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Based on kernel version 3.13. Page generated on 2014-01-20 22:03 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 - BOOLEAN
19		Disable Path MTU Discovery. If enabled 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		Default: FALSE
25	
26	min_pmtu - INTEGER
27		default 552 - minimum discovered Path MTU
28	
29	route/max_size - INTEGER
30		Maximum number of routes allowed in the kernel.  Increase
31		this when using large numbers of interfaces and/or routes.
32	
33	neigh/default/gc_thresh1 - INTEGER
34		Minimum number of entries to keep.  Garbage collector will not
35		purge entries if there are fewer than this number.
36		Default: 128
37	
38	neigh/default/gc_thresh3 - INTEGER
39		Maximum number of neighbor entries allowed.  Increase this
40		when using large numbers of interfaces and when communicating
41		with large numbers of directly-connected peers.
42		Default: 1024
43	
44	neigh/default/unres_qlen_bytes - INTEGER
45		The maximum number of bytes which may be used by packets
46		queued for each	unresolved address by other network layers.
47		(added in linux 3.3)
48		Setting negative value is meaningless and will return error.
49		Default: 65536 Bytes(64KB)
50	
51	neigh/default/unres_qlen - INTEGER
52		The maximum number of packets which may be queued for each
53		unresolved address by other network layers.
54		(deprecated in linux 3.3) : use unres_qlen_bytes instead.
55		Prior to linux 3.3, the default value is 3 which may cause
56		unexpected packet loss. The current default value is calculated
57		according to default value of unres_qlen_bytes and true size of
58		packet.
59		Default: 31
60	
61	mtu_expires - INTEGER
62		Time, in seconds, that cached PMTU information is kept.
63	
64	min_adv_mss - INTEGER
65		The advertised MSS depends on the first hop route MTU, but will
66		never be lower than this setting.
67	
68	IP Fragmentation:
69	
70	ipfrag_high_thresh - INTEGER
71		Maximum memory used to reassemble IP fragments. When
72		ipfrag_high_thresh bytes of memory is allocated for this purpose,
73		the fragment handler will toss packets until ipfrag_low_thresh
74		is reached.
75	
76	ipfrag_low_thresh - INTEGER
77		See ipfrag_high_thresh
78	
79	ipfrag_time - INTEGER
80		Time in seconds to keep an IP fragment in memory.
81	
82	ipfrag_secret_interval - INTEGER
83		Regeneration interval (in seconds) of the hash secret (or lifetime
84		for the hash secret) for IP fragments.
85		Default: 600
86	
87	ipfrag_max_dist - INTEGER
88		ipfrag_max_dist is a non-negative integer value which defines the
89		maximum "disorder" which is allowed among fragments which share a
90		common IP source address. Note that reordering of packets is
91		not unusual, but if a large number of fragments arrive from a source
92		IP address while a particular fragment queue remains incomplete, it
93		probably indicates that one or more fragments belonging to that queue
94		have been lost. When ipfrag_max_dist is positive, an additional check
95		is done on fragments before they are added to a reassembly queue - if
96		ipfrag_max_dist (or more) fragments have arrived from a particular IP
97		address between additions to any IP fragment queue using that source
98		address, it's presumed that one or more fragments in the queue are
99		lost. The existing fragment queue will be dropped, and a new one
100		started. An ipfrag_max_dist value of zero disables this check.
101	
102		Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
103		result in unnecessarily dropping fragment queues when normal
104		reordering of packets occurs, which could lead to poor application
105		performance. Using a very large value, e.g. 50000, increases the
106		likelihood of incorrectly reassembling IP fragments that originate
107		from different IP datagrams, which could result in data corruption.
108		Default: 64
109	
110	INET peer storage:
111	
112	inet_peer_threshold - INTEGER
113		The approximate size of the storage.  Starting from this threshold
114		entries will be thrown aggressively.  This threshold also determines
115		entries' time-to-live and time intervals between garbage collection
116		passes.  More entries, less time-to-live, less GC interval.
117	
118	inet_peer_minttl - INTEGER
119		Minimum time-to-live of entries.  Should be enough to cover fragment
120		time-to-live on the reassembling side.  This minimum time-to-live  is
121		guaranteed if the pool size is less than inet_peer_threshold.
122		Measured in seconds.
123	
124	inet_peer_maxttl - INTEGER
125		Maximum time-to-live of entries.  Unused entries will expire after
126		this period of time if there is no memory pressure on the pool (i.e.
127		when the number of entries in the pool is very small).
128		Measured in seconds.
129	
130	TCP variables:
131	
132	somaxconn - INTEGER
133		Limit of socket listen() backlog, known in userspace as SOMAXCONN.
134		Defaults to 128.  See also tcp_max_syn_backlog for additional tuning
135		for TCP sockets.
136	
137	tcp_abort_on_overflow - BOOLEAN
138		If listening service is too slow to accept new connections,
139		reset them. Default state is FALSE. It means that if overflow
140		occurred due to a burst, connection will recover. Enable this
141		option _only_ if you are really sure that listening daemon
142		cannot be tuned to accept connections faster. Enabling this
143		option can harm clients of your server.
144	
145	tcp_adv_win_scale - INTEGER
146		Count buffering overhead as bytes/2^tcp_adv_win_scale
147		(if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
148		if it is <= 0.
149		Possible values are [-31, 31], inclusive.
150		Default: 1
151	
152	tcp_allowed_congestion_control - STRING
153		Show/set the congestion control choices available to non-privileged
154		processes. The list is a subset of those listed in
155		tcp_available_congestion_control.
156		Default is "reno" and the default setting (tcp_congestion_control).
157	
158	tcp_app_win - INTEGER
159		Reserve max(window/2^tcp_app_win, mss) of window for application
160		buffer. Value 0 is special, it means that nothing is reserved.
161		Default: 31
162	
163	tcp_available_congestion_control - STRING
164		Shows the available congestion control choices that are registered.
165		More congestion control algorithms may be available as modules,
166		but not loaded.
167	
168	tcp_base_mss - INTEGER
169		The initial value of search_low to be used by the packetization layer
170		Path MTU discovery (MTU probing).  If MTU probing is enabled,
171		this is the initial MSS used by the connection.
172	
173	tcp_congestion_control - STRING
174		Set the congestion control algorithm to be used for new
175		connections. The algorithm "reno" is always available, but
176		additional choices may be available based on kernel configuration.
177		Default is set as part of kernel configuration.
178		For passive connections, the listener congestion control choice
179		is inherited.
180		[see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ]
181	
182	tcp_dsack - BOOLEAN
183		Allows TCP to send "duplicate" SACKs.
184	
185	tcp_early_retrans - INTEGER
186		Enable Early Retransmit (ER), per RFC 5827. ER lowers the threshold
187		for triggering fast retransmit when the amount of outstanding data is
188		small and when no previously unsent data can be transmitted (such
189		that limited transmit could be used). Also controls the use of
190		Tail loss probe (TLP) that converts RTOs occurring due to tail
191		losses into fast recovery (draft-dukkipati-tcpm-tcp-loss-probe-01).
192		Possible values:
193			0 disables ER
194			1 enables ER
195			2 enables ER but delays fast recovery and fast retransmit
196			  by a fourth of RTT. This mitigates connection falsely
197			  recovers when network has a small degree of reordering
198			  (less than 3 packets).
199			3 enables delayed ER and TLP.
200			4 enables TLP only.
201		Default: 3
202	
203	tcp_ecn - INTEGER
204		Control use of Explicit Congestion Notification (ECN) by TCP.
205		ECN is used only when both ends of the TCP connection indicate
206		support for it.  This feature is useful in avoiding losses due
207		to congestion by allowing supporting routers to signal
208		congestion before having to drop packets.
209		Possible values are:
210			0 Disable ECN.  Neither initiate nor accept ECN.
211			1 Enable ECN when requested by incoming connections and
212			  also request ECN on outgoing connection attempts.
213			2 Enable ECN when requested by incoming connections
214			  but do not request ECN on outgoing connections.
