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Based on kernel version 4.13.3. Page generated on 2017-09-23 13:55 EST.

1	/proc/sys/net/ipv4/* Variables:
2	
3	ip_forward - BOOLEAN
4		0 - disabled (default)
5		not 0 - enabled
6	
7		Forward Packets between interfaces.
8	
9		This variable is special, its change resets all configuration
10		parameters to their default state (RFC1122 for hosts, RFC1812
11		for routers)
12	
13	ip_default_ttl - INTEGER
14		Default value of TTL field (Time To Live) for outgoing (but not
15		forwarded) IP packets. Should be between 1 and 255 inclusive.
16		Default: 64 (as recommended by RFC1700)
17	
18	ip_no_pmtu_disc - INTEGER
19		Disable Path MTU Discovery. If enabled in mode 1 and a
20		fragmentation-required ICMP is received, the PMTU to this
21		destination will be set to min_pmtu (see below). You will need
22		to raise min_pmtu to the smallest interface MTU on your system
23		manually if you want to avoid locally generated fragments.
24	
25		In mode 2 incoming Path MTU Discovery messages will be
26		discarded. Outgoing frames are handled the same as in mode 1,
27		implicitly setting IP_PMTUDISC_DONT on every created socket.
28	
29		Mode 3 is a hardend pmtu discover mode. The kernel will only
30		accept fragmentation-needed errors if the underlying protocol
31		can verify them besides a plain socket lookup. Current
32		protocols for which pmtu events will be honored are TCP, SCTP
33		and DCCP as they verify e.g. the sequence number or the
34		association. This mode should not be enabled globally but is
35		only intended to secure e.g. name servers in namespaces where
36		TCP path mtu must still work but path MTU information of other
37		protocols should be discarded. If enabled globally this mode
38		could break other protocols.
39	
40		Possible values: 0-3
41		Default: FALSE
42	
43	min_pmtu - INTEGER
44		default 552 - minimum discovered Path MTU
45	
46	ip_forward_use_pmtu - BOOLEAN
47		By default we don't trust protocol path MTUs while forwarding
48		because they could be easily forged and can lead to unwanted
49		fragmentation by the router.
50		You only need to enable this if you have user-space software
51		which tries to discover path mtus by itself and depends on the
52		kernel honoring this information. This is normally not the
53		case.
54		Default: 0 (disabled)
55		Possible values:
56		0 - disabled
57		1 - enabled
58	
59	fwmark_reflect - BOOLEAN
60		Controls the fwmark of kernel-generated IPv4 reply packets that are not
61		associated with a socket for example, TCP RSTs or ICMP echo replies).
62		If unset, these packets have a fwmark of zero. If set, they have the
63		fwmark of the packet they are replying to.
64		Default: 0
65	
66	fib_multipath_use_neigh - BOOLEAN
67		Use status of existing neighbor entry when determining nexthop for
68		multipath routes. If disabled, neighbor information is not used and
69		packets could be directed to a failed nexthop. Only valid for kernels
70		built with CONFIG_IP_ROUTE_MULTIPATH enabled.
71		Default: 0 (disabled)
72		Possible values:
73		0 - disabled
74		1 - enabled
75	
76	fib_multipath_hash_policy - INTEGER
77		Controls which hash policy to use for multipath routes. Only valid
78		for kernels built with CONFIG_IP_ROUTE_MULTIPATH enabled.
79		Default: 0 (Layer 3)
80		Possible values:
81		0 - Layer 3
82		1 - Layer 4
83	
84	route/max_size - INTEGER
85		Maximum number of routes allowed in the kernel.  Increase
86		this when using large numbers of interfaces and/or routes.
87		From linux kernel 3.6 onwards, this is deprecated for ipv4
88		as route cache is no longer used.
89	
90	neigh/default/gc_thresh1 - INTEGER
91		Minimum number of entries to keep.  Garbage collector will not
92		purge entries if there are fewer than this number.
93		Default: 128
94	
95	neigh/default/gc_thresh2 - INTEGER
96		Threshold when garbage collector becomes more aggressive about
97		purging entries. Entries older than 5 seconds will be cleared
98		when over this number.
99		Default: 512
100	
101	neigh/default/gc_thresh3 - INTEGER
102		Maximum number of neighbor entries allowed.  Increase this
103		when using large numbers of interfaces and when communicating
104		with large numbers of directly-connected peers.
105		Default: 1024
106	
107	neigh/default/unres_qlen_bytes - INTEGER
108		The maximum number of bytes which may be used by packets
109		queued for each	unresolved address by other network layers.
110		(added in linux 3.3)
111		Setting negative value is meaningless and will return error.
112		Default: 65536 Bytes(64KB)
113	
114	neigh/default/unres_qlen - INTEGER
115		The maximum number of packets which may be queued for each
116		unresolved address by other network layers.
117		(deprecated in linux 3.3) : use unres_qlen_bytes instead.
118		Prior to linux 3.3, the default value is 3 which may cause
119		unexpected packet loss. The current default value is calculated
120		according to default value of unres_qlen_bytes and true size of
121		packet.
122		Default: 31
123	
124	mtu_expires - INTEGER
125		Time, in seconds, that cached PMTU information is kept.
126	
127	min_adv_mss - INTEGER
128		The advertised MSS depends on the first hop route MTU, but will
129		never be lower than this setting.
130	
131	IP Fragmentation:
132	
133	ipfrag_high_thresh - INTEGER
134		Maximum memory used to reassemble IP fragments. When
135		ipfrag_high_thresh bytes of memory is allocated for this purpose,
136		the fragment handler will toss packets until ipfrag_low_thresh
137		is reached. This also serves as a maximum limit to namespaces
138		different from the initial one.
139	
140	ipfrag_low_thresh - INTEGER
141		Maximum memory used to reassemble IP fragments before the kernel
142		begins to remove incomplete fragment queues to free up resources.
143		The kernel still accepts new fragments for defragmentation.
144	
145	ipfrag_time - INTEGER
146		Time in seconds to keep an IP fragment in memory.
147	
148	ipfrag_max_dist - INTEGER
149		ipfrag_max_dist is a non-negative integer value which defines the
150		maximum "disorder" which is allowed among fragments which share a
151		common IP source address. Note that reordering of packets is
152		not unusual, but if a large number of fragments arrive from a source
153		IP address while a particular fragment queue remains incomplete, it
154		probably indicates that one or more fragments belonging to that queue
155		have been lost. When ipfrag_max_dist is positive, an additional check
156		is done on fragments before they are added to a reassembly queue - if
157		ipfrag_max_dist (or more) fragments have arrived from a particular IP
158		address between additions to any IP fragment queue using that source
159		address, it's presumed that one or more fragments in the queue are
160		lost. The existing fragment queue will be dropped, and a new one
161		started. An ipfrag_max_dist value of zero disables this check.
162	
163		Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
164		result in unnecessarily dropping fragment queues when normal
165		reordering of packets occurs, which could lead to poor application
166		performance. Using a very large value, e.g. 50000, increases the
167		likelihood of incorrectly reassembling IP fragments that originate
168		from different IP datagrams, which could result in data corruption.
169		Default: 64
170	
171	INET peer storage:
172	
173	inet_peer_threshold - INTEGER
174		The approximate size of the storage.  Starting from this threshold
175		entries will be thrown aggressively.  This threshold also determines
176		entries' time-to-live and time intervals between garbage collection
177		passes.  More entries, less time-to-live, less GC interval.
178	
179	inet_peer_minttl - INTEGER
180		Minimum time-to-live of entries.  Should be enough to cover fragment
181		time-to-live on the reassembling side.  This minimum time-to-live  is
182		guaranteed if the pool size is less than inet_peer_threshold.
183		Measured in seconds.
184	
185	inet_peer_maxttl - INTEGER
186		Maximum time-to-live of entries.  Unused entries will expire after
187		this period of time if there is no memory pressure on the pool (i.e.
188		when the number of entries in the pool is very small).
189		Measured in seconds.
190	
191	TCP variables:
192	
193	somaxconn - INTEGER
194		Limit of socket listen() backlog, known in userspace as SOMAXCONN.
195		Defaults to 128.  See also tcp_max_syn_backlog for additional tuning
196		for TCP sockets.
197	
198	tcp_abort_on_overflow - BOOLEAN
199		If listening service is too slow to accept new connections,
200		reset them. Default state is FALSE. It means that if overflow
201		occurred due to a burst, connection will recover. Enable this
202		option _only_ if you are really sure that listening daemon
203		cannot be tuned to accept connections faster. Enabling this
204		option can harm clients of your server.
205	
206	tcp_adv_win_scale - INTEGER
207		Count buffering overhead as bytes/2^tcp_adv_win_scale
208		(if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
209		if it is <= 0.
210		Possible values are [-31, 31], inclusive.
211		Default: 1
212	
213	tcp_allowed_congestion_control - STRING
214		Show/set the congestion control choices available to non-privileged
215		processes. The list is a subset of those listed in
216		tcp_available_congestion_control.
217		Default is "reno" and the default setting (tcp_congestion_control).
218	
219	tcp_app_win - INTEGER
220		Reserve max(window/2^tcp_app_win, mss) of window for application
221		buffer. Value 0 is special, it means that nothing is reserved.
222		Default: 31
223	
224	tcp_autocorking - BOOLEAN
225		Enable TCP auto corking :
226		When applications do consecutive small write()/sendmsg() system calls,
227		we try to coalesce these small writes as much as possible, to lower
228		total amount of sent packets. This is done if at least one prior
229		packet for the flow is waiting in Qdisc queues or device transmit
230		queue. Applications can still use TCP_CORK for optimal behavior
231		when they know how/when to uncork their sockets.
232		Default : 1
233	
234	tcp_available_congestion_control - STRING
235		Shows the available congestion control choices that are registered.
236		More congestion control algorithms may be available as modules,
237		but not loaded.
238	
239	tcp_base_mss - INTEGER
240		The initial value of search_low to be used by the packetization layer
241		Path MTU discovery (MTU probing).  If MTU probing is enabled,
242		this is the initial MSS used by the connection.
243	
244	tcp_congestion_control - STRING
245		Set the congestion control algorithm to be used for new
246		connections. The algorithm "reno" is always available, but
247		additional choices may be available based on kernel configuration.
248		Default is set as part of kernel configuration.
249		For passive connections, the listener congestion control choice
250		is inherited.
