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Based on kernel version 4.7.2. Page generated on 2016-08-22 22:47 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	route/max_size - INTEGER
77		Maximum number of routes allowed in the kernel.  Increase
78		this when using large numbers of interfaces and/or routes.
79		From linux kernel 3.6 onwards, this is deprecated for ipv4
80		as route cache is no longer used.
81	
82	neigh/default/gc_thresh1 - INTEGER
83		Minimum number of entries to keep.  Garbage collector will not
84		purge entries if there are fewer than this number.
85		Default: 128
86	
87	neigh/default/gc_thresh2 - INTEGER
88		Threshold when garbage collector becomes more aggressive about
89		purging entries. Entries older than 5 seconds will be cleared
90		when over this number.
91		Default: 512
92	
93	neigh/default/gc_thresh3 - INTEGER
94		Maximum number of neighbor entries allowed.  Increase this
95		when using large numbers of interfaces and when communicating
96		with large numbers of directly-connected peers.
97		Default: 1024
98	
99	neigh/default/unres_qlen_bytes - INTEGER
100		The maximum number of bytes which may be used by packets
101		queued for each	unresolved address by other network layers.
102		(added in linux 3.3)
103		Setting negative value is meaningless and will return error.
104		Default: 65536 Bytes(64KB)
105	
106	neigh/default/unres_qlen - INTEGER
107		The maximum number of packets which may be queued for each
108		unresolved address by other network layers.
109		(deprecated in linux 3.3) : use unres_qlen_bytes instead.
110		Prior to linux 3.3, the default value is 3 which may cause
111		unexpected packet loss. The current default value is calculated
112		according to default value of unres_qlen_bytes and true size of
113		packet.
114		Default: 31
115	
116	mtu_expires - INTEGER
117		Time, in seconds, that cached PMTU information is kept.
118	
119	min_adv_mss - INTEGER
120		The advertised MSS depends on the first hop route MTU, but will
121		never be lower than this setting.
122	
123	IP Fragmentation:
124	
125	ipfrag_high_thresh - INTEGER
126		Maximum memory used to reassemble IP fragments. When
127		ipfrag_high_thresh bytes of memory is allocated for this purpose,
128		the fragment handler will toss packets until ipfrag_low_thresh
129		is reached. This also serves as a maximum limit to namespaces
130		different from the initial one.
131	
132	ipfrag_low_thresh - INTEGER
133		Maximum memory used to reassemble IP fragments before the kernel
134		begins to remove incomplete fragment queues to free up resources.
135		The kernel still accepts new fragments for defragmentation.
136	
137	ipfrag_time - INTEGER
138		Time in seconds to keep an IP fragment in memory.
139	
140	ipfrag_max_dist - INTEGER
141		ipfrag_max_dist is a non-negative integer value which defines the
142		maximum "disorder" which is allowed among fragments which share a
143		common IP source address. Note that reordering of packets is
144		not unusual, but if a large number of fragments arrive from a source
145		IP address while a particular fragment queue remains incomplete, it
146		probably indicates that one or more fragments belonging to that queue
147		have been lost. When ipfrag_max_dist is positive, an additional check
148		is done on fragments before they are added to a reassembly queue - if
149		ipfrag_max_dist (or more) fragments have arrived from a particular IP
150		address between additions to any IP fragment queue using that source
151		address, it's presumed that one or more fragments in the queue are
152		lost. The existing fragment queue will be dropped, and a new one
153		started. An ipfrag_max_dist value of zero disables this check.
154	
155		Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
156		result in unnecessarily dropping fragment queues when normal
157		reordering of packets occurs, which could lead to poor application
158		performance. Using a very large value, e.g. 50000, increases the
159		likelihood of incorrectly reassembling IP fragments that originate
160		from different IP datagrams, which could result in data corruption.
161		Default: 64
162	
163	INET peer storage:
164	
165	inet_peer_threshold - INTEGER
166		The approximate size of the storage.  Starting from this threshold
167		entries will be thrown aggressively.  This threshold also determines
168		entries' time-to-live and time intervals between garbage collection
169		passes.  More entries, less time-to-live, less GC interval.
170	
171	inet_peer_minttl - INTEGER
172		Minimum time-to-live of entries.  Should be enough to cover fragment
173		time-to-live on the reassembling side.  This minimum time-to-live  is
174		guaranteed if the pool size is less than inet_peer_threshold.
175		Measured in seconds.
176	
177	inet_peer_maxttl - INTEGER
178		Maximum time-to-live of entries.  Unused entries will expire after
179		this period of time if there is no memory pressure on the pool (i.e.
180		when the number of entries in the pool is very small).
181		Measured in seconds.
182	
183	TCP variables:
184	
185	somaxconn - INTEGER
186		Limit of socket listen() backlog, known in userspace as SOMAXCONN.
187		Defaults to 128.  See also tcp_max_syn_backlog for additional tuning
188		for TCP sockets.
189	
190	tcp_abort_on_overflow - BOOLEAN
191		If listening service is too slow to accept new connections,
192		reset them. Default state is FALSE. It means that if overflow
193		occurred due to a burst, connection will recover. Enable this
194		option _only_ if you are really sure that listening daemon
195		cannot be tuned to accept connections faster. Enabling this
196		option can harm clients of your server.
197	
198	tcp_adv_win_scale - INTEGER
199		Count buffering overhead as bytes/2^tcp_adv_win_scale
200		(if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
201		if it is <= 0.
202		Possible values are [-31, 31], inclusive.
203		Default: 1
204	
205	tcp_allowed_congestion_control - STRING
206		Show/set the congestion control choices available to non-privileged
207		processes. The list is a subset of those listed in
208		tcp_available_congestion_control.
209		Default is "reno" and the default setting (tcp_congestion_control).
210	
211	tcp_app_win - INTEGER
212		Reserve max(window/2^tcp_app_win, mss) of window for application
213		buffer. Value 0 is special, it means that nothing is reserved.
214		Default: 31
215	
216	tcp_autocorking - BOOLEAN
217		Enable TCP auto corking :
218		When applications do consecutive small write()/sendmsg() system calls,
219		we try to coalesce these small writes as much as possible, to lower
220		total amount of sent packets. This is done if at least one prior
221		packet for the flow is waiting in Qdisc queues or device transmit
222		queue. Applications can still use TCP_CORK for optimal behavior
223		when they know how/when to uncork their sockets.
224		Default : 1
225	
226	tcp_available_congestion_control - STRING
227		Shows the available congestion control choices that are registered.
228		More congestion control algorithms may be available as modules,
229		but not loaded.
230	
231	tcp_base_mss - INTEGER
232		The initial value of search_low to be used by the packetization layer
233		Path MTU discovery (MTU probing).  If MTU probing is enabled,
234		this is the initial MSS used by the connection.
235	
236	tcp_congestion_control - STRING
237		Set the congestion control algorithm to be used for new
238		connections. The algorithm "reno" is always available, but
239		additional choices may be available based on kernel configuration.
240		Default is set as part of kernel configuration.
241		For passive connections, the listener congestion control choice
242		is inherited.
243		[see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ]
244	
245	tcp_dsack - BOOLEAN
246		Allows TCP to send "duplicate" SACKs.
247	
248	tcp_early_retrans - INTEGER
249		Enable Early Retransmit (ER), per RFC 5827. ER lowers the threshold
250		for triggering fast retransmit when the amount of outstanding data is
251		small and when no previously unsent data can be transmitted (such
252		that limited transmit could be used). Also controls the use of
253		Tail loss probe (TLP) that converts RTOs occurring due to tail
254		losses into fast recovery (draft-dukkipati-tcpm-tcp-loss-probe-01).
255		Possible values:
256			0 disables ER
257			1 enables ER
258			2 enables ER but delays fast recovery and fast retransmit
259			  by a fourth of RTT. This mitigates connection falsely
260			  recovers when network has a small degree of reordering
261			  (less than 3 packets).
262			3 enables delayed ER and TLP.
263			4 enables TLP only.
264		Default: 3
265	
266	tcp_ecn - INTEGER
267		Control use of Explicit Congestion Notification (ECN) by TCP.
268		ECN is used only when both ends of the TCP connection indicate
269		support for it.  This feature is useful in avoiding losses due
270		to congestion by allowing supporting routers to signal
271		congestion before having to drop packets.
272		Possible values are:
273			0 Disable ECN.  Neither initiate nor accept ECN.
274			1 Enable ECN when requested by incoming connections and
275			  also request ECN on outgoing connection attempts.
276			2 Enable ECN when requested by incoming connections
277			  but do not request ECN on outgoing connections.
278		Default: 2
279	
280	tcp_ecn_fallback - BOOLEAN
281		If the kernel detects that ECN connection misbehaves, enable fall
282		back to non-ECN. Currently, this knob implements the fallback
283		from RFC3168, section 6.1.1.1., but we reserve that in future,
284		additional detection mechanisms could be implemented under this
285		knob. The value	is not used, if tcp_ecn or per route (or congestion
286		control) ECN settings are disabled.
287		Default: 1 (fallback enabled)
288	
289	tcp_fack - BOOLEAN
290		Enable FACK congestion avoidance and fast retransmission.
291		The value is not used, if tcp_sack is not enabled.
292	
293	tcp_fin_timeout - INTEGER
294		The length of time an orphaned (no longer referenced by any
295		application) connection will remain in the FIN_WAIT_2 state
296		before it is aborted at the local end.  While a perfectly
297		valid "receive only" state for an un-orphaned connection, an
298		orphaned connection in FIN_WAIT_2 state could otherwise wait
299		forever for the remote to close its end of the connection.
