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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:04 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	route/max_size - INTEGER
60		Maximum number of routes allowed in the kernel.  Increase
61		this when using large numbers of interfaces and/or routes.
62	
63	neigh/default/gc_thresh1 - INTEGER
64		Minimum number of entries to keep.  Garbage collector will not
65		purge entries if there are fewer than this number.
66		Default: 128
67	
68	neigh/default/gc_thresh3 - INTEGER
69		Maximum number of neighbor entries allowed.  Increase this
70		when using large numbers of interfaces and when communicating
71		with large numbers of directly-connected peers.
72		Default: 1024
73	
74	neigh/default/unres_qlen_bytes - INTEGER
75		The maximum number of bytes which may be used by packets
76		queued for each	unresolved address by other network layers.
77		(added in linux 3.3)
78		Setting negative value is meaningless and will return error.
79		Default: 65536 Bytes(64KB)
80	
81	neigh/default/unres_qlen - INTEGER
82		The maximum number of packets which may be queued for each
83		unresolved address by other network layers.
84		(deprecated in linux 3.3) : use unres_qlen_bytes instead.
85		Prior to linux 3.3, the default value is 3 which may cause
86		unexpected packet loss. The current default value is calculated
87		according to default value of unres_qlen_bytes and true size of
88		packet.
89		Default: 31
90	
91	mtu_expires - INTEGER
92		Time, in seconds, that cached PMTU information is kept.
93	
94	min_adv_mss - INTEGER
95		The advertised MSS depends on the first hop route MTU, but will
96		never be lower than this setting.
97	
98	IP Fragmentation:
99	
100	ipfrag_high_thresh - INTEGER
101		Maximum memory used to reassemble IP fragments. When
102		ipfrag_high_thresh bytes of memory is allocated for this purpose,
103		the fragment handler will toss packets until ipfrag_low_thresh
104		is reached.
105	
106	ipfrag_low_thresh - INTEGER
107		See ipfrag_high_thresh
108	
109	ipfrag_time - INTEGER
110		Time in seconds to keep an IP fragment in memory.
111	
112	ipfrag_secret_interval - INTEGER
113		Regeneration interval (in seconds) of the hash secret (or lifetime
114		for the hash secret) for IP fragments.
115		Default: 600
116	
117	ipfrag_max_dist - INTEGER
118		ipfrag_max_dist is a non-negative integer value which defines the
119		maximum "disorder" which is allowed among fragments which share a
120		common IP source address. Note that reordering of packets is
121		not unusual, but if a large number of fragments arrive from a source
122		IP address while a particular fragment queue remains incomplete, it
123		probably indicates that one or more fragments belonging to that queue
124		have been lost. When ipfrag_max_dist is positive, an additional check
125		is done on fragments before they are added to a reassembly queue - if
126		ipfrag_max_dist (or more) fragments have arrived from a particular IP
127		address between additions to any IP fragment queue using that source
128		address, it's presumed that one or more fragments in the queue are
129		lost. The existing fragment queue will be dropped, and a new one
130		started. An ipfrag_max_dist value of zero disables this check.
131	
132		Using a very small value, e.g. 1 or 2, for ipfrag_max_dist can
133		result in unnecessarily dropping fragment queues when normal
134		reordering of packets occurs, which could lead to poor application
135		performance. Using a very large value, e.g. 50000, increases the
136		likelihood of incorrectly reassembling IP fragments that originate
137		from different IP datagrams, which could result in data corruption.
138		Default: 64
139	
140	INET peer storage:
141	
142	inet_peer_threshold - INTEGER
143		The approximate size of the storage.  Starting from this threshold
144		entries will be thrown aggressively.  This threshold also determines
145		entries' time-to-live and time intervals between garbage collection
146		passes.  More entries, less time-to-live, less GC interval.
147	
148	inet_peer_minttl - INTEGER
149		Minimum time-to-live of entries.  Should be enough to cover fragment
150		time-to-live on the reassembling side.  This minimum time-to-live  is
151		guaranteed if the pool size is less than inet_peer_threshold.
152		Measured in seconds.
153	
154	inet_peer_maxttl - INTEGER
155		Maximum time-to-live of entries.  Unused entries will expire after
156		this period of time if there is no memory pressure on the pool (i.e.
157		when the number of entries in the pool is very small).
158		Measured in seconds.
159	
160	TCP variables:
161	
162	somaxconn - INTEGER
163		Limit of socket listen() backlog, known in userspace as SOMAXCONN.
164		Defaults to 128.  See also tcp_max_syn_backlog for additional tuning
165		for TCP sockets.
166	
167	tcp_abort_on_overflow - BOOLEAN
168		If listening service is too slow to accept new connections,
169		reset them. Default state is FALSE. It means that if overflow
170		occurred due to a burst, connection will recover. Enable this
171		option _only_ if you are really sure that listening daemon
172		cannot be tuned to accept connections faster. Enabling this
173		option can harm clients of your server.
174	
175	tcp_adv_win_scale - INTEGER
176		Count buffering overhead as bytes/2^tcp_adv_win_scale
177		(if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
178		if it is <= 0.
179		Possible values are [-31, 31], inclusive.
180		Default: 1
181	
182	tcp_allowed_congestion_control - STRING
183		Show/set the congestion control choices available to non-privileged
184		processes. The list is a subset of those listed in
185		tcp_available_congestion_control.
186		Default is "reno" and the default setting (tcp_congestion_control).
187	
188	tcp_app_win - INTEGER
189		Reserve max(window/2^tcp_app_win, mss) of window for application
190		buffer. Value 0 is special, it means that nothing is reserved.
191		Default: 31
192	
193	tcp_autocorking - BOOLEAN
194		Enable TCP auto corking :
195		When applications do consecutive small write()/sendmsg() system calls,
196		we try to coalesce these small writes as much as possible, to lower
197		total amount of sent packets. This is done if at least one prior
198		packet for the flow is waiting in Qdisc queues or device transmit
199		queue. Applications can still use TCP_CORK for optimal behavior
200		when they know how/when to uncork their sockets.