251		[see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ]
252	
253	tcp_dsack - BOOLEAN
254		Allows TCP to send "duplicate" SACKs.
255	
256	tcp_early_retrans - INTEGER
257		Tail loss probe (TLP) converts RTOs occurring due to tail
258		losses into fast recovery (draft-ietf-tcpm-rack). Note that
259		TLP requires RACK to function properly (see tcp_recovery below)
260		Possible values:
261			0 disables TLP
262			3 or 4 enables TLP
263		Default: 3
264	
265	tcp_ecn - INTEGER
266		Control use of Explicit Congestion Notification (ECN) by TCP.
267		ECN is used only when both ends of the TCP connection indicate
268		support for it.  This feature is useful in avoiding losses due
269		to congestion by allowing supporting routers to signal
270		congestion before having to drop packets.
271		Possible values are:
272			0 Disable ECN.  Neither initiate nor accept ECN.
273			1 Enable ECN when requested by incoming connections and
274			  also request ECN on outgoing connection attempts.
275			2 Enable ECN when requested by incoming connections
276			  but do not request ECN on outgoing connections.
277		Default: 2
278	
279	tcp_ecn_fallback - BOOLEAN
280		If the kernel detects that ECN connection misbehaves, enable fall
281		back to non-ECN. Currently, this knob implements the fallback
282		from RFC3168, section 6.1.1.1., but we reserve that in future,
283		additional detection mechanisms could be implemented under this
284		knob. The value	is not used, if tcp_ecn or per route (or congestion
285		control) ECN settings are disabled.
286		Default: 1 (fallback enabled)
287	
288	tcp_fack - BOOLEAN
289		Enable FACK congestion avoidance and fast retransmission.
290		The value is not used, if tcp_sack is not enabled.
291	
292	tcp_fin_timeout - INTEGER
293		The length of time an orphaned (no longer referenced by any
294		application) connection will remain in the FIN_WAIT_2 state
295		before it is aborted at the local end.  While a perfectly
296		valid "receive only" state for an un-orphaned connection, an
297		orphaned connection in FIN_WAIT_2 state could otherwise wait
298		forever for the remote to close its end of the connection.
299		Cf. tcp_max_orphans
300		Default: 60 seconds
301	
302	tcp_frto - INTEGER
303		Enables Forward RTO-Recovery (F-RTO) defined in RFC5682.
304		F-RTO is an enhanced recovery algorithm for TCP retransmission
305		timeouts.  It is particularly beneficial in networks where the
306		RTT fluctuates (e.g., wireless). F-RTO is sender-side only
307		modification. It does not require any support from the peer.
308	
309		By default it's enabled with a non-zero value. 0 disables F-RTO.
310	
311	tcp_invalid_ratelimit - INTEGER
312		Limit the maximal rate for sending duplicate acknowledgments
313		in response to incoming TCP packets that are for an existing
314		connection but that are invalid due to any of these reasons:
315	
316		  (a) out-of-window sequence number,
317		  (b) out-of-window acknowledgment number, or
318		  (c) PAWS (Protection Against Wrapped Sequence numbers) check failure
319	
320		This can help mitigate simple "ack loop" DoS attacks, wherein
321		a buggy or malicious middlebox or man-in-the-middle can
322		rewrite TCP header fields in manner that causes each endpoint
323		to think that the other is sending invalid TCP segments, thus
324		causing each side to send an unterminating stream of duplicate
325		acknowledgments for invalid segments.
326	
327		Using 0 disables rate-limiting of dupacks in response to
328		invalid segments; otherwise this value specifies the minimal
329		space between sending such dupacks, in milliseconds.
330	
331		Default: 500 (milliseconds).
332	
333	tcp_keepalive_time - INTEGER
334		How often TCP sends out keepalive messages when keepalive is enabled.
335		Default: 2hours.
336	
337	tcp_keepalive_probes - INTEGER
338		How many keepalive probes TCP sends out, until it decides that the
339		connection is broken. Default value: 9.
340	
341	tcp_keepalive_intvl - INTEGER
342		How frequently the probes are send out. Multiplied by
343		tcp_keepalive_probes it is time to kill not responding connection,
344		after probes started. Default value: 75sec i.e. connection
345		will be aborted after ~11 minutes of retries.
346	
347	tcp_l3mdev_accept - BOOLEAN
348		Enables child sockets to inherit the L3 master device index.
349		Enabling this option allows a "global" listen socket to work
350		across L3 master domains (e.g., VRFs) with connected sockets
351		derived from the listen socket to be bound to the L3 domain in
352		which the packets originated. Only valid when the kernel was
353		compiled with CONFIG_NET_L3_MASTER_DEV.
354	
355	tcp_low_latency - BOOLEAN
356		If set, the TCP stack makes decisions that prefer lower
357		latency as opposed to higher throughput.  By default, this
358		option is not set meaning that higher throughput is preferred.
359		An example of an application where this default should be
360		changed would be a Beowulf compute cluster.
361		Default: 0
362	
363	tcp_max_orphans - INTEGER
364		Maximal number of TCP sockets not attached to any user file handle,
365		held by system.	If this number is exceeded orphaned connections are
366		reset immediately and warning is printed. This limit exists
367		only to prevent simple DoS attacks, you _must_ not rely on this
368		or lower the limit artificially, but rather increase it
369		(probably, after increasing installed memory),
370		if network conditions require more than default value,
371		and tune network services to linger and kill such states
372		more aggressively. Let me to remind again: each orphan eats
373		up to ~64K of unswappable memory.
374	
375	tcp_max_syn_backlog - INTEGER
376		Maximal number of remembered connection requests, which have not
377		received an acknowledgment from connecting client.
378		The minimal value is 128 for low memory machines, and it will
379		increase in proportion to the memory of machine.
380		If server suffers from overload, try increasing this number.
381	
382	tcp_max_tw_buckets - INTEGER
383		Maximal number of timewait sockets held by system simultaneously.
384		If this number is exceeded time-wait socket is immediately destroyed
385		and warning is printed. This limit exists only to prevent
386		simple DoS attacks, you _must_ not lower the limit artificially,
387		but rather increase it (probably, after increasing installed memory),
388		if network conditions require more than default value.
389	
390	tcp_mem - vector of 3 INTEGERs: min, pressure, max
391		min: below this number of pages TCP is not bothered about its
392		memory appetite.
393	
394		pressure: when amount of memory allocated by TCP exceeds this number
395		of pages, TCP moderates its memory consumption and enters memory
396		pressure mode, which is exited when memory consumption falls
397		under "min".
398	
399		max: number of pages allowed for queueing by all TCP sockets.
400	
401		Defaults are calculated at boot time from amount of available
402		memory.
403	
404	tcp_min_rtt_wlen - INTEGER
405		The window length of the windowed min filter to track the minimum RTT.
406		A shorter window lets a flow more quickly pick up new (higher)
407		minimum RTT when it is moved to a longer path (e.g., due to traffic
408		engineering). A longer window makes the filter more resistant to RTT
409		inflations such as transient congestion. The unit is seconds.
410		Default: 300
411	
412	tcp_moderate_rcvbuf - BOOLEAN
413		If set, TCP performs receive buffer auto-tuning, attempting to
414		automatically size the buffer (no greater than tcp_rmem[2]) to
415		match the size required by the path for full throughput.  Enabled by
416		default.
417	
418	tcp_mtu_probing - INTEGER
419		Controls TCP Packetization-Layer Path MTU Discovery.  Takes three
420		values:
421		  0 - Disabled
422		  1 - Disabled by default, enabled when an ICMP black hole detected
423		  2 - Always enabled, use initial MSS of tcp_base_mss.
424	
425	tcp_probe_interval - INTEGER
426		Controls how often to start TCP Packetization-Layer Path MTU
427		Discovery reprobe. The default is reprobing every 10 minutes as
428		per RFC4821.
429	
430	tcp_probe_threshold - INTEGER
431		Controls when TCP Packetization-Layer Path MTU Discovery probing
432		will stop in respect to the width of search range in bytes. Default
433		is 8 bytes.
434	
435	tcp_no_metrics_save - BOOLEAN
436		By default, TCP saves various connection metrics in the route cache
437		when the connection closes, so that connections established in the
438		near future can use these to set initial conditions.  Usually, this
439		increases overall performance, but may sometimes cause performance
440		degradation.  If set, TCP will not cache metrics on closing
441		connections.
442	
443	tcp_orphan_retries - INTEGER
444		This value influences the timeout of a locally closed TCP connection,
445		when RTO retransmissions remain unacknowledged.
446		See tcp_retries2 for more details.
447	
448		The default value is 8.
449		If your machine is a loaded WEB server,
450		you should think about lowering this value, such sockets
451		may consume significant resources. Cf. tcp_max_orphans.
452	
453	tcp_recovery - INTEGER
454		This value is a bitmap to enable various experimental loss recovery
455		features.
456	
457		RACK: 0x1 enables the RACK loss detection for fast detection of lost
458		      retransmissions and tail drops.
459	
460		Default: 0x1
461	
462	tcp_reordering - INTEGER
463		Initial reordering level of packets in a TCP stream.
464		TCP stack can then dynamically adjust flow reordering level
465		between this initial value and tcp_max_reordering
466		Default: 3
467	
468	tcp_max_reordering - INTEGER
469		Maximal reordering level of packets in a TCP stream.
470		300 is a fairly conservative value, but you might increase it
471		if paths are using per packet load balancing (like bonding rr mode)
472		Default: 300
473	
474	tcp_retrans_collapse - BOOLEAN
475		Bug-to-bug compatibility with some broken printers.
476		On retransmit try to send bigger packets to work around bugs in
477		certain TCP stacks.
478	
479	tcp_retries1 - INTEGER
480		This value influences the time, after which TCP decides, that
481		something is wrong due to unacknowledged RTO retransmissions,
482		and reports this suspicion to the network layer.
483		See tcp_retries2 for more details.
484	
485		RFC 1122 recommends at least 3 retransmissions, which is the
486		default.
487	
488	tcp_retries2 - INTEGER
489		This value influences the timeout of an alive TCP connection,
490		when RTO retransmissions remain unacknowledged.
491		Given a value of N, a hypothetical TCP connection following
492		exponential backoff with an initial RTO of TCP_RTO_MIN would
493		retransmit N times before killing the connection at the (N+1)th RTO.
494	
495		The default value of 15 yields a hypothetical timeout of 924.6
496		seconds and is a lower bound for the effective timeout.
497		TCP will effectively time out at the first RTO which exceeds the
498		hypothetical timeout.