300		Cf. tcp_max_orphans
301		Default: 60 seconds
302	
303	tcp_frto - INTEGER
304		Enables Forward RTO-Recovery (F-RTO) defined in RFC5682.
305		F-RTO is an enhanced recovery algorithm for TCP retransmission
306		timeouts.  It is particularly beneficial in networks where the
307		RTT fluctuates (e.g., wireless). F-RTO is sender-side only
308		modification. It does not require any support from the peer.
309	
310		By default it's enabled with a non-zero value. 0 disables F-RTO.
311	
312	tcp_invalid_ratelimit - INTEGER
313		Limit the maximal rate for sending duplicate acknowledgments
314		in response to incoming TCP packets that are for an existing
315		connection but that are invalid due to any of these reasons:
316	
317		  (a) out-of-window sequence number,
318		  (b) out-of-window acknowledgment number, or
319		  (c) PAWS (Protection Against Wrapped Sequence numbers) check failure
320	
321		This can help mitigate simple "ack loop" DoS attacks, wherein
322		a buggy or malicious middlebox or man-in-the-middle can
323		rewrite TCP header fields in manner that causes each endpoint
324		to think that the other is sending invalid TCP segments, thus
325		causing each side to send an unterminating stream of duplicate
326		acknowledgments for invalid segments.
327	
328		Using 0 disables rate-limiting of dupacks in response to
329		invalid segments; otherwise this value specifies the minimal
330		space between sending such dupacks, in milliseconds.
331	
332		Default: 500 (milliseconds).
333	
334	tcp_keepalive_time - INTEGER
335		How often TCP sends out keepalive messages when keepalive is enabled.
336		Default: 2hours.
337	
338	tcp_keepalive_probes - INTEGER
339		How many keepalive probes TCP sends out, until it decides that the
340		connection is broken. Default value: 9.
341	
342	tcp_keepalive_intvl - INTEGER
343		How frequently the probes are send out. Multiplied by
344		tcp_keepalive_probes it is time to kill not responding connection,
345		after probes started. Default value: 75sec i.e. connection
346		will be aborted after ~11 minutes of retries.
347	
348	tcp_l3mdev_accept - BOOLEAN
349		Enables child sockets to inherit the L3 master device index.
350		Enabling this option allows a "global" listen socket to work
351		across L3 master domains (e.g., VRFs) with connected sockets
352		derived from the listen socket to be bound to the L3 domain in
353		which the packets originated. Only valid when the kernel was
354		compiled with CONFIG_NET_L3_MASTER_DEV.
355	
356	tcp_low_latency - BOOLEAN
357		If set, the TCP stack makes decisions that prefer lower
358		latency as opposed to higher throughput.  By default, this
359		option is not set meaning that higher throughput is preferred.
360		An example of an application where this default should be
361		changed would be a Beowulf compute cluster.
362		Default: 0
363	
364	tcp_max_orphans - INTEGER
365		Maximal number of TCP sockets not attached to any user file handle,
366		held by system.	If this number is exceeded orphaned connections are
367		reset immediately and warning is printed. This limit exists
368		only to prevent simple DoS attacks, you _must_ not rely on this
369		or lower the limit artificially, but rather increase it
370		(probably, after increasing installed memory),
371		if network conditions require more than default value,
372		and tune network services to linger and kill such states
373		more aggressively. Let me to remind again: each orphan eats
374		up to ~64K of unswappable memory.
375	
376	tcp_max_syn_backlog - INTEGER
377		Maximal number of remembered connection requests, which have not
378		received an acknowledgment from connecting client.
379		The minimal value is 128 for low memory machines, and it will
380		increase in proportion to the memory of machine.
381		If server suffers from overload, try increasing this number.
382	
383	tcp_max_tw_buckets - INTEGER
384		Maximal number of timewait sockets held by system simultaneously.
385		If this number is exceeded time-wait socket is immediately destroyed
386		and warning is printed. This limit exists only to prevent
387		simple DoS attacks, you _must_ not lower the limit artificially,
388		but rather increase it (probably, after increasing installed memory),
389		if network conditions require more than default value.
390	
391	tcp_mem - vector of 3 INTEGERs: min, pressure, max
392		min: below this number of pages TCP is not bothered about its
393		memory appetite.
394	
395		pressure: when amount of memory allocated by TCP exceeds this number
396		of pages, TCP moderates its memory consumption and enters memory
397		pressure mode, which is exited when memory consumption falls
398		under "min".
399	
400		max: number of pages allowed for queueing by all TCP sockets.
401	
402		Defaults are calculated at boot time from amount of available
403		memory.
404	
405	tcp_min_rtt_wlen - INTEGER
406		The window length of the windowed min filter to track the minimum RTT.
407		A shorter window lets a flow more quickly pick up new (higher)
408		minimum RTT when it is moved to a longer path (e.g., due to traffic
409		engineering). A longer window makes the filter more resistant to RTT
410		inflations such as transient congestion. The unit is seconds.
411		Default: 300
412	
413	tcp_moderate_rcvbuf - BOOLEAN
414		If set, TCP performs receive buffer auto-tuning, attempting to
415		automatically size the buffer (no greater than tcp_rmem[2]) to
416		match the size required by the path for full throughput.  Enabled by
417		default.
418	
419	tcp_mtu_probing - INTEGER
420		Controls TCP Packetization-Layer Path MTU Discovery.  Takes three
421		values:
422		  0 - Disabled
423		  1 - Disabled by default, enabled when an ICMP black hole detected
424		  2 - Always enabled, use initial MSS of tcp_base_mss.
425	
426	tcp_probe_interval - INTEGER
427		Controls how often to start TCP Packetization-Layer Path MTU
428		Discovery reprobe. The default is reprobing every 10 minutes as
429		per RFC4821.
430	
431	tcp_probe_threshold - INTEGER
432		Controls when TCP Packetization-Layer Path MTU Discovery probing
433		will stop in respect to the width of search range in bytes. Default
434		is 8 bytes.
435	
436	tcp_no_metrics_save - BOOLEAN
437		By default, TCP saves various connection metrics in the route cache
438		when the connection closes, so that connections established in the
439		near future can use these to set initial conditions.  Usually, this
440		increases overall performance, but may sometimes cause performance
441		degradation.  If set, TCP will not cache metrics on closing
442		connections.
443	
444	tcp_orphan_retries - INTEGER
445		This value influences the timeout of a locally closed TCP connection,
446		when RTO retransmissions remain unacknowledged.
447		See tcp_retries2 for more details.
448	
449		The default value is 8.
450		If your machine is a loaded WEB server,
451		you should think about lowering this value, such sockets
452		may consume significant resources. Cf. tcp_max_orphans.
453	
454	tcp_recovery - INTEGER
455		This value is a bitmap to enable various experimental loss recovery
456		features.
457	
458		RACK: 0x1 enables the RACK loss detection for fast detection of lost
459		      retransmissions and tail drops.
460	
461		Default: 0x1
462	
463	tcp_reordering - INTEGER
464		Initial reordering level of packets in a TCP stream.
465		TCP stack can then dynamically adjust flow reordering level
466		between this initial value and tcp_max_reordering
467		Default: 3
468	
469	tcp_max_reordering - INTEGER
470		Maximal reordering level of packets in a TCP stream.
471		300 is a fairly conservative value, but you might increase it
472		if paths are using per packet load balancing (like bonding rr mode)
473		Default: 300
474	
475	tcp_retrans_collapse - BOOLEAN
476		Bug-to-bug compatibility with some broken printers.
477		On retransmit try to send bigger packets to work around bugs in
478		certain TCP stacks.
479	
480	tcp_retries1 - INTEGER
481		This value influences the time, after which TCP decides, that
482		something is wrong due to unacknowledged RTO retransmissions,
483		and reports this suspicion to the network layer.
484		See tcp_retries2 for more details.
485	
486		RFC 1122 recommends at least 3 retransmissions, which is the
487		default.
488	
489	tcp_retries2 - INTEGER
490		This value influences the timeout of an alive TCP connection,
491		when RTO retransmissions remain unacknowledged.
492		Given a value of N, a hypothetical TCP connection following
493		exponential backoff with an initial RTO of TCP_RTO_MIN would
494		retransmit N times before killing the connection at the (N+1)th RTO.
495	
496		The default value of 15 yields a hypothetical timeout of 924.6
497		seconds and is a lower bound for the effective timeout.
498		TCP will effectively time out at the first RTO which exceeds the
499		hypothetical timeout.
500	
501		RFC 1122 recommends at least 100 seconds for the timeout,
502		which corresponds to a value of at least 8.
503	
504	tcp_rfc1337 - BOOLEAN
505		If set, the TCP stack behaves conforming to RFC1337. If unset,
506		we are not conforming to RFC, but prevent TCP TIME_WAIT
507		assassination.
508		Default: 0
509	
510	tcp_rmem - vector of 3 INTEGERs: min, default, max
511		min: Minimal size of receive buffer used by TCP sockets.
512		It is guaranteed to each TCP socket, even under moderate memory
513		pressure.
514		Default: 1 page
515	
516		default: initial size of receive buffer used by TCP sockets.
517		This value overrides net.core.rmem_default used by other protocols.
518		Default: 87380 bytes. This value results in window of 65535 with
519		default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
520		less for default tcp_app_win. See below about these variables.
521	
522		max: maximal size of receive buffer allowed for automatically
523		selected receiver buffers for TCP socket. This value does not override
524		net.core.rmem_max.  Calling setsockopt() with SO_RCVBUF disables
525		automatic tuning of that socket's receive buffer size, in which
526		case this value is ignored.
527		Default: between 87380B and 6MB, depending on RAM size.
528	
529	tcp_sack - BOOLEAN
530		Enable select acknowledgments (SACKS).
531	
532	tcp_slow_start_after_idle - BOOLEAN
533		If set, provide RFC2861 behavior and time out the congestion
534		window after an idle period.  An idle period is defined at
535		the current RTO.  If unset, the congestion window will not
536		be timed out after an idle period.
