docs: networking: convert ip-sysctl.txt to ReST

- add SPDX header;
- adjust titles and chapters, adding proper markups;
- mark code blocks and literals as such;
- mark lists as such;
- mark tables as such;
- use footnote markup;
- adjust identation, whitespaces and blank lines;
- add to networking/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2649 insertions, 0 deletions

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+=========
+IP Sysctl
+=========
+
+/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 hardened 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
+
+fib_multipath_use_neigh - BOOLEAN
+	Use status of existing neighbor entry when determining nexthop for
+	multipath routes. If disabled, neighbor information is not used and
+	packets could be directed to a failed nexthop. Only valid for kernels
+	built with CONFIG_IP_ROUTE_MULTIPATH enabled.
+
+	Default: 0 (disabled)
+
+	Possible values:
+
+	- 0 - disabled
+	- 1 - enabled
+
+fib_multipath_hash_policy - INTEGER
+	Controls which hash policy to use for multipath routes. Only valid
+	for kernels built with CONFIG_IP_ROUTE_MULTIPATH enabled.
+
+	Default: 0 (Layer 3)
+
+	Possible values:
+
+	- 0 - Layer 3
+	- 1 - Layer 4
+	- 2 - Layer 3 or inner Layer 3 if present
+
+fib_sync_mem - UNSIGNED INTEGER
+	Amount of dirty memory from fib entries that can be backlogged before
+	synchronize_rcu is forced.
+
+	Default: 512kB   Minimum: 64kB   Maximum: 64MB
+
+ip_forward_update_priority - INTEGER
+	Whether to update SKB priority from "TOS" field in IPv4 header after it
+	is forwarded. The new SKB priority is mapped from TOS field value
+	according to an rt_tos2priority table (see e.g. man tc-prio).
+
+	Default: 1 (Update priority.)
+
+	Possible values:
+
+	- 0 - Do not update priority.
+	- 1 - Update priority.
+
+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 non-PERMANENT 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: SK_WMEM_MAX, (same as net.core.wmem_default).
+
+		Exact value depends on architecture and kernel options,
+		but should be enough to allow queuing 256 packets
+		of medium size.
+
+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: 101
+
+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 - LONG INTEGER
+	Maximum memory used to reassemble IP fragments.
+
+ipfrag_low_thresh - LONG INTEGER
+	(Obsolete since linux-4.17)
+	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 4096. (Was 128 before linux-5.4)
+	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_mtu_probe_floor - INTEGER
+	If MTU probing is enabled this caps the minimum MSS used for search_low
+	for the connection.
+
+	Default : 48
+
+tcp_min_snd_mss - INTEGER
+	TCP SYN and SYNACK messages usually advertise an ADVMSS option,
+	as described in RFC 1122 and RFC 6691.
+
+	If this ADVMSS option is smaller than tcp_min_snd_mss,
+	it is silently capped to tcp_min_snd_mss.
+
+	Default : 48 (at least 8 bytes of payload per segment)
+
+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
+	Tail loss probe (TLP) converts RTOs occurring due to tail
+	losses into fast recovery (draft-ietf-tcpm-rack). Note that
+	TLP requires RACK to function properly (see tcp_recovery below)
+
+	Possible values:
+
+		- 0 disables TLP
+		- 3 or 4 enables TLP
+
+	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_ecn_fallback - BOOLEAN
+	If the kernel detects that ECN connection misbehaves, enable fall
+	back to non-ECN. Currently, this knob implements the fallback
+	from RFC3168, section 6.1.1.1., but we reserve that in future,
+	additional detection mechanisms could be implemented under this
+	knob. The value	is not used, if tcp_ecn or per route (or congestion
+	control) ECN settings are disabled.
+
+	Default: 1 (fallback enabled)
+
+tcp_fack - BOOLEAN
+	This is a legacy option, it has no effect anymore.
