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Based on kernel version 4.1. Page generated on 2015-06-28 12:13 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	route/max_size - INTEGER
67		Maximum number of routes allowed in the kernel.  Increase
68		this when using large numbers of interfaces and/or routes.
69		From linux kernel 3.6 onwards, this is deprecated for ipv4
70		as route cache is no longer used.
71	
72	neigh/default/gc_thresh1 - INTEGER
73		Minimum number of entries to keep.  Garbage collector will not
74		purge entries if there are fewer than this number.
75		Default: 128
76	
77	neigh/default/gc_thresh2 - INTEGER
78		Threshold when garbage collector becomes more aggressive about
79		purging entries. Entries older than 5 seconds will be cleared
80		when over this number.
81		Default: 512
82	
83	neigh/default/gc_thresh3 - INTEGER
84		Maximum number of neighbor entries allowed.  Increase this
85		when using large numbers of interfaces and when communicating
86		with large numbers of directly-connected peers.
87		Default: 1024
88	
89	neigh/default/unres_qlen_bytes - INTEGER
90		The maximum number of bytes which may be used by packets
91		queued for each	unresolved address by other network layers.
92		(added in linux 3.3)
93		Setting negative value is meaningless and will return error.
94		Default: 65536 Bytes(64KB)
95	
96	neigh/default/unres_qlen - INTEGER
97		The maximum number of packets which may be queued for each
98		unresolved address by other network layers.
99		(deprecated in linux 3.3) : use unres_qlen_bytes instead.
100		Prior to linux 3.3, the default value is 3 which may cause
101		unexpected packet loss. The current default value is calculated
102		according to default value of unres_qlen_bytes and true size of
103		packet.
104		Default: 31
105	
106	mtu_expires - INTEGER
107		Time, in seconds, that cached PMTU information is kept.
108	
109	min_adv_mss - INTEGER
110		The advertised MSS depends on the first hop route MTU, but will
111		never be lower than this setting.
112	
113	IP Fragmentation:
114	
115	ipfrag_high_thresh - INTEGER
116		Maximum memory used to reassemble IP fragments. When
117		ipfrag_high_thresh bytes of memory is allocated for this purpose,
118		the fragment handler will toss packets until ipfrag_low_thresh
119		is reached. This also serves as a maximum limit to namespaces
120		different from the initial one.
121	
122	ipfrag_low_thresh - INTEGER
123		Maximum memory used to reassemble IP fragments before the kernel
124		begins to remove incomplete fragment queues to free up resources.
125		The kernel still accepts new fragments for defragmentation.
126	
127	ipfrag_time - INTEGER
128		Time in seconds to keep an IP fragment in memory.
129	
130	ipfrag_max_dist - INTEGER
131		ipfrag_max_dist is a non-negative integer value which defines the
132		maximum "disorder" which is allowed among fragments which share a
133		common IP source address. Note that reordering of packets is
134		not unusual, but if a large number of fragments arrive from a source
135		IP address while a particular fragment queue remains incomplete, it
136		probably indicates that one or more fragments belonging to that queue
137		have been lost. When ipfrag_max_dist is positive, an additional check
138		is done on fragments before they are added to a reassembly queue - if
139		ipfrag_max_dist (or more) fragments have arrived from a particular IP
140		address between additions to any IP fragment queue using that source
141		address, it's presumed that one or more fragments in the queue are
142		lost. The existing fragment queue will be dropped, and a new one
143		started. An ipfrag_max_dist value of zero disables this check.
144	
145		Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
146		result in unnecessarily dropping fragment queues when normal
147		reordering of packets occurs, which could lead to poor application
148		performance. Using a very large value, e.g. 50000, increases the
149		likelihood of incorrectly reassembling IP fragments that originate
150		from different IP datagrams, which could result in data corruption.
151		Default: 64
152	
153	INET peer storage:
154	
155	inet_peer_threshold - INTEGER
156		The approximate size of the storage.  Starting from this threshold
157		entries will be thrown aggressively.  This threshold also determines
158		entries' time-to-live and time intervals between garbage collection
159		passes.  More entries, less time-to-live, less GC interval.
160	
161	inet_peer_minttl - INTEGER
162		Minimum time-to-live of entries.  Should be enough to cover fragment
163		time-to-live on the reassembling side.  This minimum time-to-live  is
164		guaranteed if the pool size is less than inet_peer_threshold.
165		Measured in seconds.
166	
167	inet_peer_maxttl - INTEGER
168		Maximum time-to-live of entries.  Unused entries will expire after
169		this period of time if there is no memory pressure on the pool (i.e.
170		when the number of entries in the pool is very small).
171		Measured in seconds.
172	
173	TCP variables:
174	
175	somaxconn - INTEGER
176		Limit of socket listen() backlog, known in userspace as SOMAXCONN.
177		Defaults to 128.  See also tcp_max_syn_backlog for additional tuning
178		for TCP sockets.
179	
180	tcp_abort_on_overflow - BOOLEAN
181		If listening service is too slow to accept new connections,
182		reset them. Default state is FALSE. It means that if overflow
183		occurred due to a burst, connection will recover. Enable this
184		option _only_ if you are really sure that listening daemon
185		cannot be tuned to accept connections faster. Enabling this
186		option can harm clients of your server.
187	
188	tcp_adv_win_scale - INTEGER
189		Count buffering overhead as bytes/2^tcp_adv_win_scale
190		(if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
191		if it is <= 0.
192		Possible values are [-31, 31], inclusive.
193		Default: 1
194	
195	tcp_allowed_congestion_control - STRING
196		Show/set the congestion control choices available to non-privileged
197		processes. The list is a subset of those listed in
198		tcp_available_congestion_control.
199		Default is "reno" and the default setting (tcp_congestion_control).
200	
201	tcp_app_win - INTEGER
202		Reserve max(window/2^tcp_app_win, mss) of window for application
203		buffer. Value 0 is special, it means that nothing is reserved.
204		Default: 31
205	
206	tcp_autocorking - BOOLEAN
207		Enable TCP auto corking :
208		When applications do consecutive small write()/sendmsg() system calls,
209		we try to coalesce these small writes as much as possible, to lower
210		total amount of sent packets. This is done if at least one prior
211		packet for the flow is waiting in Qdisc queues or device transmit
212		queue. Applications can still use TCP_CORK for optimal behavior
213		when they know how/when to uncork their sockets.
214		Default : 1
215	
216	tcp_available_congestion_control - STRING
217		Shows the available congestion control choices that are registered.
218		More congestion control algorithms may be available as modules,
219		but not loaded.
220	
221	tcp_base_mss - INTEGER
222		The initial value of search_low to be used by the packetization layer
223		Path MTU discovery (MTU probing).  If MTU probing is enabled,
224		this is the initial MSS used by the connection.
225	
226	tcp_congestion_control - STRING
227		Set the congestion control algorithm to be used for new
228		connections. The algorithm "reno" is always available, but
229		additional choices may be available based on kernel configuration.
230		Default is set as part of kernel configuration.
231		For passive connections, the listener congestion control choice
232		is inherited.
233		[see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ]
234	
235	tcp_dsack - BOOLEAN
236		Allows TCP to send "duplicate" SACKs.
237	
238	tcp_early_retrans - INTEGER
239		Enable Early Retransmit (ER), per RFC 5827. ER lowers the threshold
240		for triggering fast retransmit when the amount of outstanding data is
241		small and when no previously unsent data can be transmitted (such
242		that limited transmit could be used). Also controls the use of
243		Tail loss probe (TLP) that converts RTOs occurring due to tail
244		losses into fast recovery (draft-dukkipati-tcpm-tcp-loss-probe-01).
245		Possible values:
246			0 disables ER
247			1 enables ER
248			2 enables ER but delays fast recovery and fast retransmit
249			  by a fourth of RTT. This mitigates connection falsely
250			  recovers when network has a small degree of reordering
251			  (less than 3 packets).
252			3 enables delayed ER and TLP.
253			4 enables TLP only.
254		Default: 3
255	
256	tcp_ecn - INTEGER
257		Control use of Explicit Congestion Notification (ECN) by TCP.
258		ECN is used only when both ends of the TCP connection indicate
259		support for it.  This feature is useful in avoiding losses due
260		to congestion by allowing supporting routers to signal
261		congestion before having to drop packets.
262		Possible values are:
263			0 Disable ECN.  Neither initiate nor accept ECN.
264			1 Enable ECN when requested by incoming connections and
265			  also request ECN on outgoing connection attempts.
266			2 Enable ECN when requested by incoming connections
267			  but do not request ECN on outgoing connections.
268		Default: 2
269	
270	tcp_fack - BOOLEAN
271		Enable FACK congestion avoidance and fast retransmission.
272		The value is not used, if tcp_sack is not enabled.
273	
274	tcp_fin_timeout - INTEGER
275		The length of time an orphaned (no longer referenced by any
276		application) connection will remain in the FIN_WAIT_2 state
277		before it is aborted at the local end.  While a perfectly
278		valid "receive only" state for an un-orphaned connection, an
279		orphaned connection in FIN_WAIT_2 state could otherwise wait
280		forever for the remote to close its end of the connection.