537		Default: 1
538	
539	tcp_stdurg - BOOLEAN
540		Use the Host requirements interpretation of the TCP urgent pointer field.
541		Most hosts use the older BSD interpretation, so if you turn this on
542		Linux might not communicate correctly with them.
543		Default: FALSE
544	
545	tcp_synack_retries - INTEGER
546		Number of times SYNACKs for a passive TCP connection attempt will
547		be retransmitted. Should not be higher than 255. Default value
548		is 5, which corresponds to 31seconds till the last retransmission
549		with the current initial RTO of 1second. With this the final timeout
550		for a passive TCP connection will happen after 63seconds.
551	
552	tcp_syncookies - BOOLEAN
553		Only valid when the kernel was compiled with CONFIG_SYN_COOKIES
554		Send out syncookies when the syn backlog queue of a socket
555		overflows. This is to prevent against the common 'SYN flood attack'
556		Default: 1
557	
558		Note, that syncookies is fallback facility.
559		It MUST NOT be used to help highly loaded servers to stand
560		against legal connection rate. If you see SYN flood warnings
561		in your logs, but investigation	shows that they occur
562		because of overload with legal connections, you should tune
563		another parameters until this warning disappear.
564		See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
565	
566		syncookies seriously violate TCP protocol, do not allow
567		to use TCP extensions, can result in serious degradation
568		of some services (f.e. SMTP relaying), visible not by you,
569		but your clients and relays, contacting you. While you see
570		SYN flood warnings in logs not being really flooded, your server
571		is seriously misconfigured.
572	
573		If you want to test which effects syncookies have to your
574		network connections you can set this knob to 2 to enable
575		unconditionally generation of syncookies.
576	
577	tcp_fastopen - INTEGER
578		Enable TCP Fast Open feature (draft-ietf-tcpm-fastopen) to send data
579		in the opening SYN packet. To use this feature, the client application
580		must use sendmsg() or sendto() with MSG_FASTOPEN flag rather than
581		connect() to perform a TCP handshake automatically.
582	
583		The values (bitmap) are
584		1: Enables sending data in the opening SYN on the client w/ MSG_FASTOPEN.
585		2: Enables TCP Fast Open on the server side, i.e., allowing data in
586		   a SYN packet to be accepted and passed to the application before
587		   3-way hand shake finishes.
588		4: Send data in the opening SYN regardless of cookie availability and
589		   without a cookie option.
590		0x100: Accept SYN data w/o validating the cookie.
591		0x200: Accept data-in-SYN w/o any cookie option present.
592		0x400/0x800: Enable Fast Open on all listeners regardless of the
593		   TCP_FASTOPEN socket option. The two different flags designate two
594		   different ways of setting max_qlen without the TCP_FASTOPEN socket
595		   option.
596	
597		Default: 1
598	
599		Note that the client & server side Fast Open flags (1 and 2
600		respectively) must be also enabled before the rest of flags can take
601		effect.
602	
603		See include/net/tcp.h and the code for more details.
604	
605	tcp_syn_retries - INTEGER
606		Number of times initial SYNs for an active TCP connection attempt
607		will be retransmitted. Should not be higher than 127. Default value
608		is 6, which corresponds to 63seconds till the last retransmission
609		with the current initial RTO of 1second. With this the final timeout
610		for an active TCP connection attempt will happen after 127seconds.
611	
612	tcp_timestamps - BOOLEAN
613		Enable timestamps as defined in RFC1323.
614	
615	tcp_min_tso_segs - INTEGER
616		Minimal number of segments per TSO frame.
617		Since linux-3.12, TCP does an automatic sizing of TSO frames,
618		depending on flow rate, instead of filling 64Kbytes packets.
619		For specific usages, it's possible to force TCP to build big
620		TSO frames. Note that TCP stack might split too big TSO packets
621		if available window is too small.
622		Default: 2
623	
624	tcp_pacing_ss_ratio - INTEGER
625		sk->sk_pacing_rate is set by TCP stack using a ratio applied
626		to current rate. (current_rate = cwnd * mss / srtt)
627		If TCP is in slow start, tcp_pacing_ss_ratio is applied
628		to let TCP probe for bigger speeds, assuming cwnd can be
629		doubled every other RTT.
630		Default: 200
631	
632	tcp_pacing_ca_ratio - INTEGER
633		sk->sk_pacing_rate is set by TCP stack using a ratio applied
634		to current rate. (current_rate = cwnd * mss / srtt)
635		If TCP is in congestion avoidance phase, tcp_pacing_ca_ratio
636		is applied to conservatively probe for bigger throughput.
637		Default: 120
638	
639	tcp_tso_win_divisor - INTEGER
640		This allows control over what percentage of the congestion window
641		can be consumed by a single TSO frame.
642		The setting of this parameter is a choice between burstiness and
643		building larger TSO frames.
644		Default: 3
645	
646	tcp_tw_recycle - BOOLEAN
647		Enable fast recycling TIME-WAIT sockets. Default value is 0.
648		It should not be changed without advice/request of technical
649		experts.
650	
651	tcp_tw_reuse - BOOLEAN
652		Allow to reuse TIME-WAIT sockets for new connections when it is
653		safe from protocol viewpoint. Default value is 0.
654		It should not be changed without advice/request of technical
655		experts.
656	
657	tcp_window_scaling - BOOLEAN
658		Enable window scaling as defined in RFC1323.
659	
660	tcp_wmem - vector of 3 INTEGERs: min, default, max
661		min: Amount of memory reserved for send buffers for TCP sockets.
662		Each TCP socket has rights to use it due to fact of its birth.
663		Default: 1 page
664	
665		default: initial size of send buffer used by TCP sockets.  This
666		value overrides net.core.wmem_default used by other protocols.
667		It is usually lower than net.core.wmem_default.
668		Default: 16K
669	
670		max: Maximal amount of memory allowed for automatically tuned
671		send buffers for TCP sockets. This value does not override
672		net.core.wmem_max.  Calling setsockopt() with SO_SNDBUF disables
673		automatic tuning of that socket's send buffer size, in which case
674		this value is ignored.
675		Default: between 64K and 4MB, depending on RAM size.
676	
677	tcp_notsent_lowat - UNSIGNED INTEGER
678		A TCP socket can control the amount of unsent bytes in its write queue,
679		thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll()
680		reports POLLOUT events if the amount of unsent bytes is below a per
681		socket value, and if the write queue is not full. sendmsg() will
682		also not add new buffers if the limit is hit.
683	
684		This global variable controls the amount of unsent data for
685		sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change
686		to the global variable has immediate effect.
687	
688		Default: UINT_MAX (0xFFFFFFFF)
689	
690	tcp_workaround_signed_windows - BOOLEAN
691		If set, assume no receipt of a window scaling option means the
692		remote TCP is broken and treats the window as a signed quantity.
693		If unset, assume the remote TCP is not broken even if we do
694		not receive a window scaling option from them.
695		Default: 0
696	
697	tcp_thin_linear_timeouts - BOOLEAN
698		Enable dynamic triggering of linear timeouts for thin streams.
699		If set, a check is performed upon retransmission by timeout to
700		determine if the stream is thin (less than 4 packets in flight).
701		As long as the stream is found to be thin, up to 6 linear
702		timeouts may be performed before exponential backoff mode is
703		initiated. This improves retransmission latency for
704		non-aggressive thin streams, often found to be time-dependent.
705		For more information on thin streams, see
706		Documentation/networking/tcp-thin.txt
707		Default: 0
708	
709	tcp_thin_dupack - BOOLEAN
710		Enable dynamic triggering of retransmissions after one dupACK
711		for thin streams. If set, a check is performed upon reception
712		of a dupACK to determine if the stream is thin (less than 4
713		packets in flight). As long as the stream is found to be thin,
714		data is retransmitted on the first received dupACK. This
715		improves retransmission latency for non-aggressive thin
716		streams, often found to be time-dependent.
717		For more information on thin streams, see
718		Documentation/networking/tcp-thin.txt
719		Default: 0
720	
721	tcp_limit_output_bytes - INTEGER
722		Controls TCP Small Queue limit per tcp socket.
723		TCP bulk sender tends to increase packets in flight until it
724		gets losses notifications. With SNDBUF autotuning, this can
725		result in a large amount of packets queued in qdisc/device
726		on the local machine, hurting latency of other flows, for
727		typical pfifo_fast qdiscs.
728		tcp_limit_output_bytes limits the number of bytes on qdisc
729		or device to reduce artificial RTT/cwnd and reduce bufferbloat.
730		Default: 262144
731	
732	tcp_challenge_ack_limit - INTEGER
733		Limits number of Challenge ACK sent per second, as recommended
734		in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
735		Default: 100
736	
737	UDP variables:
738	
739	udp_mem - vector of 3 INTEGERs: min, pressure, max
740		Number of pages allowed for queueing by all UDP sockets.
741	
742		min: Below this number of pages UDP is not bothered about its
743		memory appetite. When amount of memory allocated by UDP exceeds
744		this number, UDP starts to moderate memory usage.
745	
746		pressure: This value was introduced to follow format of tcp_mem.
747	
748		max: Number of pages allowed for queueing by all UDP sockets.
749	
750		Default is calculated at boot time from amount of available memory.
751	
752	udp_rmem_min - INTEGER
753		Minimal size of receive buffer used by UDP sockets in moderation.
754		Each UDP socket is able to use the size for receiving data, even if
755		total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
756		Default: 1 page
757	
758	udp_wmem_min - INTEGER
759		Minimal size of send buffer used by UDP sockets in moderation.
760		Each UDP socket is able to use the size for sending data, even if
761		total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
762		Default: 1 page
763	
764	CIPSOv4 Variables:
765	
766	cipso_cache_enable - BOOLEAN
767		If set, enable additions to and lookups from the CIPSO label mapping
768		cache.  If unset, additions are ignored and lookups always result in a
769		miss.  However, regardless of the setting the cache is still
770		invalidated when required when means you can safely toggle this on and
771		off and the cache will always be "safe".