+
+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_fwmark_accept - BOOLEAN
+	If set, incoming connections to listening sockets that do not have a
+	socket mark will set the mark of the accepting socket to the fwmark of
+	the incoming SYN packet. This will cause all packets on that connection
+	(starting from the first SYNACK) to be sent with that fwmark. The
+	listening socket's mark is unchanged. Listening sockets that already
+	have a fwmark set via setsockopt(SOL_SOCKET, SO_MARK, ...) are
+	unaffected.
+
+	Default: 0
+
+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_l3mdev_accept - BOOLEAN
+	Enables child sockets to inherit the L3 master device index.
+	Enabling this option allows a "global" listen socket to work
+	across L3 master domains (e.g., VRFs) with connected sockets
+	derived from the listen socket to be bound to the L3 domain in
+	which the packets originated. Only valid when the kernel was
+	compiled with CONFIG_NET_L3_MASTER_DEV.
+
+	Default: 0 (disabled)
+
+tcp_low_latency - BOOLEAN
+	This is a legacy option, it has no effect anymore.
+
+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 (SYN_RECV),
+	which have not received an acknowledgment from connecting client.
+
+	This is a per-listener limit.
+
+	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.
+
+	Remember to also check /proc/sys/net/core/somaxconn
+	A SYN_RECV request socket consumes about 304 bytes of memory.
+
+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_min_rtt_wlen - INTEGER
+	The window length of the windowed min filter to track the minimum RTT.
+	A shorter window lets a flow more quickly pick up new (higher)
+	minimum RTT when it is moved to a longer path (e.g., due to traffic
+	engineering). A longer window makes the filter more resistant to RTT
+	inflations such as transient congestion. The unit is seconds.
+
+	Possible values: 0 - 86400 (1 day)
+
+	Default: 300
+
+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 - UNSIGNED 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_no_ssthresh_metrics_save - BOOLEAN
+	Controls whether TCP saves ssthresh metrics in the route cache.
+
+	Default is 1, which disables ssthresh metrics.
+
+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_recovery - INTEGER
+	This value is a bitmap to enable various experimental loss recovery
+	features.
+
+	=========   =============================================================
+	RACK: 0x1   enables the RACK loss detection for fast detection of lost
+		    retransmissions and tail drops. It also subsumes and disables
+		    RFC6675 recovery for SACK connections.
+
+	RACK: 0x2   makes RACK's reordering window static (min_rtt/4).
+
+	RACK: 0x4   disables RACK's DUPACK threshold heuristic
+	=========   =============================================================
+
+	Default: 0x1
+
+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: 4K
+
+	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_comp_sack_delay_ns - LONG INTEGER
+	TCP tries to reduce number of SACK sent, using a timer
+	based on 5% of SRTT, capped by this sysctl, in nano seconds.
+	The default is 1ms, based on TSO autosizing period.
+
+	Default : 1,000,000 ns (1 ms)
+
+tcp_comp_sack_nr - INTEGER
+	Max number of SACK that can be compressed.
+	Using 0 disables SACK compression.
+
+	Default : 44
+
+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 - INTEGER
+	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 (RFC7413) to send and accept data in the opening
+	SYN packet.
+
+	The client support is enabled by flag 0x1 (on by default). The client
+	then must use sendmsg() or sendto() with the MSG_FASTOPEN flag,
+	rather than connect() to send data in SYN.
+
+	The server support is enabled by flag 0x2 (off by default). Then
+	either enable for all listeners with another flag (0x400) or
+	enable individual listeners via TCP_FASTOPEN socket option with
+	the option value being the length of the syn-data backlog.
+
+	The values (bitmap) are
+
+	=====  ======== ======================================================
+	  0x1  (client) enables sending data in the opening SYN on the client.
+	  0x2  (server) enables the server support, i.e., allowing data in
+			a SYN packet to be accepted and passed to the
+			application before 3-way handshake finishes.
+	  0x4  (client) send data in the opening SYN regardless of cookie
+			availability and without a cookie option.
+	0x200  (server) accept data-in-SYN w/o any cookie option present.