281		Cf. tcp_max_orphans
282		Default: 60 seconds
283	
284	tcp_frto - INTEGER
285		Enables Forward RTO-Recovery (F-RTO) defined in RFC5682.
286		F-RTO is an enhanced recovery algorithm for TCP retransmission
287		timeouts.  It is particularly beneficial in networks where the
288		RTT fluctuates (e.g., wireless). F-RTO is sender-side only
289		modification. It does not require any support from the peer.
290	
291		By default it's enabled with a non-zero value. 0 disables F-RTO.
292	
293	tcp_invalid_ratelimit - INTEGER
294		Limit the maximal rate for sending duplicate acknowledgments
295		in response to incoming TCP packets that are for an existing
296		connection but that are invalid due to any of these reasons:
297	
298		  (a) out-of-window sequence number,
299		  (b) out-of-window acknowledgment number, or
300		  (c) PAWS (Protection Against Wrapped Sequence numbers) check failure
301	
302		This can help mitigate simple "ack loop" DoS attacks, wherein
303		a buggy or malicious middlebox or man-in-the-middle can
304		rewrite TCP header fields in manner that causes each endpoint
305		to think that the other is sending invalid TCP segments, thus
306		causing each side to send an unterminating stream of duplicate
307		acknowledgments for invalid segments.
308	
309		Using 0 disables rate-limiting of dupacks in response to
310		invalid segments; otherwise this value specifies the minimal
311		space between sending such dupacks, in milliseconds.
312	
313		Default: 500 (milliseconds).
314	
315	tcp_keepalive_time - INTEGER
316		How often TCP sends out keepalive messages when keepalive is enabled.
317		Default: 2hours.
318	
319	tcp_keepalive_probes - INTEGER
320		How many keepalive probes TCP sends out, until it decides that the
321		connection is broken. Default value: 9.
322	
323	tcp_keepalive_intvl - INTEGER
324		How frequently the probes are send out. Multiplied by
325		tcp_keepalive_probes it is time to kill not responding connection,
326		after probes started. Default value: 75sec i.e. connection
327		will be aborted after ~11 minutes of retries.
328	
329	tcp_low_latency - BOOLEAN
330		If set, the TCP stack makes decisions that prefer lower
331		latency as opposed to higher throughput.  By default, this
332		option is not set meaning that higher throughput is preferred.
333		An example of an application where this default should be
334		changed would be a Beowulf compute cluster.
335		Default: 0
336	
337	tcp_max_orphans - INTEGER
338		Maximal number of TCP sockets not attached to any user file handle,
339		held by system.	If this number is exceeded orphaned connections are
340		reset immediately and warning is printed. This limit exists
341		only to prevent simple DoS attacks, you _must_ not rely on this
342		or lower the limit artificially, but rather increase it
343		(probably, after increasing installed memory),
344		if network conditions require more than default value,
345		and tune network services to linger and kill such states
346		more aggressively. Let me to remind again: each orphan eats
347		up to ~64K of unswappable memory.
348	
349	tcp_max_syn_backlog - INTEGER
350		Maximal number of remembered connection requests, which have not
351		received an acknowledgment from connecting client.
352		The minimal value is 128 for low memory machines, and it will
353		increase in proportion to the memory of machine.
354		If server suffers from overload, try increasing this number.
355	
356	tcp_max_tw_buckets - INTEGER
357		Maximal number of timewait sockets held by system simultaneously.
358		If this number is exceeded time-wait socket is immediately destroyed
359		and warning is printed. This limit exists only to prevent
360		simple DoS attacks, you _must_ not lower the limit artificially,
361		but rather increase it (probably, after increasing installed memory),
362		if network conditions require more than default value.
363	
364	tcp_mem - vector of 3 INTEGERs: min, pressure, max
365		min: below this number of pages TCP is not bothered about its
366		memory appetite.
367	
368		pressure: when amount of memory allocated by TCP exceeds this number
369		of pages, TCP moderates its memory consumption and enters memory
370		pressure mode, which is exited when memory consumption falls
371		under "min".
372	
373		max: number of pages allowed for queueing by all TCP sockets.
374	
375		Defaults are calculated at boot time from amount of available
376		memory.
377	
378	tcp_moderate_rcvbuf - BOOLEAN
379		If set, TCP performs receive buffer auto-tuning, attempting to
380		automatically size the buffer (no greater than tcp_rmem[2]) to
381		match the size required by the path for full throughput.  Enabled by
382		default.
383	
384	tcp_mtu_probing - INTEGER
385		Controls TCP Packetization-Layer Path MTU Discovery.  Takes three
386		values:
387		  0 - Disabled
388		  1 - Disabled by default, enabled when an ICMP black hole detected
389		  2 - Always enabled, use initial MSS of tcp_base_mss.
390	
391	tcp_probe_interval - INTEGER
392		Controls how often to start TCP Packetization-Layer Path MTU
393		Discovery reprobe. The default is reprobing every 10 minutes as
394		per RFC4821.
395	
396	tcp_probe_threshold - INTEGER
397		Controls when TCP Packetization-Layer Path MTU Discovery probing
398		will stop in respect to the width of search range in bytes. Default
399		is 8 bytes.
400	
401	tcp_no_metrics_save - BOOLEAN
402		By default, TCP saves various connection metrics in the route cache
403		when the connection closes, so that connections established in the
404		near future can use these to set initial conditions.  Usually, this
405		increases overall performance, but may sometimes cause performance
406		degradation.  If set, TCP will not cache metrics on closing
407		connections.
408	
409	tcp_orphan_retries - INTEGER
410		This value influences the timeout of a locally closed TCP connection,
411		when RTO retransmissions remain unacknowledged.
412		See tcp_retries2 for more details.
413	
414		The default value is 8.
415		If your machine is a loaded WEB server,
416		you should think about lowering this value, such sockets
417		may consume significant resources. Cf. tcp_max_orphans.
418	
419	tcp_reordering - INTEGER
420		Initial reordering level of packets in a TCP stream.
421		TCP stack can then dynamically adjust flow reordering level
422		between this initial value and tcp_max_reordering
423		Default: 3
424	
425	tcp_max_reordering - INTEGER
426		Maximal reordering level of packets in a TCP stream.
427		300 is a fairly conservative value, but you might increase it
428		if paths are using per packet load balancing (like bonding rr mode)
429		Default: 300
430	
431	tcp_retrans_collapse - BOOLEAN
432		Bug-to-bug compatibility with some broken printers.
433		On retransmit try to send bigger packets to work around bugs in
434		certain TCP stacks.
435	
436	tcp_retries1 - INTEGER
437		This value influences the time, after which TCP decides, that
438		something is wrong due to unacknowledged RTO retransmissions,
439		and reports this suspicion to the network layer.
440		See tcp_retries2 for more details.
441	
442		RFC 1122 recommends at least 3 retransmissions, which is the
443		default.
444	
445	tcp_retries2 - INTEGER
446		This value influences the timeout of an alive TCP connection,
447		when RTO retransmissions remain unacknowledged.
448		Given a value of N, a hypothetical TCP connection following
449		exponential backoff with an initial RTO of TCP_RTO_MIN would
450		retransmit N times before killing the connection at the (N+1)th RTO.
451	
452		The default value of 15 yields a hypothetical timeout of 924.6
453		seconds and is a lower bound for the effective timeout.
454		TCP will effectively time out at the first RTO which exceeds the
455		hypothetical timeout.
456	
457		RFC 1122 recommends at least 100 seconds for the timeout,
458		which corresponds to a value of at least 8.
459	
460	tcp_rfc1337 - BOOLEAN
461		If set, the TCP stack behaves conforming to RFC1337. If unset,
462		we are not conforming to RFC, but prevent TCP TIME_WAIT
463		assassination.
464		Default: 0
465	
466	tcp_rmem - vector of 3 INTEGERs: min, default, max
467		min: Minimal size of receive buffer used by TCP sockets.
468		It is guaranteed to each TCP socket, even under moderate memory
469		pressure.
470		Default: 1 page
471	
472		default: initial size of receive buffer used by TCP sockets.
473		This value overrides net.core.rmem_default used by other protocols.
474		Default: 87380 bytes. This value results in window of 65535 with
475		default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
476		less for default tcp_app_win. See below about these variables.
477	
478		max: maximal size of receive buffer allowed for automatically
479		selected receiver buffers for TCP socket. This value does not override
480		net.core.rmem_max.  Calling setsockopt() with SO_RCVBUF disables
481		automatic tuning of that socket's receive buffer size, in which
482		case this value is ignored.