201		Default : 1
202	
203	tcp_available_congestion_control - STRING
204		Shows the available congestion control choices that are registered.
205		More congestion control algorithms may be available as modules,
206		but not loaded.
207	
208	tcp_base_mss - INTEGER
209		The initial value of search_low to be used by the packetization layer
210		Path MTU discovery (MTU probing).  If MTU probing is enabled,
211		this is the initial MSS used by the connection.
212	
213	tcp_congestion_control - STRING
214		Set the congestion control algorithm to be used for new
215		connections. The algorithm "reno" is always available, but
216		additional choices may be available based on kernel configuration.
217		Default is set as part of kernel configuration.
218		For passive connections, the listener congestion control choice
219		is inherited.
220		[see setsockopt(listenfd, SOL_TCP, TCP_CONGESTION, "name" ...) ]
221	
222	tcp_dsack - BOOLEAN
223		Allows TCP to send "duplicate" SACKs.
224	
225	tcp_early_retrans - INTEGER
226		Enable Early Retransmit (ER), per RFC 5827. ER lowers the threshold
227		for triggering fast retransmit when the amount of outstanding data is
228		small and when no previously unsent data can be transmitted (such
229		that limited transmit could be used). Also controls the use of
230		Tail loss probe (TLP) that converts RTOs occurring due to tail
231		losses into fast recovery (draft-dukkipati-tcpm-tcp-loss-probe-01).
232		Possible values:
233			0 disables ER
234			1 enables ER
235			2 enables ER but delays fast recovery and fast retransmit
236			  by a fourth of RTT. This mitigates connection falsely
237			  recovers when network has a small degree of reordering
238			  (less than 3 packets).
239			3 enables delayed ER and TLP.
240			4 enables TLP only.
241		Default: 3
242	
243	tcp_ecn - INTEGER
244		Control use of Explicit Congestion Notification (ECN) by TCP.
245		ECN is used only when both ends of the TCP connection indicate
246		support for it.  This feature is useful in avoiding losses due
247		to congestion by allowing supporting routers to signal
248		congestion before having to drop packets.
249		Possible values are:
250			0 Disable ECN.  Neither initiate nor accept ECN.
251			1 Enable ECN when requested by incoming connections and
252			  also request ECN on outgoing connection attempts.
253			2 Enable ECN when requested by incoming connections
254			  but do not request ECN on outgoing connections.
255		Default: 2
256	
257	tcp_fack - BOOLEAN
258		Enable FACK congestion avoidance and fast retransmission.
259		The value is not used, if tcp_sack is not enabled.
260	
261	tcp_fin_timeout - INTEGER
262		The length of time an orphaned (no longer referenced by any
263		application) connection will remain in the FIN_WAIT_2 state
264		before it is aborted at the local end.  While a perfectly
265		valid "receive only" state for an un-orphaned connection, an
266		orphaned connection in FIN_WAIT_2 state could otherwise wait
267		forever for the remote to close its end of the connection.
268		Cf. tcp_max_orphans
269		Default: 60 seconds
270	
271	tcp_frto - INTEGER
272		Enables Forward RTO-Recovery (F-RTO) defined in RFC5682.
273		F-RTO is an enhanced recovery algorithm for TCP retransmission
274		timeouts.  It is particularly beneficial in networks where the
275		RTT fluctuates (e.g., wireless). F-RTO is sender-side only
276		modification. It does not require any support from the peer.
277	
278		By default it's enabled with a non-zero value. 0 disables F-RTO.
279	
280	tcp_keepalive_time - INTEGER
281		How often TCP sends out keepalive messages when keepalive is enabled.
282		Default: 2hours.
283	
284	tcp_keepalive_probes - INTEGER
285		How many keepalive probes TCP sends out, until it decides that the
286		connection is broken. Default value: 9.
287	
288	tcp_keepalive_intvl - INTEGER
289		How frequently the probes are send out. Multiplied by
290		tcp_keepalive_probes it is time to kill not responding connection,
291		after probes started. Default value: 75sec i.e. connection
292		will be aborted after ~11 minutes of retries.
293	
294	tcp_low_latency - BOOLEAN
295		If set, the TCP stack makes decisions that prefer lower
296		latency as opposed to higher throughput.  By default, this
297		option is not set meaning that higher throughput is preferred.
298		An example of an application where this default should be
299		changed would be a Beowulf compute cluster.
300		Default: 0
301	
302	tcp_max_orphans - INTEGER
303		Maximal number of TCP sockets not attached to any user file handle,
304		held by system.	If this number is exceeded orphaned connections are
305		reset immediately and warning is printed. This limit exists
306		only to prevent simple DoS attacks, you _must_ not rely on this
307		or lower the limit artificially, but rather increase it
308		(probably, after increasing installed memory),
309		if network conditions require more than default value,
310		and tune network services to linger and kill such states
311		more aggressively. Let me to remind again: each orphan eats
312		up to ~64K of unswappable memory.
313	
314	tcp_max_syn_backlog - INTEGER
315		Maximal number of remembered connection requests, which have not
316		received an acknowledgment from connecting client.
317		The minimal value is 128 for low memory machines, and it will
318		increase in proportion to the memory of machine.
319		If server suffers from overload, try increasing this number.
320	
321	tcp_max_tw_buckets - INTEGER
322		Maximal number of timewait sockets held by system simultaneously.
323		If this number is exceeded time-wait socket is immediately destroyed
324		and warning is printed. This limit exists only to prevent
325		simple DoS attacks, you _must_ not lower the limit artificially,
326		but rather increase it (probably, after increasing installed memory),
327		if network conditions require more than default value.
328	
329	tcp_mem - vector of 3 INTEGERs: min, pressure, max
330		min: below this number of pages TCP is not bothered about its
331		memory appetite.
332	
333		pressure: when amount of memory allocated by TCP exceeds this number
334		of pages, TCP moderates its memory consumption and enters memory
335		pressure mode, which is exited when memory consumption falls
336		under "min".
337	
338		max: number of pages allowed for queueing by all TCP sockets.