+	0x400  (server) enable all listeners to support Fast Open by
+			default without explicit TCP_FASTOPEN socket option.
+	=====  ======== ======================================================
+
+	Default: 0x1
+
+	Note that that additional client or server features are only
+	effective if the basic support (0x1 and 0x2) are enabled respectively.
+
+tcp_fastopen_blackhole_timeout_sec - INTEGER
+	Initial time period in second to disable Fastopen on active TCP sockets
+	when a TFO firewall blackhole issue happens.
+	This time period will grow exponentially when more blackhole issues
+	get detected right after Fastopen is re-enabled and will reset to
+	initial value when the blackhole issue goes away.
+	0 to disable the blackhole detection.
+
+	By default, it is set to 1hr.
+
+tcp_fastopen_key - list of comma separated 32-digit hexadecimal INTEGERs
+	The list consists of a primary key and an optional backup key. The
+	primary key is used for both creating and validating cookies, while the
+	optional backup key is only used for validating cookies. The purpose of
+	the backup key is to maximize TFO validation when keys are rotated.
+
+	A randomly chosen primary key may be configured by the kernel if
+	the tcp_fastopen sysctl is set to 0x400 (see above), or if the
+	TCP_FASTOPEN setsockopt() optname is set and a key has not been
+	previously configured via sysctl. If keys are configured via
+	setsockopt() by using the TCP_FASTOPEN_KEY optname, then those
+	per-socket keys will be used instead of any keys that are specified via
+	sysctl.
+
+	A key is specified as 4 8-digit hexadecimal integers which are separated
+	by a '-' as: xxxxxxxx-xxxxxxxx-xxxxxxxx-xxxxxxxx. Leading zeros may be
+	omitted. A primary and a backup key may be specified by separating them
+	by a comma. If only one key is specified, it becomes the primary key and
+	any previously configured backup keys are removed.
+
+tcp_syn_retries - INTEGER
+	Number of times initial SYNs for an active TCP connection attempt
+	will be retransmitted. Should not be higher than 127. 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 - INTEGER
+	Enable timestamps as defined in RFC1323.
+
+	- 0: Disabled.
+	- 1: Enable timestamps as defined in RFC1323 and use random offset for
+	  each connection rather than only using the current time.
+	- 2: Like 1, but without random offsets.
+
+	Default: 1
+
+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_pacing_ss_ratio - INTEGER
+	sk->sk_pacing_rate is set by TCP stack using a ratio applied
+	to current rate. (current_rate = cwnd * mss / srtt)
+	If TCP is in slow start, tcp_pacing_ss_ratio is applied
+	to let TCP probe for bigger speeds, assuming cwnd can be
+	doubled every other RTT.
+
+	Default: 200
+
+tcp_pacing_ca_ratio - INTEGER
+	sk->sk_pacing_rate is set by TCP stack using a ratio applied
+	to current rate. (current_rate = cwnd * mss / srtt)
+	If TCP is in congestion avoidance phase, tcp_pacing_ca_ratio
+	is applied to conservatively probe for bigger throughput.
+
+	Default: 120
+
+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_reuse - INTEGER
+	Enable reuse of TIME-WAIT sockets for new connections when it is
+	safe from protocol viewpoint.
+
+	- 0 - disable
+	- 1 - global enable
+	- 2 - enable for loopback traffic only
+
+	It should not be changed without advice/request of technical
+	experts.
+
+	Default: 2
+
+tcp_window_scaling - BOOLEAN
+	Enable window scaling as defined in RFC1323.
+
+tcp_wmem - vector of 3 INTEGERs: min, default, max
+	min: Amount of memory reserved for send buffers for TCP sockets.
+	Each TCP socket has rights to use it due to fact of its birth.
+
+	Default: 4K
+
+	default: initial size of send buffer used by TCP sockets.  This
+	value overrides net.core.wmem_default used by other protocols.
+
+	It is usually lower than net.core.wmem_default.