483		Default: between 87380B and 6MB, depending on RAM size.
484	
485	tcp_sack - BOOLEAN
486		Enable select acknowledgments (SACKS).
487	
488	tcp_slow_start_after_idle - BOOLEAN
489		If set, provide RFC2861 behavior and time out the congestion
490		window after an idle period.  An idle period is defined at
491		the current RTO.  If unset, the congestion window will not
492		be timed out after an idle period.
493		Default: 1
494	
495	tcp_stdurg - BOOLEAN
496		Use the Host requirements interpretation of the TCP urgent pointer field.
497		Most hosts use the older BSD interpretation, so if you turn this on
498		Linux might not communicate correctly with them.
499		Default: FALSE
500	
501	tcp_synack_retries - INTEGER
502		Number of times SYNACKs for a passive TCP connection attempt will
503		be retransmitted. Should not be higher than 255. Default value
504		is 5, which corresponds to 31seconds till the last retransmission
505		with the current initial RTO of 1second. With this the final timeout
506		for a passive TCP connection will happen after 63seconds.
507	
508	tcp_syncookies - BOOLEAN
509		Only valid when the kernel was compiled with CONFIG_SYN_COOKIES
510		Send out syncookies when the syn backlog queue of a socket
511		overflows. This is to prevent against the common 'SYN flood attack'
512		Default: 1
513	
514		Note, that syncookies is fallback facility.
515		It MUST NOT be used to help highly loaded servers to stand
516		against legal connection rate. If you see SYN flood warnings
517		in your logs, but investigation	shows that they occur
518		because of overload with legal connections, you should tune
519		another parameters until this warning disappear.
520		See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
521	
522		syncookies seriously violate TCP protocol, do not allow
523		to use TCP extensions, can result in serious degradation
524		of some services (f.e. SMTP relaying), visible not by you,
525		but your clients and relays, contacting you. While you see
526		SYN flood warnings in logs not being really flooded, your server
527		is seriously misconfigured.
528	
529		If you want to test which effects syncookies have to your
530		network connections you can set this knob to 2 to enable
531		unconditionally generation of syncookies.
532	
533	tcp_fastopen - INTEGER
534		Enable TCP Fast Open feature (draft-ietf-tcpm-fastopen) to send data
535		in the opening SYN packet. To use this feature, the client application
536		must use sendmsg() or sendto() with MSG_FASTOPEN flag rather than
537		connect() to perform a TCP handshake automatically.
538	
539		The values (bitmap) are
540		1: Enables sending data in the opening SYN on the client w/ MSG_FASTOPEN.
541		2: Enables TCP Fast Open on the server side, i.e., allowing data in
542		   a SYN packet to be accepted and passed to the application before
543		   3-way hand shake finishes.
544		4: Send data in the opening SYN regardless of cookie availability and
545		   without a cookie option.
546		0x100: Accept SYN data w/o validating the cookie.
547		0x200: Accept data-in-SYN w/o any cookie option present.
548		0x400/0x800: Enable Fast Open on all listeners regardless of the
549		   TCP_FASTOPEN socket option. The two different flags designate two
550		   different ways of setting max_qlen without the TCP_FASTOPEN socket
551		   option.
552	
553		Default: 1
554	
555		Note that the client & server side Fast Open flags (1 and 2
556		respectively) must be also enabled before the rest of flags can take
557		effect.
558	
559		See include/net/tcp.h and the code for more details.
560	
561	tcp_syn_retries - INTEGER
562		Number of times initial SYNs for an active TCP connection attempt
563		will be retransmitted. Should not be higher than 255. Default value
564		is 6, which corresponds to 63seconds till the last retransmission
565		with the current initial RTO of 1second. With this the final timeout
566		for an active TCP connection attempt will happen after 127seconds.
567	
568	tcp_timestamps - BOOLEAN
569		Enable timestamps as defined in RFC1323.
570	
571	tcp_min_tso_segs - INTEGER
572		Minimal number of segments per TSO frame.
573		Since linux-3.12, TCP does an automatic sizing of TSO frames,
574		depending on flow rate, instead of filling 64Kbytes packets.
575		For specific usages, it's possible to force TCP to build big
576		TSO frames. Note that TCP stack might split too big TSO packets
577		if available window is too small.
578		Default: 2
579	
580	tcp_tso_win_divisor - INTEGER
581		This allows control over what percentage of the congestion window
582		can be consumed by a single TSO frame.
583		The setting of this parameter is a choice between burstiness and
584		building larger TSO frames.
585		Default: 3
586	
587	tcp_tw_recycle - BOOLEAN
588		Enable fast recycling TIME-WAIT sockets. Default value is 0.
589		It should not be changed without advice/request of technical
590		experts.
591	
592	tcp_tw_reuse - BOOLEAN
593		Allow to reuse TIME-WAIT sockets for new connections when it is
594		safe from protocol viewpoint. Default value is 0.
595		It should not be changed without advice/request of technical
596		experts.
597	
598	tcp_window_scaling - BOOLEAN
599		Enable window scaling as defined in RFC1323.
600	
601	tcp_wmem - vector of 3 INTEGERs: min, default, max
602		min: Amount of memory reserved for send buffers for TCP sockets.
603		Each TCP socket has rights to use it due to fact of its birth.
604		Default: 1 page
605	
606		default: initial size of send buffer used by TCP sockets.  This
607		value overrides net.core.wmem_default used by other protocols.
608		It is usually lower than net.core.wmem_default.
609		Default: 16K
610	
611		max: Maximal amount of memory allowed for automatically tuned
612		send buffers for TCP sockets. This value does not override
613		net.core.wmem_max.  Calling setsockopt() with SO_SNDBUF disables
614		automatic tuning of that socket's send buffer size, in which case
615		this value is ignored.
616		Default: between 64K and 4MB, depending on RAM size.
617	
618	tcp_notsent_lowat - UNSIGNED INTEGER
619		A TCP socket can control the amount of unsent bytes in its write queue,
620		thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll()
621		reports POLLOUT events if the amount of unsent bytes is below a per
622		socket value, and if the write queue is not full. sendmsg() will
623		also not add new buffers if the limit is hit.
624	
625		This global variable controls the amount of unsent data for
626		sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change
627		to the global variable has immediate effect.
628	
629		Default: UINT_MAX (0xFFFFFFFF)
630	
631	tcp_workaround_signed_windows - BOOLEAN
632		If set, assume no receipt of a window scaling option means the
633		remote TCP is broken and treats the window as a signed quantity.
634		If unset, assume the remote TCP is not broken even if we do
635		not receive a window scaling option from them.
636		Default: 0
637	
638	tcp_thin_linear_timeouts - BOOLEAN
639		Enable dynamic triggering of linear timeouts for thin streams.
640		If set, a check is performed upon retransmission by timeout to
641		determine if the stream is thin (less than 4 packets in flight).
642		As long as the stream is found to be thin, up to 6 linear
643		timeouts may be performed before exponential backoff mode is
644		initiated. This improves retransmission latency for
645		non-aggressive thin streams, often found to be time-dependent.
646		For more information on thin streams, see
647		Documentation/networking/tcp-thin.txt
648		Default: 0
649	
650	tcp_thin_dupack - BOOLEAN
651		Enable dynamic triggering of retransmissions after one dupACK
652		for thin streams. If set, a check is performed upon reception
653		of a dupACK to determine if the stream is thin (less than 4
654		packets in flight). As long as the stream is found to be thin,
655		data is retransmitted on the first received dupACK. This
656		improves retransmission latency for non-aggressive thin
657		streams, often found to be time-dependent.
658		For more information on thin streams, see
659		Documentation/networking/tcp-thin.txt
660		Default: 0
661	
662	tcp_limit_output_bytes - INTEGER
663		Controls TCP Small Queue limit per tcp socket.
664		TCP bulk sender tends to increase packets in flight until it
665		gets losses notifications. With SNDBUF autotuning, this can
666		result in a large amount of packets queued in qdisc/device
667		on the local machine, hurting latency of other flows, for
668		typical pfifo_fast qdiscs.
669		tcp_limit_output_bytes limits the number of bytes on qdisc
670		or device to reduce artificial RTT/cwnd and reduce bufferbloat.
671		Default: 131072
672	
673	tcp_challenge_ack_limit - INTEGER
674		Limits number of Challenge ACK sent per second, as recommended
675		in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
676		Default: 100
677	
678	UDP variables:
679	
680	udp_mem - vector of 3 INTEGERs: min, pressure, max
681		Number of pages allowed for queueing by all UDP sockets.
682	
683		min: Below this number of pages UDP is not bothered about its
684		memory appetite. When amount of memory allocated by UDP exceeds
685		this number, UDP starts to moderate memory usage.
686	
687		pressure: This value was introduced to follow format of tcp_mem.
688	
689		max: Number of pages allowed for queueing by all UDP sockets.