499	
500		RFC 1122 recommends at least 100 seconds for the timeout,
501		which corresponds to a value of at least 8.
502	
503	tcp_rfc1337 - BOOLEAN
504		If set, the TCP stack behaves conforming to RFC1337. If unset,
505		we are not conforming to RFC, but prevent TCP TIME_WAIT
506		assassination.
507		Default: 0
508	
509	tcp_rmem - vector of 3 INTEGERs: min, default, max
510		min: Minimal size of receive buffer used by TCP sockets.
511		It is guaranteed to each TCP socket, even under moderate memory
512		pressure.
513		Default: 1 page
514	
515		default: initial size of receive buffer used by TCP sockets.
516		This value overrides net.core.rmem_default used by other protocols.
517		Default: 87380 bytes. This value results in window of 65535 with
518		default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
519		less for default tcp_app_win. See below about these variables.
520	
521		max: maximal size of receive buffer allowed for automatically
522		selected receiver buffers for TCP socket. This value does not override
523		net.core.rmem_max.  Calling setsockopt() with SO_RCVBUF disables
524		automatic tuning of that socket's receive buffer size, in which
525		case this value is ignored.
526		Default: between 87380B and 6MB, depending on RAM size.
527	
528	tcp_sack - BOOLEAN
529		Enable select acknowledgments (SACKS).
530	
531	tcp_slow_start_after_idle - BOOLEAN
532		If set, provide RFC2861 behavior and time out the congestion
533		window after an idle period.  An idle period is defined at
534		the current RTO.  If unset, the congestion window will not
535		be timed out after an idle period.
536		Default: 1
537	
538	tcp_stdurg - BOOLEAN
539		Use the Host requirements interpretation of the TCP urgent pointer field.
540		Most hosts use the older BSD interpretation, so if you turn this on
541		Linux might not communicate correctly with them.
542		Default: FALSE
543	
544	tcp_synack_retries - INTEGER
545		Number of times SYNACKs for a passive TCP connection attempt will
546		be retransmitted. Should not be higher than 255. Default value
547		is 5, which corresponds to 31seconds till the last retransmission
548		with the current initial RTO of 1second. With this the final timeout
549		for a passive TCP connection will happen after 63seconds.
550	
551	tcp_syncookies - BOOLEAN
552		Only valid when the kernel was compiled with CONFIG_SYN_COOKIES
553		Send out syncookies when the syn backlog queue of a socket
554		overflows. This is to prevent against the common 'SYN flood attack'
555		Default: 1
556	
557		Note, that syncookies is fallback facility.
558		It MUST NOT be used to help highly loaded servers to stand
559		against legal connection rate. If you see SYN flood warnings
560		in your logs, but investigation	shows that they occur
561		because of overload with legal connections, you should tune
562		another parameters until this warning disappear.
563		See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
564	
565		syncookies seriously violate TCP protocol, do not allow
566		to use TCP extensions, can result in serious degradation
567		of some services (f.e. SMTP relaying), visible not by you,
568		but your clients and relays, contacting you. While you see
569		SYN flood warnings in logs not being really flooded, your server
570		is seriously misconfigured.
571	
572		If you want to test which effects syncookies have to your
573		network connections you can set this knob to 2 to enable
574		unconditionally generation of syncookies.
575	
576	tcp_fastopen - INTEGER
577		Enable TCP Fast Open (RFC7413) to send and accept data in the opening
578		SYN packet.
579	
580		The client support is enabled by flag 0x1 (on by default). The client
581		then must use sendmsg() or sendto() with the MSG_FASTOPEN flag,
582		rather than connect() to send data in SYN.
583	
584		The server support is enabled by flag 0x2 (off by default). Then
585		either enable for all listeners with another flag (0x400) or
586		enable individual listeners via TCP_FASTOPEN socket option with
587		the option value being the length of the syn-data backlog.
588	
589		The values (bitmap) are
590		  0x1: (client) enables sending data in the opening SYN on the client.
591		  0x2: (server) enables the server support, i.e., allowing data in
592				a SYN packet to be accepted and passed to the
593				application before 3-way handshake finishes.
594		  0x4: (client) send data in the opening SYN regardless of cookie
595				availability and without a cookie option.
596		0x200: (server) accept data-in-SYN w/o any cookie option present.
597		0x400: (server) enable all listeners to support Fast Open by
598				default without explicit TCP_FASTOPEN socket option.
599	
600		Default: 0x1
601	
602		Note that that additional client or server features are only
603		effective if the basic support (0x1 and 0x2) are enabled respectively.
604	
605	tcp_fastopen_blackhole_timeout_sec - INTEGER
606		Initial time period in second to disable Fastopen on active TCP sockets
607		when a TFO firewall blackhole issue happens.
608		This time period will grow exponentially when more blackhole issues
609		get detected right after Fastopen is re-enabled and will reset to
610		initial value when the blackhole issue goes away.
611		By default, it is set to 1hr.
612	
613	tcp_syn_retries - INTEGER
614		Number of times initial SYNs for an active TCP connection attempt
615		will be retransmitted. Should not be higher than 127. Default value
616		is 6, which corresponds to 63seconds till the last retransmission
617		with the current initial RTO of 1second. With this the final timeout
618		for an active TCP connection attempt will happen after 127seconds.
619	
620	tcp_timestamps - INTEGER
621	Enable timestamps as defined in RFC1323.
622		0: Disabled.
623		1: Enable timestamps as defined in RFC1323 and use random offset for
624		each connection rather than only using the current time.
625		2: Like 1, but without random offsets.
626		Default: 1
627	
628	tcp_min_tso_segs - INTEGER
629		Minimal number of segments per TSO frame.
630		Since linux-3.12, TCP does an automatic sizing of TSO frames,
631		depending on flow rate, instead of filling 64Kbytes packets.
632		For specific usages, it's possible to force TCP to build big
633		TSO frames. Note that TCP stack might split too big TSO packets
634		if available window is too small.
635		Default: 2
636	
637	tcp_pacing_ss_ratio - INTEGER
638		sk->sk_pacing_rate is set by TCP stack using a ratio applied
639		to current rate. (current_rate = cwnd * mss / srtt)
640		If TCP is in slow start, tcp_pacing_ss_ratio is applied
641		to let TCP probe for bigger speeds, assuming cwnd can be
642		doubled every other RTT.
643		Default: 200
644	
645	tcp_pacing_ca_ratio - INTEGER
646		sk->sk_pacing_rate is set by TCP stack using a ratio applied
647		to current rate. (current_rate = cwnd * mss / srtt)
648		If TCP is in congestion avoidance phase, tcp_pacing_ca_ratio
649		is applied to conservatively probe for bigger throughput.
650		Default: 120
651	
652	tcp_tso_win_divisor - INTEGER
653		This allows control over what percentage of the congestion window
654		can be consumed by a single TSO frame.
655		The setting of this parameter is a choice between burstiness and
656		building larger TSO frames.
657		Default: 3
658	
659	tcp_tw_reuse - BOOLEAN
660		Allow to reuse TIME-WAIT sockets for new connections when it is
661		safe from protocol viewpoint. Default value is 0.
662		It should not be changed without advice/request of technical
663		experts.
664	
665	tcp_window_scaling - BOOLEAN
666		Enable window scaling as defined in RFC1323.
667	
668	tcp_wmem - vector of 3 INTEGERs: min, default, max
669		min: Amount of memory reserved for send buffers for TCP sockets.
670		Each TCP socket has rights to use it due to fact of its birth.
671		Default: 1 page
672	
673		default: initial size of send buffer used by TCP sockets.  This
674		value overrides net.core.wmem_default used by other protocols.
675		It is usually lower than net.core.wmem_default.
676		Default: 16K
677	
678		max: Maximal amount of memory allowed for automatically tuned
679		send buffers for TCP sockets. This value does not override
680		net.core.wmem_max.  Calling setsockopt() with SO_SNDBUF disables
681		automatic tuning of that socket's send buffer size, in which case
682		this value is ignored.
683		Default: between 64K and 4MB, depending on RAM size.
684	
685	tcp_notsent_lowat - UNSIGNED INTEGER
686		A TCP socket can control the amount of unsent bytes in its write queue,
687		thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll()
688		reports POLLOUT events if the amount of unsent bytes is below a per
689		socket value, and if the write queue is not full. sendmsg() will
690		also not add new buffers if the limit is hit.
691	
692		This global variable controls the amount of unsent data for
693		sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change
694		to the global variable has immediate effect.
695	
696		Default: UINT_MAX (0xFFFFFFFF)
697	
698	tcp_workaround_signed_windows - BOOLEAN
699		If set, assume no receipt of a window scaling option means the
700		remote TCP is broken and treats the window as a signed quantity.
701		If unset, assume the remote TCP is not broken even if we do
702		not receive a window scaling option from them.
703		Default: 0
704	
705	tcp_thin_linear_timeouts - BOOLEAN
706		Enable dynamic triggering of linear timeouts for thin streams.
707		If set, a check is performed upon retransmission by timeout to
708		determine if the stream is thin (less than 4 packets in flight).
709		As long as the stream is found to be thin, up to 6 linear
710		timeouts may be performed before exponential backoff mode is
711		initiated. This improves retransmission latency for
712		non-aggressive thin streams, often found to be time-dependent.
713		For more information on thin streams, see
714		Documentation/networking/tcp-thin.txt
715		Default: 0
716	
717	tcp_limit_output_bytes - INTEGER
718		Controls TCP Small Queue limit per tcp socket.
719		TCP bulk sender tends to increase packets in flight until it
720		gets losses notifications. With SNDBUF autotuning, this can
721		result in a large amount of packets queued in qdisc/device
722		on the local machine, hurting latency of other flows, for
723		typical pfifo_fast qdiscs.
724		tcp_limit_output_bytes limits the number of bytes on qdisc
725		or device to reduce artificial RTT/cwnd and reduce bufferbloat.
726		Default: 262144
727	
728	tcp_challenge_ack_limit - INTEGER
729		Limits number of Challenge ACK sent per second, as recommended
730		in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
731		Default: 100
732	
733	UDP variables:
734	
735	udp_l3mdev_accept - BOOLEAN
736		Enabling this option allows a "global" bound socket to work
737		across L3 master domains (e.g., VRFs) with packets capable of
738		being received regardless of the L3 domain in which they
739		originated. Only valid when the kernel was compiled with
740		CONFIG_NET_L3_MASTER_DEV.
741	
742	udp_mem - vector of 3 INTEGERs: min, pressure, max
743		Number of pages allowed for queueing by all UDP sockets.
744	
745		min: Below this number of pages UDP is not bothered about its
746		memory appetite. When amount of memory allocated by UDP exceeds
747		this number, UDP starts to moderate memory usage.