+
+	Default: 16K
+
+	max: Maximal amount of memory allowed for automatically tuned
+	send buffers for TCP sockets. This value does not override
+	net.core.wmem_max.  Calling setsockopt() with SO_SNDBUF disables
+	automatic tuning of that socket's send buffer size, in which case
+	this value is ignored.
+
+	Default: between 64K and 4MB, depending on RAM size.
+
+tcp_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_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 on the local machine
+	(e.g.: qdiscs, CPU backlog, or device) 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: 1048576 (16 * 65536)
+
+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: 1000
+
+tcp_rx_skb_cache - BOOLEAN
+	Controls a per TCP socket cache of one skb, that might help
+	performance of some workloads. This might be dangerous
+	on systems with a lot of TCP sockets, since it increases
+	memory usage.
+
+	Default: 0 (disabled)
+
+UDP variables
+=============
+
+udp_l3mdev_accept - BOOLEAN
+	Enabling this option allows a "global" bound socket to work
+	across L3 master domains (e.g., VRFs) with packets capable of
+	being received regardless of the L3 domain in which they
+	originated. Only valid when the kernel was compiled with
+	CONFIG_NET_L3_MASTER_DEV.
+
+	Default: 0 (disabled)
+
+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: 4K
+
+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: 4K
+
+RAW variables
+=============
+
+raw_l3mdev_accept - BOOLEAN
+	Enabling this option allows a "global" bound socket to work
+	across L3 master domains (e.g., VRFs) with packets capable of
+	being received regardless of the L3 domain in which they
+	originated. Only valid when the kernel was compiled with
+	CONFIG_NET_L3_MASTER_DEV.
+
+	Default: 1 (enabled)
+
+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.
+	If possible, it is better these numbers have different parity
+	(one even and one odd value).
+	Must be greater than or equal to ip_unprivileged_port_start.
+	The default values are 32768 and 60999 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	60999
+	    $ 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_unprivileged_port_start - INTEGER
+	This is a per-namespace sysctl.  It defines the first
+	unprivileged port in the network namespace.  Privileged ports
+	require root or CAP_NET_BIND_SERVICE in order to bind to them.
+	To disable all privileged ports, set this to 0.  They must not
+	overlap with the ip_local_port_range.
+
+	Default: 1024
+
+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_autobind_reuse - BOOLEAN
+	By default, bind() does not select the ports automatically even if
+	the new socket and all sockets bound to the port have SO_REUSEADDR.
+	ip_autobind_reuse allows bind() to reuse the port and this is useful
+	when you use bind()+connect(), but may break some applications.
+	The preferred solution is to use IP_BIND_ADDRESS_NO_PORT and this
+	option should only be set by experts.
+	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 and connected UDP sockets.
+
+	It may add an additional cost for pure routing workloads that
+	reduces overall throughput, in such case you should disable it.
+
+	Default: 1
+
+ping_group_range - 2 INTEGERS
+	Restrict ICMP_PROTO datagram sockets to users in the group range.
+	The default is "1 0", meaning, that nobody (not even root) may
+	create ping sockets.  Setting it to "100 100" would grant permissions
+	to the single group. "0 4294967295" would enable it for the world, "100
+	4294967295" would enable it for the users, but not daemons.
+
+tcp_early_demux - BOOLEAN
+	Enable early demux for established TCP sockets.
+
+	Default: 1
+
+udp_early_demux - BOOLEAN
+	Enable early demux for connected UDP sockets. Disable this if
+	your system could experience more unconnected load.
+
+	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 [1]_
+		4 Source Quench [1]_
+		5 Redirect
+		8 Echo Request
+		B Time Exceeded [1]_
+		C Parameter Problem [1]_
+		D Timestamp Request
+		E Timestamp Reply
+		F Info Request
+		G Info Reply
+		H Address Mask Request
+		I Address Mask Reply
+		= =========================
+
+	.. [1] 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.