772		Default: 1
773	
774	cipso_cache_bucket_size - INTEGER
775		The CIPSO label cache consists of a fixed size hash table with each
776		hash bucket containing a number of cache entries.  This variable limits
777		the number of entries in each hash bucket; the larger the value the
778		more CIPSO label mappings that can be cached.  When the number of
779		entries in a given hash bucket reaches this limit adding new entries
780		causes the oldest entry in the bucket to be removed to make room.
781		Default: 10
782	
783	cipso_rbm_optfmt - BOOLEAN
784		Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
785		the CIPSO draft specification (see Documentation/netlabel for details).
786		This means that when set the CIPSO tag will be padded with empty
787		categories in order to make the packet data 32-bit aligned.
788		Default: 0
789	
790	cipso_rbm_structvalid - BOOLEAN
791		If set, do a very strict check of the CIPSO option when
792		ip_options_compile() is called.  If unset, relax the checks done during
793		ip_options_compile().  Either way is "safe" as errors are caught else
794		where in the CIPSO processing code but setting this to 0 (False) should
795		result in less work (i.e. it should be faster) but could cause problems
796		with other implementations that require strict checking.
797		Default: 0
798	
799	IP Variables:
800	
801	ip_local_port_range - 2 INTEGERS
802		Defines the local port range that is used by TCP and UDP to
803		choose the local port. The first number is the first, the
804		second the last local port number.
805		If possible, it is better these numbers have different parity.
806		(one even and one odd values)
807		The default values are 32768 and 60999 respectively.
808	
809	ip_local_reserved_ports - list of comma separated ranges
810		Specify the ports which are reserved for known third-party
811		applications. These ports will not be used by automatic port
812		assignments (e.g. when calling connect() or bind() with port
813		number 0). Explicit port allocation behavior is unchanged.
814	
815		The format used for both input and output is a comma separated
816		list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and
817		10). Writing to the file will clear all previously reserved
818		ports and update the current list with the one given in the
819		input.
820	
821		Note that ip_local_port_range and ip_local_reserved_ports
822		settings are independent and both are considered by the kernel
823		when determining which ports are available for automatic port
824		assignments.
825	
826		You can reserve ports which are not in the current
827		ip_local_port_range, e.g.:
828	
829		$ cat /proc/sys/net/ipv4/ip_local_port_range
830		32000	60999
831		$ cat /proc/sys/net/ipv4/ip_local_reserved_ports
832		8080,9148
833	
834		although this is redundant. However such a setting is useful
835		if later the port range is changed to a value that will
836		include the reserved ports.
837	
838		Default: Empty
839	
840	ip_nonlocal_bind - BOOLEAN
841		If set, allows processes to bind() to non-local IP addresses,
842		which can be quite useful - but may break some applications.
843		Default: 0
844	
845	ip_dynaddr - BOOLEAN
846		If set non-zero, enables support for dynamic addresses.
847		If set to a non-zero value larger than 1, a kernel log
848		message will be printed when dynamic address rewriting
849		occurs.
850		Default: 0
851	
852	ip_early_demux - BOOLEAN
853		Optimize input packet processing down to one demux for
854		certain kinds of local sockets.  Currently we only do this
855		for established TCP sockets.
856	
857		It may add an additional cost for pure routing workloads that
858		reduces overall throughput, in such case you should disable it.
859		Default: 1
860	
861	icmp_echo_ignore_all - BOOLEAN
862		If set non-zero, then the kernel will ignore all ICMP ECHO
863		requests sent to it.
864		Default: 0
865	
866	icmp_echo_ignore_broadcasts - BOOLEAN
867		If set non-zero, then the kernel will ignore all ICMP ECHO and
868		TIMESTAMP requests sent to it via broadcast/multicast.
869		Default: 1
870	
871	icmp_ratelimit - INTEGER
872		Limit the maximal rates for sending ICMP packets whose type matches
873		icmp_ratemask (see below) to specific targets.
874		0 to disable any limiting,
875		otherwise the minimal space between responses in milliseconds.
876		Note that another sysctl, icmp_msgs_per_sec limits the number
877		of ICMP packets	sent on all targets.
878		Default: 1000
879	
880	icmp_msgs_per_sec - INTEGER
881		Limit maximal number of ICMP packets sent per second from this host.
882		Only messages whose type matches icmp_ratemask (see below) are
883		controlled by this limit.
884		Default: 1000
885	
886	icmp_msgs_burst - INTEGER
887		icmp_msgs_per_sec controls number of ICMP packets sent per second,
888		while icmp_msgs_burst controls the burst size of these packets.
889		Default: 50
890	
891	icmp_ratemask - INTEGER
892		Mask made of ICMP types for which rates are being limited.
893		Significant bits: IHGFEDCBA9876543210
894		Default mask:     0000001100000011000 (6168)
895	
896		Bit definitions (see include/linux/icmp.h):
897			0 Echo Reply
898			3 Destination Unreachable *
899			4 Source Quench *
900			5 Redirect
901			8 Echo Request
902			B Time Exceeded *
903			C Parameter Problem *
904			D Timestamp Request
905			E Timestamp Reply
906			F Info Request
907			G Info Reply
908			H Address Mask Request
909			I Address Mask Reply
910	
911		* These are rate limited by default (see default mask above)
912	
913	icmp_ignore_bogus_error_responses - BOOLEAN
914		Some routers violate RFC1122 by sending bogus responses to broadcast
915		frames.  Such violations are normally logged via a kernel warning.
916		If this is set to TRUE, the kernel will not give such warnings, which
917		will avoid log file clutter.
918		Default: 1
919	
920	icmp_errors_use_inbound_ifaddr - BOOLEAN
921	
922		If zero, icmp error messages are sent with the primary address of
923		the exiting interface.
924	
925		If non-zero, the message will be sent with the primary address of
926		the interface that received the packet that caused the icmp error.
927		This is the behaviour network many administrators will expect from
928		a router. And it can make debugging complicated network layouts
929		much easier.
930	
931		Note that if no primary address exists for the interface selected,
932		then the primary address of the first non-loopback interface that
933		has one will be used regardless of this setting.
934	
935		Default: 0
936	
937	igmp_max_memberships - INTEGER
938		Change the maximum number of multicast groups we can subscribe to.
939		Default: 20
940	
941		Theoretical maximum value is bounded by having to send a membership
942		report in a single datagram (i.e. the report can't span multiple
943		datagrams, or risk confusing the switch and leaving groups you don't
944		intend to).
945	
946		The number of supported groups 'M' is bounded by the number of group
947		report entries you can fit into a single datagram of 65535 bytes.
948	
949		M = 65536-sizeof (ip header)/(sizeof(Group record))
950	
951		Group records are variable length, with a minimum of 12 bytes.
952		So net.ipv4.igmp_max_memberships should not be set higher than:
953	
954		(65536-24) / 12 = 5459
955	
956		The value 5459 assumes no IP header options, so in practice
957		this number may be lower.
958	
959	igmp_max_msf - INTEGER
960		Maximum number of addresses allowed in the source filter list for a
961		multicast group.
962		Default: 10
963	
964	igmp_qrv - INTEGER
965		Controls the IGMP query robustness variable (see RFC2236 8.1).
966		Default: 2 (as specified by RFC2236 8.1)
967		Minimum: 1 (as specified by RFC6636 4.5)
968	
969	conf/interface/*  changes special settings per interface (where
970	"interface" is the name of your network interface)
971	
972	conf/all/*	  is special, changes the settings for all interfaces
973	
974	log_martians - BOOLEAN
975		Log packets with impossible addresses to kernel log.
976		log_martians for the interface will be enabled if at least one of
977		conf/{all,interface}/log_martians is set to TRUE,
978		it will be disabled otherwise
979	
980	accept_redirects - BOOLEAN
981		Accept ICMP redirect messages.
982		accept_redirects for the interface will be enabled if:
983		- both conf/{all,interface}/accept_redirects are TRUE in the case
984		  forwarding for the interface is enabled
985		or
986		- at least one of conf/{all,interface}/accept_redirects is TRUE in the
987		  case forwarding for the interface is disabled
988		accept_redirects for the interface will be disabled otherwise
989		default TRUE (host)
990			FALSE (router)
991	
992	forwarding - BOOLEAN
993		Enable IP forwarding on this interface.
994	
995	mc_forwarding - BOOLEAN
996		Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
997		and a multicast routing daemon is required.
998		conf/all/mc_forwarding must also be set to TRUE to enable multicast
999		routing	for the interface
1000	
1001	medium_id - INTEGER
1002		Integer value used to differentiate the devices by the medium they
1003		are attached to. Two devices can have different id values when
1004		the broadcast packets are received only on one of them.
1005		The default value 0 means that the device is the only interface
1006		to its medium, value of -1 means that medium is not known.
1007	
1008		Currently, it is used to change the proxy_arp behavior:
1009		the proxy_arp feature is enabled for packets forwarded between
1010		two devices attached to different media.
1011	
1012	proxy_arp - BOOLEAN
1013		Do proxy arp.
1014		proxy_arp for the interface will be enabled if at least one of
1015		conf/{all,interface}/proxy_arp is set to TRUE,
1016		it will be disabled otherwise
1017	
1018	proxy_arp_pvlan - BOOLEAN
1019		Private VLAN proxy arp.
1020		Basically allow proxy arp replies back to the same interface
1021		(from which the ARP request/solicitation was received).