748	
749		pressure: This value was introduced to follow format of tcp_mem.
750	
751		max: Number of pages allowed for queueing by all UDP sockets.
752	
753		Default is calculated at boot time from amount of available memory.
754	
755	udp_rmem_min - INTEGER
756		Minimal size of receive buffer used by UDP sockets in moderation.
757		Each UDP socket is able to use the size for receiving data, even if
758		total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
759		Default: 1 page
760	
761	udp_wmem_min - INTEGER
762		Minimal size of send buffer used by UDP sockets in moderation.
763		Each UDP socket is able to use the size for sending data, even if
764		total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
765		Default: 1 page
766	
767	CIPSOv4 Variables:
768	
769	cipso_cache_enable - BOOLEAN
770		If set, enable additions to and lookups from the CIPSO label mapping
771		cache.  If unset, additions are ignored and lookups always result in a
772		miss.  However, regardless of the setting the cache is still
773		invalidated when required when means you can safely toggle this on and
774		off and the cache will always be "safe".
775		Default: 1
776	
777	cipso_cache_bucket_size - INTEGER
778		The CIPSO label cache consists of a fixed size hash table with each
779		hash bucket containing a number of cache entries.  This variable limits
780		the number of entries in each hash bucket; the larger the value the
781		more CIPSO label mappings that can be cached.  When the number of
782		entries in a given hash bucket reaches this limit adding new entries
783		causes the oldest entry in the bucket to be removed to make room.
784		Default: 10
785	
786	cipso_rbm_optfmt - BOOLEAN
787		Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
788		the CIPSO draft specification (see Documentation/netlabel for details).
789		This means that when set the CIPSO tag will be padded with empty
790		categories in order to make the packet data 32-bit aligned.
791		Default: 0
792	
793	cipso_rbm_structvalid - BOOLEAN
794		If set, do a very strict check of the CIPSO option when
795		ip_options_compile() is called.  If unset, relax the checks done during
796		ip_options_compile().  Either way is "safe" as errors are caught else
797		where in the CIPSO processing code but setting this to 0 (False) should
798		result in less work (i.e. it should be faster) but could cause problems
799		with other implementations that require strict checking.
800		Default: 0
801	
802	IP Variables:
803	
804	ip_local_port_range - 2 INTEGERS
805		Defines the local port range that is used by TCP and UDP to
806		choose the local port. The first number is the first, the
807		second the last local port number.
808		If possible, it is better these numbers have different parity.
809		(one even and one odd values)
810		The default values are 32768 and 60999 respectively.
811	
812	ip_local_reserved_ports - list of comma separated ranges
813		Specify the ports which are reserved for known third-party
814		applications. These ports will not be used by automatic port
815		assignments (e.g. when calling connect() or bind() with port
816		number 0). Explicit port allocation behavior is unchanged.
817	
818		The format used for both input and output is a comma separated
819		list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and
820		10). Writing to the file will clear all previously reserved
821		ports and update the current list with the one given in the
822		input.
823	
824		Note that ip_local_port_range and ip_local_reserved_ports
825		settings are independent and both are considered by the kernel
826		when determining which ports are available for automatic port
827		assignments.
828	
829		You can reserve ports which are not in the current
830		ip_local_port_range, e.g.:
831	
832		$ cat /proc/sys/net/ipv4/ip_local_port_range
833		32000	60999
834		$ cat /proc/sys/net/ipv4/ip_local_reserved_ports
835		8080,9148
836	
837		although this is redundant. However such a setting is useful
838		if later the port range is changed to a value that will
839		include the reserved ports.
840	
841		Default: Empty
842	
843	ip_unprivileged_port_start - INTEGER
844		This is a per-namespace sysctl.  It defines the first
845		unprivileged port in the network namespace.  Privileged ports
846		require root or CAP_NET_BIND_SERVICE in order to bind to them.
847		To disable all privileged ports, set this to 0.  It may not
848		overlap with the ip_local_reserved_ports range.
849	
850		Default: 1024
851	
852	ip_nonlocal_bind - BOOLEAN
853		If set, allows processes to bind() to non-local IP addresses,
854		which can be quite useful - but may break some applications.
855		Default: 0
856	
857	ip_dynaddr - BOOLEAN
858		If set non-zero, enables support for dynamic addresses.
859		If set to a non-zero value larger than 1, a kernel log
860		message will be printed when dynamic address rewriting
861		occurs.
862		Default: 0
863	
864	ip_early_demux - BOOLEAN
865		Optimize input packet processing down to one demux for
866		certain kinds of local sockets.  Currently we only do this
867		for established TCP and connected UDP sockets.
868	
869		It may add an additional cost for pure routing workloads that
870		reduces overall throughput, in such case you should disable it.
871		Default: 1
872	
873	tcp_early_demux - BOOLEAN
874		Enable early demux for established TCP sockets.
875		Default: 1
876	
877	udp_early_demux - BOOLEAN
878		Enable early demux for connected UDP sockets. Disable this if
879		your system could experience more unconnected load.
880		Default: 1
881	
882	icmp_echo_ignore_all - BOOLEAN
883		If set non-zero, then the kernel will ignore all ICMP ECHO
884		requests sent to it.
885		Default: 0
886	
887	icmp_echo_ignore_broadcasts - BOOLEAN
888		If set non-zero, then the kernel will ignore all ICMP ECHO and
889		TIMESTAMP requests sent to it via broadcast/multicast.
890		Default: 1
891	
892	icmp_ratelimit - INTEGER
893		Limit the maximal rates for sending ICMP packets whose type matches
894		icmp_ratemask (see below) to specific targets.
895		0 to disable any limiting,
896		otherwise the minimal space between responses in milliseconds.
897		Note that another sysctl, icmp_msgs_per_sec limits the number
898		of ICMP packets	sent on all targets.
899		Default: 1000
900	
901	icmp_msgs_per_sec - INTEGER
902		Limit maximal number of ICMP packets sent per second from this host.
903		Only messages whose type matches icmp_ratemask (see below) are
904		controlled by this limit.
905		Default: 1000
906	
907	icmp_msgs_burst - INTEGER
908		icmp_msgs_per_sec controls number of ICMP packets sent per second,
909		while icmp_msgs_burst controls the burst size of these packets.
910		Default: 50
911	
912	icmp_ratemask - INTEGER
913		Mask made of ICMP types for which rates are being limited.
914		Significant bits: IHGFEDCBA9876543210
915		Default mask:     0000001100000011000 (6168)
916	
917		Bit definitions (see include/linux/icmp.h):
918			0 Echo Reply
919			3 Destination Unreachable *
920			4 Source Quench *
921			5 Redirect
922			8 Echo Request
923			B Time Exceeded *
924			C Parameter Problem *
925			D Timestamp Request
926			E Timestamp Reply
927			F Info Request
928			G Info Reply
929			H Address Mask Request
930			I Address Mask Reply
931	
932		* These are rate limited by default (see default mask above)
933	
934	icmp_ignore_bogus_error_responses - BOOLEAN
935		Some routers violate RFC1122 by sending bogus responses to broadcast
936		frames.  Such violations are normally logged via a kernel warning.
937		If this is set to TRUE, the kernel will not give such warnings, which
938		will avoid log file clutter.
939		Default: 1
940	
941	icmp_errors_use_inbound_ifaddr - BOOLEAN
942	
943		If zero, icmp error messages are sent with the primary address of
944		the exiting interface.
945	
946		If non-zero, the message will be sent with the primary address of
947		the interface that received the packet that caused the icmp error.
948		This is the behaviour network many administrators will expect from
949		a router. And it can make debugging complicated network layouts
950		much easier.
951	
952		Note that if no primary address exists for the interface selected,
953		then the primary address of the first non-loopback interface that
954		has one will be used regardless of this setting.
955	
956		Default: 0
957	
958	igmp_max_memberships - INTEGER
959		Change the maximum number of multicast groups we can subscribe to.
960		Default: 20
961	
962		Theoretical maximum value is bounded by having to send a membership
963		report in a single datagram (i.e. the report can't span multiple
964		datagrams, or risk confusing the switch and leaving groups you don't
965		intend to).
966	
967		The number of supported groups 'M' is bounded by the number of group
968		report entries you can fit into a single datagram of 65535 bytes.
969	
970		M = 65536-sizeof (ip header)/(sizeof(Group record))
971	
972		Group records are variable length, with a minimum of 12 bytes.
973		So net.ipv4.igmp_max_memberships should not be set higher than:
974	
975		(65536-24) / 12 = 5459
976	
977		The value 5459 assumes no IP header options, so in practice
978		this number may be lower.
979	
980	igmp_max_msf - INTEGER
981		Maximum number of addresses allowed in the source filter list for a
982		multicast group.
983		Default: 10
984	
985	igmp_qrv - INTEGER
986		Controls the IGMP query robustness variable (see RFC2236 8.1).
987		Default: 2 (as specified by RFC2236 8.1)
988		Minimum: 1 (as specified by RFC6636 4.5)
989	
990	force_igmp_version - INTEGER
991		0 - (default) No enforcement of a IGMP version, IGMPv1/v2 fallback
992		    allowed. Will back to IGMPv3 mode again if all IGMPv1/v2 Querier
993		    Present timer expires.
994		1 - Enforce to use IGMP version 1. Will also reply IGMPv1 report if
995		    receive IGMPv2/v3 query.
996		2 - Enforce to use IGMP version 2. Will fallback to IGMPv1 if receive
997		    IGMPv1 query message. Will reply report if receive IGMPv3 query.
998		3 - Enforce to use IGMP version 3. The same react with default 0.
999	
1000		Note: this is not the same with force_mld_version because IGMPv3 RFC3376
1001		Security Considerations does not have clear description that we could
1002		ignore other version messages completely as MLDv2 RFC3810. So make
1003		this value as default 0 is recommended.