339	
340		Defaults are calculated at boot time from amount of available
341		memory.
342	
343	tcp_moderate_rcvbuf - BOOLEAN
344		If set, TCP performs receive buffer auto-tuning, attempting to
345		automatically size the buffer (no greater than tcp_rmem[2]) to
346		match the size required by the path for full throughput.  Enabled by
347		default.
348	
349	tcp_mtu_probing - INTEGER
350		Controls TCP Packetization-Layer Path MTU Discovery.  Takes three
351		values:
352		  0 - Disabled
353		  1 - Disabled by default, enabled when an ICMP black hole detected
354		  2 - Always enabled, use initial MSS of tcp_base_mss.
355	
356	tcp_no_metrics_save - BOOLEAN
357		By default, TCP saves various connection metrics in the route cache
358		when the connection closes, so that connections established in the
359		near future can use these to set initial conditions.  Usually, this
360		increases overall performance, but may sometimes cause performance
361		degradation.  If set, TCP will not cache metrics on closing
362		connections.
363	
364	tcp_orphan_retries - INTEGER
365		This value influences the timeout of a locally closed TCP connection,
366		when RTO retransmissions remain unacknowledged.
367		See tcp_retries2 for more details.
368	
369		The default value is 8.
370		If your machine is a loaded WEB server,
371		you should think about lowering this value, such sockets
372		may consume significant resources. Cf. tcp_max_orphans.
373	
374	tcp_reordering - INTEGER
375		Maximal reordering of packets in a TCP stream.
376		Default: 3
377	
378	tcp_retrans_collapse - BOOLEAN
379		Bug-to-bug compatibility with some broken printers.
380		On retransmit try to send bigger packets to work around bugs in
381		certain TCP stacks.
382	
383	tcp_retries1 - INTEGER
384		This value influences the time, after which TCP decides, that
385		something is wrong due to unacknowledged RTO retransmissions,
386		and reports this suspicion to the network layer.
387		See tcp_retries2 for more details.
388	
389		RFC 1122 recommends at least 3 retransmissions, which is the
390		default.
391	
392	tcp_retries2 - INTEGER
393		This value influences the timeout of an alive TCP connection,
394		when RTO retransmissions remain unacknowledged.
395		Given a value of N, a hypothetical TCP connection following
396		exponential backoff with an initial RTO of TCP_RTO_MIN would
397		retransmit N times before killing the connection at the (N+1)th RTO.
398	
399		The default value of 15 yields a hypothetical timeout of 924.6
400		seconds and is a lower bound for the effective timeout.
401		TCP will effectively time out at the first RTO which exceeds the
402		hypothetical timeout.
403	
404		RFC 1122 recommends at least 100 seconds for the timeout,
405		which corresponds to a value of at least 8.
406	
407	tcp_rfc1337 - BOOLEAN
408		If set, the TCP stack behaves conforming to RFC1337. If unset,
409		we are not conforming to RFC, but prevent TCP TIME_WAIT
410		assassination.
411		Default: 0
412	
413	tcp_rmem - vector of 3 INTEGERs: min, default, max
414		min: Minimal size of receive buffer used by TCP sockets.
415		It is guaranteed to each TCP socket, even under moderate memory
416		pressure.
417		Default: 1 page
418	
419		default: initial size of receive buffer used by TCP sockets.
420		This value overrides net.core.rmem_default used by other protocols.
421		Default: 87380 bytes. This value results in window of 65535 with
422		default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit
423		less for default tcp_app_win. See below about these variables.
424	
425		max: maximal size of receive buffer allowed for automatically
426		selected receiver buffers for TCP socket. This value does not override
427		net.core.rmem_max.  Calling setsockopt() with SO_RCVBUF disables
428		automatic tuning of that socket's receive buffer size, in which
429		case this value is ignored.
430		Default: between 87380B and 6MB, depending on RAM size.
431	
432	tcp_sack - BOOLEAN
433		Enable select acknowledgments (SACKS).
434	
435	tcp_slow_start_after_idle - BOOLEAN
436		If set, provide RFC2861 behavior and time out the congestion
437		window after an idle period.  An idle period is defined at
438		the current RTO.  If unset, the congestion window will not
439		be timed out after an idle period.
440		Default: 1
441	
442	tcp_stdurg - BOOLEAN
443		Use the Host requirements interpretation of the TCP urgent pointer field.
444		Most hosts use the older BSD interpretation, so if you turn this on
445		Linux might not communicate correctly with them.
446		Default: FALSE
447	
448	tcp_synack_retries - INTEGER
449		Number of times SYNACKs for a passive TCP connection attempt will
450		be retransmitted. Should not be higher than 255. Default value
451		is 5, which corresponds to 31seconds till the last retransmission
452		with the current initial RTO of 1second. With this the final timeout
453		for a passive TCP connection will happen after 63seconds.
454	
455	tcp_syncookies - BOOLEAN
456		Only valid when the kernel was compiled with CONFIG_SYN_COOKIES
457		Send out syncookies when the syn backlog queue of a socket
458		overflows. This is to prevent against the common 'SYN flood attack'
459		Default: 1
460	
461		Note, that syncookies is fallback facility.
462		It MUST NOT be used to help highly loaded servers to stand
463		against legal connection rate. If you see SYN flood warnings
464		in your logs, but investigation	shows that they occur
465		because of overload with legal connections, you should tune
466		another parameters until this warning disappear.
467		See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.
468	
469		syncookies seriously violate TCP protocol, do not allow
470		to use TCP extensions, can result in serious degradation
471		of some services (f.e. SMTP relaying), visible not by you,
472		but your clients and relays, contacting you. While you see
473		SYN flood warnings in logs not being really flooded, your server
474		is seriously misconfigured.
475	
476		If you want to test which effects syncookies have to your
477		network connections you can set this knob to 2 to enable
478		unconditionally generation of syncookies.
479	
480	tcp_fastopen - INTEGER
481		Enable TCP Fast Open feature (draft-ietf-tcpm-fastopen) to send data
482		in the opening SYN packet. To use this feature, the client application
483		must use sendmsg() or sendto() with MSG_FASTOPEN flag rather than
484		connect() to perform a TCP handshake automatically.