215		Default: 2
216	
217	tcp_fack - BOOLEAN
218		Enable FACK congestion avoidance and fast retransmission.
219		The value is not used, if tcp_sack is not enabled.
220	
221	tcp_fin_timeout - INTEGER
222		The length of time an orphaned (no longer referenced by any
223		application) connection will remain in the FIN_WAIT_2 state
224		before it is aborted at the local end.  While a perfectly
225		valid "receive only" state for an un-orphaned connection, an
226		orphaned connection in FIN_WAIT_2 state could otherwise wait
227		forever for the remote to close its end of the connection.
228		Cf. tcp_max_orphans
229		Default: 60 seconds
230	
231	tcp_frto - INTEGER
232		Enables Forward RTO-Recovery (F-RTO) defined in RFC5682.
233		F-RTO is an enhanced recovery algorithm for TCP retransmission
234		timeouts.  It is particularly beneficial in networks where the
235		RTT fluctuates (e.g., wireless). F-RTO is sender-side only
236		modification. It does not require any support from the peer.
237	
238		By default it's enabled with a non-zero value. 0 disables F-RTO.
239	
240	tcp_keepalive_time - INTEGER
241		How often TCP sends out keepalive messages when keepalive is enabled.
242		Default: 2hours.
243	
244	tcp_keepalive_probes - INTEGER
245		How many keepalive probes TCP sends out, until it decides that the
246		connection is broken. Default value: 9.
247	
248	tcp_keepalive_intvl - INTEGER
249		How frequently the probes are send out. Multiplied by
250		tcp_keepalive_probes it is time to kill not responding connection,
251		after probes started. Default value: 75sec i.e. connection
252		will be aborted after ~11 minutes of retries.
253	
254	tcp_low_latency - BOOLEAN
255		If set, the TCP stack makes decisions that prefer lower
256		latency as opposed to higher throughput.  By default, this
257		option is not set meaning that higher throughput is preferred.
258		An example of an application where this default should be
259		changed would be a Beowulf compute cluster.
260		Default: 0
261	
262	tcp_max_orphans - INTEGER
263		Maximal number of TCP sockets not attached to any user file handle,
264		held by system.	If this number is exceeded orphaned connections are
265		reset immediately and warning is printed. This limit exists
266		only to prevent simple DoS attacks, you _must_ not rely on this
267		or lower the limit artificially, but rather increase it
268		(probably, after increasing installed memory),
269		if network conditions require more than default value,
270		and tune network services to linger and kill such states
271		more aggressively. Let me to remind again: each orphan eats
272		up to ~64K of unswappable memory.
273	
274	tcp_max_syn_backlog - INTEGER
275		Maximal number of remembered connection requests, which have not
276		received an acknowledgment from connecting client.
277		The minimal value is 128 for low memory machines, and it will
278		increase in proportion to the memory of machine.
279		If server suffers from overload, try increasing this number.
280	
281	tcp_max_tw_buckets - INTEGER
282		Maximal number of timewait sockets held by system simultaneously.
283		If this number is exceeded time-wait socket is immediately destroyed
284		and warning is printed. This limit exists only to prevent
285		simple DoS attacks, you _must_ not lower the limit artificially,
286		but rather increase it (probably, after increasing installed memory),
287		if network conditions require more than default value.
288	
289	tcp_mem - vector of 3 INTEGERs: min, pressure, max
290		min: below this number of pages TCP is not bothered about its
291		memory appetite.
292	
293		pressure: when amount of memory allocated by TCP exceeds this number
294		of pages, TCP moderates its memory consumption and enters memory
295		pressure mode, which is exited when memory consumption falls
296		under "min".
297	
298		max: number of pages allowed for queueing by all TCP sockets.
299	
300		Defaults are calculated at boot time from amount of available
301		memory.
302	
303	tcp_moderate_rcvbuf - BOOLEAN
304		If set, TCP performs receive buffer auto-tuning, attempting to
305		automatically size the buffer (no greater than tcp_rmem[2]) to
306		match the size required by the path for full throughput.  Enabled by
307		default.
308	
309	tcp_mtu_probing - INTEGER
310		Controls TCP Packetization-Layer Path MTU Discovery.  Takes three
311		values:
312		  0 - Disabled
313		  1 - Disabled by default, enabled when an ICMP black hole detected
314		  2 - Always enabled, use initial MSS of tcp_base_mss.
315	
316	tcp_no_metrics_save - BOOLEAN
317		By default, TCP saves various connection metrics in the route cache
318		when the connection closes, so that connections established in the
319		near future can use these to set initial conditions.  Usually, this
320		increases overall performance, but may sometimes cause performance
321		degradation.  If set, TCP will not cache metrics on closing
322		connections.
323	
324	tcp_orphan_retries - INTEGER
325		This value influences the timeout of a locally closed TCP connection,
326		when RTO retransmissions remain unacknowledged.
327		See tcp_retries2 for more details.
328	
329		The default value is 8.
330		If your machine is a loaded WEB server,
331		you should think about lowering this value, such sockets
332		may consume significant resources. Cf. tcp_max_orphans.
333	
334	tcp_reordering - INTEGER
335		Maximal reordering of packets in a TCP stream.
336		Default: 3
337	
338	tcp_retrans_collapse - BOOLEAN
339		Bug-to-bug compatibility with some broken printers.
340		On retransmit try to send bigger packets to work around bugs in
341		certain TCP stacks.
342	
343	tcp_retries1 - INTEGER
344		This value influences the time, after which TCP decides, that
345		something is wrong due to unacknowledged RTO retransmissions,
346		and reports this suspicion to the network layer.
347		See tcp_retries2 for more details.
348	
349		RFC 1122 recommends at least 3 retransmissions, which is the
350		default.
351	
352	tcp_retries2 - INTEGER
353		This value influences the timeout of an alive TCP connection,
354		when RTO retransmissions remain unacknowledged.
355		Given a value of N, a hypothetical TCP connection following
356		exponential backoff with an initial RTO of TCP_RTO_MIN would
357		retransmit N times before killing the connection at the (N+1)th RTO.
358	
359		The default value of 15 yields a hypothetical timeout of 924.6
360		seconds and is a lower bound for the effective timeout.
361		TCP will effectively time out at the first RTO which exceeds the
362		hypothetical timeout.
363	
364		RFC 1122 recommends at least 100 seconds for the timeout,
365		which corresponds to a value of at least 8.
366	
367	tcp_rfc1337 - BOOLEAN
368		If set, the TCP stack behaves conforming to RFC1337. If unset,
369		we are not conforming to RFC, but prevent TCP TIME_WAIT
370		assassination.
371		Default: 0
372	
373	tcp_rmem - vector of 3 INTEGERs: min, default, max
374		min: Minimal size of receive buffer used by TCP sockets.
375		It is guaranteed to each TCP socket, even under moderate memory
376		pressure.
377		Default: 1 page
378	
379		default: initial size of receive buffer used by TCP sockets.
380		This value overrides net.core.rmem_default used by other protocols.
381		Default: 87380 bytes. This value results in window of 65535 with
382		default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
383		less for default tcp_app_win. See below about these variables.
384	
385		max: maximal size of receive buffer allowed for automatically
386		selected receiver buffers for TCP socket. This value does not override
387		net.core.rmem_max.  Calling setsockopt() with SO_RCVBUF disables
388		automatic tuning of that socket's receive buffer size, in which
389		case this value is ignored.
390		Default: between 87380B and 6MB, depending on RAM size.
391	
392	tcp_sack - BOOLEAN
393		Enable select acknowledgments (SACKS).
394	
395	tcp_slow_start_after_idle - BOOLEAN
396		If set, provide RFC2861 behavior and time out the congestion
397		window after an idle period.  An idle period is defined at
398		the current RTO.  If unset, the congestion window will not
399		be timed out after an idle period.