+
+igmp_max_msf - INTEGER
+	Maximum number of addresses allowed in the source filter list for a
+	multicast group.
+
+	Default: 10
+
+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)
+
+force_igmp_version - INTEGER
+	- 0 - (default) No enforcement of a IGMP version, IGMPv1/v2 fallback
+	  allowed. Will back to IGMPv3 mode again if all IGMPv1/v2 Querier
+	  Present timer expires.
+	- 1 - Enforce to use IGMP version 1. Will also reply IGMPv1 report if
+	  receive IGMPv2/v3 query.
+	- 2 - Enforce to use IGMP version 2. Will fallback to IGMPv1 if receive
+	  IGMPv1 query message. Will reply report if receive IGMPv3 query.
+	- 3 - Enforce to use IGMP version 3. The same react with default 0.
+
+	.. note::
+
+	   this is not the same with force_mld_version because IGMPv3 RFC3376
+	   Security Considerations does not have clear description that we could
+	   ignore other version messages completely as MLDv2 RFC3810. So make
+	   this value as default 0 is recommended.
+
+``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.  This controls whether packets
+	received _on_ this interface can be forwarded.
+
+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 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 to gateways listed in the
+	interface's current gateway list. Even if disabled, RFC1122 redirect
+	rules still apply.
+
+	Overridden by shared_media.
+
+	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.
+
+drop_unicast_in_l2_multicast - BOOLEAN
+	Drop any unicast IP packets that are received in link-layer
+	multicast (or broadcast) frames.
+
+	This behavior (for multicast) is actually a SHOULD in RFC
+	1122, but is disabled by default for compatibility reasons.
+
+	Default: off (0)
+
+drop_gratuitous_arp - BOOLEAN
+	Drop all gratuitous ARP frames, for example if there's a known
+	good ARP proxy on the network and such frames need not be used
+	(or in the case of 802.11, must not be used to prevent attacks.)
+
+	Default: off (0)
+
+
+tag - INTEGER
+	Allows you to write a number, which can be used as required.
+
+	Default value is 0.
+
+xfrm4_gc_thresh - INTEGER
+	(Obsolete since linux-4.14)
+	The threshold at which we will start garbage collecting for IPv4
+	destination cache entries.  At twice this value the system will
+	refuse new allocations.
+
+igmp_link_local_mcast_reports - BOOLEAN
+	Enable IGMP reports for link local multicast groups in the
+	224.0.0.X range.
+
+	Default TRUE
+
+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 - INTEGER
+	Automatically generate flow labels based on a flow hash of the
+	packet. This allows intermediate devices, such as routers, to
+	identify packet flows for mechanisms like Equal Cost Multipath
+	Routing (see RFC 6438).
+
+	=  ===========================================================
+	0  automatic flow labels are completely disabled
+	1  automatic flow labels are enabled by default, they can be
+	   disabled on a per socket basis using the IPV6_AUTOFLOWLABEL
+	   socket option
+	2  automatic flow labels are allowed, they may be enabled on a
+	   per socket basis using the IPV6_AUTOFLOWLABEL socket option
+	3  automatic flow labels are enabled and enforced, they cannot
+	   be disabled by the socket option
+	=  ===========================================================
+
+	Default: 1
+
+flowlabel_state_ranges - BOOLEAN
+	Split the flow label number space into two ranges. 0-0x7FFFF is
+	reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF
+	is reserved for stateless flow labels as described in RFC6437.
+
+	- TRUE: enabled
+	- FALSE: disabled
+
+	Default: true
+
+flowlabel_reflect - INTEGER
+	Control flow label reflection. Needed for Path MTU
+	Discovery to work with Equal Cost Multipath Routing in anycast
+	environments. See RFC 7690 and:
+	https://tools.ietf.org/html/draft-wang-6man-flow-label-reflection-01
+
+	This is a bitmask.