485	
486		The values (bitmap) are
487		1: Enables sending data in the opening SYN on the client w/ MSG_FASTOPEN.
488		2: Enables TCP Fast Open on the server side, i.e., allowing data in
489		   a SYN packet to be accepted and passed to the application before
490		   3-way hand shake finishes.
491		4: Send data in the opening SYN regardless of cookie availability and
492		   without a cookie option.
493		0x100: Accept SYN data w/o validating the cookie.
494		0x200: Accept data-in-SYN w/o any cookie option present.
495		0x400/0x800: Enable Fast Open on all listeners regardless of the
496		   TCP_FASTOPEN socket option. The two different flags designate two
497		   different ways of setting max_qlen without the TCP_FASTOPEN socket
498		   option.
499	
500		Default: 1
501	
502		Note that the client & server side Fast Open flags (1 and 2
503		respectively) must be also enabled before the rest of flags can take
504		effect.
505	
506		See include/net/tcp.h and the code for more details.
507	
508	tcp_syn_retries - INTEGER
509		Number of times initial SYNs for an active TCP connection attempt
510		will be retransmitted. Should not be higher than 255. Default value
511		is 6, which corresponds to 63seconds till the last retransmission
512		with the current initial RTO of 1second. With this the final timeout
513		for an active TCP connection attempt will happen after 127seconds.
514	
515	tcp_timestamps - BOOLEAN
516		Enable timestamps as defined in RFC1323.
517	
518	tcp_min_tso_segs - INTEGER
519		Minimal number of segments per TSO frame.
520		Since linux-3.12, TCP does an automatic sizing of TSO frames,
521		depending on flow rate, instead of filling 64Kbytes packets.
522		For specific usages, it's possible to force TCP to build big
523		TSO frames. Note that TCP stack might split too big TSO packets
524		if available window is too small.
525		Default: 2
526	
527	tcp_tso_win_divisor - INTEGER
528		This allows control over what percentage of the congestion window
529		can be consumed by a single TSO frame.
530		The setting of this parameter is a choice between burstiness and
531		building larger TSO frames.
532		Default: 3
533	
534	tcp_tw_recycle - BOOLEAN
535		Enable fast recycling TIME-WAIT sockets. Default value is 0.
536		It should not be changed without advice/request of technical
537		experts.
538	
539	tcp_tw_reuse - BOOLEAN
540		Allow to reuse TIME-WAIT sockets for new connections when it is
541		safe from protocol viewpoint. Default value is 0.
542		It should not be changed without advice/request of technical
543		experts.
544	
545	tcp_window_scaling - BOOLEAN
546		Enable window scaling as defined in RFC1323.
547	
548	tcp_wmem - vector of 3 INTEGERs: min, default, max
549		min: Amount of memory reserved for send buffers for TCP sockets.
550		Each TCP socket has rights to use it due to fact of its birth.
551		Default: 1 page
552	
553		default: initial size of send buffer used by TCP sockets.  This
554		value overrides net.core.wmem_default used by other protocols.
555		It is usually lower than net.core.wmem_default.
556		Default: 16K
557	
558		max: Maximal amount of memory allowed for automatically tuned
559		send buffers for TCP sockets. This value does not override
560		net.core.wmem_max.  Calling setsockopt() with SO_SNDBUF disables
561		automatic tuning of that socket's send buffer size, in which case
562		this value is ignored.
563		Default: between 64K and 4MB, depending on RAM size.
564	
565	tcp_notsent_lowat - UNSIGNED INTEGER
566		A TCP socket can control the amount of unsent bytes in its write queue,
567		thanks to TCP_NOTSENT_LOWAT socket option. poll()/select()/epoll()
568		reports POLLOUT events if the amount of unsent bytes is below a per
569		socket value, and if the write queue is not full. sendmsg() will
570		also not add new buffers if the limit is hit.
571	
572		This global variable controls the amount of unsent data for
573		sockets not using TCP_NOTSENT_LOWAT. For these sockets, a change
574		to the global variable has immediate effect.
575	
576		Default: UINT_MAX (0xFFFFFFFF)
577	
578	tcp_workaround_signed_windows - BOOLEAN
579		If set, assume no receipt of a window scaling option means the
580		remote TCP is broken and treats the window as a signed quantity.
581		If unset, assume the remote TCP is not broken even if we do
582		not receive a window scaling option from them.
583		Default: 0
584	
585	tcp_dma_copybreak - INTEGER
586		Lower limit, in bytes, of the size of socket reads that will be
587		offloaded to a DMA copy engine, if one is present in the system
588		and CONFIG_NET_DMA is enabled.
589		Default: 4096
590	
591	tcp_thin_linear_timeouts - BOOLEAN
592		Enable dynamic triggering of linear timeouts for thin streams.
593		If set, a check is performed upon retransmission by timeout to
594		determine if the stream is thin (less than 4 packets in flight).
595		As long as the stream is found to be thin, up to 6 linear
596		timeouts may be performed before exponential backoff mode is
597		initiated. This improves retransmission latency for
598		non-aggressive thin streams, often found to be time-dependent.
599		For more information on thin streams, see
600		Documentation/networking/tcp-thin.txt
601		Default: 0
602	
603	tcp_thin_dupack - BOOLEAN
604		Enable dynamic triggering of retransmissions after one dupACK
605		for thin streams. If set, a check is performed upon reception
606		of a dupACK to determine if the stream is thin (less than 4
607		packets in flight). As long as the stream is found to be thin,
608		data is retransmitted on the first received dupACK. This
609		improves retransmission latency for non-aggressive thin
610		streams, often found to be time-dependent.
611		For more information on thin streams, see
612		Documentation/networking/tcp-thin.txt
613		Default: 0
614	
615	tcp_limit_output_bytes - INTEGER
616		Controls TCP Small Queue limit per tcp socket.
617		TCP bulk sender tends to increase packets in flight until it
618		gets losses notifications. With SNDBUF autotuning, this can
619		result in a large amount of packets queued in qdisc/device
620		on the local machine, hurting latency of other flows, for
621		typical pfifo_fast qdiscs.