1004	
1005	conf/interface/*  changes special settings per interface (where
1006	"interface" is the name of your network interface)
1007	
1008	conf/all/*	  is special, changes the settings for all interfaces
1009	
1010	log_martians - BOOLEAN
1011		Log packets with impossible addresses to kernel log.
1012		log_martians for the interface will be enabled if at least one of
1013		conf/{all,interface}/log_martians is set to TRUE,
1014		it will be disabled otherwise
1015	
1016	accept_redirects - BOOLEAN
1017		Accept ICMP redirect messages.
1018		accept_redirects for the interface will be enabled if:
1019		- both conf/{all,interface}/accept_redirects are TRUE in the case
1020		  forwarding for the interface is enabled
1021		or
1022		- at least one of conf/{all,interface}/accept_redirects is TRUE in the
1023		  case forwarding for the interface is disabled
1024		accept_redirects for the interface will be disabled otherwise
1025		default TRUE (host)
1026			FALSE (router)
1027	
1028	forwarding - BOOLEAN
1029		Enable IP forwarding on this interface.  This controls whether packets
1030		received _on_ this interface can be forwarded.
1031	
1032	mc_forwarding - BOOLEAN
1033		Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
1034		and a multicast routing daemon is required.
1035		conf/all/mc_forwarding must also be set to TRUE to enable multicast
1036		routing	for the interface
1037	
1038	medium_id - INTEGER
1039		Integer value used to differentiate the devices by the medium they
1040		are attached to. Two devices can have different id values when
1041		the broadcast packets are received only on one of them.
1042		The default value 0 means that the device is the only interface
1043		to its medium, value of -1 means that medium is not known.
1044	
1045		Currently, it is used to change the proxy_arp behavior:
1046		the proxy_arp feature is enabled for packets forwarded between
1047		two devices attached to different media.
1048	
1049	proxy_arp - BOOLEAN
1050		Do proxy arp.
1051		proxy_arp for the interface will be enabled if at least one of
1052		conf/{all,interface}/proxy_arp is set to TRUE,
1053		it will be disabled otherwise
1054	
1055	proxy_arp_pvlan - BOOLEAN
1056		Private VLAN proxy arp.
1057		Basically allow proxy arp replies back to the same interface
1058		(from which the ARP request/solicitation was received).
1059	
1060		This is done to support (ethernet) switch features, like RFC
1061		3069, where the individual ports are NOT allowed to
1062		communicate with each other, but they are allowed to talk to
1063		the upstream router.  As described in RFC 3069, it is possible
1064		to allow these hosts to communicate through the upstream
1065		router by proxy_arp'ing. Don't need to be used together with
1066		proxy_arp.
1067	
1068		This technology is known by different names:
1069		  In RFC 3069 it is called VLAN Aggregation.
1070		  Cisco and Allied Telesyn call it Private VLAN.
1071		  Hewlett-Packard call it Source-Port filtering or port-isolation.
1072		  Ericsson call it MAC-Forced Forwarding (RFC Draft).
1073	
1074	shared_media - BOOLEAN
1075		Send(router) or accept(host) RFC1620 shared media redirects.
1076		Overrides secure_redirects.
1077		shared_media for the interface will be enabled if at least one of
1078		conf/{all,interface}/shared_media is set to TRUE,
1079		it will be disabled otherwise
1080		default TRUE
1081	
1082	secure_redirects - BOOLEAN
1083		Accept ICMP redirect messages only to gateways listed in the
1084		interface's current gateway list. Even if disabled, RFC1122 redirect
1085		rules still apply.
1086		Overridden by shared_media.
1087		secure_redirects for the interface will be enabled if at least one of
1088		conf/{all,interface}/secure_redirects is set to TRUE,
1089		it will be disabled otherwise
1090		default TRUE
1091	
1092	send_redirects - BOOLEAN
1093		Send redirects, if router.
1094		send_redirects for the interface will be enabled if at least one of
1095		conf/{all,interface}/send_redirects is set to TRUE,
1096		it will be disabled otherwise
1097		Default: TRUE
1098	
1099	bootp_relay - BOOLEAN
1100		Accept packets with source address 0.b.c.d destined
1101		not to this host as local ones. It is supposed, that
1102		BOOTP relay daemon will catch and forward such packets.
1103		conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
1104		for the interface
1105		default FALSE
1106		Not Implemented Yet.
1107	
1108	accept_source_route - BOOLEAN
1109		Accept packets with SRR option.
1110		conf/all/accept_source_route must also be set to TRUE to accept packets
1111		with SRR option on the interface
1112		default TRUE (router)
1113			FALSE (host)
1114	
1115	accept_local - BOOLEAN
1116		Accept packets with local source addresses. In combination with
1117		suitable routing, this can be used to direct packets between two
1118		local interfaces over the wire and have them accepted properly.
1119		default FALSE
1120	
1121	route_localnet - BOOLEAN
1122		Do not consider loopback addresses as martian source or destination
1123		while routing. This enables the use of 127/8 for local routing purposes.
1124		default FALSE
1125	
1126	rp_filter - INTEGER
1127		0 - No source validation.
1128		1 - Strict mode as defined in RFC3704 Strict Reverse Path
1129		    Each incoming packet is tested against the FIB and if the interface
1130		    is not the best reverse path the packet check will fail.
1131		    By default failed packets are discarded.
1132		2 - Loose mode as defined in RFC3704 Loose Reverse Path
1133		    Each incoming packet's source address is also tested against the FIB
1134		    and if the source address is not reachable via any interface
1135		    the packet check will fail.
1136	
1137		Current recommended practice in RFC3704 is to enable strict mode
1138		to prevent IP spoofing from DDos attacks. If using asymmetric routing
1139		or other complicated routing, then loose mode is recommended.
1140	
1141		The max value from conf/{all,interface}/rp_filter is used
1142		when doing source validation on the {interface}.
1143	
1144		Default value is 0. Note that some distributions enable it
1145		in startup scripts.
1146	
1147	arp_filter - BOOLEAN
1148		1 - Allows you to have multiple network interfaces on the same
1149		subnet, and have the ARPs for each interface be answered
1150		based on whether or not the kernel would route a packet from
1151		the ARP'd IP out that interface (therefore you must use source
1152		based routing for this to work). In other words it allows control
1153		of which cards (usually 1) will respond to an arp request.
1154	
1155		0 - (default) The kernel can respond to arp requests with addresses
1156		from other interfaces. This may seem wrong but it usually makes
1157		sense, because it increases the chance of successful communication.
1158		IP addresses are owned by the complete host on Linux, not by
1159		particular interfaces. Only for more complex setups like load-
1160		balancing, does this behaviour cause problems.
1161	
1162		arp_filter for the interface will be enabled if at least one of
1163		conf/{all,interface}/arp_filter is set to TRUE,
1164		it will be disabled otherwise
1165	
1166	arp_announce - INTEGER
1167		Define different restriction levels for announcing the local
1168		source IP address from IP packets in ARP requests sent on
1169		interface:
1170		0 - (default) Use any local address, configured on any interface
1171		1 - Try to avoid local addresses that are not in the target's
1172		subnet for this interface. This mode is useful when target
1173		hosts reachable via this interface require the source IP
1174		address in ARP requests to be part of their logical network
1175		configured on the receiving interface. When we generate the
1176		request we will check all our subnets that include the
1177		target IP and will preserve the source address if it is from
1178		such subnet. If there is no such subnet we select source
1179		address according to the rules for level 2.
1180		2 - Always use the best local address for this target.
1181		In this mode we ignore the source address in the IP packet
1182		and try to select local address that we prefer for talks with
1183		the target host. Such local address is selected by looking
1184		for primary IP addresses on all our subnets on the outgoing
1185		interface that include the target IP address. If no suitable
1186		local address is found we select the first local address
1187		we have on the outgoing interface or on all other interfaces,
1188		with the hope we will receive reply for our request and
1189		even sometimes no matter the source IP address we announce.
1190	
1191		The max value from conf/{all,interface}/arp_announce is used.
1192	
1193		Increasing the restriction level gives more chance for
1194		receiving answer from the resolved target while decreasing
1195		the level announces more valid sender's information.
1196	
1197	arp_ignore - INTEGER
1198		Define different modes for sending replies in response to
1199		received ARP requests that resolve local target IP addresses:
1200		0 - (default): reply for any local target IP address, configured
1201		on any interface
1202		1 - reply only if the target IP address is local address
1203		configured on the incoming interface
1204		2 - reply only if the target IP address is local address
1205		configured on the incoming interface and both with the
1206		sender's IP address are part from same subnet on this interface
1207		3 - do not reply for local addresses configured with scope host,
1208		only resolutions for global and link addresses are replied
1209		4-7 - reserved
1210		8 - do not reply for all local addresses
1211	
1212		The max value from conf/{all,interface}/arp_ignore is used
1213		when ARP request is received on the {interface}
1214	
1215	arp_notify - BOOLEAN
1216		Define mode for notification of address and device changes.
1217		0 - (default): do nothing
1218		1 - Generate gratuitous arp requests when device is brought up
1219		    or hardware address changes.
1220	
1221	arp_accept - BOOLEAN
1222		Define behavior for gratuitous ARP frames who's IP is not
1223		already present in the ARP table:
1224		0 - don't create new entries in the ARP table
1225		1 - create new entries in the ARP table
1226	
1227		Both replies and requests type gratuitous arp will trigger the
1228		ARP table to be updated, if this setting is on.
1229	
1230		If the ARP table already contains the IP address of the
1231		gratuitous arp frame, the arp table will be updated regardless
1232		if this setting is on or off.
1233	
1234	mcast_solicit - INTEGER
1235		The maximum number of multicast probes in INCOMPLETE state,
1236		when the associated hardware address is unknown.  Defaults
1237		to 3.
1238	
1239	ucast_solicit - INTEGER
1240		The maximum number of unicast probes in PROBE state, when
1241		the hardware address is being reconfirmed.  Defaults to 3.
1242	
1243	app_solicit - INTEGER
1244		The maximum number of probes to send to the user space ARP daemon
1245		via netlink before dropping back to multicast probes (see
1246		mcast_resolicit).  Defaults to 0.
1247	
1248	mcast_resolicit - INTEGER
1249		The maximum number of multicast probes after unicast and
1250		app probes in PROBE state.  Defaults to 0.
1251	
1252	disable_policy - BOOLEAN
1253		Disable IPSEC policy (SPD) for this interface
1254	
1255	disable_xfrm - BOOLEAN
1256		Disable IPSEC encryption on this interface, whatever the policy
1257	
1258	igmpv2_unsolicited_report_interval - INTEGER
1259		The interval in milliseconds in which the next unsolicited
1260		IGMPv1 or IGMPv2 report retransmit will take place.
1261		Default: 10000 (10 seconds)
1262	
1263	igmpv3_unsolicited_report_interval - INTEGER
1264		The interval in milliseconds in which the next unsolicited
1265		IGMPv3 report retransmit will take place.
1266		Default: 1000 (1 seconds)
1267	
1268	promote_secondaries - BOOLEAN
1269		When a primary IP address is removed from this interface
1270		promote a corresponding secondary IP address instead of
1271		removing all the corresponding secondary IP addresses.