+
+	- 1: enabled for established flows
+
+	  Note that this prevents automatic flowlabel changes, as done
+	  in "tcp: change IPv6 flow-label upon receiving spurious retransmission"
+	  and "tcp: Change txhash on every SYN and RTO retransmit"
+
+	- 2: enabled for TCP RESET packets (no active listener)
+	  If set, a RST packet sent in response to a SYN packet on a closed
+	  port will reflect the incoming flow label.
+
+	- 4: enabled for ICMPv6 echo reply messages.
+
+	Default: 0
+
+fib_multipath_hash_policy - INTEGER
+	Controls which hash policy to use for multipath routes.
+
+	Default: 0 (Layer 3)
+
+	Possible values:
+
+	- 0 - Layer 3 (source and destination addresses plus flow label)
+	- 1 - Layer 4 (standard 5-tuple)
+	- 2 - Layer 3 or inner Layer 3 if present
+
+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)
+
+max_dst_opts_number - INTEGER
+	Maximum number of non-padding TLVs allowed in a Destination
+	options extension header. If this value is less than zero
+	then unknown options are disallowed and the number of known
+	TLVs allowed is the absolute value of this number.
+
+	Default: 8
+
+max_hbh_opts_number - INTEGER
+	Maximum number of non-padding TLVs allowed in a Hop-by-Hop
+	options extension header. If this value is less than zero
+	then unknown options are disallowed and the number of known
+	TLVs allowed is the absolute value of this number.
+
+	Default: 8
+
+max_dst_opts_length - INTEGER
+	Maximum length allowed for a Destination options extension
+	header.
+
+	Default: INT_MAX (unlimited)
+
+max_hbh_length - INTEGER
+	Maximum length allowed for a Hop-by-Hop options extension
+	header.
+
+	Default: INT_MAX (unlimited)
+
+skip_notify_on_dev_down - BOOLEAN
+	Controls whether an RTM_DELROUTE message is generated for routes
+	removed when a device is taken down or deleted. IPv4 does not
+	generate this message; IPv6 does by default. Setting this sysctl
+	to true skips the message, making IPv4 and IPv6 on par in relying
+	on userspace caches to track link events and evict routes.
+
+	Default: false (generate message)
+
+nexthop_compat_mode - BOOLEAN
+	New nexthop API provides a means for managing nexthops independent of
+	prefixes. Backwards compatibilty with old route format is enabled by
+	default which means route dumps and notifications contain the new
+	nexthop attribute but also the full, expanded nexthop definition.
+	Further, updates or deletes of a nexthop configuration generate route
+	notifications for each fib entry using the nexthop. Once a system
+	understands the new API, this sysctl can be disabled to achieve full
+	performance benefits of the new API by disabling the nexthop expansion
+	and extraneous notifications.
+	Default: true (backward compat mode)
+
+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.
+
+IPv6 Segment Routing:
+
+seg6_flowlabel - INTEGER
+	Controls the behaviour of computing the flowlabel of outer
+	IPv6 header in case of SR T.encaps
+
+	 == =======================================================
+	 -1  set flowlabel to zero.
+	  0  copy flowlabel from Inner packet in case of Inner IPv6
+	     (Set flowlabel to 0 in case IPv4/L2)
+	  1  Compute the flowlabel using seg6_make_flowlabel()
+	 == =======================================================
+
+	Default is 0.
+
+``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_min_hop_limit - INTEGER
+	Minimum hop limit Information in Router Advertisement.
+
+	Hop limit Information in Router Advertisement less than this
+	variable shall be ignored.
+
+	Default: 1
+
+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_min_plen - INTEGER
+	Minimum prefix length of Route Information in RA.
+
+	Route Information w/ prefix smaller than 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_rt_info_max_plen - INTEGER
+	Maximum prefix length of Route Information in RA.
+
+	Route Information w/ prefix larger than 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)
+
+ip_nonlocal_bind - BOOLEAN
+	If set, allows processes to bind() to non-local IPv6 addresses,
+	which can be quite useful - but may break some applications.