690	
691		Default is calculated at boot time from amount of available memory.
692	
693	udp_rmem_min - INTEGER
694		Minimal size of receive buffer used by UDP sockets in moderation.
695		Each UDP socket is able to use the size for receiving data, even if
696		total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
697		Default: 1 page
698	
699	udp_wmem_min - INTEGER
700		Minimal size of send buffer used by UDP sockets in moderation.
701		Each UDP socket is able to use the size for sending data, even if
702		total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
703		Default: 1 page
704	
705	CIPSOv4 Variables:
706	
707	cipso_cache_enable - BOOLEAN
708		If set, enable additions to and lookups from the CIPSO label mapping
709		cache.  If unset, additions are ignored and lookups always result in a
710		miss.  However, regardless of the setting the cache is still
711		invalidated when required when means you can safely toggle this on and
712		off and the cache will always be "safe".
713		Default: 1
714	
715	cipso_cache_bucket_size - INTEGER
716		The CIPSO label cache consists of a fixed size hash table with each
717		hash bucket containing a number of cache entries.  This variable limits
718		the number of entries in each hash bucket; the larger the value the
719		more CIPSO label mappings that can be cached.  When the number of
720		entries in a given hash bucket reaches this limit adding new entries
721		causes the oldest entry in the bucket to be removed to make room.
722		Default: 10
723	
724	cipso_rbm_optfmt - BOOLEAN
725		Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
726		the CIPSO draft specification (see Documentation/netlabel for details).
727		This means that when set the CIPSO tag will be padded with empty
728		categories in order to make the packet data 32-bit aligned.
729		Default: 0
730	
731	cipso_rbm_structvalid - BOOLEAN
732		If set, do a very strict check of the CIPSO option when
733		ip_options_compile() is called.  If unset, relax the checks done during
734		ip_options_compile().  Either way is "safe" as errors are caught else
735		where in the CIPSO processing code but setting this to 0 (False) should
736		result in less work (i.e. it should be faster) but could cause problems
737		with other implementations that require strict checking.
738		Default: 0
739	
740	IP Variables:
741	
742	ip_local_port_range - 2 INTEGERS
743		Defines the local port range that is used by TCP and UDP to
744		choose the local port. The first number is the first, the
745		second the last local port number. The default values are
746		32768 and 61000 respectively.
747	
748	ip_local_reserved_ports - list of comma separated ranges
749		Specify the ports which are reserved for known third-party
750		applications. These ports will not be used by automatic port
751		assignments (e.g. when calling connect() or bind() with port
752		number 0). Explicit port allocation behavior is unchanged.
753	
754		The format used for both input and output is a comma separated
755		list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and
756		10). Writing to the file will clear all previously reserved
757		ports and update the current list with the one given in the
758		input.
759	
760		Note that ip_local_port_range and ip_local_reserved_ports
761		settings are independent and both are considered by the kernel
762		when determining which ports are available for automatic port
763		assignments.
764	
765		You can reserve ports which are not in the current
766		ip_local_port_range, e.g.:
767	
768		$ cat /proc/sys/net/ipv4/ip_local_port_range
769		32000	61000
770		$ cat /proc/sys/net/ipv4/ip_local_reserved_ports
771		8080,9148
772	
773		although this is redundant. However such a setting is useful
774		if later the port range is changed to a value that will
775		include the reserved ports.
776	
777		Default: Empty
778	
779	ip_nonlocal_bind - BOOLEAN
780		If set, allows processes to bind() to non-local IP addresses,
781		which can be quite useful - but may break some applications.
782		Default: 0
783	
784	ip_dynaddr - BOOLEAN
785		If set non-zero, enables support for dynamic addresses.
786		If set to a non-zero value larger than 1, a kernel log
787		message will be printed when dynamic address rewriting
788		occurs.
789		Default: 0
790	
791	ip_early_demux - BOOLEAN
792		Optimize input packet processing down to one demux for
793		certain kinds of local sockets.  Currently we only do this
794		for established TCP sockets.
795	
796		It may add an additional cost for pure routing workloads that
797		reduces overall throughput, in such case you should disable it.
798		Default: 1
799	
800	icmp_echo_ignore_all - BOOLEAN
801		If set non-zero, then the kernel will ignore all ICMP ECHO
802		requests sent to it.
803		Default: 0
804	
805	icmp_echo_ignore_broadcasts - BOOLEAN
806		If set non-zero, then the kernel will ignore all ICMP ECHO and
807		TIMESTAMP requests sent to it via broadcast/multicast.
808		Default: 1
809	
810	icmp_ratelimit - INTEGER
811		Limit the maximal rates for sending ICMP packets whose type matches
812		icmp_ratemask (see below) to specific targets.
813		0 to disable any limiting,
814		otherwise the minimal space between responses in milliseconds.
815		Note that another sysctl, icmp_msgs_per_sec limits the number
816		of ICMP packets	sent on all targets.
817		Default: 1000
818	
819	icmp_msgs_per_sec - INTEGER
820		Limit maximal number of ICMP packets sent per second from this host.
821		Only messages whose type matches icmp_ratemask (see below) are
822		controlled by this limit.
823		Default: 1000
824	
825	icmp_msgs_burst - INTEGER
826		icmp_msgs_per_sec controls number of ICMP packets sent per second,
827		while icmp_msgs_burst controls the burst size of these packets.
828		Default: 50
829	
830	icmp_ratemask - INTEGER
831		Mask made of ICMP types for which rates are being limited.
832		Significant bits: IHGFEDCBA9876543210
833		Default mask:     0000001100000011000 (6168)
834	
835		Bit definitions (see include/linux/icmp.h):
836			0 Echo Reply
837			3 Destination Unreachable *
838			4 Source Quench *
839			5 Redirect
840			8 Echo Request
841			B Time Exceeded *
842			C Parameter Problem *
843			D Timestamp Request
844			E Timestamp Reply
845			F Info Request
846			G Info Reply
847			H Address Mask Request
848			I Address Mask Reply
849	
850		* These are rate limited by default (see default mask above)
851	
852	icmp_ignore_bogus_error_responses - BOOLEAN
853		Some routers violate RFC1122 by sending bogus responses to broadcast
854		frames.  Such violations are normally logged via a kernel warning.
855		If this is set to TRUE, the kernel will not give such warnings, which
856		will avoid log file clutter.
857		Default: 1
858	
859	icmp_errors_use_inbound_ifaddr - BOOLEAN
860	
861		If zero, icmp error messages are sent with the primary address of
862		the exiting interface.
863	
864		If non-zero, the message will be sent with the primary address of
865		the interface that received the packet that caused the icmp error.
866		This is the behaviour network many administrators will expect from
867		a router. And it can make debugging complicated network layouts
868		much easier.
869	
870		Note that if no primary address exists for the interface selected,
871		then the primary address of the first non-loopback interface that
872		has one will be used regardless of this setting.
873	
874		Default: 0
875	
876	igmp_max_memberships - INTEGER
877		Change the maximum number of multicast groups we can subscribe to.
878		Default: 20
879	
880		Theoretical maximum value is bounded by having to send a membership
881		report in a single datagram (i.e. the report can't span multiple
882		datagrams, or risk confusing the switch and leaving groups you don't
883		intend to).
884	
885		The number of supported groups 'M' is bounded by the number of group
886		report entries you can fit into a single datagram of 65535 bytes.
887	
888		M = 65536-sizeof (ip header)/(sizeof(Group record))
889	
890		Group records are variable length, with a minimum of 12 bytes.
891		So net.ipv4.igmp_max_memberships should not be set higher than:
892	
893		(65536-24) / 12 = 5459
894	
895		The value 5459 assumes no IP header options, so in practice
896		this number may be lower.
897	
898		conf/interface/*  changes special settings per interface (where
899		"interface" is the name of your network interface)
900	
901		conf/all/*	  is special, changes the settings for all interfaces
902	
903	igmp_qrv - INTEGER
904		 Controls the IGMP query robustness variable (see RFC2236 8.1).
905		 Default: 2 (as specified by RFC2236 8.1)
906		 Minimum: 1 (as specified by RFC6636 4.5)
907	
908	log_martians - BOOLEAN
909		Log packets with impossible addresses to kernel log.
910		log_martians for the interface will be enabled if at least one of
911		conf/{all,interface}/log_martians is set to TRUE,
912		it will be disabled otherwise
913	
914	accept_redirects - BOOLEAN
915		Accept ICMP redirect messages.
916		accept_redirects for the interface will be enabled if:
917		- both conf/{all,interface}/accept_redirects are TRUE in the case
918		  forwarding for the interface is enabled
919		or
920		- at least one of conf/{all,interface}/accept_redirects is TRUE in the
921		  case forwarding for the interface is disabled
922		accept_redirects for the interface will be disabled otherwise
923		default TRUE (host)
924			FALSE (router)
925	
926	forwarding - BOOLEAN
927		Enable IP forwarding on this interface.
928	
929	mc_forwarding - BOOLEAN
930		Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
931		and a multicast routing daemon is required.