400		Default: 1
401	
402	tcp_stdurg - BOOLEAN
403		Use the Host requirements interpretation of the TCP urgent pointer field.
404		Most hosts use the older BSD interpretation, so if you turn this on
405		Linux might not communicate correctly with them.
406		Default: FALSE
407	
408	tcp_synack_retries - INTEGER
409		Number of times SYNACKs for a passive TCP connection attempt will
410		be retransmitted. Should not be higher than 255. Default value
411		is 5, which corresponds to 31seconds till the last retransmission
412		with the current initial RTO of 1second. With this the final timeout
413		for a passive TCP connection will happen after 63seconds.
414	
415	tcp_syncookies - BOOLEAN
416		Only valid when the kernel was compiled with CONFIG_SYN_COOKIES
417		Send out syncookies when the syn backlog queue of a socket
418		overflows. This is to prevent against the common 'SYN flood attack'
419		Default: 1
420	
421		Note, that syncookies is fallback facility.
422		It MUST NOT be used to help highly loaded servers to stand
423		against legal connection rate. If you see SYN flood warnings
424		in your logs, but investigation	shows that they occur
425		because of overload with legal connections, you should tune
426		another parameters until this warning disappear.
427		See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
428	
429		syncookies seriously violate TCP protocol, do not allow
430		to use TCP extensions, can result in serious degradation
431		of some services (f.e. SMTP relaying), visible not by you,
432		but your clients and relays, contacting you. While you see
433		SYN flood warnings in logs not being really flooded, your server
434		is seriously misconfigured.
435	
436		If you want to test which effects syncookies have to your
437		network connections you can set this knob to 2 to enable
438		unconditionally generation of syncookies.
439	
440	tcp_fastopen - INTEGER
441		Enable TCP Fast Open feature (draft-ietf-tcpm-fastopen) to send data
442		in the opening SYN packet. To use this feature, the client application
443		must use sendmsg() or sendto() with MSG_FASTOPEN flag rather than
444		connect() to perform a TCP handshake automatically.
445	
446		The values (bitmap) are
447		1: Enables sending data in the opening SYN on the client w/ MSG_FASTOPEN.
448		2: Enables TCP Fast Open on the server side, i.e., allowing data in
449		   a SYN packet to be accepted and passed to the application before
450		   3-way hand shake finishes.
451		4: Send data in the opening SYN regardless of cookie availability and
452		   without a cookie option.
453		0x100: Accept SYN data w/o validating the cookie.
454		0x200: Accept data-in-SYN w/o any cookie option present.
455		0x400/0x800: Enable Fast Open on all listeners regardless of the
456		   TCP_FASTOPEN socket option. The two different flags designate two
457		   different ways of setting max_qlen without the TCP_FASTOPEN socket
458		   option.
459	
460		Default: 1
461	
462		Note that the client & server side Fast Open flags (1 and 2
463		respectively) must be also enabled before the rest of flags can take
464		effect.
465	
466		See include/net/tcp.h and the code for more details.
467	
468	tcp_syn_retries - INTEGER
469		Number of times initial SYNs for an active TCP connection attempt
470		will be retransmitted. Should not be higher than 255. Default value
471		is 6, which corresponds to 63seconds till the last retransmission
472		with the current initial RTO of 1second. With this the final timeout
473		for an active TCP connection attempt will happen after 127seconds.
474	
475	tcp_timestamps - BOOLEAN
476		Enable timestamps as defined in RFC1323.
477	
478	tcp_min_tso_segs - INTEGER
479		Minimal number of segments per TSO frame.
480		Since linux-3.12, TCP does an automatic sizing of TSO frames,
481		depending on flow rate, instead of filling 64Kbytes packets.
482		For specific usages, it's possible to force TCP to build big
483		TSO frames. Note that TCP stack might split too big TSO packets
484		if available window is too small.
485		Default: 2
486	
487	tcp_tso_win_divisor - INTEGER
488		This allows control over what percentage of the congestion window
489		can be consumed by a single TSO frame.
490		The setting of this parameter is a choice between burstiness and
491		building larger TSO frames.
492		Default: 3
493	
494	tcp_tw_recycle - BOOLEAN
495		Enable fast recycling TIME-WAIT sockets. Default value is 0.
496		It should not be changed without advice/request of technical
497		experts.
498	
499	tcp_tw_reuse - BOOLEAN
500		Allow to reuse TIME-WAIT sockets for new connections when it is
501		safe from protocol viewpoint. Default value is 0.
502		It should not be changed without advice/request of technical
503		experts.
504	
505	tcp_window_scaling - BOOLEAN
506		Enable window scaling as defined in RFC1323.
507	
508	tcp_wmem - vector of 3 INTEGERs: min, default, max
509		min: Amount of memory reserved for send buffers for TCP sockets.
510		Each TCP socket has rights to use it due to fact of its birth.
511		Default: 1 page
512	
513		default: initial size of send buffer used by TCP sockets.  This
514		value overrides net.core.wmem_default used by other protocols.
515		It is usually lower than net.core.wmem_default.
516		Default: 16K
517	
518		max: Maximal amount of memory allowed for automatically tuned
519		send buffers for TCP sockets. This value does not override
520		net.core.wmem_max.  Calling setsockopt() with SO_SNDBUF disables
521		automatic tuning of that socket's send buffer size, in which case
522		this value is ignored.
523		Default: between 64K and 4MB, depending on RAM size.
524	
525	tcp_notsent_lowat - UNSIGNED INTEGER
526		A TCP socket can control the amount of unsent bytes in its write queue,
527		thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll()
528		reports POLLOUT events if the amount of unsent bytes is below a per
529		socket value, and if the write queue is not full. sendmsg() will
530		also not add new buffers if the limit is hit.
531	
532		This global variable controls the amount of unsent data for
533		sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change
534		to the global variable has immediate effect.
535	
536		Default: UINT_MAX (0xFFFFFFFF)
537	
538	tcp_workaround_signed_windows - BOOLEAN
539		If set, assume no receipt of a window scaling option means the
540		remote TCP is broken and treats the window as a signed quantity.
541		If unset, assume the remote TCP is not broken even if we do
542		not receive a window scaling option from them.
543		Default: 0
544	
545	tcp_dma_copybreak - INTEGER
546		Lower limit, in bytes, of the size of socket reads that will be
547		offloaded to a DMA copy engine, if one is present in the system
548		and CONFIG_NET_DMA is enabled.
549		Default: 4096
550	
551	tcp_thin_linear_timeouts - BOOLEAN
552		Enable dynamic triggering of linear timeouts for thin streams.
553		If set, a check is performed upon retransmission by timeout to
554		determine if the stream is thin (less than 4 packets in flight).
555		As long as the stream is found to be thin, up to 6 linear
556		timeouts may be performed before exponential backoff mode is
557		initiated. This improves retransmission latency for
558		non-aggressive thin streams, often found to be time-dependent.
559		For more information on thin streams, see
560		Documentation/networking/tcp-thin.txt
561		Default: 0
562	
563	tcp_thin_dupack - BOOLEAN
564		Enable dynamic triggering of retransmissions after one dupACK
565		for thin streams. If set, a check is performed upon reception
566		of a dupACK to determine if the stream is thin (less than 4
567		packets in flight). As long as the stream is found to be thin,
568		data is retransmitted on the first received dupACK. This
569		improves retransmission latency for non-aggressive thin
570		streams, often found to be time-dependent.
571		For more information on thin streams, see
572		Documentation/networking/tcp-thin.txt
573		Default: 0
574	
575	tcp_limit_output_bytes - INTEGER
576		Controls TCP Small Queue limit per tcp socket.
577		TCP bulk sender tends to increase packets in flight until it
578		gets losses notifications. With SNDBUF autotuning, this can
579		result in a large amount of packets queued in qdisc/device
580		on the local machine, hurting latency of other flows, for
581		typical pfifo_fast qdiscs.
582		tcp_limit_output_bytes limits the number of bytes on qdisc
583		or device to reduce artificial RTT/cwnd and reduce bufferbloat.