+
+	Default: 0
+
+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_oif_addrs_only - BOOLEAN
+	When enabled, the candidate source addresses for destinations
+	routed via this interface are restricted to the set of addresses
+	configured on this interface (vis. RFC 6724, section 4).
+
+	Default: false
+
+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)
+
+keep_addr_on_down - INTEGER
+	Keep all IPv6 addresses on an interface down event. If set static
+	global addresses with no expiration time are not flushed.
+
+	*   >0 : enabled
+	*    0 : system default
+	*   <0 : disabled
+
+	Default: 0 (addresses are removed)
+
+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 addresses and routes on the given
+	interface. From now on it will not possible to add addresses/routes
+	to the selected 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.
+	 == ==============================================================
+
+	DAD operation and mode on a given interface will be selected according
+	to the maximum value of conf/{all,interface}/accept_dad.
+
+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.
+
+ndisc_tclass - INTEGER
+	The IPv6 Traffic Class to use by default when sending IPv6 Neighbor
+	Discovery (Router Solicitation, Router Advertisement, Neighbor
+	Solicitation, Neighbor Advertisement, Redirect) messages.
+	These 8 bits can be interpreted as 6 high order bits holding the DSCP
+	value and 2 low order bits representing ECN (which you probably want
+	to leave cleared).
+
+	* 0 - (default)
+
+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
+
+	Optimistic Duplicate Address Detection for the interface will be enabled
+	if at least one of conf/{all,interface}/optimistic_dad is set to 1,
+	it will be disabled otherwise.
+
+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
+
+	This will be enabled if at least one of
+	conf/{all,interface}/use_optimistic is set to 1, disabled otherwise.
+
+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.
+
+addr_gen_mode - INTEGER
+	Defines how link-local and autoconf addresses are generated.
+
+	=  =================================================================
+	0  generate address based on EUI64 (default)
+	1  do no generate a link-local address, use EUI64 for addresses
+	   generated from autoconf
+	2  generate stable privacy addresses, using the secret from
+	   stable_secret (RFC7217)
+	3  generate stable privacy addresses, using a random secret if unset
+	=  =================================================================
+
+drop_unicast_in_l2_multicast - BOOLEAN
+	Drop any unicast IPv6 packets that are received in link-layer
+	multicast (or broadcast) frames.
+
+	By default this is turned off.
+
+drop_unsolicited_na - BOOLEAN
+	Drop all unsolicited neighbor advertisements, for example if there's
+	a known good NA proxy on the network and such frames need not be used
+	(or in the case of 802.11, must not be used to prevent attacks.)
+
+	By default this is turned off.
+
+enhanced_dad - BOOLEAN
+	Include a nonce option in the IPv6 neighbor solicitation messages used for
+	duplicate address detection per RFC7527. A received DAD NS will only signal
+	a duplicate address if the nonce is different. This avoids any false
+	detection of duplicates due to loopback of the NS messages that we send.
+	The nonce option will be sent on an interface unless both of
+	conf/{all,interface}/enhanced_dad are set to FALSE.
+
+	Default: TRUE
+
+``icmp/*``:
+===========
+
+ratelimit - INTEGER
+	Limit the maximal rates for sending ICMPv6 messages.
+
+	0 to disable any limiting,
+	otherwise the minimal space between responses in milliseconds.
+
+	Default: 1000
+
+ratemask - list of comma separated ranges
+	For ICMPv6 message types matching the ranges in the ratemask, limit
+	the sending of the message according to ratelimit parameter.
+
+	The format used for both input and output is a comma separated
+	list of ranges (e.g. "0-127,129" for ICMPv6 message type 0 to 127 and
+	129). Writing to the file will clear all previous ranges of ICMPv6
+	message types and update the current list with the input.
+
+	Refer to: https://www.iana.org/assignments/icmpv6-parameters/icmpv6-parameters.xhtml
+	for numerical values of ICMPv6 message types, e.g. echo request is 128
+	and echo reply is 129.