932		conf/all/mc_forwarding must also be set to TRUE to enable multicast
933		routing	for the interface
934	
935	medium_id - INTEGER
936		Integer value used to differentiate the devices by the medium they
937		are attached to. Two devices can have different id values when
938		the broadcast packets are received only on one of them.
939		The default value 0 means that the device is the only interface
940		to its medium, value of -1 means that medium is not known.
941	
942		Currently, it is used to change the proxy_arp behavior:
943		the proxy_arp feature is enabled for packets forwarded between
944		two devices attached to different media.
945	
946	proxy_arp - BOOLEAN
947		Do proxy arp.
948		proxy_arp for the interface will be enabled if at least one of
949		conf/{all,interface}/proxy_arp is set to TRUE,
950		it will be disabled otherwise
951	
952	proxy_arp_pvlan - BOOLEAN
953		Private VLAN proxy arp.
954		Basically allow proxy arp replies back to the same interface
955		(from which the ARP request/solicitation was received).
956	
957		This is done to support (ethernet) switch features, like RFC
958		3069, where the individual ports are NOT allowed to
959		communicate with each other, but they are allowed to talk to
960		the upstream router.  As described in RFC 3069, it is possible
961		to allow these hosts to communicate through the upstream
962		router by proxy_arp'ing. Don't need to be used together with
963		proxy_arp.
964	
965		This technology is known by different names:
966		  In RFC 3069 it is called VLAN Aggregation.
967		  Cisco and Allied Telesyn call it Private VLAN.
968		  Hewlett-Packard call it Source-Port filtering or port-isolation.
969		  Ericsson call it MAC-Forced Forwarding (RFC Draft).
970	
971	shared_media - BOOLEAN
972		Send(router) or accept(host) RFC1620 shared media redirects.
973		Overrides ip_secure_redirects.
974		shared_media for the interface will be enabled if at least one of
975		conf/{all,interface}/shared_media is set to TRUE,
976		it will be disabled otherwise
977		default TRUE
978	
979	secure_redirects - BOOLEAN
980		Accept ICMP redirect messages only for gateways,
981		listed in default gateway list.
982		secure_redirects for the interface will be enabled if at least one of
983		conf/{all,interface}/secure_redirects is set to TRUE,
984		it will be disabled otherwise
985		default TRUE
986	
987	send_redirects - BOOLEAN
988		Send redirects, if router.
989		send_redirects for the interface will be enabled if at least one of
990		conf/{all,interface}/send_redirects is set to TRUE,
991		it will be disabled otherwise
992		Default: TRUE
993	
994	bootp_relay - BOOLEAN
995		Accept packets with source address 0.b.c.d destined
996		not to this host as local ones. It is supposed, that
997		BOOTP relay daemon will catch and forward such packets.
998		conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
999		for the interface
1000		default FALSE
1001		Not Implemented Yet.
1002	
1003	accept_source_route - BOOLEAN
1004		Accept packets with SRR option.
1005		conf/all/accept_source_route must also be set to TRUE to accept packets
1006		with SRR option on the interface
1007		default TRUE (router)
1008			FALSE (host)
1009	
1010	accept_local - BOOLEAN
1011		Accept packets with local source addresses. In combination with
1012		suitable routing, this can be used to direct packets between two
1013		local interfaces over the wire and have them accepted properly.
1014		default FALSE
1015	
1016	route_localnet - BOOLEAN
1017		Do not consider loopback addresses as martian source or destination
1018		while routing. This enables the use of 127/8 for local routing purposes.
1019		default FALSE
1020	
1021	rp_filter - INTEGER
1022		0 - No source validation.
1023		1 - Strict mode as defined in RFC3704 Strict Reverse Path
1024		    Each incoming packet is tested against the FIB and if the interface
1025		    is not the best reverse path the packet check will fail.
1026		    By default failed packets are discarded.
1027		2 - Loose mode as defined in RFC3704 Loose Reverse Path
1028		    Each incoming packet's source address is also tested against the FIB
1029		    and if the source address is not reachable via any interface
1030		    the packet check will fail.
1031	
1032		Current recommended practice in RFC3704 is to enable strict mode
1033		to prevent IP spoofing from DDos attacks. If using asymmetric routing
1034		or other complicated routing, then loose mode is recommended.
1035	
1036		The max value from conf/{all,interface}/rp_filter is used
1037		when doing source validation on the {interface}.
1038	
1039		Default value is 0. Note that some distributions enable it
1040		in startup scripts.
1041	
1042	arp_filter - BOOLEAN
1043		1 - Allows you to have multiple network interfaces on the same
1044		subnet, and have the ARPs for each interface be answered
1045		based on whether or not the kernel would route a packet from
1046		the ARP'd IP out that interface (therefore you must use source
1047		based routing for this to work). In other words it allows control
1048		of which cards (usually 1) will respond to an arp request.
1049	
1050		0 - (default) The kernel can respond to arp requests with addresses
1051		from other interfaces. This may seem wrong but it usually makes
1052		sense, because it increases the chance of successful communication.
1053		IP addresses are owned by the complete host on Linux, not by
1054		particular interfaces. Only for more complex setups like load-
1055		balancing, does this behaviour cause problems.
1056	
1057		arp_filter for the interface will be enabled if at least one of
1058		conf/{all,interface}/arp_filter is set to TRUE,
1059		it will be disabled otherwise
1060	
1061	arp_announce - INTEGER
1062		Define different restriction levels for announcing the local
1063		source IP address from IP packets in ARP requests sent on
1064		interface:
1065		0 - (default) Use any local address, configured on any interface
1066		1 - Try to avoid local addresses that are not in the target's
1067		subnet for this interface. This mode is useful when target
1068		hosts reachable via this interface require the source IP
1069		address in ARP requests to be part of their logical network
1070		configured on the receiving interface. When we generate the
1071		request we will check all our subnets that include the
1072		target IP and will preserve the source address if it is from
1073		such subnet. If there is no such subnet we select source
1074		address according to the rules for level 2.
1075		2 - Always use the best local address for this target.
1076		In this mode we ignore the source address in the IP packet
1077		and try to select local address that we prefer for talks with
1078		the target host. Such local address is selected by looking
1079		for primary IP addresses on all our subnets on the outgoing
1080		interface that include the target IP address. If no suitable
1081		local address is found we select the first local address
1082		we have on the outgoing interface or on all other interfaces,
1083		with the hope we will receive reply for our request and
1084		even sometimes no matter the source IP address we announce.
1085	
1086		The max value from conf/{all,interface}/arp_announce is used.
1087	
1088		Increasing the restriction level gives more chance for
1089		receiving answer from the resolved target while decreasing
1090		the level announces more valid sender's information.
1091	
1092	arp_ignore - INTEGER
1093		Define different modes for sending replies in response to
1094		received ARP requests that resolve local target IP addresses:
1095		0 - (default): reply for any local target IP address, configured
1096		on any interface
1097		1 - reply only if the target IP address is local address
1098		configured on the incoming interface
1099		2 - reply only if the target IP address is local address
1100		configured on the incoming interface and both with the
1101		sender's IP address are part from same subnet on this interface
1102		3 - do not reply for local addresses configured with scope host,
1103		only resolutions for global and link addresses are replied
1104		4-7 - reserved
1105		8 - do not reply for all local addresses
1106	
1107		The max value from conf/{all,interface}/arp_ignore is used
1108		when ARP request is received on the {interface}
1109	
1110	arp_notify - BOOLEAN
1111		Define mode for notification of address and device changes.
1112		0 - (default): do nothing
1113		1 - Generate gratuitous arp requests when device is brought up
1114		    or hardware address changes.
1115	
1116	arp_accept - BOOLEAN
1117		Define behavior for gratuitous ARP frames who's IP is not
1118		already present in the ARP table:
1119		0 - don't create new entries in the ARP table
1120		1 - create new entries in the ARP table
1121	
1122		Both replies and requests type gratuitous arp will trigger the
1123		ARP table to be updated, if this setting is on.
1124	
1125		If the ARP table already contains the IP address of the
1126		gratuitous arp frame, the arp table will be updated regardless
1127		if this setting is on or off.
1128	
1129	mcast_solicit - INTEGER
1130		The maximum number of multicast probes in INCOMPLETE state,
1131		when the associated hardware address is unknown.  Defaults
1132		to 3.
1133	
1134	ucast_solicit - INTEGER
1135		The maximum number of unicast probes in PROBE state, when
1136		the hardware address is being reconfirmed.  Defaults to 3.
1137	
1138	app_solicit - INTEGER
1139		The maximum number of probes to send to the user space ARP daemon
1140		via netlink before dropping back to multicast probes (see
1141		mcast_resolicit).  Defaults to 0.
1142	
1143	mcast_resolicit - INTEGER
1144		The maximum number of multicast probes after unicast and
1145		app probes in PROBE state.  Defaults to 0.