1022	
1023		This is done to support (ethernet) switch features, like RFC
1024		3069, where the individual ports are NOT allowed to
1025		communicate with each other, but they are allowed to talk to
1026		the upstream router.  As described in RFC 3069, it is possible
1027		to allow these hosts to communicate through the upstream
1028		router by proxy_arp'ing. Don't need to be used together with
1029		proxy_arp.
1030	
1031		This technology is known by different names:
1032		  In RFC 3069 it is called VLAN Aggregation.
1033		  Cisco and Allied Telesyn call it Private VLAN.
1034		  Hewlett-Packard call it Source-Port filtering or port-isolation.
1035		  Ericsson call it MAC-Forced Forwarding (RFC Draft).
1036	
1037	shared_media - BOOLEAN
1038		Send(router) or accept(host) RFC1620 shared media redirects.
1039		Overrides secure_redirects.
1040		shared_media for the interface will be enabled if at least one of
1041		conf/{all,interface}/shared_media is set to TRUE,
1042		it will be disabled otherwise
1043		default TRUE
1044	
1045	secure_redirects - BOOLEAN
1046		Accept ICMP redirect messages only to gateways listed in the
1047		interface's current gateway list. Even if disabled, RFC1122 redirect
1048		rules still apply.
1049		Overridden by shared_media.
1050		secure_redirects for the interface will be enabled if at least one of
1051		conf/{all,interface}/secure_redirects is set to TRUE,
1052		it will be disabled otherwise
1053		default TRUE
1054	
1055	send_redirects - BOOLEAN
1056		Send redirects, if router.
1057		send_redirects for the interface will be enabled if at least one of
1058		conf/{all,interface}/send_redirects is set to TRUE,
1059		it will be disabled otherwise
1060		Default: TRUE
1061	
1062	bootp_relay - BOOLEAN
1063		Accept packets with source address 0.b.c.d destined
1064		not to this host as local ones. It is supposed, that
1065		BOOTP relay daemon will catch and forward such packets.
1066		conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
1067		for the interface
1068		default FALSE
1069		Not Implemented Yet.
1070	
1071	accept_source_route - BOOLEAN
1072		Accept packets with SRR option.
1073		conf/all/accept_source_route must also be set to TRUE to accept packets
1074		with SRR option on the interface
1075		default TRUE (router)
1076			FALSE (host)
1077	
1078	accept_local - BOOLEAN
1079		Accept packets with local source addresses. In combination with
1080		suitable routing, this can be used to direct packets between two
1081		local interfaces over the wire and have them accepted properly.
1082		default FALSE
1083	
1084	route_localnet - BOOLEAN
1085		Do not consider loopback addresses as martian source or destination
1086		while routing. This enables the use of 127/8 for local routing purposes.
1087		default FALSE
1088	
1089	rp_filter - INTEGER
1090		0 - No source validation.
1091		1 - Strict mode as defined in RFC3704 Strict Reverse Path
1092		    Each incoming packet is tested against the FIB and if the interface
1093		    is not the best reverse path the packet check will fail.
1094		    By default failed packets are discarded.
1095		2 - Loose mode as defined in RFC3704 Loose Reverse Path
1096		    Each incoming packet's source address is also tested against the FIB
1097		    and if the source address is not reachable via any interface
1098		    the packet check will fail.
1099	
1100		Current recommended practice in RFC3704 is to enable strict mode
1101		to prevent IP spoofing from DDos attacks. If using asymmetric routing
1102		or other complicated routing, then loose mode is recommended.
1103	
1104		The max value from conf/{all,interface}/rp_filter is used
1105		when doing source validation on the {interface}.
1106	
1107		Default value is 0. Note that some distributions enable it
1108		in startup scripts.
1109	
1110	arp_filter - BOOLEAN
1111		1 - Allows you to have multiple network interfaces on the same
1112		subnet, and have the ARPs for each interface be answered
1113		based on whether or not the kernel would route a packet from
1114		the ARP'd IP out that interface (therefore you must use source
1115		based routing for this to work). In other words it allows control
1116		of which cards (usually 1) will respond to an arp request.
1117	
1118		0 - (default) The kernel can respond to arp requests with addresses
1119		from other interfaces. This may seem wrong but it usually makes
1120		sense, because it increases the chance of successful communication.
1121		IP addresses are owned by the complete host on Linux, not by
1122		particular interfaces. Only for more complex setups like load-
1123		balancing, does this behaviour cause problems.
1124	
1125		arp_filter for the interface will be enabled if at least one of
1126		conf/{all,interface}/arp_filter is set to TRUE,
1127		it will be disabled otherwise
1128	
1129	arp_announce - INTEGER
1130		Define different restriction levels for announcing the local
1131		source IP address from IP packets in ARP requests sent on
1132		interface:
1133		0 - (default) Use any local address, configured on any interface
1134		1 - Try to avoid local addresses that are not in the target's
1135		subnet for this interface. This mode is useful when target
1136		hosts reachable via this interface require the source IP
1137		address in ARP requests to be part of their logical network
1138		configured on the receiving interface. When we generate the
1139		request we will check all our subnets that include the
1140		target IP and will preserve the source address if it is from
1141		such subnet. If there is no such subnet we select source
1142		address according to the rules for level 2.
1143		2 - Always use the best local address for this target.
1144		In this mode we ignore the source address in the IP packet
1145		and try to select local address that we prefer for talks with
1146		the target host. Such local address is selected by looking
1147		for primary IP addresses on all our subnets on the outgoing
1148		interface that include the target IP address. If no suitable
1149		local address is found we select the first local address
1150		we have on the outgoing interface or on all other interfaces,
1151		with the hope we will receive reply for our request and
1152		even sometimes no matter the source IP address we announce.
1153	
1154		The max value from conf/{all,interface}/arp_announce is used.
1155	
1156		Increasing the restriction level gives more chance for
1157		receiving answer from the resolved target while decreasing
1158		the level announces more valid sender's information.
1159	
1160	arp_ignore - INTEGER
1161		Define different modes for sending replies in response to
1162		received ARP requests that resolve local target IP addresses:
1163		0 - (default): reply for any local target IP address, configured
1164		on any interface
1165		1 - reply only if the target IP address is local address
1166		configured on the incoming interface
1167		2 - reply only if the target IP address is local address
1168		configured on the incoming interface and both with the
1169		sender's IP address are part from same subnet on this interface
1170		3 - do not reply for local addresses configured with scope host,
1171		only resolutions for global and link addresses are replied
1172		4-7 - reserved
1173		8 - do not reply for all local addresses
1174	
1175		The max value from conf/{all,interface}/arp_ignore is used
1176		when ARP request is received on the {interface}
1177	
1178	arp_notify - BOOLEAN
1179		Define mode for notification of address and device changes.
1180		0 - (default): do nothing
1181		1 - Generate gratuitous arp requests when device is brought up
1182		    or hardware address changes.
1183	
1184	arp_accept - BOOLEAN
1185		Define behavior for gratuitous ARP frames who's IP is not
1186		already present in the ARP table:
1187		0 - don't create new entries in the ARP table
1188		1 - create new entries in the ARP table
1189	
1190		Both replies and requests type gratuitous arp will trigger the
1191		ARP table to be updated, if this setting is on.
1192	
1193		If the ARP table already contains the IP address of the
1194		gratuitous arp frame, the arp table will be updated regardless
1195		if this setting is on or off.
1196	
1197	mcast_solicit - INTEGER
1198		The maximum number of multicast probes in INCOMPLETE state,
1199		when the associated hardware address is unknown.  Defaults
1200		to 3.
1201	
1202	ucast_solicit - INTEGER
1203		The maximum number of unicast probes in PROBE state, when
1204		the hardware address is being reconfirmed.  Defaults to 3.
1205	
1206	app_solicit - INTEGER
1207		The maximum number of probes to send to the user space ARP daemon
1208		via netlink before dropping back to multicast probes (see
1209		mcast_resolicit).  Defaults to 0.
1210	
1211	mcast_resolicit - INTEGER
1212		The maximum number of multicast probes after unicast and
1213		app probes in PROBE state.  Defaults to 0.
1214	
1215	disable_policy - BOOLEAN
1216		Disable IPSEC policy (SPD) for this interface
1217	
1218	disable_xfrm - BOOLEAN
1219		Disable IPSEC encryption on this interface, whatever the policy
1220	
1221	igmpv2_unsolicited_report_interval - INTEGER
1222		The interval in milliseconds in which the next unsolicited
1223		IGMPv1 or IGMPv2 report retransmit will take place.
1224		Default: 10000 (10 seconds)
1225	
1226	igmpv3_unsolicited_report_interval - INTEGER
1227		The interval in milliseconds in which the next unsolicited
1228		IGMPv3 report retransmit will take place.
1229		Default: 1000 (1 seconds)
1230	
1231	promote_secondaries - BOOLEAN
1232		When a primary IP address is removed from this interface
1233		promote a corresponding secondary IP address instead of
1234		removing all the corresponding secondary IP addresses.
1235	
1236	drop_unicast_in_l2_multicast - BOOLEAN
1237		Drop any unicast IP packets that are received in link-layer
1238		multicast (or broadcast) frames.
1239		This behavior (for multicast) is actually a SHOULD in RFC
1240		1122, but is disabled by default for compatibility reasons.
1241		Default: off (0)
1242	
1243	drop_gratuitous_arp - BOOLEAN
1244		Drop all gratuitous ARP frames, for example if there's a known
1245		good ARP proxy on the network and such frames need not be used
1246		(or in the case of 802.11, must not be used to prevent attacks.)
1247		Default: off (0)
1248	
1249	
1250	tag - INTEGER
1251		Allows you to write a number, which can be used as required.
1252		Default value is 0.
1253	
1254	xfrm4_gc_thresh - INTEGER
1255		The threshold at which we will start garbage collecting for IPv4
1256		destination cache entries.  At twice this value the system will
1257		refuse new allocations. The value must be set below the flowcache
1258		limit (4096 * number of online cpus) to take effect.
