4 private addresses
+	3   - Follow draft but allow IPv4 link local addresses
+
+	Default: 1
+
+
+/proc/sys/net/core/*
+	Please see: Documentation/sysctl/net.txt for descriptions of these entries.
+
+
+/proc/sys/net/unix/*
+max_dgram_qlen - INTEGER
+	The maximum length of dgram socket receive queue
+
+	Default: 10
+
+
+UNDOCUMENTED:
+
+/proc/sys/net/irda/*
+	fast_poll_increase FIXME
+	warn_noreply_time FIXME
+	discovery_slots FIXME
+	slot_timeout FIXME
+	max_baud_rate FIXME
+	discovery_timeout FIXME
+	lap_keepalive_time FIXME
+	max_noreply_time FIXME
+	max_tx_data_size FIXME
+	max_tx_window FIXME
+	min_tx_turn_time FIXME