1272	
1273	drop_unicast_in_l2_multicast - BOOLEAN
1274		Drop any unicast IP packets that are received in link-layer
1275		multicast (or broadcast) frames.
1276		This behavior (for multicast) is actually a SHOULD in RFC
1277		1122, but is disabled by default for compatibility reasons.
1278		Default: off (0)
1279	
1280	drop_gratuitous_arp - BOOLEAN
1281		Drop all gratuitous ARP frames, for example if there's a known
1282		good ARP proxy on the network and such frames need not be used
1283		(or in the case of 802.11, must not be used to prevent attacks.)
1284		Default: off (0)
1285	
1286	
1287	tag - INTEGER
1288		Allows you to write a number, which can be used as required.
1289		Default value is 0.
1290	
1291	xfrm4_gc_thresh - INTEGER
1292		The threshold at which we will start garbage collecting for IPv4
1293		destination cache entries.  At twice this value the system will
1294		refuse new allocations. The value must be set below the flowcache
1295		limit (4096 * number of online cpus) to take effect.
1296	
1297	igmp_link_local_mcast_reports - BOOLEAN
1298		Enable IGMP reports for link local multicast groups in the
1299		224.0.0.X range.
1300		Default TRUE
1301	
1302	Alexey Kuznetsov.
1303	kuznet@ms2.inr.ac.ru
1304	
1305	Updated by:
1306	Andi Kleen
1307	ak@muc.de
1308	Nicolas Delon
1309	delon.nicolas@wanadoo.fr
1310	
1311	
1312	
1313	
1314	/proc/sys/net/ipv6/* Variables:
1315	
1316	IPv6 has no global variables such as tcp_*.  tcp_* settings under ipv4/ also
1317	apply to IPv6 [XXX?].
1318	
1319	bindv6only - BOOLEAN
1320		Default value for IPV6_V6ONLY socket option,
1321		which restricts use of the IPv6 socket to IPv6 communication
1322		only.
1323			TRUE: disable IPv4-mapped address feature
1324			FALSE: enable IPv4-mapped address feature
1325	
1326		Default: FALSE (as specified in RFC3493)
1327	
1328	flowlabel_consistency - BOOLEAN
1329		Protect the consistency (and unicity) of flow label.
1330		You have to disable it to use IPV6_FL_F_REFLECT flag on the
1331		flow label manager.
1332		TRUE: enabled
1333		FALSE: disabled
1334		Default: TRUE
1335	
1336	auto_flowlabels - INTEGER
1337		Automatically generate flow labels based on a flow hash of the
1338		packet. This allows intermediate devices, such as routers, to
1339		identify packet flows for mechanisms like Equal Cost Multipath
1340		Routing (see RFC 6438).
1341		0: automatic flow labels are completely disabled
1342		1: automatic flow labels are enabled by default, they can be
1343		   disabled on a per socket basis using the IPV6_AUTOFLOWLABEL
1344		   socket option
1345		2: automatic flow labels are allowed, they may be enabled on a
1346		   per socket basis using the IPV6_AUTOFLOWLABEL socket option
1347		3: automatic flow labels are enabled and enforced, they cannot
1348		   be disabled by the socket option
1349		Default: 1
1350	
1351	flowlabel_state_ranges - BOOLEAN
1352		Split the flow label number space into two ranges. 0-0x7FFFF is
1353		reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF
1354		is reserved for stateless flow labels as described in RFC6437.
1355		TRUE: enabled
1356		FALSE: disabled
1357		Default: true
1358	
1359	anycast_src_echo_reply - BOOLEAN
1360		Controls the use of anycast addresses as source addresses for ICMPv6
1361		echo reply
1362		TRUE:  enabled
1363		FALSE: disabled
1364		Default: FALSE
1365	
1366	idgen_delay - INTEGER
1367		Controls the delay in seconds after which time to retry
1368		privacy stable address generation if a DAD conflict is
1369		detected.
1370		Default: 1 (as specified in RFC7217)
1371	
1372	idgen_retries - INTEGER
1373		Controls the number of retries to generate a stable privacy
1374		address if a DAD conflict is detected.
1375		Default: 3 (as specified in RFC7217)
1376	
1377	mld_qrv - INTEGER
1378		Controls the MLD query robustness variable (see RFC3810 9.1).
1379		Default: 2 (as specified by RFC3810 9.1)
1380		Minimum: 1 (as specified by RFC6636 4.5)
1381	
1382	IPv6 Fragmentation:
1383	
1384	ip6frag_high_thresh - INTEGER
1385		Maximum memory used to reassemble IPv6 fragments. When
1386		ip6frag_high_thresh bytes of memory is allocated for this purpose,
1387		the fragment handler will toss packets until ip6frag_low_thresh
1388		is reached.
1389	
1390	ip6frag_low_thresh - INTEGER
1391		See ip6frag_high_thresh
1392	
1393	ip6frag_time - INTEGER
1394		Time in seconds to keep an IPv6 fragment in memory.
1395	
1396	conf/default/*:
1397		Change the interface-specific default settings.
1398	
1399	
1400	conf/all/*:
1401		Change all the interface-specific settings.
1402	
1403		[XXX:  Other special features than forwarding?]
1404	
1405	conf/all/forwarding - BOOLEAN
1406		Enable global IPv6 forwarding between all interfaces.
1407	
1408		IPv4 and IPv6 work differently here; e.g. netfilter must be used
1409		to control which interfaces may forward packets and which not.
1410	
1411		This also sets all interfaces' Host/Router setting
1412		'forwarding' to the specified value.  See below for details.
1413	
1414		This referred to as global forwarding.
1415	
1416	proxy_ndp - BOOLEAN
1417		Do proxy ndp.
1418	
1419	fwmark_reflect - BOOLEAN
1420		Controls the fwmark of kernel-generated IPv6 reply packets that are not
1421		associated with a socket for example, TCP RSTs or ICMPv6 echo replies).
1422		If unset, these packets have a fwmark of zero. If set, they have the
1423		fwmark of the packet they are replying to.
1424		Default: 0
1425	
1426	conf/interface/*:
1427		Change special settings per interface.
1428	
1429		The functional behaviour for certain settings is different
1430		depending on whether local forwarding is enabled or not.
1431	
1432	accept_ra - INTEGER
1433		Accept Router Advertisements; autoconfigure using them.
1434	
1435		It also determines whether or not to transmit Router
1436		Solicitations. If and only if the functional setting is to
1437		accept Router Advertisements, Router Solicitations will be
1438		transmitted.
1439	
1440		Possible values are:
1441			0 Do not accept Router Advertisements.
1442			1 Accept Router Advertisements if forwarding is disabled.
1443			2 Overrule forwarding behaviour. Accept Router Advertisements
1444			  even if forwarding is enabled.
1445	
1446		Functional default: enabled if local forwarding is disabled.
1447				    disabled if local forwarding is enabled.
1448	
1449	accept_ra_defrtr - BOOLEAN
1450		Learn default router in Router Advertisement.
1451	
1452		Functional default: enabled if accept_ra is enabled.
1453				    disabled if accept_ra is disabled.
1454	
1455	accept_ra_from_local - BOOLEAN
1456		Accept RA with source-address that is found on local machine
1457	        if the RA is otherwise proper and able to be accepted.
1458	        Default is to NOT accept these as it may be an un-intended
1459	        network loop.
1460	
1461		Functional default:
1462	           enabled if accept_ra_from_local is enabled
1463	               on a specific interface.
1464		   disabled if accept_ra_from_local is disabled
1465	               on a specific interface.
1466	
1467	accept_ra_min_hop_limit - INTEGER
1468		Minimum hop limit Information in Router Advertisement.
1469	
1470		Hop limit Information in Router Advertisement less than this
1471		variable shall be ignored.
1472	
1473		Default: 1
1474	
1475	accept_ra_pinfo - BOOLEAN
1476		Learn Prefix Information in Router Advertisement.
1477	
1478		Functional default: enabled if accept_ra is enabled.
1479				    disabled if accept_ra is disabled.
1480	
1481	accept_ra_rt_info_min_plen - INTEGER
1482		Minimum prefix length of Route Information in RA.
1483	
1484		Route Information w/ prefix smaller than this variable shall
1485		be ignored.
1486	
1487		Functional default: 0 if accept_ra_rtr_pref is enabled.
1488				    -1 if accept_ra_rtr_pref is disabled.
1489	
1490	accept_ra_rt_info_max_plen - INTEGER
1491		Maximum prefix length of Route Information in RA.
1492	
1493		Route Information w/ prefix larger than this variable shall
1494		be ignored.
1495	
1496		Functional default: 0 if accept_ra_rtr_pref is enabled.
1497				    -1 if accept_ra_rtr_pref is disabled.
1498	
1499	accept_ra_rtr_pref - BOOLEAN
1500		Accept Router Preference in RA.
1501	
1502		Functional default: enabled if accept_ra is enabled.
1503				    disabled if accept_ra is disabled.
1504	
1505	accept_ra_mtu - BOOLEAN
1506		Apply the MTU value specified in RA option 5 (RFC4861). If
1507		disabled, the MTU specified in the RA will be ignored.
1508	
1509		Functional default: enabled if accept_ra is enabled.
1510				    disabled if accept_ra is disabled.
1511	
1512	accept_redirects - BOOLEAN
1513		Accept Redirects.
1514	
1515		Functional default: enabled if local forwarding is disabled.
1516				    disabled if local forwarding is enabled.
1517	
1518	accept_source_route - INTEGER
1519		Accept source routing (routing extension header).
1520	
1521		>= 0: Accept only routing header type 2.
1522		< 0: Do not accept routing header.
1523	
1524		Default: 0
1525	
1526	autoconf - BOOLEAN
1527		Autoconfigure addresses using Prefix Information in Router
1528		Advertisements.
1529	
1530		Functional default: enabled if accept_ra_pinfo is enabled.
1531				    disabled if accept_ra_pinfo is disabled.