1146	
1147	disable_policy - BOOLEAN
1148		Disable IPSEC policy (SPD) for this interface
1149	
1150	disable_xfrm - BOOLEAN
1151		Disable IPSEC encryption on this interface, whatever the policy
1152	
1153	igmpv2_unsolicited_report_interval - INTEGER
1154		The interval in milliseconds in which the next unsolicited
1155		IGMPv1 or IGMPv2 report retransmit will take place.
1156		Default: 10000 (10 seconds)
1157	
1158	igmpv3_unsolicited_report_interval - INTEGER
1159		The interval in milliseconds in which the next unsolicited
1160		IGMPv3 report retransmit will take place.
1161		Default: 1000 (1 seconds)
1162	
1163	promote_secondaries - BOOLEAN
1164		When a primary IP address is removed from this interface
1165		promote a corresponding secondary IP address instead of
1166		removing all the corresponding secondary IP addresses.
1167	
1168	
1169	tag - INTEGER
1170		Allows you to write a number, which can be used as required.
1171		Default value is 0.
1172	
1173	Alexey Kuznetsov.
1174	kuznet@ms2.inr.ac.ru
1175	
1176	Updated by:
1177	Andi Kleen
1178	ak@muc.de
1179	Nicolas Delon
1180	delon.nicolas@wanadoo.fr
1181	
1182	
1183	
1184	
1185	/proc/sys/net/ipv6/* Variables:
1186	
1187	IPv6 has no global variables such as tcp_*.  tcp_* settings under ipv4/ also
1188	apply to IPv6 [XXX?].
1189	
1190	bindv6only - BOOLEAN
1191		Default value for IPV6_V6ONLY socket option,
1192		which restricts use of the IPv6 socket to IPv6 communication
1193		only.
1194			TRUE: disable IPv4-mapped address feature
1195			FALSE: enable IPv4-mapped address feature
1196	
1197		Default: FALSE (as specified in RFC3493)
1198	
1199	flowlabel_consistency - BOOLEAN
1200		Protect the consistency (and unicity) of flow label.
1201		You have to disable it to use IPV6_FL_F_REFLECT flag on the
1202		flow label manager.
1203		TRUE: enabled
1204		FALSE: disabled
1205		Default: TRUE
1206	
1207	auto_flowlabels - BOOLEAN
1208		Automatically generate flow labels based based on a flow hash
1209		of the packet. This allows intermediate devices, such as routers,
1210		to idenfify packet flows for mechanisms like Equal Cost Multipath
1211		Routing (see RFC 6438).
1212		TRUE: enabled
1213		FALSE: disabled
1214		Default: false
1215	
1216	anycast_src_echo_reply - BOOLEAN
1217		Controls the use of anycast addresses as source addresses for ICMPv6
1218		echo reply
1219		TRUE:  enabled
1220		FALSE: disabled
1221		Default: FALSE
1222	
1223	idgen_delay - INTEGER
1224		Controls the delay in seconds after which time to retry
1225		privacy stable address generation if a DAD conflict is
1226		detected.
1227		Default: 1 (as specified in RFC7217)
1228	
1229	idgen_retries - INTEGER
1230		Controls the number of retries to generate a stable privacy
1231		address if a DAD conflict is detected.
1232		Default: 3 (as specified in RFC7217)
1233	
1234	mld_qrv - INTEGER
1235		Controls the MLD query robustness variable (see RFC3810 9.1).
1236		Default: 2 (as specified by RFC3810 9.1)
1237		Minimum: 1 (as specified by RFC6636 4.5)
1238	
1239	IPv6 Fragmentation:
1240	
1241	ip6frag_high_thresh - INTEGER
1242		Maximum memory used to reassemble IPv6 fragments. When
1243		ip6frag_high_thresh bytes of memory is allocated for this purpose,
1244		the fragment handler will toss packets until ip6frag_low_thresh
1245		is reached.
1246	
1247	ip6frag_low_thresh - INTEGER
1248		See ip6frag_high_thresh
1249	
1250	ip6frag_time - INTEGER
1251		Time in seconds to keep an IPv6 fragment in memory.
1252	
1253	conf/default/*:
1254		Change the interface-specific default settings.
1255	
1256	
1257	conf/all/*:
1258		Change all the interface-specific settings.
1259	
1260		[XXX:  Other special features than forwarding?]
1261	
1262	conf/all/forwarding - BOOLEAN
1263		Enable global IPv6 forwarding between all interfaces.
1264	
1265		IPv4 and IPv6 work differently here; e.g. netfilter must be used
1266		to control which interfaces may forward packets and which not.
1267	
1268		This also sets all interfaces' Host/Router setting
1269		'forwarding' to the specified value.  See below for details.
1270	
1271		This referred to as global forwarding.
1272	
1273	proxy_ndp - BOOLEAN
1274		Do proxy ndp.
1275	
1276	fwmark_reflect - BOOLEAN
1277		Controls the fwmark of kernel-generated IPv6 reply packets that are not
1278		associated with a socket for example, TCP RSTs or ICMPv6 echo replies).
1279		If unset, these packets have a fwmark of zero. If set, they have the
1280		fwmark of the packet they are replying to.
1281		Default: 0
1282	
1283	conf/interface/*:
1284		Change special settings per interface.
1285	
1286		The functional behaviour for certain settings is different
1287		depending on whether local forwarding is enabled or not.
1288	
1289	accept_ra - INTEGER
1290		Accept Router Advertisements; autoconfigure using them.
1291	
1292		It also determines whether or not to transmit Router
1293		Solicitations. If and only if the functional setting is to
1294		accept Router Advertisements, Router Solicitations will be
1295		transmitted.
1296	
1297		Possible values are:
1298			0 Do not accept Router Advertisements.
1299			1 Accept Router Advertisements if forwarding is disabled.
1300			2 Overrule forwarding behaviour. Accept Router Advertisements
1301			  even if forwarding is enabled.
1302	
1303		Functional default: enabled if local forwarding is disabled.
1304				    disabled if local forwarding is enabled.
1305	
1306	accept_ra_defrtr - BOOLEAN
1307		Learn default router in Router Advertisement.
1308	
1309		Functional default: enabled if accept_ra is enabled.
1310				    disabled if accept_ra is disabled.
1311	
1312	accept_ra_from_local - BOOLEAN
1313		Accept RA with source-address that is found on local machine
1314	        if the RA is otherwise proper and able to be accepted.
1315	        Default is to NOT accept these as it may be an un-intended
1316	        network loop.
1317	
1318		Functional default:
1319	           enabled if accept_ra_from_local is enabled
1320	               on a specific interface.
1321		   disabled if accept_ra_from_local is disabled
1322	               on a specific interface.
1323	
1324	accept_ra_pinfo - BOOLEAN
1325		Learn Prefix Information in Router Advertisement.
1326	
1327		Functional default: enabled if accept_ra is enabled.
1328				    disabled if accept_ra is disabled.
1329	
1330	accept_ra_rt_info_max_plen - INTEGER
1331		Maximum prefix length of Route Information in RA.
1332	
1333		Route Information w/ prefix larger than or equal to this
1334		variable shall be ignored.
1335	
1336		Functional default: 0 if accept_ra_rtr_pref is enabled.
1337				    -1 if accept_ra_rtr_pref is disabled.
1338	
1339	accept_ra_rtr_pref - BOOLEAN
1340		Accept Router Preference in RA.
1341	
1342		Functional default: enabled if accept_ra is enabled.
1343				    disabled if accept_ra is disabled.
1344	
1345	accept_ra_mtu - BOOLEAN
1346		Apply the MTU value specified in RA option 5 (RFC4861). If
1347		disabled, the MTU specified in the RA will be ignored.
1348	
1349		Functional default: enabled if accept_ra is enabled.
1350				    disabled if accept_ra is disabled.
1351	
1352	accept_redirects - BOOLEAN
1353		Accept Redirects.
1354	
1355		Functional default: enabled if local forwarding is disabled.
1356				    disabled if local forwarding is enabled.
1357	
1358	accept_source_route - INTEGER
1359		Accept source routing (routing extension header).
1360	
1361		>= 0: Accept only routing header type 2.
1362		< 0: Do not accept routing header.
1363	
1364		Default: 0
1365	
1366	autoconf - BOOLEAN
1367		Autoconfigure addresses using Prefix Information in Router
1368		Advertisements.
1369	
1370		Functional default: enabled if accept_ra_pinfo is enabled.
1371				    disabled if accept_ra_pinfo is disabled.
1372	
1373	dad_transmits - INTEGER
1374		The amount of Duplicate Address Detection probes to send.
1375		Default: 1
1376	
1377	forwarding - INTEGER
1378		Configure interface-specific Host/Router behaviour.
1379	
1380		Note: It is recommended to have the same setting on all
1381		interfaces; mixed router/host scenarios are rather uncommon.