1259	
1260	igmp_link_local_mcast_reports - BOOLEAN
1261		Enable IGMP reports for link local multicast groups in the
1262		224.0.0.X range.
1263		Default TRUE
1264	
1265	Alexey Kuznetsov.
1266	kuznet@ms2.inr.ac.ru
1267	
1268	Updated by:
1269	Andi Kleen
1270	ak@muc.de
1271	Nicolas Delon
1272	delon.nicolas@wanadoo.fr
1273	
1274	
1275	
1276	
1277	/proc/sys/net/ipv6/* Variables:
1278	
1279	IPv6 has no global variables such as tcp_*.  tcp_* settings under ipv4/ also
1280	apply to IPv6 [XXX?].
1281	
1282	bindv6only - BOOLEAN
1283		Default value for IPV6_V6ONLY socket option,
1284		which restricts use of the IPv6 socket to IPv6 communication
1285		only.
1286			TRUE: disable IPv4-mapped address feature
1287			FALSE: enable IPv4-mapped address feature
1288	
1289		Default: FALSE (as specified in RFC3493)
1290	
1291	flowlabel_consistency - BOOLEAN
1292		Protect the consistency (and unicity) of flow label.
1293		You have to disable it to use IPV6_FL_F_REFLECT flag on the
1294		flow label manager.
1295		TRUE: enabled
1296		FALSE: disabled
1297		Default: TRUE
1298	
1299	auto_flowlabels - INTEGER
1300		Automatically generate flow labels based on a flow hash of the
1301		packet. This allows intermediate devices, such as routers, to
1302		identify packet flows for mechanisms like Equal Cost Multipath
1303		Routing (see RFC 6438).
1304		0: automatic flow labels are completely disabled
1305		1: automatic flow labels are enabled by default, they can be
1306		   disabled on a per socket basis using the IPV6_AUTOFLOWLABEL
1307		   socket option
1308		2: automatic flow labels are allowed, they may be enabled on a
1309		   per socket basis using the IPV6_AUTOFLOWLABEL socket option
1310		3: automatic flow labels are enabled and enforced, they cannot
1311		   be disabled by the socket option
1312		Default: 1
1313	
1314	flowlabel_state_ranges - BOOLEAN
1315		Split the flow label number space into two ranges. 0-0x7FFFF is
1316		reserved for the IPv6 flow manager facility, 0x80000-0xFFFFF
1317		is reserved for stateless flow labels as described in RFC6437.
1318		TRUE: enabled
1319		FALSE: disabled
1320		Default: true
1321	
1322	anycast_src_echo_reply - BOOLEAN
1323		Controls the use of anycast addresses as source addresses for ICMPv6
1324		echo reply
1325		TRUE:  enabled
1326		FALSE: disabled
1327		Default: FALSE
1328	
1329	idgen_delay - INTEGER
1330		Controls the delay in seconds after which time to retry
1331		privacy stable address generation if a DAD conflict is
1332		detected.
1333		Default: 1 (as specified in RFC7217)
1334	
1335	idgen_retries - INTEGER
1336		Controls the number of retries to generate a stable privacy
1337		address if a DAD conflict is detected.
1338		Default: 3 (as specified in RFC7217)
1339	
1340	mld_qrv - INTEGER
1341		Controls the MLD query robustness variable (see RFC3810 9.1).
1342		Default: 2 (as specified by RFC3810 9.1)
1343		Minimum: 1 (as specified by RFC6636 4.5)
1344	
1345	IPv6 Fragmentation:
1346	
1347	ip6frag_high_thresh - INTEGER
1348		Maximum memory used to reassemble IPv6 fragments. When
1349		ip6frag_high_thresh bytes of memory is allocated for this purpose,
1350		the fragment handler will toss packets until ip6frag_low_thresh
1351		is reached.
1352	
1353	ip6frag_low_thresh - INTEGER
1354		See ip6frag_high_thresh
1355	
1356	ip6frag_time - INTEGER
1357		Time in seconds to keep an IPv6 fragment in memory.
1358	
1359	conf/default/*:
1360		Change the interface-specific default settings.
1361	
1362	
1363	conf/all/*:
1364		Change all the interface-specific settings.
1365	
1366		[XXX:  Other special features than forwarding?]
1367	
1368	conf/all/forwarding - BOOLEAN
1369		Enable global IPv6 forwarding between all interfaces.
1370	
1371		IPv4 and IPv6 work differently here; e.g. netfilter must be used
1372		to control which interfaces may forward packets and which not.
1373	
1374		This also sets all interfaces' Host/Router setting
1375		'forwarding' to the specified value.  See below for details.
1376	
1377		This referred to as global forwarding.
1378	
1379	proxy_ndp - BOOLEAN
1380		Do proxy ndp.
1381	
1382	fwmark_reflect - BOOLEAN
1383		Controls the fwmark of kernel-generated IPv6 reply packets that are not
1384		associated with a socket for example, TCP RSTs or ICMPv6 echo replies).
1385		If unset, these packets have a fwmark of zero. If set, they have the
1386		fwmark of the packet they are replying to.
1387		Default: 0
1388	
1389	conf/interface/*:
1390		Change special settings per interface.
1391	
1392		The functional behaviour for certain settings is different
1393		depending on whether local forwarding is enabled or not.
1394	
1395	accept_ra - INTEGER
1396		Accept Router Advertisements; autoconfigure using them.
1397	
1398		It also determines whether or not to transmit Router
1399		Solicitations. If and only if the functional setting is to
1400		accept Router Advertisements, Router Solicitations will be
1401		transmitted.
1402	
1403		Possible values are:
1404			0 Do not accept Router Advertisements.
1405			1 Accept Router Advertisements if forwarding is disabled.
1406			2 Overrule forwarding behaviour. Accept Router Advertisements
1407			  even if forwarding is enabled.
1408	
1409		Functional default: enabled if local forwarding is disabled.
1410				    disabled if local forwarding is enabled.
1411	
1412	accept_ra_defrtr - BOOLEAN
1413		Learn default router in Router Advertisement.
1414	
1415		Functional default: enabled if accept_ra is enabled.
1416				    disabled if accept_ra is disabled.
1417	
1418	accept_ra_from_local - BOOLEAN
1419		Accept RA with source-address that is found on local machine
1420	        if the RA is otherwise proper and able to be accepted.
1421	        Default is to NOT accept these as it may be an un-intended
1422	        network loop.
1423	
1424		Functional default:
1425	           enabled if accept_ra_from_local is enabled
1426	               on a specific interface.
1427		   disabled if accept_ra_from_local is disabled
1428	               on a specific interface.
1429	
1430	accept_ra_min_hop_limit - INTEGER
1431		Minimum hop limit Information in Router Advertisement.
1432	
1433		Hop limit Information in Router Advertisement less than this
1434		variable shall be ignored.
1435	
1436		Default: 1
1437	
1438	accept_ra_pinfo - BOOLEAN
1439		Learn Prefix Information in Router Advertisement.
1440	
1441		Functional default: enabled if accept_ra is enabled.
1442				    disabled if accept_ra is disabled.
1443	
1444	accept_ra_rt_info_max_plen - INTEGER
1445		Maximum prefix length of Route Information in RA.
1446	
1447		Route Information w/ prefix larger than or equal to this
1448		variable shall be ignored.
1449	
1450		Functional default: 0 if accept_ra_rtr_pref is enabled.
1451				    -1 if accept_ra_rtr_pref is disabled.
1452	
1453	accept_ra_rtr_pref - BOOLEAN
1454		Accept Router Preference in RA.
1455	
1456		Functional default: enabled if accept_ra is enabled.
1457				    disabled if accept_ra is disabled.
1458	
1459	accept_ra_mtu - BOOLEAN
1460		Apply the MTU value specified in RA option 5 (RFC4861). If
1461		disabled, the MTU specified in the RA will be ignored.
1462	
1463		Functional default: enabled if accept_ra is enabled.
1464				    disabled if accept_ra is disabled.
1465	
1466	accept_redirects - BOOLEAN
1467		Accept Redirects.
1468	
1469		Functional default: enabled if local forwarding is disabled.
1470				    disabled if local forwarding is enabled.
1471	
1472	accept_source_route - INTEGER
1473		Accept source routing (routing extension header).
1474	
1475		>= 0: Accept only routing header type 2.
1476		< 0: Do not accept routing header.
1477	
1478		Default: 0
1479	
1480	autoconf - BOOLEAN
1481		Autoconfigure addresses using Prefix Information in Router
1482		Advertisements.
1483	
1484		Functional default: enabled if accept_ra_pinfo is enabled.
1485				    disabled if accept_ra_pinfo is disabled.
1486	
1487	dad_transmits - INTEGER
1488		The amount of Duplicate Address Detection probes to send.
1489		Default: 1
1490	
1491	forwarding - INTEGER
1492		Configure interface-specific Host/Router behaviour.
1493	
1494		Note: It is recommended to have the same setting on all
1495		interfaces; mixed router/host scenarios are rather uncommon.
1496	
1497		Possible values are:
1498			0 Forwarding disabled
1499			1 Forwarding enabled
1500	
1501		FALSE (0):
1502	
1503		By default, Host behaviour is assumed.  This means:
1504	
1505		1. IsRouter flag is not set in Neighbour Advertisements.
1506		2. If accept_ra is TRUE (default), transmit Router
1507		   Solicitations.
1508		3. If accept_ra is TRUE (default), accept Router
1509		   Advertisements (and do autoconfiguration).
1510		4. If accept_redirects is TRUE (default), accept Redirects.
1511	
1512		TRUE (1):
1513	
1514		If local forwarding is enabled, Router behaviour is assumed.
1515		This means exactly the reverse from the above:
1516	
1517		1. IsRouter flag is set in Neighbour Advertisements.