584		Default: 131072
585	
586	tcp_challenge_ack_limit - INTEGER
587		Limits number of Challenge ACK sent per second, as recommended
588		in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
589		Default: 100
590	
591	UDP variables:
592	
593	udp_mem - vector of 3 INTEGERs: min, pressure, max
594		Number of pages allowed for queueing by all UDP sockets.
595	
596		min: Below this number of pages UDP is not bothered about its
597		memory appetite. When amount of memory allocated by UDP exceeds
598		this number, UDP starts to moderate memory usage.
599	
600		pressure: This value was introduced to follow format of tcp_mem.
601	
602		max: Number of pages allowed for queueing by all UDP sockets.
603	
604		Default is calculated at boot time from amount of available memory.
605	
606	udp_rmem_min - INTEGER
607		Minimal size of receive buffer used by UDP sockets in moderation.
608		Each UDP socket is able to use the size for receiving data, even if
609		total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
610		Default: 1 page
611	
612	udp_wmem_min - INTEGER
613		Minimal size of send buffer used by UDP sockets in moderation.
614		Each UDP socket is able to use the size for sending data, even if
615		total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
616		Default: 1 page
617	
618	CIPSOv4 Variables:
619	
620	cipso_cache_enable - BOOLEAN
621		If set, enable additions to and lookups from the CIPSO label mapping
622		cache.  If unset, additions are ignored and lookups always result in a
623		miss.  However, regardless of the setting the cache is still
624		invalidated when required when means you can safely toggle this on and
625		off and the cache will always be "safe".
626		Default: 1
627	
628	cipso_cache_bucket_size - INTEGER
629		The CIPSO label cache consists of a fixed size hash table with each
630		hash bucket containing a number of cache entries.  This variable limits
631		the number of entries in each hash bucket; the larger the value the
632		more CIPSO label mappings that can be cached.  When the number of
633		entries in a given hash bucket reaches this limit adding new entries
634		causes the oldest entry in the bucket to be removed to make room.
635		Default: 10
636	
637	cipso_rbm_optfmt - BOOLEAN
638		Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
639		the CIPSO draft specification (see Documentation/netlabel for details).
640		This means that when set the CIPSO tag will be padded with empty
641		categories in order to make the packet data 32-bit aligned.
642		Default: 0
643	
644	cipso_rbm_structvalid - BOOLEAN
645		If set, do a very strict check of the CIPSO option when
646		ip_options_compile() is called.  If unset, relax the checks done during
647		ip_options_compile().  Either way is "safe" as errors are caught else
648		where in the CIPSO processing code but setting this to 0 (False) should
649		result in less work (i.e. it should be faster) but could cause problems
650		with other implementations that require strict checking.
651		Default: 0
652	
653	IP Variables:
654	
655	ip_local_port_range - 2 INTEGERS
656		Defines the local port range that is used by TCP and UDP to
657		choose the local port. The first number is the first, the
658		second the last local port number. The default values are
659		32768 and 61000 respectively.
660	
661	ip_local_reserved_ports - list of comma separated ranges
662		Specify the ports which are reserved for known third-party
663		applications. These ports will not be used by automatic port
664		assignments (e.g. when calling connect() or bind() with port
665		number 0). Explicit port allocation behavior is unchanged.
666	
667		The format used for both input and output is a comma separated
668		list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and
669		10). Writing to the file will clear all previously reserved
670		ports and update the current list with the one given in the
671		input.
672	
673		Note that ip_local_port_range and ip_local_reserved_ports
674		settings are independent and both are considered by the kernel
675		when determining which ports are available for automatic port
676		assignments.
677	
678		You can reserve ports which are not in the current
679		ip_local_port_range, e.g.:
680	
681		$ cat /proc/sys/net/ipv4/ip_local_port_range
682		32000	61000
683		$ cat /proc/sys/net/ipv4/ip_local_reserved_ports
684		8080,9148
685	
686		although this is redundant. However such a setting is useful
687		if later the port range is changed to a value that will
688		include the reserved ports.
689	
690		Default: Empty
691	
692	ip_nonlocal_bind - BOOLEAN
693		If set, allows processes to bind() to non-local IP addresses,
694		which can be quite useful - but may break some applications.
695		Default: 0
696	
697	ip_dynaddr - BOOLEAN
698		If set non-zero, enables support for dynamic addresses.
699		If set to a non-zero value larger than 1, a kernel log
700		message will be printed when dynamic address rewriting
701		occurs.
702		Default: 0
703	
704	ip_early_demux - BOOLEAN
705		Optimize input packet processing down to one demux for
706		certain kinds of local sockets.  Currently we only do this
707		for established TCP sockets.
708	
709		It may add an additional cost for pure routing workloads that
710		reduces overall throughput, in such case you should disable it.
711		Default: 1
712	
713	icmp_echo_ignore_all - BOOLEAN
714		If set non-zero, then the kernel will ignore all ICMP ECHO
715		requests sent to it.
716		Default: 0
717	
718	icmp_echo_ignore_broadcasts - BOOLEAN
719		If set non-zero, then the kernel will ignore all ICMP ECHO and
720		TIMESTAMP requests sent to it via broadcast/multicast.
721		Default: 1
722	
723	icmp_ratelimit - INTEGER
724		Limit the maximal rates for sending ICMP packets whose type matches
725		icmp_ratemask (see below) to specific targets.
726		0 to disable any limiting,
727		otherwise the minimal space between responses in milliseconds.
728		Default: 1000
729	
730	icmp_ratemask - INTEGER
731		Mask made of ICMP types for which rates are being limited.
732		Significant bits: IHGFEDCBA9876543210
733		Default mask:     0000001100000011000 (6168)
734	
735		Bit definitions (see include/linux/icmp.h):
736			0 Echo Reply
737			3 Destination Unreachable *
738			4 Source Quench *
739			5 Redirect
740			8 Echo Request
741			B Time Exceeded *
742			C Parameter Problem *
743			D Timestamp Request
744			E Timestamp Reply
745			F Info Request
746			G Info Reply
747			H Address Mask Request
748			I Address Mask Reply
749	
750		* These are rate limited by default (see default mask above)
751	
752	icmp_ignore_bogus_error_responses - BOOLEAN
753		Some routers violate RFC1122 by sending bogus responses to broadcast
754		frames.  Such violations are normally logged via a kernel warning.
755		If this is set to TRUE, the kernel will not give such warnings, which
756		will avoid log file clutter.
757		Default: 1
758	
759	icmp_errors_use_inbound_ifaddr - BOOLEAN
760	
761		If zero, icmp error messages are sent with the primary address of
762		the exiting interface.
763	
764		If non-zero, the message will be sent with the primary address of
765		the interface that received the packet that caused the icmp error.
766		This is the behaviour network many administrators will expect from
767		a router. And it can make debugging complicated network layouts
768		much easier.
769	
770		Note that if no primary address exists for the interface selected,
771		then the primary address of the first non-loopback interface that
772		has one will be used regardless of this setting.
773	
774		Default: 0
775	
776	igmp_max_memberships - INTEGER
777		Change the maximum number of multicast groups we can subscribe to.
778		Default: 20
779	
780		Theoretical maximum value is bounded by having to send a membership
781		report in a single datagram (i.e. the report can't span multiple
782		datagrams, or risk confusing the switch and leaving groups you don't
783		intend to).
784	
785		The number of supported groups 'M' is bounded by the number of group
786		report entries you can fit into a single datagram of 65535 bytes.
787	
788		M = 65536-sizeof (ip header)/(sizeof(Group record))
789	
790		Group records are variable length, with a minimum of 12 bytes.
791		So net.ipv4.igmp_max_memberships should not be set higher than:
792	
793		(65536-24) / 12 = 5459
794	
795		The value 5459 assumes no IP header options, so in practice
796		this number may be lower.