1532	
1533	dad_transmits - INTEGER
1534		The amount of Duplicate Address Detection probes to send.
1535		Default: 1
1536	
1537	forwarding - INTEGER
1538		Configure interface-specific Host/Router behaviour.
1539	
1540		Note: It is recommended to have the same setting on all
1541		interfaces; mixed router/host scenarios are rather uncommon.
1542	
1543		Possible values are:
1544			0 Forwarding disabled
1545			1 Forwarding enabled
1546	
1547		FALSE (0):
1548	
1549		By default, Host behaviour is assumed.  This means:
1550	
1551		1. IsRouter flag is not set in Neighbour Advertisements.
1552		2. If accept_ra is TRUE (default), transmit Router
1553		   Solicitations.
1554		3. If accept_ra is TRUE (default), accept Router
1555		   Advertisements (and do autoconfiguration).
1556		4. If accept_redirects is TRUE (default), accept Redirects.
1557	
1558		TRUE (1):
1559	
1560		If local forwarding is enabled, Router behaviour is assumed.
1561		This means exactly the reverse from the above:
1562	
1563		1. IsRouter flag is set in Neighbour Advertisements.
1564		2. Router Solicitations are not sent unless accept_ra is 2.
1565		3. Router Advertisements are ignored unless accept_ra is 2.
1566		4. Redirects are ignored.
1567	
1568		Default: 0 (disabled) if global forwarding is disabled (default),
1569			 otherwise 1 (enabled).
1570	
1571	hop_limit - INTEGER
1572		Default Hop Limit to set.
1573		Default: 64
1574	
1575	mtu - INTEGER
1576		Default Maximum Transfer Unit
1577		Default: 1280 (IPv6 required minimum)
1578	
1579	ip_nonlocal_bind - BOOLEAN
1580		If set, allows processes to bind() to non-local IPv6 addresses,
1581		which can be quite useful - but may break some applications.
1582		Default: 0
1583	
1584	router_probe_interval - INTEGER
1585		Minimum interval (in seconds) between Router Probing described
1586		in RFC4191.
1587	
1588		Default: 60
1589	
1590	router_solicitation_delay - INTEGER
1591		Number of seconds to wait after interface is brought up
1592		before sending Router Solicitations.
1593		Default: 1
1594	
1595	router_solicitation_interval - INTEGER
1596		Number of seconds to wait between Router Solicitations.
1597		Default: 4
1598	
1599	router_solicitations - INTEGER
1600		Number of Router Solicitations to send until assuming no
1601		routers are present.
1602		Default: 3
1603	
1604	use_oif_addrs_only - BOOLEAN
1605		When enabled, the candidate source addresses for destinations
1606		routed via this interface are restricted to the set of addresses
1607		configured on this interface (vis. RFC 6724, section 4).
1608	
1609		Default: false
1610	
1611	use_tempaddr - INTEGER
1612		Preference for Privacy Extensions (RFC3041).
1613		  <= 0 : disable Privacy Extensions
1614		  == 1 : enable Privacy Extensions, but prefer public
1615		         addresses over temporary addresses.
1616		  >  1 : enable Privacy Extensions and prefer temporary
1617		         addresses over public addresses.
1618		Default:  0 (for most devices)
1619			 -1 (for point-to-point devices and loopback devices)
1620	
1621	temp_valid_lft - INTEGER
1622		valid lifetime (in seconds) for temporary addresses.
1623		Default: 604800 (7 days)
1624	
1625	temp_prefered_lft - INTEGER
1626		Preferred lifetime (in seconds) for temporary addresses.
1627		Default: 86400 (1 day)
1628	
1629	keep_addr_on_down - INTEGER
1630		Keep all IPv6 addresses on an interface down event. If set static
1631		global addresses with no expiration time are not flushed.
1632		  >0 : enabled
1633		   0 : system default
1634		  <0 : disabled
1635	
1636		Default: 0 (addresses are removed)
1637	
1638	max_desync_factor - INTEGER
1639		Maximum value for DESYNC_FACTOR, which is a random value
1640		that ensures that clients don't synchronize with each
1641		other and generate new addresses at exactly the same time.
1642		value is in seconds.
1643		Default: 600
1644	
1645	regen_max_retry - INTEGER
1646		Number of attempts before give up attempting to generate
1647		valid temporary addresses.
1648		Default: 5
1649	
1650	max_addresses - INTEGER
1651		Maximum number of autoconfigured addresses per interface.  Setting
1652		to zero disables the limitation.  It is not recommended to set this
1653		value too large (or to zero) because it would be an easy way to
1654		crash the kernel by allowing too many addresses to be created.
1655		Default: 16
1656	
1657	disable_ipv6 - BOOLEAN
1658		Disable IPv6 operation.  If accept_dad is set to 2, this value
1659		will be dynamically set to TRUE if DAD fails for the link-local
1660		address.
1661		Default: FALSE (enable IPv6 operation)
1662	
1663		When this value is changed from 1 to 0 (IPv6 is being enabled),
1664		it will dynamically create a link-local address on the given
1665		interface and start Duplicate Address Detection, if necessary.
1666	
1667		When this value is changed from 0 to 1 (IPv6 is being disabled),
1668		it will dynamically delete all address on the given interface.
1669	
1670	accept_dad - INTEGER
1671		Whether to accept DAD (Duplicate Address Detection).
1672		0: Disable DAD
1673		1: Enable DAD (default)
1674		2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
1675		   link-local address has been found.
1676	
1677	force_tllao - BOOLEAN
1678		Enable sending the target link-layer address option even when
1679		responding to a unicast neighbor solicitation.
1680		Default: FALSE
1681	
1682		Quoting from RFC 2461, section 4.4, Target link-layer address:
1683	
1684		"The option MUST be included for multicast solicitations in order to
1685		avoid infinite Neighbor Solicitation "recursion" when the peer node
1686		does not have a cache entry to return a Neighbor Advertisements
1687		message.  When responding to unicast solicitations, the option can be
1688		omitted since the sender of the solicitation has the correct link-
1689		layer address; otherwise it would not have be able to send the unicast
1690		solicitation in the first place. However, including the link-layer
1691		address in this case adds little overhead and eliminates a potential
1692		race condition where the sender deletes the cached link-layer address
1693		prior to receiving a response to a previous solicitation."
1694	
1695	ndisc_notify - BOOLEAN
1696		Define mode for notification of address and device changes.
1697		0 - (default): do nothing
1698		1 - Generate unsolicited neighbour advertisements when device is brought
1699		    up or hardware address changes.
1700	
1701	mldv1_unsolicited_report_interval - INTEGER
1702		The interval in milliseconds in which the next unsolicited
1703		MLDv1 report retransmit will take place.
1704		Default: 10000 (10 seconds)
1705	
1706	mldv2_unsolicited_report_interval - INTEGER
1707		The interval in milliseconds in which the next unsolicited
1708		MLDv2 report retransmit will take place.
1709		Default: 1000 (1 second)
1710	
1711	force_mld_version - INTEGER
1712		0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed
1713		1 - Enforce to use MLD version 1
1714		2 - Enforce to use MLD version 2
1715	
1716	suppress_frag_ndisc - INTEGER
1717		Control RFC 6980 (Security Implications of IPv6 Fragmentation
1718		with IPv6 Neighbor Discovery) behavior:
1719		1 - (default) discard fragmented neighbor discovery packets
1720		0 - allow fragmented neighbor discovery packets
1721	
1722	optimistic_dad - BOOLEAN
1723		Whether to perform Optimistic Duplicate Address Detection (RFC 4429).
1724			0: disabled (default)
1725			1: enabled
1726	
1727	use_optimistic - BOOLEAN
1728		If enabled, do not classify optimistic addresses as deprecated during
1729		source address selection.  Preferred addresses will still be chosen
1730		before optimistic addresses, subject to other ranking in the source
1731		address selection algorithm.
1732			0: disabled (default)
1733			1: enabled
1734	
1735	stable_secret - IPv6 address
1736		This IPv6 address will be used as a secret to generate IPv6
1737		addresses for link-local addresses and autoconfigured
1738		ones. All addresses generated after setting this secret will
1739		be stable privacy ones by default. This can be changed via the
1740		addrgenmode ip-link. conf/default/stable_secret is used as the
1741		secret for the namespace, the interface specific ones can
1742		overwrite that. Writes to conf/all/stable_secret are refused.
1743	
1744		It is recommended to generate this secret during installation
1745		of a system and keep it stable after that.
1746	
1747		By default the stable secret is unset.
1748	
1749	drop_unicast_in_l2_multicast - BOOLEAN
1750		Drop any unicast IPv6 packets that are received in link-layer
1751		multicast (or broadcast) frames.
1752	
1753		By default this is turned off.
1754	
1755	drop_unsolicited_na - BOOLEAN
1756		Drop all unsolicited neighbor advertisements, for example if there's
1757		a known good NA proxy on the network and such frames need not be used
1758		(or in the case of 802.11, must not be used to prevent attacks.)
1759	
1760		By default this is turned off.
1761	
1762	enhanced_dad - BOOLEAN
1763		Include a nonce option in the IPv6 neighbor solicitation messages used for
1764		duplicate address detection per RFC7527. A received DAD NS will only signal
1765		a duplicate address if the nonce is different. This avoids any false
1766		detection of duplicates due to loopback of the NS messages that we send.
1767		The nonce option will be sent on an interface unless both of
1768		conf/{all,interface}/enhanced_dad are set to FALSE.
1769		Default: TRUE
1770	
1771	icmp/*:
1772	ratelimit - INTEGER
1773		Limit the maximal rates for sending ICMPv6 packets.
1774		0 to disable any limiting,
1775		otherwise the minimal space between responses in milliseconds.
1776		Default: 1000
1777	
1778	xfrm6_gc_thresh - INTEGER
1779		The threshold at which we will start garbage collecting for IPv6
1780		destination cache entries.  At twice this value the system will
1781		refuse new allocations. The value must be set below the flowcache
1782		limit (4096 * number of online cpus) to take effect.
1783	
1784	
1785	IPv6 Update by:
1786	Pekka Savola <pekkas@netcore.fi>
1787	YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
1788	
1789	
1790	/proc/sys/net/bridge/* Variables:
1791	
1792	bridge-nf-call-arptables - BOOLEAN
1793		1 : pass bridged ARP traffic to arptables' FORWARD chain.
1794		0 : disable this.
1795		Default: 1
1796	
1797	bridge-nf-call-iptables - BOOLEAN
1798		1 : pass bridged IPv4 traffic to iptables' chains.
1799		0 : disable this.