1518		2. Router Solicitations are not sent unless accept_ra is 2.
1519		3. Router Advertisements are ignored unless accept_ra is 2.
1520		4. Redirects are ignored.
1521	
1522		Default: 0 (disabled) if global forwarding is disabled (default),
1523			 otherwise 1 (enabled).
1524	
1525	hop_limit - INTEGER
1526		Default Hop Limit to set.
1527		Default: 64
1528	
1529	mtu - INTEGER
1530		Default Maximum Transfer Unit
1531		Default: 1280 (IPv6 required minimum)
1532	
1533	ip_nonlocal_bind - BOOLEAN
1534		If set, allows processes to bind() to non-local IPv6 addresses,
1535		which can be quite useful - but may break some applications.
1536		Default: 0
1537	
1538	router_probe_interval - INTEGER
1539		Minimum interval (in seconds) between Router Probing described
1540		in RFC4191.
1541	
1542		Default: 60
1543	
1544	router_solicitation_delay - INTEGER
1545		Number of seconds to wait after interface is brought up
1546		before sending Router Solicitations.
1547		Default: 1
1548	
1549	router_solicitation_interval - INTEGER
1550		Number of seconds to wait between Router Solicitations.
1551		Default: 4
1552	
1553	router_solicitations - INTEGER
1554		Number of Router Solicitations to send until assuming no
1555		routers are present.
1556		Default: 3
1557	
1558	use_oif_addrs_only - BOOLEAN
1559		When enabled, the candidate source addresses for destinations
1560		routed via this interface are restricted to the set of addresses
1561		configured on this interface (vis. RFC 6724, section 4).
1562	
1563		Default: false
1564	
1565	use_tempaddr - INTEGER
1566		Preference for Privacy Extensions (RFC3041).
1567		  <= 0 : disable Privacy Extensions
1568		  == 1 : enable Privacy Extensions, but prefer public
1569		         addresses over temporary addresses.
1570		  >  1 : enable Privacy Extensions and prefer temporary
1571		         addresses over public addresses.
1572		Default:  0 (for most devices)
1573			 -1 (for point-to-point devices and loopback devices)
1574	
1575	temp_valid_lft - INTEGER
1576		valid lifetime (in seconds) for temporary addresses.
1577		Default: 604800 (7 days)
1578	
1579	temp_prefered_lft - INTEGER
1580		Preferred lifetime (in seconds) for temporary addresses.
1581		Default: 86400 (1 day)
1582	
1583	keep_addr_on_down - INTEGER
1584		Keep all IPv6 addresses on an interface down event. If set static
1585		global addresses with no expiration time are not flushed.
1586		  >0 : enabled
1587		   0 : system default
1588		  <0 : disabled
1589	
1590		Default: 0 (addresses are removed)
1591	
1592	max_desync_factor - INTEGER
1593		Maximum value for DESYNC_FACTOR, which is a random value
1594		that ensures that clients don't synchronize with each
1595		other and generate new addresses at exactly the same time.
1596		value is in seconds.
1597		Default: 600
1598	
1599	regen_max_retry - INTEGER
1600		Number of attempts before give up attempting to generate
1601		valid temporary addresses.
1602		Default: 5
1603	
1604	max_addresses - INTEGER
1605		Maximum number of autoconfigured addresses per interface.  Setting
1606		to zero disables the limitation.  It is not recommended to set this
1607		value too large (or to zero) because it would be an easy way to
1608		crash the kernel by allowing too many addresses to be created.
1609		Default: 16
1610	
1611	disable_ipv6 - BOOLEAN
1612		Disable IPv6 operation.  If accept_dad is set to 2, this value
1613		will be dynamically set to TRUE if DAD fails for the link-local
1614		address.
1615		Default: FALSE (enable IPv6 operation)
1616	
1617		When this value is changed from 1 to 0 (IPv6 is being enabled),
1618		it will dynamically create a link-local address on the given
1619		interface and start Duplicate Address Detection, if necessary.
1620	
1621		When this value is changed from 0 to 1 (IPv6 is being disabled),
1622		it will dynamically delete all address on the given interface.
1623	
1624	accept_dad - INTEGER
1625		Whether to accept DAD (Duplicate Address Detection).
1626		0: Disable DAD
1627		1: Enable DAD (default)
1628		2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
1629		   link-local address has been found.
1630	
1631	force_tllao - BOOLEAN
1632		Enable sending the target link-layer address option even when
1633		responding to a unicast neighbor solicitation.
1634		Default: FALSE
1635	
1636		Quoting from RFC 2461, section 4.4, Target link-layer address:
1637	
1638		"The option MUST be included for multicast solicitations in order to
1639		avoid infinite Neighbor Solicitation "recursion" when the peer node
1640		does not have a cache entry to return a Neighbor Advertisements
1641		message.  When responding to unicast solicitations, the option can be
1642		omitted since the sender of the solicitation has the correct link-
1643		layer address; otherwise it would not have be able to send the unicast
1644		solicitation in the first place. However, including the link-layer
1645		address in this case adds little overhead and eliminates a potential
1646		race condition where the sender deletes the cached link-layer address
1647		prior to receiving a response to a previous solicitation."
1648	
1649	ndisc_notify - BOOLEAN
1650		Define mode for notification of address and device changes.
1651		0 - (default): do nothing
1652		1 - Generate unsolicited neighbour advertisements when device is brought
1653		    up or hardware address changes.
1654	
1655	mldv1_unsolicited_report_interval - INTEGER
1656		The interval in milliseconds in which the next unsolicited
1657		MLDv1 report retransmit will take place.
1658		Default: 10000 (10 seconds)
1659	
1660	mldv2_unsolicited_report_interval - INTEGER
1661		The interval in milliseconds in which the next unsolicited
1662		MLDv2 report retransmit will take place.
1663		Default: 1000 (1 second)
1664	
1665	force_mld_version - INTEGER
1666		0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed
1667		1 - Enforce to use MLD version 1
1668		2 - Enforce to use MLD version 2
1669	
1670	suppress_frag_ndisc - INTEGER
1671		Control RFC 6980 (Security Implications of IPv6 Fragmentation
1672		with IPv6 Neighbor Discovery) behavior:
1673		1 - (default) discard fragmented neighbor discovery packets
1674		0 - allow fragmented neighbor discovery packets
1675	
1676	optimistic_dad - BOOLEAN
1677		Whether to perform Optimistic Duplicate Address Detection (RFC 4429).
1678			0: disabled (default)
1679			1: enabled
1680	
1681	use_optimistic - BOOLEAN
1682		If enabled, do not classify optimistic addresses as deprecated during
1683		source address selection.  Preferred addresses will still be chosen
1684		before optimistic addresses, subject to other ranking in the source
1685		address selection algorithm.
1686			0: disabled (default)
1687			1: enabled
1688	
1689	stable_secret - IPv6 address
1690		This IPv6 address will be used as a secret to generate IPv6
1691		addresses for link-local addresses and autoconfigured
1692		ones. All addresses generated after setting this secret will
1693		be stable privacy ones by default. This can be changed via the
1694		addrgenmode ip-link. conf/default/stable_secret is used as the
1695		secret for the namespace, the interface specific ones can
1696		overwrite that. Writes to conf/all/stable_secret are refused.
1697	
1698		It is recommended to generate this secret during installation
1699		of a system and keep it stable after that.
1700	
1701		By default the stable secret is unset.
1702	
1703	drop_unicast_in_l2_multicast - BOOLEAN
1704		Drop any unicast IPv6 packets that are received in link-layer
1705		multicast (or broadcast) frames.
1706	
1707		By default this is turned off.
1708	
1709	drop_unsolicited_na - BOOLEAN
1710		Drop all unsolicited neighbor advertisements, for example if there's
1711		a known good NA proxy on the network and such frames need not be used
1712		(or in the case of 802.11, must not be used to prevent attacks.)
1713	
1714		By default this is turned off.
1715	
1716	icmp/*:
1717	ratelimit - INTEGER
1718		Limit the maximal rates for sending ICMPv6 packets.
1719		0 to disable any limiting,
1720		otherwise the minimal space between responses in milliseconds.
1721		Default: 1000
1722	
1723	xfrm6_gc_thresh - INTEGER
1724		The threshold at which we will start garbage collecting for IPv6
1725		destination cache entries.  At twice this value the system will
1726		refuse new allocations. The value must be set below the flowcache
1727		limit (4096 * number of online cpus) to take effect.
1728	
1729	
1730	IPv6 Update by:
1731	Pekka Savola <pekkas@netcore.fi>
1732	YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
1733	
1734	
1735	/proc/sys/net/bridge/* Variables:
1736	
1737	bridge-nf-call-arptables - BOOLEAN
1738		1 : pass bridged ARP traffic to arptables' FORWARD chain.
1739		0 : disable this.
1740		Default: 1
1741	
1742	bridge-nf-call-iptables - BOOLEAN
1743		1 : pass bridged IPv4 traffic to iptables' chains.
1744		0 : disable this.
1745		Default: 1
1746	
1747	bridge-nf-call-ip6tables - BOOLEAN
1748		1 : pass bridged IPv6 traffic to ip6tables' chains.
1749		0 : disable this.
1750		Default: 1
1751	
1752	bridge-nf-filter-vlan-tagged - BOOLEAN
1753		1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
1754		0 : disable this.
1755		Default: 0
1756	
1757	bridge-nf-filter-pppoe-tagged - BOOLEAN
1758		1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
1759		0 : disable this.
1760		Default: 0
1761	
1762	bridge-nf-pass-vlan-input-dev - BOOLEAN
1763		1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan
1764		interface on the bridge and set the netfilter input device to the vlan.