797	
798		conf/interface/*  changes special settings per interface (where
799		"interface" is the name of your network interface)
800	
801		conf/all/*	  is special, changes the settings for all interfaces
802	
803	log_martians - BOOLEAN
804		Log packets with impossible addresses to kernel log.
805		log_martians for the interface will be enabled if at least one of
806		conf/{all,interface}/log_martians is set to TRUE,
807		it will be disabled otherwise
808	
809	accept_redirects - BOOLEAN
810		Accept ICMP redirect messages.
811		accept_redirects for the interface will be enabled if:
812		- both conf/{all,interface}/accept_redirects are TRUE in the case
813		  forwarding for the interface is enabled
814		or
815		- at least one of conf/{all,interface}/accept_redirects is TRUE in the
816		  case forwarding for the interface is disabled
817		accept_redirects for the interface will be disabled otherwise
818		default TRUE (host)
819			FALSE (router)
820	
821	forwarding - BOOLEAN
822		Enable IP forwarding on this interface.
823	
824	mc_forwarding - BOOLEAN
825		Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
826		and a multicast routing daemon is required.
827		conf/all/mc_forwarding must also be set to TRUE to enable multicast
828		routing	for the interface
829	
830	medium_id - INTEGER
831		Integer value used to differentiate the devices by the medium they
832		are attached to. Two devices can have different id values when
833		the broadcast packets are received only on one of them.
834		The default value 0 means that the device is the only interface
835		to its medium, value of -1 means that medium is not known.
836	
837		Currently, it is used to change the proxy_arp behavior:
838		the proxy_arp feature is enabled for packets forwarded between
839		two devices attached to different media.
840	
841	proxy_arp - BOOLEAN
842		Do proxy arp.
843		proxy_arp for the interface will be enabled if at least one of
844		conf/{all,interface}/proxy_arp is set to TRUE,
845		it will be disabled otherwise
846	
847	proxy_arp_pvlan - BOOLEAN
848		Private VLAN proxy arp.
849		Basically allow proxy arp replies back to the same interface
850		(from which the ARP request/solicitation was received).
851	
852		This is done to support (ethernet) switch features, like RFC
853		3069, where the individual ports are NOT allowed to
854		communicate with each other, but they are allowed to talk to
855		the upstream router.  As described in RFC 3069, it is possible
856		to allow these hosts to communicate through the upstream
857		router by proxy_arp'ing. Don't need to be used together with
858		proxy_arp.
859	
860		This technology is known by different names:
861		  In RFC 3069 it is called VLAN Aggregation.
862		  Cisco and Allied Telesyn call it Private VLAN.
863		  Hewlett-Packard call it Source-Port filtering or port-isolation.
864		  Ericsson call it MAC-Forced Forwarding (RFC Draft).
865	
866	shared_media - BOOLEAN
867		Send(router) or accept(host) RFC1620 shared media redirects.
868		Overrides ip_secure_redirects.
869		shared_media for the interface will be enabled if at least one of
870		conf/{all,interface}/shared_media is set to TRUE,
871		it will be disabled otherwise
872		default TRUE
873	
874	secure_redirects - BOOLEAN
875		Accept ICMP redirect messages only for gateways,
876		listed in default gateway list.
877		secure_redirects for the interface will be enabled if at least one of
878		conf/{all,interface}/secure_redirects is set to TRUE,
879		it will be disabled otherwise
880		default TRUE
881	
882	send_redirects - BOOLEAN
883		Send redirects, if router.
884		send_redirects for the interface will be enabled if at least one of
885		conf/{all,interface}/send_redirects is set to TRUE,
886		it will be disabled otherwise
887		Default: TRUE
888	
889	bootp_relay - BOOLEAN
890		Accept packets with source address 0.b.c.d destined
891		not to this host as local ones. It is supposed, that
892		BOOTP relay daemon will catch and forward such packets.
893		conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
894		for the interface
895		default FALSE
896		Not Implemented Yet.
897	
898	accept_source_route - BOOLEAN
899		Accept packets with SRR option.
900		conf/all/accept_source_route must also be set to TRUE to accept packets
901		with SRR option on the interface
902		default TRUE (router)
903			FALSE (host)
904	
905	accept_local - BOOLEAN
906		Accept packets with local source addresses. In combination
907		with suitable routing, this can be used to direct packets
908		between two local interfaces over the wire and have them
909		accepted properly.
910	
911		rp_filter must be set to a non-zero value in order for
912		accept_local to have an effect.
913	
914		default FALSE
915	
916	route_localnet - BOOLEAN
917		Do not consider loopback addresses as martian source or destination
918		while routing. This enables the use of 127/8 for local routing purposes.
919		default FALSE
920	
921	rp_filter - INTEGER
922		0 - No source validation.
923		1 - Strict mode as defined in RFC3704 Strict Reverse Path
924		    Each incoming packet is tested against the FIB and if the interface
925		    is not the best reverse path the packet check will fail.
926		    By default failed packets are discarded.
927		2 - Loose mode as defined in RFC3704 Loose Reverse Path
928		    Each incoming packet's source address is also tested against the FIB
929		    and if the source address is not reachable via any interface
930		    the packet check will fail.
931	
932		Current recommended practice in RFC3704 is to enable strict mode
933		to prevent IP spoofing from DDos attacks. If using asymmetric routing
934		or other complicated routing, then loose mode is recommended.
935	
936		The max value from conf/{all,interface}/rp_filter is used
937		when doing source validation on the {interface}.
938	
939		Default value is 0. Note that some distributions enable it
940		in startup scripts.
941	
942	arp_filter - BOOLEAN
943		1 - Allows you to have multiple network interfaces on the same
944		subnet, and have the ARPs for each interface be answered
945		based on whether or not the kernel would route a packet from
946		the ARP'd IP out that interface (therefore you must use source
947		based routing for this to work). In other words it allows control
948		of which cards (usually 1) will respond to an arp request.
949	
950		0 - (default) The kernel can respond to arp requests with addresses
951		from other interfaces. This may seem wrong but it usually makes
952		sense, because it increases the chance of successful communication.
953		IP addresses are owned by the complete host on Linux, not by
954		particular interfaces. Only for more complex setups like load-
955		balancing, does this behaviour cause problems.
956	
957		arp_filter for the interface will be enabled if at least one of
958		conf/{all,interface}/arp_filter is set to TRUE,
959		it will be disabled otherwise
960	
961	arp_announce - INTEGER
962		Define different restriction levels for announcing the local
963		source IP address from IP packets in ARP requests sent on
964		interface:
965		0 - (default) Use any local address, configured on any interface
966		1 - Try to avoid local addresses that are not in the target's
967		subnet for this interface. This mode is useful when target
968		hosts reachable via this interface require the source IP
969		address in ARP requests to be part of their logical network
970		configured on the receiving interface. When we generate the
971		request we will check all our subnets that include the
972		target IP and will preserve the source address if it is from
973		such subnet. If there is no such subnet we select source
974		address according to the rules for level 2.
975		2 - Always use the best local address for this target.
976		In this mode we ignore the source address in the IP packet
977		and try to select local address that we prefer for talks with
978		the target host. Such local address is selected by looking
979		for primary IP addresses on all our subnets on the outgoing
980		interface that include the target IP address. If no suitable
981		local address is found we select the first local address
982		we have on the outgoing interface or on all other interfaces,
983		with the hope we will receive reply for our request and
984		even sometimes no matter the source IP address we announce.
985	
986		The max value from conf/{all,interface}/arp_announce is used.
987	
988		Increasing the restriction level gives more chance for
989		receiving answer from the resolved target while decreasing
990		the level announces more valid sender's information.
991	
992	arp_ignore - INTEGER
993		Define different modes for sending replies in response to
994		received ARP requests that resolve local target IP addresses:
995		0 - (default): reply for any local target IP address, configured
996		on any interface
997		1 - reply only if the target IP address is local address
998		configured on the incoming interface
999		2 - reply only if the target IP address is local address
1000		configured on the incoming interface and both with the
1001		sender's IP address are part from same subnet on this interface
1002		3 - do not reply for local addresses configured with scope host,
1003		only resolutions for global and link addresses are replied
1004		4-7 - reserved
1005		8 - do not reply for all local addresses
1006	
1007		The max value from conf/{all,interface}/arp_ignore is used
1008		when ARP request is received on the {interface}
1009	
1010	arp_notify - BOOLEAN
1011		Define mode for notification of address and device changes.
1012		0 - (default): do nothing
1013		1 - Generate gratuitous arp requests when device is brought up
1014		    or hardware address changes.