622		tcp_limit_output_bytes limits the number of bytes on qdisc
623		or device to reduce artificial RTT/cwnd and reduce bufferbloat.
624		Default: 131072
625	
626	tcp_challenge_ack_limit - INTEGER
627		Limits number of Challenge ACK sent per second, as recommended
628		in RFC 5961 (Improving TCP's Robustness to Blind In-Window Attacks)
629		Default: 100
630	
631	UDP variables:
632	
633	udp_mem - vector of 3 INTEGERs: min, pressure, max
634		Number of pages allowed for queueing by all UDP sockets.
635	
636		min: Below this number of pages UDP is not bothered about its
637		memory appetite. When amount of memory allocated by UDP exceeds
638		this number, UDP starts to moderate memory usage.
639	
640		pressure: This value was introduced to follow format of tcp_mem.
641	
642		max: Number of pages allowed for queueing by all UDP sockets.
643	
644		Default is calculated at boot time from amount of available memory.
645	
646	udp_rmem_min - INTEGER
647		Minimal size of receive buffer used by UDP sockets in moderation.
648		Each UDP socket is able to use the size for receiving data, even if
649		total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
650		Default: 1 page
651	
652	udp_wmem_min - INTEGER
653		Minimal size of send buffer used by UDP sockets in moderation.
654		Each UDP socket is able to use the size for sending data, even if
655		total pages of UDP sockets exceed udp_mem pressure. The unit is byte.
656		Default: 1 page
657	
658	CIPSOv4 Variables:
659	
660	cipso_cache_enable - BOOLEAN
661		If set, enable additions to and lookups from the CIPSO label mapping
662		cache.  If unset, additions are ignored and lookups always result in a
663		miss.  However, regardless of the setting the cache is still
664		invalidated when required when means you can safely toggle this on and
665		off and the cache will always be "safe".
666		Default: 1
667	
668	cipso_cache_bucket_size - INTEGER
669		The CIPSO label cache consists of a fixed size hash table with each
670		hash bucket containing a number of cache entries.  This variable limits
671		the number of entries in each hash bucket; the larger the value the
672		more CIPSO label mappings that can be cached.  When the number of
673		entries in a given hash bucket reaches this limit adding new entries
674		causes the oldest entry in the bucket to be removed to make room.
675		Default: 10
676	
677	cipso_rbm_optfmt - BOOLEAN
678		Enable the "Optimized Tag 1 Format" as defined in section 3.4.2.6 of
679		the CIPSO draft specification (see Documentation/netlabel for details).
680		This means that when set the CIPSO tag will be padded with empty
681		categories in order to make the packet data 32-bit aligned.
682		Default: 0
683	
684	cipso_rbm_structvalid - BOOLEAN
685		If set, do a very strict check of the CIPSO option when
686		ip_options_compile() is called.  If unset, relax the checks done during
687		ip_options_compile().  Either way is "safe" as errors are caught else
688		where in the CIPSO processing code but setting this to 0 (False) should
689		result in less work (i.e. it should be faster) but could cause problems
690		with other implementations that require strict checking.
691		Default: 0
692	
693	IP Variables:
694	
695	ip_local_port_range - 2 INTEGERS
696		Defines the local port range that is used by TCP and UDP to
697		choose the local port. The first number is the first, the
698		second the last local port number. The default values are
699		32768 and 61000 respectively.
700	
701	ip_local_reserved_ports - list of comma separated ranges
702		Specify the ports which are reserved for known third-party
703		applications. These ports will not be used by automatic port
704		assignments (e.g. when calling connect() or bind() with port
705		number 0). Explicit port allocation behavior is unchanged.
706	
707		The format used for both input and output is a comma separated
708		list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and
709		10). Writing to the file will clear all previously reserved
710		ports and update the current list with the one given in the
711		input.
712	
713		Note that ip_local_port_range and ip_local_reserved_ports
714		settings are independent and both are considered by the kernel
715		when determining which ports are available for automatic port
716		assignments.
717	
718		You can reserve ports which are not in the current
719		ip_local_port_range, e.g.:
720	
721		$ cat /proc/sys/net/ipv4/ip_local_port_range
722		32000	61000
723		$ cat /proc/sys/net/ipv4/ip_local_reserved_ports
724		8080,9148
725	
726		although this is redundant. However such a setting is useful
727		if later the port range is changed to a value that will
728		include the reserved ports.
729	
730		Default: Empty
731	
732	ip_nonlocal_bind - BOOLEAN
733		If set, allows processes to bind() to non-local IP addresses,
734		which can be quite useful - but may break some applications.
735		Default: 0
736	
737	ip_dynaddr - BOOLEAN
738		If set non-zero, enables support for dynamic addresses.
739		If set to a non-zero value larger than 1, a kernel log
740		message will be printed when dynamic address rewriting
741		occurs.
742		Default: 0
743	
744	ip_early_demux - BOOLEAN
745		Optimize input packet processing down to one demux for
746		certain kinds of local sockets.  Currently we only do this
747		for established TCP sockets.
748	
749		It may add an additional cost for pure routing workloads that
750		reduces overall throughput, in such case you should disable it.
751		Default: 1
752	
753	icmp_echo_ignore_all - BOOLEAN
754		If set non-zero, then the kernel will ignore all ICMP ECHO
755		requests sent to it.
756		Default: 0
757	
758	icmp_echo_ignore_broadcasts - BOOLEAN
759		If set non-zero, then the kernel will ignore all ICMP ECHO and
760		TIMESTAMP requests sent to it via broadcast/multicast.
761		Default: 1
762	
763	icmp_ratelimit - INTEGER
764		Limit the maximal rates for sending ICMP packets whose type matches
765		icmp_ratemask (see below) to specific targets.
766		0 to disable any limiting,
767		otherwise the minimal space between responses in milliseconds.