1765		This allows use of e.g. "iptables -i br0.1" and makes the REDIRECT
1766		target work with vlan-on-top-of-bridge interfaces.  When no matching
1767		vlan interface is found, or this switch is off, the input device is
1768		set to the bridge interface.
1769		0: disable bridge netfilter vlan interface lookup.
1770		Default: 0
1771	
1772	proc/sys/net/sctp/* Variables:
1773	
1774	addip_enable - BOOLEAN
1775		Enable or disable extension of  Dynamic Address Reconfiguration
1776		(ADD-IP) functionality specified in RFC5061.  This extension provides
1777		the ability to dynamically add and remove new addresses for the SCTP
1778		associations.
1779	
1780		1: Enable extension.
1781	
1782		0: Disable extension.
1783	
1784		Default: 0
1785	
1786	pf_enable - INTEGER
1787		Enable or disable pf (pf is short for potentially failed) state. A value
1788		of pf_retrans > path_max_retrans also disables pf state. That is, one of
1789		both pf_enable and pf_retrans > path_max_retrans can disable pf state.
1790		Since pf_retrans and path_max_retrans can be changed by userspace
1791		application, sometimes user expects to disable pf state by the value of
1792		pf_retrans > path_max_retrans, but occasionally the value of pf_retrans
1793		or path_max_retrans is changed by the user application, this pf state is
1794		enabled. As such, it is necessary to add this to dynamically enable
1795		and disable pf state. See:
1796		https://datatracker.ietf.org/doc/draft-ietf-tsvwg-sctp-failover for
1797		details.
1798	
1799		1: Enable pf.
1800	
1801		0: Disable pf.
1802	
1803		Default: 1
1804	
1805	addip_noauth_enable - BOOLEAN
1806		Dynamic Address Reconfiguration (ADD-IP) requires the use of
1807		authentication to protect the operations of adding or removing new
1808		addresses.  This requirement is mandated so that unauthorized hosts
1809		would not be able to hijack associations.  However, older
1810		implementations may not have implemented this requirement while
1811		allowing the ADD-IP extension.  For reasons of interoperability,
1812		we provide this variable to control the enforcement of the
1813		authentication requirement.
1814	
1815		1: Allow ADD-IP extension to be used without authentication.  This
1816		   should only be set in a closed environment for interoperability
1817		   with older implementations.
1818	
1819		0: Enforce the authentication requirement
1820	
1821		Default: 0
1822	
1823	auth_enable - BOOLEAN
1824		Enable or disable Authenticated Chunks extension.  This extension
1825		provides the ability to send and receive authenticated chunks and is
1826		required for secure operation of Dynamic Address Reconfiguration
1827		(ADD-IP) extension.
1828	
1829		1: Enable this extension.
1830		0: Disable this extension.
1831	
1832		Default: 0
1833	
1834	prsctp_enable - BOOLEAN
1835		Enable or disable the Partial Reliability extension (RFC3758) which
1836		is used to notify peers that a given DATA should no longer be expected.
1837	
1838		1: Enable extension
1839		0: Disable
1840	
1841		Default: 1
1842	
1843	max_burst - INTEGER
1844		The limit of the number of new packets that can be initially sent.  It
1845		controls how bursty the generated traffic can be.
1846	
1847		Default: 4
1848	
1849	association_max_retrans - INTEGER
1850		Set the maximum number for retransmissions that an association can
1851		attempt deciding that the remote end is unreachable.  If this value
1852		is exceeded, the association is terminated.
1853	
1854		Default: 10
1855	
1856	max_init_retransmits - INTEGER
1857		The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
1858		that an association will attempt before declaring the destination
1859		unreachable and terminating.
1860	
1861		Default: 8
1862	
1863	path_max_retrans - INTEGER
1864		The maximum number of retransmissions that will be attempted on a given
1865		path.  Once this threshold is exceeded, the path is considered
1866		unreachable, and new traffic will use a different path when the
1867		association is multihomed.
1868	
1869		Default: 5
1870	
1871	pf_retrans - INTEGER
1872		The number of retransmissions that will be attempted on a given path
1873		before traffic is redirected to an alternate transport (should one
1874		exist).  Note this is distinct from path_max_retrans, as a path that
1875		passes the pf_retrans threshold can still be used.  Its only
1876		deprioritized when a transmission path is selected by the stack.  This
1877		setting is primarily used to enable fast failover mechanisms without
1878		having to reduce path_max_retrans to a very low value.  See:
1879		http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt
1880		for details.  Note also that a value of pf_retrans > path_max_retrans
1881		disables this feature. Since both pf_retrans and path_max_retrans can
1882		be changed by userspace application, a variable pf_enable is used to
1883		disable pf state.
1884	
1885		Default: 0
1886	
1887	rto_initial - INTEGER
1888		The initial round trip timeout value in milliseconds that will be used
1889		in calculating round trip times.  This is the initial time interval
1890		for retransmissions.
1891	
1892		Default: 3000
1893	
1894	rto_max - INTEGER
1895		The maximum value (in milliseconds) of the round trip timeout.  This
1896		is the largest time interval that can elapse between retransmissions.
1897	
1898		Default: 60000
1899	
1900	rto_min - INTEGER
1901		The minimum value (in milliseconds) of the round trip timeout.  This
1902		is the smallest time interval the can elapse between retransmissions.
1903	
1904		Default: 1000
1905	
1906	hb_interval - INTEGER
1907		The interval (in milliseconds) between HEARTBEAT chunks.  These chunks
1908		are sent at the specified interval on idle paths to probe the state of
1909		a given path between 2 associations.
1910	
1911		Default: 30000
1912	
1913	sack_timeout - INTEGER
1914		The amount of time (in milliseconds) that the implementation will wait
1915		to send a SACK.
1916	
1917		Default: 200
1918	
1919	valid_cookie_life - INTEGER
1920		The default lifetime of the SCTP cookie (in milliseconds).  The cookie
1921		is used during association establishment.
1922	
1923		Default: 60000
1924	
1925	cookie_preserve_enable - BOOLEAN
1926		Enable or disable the ability to extend the lifetime of the SCTP cookie
1927		that is used during the establishment phase of SCTP association
1928	
1929		1: Enable cookie lifetime extension.
1930		0: Disable
1931	
1932		Default: 1
1933	
1934	cookie_hmac_alg - STRING
1935		Select the hmac algorithm used when generating the cookie value sent by
1936		a listening sctp socket to a connecting client in the INIT-ACK chunk.
1937		Valid values are:
1938		* md5
1939		* sha1
1940		* none
1941		Ability to assign md5 or sha1 as the selected alg is predicated on the
1942		configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and
1943		CONFIG_CRYPTO_SHA1).
1944	
1945		Default: Dependent on configuration.  MD5 if available, else SHA1 if
1946		available, else none.
1947	
1948	rcvbuf_policy - INTEGER
1949		Determines if the receive buffer is attributed to the socket or to
1950		association.   SCTP supports the capability to create multiple
1951		associations on a single socket.  When using this capability, it is
1952		possible that a single stalled association that's buffering a lot
1953		of data may block other associations from delivering their data by
1954		consuming all of the receive buffer space.  To work around this,
1955		the rcvbuf_policy could be set to attribute the receiver buffer space
1956		to each association instead of the socket.  This prevents the described
1957		blocking.
1958	
1959		1: rcvbuf space is per association
1960		0: rcvbuf space is per socket
1961	
1962		Default: 0
1963	
1964	sndbuf_policy - INTEGER
1965		Similar to rcvbuf_policy above, this applies to send buffer space.
1966	
1967		1: Send buffer is tracked per association
1968		0: Send buffer is tracked per socket.
1969	
1970		Default: 0
1971	
1972	sctp_mem - vector of 3 INTEGERs: min, pressure, max
1973		Number of pages allowed for queueing by all SCTP sockets.
1974	
1975		min: Below this number of pages SCTP is not bothered about its
1976		memory appetite. When amount of memory allocated by SCTP exceeds
1977		this number, SCTP starts to moderate memory usage.
1978	
1979		pressure: This value was introduced to follow format of tcp_mem.
1980	
1981		max: Number of pages allowed for queueing by all SCTP sockets.
1982	
1983		Default is calculated at boot time from amount of available memory.
1984	
1985	sctp_rmem - vector of 3 INTEGERs: min, default, max
1986		Only the first value ("min") is used, "default" and "max" are
1987		ignored.
1988	
1989		min: Minimal size of receive buffer used by SCTP socket.
1990		It is guaranteed to each SCTP socket (but not association) even
1991		under moderate memory pressure.
1992	
1993		Default: 1 page
1994	
1995	sctp_wmem  - vector of 3 INTEGERs: min, default, max
1996		Currently this tunable has no effect.
1997	
1998	addr_scope_policy - INTEGER
1999		Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00
2000	
2001		0   - Disable IPv4 address scoping
2002		1   - Enable IPv4 address scoping
2003		2   - Follow draft but allow IPv4 private addresses
2004		3   - Follow draft but allow IPv4 link local addresses
2005	
2006		Default: 1
2007	
2008	
2009	/proc/sys/net/core/*
2010		Please see: Documentation/sysctl/net.txt for descriptions of these entries.
2011	
2012	
2013	/proc/sys/net/unix/*
2014	max_dgram_qlen - INTEGER
2015		The maximum length of dgram socket receive queue
2016	
2017		Default: 10
2018	
2019	
2020	UNDOCUMENTED:
2021	
2022	/proc/sys/net/irda/*
2023		fast_poll_increase FIXME
2024		warn_noreply_time FIXME
2025		discovery_slots FIXME
2026		slot_timeout FIXME
2027		max_baud_rate FIXME
2028		discovery_timeout FIXME
2029		lap_keepalive_time FIXME
2030		max_noreply_time FIXME
2031		max_tx_data_size FIXME
2032		max_tx_window FIXME
2033		min_tx_turn_time FIXME
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