1015	
1016	arp_accept - BOOLEAN
1017		Define behavior for gratuitous ARP frames who's IP is not
1018		already present in the ARP table:
1019		0 - don't create new entries in the ARP table
1020		1 - create new entries in the ARP table
1021	
1022		Both replies and requests type gratuitous arp will trigger the
1023		ARP table to be updated, if this setting is on.
1024	
1025		If the ARP table already contains the IP address of the
1026		gratuitous arp frame, the arp table will be updated regardless
1027		if this setting is on or off.
1028	
1029	
1030	app_solicit - INTEGER
1031		The maximum number of probes to send to the user space ARP daemon
1032		via netlink before dropping back to multicast probes (see
1033		mcast_solicit).  Defaults to 0.
1034	
1035	disable_policy - BOOLEAN
1036		Disable IPSEC policy (SPD) for this interface
1037	
1038	disable_xfrm - BOOLEAN
1039		Disable IPSEC encryption on this interface, whatever the policy
1040	
1041	igmpv2_unsolicited_report_interval - INTEGER
1042		The interval in milliseconds in which the next unsolicited
1043		IGMPv1 or IGMPv2 report retransmit will take place.
1044		Default: 10000 (10 seconds)
1045	
1046	igmpv3_unsolicited_report_interval - INTEGER
1047		The interval in milliseconds in which the next unsolicited
1048		IGMPv3 report retransmit will take place.
1049		Default: 1000 (1 seconds)
1050	
1051	tag - INTEGER
1052		Allows you to write a number, which can be used as required.
1053		Default value is 0.
1054	
1055	Alexey Kuznetsov.
1056	kuznet@ms2.inr.ac.ru
1057	
1058	Updated by:
1059	Andi Kleen
1060	ak@muc.de
1061	Nicolas Delon
1062	delon.nicolas@wanadoo.fr
1063	
1064	
1065	
1066	
1067	/proc/sys/net/ipv6/* Variables:
1068	
1069	IPv6 has no global variables such as tcp_*.  tcp_* settings under ipv4/ also
1070	apply to IPv6 [XXX?].
1071	
1072	bindv6only - BOOLEAN
1073		Default value for IPV6_V6ONLY socket option,
1074		which restricts use of the IPv6 socket to IPv6 communication
1075		only.
1076			TRUE: disable IPv4-mapped address feature
1077			FALSE: enable IPv4-mapped address feature
1078	
1079		Default: FALSE (as specified in RFC3493)
1080	
1081	IPv6 Fragmentation:
1082	
1083	ip6frag_high_thresh - INTEGER
1084		Maximum memory used to reassemble IPv6 fragments. When
1085		ip6frag_high_thresh bytes of memory is allocated for this purpose,
1086		the fragment handler will toss packets until ip6frag_low_thresh
1087		is reached.
1088	
1089	ip6frag_low_thresh - INTEGER
1090		See ip6frag_high_thresh
1091	
1092	ip6frag_time - INTEGER
1093		Time in seconds to keep an IPv6 fragment in memory.
1094	
1095	ip6frag_secret_interval - INTEGER
1096		Regeneration interval (in seconds) of the hash secret (or lifetime
1097		for the hash secret) for IPv6 fragments.
1098		Default: 600
1099	
1100	conf/default/*:
1101		Change the interface-specific default settings.
1102	
1103	
1104	conf/all/*:
1105		Change all the interface-specific settings.
1106	
1107		[XXX:  Other special features than forwarding?]
1108	
1109	conf/all/forwarding - BOOLEAN
1110		Enable global IPv6 forwarding between all interfaces.
1111	
1112		IPv4 and IPv6 work differently here; e.g. netfilter must be used
1113		to control which interfaces may forward packets and which not.
1114	
1115		This also sets all interfaces' Host/Router setting
1116		'forwarding' to the specified value.  See below for details.
1117	
1118		This referred to as global forwarding.
1119	
1120	proxy_ndp - BOOLEAN
1121		Do proxy ndp.
1122	
1123	conf/interface/*:
1124		Change special settings per interface.
1125	
1126		The functional behaviour for certain settings is different
1127		depending on whether local forwarding is enabled or not.
1128	
1129	accept_ra - INTEGER
1130		Accept Router Advertisements; autoconfigure using them.
1131	
1132		It also determines whether or not to transmit Router
1133		Solicitations. If and only if the functional setting is to
1134		accept Router Advertisements, Router Solicitations will be
1135		transmitted.
1136	
1137		Possible values are:
1138			0 Do not accept Router Advertisements.
1139			1 Accept Router Advertisements if forwarding is disabled.
1140			2 Overrule forwarding behaviour. Accept Router Advertisements
1141			  even if forwarding is enabled.
1142	
1143		Functional default: enabled if local forwarding is disabled.
1144				    disabled if local forwarding is enabled.
1145	
1146	accept_ra_defrtr - BOOLEAN
1147		Learn default router in Router Advertisement.
1148	
1149		Functional default: enabled if accept_ra is enabled.
1150				    disabled if accept_ra is disabled.
1151	
1152	accept_ra_pinfo - BOOLEAN
1153		Learn Prefix Information in Router Advertisement.
1154	
1155		Functional default: enabled if accept_ra is enabled.
1156				    disabled if accept_ra is disabled.
1157	
1158	accept_ra_rt_info_max_plen - INTEGER
1159		Maximum prefix length of Route Information in RA.
1160	
1161		Route Information w/ prefix larger than or equal to this
1162		variable shall be ignored.
1163	
1164		Functional default: 0 if accept_ra_rtr_pref is enabled.
1165				    -1 if accept_ra_rtr_pref is disabled.
1166	
1167	accept_ra_rtr_pref - BOOLEAN
1168		Accept Router Preference in RA.
1169	
1170		Functional default: enabled if accept_ra is enabled.
1171				    disabled if accept_ra is disabled.
1172	
1173	accept_redirects - BOOLEAN
1174		Accept Redirects.
1175	
1176		Functional default: enabled if local forwarding is disabled.
1177				    disabled if local forwarding is enabled.
1178	
1179	accept_source_route - INTEGER
1180		Accept source routing (routing extension header).
1181	
1182		>= 0: Accept only routing header type 2.
1183		< 0: Do not accept routing header.
1184	
1185		Default: 0
1186	
1187	autoconf - BOOLEAN
1188		Autoconfigure addresses using Prefix Information in Router
1189		Advertisements.
1190	
1191		Functional default: enabled if accept_ra_pinfo is enabled.
1192				    disabled if accept_ra_pinfo is disabled.
1193	
1194	dad_transmits - INTEGER
1195		The amount of Duplicate Address Detection probes to send.
1196		Default: 1
1197	
1198	forwarding - INTEGER
1199		Configure interface-specific Host/Router behaviour.
1200	
1201		Note: It is recommended to have the same setting on all
1202		interfaces; mixed router/host scenarios are rather uncommon.
1203	
1204		Possible values are:
1205			0 Forwarding disabled
1206			1 Forwarding enabled
1207	
1208		FALSE (0):
1209	
1210		By default, Host behaviour is assumed.  This means:
1211	
1212		1. IsRouter flag is not set in Neighbour Advertisements.
1213		2. If accept_ra is TRUE (default), transmit Router
1214		   Solicitations.
1215		3. If accept_ra is TRUE (default), accept Router
1216		   Advertisements (and do autoconfiguration).
1217		4. If accept_redirects is TRUE (default), accept Redirects.
1218	
1219		TRUE (1):
1220	
1221		If local forwarding is enabled, Router behaviour is assumed.
1222		This means exactly the reverse from the above:
1223	
1224		1. IsRouter flag is set in Neighbour Advertisements.