1382	
1383		Possible values are:
1384			0 Forwarding disabled
1385			1 Forwarding enabled
1386	
1387		FALSE (0):
1388	
1389		By default, Host behaviour is assumed.  This means:
1390	
1391		1. IsRouter flag is not set in Neighbour Advertisements.
1392		2. If accept_ra is TRUE (default), transmit Router
1393		   Solicitations.
1394		3. If accept_ra is TRUE (default), accept Router
1395		   Advertisements (and do autoconfiguration).
1396		4. If accept_redirects is TRUE (default), accept Redirects.
1397	
1398		TRUE (1):
1399	
1400		If local forwarding is enabled, Router behaviour is assumed.
1401		This means exactly the reverse from the above:
1402	
1403		1. IsRouter flag is set in Neighbour Advertisements.
1404		2. Router Solicitations are not sent unless accept_ra is 2.
1405		3. Router Advertisements are ignored unless accept_ra is 2.
1406		4. Redirects are ignored.
1407	
1408		Default: 0 (disabled) if global forwarding is disabled (default),
1409			 otherwise 1 (enabled).
1410	
1411	hop_limit - INTEGER
1412		Default Hop Limit to set.
1413		Default: 64
1414	
1415	mtu - INTEGER
1416		Default Maximum Transfer Unit
1417		Default: 1280 (IPv6 required minimum)
1418	
1419	router_probe_interval - INTEGER
1420		Minimum interval (in seconds) between Router Probing described
1421		in RFC4191.
1422	
1423		Default: 60
1424	
1425	router_solicitation_delay - INTEGER
1426		Number of seconds to wait after interface is brought up
1427		before sending Router Solicitations.
1428		Default: 1
1429	
1430	router_solicitation_interval - INTEGER
1431		Number of seconds to wait between Router Solicitations.
1432		Default: 4
1433	
1434	router_solicitations - INTEGER
1435		Number of Router Solicitations to send until assuming no
1436		routers are present.
1437		Default: 3
1438	
1439	use_tempaddr - INTEGER
1440		Preference for Privacy Extensions (RFC3041).
1441		  <= 0 : disable Privacy Extensions
1442		  == 1 : enable Privacy Extensions, but prefer public
1443		         addresses over temporary addresses.
1444		  >  1 : enable Privacy Extensions and prefer temporary
1445		         addresses over public addresses.
1446		Default:  0 (for most devices)
1447			 -1 (for point-to-point devices and loopback devices)
1448	
1449	temp_valid_lft - INTEGER
1450		valid lifetime (in seconds) for temporary addresses.
1451		Default: 604800 (7 days)
1452	
1453	temp_prefered_lft - INTEGER
1454		Preferred lifetime (in seconds) for temporary addresses.
1455		Default: 86400 (1 day)
1456	
1457	max_desync_factor - INTEGER
1458		Maximum value for DESYNC_FACTOR, which is a random value
1459		that ensures that clients don't synchronize with each
1460		other and generate new addresses at exactly the same time.
1461		value is in seconds.
1462		Default: 600
1463	
1464	regen_max_retry - INTEGER
1465		Number of attempts before give up attempting to generate
1466		valid temporary addresses.
1467		Default: 5
1468	
1469	max_addresses - INTEGER
1470		Maximum number of autoconfigured addresses per interface.  Setting
1471		to zero disables the limitation.  It is not recommended to set this
1472		value too large (or to zero) because it would be an easy way to
1473		crash the kernel by allowing too many addresses to be created.
1474		Default: 16
1475	
1476	disable_ipv6 - BOOLEAN
1477		Disable IPv6 operation.  If accept_dad is set to 2, this value
1478		will be dynamically set to TRUE if DAD fails for the link-local
1479		address.
1480		Default: FALSE (enable IPv6 operation)
1481	
1482		When this value is changed from 1 to 0 (IPv6 is being enabled),
1483		it will dynamically create a link-local address on the given
1484		interface and start Duplicate Address Detection, if necessary.
1485	
1486		When this value is changed from 0 to 1 (IPv6 is being disabled),
1487		it will dynamically delete all address on the given interface.
1488	
1489	accept_dad - INTEGER
1490		Whether to accept DAD (Duplicate Address Detection).
1491		0: Disable DAD
1492		1: Enable DAD (default)
1493		2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
1494		   link-local address has been found.
1495	
1496	force_tllao - BOOLEAN
1497		Enable sending the target link-layer address option even when
1498		responding to a unicast neighbor solicitation.
1499		Default: FALSE
1500	
1501		Quoting from RFC 2461, section 4.4, Target link-layer address:
1502	
1503		"The option MUST be included for multicast solicitations in order to
1504		avoid infinite Neighbor Solicitation "recursion" when the peer node
1505		does not have a cache entry to return a Neighbor Advertisements
1506		message.  When responding to unicast solicitations, the option can be
1507		omitted since the sender of the solicitation has the correct link-
1508		layer address; otherwise it would not have be able to send the unicast
1509		solicitation in the first place. However, including the link-layer
1510		address in this case adds little overhead and eliminates a potential
1511		race condition where the sender deletes the cached link-layer address
1512		prior to receiving a response to a previous solicitation."
1513	
1514	ndisc_notify - BOOLEAN
1515		Define mode for notification of address and device changes.
1516		0 - (default): do nothing
1517		1 - Generate unsolicited neighbour advertisements when device is brought
1518		    up or hardware address changes.
1519	
1520	mldv1_unsolicited_report_interval - INTEGER
1521		The interval in milliseconds in which the next unsolicited
1522		MLDv1 report retransmit will take place.
1523		Default: 10000 (10 seconds)
1524	
1525	mldv2_unsolicited_report_interval - INTEGER
1526		The interval in milliseconds in which the next unsolicited
1527		MLDv2 report retransmit will take place.
1528		Default: 1000 (1 second)
1529	
1530	force_mld_version - INTEGER
1531		0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed
1532		1 - Enforce to use MLD version 1
1533		2 - Enforce to use MLD version 2
1534	
1535	suppress_frag_ndisc - INTEGER
1536		Control RFC 6980 (Security Implications of IPv6 Fragmentation
1537		with IPv6 Neighbor Discovery) behavior:
1538		1 - (default) discard fragmented neighbor discovery packets
1539		0 - allow fragmented neighbor discovery packets
1540	
1541	optimistic_dad - BOOLEAN
1542		Whether to perform Optimistic Duplicate Address Detection (RFC 4429).
1543			0: disabled (default)
1544			1: enabled
1545	
1546	use_optimistic - BOOLEAN
1547		If enabled, do not classify optimistic addresses as deprecated during
1548		source address selection.  Preferred addresses will still be chosen
1549		before optimistic addresses, subject to other ranking in the source
1550		address selection algorithm.
1551			0: disabled (default)
1552			1: enabled
1553	
1554	stable_secret - IPv6 address
1555		This IPv6 address will be used as a secret to generate IPv6
1556		addresses for link-local addresses and autoconfigured
1557		ones. All addresses generated after setting this secret will
1558		be stable privacy ones by default. This can be changed via the
1559		addrgenmode ip-link. conf/default/stable_secret is used as the
1560		secret for the namespace, the interface specific ones can
1561		overwrite that. Writes to conf/all/stable_secret are refused.
1562	
1563		It is recommended to generate this secret during installation
1564		of a system and keep it stable after that.
1565	
1566		By default the stable secret is unset.
1567	
1568	icmp/*:
1569	ratelimit - INTEGER
1570		Limit the maximal rates for sending ICMPv6 packets.
1571		0 to disable any limiting,
1572		otherwise the minimal space between responses in milliseconds.
1573		Default: 1000
1574	
1575	
1576	IPv6 Update by:
1577	Pekka Savola <pekkas@netcore.fi>
1578	YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
1579	
1580	
1581	/proc/sys/net/bridge/* Variables:
1582	
1583	bridge-nf-call-arptables - BOOLEAN
1584		1 : pass bridged ARP traffic to arptables' FORWARD chain.
1585		0 : disable this.
1586		Default: 1
1587	
1588	bridge-nf-call-iptables - BOOLEAN
1589		1 : pass bridged IPv4 traffic to iptables' chains.
1590		0 : disable this.
1591		Default: 1
1592	
1593	bridge-nf-call-ip6tables - BOOLEAN
1594		1 : pass bridged IPv6 traffic to ip6tables' chains.
1595		0 : disable this.
1596		Default: 1
1597	
1598	bridge-nf-filter-vlan-tagged - BOOLEAN
1599		1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
1600		0 : disable this.
1601		Default: 0
1602	
1603	bridge-nf-filter-pppoe-tagged - BOOLEAN
1604		1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
1605		0 : disable this.
1606		Default: 0
1607	
1608	bridge-nf-pass-vlan-input-dev - BOOLEAN
1609		1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan
1610		interface on the bridge and set the netfilter input device to the vlan.