768		Default: 1000
769	
770	icmp_ratemask - INTEGER
771		Mask made of ICMP types for which rates are being limited.
772		Significant bits: IHGFEDCBA9876543210
773		Default mask:     0000001100000011000 (6168)
774	
775		Bit definitions (see include/linux/icmp.h):
776			0 Echo Reply
777			3 Destination Unreachable *
778			4 Source Quench *
779			5 Redirect
780			8 Echo Request
781			B Time Exceeded *
782			C Parameter Problem *
783			D Timestamp Request
784			E Timestamp Reply
785			F Info Request
786			G Info Reply
787			H Address Mask Request
788			I Address Mask Reply
789	
790		* These are rate limited by default (see default mask above)
791	
792	icmp_ignore_bogus_error_responses - BOOLEAN
793		Some routers violate RFC1122 by sending bogus responses to broadcast
794		frames.  Such violations are normally logged via a kernel warning.
795		If this is set to TRUE, the kernel will not give such warnings, which
796		will avoid log file clutter.
797		Default: 1
798	
799	icmp_errors_use_inbound_ifaddr - BOOLEAN
800	
801		If zero, icmp error messages are sent with the primary address of
802		the exiting interface.
803	
804		If non-zero, the message will be sent with the primary address of
805		the interface that received the packet that caused the icmp error.
806		This is the behaviour network many administrators will expect from
807		a router. And it can make debugging complicated network layouts
808		much easier.
809	
810		Note that if no primary address exists for the interface selected,
811		then the primary address of the first non-loopback interface that
812		has one will be used regardless of this setting.
813	
814		Default: 0
815	
816	igmp_max_memberships - INTEGER
817		Change the maximum number of multicast groups we can subscribe to.
818		Default: 20
819	
820		Theoretical maximum value is bounded by having to send a membership
821		report in a single datagram (i.e. the report can't span multiple
822		datagrams, or risk confusing the switch and leaving groups you don't
823		intend to).
824	
825		The number of supported groups 'M' is bounded by the number of group
826		report entries you can fit into a single datagram of 65535 bytes.
827	
828		M = 65536-sizeof (ip header)/(sizeof(Group record))
829	
830		Group records are variable length, with a minimum of 12 bytes.
831		So net.ipv4.igmp_max_memberships should not be set higher than:
832	
833		(65536-24) / 12 = 5459
834	
835		The value 5459 assumes no IP header options, so in practice
836		this number may be lower.
837	
838		conf/interface/*  changes special settings per interface (where
839		"interface" is the name of your network interface)
840	
841		conf/all/*	  is special, changes the settings for all interfaces
842	
843	log_martians - BOOLEAN
844		Log packets with impossible addresses to kernel log.
845		log_martians for the interface will be enabled if at least one of
846		conf/{all,interface}/log_martians is set to TRUE,
847		it will be disabled otherwise
848	
849	accept_redirects - BOOLEAN
850		Accept ICMP redirect messages.
851		accept_redirects for the interface will be enabled if:
852		- both conf/{all,interface}/accept_redirects are TRUE in the case
853		  forwarding for the interface is enabled
854		or
855		- at least one of conf/{all,interface}/accept_redirects is TRUE in the
856		  case forwarding for the interface is disabled
857		accept_redirects for the interface will be disabled otherwise
858		default TRUE (host)
859			FALSE (router)
860	
861	forwarding - BOOLEAN
862		Enable IP forwarding on this interface.
863	
864	mc_forwarding - BOOLEAN
865		Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE
866		and a multicast routing daemon is required.
867		conf/all/mc_forwarding must also be set to TRUE to enable multicast
868		routing	for the interface
869	
870	medium_id - INTEGER
871		Integer value used to differentiate the devices by the medium they
872		are attached to. Two devices can have different id values when
873		the broadcast packets are received only on one of them.
874		The default value 0 means that the device is the only interface
875		to its medium, value of -1 means that medium is not known.
876	
877		Currently, it is used to change the proxy_arp behavior:
878		the proxy_arp feature is enabled for packets forwarded between
879		two devices attached to different media.
880	
881	proxy_arp - BOOLEAN
882		Do proxy arp.
883		proxy_arp for the interface will be enabled if at least one of
884		conf/{all,interface}/proxy_arp is set to TRUE,
885		it will be disabled otherwise
886	
887	proxy_arp_pvlan - BOOLEAN
888		Private VLAN proxy arp.
889		Basically allow proxy arp replies back to the same interface
890		(from which the ARP request/solicitation was received).
891	
892		This is done to support (ethernet) switch features, like RFC
893		3069, where the individual ports are NOT allowed to
894		communicate with each other, but they are allowed to talk to
895		the upstream router.  As described in RFC 3069, it is possible
896		to allow these hosts to communicate through the upstream
897		router by proxy_arp'ing. Don't need to be used together with
898		proxy_arp.
899	
900		This technology is known by different names:
901		  In RFC 3069 it is called VLAN Aggregation.
902		  Cisco and Allied Telesyn call it Private VLAN.
903		  Hewlett-Packard call it Source-Port filtering or port-isolation.
904		  Ericsson call it MAC-Forced Forwarding (RFC Draft).
905	
906	shared_media - BOOLEAN
907		Send(router) or accept(host) RFC1620 shared media redirects.
908		Overrides ip_secure_redirects.
909		shared_media for the interface will be enabled if at least one of
910		conf/{all,interface}/shared_media is set to TRUE,
911		it will be disabled otherwise
912		default TRUE
913	
914	secure_redirects - BOOLEAN
915		Accept ICMP redirect messages only for gateways,
916		listed in default gateway list.