1225		2. Router Solicitations are not sent unless accept_ra is 2.
1226		3. Router Advertisements are ignored unless accept_ra is 2.
1227		4. Redirects are ignored.
1228	
1229		Default: 0 (disabled) if global forwarding is disabled (default),
1230			 otherwise 1 (enabled).
1231	
1232	hop_limit - INTEGER
1233		Default Hop Limit to set.
1234		Default: 64
1235	
1236	mtu - INTEGER
1237		Default Maximum Transfer Unit
1238		Default: 1280 (IPv6 required minimum)
1239	
1240	router_probe_interval - INTEGER
1241		Minimum interval (in seconds) between Router Probing described
1242		in RFC4191.
1243	
1244		Default: 60
1245	
1246	router_solicitation_delay - INTEGER
1247		Number of seconds to wait after interface is brought up
1248		before sending Router Solicitations.
1249		Default: 1
1250	
1251	router_solicitation_interval - INTEGER
1252		Number of seconds to wait between Router Solicitations.
1253		Default: 4
1254	
1255	router_solicitations - INTEGER
1256		Number of Router Solicitations to send until assuming no
1257		routers are present.
1258		Default: 3
1259	
1260	use_tempaddr - INTEGER
1261		Preference for Privacy Extensions (RFC3041).
1262		  <= 0 : disable Privacy Extensions
1263		  == 1 : enable Privacy Extensions, but prefer public
1264		         addresses over temporary addresses.
1265		  >  1 : enable Privacy Extensions and prefer temporary
1266		         addresses over public addresses.
1267		Default:  0 (for most devices)
1268			 -1 (for point-to-point devices and loopback devices)
1269	
1270	temp_valid_lft - INTEGER
1271		valid lifetime (in seconds) for temporary addresses.
1272		Default: 604800 (7 days)
1273	
1274	temp_prefered_lft - INTEGER
1275		Preferred lifetime (in seconds) for temporary addresses.
1276		Default: 86400 (1 day)
1277	
1278	max_desync_factor - INTEGER
1279		Maximum value for DESYNC_FACTOR, which is a random value
1280		that ensures that clients don't synchronize with each
1281		other and generate new addresses at exactly the same time.
1282		value is in seconds.
1283		Default: 600
1284	
1285	regen_max_retry - INTEGER
1286		Number of attempts before give up attempting to generate
1287		valid temporary addresses.
1288		Default: 5
1289	
1290	max_addresses - INTEGER
1291		Maximum number of autoconfigured addresses per interface.  Setting
1292		to zero disables the limitation.  It is not recommended to set this
1293		value too large (or to zero) because it would be an easy way to
1294		crash the kernel by allowing too many addresses to be created.
1295		Default: 16
1296	
1297	disable_ipv6 - BOOLEAN
1298		Disable IPv6 operation.  If accept_dad is set to 2, this value
1299		will be dynamically set to TRUE if DAD fails for the link-local
1300		address.
1301		Default: FALSE (enable IPv6 operation)
1302	
1303		When this value is changed from 1 to 0 (IPv6 is being enabled),
1304		it will dynamically create a link-local address on the given
1305		interface and start Duplicate Address Detection, if necessary.
1306	
1307		When this value is changed from 0 to 1 (IPv6 is being disabled),
1308		it will dynamically delete all address on the given interface.
1309	
1310	accept_dad - INTEGER
1311		Whether to accept DAD (Duplicate Address Detection).
1312		0: Disable DAD
1313		1: Enable DAD (default)
1314		2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
1315		   link-local address has been found.
1316	
1317	force_tllao - BOOLEAN
1318		Enable sending the target link-layer address option even when
1319		responding to a unicast neighbor solicitation.
1320		Default: FALSE
1321	
1322		Quoting from RFC 2461, section 4.4, Target link-layer address:
1323	
1324		"The option MUST be included for multicast solicitations in order to
1325		avoid infinite Neighbor Solicitation "recursion" when the peer node
1326		does not have a cache entry to return a Neighbor Advertisements
1327		message.  When responding to unicast solicitations, the option can be
1328		omitted since the sender of the solicitation has the correct link-
1329		layer address; otherwise it would not have be able to send the unicast
1330		solicitation in the first place. However, including the link-layer
1331		address in this case adds little overhead and eliminates a potential
1332		race condition where the sender deletes the cached link-layer address
1333		prior to receiving a response to a previous solicitation."
1334	
1335	ndisc_notify - BOOLEAN
1336		Define mode for notification of address and device changes.
1337		0 - (default): do nothing
1338		1 - Generate unsolicited neighbour advertisements when device is brought
1339		    up or hardware address changes.
1340	
1341	mldv1_unsolicited_report_interval - INTEGER
1342		The interval in milliseconds in which the next unsolicited
1343		MLDv1 report retransmit will take place.
1344		Default: 10000 (10 seconds)
1345	
1346	mldv2_unsolicited_report_interval - INTEGER
1347		The interval in milliseconds in which the next unsolicited
1348		MLDv2 report retransmit will take place.
1349		Default: 1000 (1 second)
1350	
1351	force_mld_version - INTEGER
1352		0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed
1353		1 - Enforce to use MLD version 1
1354		2 - Enforce to use MLD version 2
1355	
1356	suppress_frag_ndisc - INTEGER
1357		Control RFC 6980 (Security Implications of IPv6 Fragmentation
1358		with IPv6 Neighbor Discovery) behavior:
1359		1 - (default) discard fragmented neighbor discovery packets
1360		0 - allow fragmented neighbor discovery packets
1361	
1362	icmp/*:
1363	ratelimit - INTEGER
1364		Limit the maximal rates for sending ICMPv6 packets.
1365		0 to disable any limiting,
1366		otherwise the minimal space between responses in milliseconds.
1367		Default: 1000
1368	
1369	
1370	IPv6 Update by:
1371	Pekka Savola <pekkas@netcore.fi>
1372	YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
1373	
1374	
1375	/proc/sys/net/bridge/* Variables:
1376	
1377	bridge-nf-call-arptables - BOOLEAN
1378		1 : pass bridged ARP traffic to arptables' FORWARD chain.
1379		0 : disable this.
1380		Default: 1
1381	
1382	bridge-nf-call-iptables - BOOLEAN
1383		1 : pass bridged IPv4 traffic to iptables' chains.
1384		0 : disable this.
1385		Default: 1
1386	
1387	bridge-nf-call-ip6tables - BOOLEAN
1388		1 : pass bridged IPv6 traffic to ip6tables' chains.
1389		0 : disable this.
1390		Default: 1
1391	
1392	bridge-nf-filter-vlan-tagged - BOOLEAN
1393		1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
1394		0 : disable this.
1395		Default: 0
1396	
1397	bridge-nf-filter-pppoe-tagged - BOOLEAN
1398		1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
1399		0 : disable this.
1400		Default: 0
1401	
1402	bridge-nf-pass-vlan-input-dev - BOOLEAN
1403		1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan
1404		interface on the bridge and set the netfilter input device to the vlan.
1405		This allows use of e.g. "iptables -i br0.1" and makes the REDIRECT
1406		target work with vlan-on-top-of-bridge interfaces.  When no matching
1407		vlan interface is found, or this switch is off, the input device is
1408		set to the bridge interface.
1409		0: disable bridge netfilter vlan interface lookup.
1410		Default: 0
1411	
1412	proc/sys/net/sctp/* Variables:
1413	
1414	addip_enable - BOOLEAN
1415		Enable or disable extension of  Dynamic Address Reconfiguration
1416		(ADD-IP) functionality specified in RFC5061.  This extension provides
1417		the ability to dynamically add and remove new addresses for the SCTP
1418		associations.
1419	
1420		1: Enable extension.
1421	
1422		0: Disable extension.