+
+	Default: 0-1,3-127 (rate limit ICMPv6 errors except Packet Too Big)
+
+echo_ignore_all - BOOLEAN
+	If set non-zero, then the kernel will ignore all ICMP ECHO
+	requests sent to it over the IPv6 protocol.
+
+	Default: 0
+
+echo_ignore_multicast - BOOLEAN
+	If set non-zero, then the kernel will ignore all ICMP ECHO
+	requests sent to it over the IPv6 protocol via multicast.
+
+	Default: 0
+
+echo_ignore_anycast - BOOLEAN
+	If set non-zero, then the kernel will ignore all ICMP ECHO
+	requests sent to it over the IPv6 protocol destined to anycast address.
+
+	Default: 0
+
+xfrm6_gc_thresh - INTEGER
+	(Obsolete since linux-4.14)
+	The threshold at which we will start garbage collecting for IPv6
+	destination cache entries.  At twice this value the system will
+	refuse new allocations.
+
+
+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
+
+pf_enable - INTEGER
+	Enable or disable pf (pf is short for potentially failed) state. A value
+	of pf_retrans > path_max_retrans also disables pf state. That is, one of
+	both pf_enable and pf_retrans > path_max_retrans can disable pf state.
+	Since pf_retrans and path_max_retrans can be changed by userspace
+	application, sometimes user expects to disable pf state by the value of
+	pf_retrans > path_max_retrans, but occasionally the value of pf_retrans
+	or path_max_retrans is changed by the user application, this pf state is
+	enabled. As such, it is necessary to add this to dynamically enable
+	and disable pf state. See:
+	https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover for
+	details.
+
+	1: Enable pf.
+
+	0: Disable pf.
+
+	Default: 1
+
+pf_expose - INTEGER
+	Unset or enable/disable pf (pf is short for potentially failed) state
+	exposure.  Applications can control the exposure of the PF path state
+	in the SCTP_PEER_ADDR_CHANGE event and the SCTP_GET_PEER_ADDR_INFO
+	sockopt.   When it's unset, no SCTP_PEER_ADDR_CHANGE event with
+	SCTP_ADDR_PF state will be sent and a SCTP_PF-state transport info
+	can be got via SCTP_GET_PEER_ADDR_INFO sockopt;  When it's enabled,
+	a SCTP_PEER_ADDR_CHANGE event will be sent for a transport becoming
+	SCTP_PF state and a SCTP_PF-state transport info can be got via
+	SCTP_GET_PEER_ADDR_INFO sockopt;  When it's diabled, no
+	SCTP_PEER_ADDR_CHANGE event will be sent and it returns -EACCES when
+	trying to get a SCTP_PF-state transport info via SCTP_GET_PEER_ADDR_INFO
+	sockopt.
+
+	0: Unset pf state exposure, Compatible with old applications.
+
+	1: Disable pf state exposure.
+
+	2: Enable pf state exposure.
+
+	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. Since both pf_retrans and path_max_retrans can
+	be changed by userspace application, a variable pf_enable is used to
+	disable pf state.
+
+	Default: 0
+
+ps_retrans - INTEGER
+	Primary.Switchover.Max.Retrans (PSMR), it's a tunable parameter coming
+	from section-5 "Primary Path Switchover" in rfc7829.  The primary path
+	will be changed to another active path when the path error counter on
+	the old primary path exceeds PSMR, so that "the SCTP sender is allowed
+	to continue data transmission on a new working path even when the old
+	primary destination address becomes active again".   Note this feature
+	is disabled by initializing 'ps_retrans' per netns as 0xffff by default,
+	and its value can't be less than 'pf_retrans' when changing by sysctl.
+
+	Default: 0xffff
+
+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: 4K
+
+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/admin-guide/sysctl/net.rst for descriptions of these entries.
+
+
+``/proc/sys/net/unix/*``
+========================
+
+max_dgram_qlen - INTEGER
+	The maximum length of dgram socket receive queue
+
+	Default: 10
+