917		secure_redirects for the interface will be enabled if at least one of
918		conf/{all,interface}/secure_redirects is set to TRUE,
919		it will be disabled otherwise
920		default TRUE
921	
922	send_redirects - BOOLEAN
923		Send redirects, if router.
924		send_redirects for the interface will be enabled if at least one of
925		conf/{all,interface}/send_redirects is set to TRUE,
926		it will be disabled otherwise
927		Default: TRUE
928	
929	bootp_relay - BOOLEAN
930		Accept packets with source address 0.b.c.d destined
931		not to this host as local ones. It is supposed, that
932		BOOTP relay daemon will catch and forward such packets.
933		conf/all/bootp_relay must also be set to TRUE to enable BOOTP relay
934		for the interface
935		default FALSE
936		Not Implemented Yet.
937	
938	accept_source_route - BOOLEAN
939		Accept packets with SRR option.
940		conf/all/accept_source_route must also be set to TRUE to accept packets
941		with SRR option on the interface
942		default TRUE (router)
943			FALSE (host)
944	
945	accept_local - BOOLEAN
946		Accept packets with local source addresses. In combination
947		with suitable routing, this can be used to direct packets
948		between two local interfaces over the wire and have them
949		accepted properly.
950	
951		rp_filter must be set to a non-zero value in order for
952		accept_local to have an effect.
953	
954		default FALSE
955	
956	route_localnet - BOOLEAN
957		Do not consider loopback addresses as martian source or destination
958		while routing. This enables the use of 127/8 for local routing purposes.
959		default FALSE
960	
961	rp_filter - INTEGER
962		0 - No source validation.
963		1 - Strict mode as defined in RFC3704 Strict Reverse Path
964		    Each incoming packet is tested against the FIB and if the interface
965		    is not the best reverse path the packet check will fail.
966		    By default failed packets are discarded.
967		2 - Loose mode as defined in RFC3704 Loose Reverse Path
968		    Each incoming packet's source address is also tested against the FIB
969		    and if the source address is not reachable via any interface
970		    the packet check will fail.
971	
972		Current recommended practice in RFC3704 is to enable strict mode
973		to prevent IP spoofing from DDos attacks. If using asymmetric routing
974		or other complicated routing, then loose mode is recommended.
975	
976		The max value from conf/{all,interface}/rp_filter is used
977		when doing source validation on the {interface}.
978	
979		Default value is 0. Note that some distributions enable it
980		in startup scripts.
981	
982	arp_filter - BOOLEAN
983		1 - Allows you to have multiple network interfaces on the same
984		subnet, and have the ARPs for each interface be answered
985		based on whether or not the kernel would route a packet from
986		the ARP'd IP out that interface (therefore you must use source
987		based routing for this to work). In other words it allows control
988		of which cards (usually 1) will respond to an arp request.
989	
990		0 - (default) The kernel can respond to arp requests with addresses
991		from other interfaces. This may seem wrong but it usually makes
992		sense, because it increases the chance of successful communication.
993		IP addresses are owned by the complete host on Linux, not by
994		particular interfaces. Only for more complex setups like load-
995		balancing, does this behaviour cause problems.
996	
997		arp_filter for the interface will be enabled if at least one of
998		conf/{all,interface}/arp_filter is set to TRUE,
999		it will be disabled otherwise
1000	
1001	arp_announce - INTEGER
1002		Define different restriction levels for announcing the local
1003		source IP address from IP packets in ARP requests sent on
1004		interface:
1005		0 - (default) Use any local address, configured on any interface
1006		1 - Try to avoid local addresses that are not in the target's
1007		subnet for this interface. This mode is useful when target
1008		hosts reachable via this interface require the source IP
1009		address in ARP requests to be part of their logical network
1010		configured on the receiving interface. When we generate the
1011		request we will check all our subnets that include the
1012		target IP and will preserve the source address if it is from
1013		such subnet. If there is no such subnet we select source
1014		address according to the rules for level 2.
1015		2 - Always use the best local address for this target.
1016		In this mode we ignore the source address in the IP packet
1017		and try to select local address that we prefer for talks with
1018		the target host. Such local address is selected by looking
1019		for primary IP addresses on all our subnets on the outgoing
1020		interface that include the target IP address. If no suitable
1021		local address is found we select the first local address
1022		we have on the outgoing interface or on all other interfaces,
1023		with the hope we will receive reply for our request and
1024		even sometimes no matter the source IP address we announce.
1025	
1026		The max value from conf/{all,interface}/arp_announce is used.
1027	
1028		Increasing the restriction level gives more chance for
1029		receiving answer from the resolved target while decreasing
1030		the level announces more valid sender's information.
1031	
1032	arp_ignore - INTEGER
1033		Define different modes for sending replies in response to
1034		received ARP requests that resolve local target IP addresses:
1035		0 - (default): reply for any local target IP address, configured
1036		on any interface
1037		1 - reply only if the target IP address is local address
1038		configured on the incoming interface
1039		2 - reply only if the target IP address is local address
1040		configured on the incoming interface and both with the
1041		sender's IP address are part from same subnet on this interface
1042		3 - do not reply for local addresses configured with scope host,
1043		only resolutions for global and link addresses are replied
1044		4-7 - reserved
1045		8 - do not reply for all local addresses
1046	
1047		The max value from conf/{all,interface}/arp_ignore is used
1048		when ARP request is received on the {interface}
1049	
1050	arp_notify - BOOLEAN
1051		Define mode for notification of address and device changes.
1052		0 - (default): do nothing
1053		1 - Generate gratuitous arp requests when device is brought up
1054		    or hardware address changes.
1055	
1056	arp_accept - BOOLEAN
1057		Define behavior for gratuitous ARP frames who's IP is not
1058		already present in the ARP table:
1059		0 - don't create new entries in the ARP table
1060		1 - create new entries in the ARP table
1061	
1062		Both replies and requests type gratuitous arp will trigger the
1063		ARP table to be updated, if this setting is on.
1064	
1065		If the ARP table already contains the IP address of the
1066		gratuitous arp frame, the arp table will be updated regardless
1067		if this setting is on or off.
1068	
1069	
1070	app_solicit - INTEGER
1071		The maximum number of probes to send to the user space ARP daemon
1072		via netlink before dropping back to multicast probes (see
1073		mcast_solicit).  Defaults to 0.