1800		Default: 1
1801	
1802	bridge-nf-call-ip6tables - BOOLEAN
1803		1 : pass bridged IPv6 traffic to ip6tables' chains.
1804		0 : disable this.
1805		Default: 1
1806	
1807	bridge-nf-filter-vlan-tagged - BOOLEAN
1808		1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
1809		0 : disable this.
1810		Default: 0
1811	
1812	bridge-nf-filter-pppoe-tagged - BOOLEAN
1813		1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
1814		0 : disable this.
1815		Default: 0
1816	
1817	bridge-nf-pass-vlan-input-dev - BOOLEAN
1818		1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan
1819		interface on the bridge and set the netfilter input device to the vlan.
1820		This allows use of e.g. "iptables -i br0.1" and makes the REDIRECT
1821		target work with vlan-on-top-of-bridge interfaces.  When no matching
1822		vlan interface is found, or this switch is off, the input device is
1823		set to the bridge interface.
1824		0: disable bridge netfilter vlan interface lookup.
1825		Default: 0
1826	
1827	proc/sys/net/sctp/* Variables:
1828	
1829	addip_enable - BOOLEAN
1830		Enable or disable extension of  Dynamic Address Reconfiguration
1831		(ADD-IP) functionality specified in RFC5061.  This extension provides
1832		the ability to dynamically add and remove new addresses for the SCTP
1833		associations.
1834	
1835		1: Enable extension.
1836	
1837		0: Disable extension.
1838	
1839		Default: 0
1840	
1841	pf_enable - INTEGER
1842		Enable or disable pf (pf is short for potentially failed) state. A value
1843		of pf_retrans > path_max_retrans also disables pf state. That is, one of
1844		both pf_enable and pf_retrans > path_max_retrans can disable pf state.
1845		Since pf_retrans and path_max_retrans can be changed by userspace
1846		application, sometimes user expects to disable pf state by the value of
1847		pf_retrans > path_max_retrans, but occasionally the value of pf_retrans
1848		or path_max_retrans is changed by the user application, this pf state is
1849		enabled. As such, it is necessary to add this to dynamically enable
1850		and disable pf state. See:
1851		https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover for
1852		details.
1853	
1854		1: Enable pf.
1855	
1856		0: Disable pf.
1857	
1858		Default: 1
1859	
1860	addip_noauth_enable - BOOLEAN
1861		Dynamic Address Reconfiguration (ADD-IP) requires the use of
1862		authentication to protect the operations of adding or removing new
1863		addresses.  This requirement is mandated so that unauthorized hosts
1864		would not be able to hijack associations.  However, older
1865		implementations may not have implemented this requirement while
1866		allowing the ADD-IP extension.  For reasons of interoperability,
1867		we provide this variable to control the enforcement of the
1868		authentication requirement.
1869	
1870		1: Allow ADD-IP extension to be used without authentication.  This
1871		   should only be set in a closed environment for interoperability
1872		   with older implementations.
1873	
1874		0: Enforce the authentication requirement
1875	
1876		Default: 0
1877	
1878	auth_enable - BOOLEAN
1879		Enable or disable Authenticated Chunks extension.  This extension
1880		provides the ability to send and receive authenticated chunks and is
1881		required for secure operation of Dynamic Address Reconfiguration
1882		(ADD-IP) extension.
1883	
1884		1: Enable this extension.
1885		0: Disable this extension.
1886	
1887		Default: 0
1888	
1889	prsctp_enable - BOOLEAN
1890		Enable or disable the Partial Reliability extension (RFC3758) which
1891		is used to notify peers that a given DATA should no longer be expected.
1892	
1893		1: Enable extension
1894		0: Disable
1895	
1896		Default: 1
1897	
1898	max_burst - INTEGER
1899		The limit of the number of new packets that can be initially sent.  It
1900		controls how bursty the generated traffic can be.
1901	
1902		Default: 4
1903	
1904	association_max_retrans - INTEGER
1905		Set the maximum number for retransmissions that an association can
1906		attempt deciding that the remote end is unreachable.  If this value
1907		is exceeded, the association is terminated.
1908	
1909		Default: 10
1910	
1911	max_init_retransmits - INTEGER
1912		The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
1913		that an association will attempt before declaring the destination
1914		unreachable and terminating.
1915	
1916		Default: 8
1917	
1918	path_max_retrans - INTEGER
1919		The maximum number of retransmissions that will be attempted on a given
1920		path.  Once this threshold is exceeded, the path is considered
1921		unreachable, and new traffic will use a different path when the
1922		association is multihomed.
1923	
1924		Default: 5
1925	
1926	pf_retrans - INTEGER
1927		The number of retransmissions that will be attempted on a given path
1928		before traffic is redirected to an alternate transport (should one
1929		exist).  Note this is distinct from path_max_retrans, as a path that
1930		passes the pf_retrans threshold can still be used.  Its only
1931		deprioritized when a transmission path is selected by the stack.  This
1932		setting is primarily used to enable fast failover mechanisms without
1933		having to reduce path_max_retrans to a very low value.  See:
1934		http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt
1935		for details.  Note also that a value of pf_retrans > path_max_retrans
1936		disables this feature. Since both pf_retrans and path_max_retrans can
1937		be changed by userspace application, a variable pf_enable is used to
1938		disable pf state.
1939	
1940		Default: 0
1941	
1942	rto_initial - INTEGER
1943		The initial round trip timeout value in milliseconds that will be used
1944		in calculating round trip times.  This is the initial time interval
1945		for retransmissions.
1946	
1947		Default: 3000
1948	
1949	rto_max - INTEGER
1950		The maximum value (in milliseconds) of the round trip timeout.  This
1951		is the largest time interval that can elapse between retransmissions.
1952	
1953		Default: 60000
1954	
1955	rto_min - INTEGER
1956		The minimum value (in milliseconds) of the round trip timeout.  This
1957		is the smallest time interval the can elapse between retransmissions.
1958	
1959		Default: 1000
1960	
1961	hb_interval - INTEGER
1962		The interval (in milliseconds) between HEARTBEAT chunks.  These chunks
1963		are sent at the specified interval on idle paths to probe the state of
1964		a given path between 2 associations.
1965	
1966		Default: 30000
1967	
1968	sack_timeout - INTEGER
1969		The amount of time (in milliseconds) that the implementation will wait
1970		to send a SACK.
1971	
1972		Default: 200
1973	
1974	valid_cookie_life - INTEGER
1975		The default lifetime of the SCTP cookie (in milliseconds).  The cookie
1976		is used during association establishment.
1977	
1978		Default: 60000
1979	
1980	cookie_preserve_enable - BOOLEAN
1981		Enable or disable the ability to extend the lifetime of the SCTP cookie
1982		that is used during the establishment phase of SCTP association
1983	
1984		1: Enable cookie lifetime extension.
1985		0: Disable
1986	
1987		Default: 1
1988	
1989	cookie_hmac_alg - STRING
1990		Select the hmac algorithm used when generating the cookie value sent by
1991		a listening sctp socket to a connecting client in the INIT-ACK chunk.
1992		Valid values are:
1993		* md5
1994		* sha1
1995		* none
1996		Ability to assign md5 or sha1 as the selected alg is predicated on the
1997		configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and
1998		CONFIG_CRYPTO_SHA1).
1999	
2000		Default: Dependent on configuration.  MD5 if available, else SHA1 if
2001		available, else none.
2002	
2003	rcvbuf_policy - INTEGER
2004		Determines if the receive buffer is attributed to the socket or to
2005		association.   SCTP supports the capability to create multiple
2006		associations on a single socket.  When using this capability, it is
2007		possible that a single stalled association that's buffering a lot
2008		of data may block other associations from delivering their data by
2009		consuming all of the receive buffer space.  To work around this,
2010		the rcvbuf_policy could be set to attribute the receiver buffer space
2011		to each association instead of the socket.  This prevents the described
2012		blocking.
2013	
2014		1: rcvbuf space is per association
2015		0: rcvbuf space is per socket
2016	
2017		Default: 0
2018	
2019	sndbuf_policy - INTEGER
2020		Similar to rcvbuf_policy above, this applies to send buffer space.
2021	
2022		1: Send buffer is tracked per association
2023		0: Send buffer is tracked per socket.
2024	
2025		Default: 0
2026	
2027	sctp_mem - vector of 3 INTEGERs: min, pressure, max
2028		Number of pages allowed for queueing by all SCTP sockets.
2029	
2030		min: Below this number of pages SCTP is not bothered about its
2031		memory appetite. When amount of memory allocated by SCTP exceeds
2032		this number, SCTP starts to moderate memory usage.
2033	
2034		pressure: This value was introduced to follow format of tcp_mem.
2035	
2036		max: Number of pages allowed for queueing by all SCTP sockets.
2037	
2038		Default is calculated at boot time from amount of available memory.
2039	
2040	sctp_rmem - vector of 3 INTEGERs: min, default, max
2041		Only the first value ("min") is used, "default" and "max" are
2042		ignored.
2043	
2044		min: Minimal size of receive buffer used by SCTP socket.
2045		It is guaranteed to each SCTP socket (but not association) even
2046		under moderate memory pressure.
2047	
2048		Default: 1 page
2049	
2050	sctp_wmem  - vector of 3 INTEGERs: min, default, max
2051		Currently this tunable has no effect.
2052	
2053	addr_scope_policy - INTEGER
2054		Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00
2055	
2056		0   - Disable IPv4 address scoping
2057		1   - Enable IPv4 address scoping
2058		2   - Follow draft but allow IPv4 private addresses
2059		3   - Follow draft but allow IPv4 link local addresses
2060	
2061		Default: 1
2062	
2063	
2064	/proc/sys/net/core/*
2065		Please see: Documentation/sysctl/net.txt for descriptions of these entries.
2066	
2067	
2068	/proc/sys/net/unix/*
2069	max_dgram_qlen - INTEGER
2070		The maximum length of dgram socket receive queue
2071	
2072		Default: 10
2073	
2074	
2075	UNDOCUMENTED:
2076	
2077	/proc/sys/net/irda/*
2078		fast_poll_increase FIXME
2079		warn_noreply_time FIXME
2080		discovery_slots FIXME
2081		slot_timeout FIXME
2082		max_baud_rate FIXME
2083		discovery_timeout FIXME
2084		lap_keepalive_time FIXME
2085		max_noreply_time FIXME
2086		max_tx_data_size FIXME
2087		max_tx_window FIXME
2088		min_tx_turn_time FIXME
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