1423	
1424		Default: 0
1425	
1426	addip_noauth_enable - BOOLEAN
1427		Dynamic Address Reconfiguration (ADD-IP) requires the use of
1428		authentication to protect the operations of adding or removing new
1429		addresses.  This requirement is mandated so that unauthorized hosts
1430		would not be able to hijack associations.  However, older
1431		implementations may not have implemented this requirement while
1432		allowing the ADD-IP extension.  For reasons of interoperability,
1433		we provide this variable to control the enforcement of the
1434		authentication requirement.
1435	
1436		1: Allow ADD-IP extension to be used without authentication.  This
1437		   should only be set in a closed environment for interoperability
1438		   with older implementations.
1439	
1440		0: Enforce the authentication requirement
1441	
1442		Default: 0
1443	
1444	auth_enable - BOOLEAN
1445		Enable or disable Authenticated Chunks extension.  This extension
1446		provides the ability to send and receive authenticated chunks and is
1447		required for secure operation of Dynamic Address Reconfiguration
1448		(ADD-IP) extension.
1449	
1450		1: Enable this extension.
1451		0: Disable this extension.
1452	
1453		Default: 0
1454	
1455	prsctp_enable - BOOLEAN
1456		Enable or disable the Partial Reliability extension (RFC3758) which
1457		is used to notify peers that a given DATA should no longer be expected.
1458	
1459		1: Enable extension
1460		0: Disable
1461	
1462		Default: 1
1463	
1464	max_burst - INTEGER
1465		The limit of the number of new packets that can be initially sent.  It
1466		controls how bursty the generated traffic can be.
1467	
1468		Default: 4
1469	
1470	association_max_retrans - INTEGER
1471		Set the maximum number for retransmissions that an association can
1472		attempt deciding that the remote end is unreachable.  If this value
1473		is exceeded, the association is terminated.
1474	
1475		Default: 10
1476	
1477	max_init_retransmits - INTEGER
1478		The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
1479		that an association will attempt before declaring the destination
1480		unreachable and terminating.
1481	
1482		Default: 8
1483	
1484	path_max_retrans - INTEGER
1485		The maximum number of retransmissions that will be attempted on a given
1486		path.  Once this threshold is exceeded, the path is considered
1487		unreachable, and new traffic will use a different path when the
1488		association is multihomed.
1489	
1490		Default: 5
1491	
1492	pf_retrans - INTEGER
1493		The number of retransmissions that will be attempted on a given path
1494		before traffic is redirected to an alternate transport (should one
1495		exist).  Note this is distinct from path_max_retrans, as a path that
1496		passes the pf_retrans threshold can still be used.  Its only
1497		deprioritized when a transmission path is selected by the stack.  This
1498		setting is primarily used to enable fast failover mechanisms without
1499		having to reduce path_max_retrans to a very low value.  See:
1500		http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt
1501		for details.  Note also that a value of pf_retrans > path_max_retrans
1502		disables this feature
1503	
1504		Default: 0
1505	
1506	rto_initial - INTEGER
1507		The initial round trip timeout value in milliseconds that will be used
1508		in calculating round trip times.  This is the initial time interval
1509		for retransmissions.
1510	
1511		Default: 3000
1512	
1513	rto_max - INTEGER
1514		The maximum value (in milliseconds) of the round trip timeout.  This
1515		is the largest time interval that can elapse between retransmissions.
1516	
1517		Default: 60000
1518	
1519	rto_min - INTEGER
1520		The minimum value (in milliseconds) of the round trip timeout.  This
1521		is the smallest time interval the can elapse between retransmissions.
1522	
1523		Default: 1000
1524	
1525	hb_interval - INTEGER
1526		The interval (in milliseconds) between HEARTBEAT chunks.  These chunks
1527		are sent at the specified interval on idle paths to probe the state of
1528		a given path between 2 associations.
1529	
1530		Default: 30000
1531	
1532	sack_timeout - INTEGER
1533		The amount of time (in milliseconds) that the implementation will wait
1534		to send a SACK.
1535	
1536		Default: 200
1537	
1538	valid_cookie_life - INTEGER
1539		The default lifetime of the SCTP cookie (in milliseconds).  The cookie
1540		is used during association establishment.
1541	
1542		Default: 60000
1543	
1544	cookie_preserve_enable - BOOLEAN
1545		Enable or disable the ability to extend the lifetime of the SCTP cookie
1546		that is used during the establishment phase of SCTP association
1547	
1548		1: Enable cookie lifetime extension.
1549		0: Disable
1550	
1551		Default: 1
1552	
1553	cookie_hmac_alg - STRING
1554		Select the hmac algorithm used when generating the cookie value sent by
1555		a listening sctp socket to a connecting client in the INIT-ACK chunk.
1556		Valid values are:
1557		* md5
1558		* sha1
1559		* none
1560		Ability to assign md5 or sha1 as the selected alg is predicated on the
1561		configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and
1562		CONFIG_CRYPTO_SHA1).
1563	
1564		Default: Dependent on configuration.  MD5 if available, else SHA1 if
1565		available, else none.
1566	
1567	rcvbuf_policy - INTEGER
1568		Determines if the receive buffer is attributed to the socket or to
1569		association.   SCTP supports the capability to create multiple
1570		associations on a single socket.  When using this capability, it is
1571		possible that a single stalled association that's buffering a lot
1572		of data may block other associations from delivering their data by
1573		consuming all of the receive buffer space.  To work around this,
1574		the rcvbuf_policy could be set to attribute the receiver buffer space
1575		to each association instead of the socket.  This prevents the described
1576		blocking.
1577	
1578		1: rcvbuf space is per association
1579		0: rcvbuf space is per socket
1580	
1581		Default: 0
1582	
1583	sndbuf_policy - INTEGER
1584		Similar to rcvbuf_policy above, this applies to send buffer space.
1585	
1586		1: Send buffer is tracked per association
1587		0: Send buffer is tracked per socket.
1588	
1589		Default: 0
1590	
1591	sctp_mem - vector of 3 INTEGERs: min, pressure, max
1592		Number of pages allowed for queueing by all SCTP sockets.
1593	
1594		min: Below this number of pages SCTP is not bothered about its
1595		memory appetite. When amount of memory allocated by SCTP exceeds
1596		this number, SCTP starts to moderate memory usage.
1597	
1598		pressure: This value was introduced to follow format of tcp_mem.
1599	
1600		max: Number of pages allowed for queueing by all SCTP sockets.
1601	
1602		Default is calculated at boot time from amount of available memory.
1603	
1604	sctp_rmem - vector of 3 INTEGERs: min, default, max
1605		Only the first value ("min") is used, "default" and "max" are
1606		ignored.
1607	
1608		min: Minimal size of receive buffer used by SCTP socket.
1609		It is guaranteed to each SCTP socket (but not association) even
1610		under moderate memory pressure.
1611	
1612		Default: 1 page
1613	
1614	sctp_wmem  - vector of 3 INTEGERs: min, default, max
1615		Currently this tunable has no effect.
1616	
1617	addr_scope_policy - INTEGER
1618		Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00
1619	
1620		0   - Disable IPv4 address scoping
1621		1   - Enable IPv4 address scoping
1622		2   - Follow draft but allow IPv4 private addresses
1623		3   - Follow draft but allow IPv4 link local addresses
1624	
1625		Default: 1
1626	
1627	
1628	/proc/sys/net/core/*
1629		Please see: Documentation/sysctl/net.txt for descriptions of these entries.
1630	
1631	
1632	/proc/sys/net/unix/*
1633	max_dgram_qlen - INTEGER
1634		The maximum length of dgram socket receive queue
1635	
1636		Default: 10
1637	
1638	
1639	UNDOCUMENTED:
1640	
1641	/proc/sys/net/irda/*
1642		fast_poll_increase FIXME
1643		warn_noreply_time FIXME
1644		discovery_slots FIXME
1645		slot_timeout FIXME
1646		max_baud_rate FIXME
1647		discovery_timeout FIXME
1648		lap_keepalive_time FIXME
1649		max_noreply_time FIXME
1650		max_tx_data_size FIXME
1651		max_tx_window FIXME
1652		min_tx_turn_time FIXME
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