1611		This allows use of e.g. "iptables -i br0.1" and makes the REDIRECT
1612		target work with vlan-on-top-of-bridge interfaces.  When no matching
1613		vlan interface is found, or this switch is off, the input device is
1614		set to the bridge interface.
1615		0: disable bridge netfilter vlan interface lookup.
1616		Default: 0
1617	
1618	proc/sys/net/sctp/* Variables:
1619	
1620	addip_enable - BOOLEAN
1621		Enable or disable extension of  Dynamic Address Reconfiguration
1622		(ADD-IP) functionality specified in RFC5061.  This extension provides
1623		the ability to dynamically add and remove new addresses for the SCTP
1624		associations.
1625	
1626		1: Enable extension.
1627	
1628		0: Disable extension.
1629	
1630		Default: 0
1631	
1632	addip_noauth_enable - BOOLEAN
1633		Dynamic Address Reconfiguration (ADD-IP) requires the use of
1634		authentication to protect the operations of adding or removing new
1635		addresses.  This requirement is mandated so that unauthorized hosts
1636		would not be able to hijack associations.  However, older
1637		implementations may not have implemented this requirement while
1638		allowing the ADD-IP extension.  For reasons of interoperability,
1639		we provide this variable to control the enforcement of the
1640		authentication requirement.
1641	
1642		1: Allow ADD-IP extension to be used without authentication.  This
1643		   should only be set in a closed environment for interoperability
1644		   with older implementations.
1645	
1646		0: Enforce the authentication requirement
1647	
1648		Default: 0
1649	
1650	auth_enable - BOOLEAN
1651		Enable or disable Authenticated Chunks extension.  This extension
1652		provides the ability to send and receive authenticated chunks and is
1653		required for secure operation of Dynamic Address Reconfiguration
1654		(ADD-IP) extension.
1655	
1656		1: Enable this extension.
1657		0: Disable this extension.
1658	
1659		Default: 0
1660	
1661	prsctp_enable - BOOLEAN
1662		Enable or disable the Partial Reliability extension (RFC3758) which
1663		is used to notify peers that a given DATA should no longer be expected.
1664	
1665		1: Enable extension
1666		0: Disable
1667	
1668		Default: 1
1669	
1670	max_burst - INTEGER
1671		The limit of the number of new packets that can be initially sent.  It
1672		controls how bursty the generated traffic can be.
1673	
1674		Default: 4
1675	
1676	association_max_retrans - INTEGER
1677		Set the maximum number for retransmissions that an association can
1678		attempt deciding that the remote end is unreachable.  If this value
1679		is exceeded, the association is terminated.
1680	
1681		Default: 10
1682	
1683	max_init_retransmits - INTEGER
1684		The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
1685		that an association will attempt before declaring the destination
1686		unreachable and terminating.
1687	
1688		Default: 8
1689	
1690	path_max_retrans - INTEGER
1691		The maximum number of retransmissions that will be attempted on a given
1692		path.  Once this threshold is exceeded, the path is considered
1693		unreachable, and new traffic will use a different path when the
1694		association is multihomed.
1695	
1696		Default: 5
1697	
1698	pf_retrans - INTEGER
1699		The number of retransmissions that will be attempted on a given path
1700		before traffic is redirected to an alternate transport (should one
1701		exist).  Note this is distinct from path_max_retrans, as a path that
1702		passes the pf_retrans threshold can still be used.  Its only
1703		deprioritized when a transmission path is selected by the stack.  This
1704		setting is primarily used to enable fast failover mechanisms without
1705		having to reduce path_max_retrans to a very low value.  See:
1706		http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt
1707		for details.  Note also that a value of pf_retrans > path_max_retrans
1708		disables this feature
1709	
1710		Default: 0
1711	
1712	rto_initial - INTEGER
1713		The initial round trip timeout value in milliseconds that will be used
1714		in calculating round trip times.  This is the initial time interval
1715		for retransmissions.
1716	
1717		Default: 3000
1718	
1719	rto_max - INTEGER
1720		The maximum value (in milliseconds) of the round trip timeout.  This
1721		is the largest time interval that can elapse between retransmissions.
1722	
1723		Default: 60000
1724	
1725	rto_min - INTEGER
1726		The minimum value (in milliseconds) of the round trip timeout.  This
1727		is the smallest time interval the can elapse between retransmissions.
1728	
1729		Default: 1000
1730	
1731	hb_interval - INTEGER
1732		The interval (in milliseconds) between HEARTBEAT chunks.  These chunks
1733		are sent at the specified interval on idle paths to probe the state of
1734		a given path between 2 associations.
1735	
1736		Default: 30000
1737	
1738	sack_timeout - INTEGER
1739		The amount of time (in milliseconds) that the implementation will wait
1740		to send a SACK.
1741	
1742		Default: 200
1743	
1744	valid_cookie_life - INTEGER
1745		The default lifetime of the SCTP cookie (in milliseconds).  The cookie
1746		is used during association establishment.
1747	
1748		Default: 60000
1749	
1750	cookie_preserve_enable - BOOLEAN
1751		Enable or disable the ability to extend the lifetime of the SCTP cookie
1752		that is used during the establishment phase of SCTP association
1753	
1754		1: Enable cookie lifetime extension.
1755		0: Disable
1756	
1757		Default: 1
1758	
1759	cookie_hmac_alg - STRING
1760		Select the hmac algorithm used when generating the cookie value sent by
1761		a listening sctp socket to a connecting client in the INIT-ACK chunk.
1762		Valid values are:
1763		* md5
1764		* sha1
1765		* none
1766		Ability to assign md5 or sha1 as the selected alg is predicated on the
1767		configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and
1768		CONFIG_CRYPTO_SHA1).
1769	
1770		Default: Dependent on configuration.  MD5 if available, else SHA1 if
1771		available, else none.
1772	
1773	rcvbuf_policy - INTEGER
1774		Determines if the receive buffer is attributed to the socket or to
1775		association.   SCTP supports the capability to create multiple
1776		associations on a single socket.  When using this capability, it is
1777		possible that a single stalled association that's buffering a lot
1778		of data may block other associations from delivering their data by
1779		consuming all of the receive buffer space.  To work around this,
1780		the rcvbuf_policy could be set to attribute the receiver buffer space
1781		to each association instead of the socket.  This prevents the described
1782		blocking.
1783	
1784		1: rcvbuf space is per association
1785		0: rcvbuf space is per socket
1786	
1787		Default: 0
1788	
1789	sndbuf_policy - INTEGER
1790		Similar to rcvbuf_policy above, this applies to send buffer space.
1791	
1792		1: Send buffer is tracked per association
1793		0: Send buffer is tracked per socket.
1794	
1795		Default: 0
1796	
1797	sctp_mem - vector of 3 INTEGERs: min, pressure, max
1798		Number of pages allowed for queueing by all SCTP sockets.
1799	
1800		min: Below this number of pages SCTP is not bothered about its
1801		memory appetite. When amount of memory allocated by SCTP exceeds
1802		this number, SCTP starts to moderate memory usage.
1803	
1804		pressure: This value was introduced to follow format of tcp_mem.
1805	
1806		max: Number of pages allowed for queueing by all SCTP sockets.
1807	
1808		Default is calculated at boot time from amount of available memory.
1809	
1810	sctp_rmem - vector of 3 INTEGERs: min, default, max
1811		Only the first value ("min") is used, "default" and "max" are
1812		ignored.
1813	
1814		min: Minimal size of receive buffer used by SCTP socket.
1815		It is guaranteed to each SCTP socket (but not association) even
1816		under moderate memory pressure.
1817	
1818		Default: 1 page
1819	
1820	sctp_wmem  - vector of 3 INTEGERs: min, default, max
1821		Currently this tunable has no effect.
1822	
1823	addr_scope_policy - INTEGER
1824		Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00
1825	
1826		0   - Disable IPv4 address scoping
1827		1   - Enable IPv4 address scoping
1828		2   - Follow draft but allow IPv4 private addresses
1829		3   - Follow draft but allow IPv4 link local addresses
1830	
1831		Default: 1
1832	
1833	
1834	/proc/sys/net/core/*
1835		Please see: Documentation/sysctl/net.txt for descriptions of these entries.
1836	
1837	
1838	/proc/sys/net/unix/*
1839	max_dgram_qlen - INTEGER
1840		The maximum length of dgram socket receive queue
1841	
1842		Default: 10
1843	
1844	
1845	UNDOCUMENTED:
1846	
1847	/proc/sys/net/irda/*
1848		fast_poll_increase FIXME
1849		warn_noreply_time FIXME
1850		discovery_slots FIXME
1851		slot_timeout FIXME
1852		max_baud_rate FIXME
1853		discovery_timeout FIXME
1854		lap_keepalive_time FIXME
1855		max_noreply_time FIXME
1856		max_tx_data_size FIXME
1857		max_tx_window FIXME
1858		min_tx_turn_time FIXME
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