1074	
1075	disable_policy - BOOLEAN
1076		Disable IPSEC policy (SPD) for this interface
1077	
1078	disable_xfrm - BOOLEAN
1079		Disable IPSEC encryption on this interface, whatever the policy
1080	
1081	igmpv2_unsolicited_report_interval - INTEGER
1082		The interval in milliseconds in which the next unsolicited
1083		IGMPv1 or IGMPv2 report retransmit will take place.
1084		Default: 10000 (10 seconds)
1085	
1086	igmpv3_unsolicited_report_interval - INTEGER
1087		The interval in milliseconds in which the next unsolicited
1088		IGMPv3 report retransmit will take place.
1089		Default: 1000 (1 seconds)
1090	
1091	promote_secondaries - BOOLEAN
1092		When a primary IP address is removed from this interface
1093		promote a corresponding secondary IP address instead of
1094		removing all the corresponding secondary IP addresses.
1095	
1096	
1097	tag - INTEGER
1098		Allows you to write a number, which can be used as required.
1099		Default value is 0.
1100	
1101	Alexey Kuznetsov.
1102	kuznet@ms2.inr.ac.ru
1103	
1104	Updated by:
1105	Andi Kleen
1106	ak@muc.de
1107	Nicolas Delon
1108	delon.nicolas@wanadoo.fr
1109	
1110	
1111	
1112	
1113	/proc/sys/net/ipv6/* Variables:
1114	
1115	IPv6 has no global variables such as tcp_*.  tcp_* settings under ipv4/ also
1116	apply to IPv6 [XXX?].
1117	
1118	bindv6only - BOOLEAN
1119		Default value for IPV6_V6ONLY socket option,
1120		which restricts use of the IPv6 socket to IPv6 communication
1121		only.
1122			TRUE: disable IPv4-mapped address feature
1123			FALSE: enable IPv4-mapped address feature
1124	
1125		Default: FALSE (as specified in RFC3493)
1126	
1127	flowlabel_consistency - BOOLEAN
1128		Protect the consistency (and unicity) of flow label.
1129		You have to disable it to use IPV6_FL_F_REFLECT flag on the
1130		flow label manager.
1131		TRUE: enabled
1132		FALSE: disabled
1133		Default: TRUE
1134	
1135	anycast_src_echo_reply - BOOLEAN
1136		Controls the use of anycast addresses as source addresses for ICMPv6
1137		echo reply
1138		TRUE:  enabled
1139		FALSE: disabled
1140		Default: FALSE
1141	
1142	IPv6 Fragmentation:
1143	
1144	ip6frag_high_thresh - INTEGER
1145		Maximum memory used to reassemble IPv6 fragments. When
1146		ip6frag_high_thresh bytes of memory is allocated for this purpose,
1147		the fragment handler will toss packets until ip6frag_low_thresh
1148		is reached.
1149	
1150	ip6frag_low_thresh - INTEGER
1151		See ip6frag_high_thresh
1152	
1153	ip6frag_time - INTEGER
1154		Time in seconds to keep an IPv6 fragment in memory.
1155	
1156	ip6frag_secret_interval - INTEGER
1157		Regeneration interval (in seconds) of the hash secret (or lifetime
1158		for the hash secret) for IPv6 fragments.
1159		Default: 600
1160	
1161	conf/default/*:
1162		Change the interface-specific default settings.
1163	
1164	
1165	conf/all/*:
1166		Change all the interface-specific settings.
1167	
1168		[XXX:  Other special features than forwarding?]
1169	
1170	conf/all/forwarding - BOOLEAN
1171		Enable global IPv6 forwarding between all interfaces.
1172	
1173		IPv4 and IPv6 work differently here; e.g. netfilter must be used
1174		to control which interfaces may forward packets and which not.
1175	
1176		This also sets all interfaces' Host/Router setting
1177		'forwarding' to the specified value.  See below for details.
1178	
1179		This referred to as global forwarding.
1180	
1181	proxy_ndp - BOOLEAN
1182		Do proxy ndp.
1183	
1184	conf/interface/*:
1185		Change special settings per interface.
1186	
1187		The functional behaviour for certain settings is different
1188		depending on whether local forwarding is enabled or not.
1189	
1190	accept_ra - INTEGER
1191		Accept Router Advertisements; autoconfigure using them.
1192	
1193		It also determines whether or not to transmit Router
1194		Solicitations. If and only if the functional setting is to
1195		accept Router Advertisements, Router Solicitations will be
1196		transmitted.
1197	
1198		Possible values are:
1199			0 Do not accept Router Advertisements.
1200			1 Accept Router Advertisements if forwarding is disabled.
1201			2 Overrule forwarding behaviour. Accept Router Advertisements
1202			  even if forwarding is enabled.
1203	
1204		Functional default: enabled if local forwarding is disabled.
1205				    disabled if local forwarding is enabled.
1206	
1207	accept_ra_defrtr - BOOLEAN
1208		Learn default router in Router Advertisement.
1209	
1210		Functional default: enabled if accept_ra is enabled.
1211				    disabled if accept_ra is disabled.
1212	
1213	accept_ra_pinfo - BOOLEAN
1214		Learn Prefix Information in Router Advertisement.
1215	
1216		Functional default: enabled if accept_ra is enabled.
1217				    disabled if accept_ra is disabled.
1218	
1219	accept_ra_rt_info_max_plen - INTEGER
1220		Maximum prefix length of Route Information in RA.
1221	
1222		Route Information w/ prefix larger than or equal to this
1223		variable shall be ignored.
1224	
1225		Functional default: 0 if accept_ra_rtr_pref is enabled.
1226				    -1 if accept_ra_rtr_pref is disabled.
1227	
1228	accept_ra_rtr_pref - BOOLEAN
1229		Accept Router Preference in RA.
1230	
1231		Functional default: enabled if accept_ra is enabled.
1232				    disabled if accept_ra is disabled.
1233	
1234	accept_redirects - BOOLEAN
1235		Accept Redirects.
1236	
1237		Functional default: enabled if local forwarding is disabled.
1238				    disabled if local forwarding is enabled.
1239	
1240	accept_source_route - INTEGER
1241		Accept source routing (routing extension header).
1242	
1243		>= 0: Accept only routing header type 2.
1244		< 0: Do not accept routing header.
1245	
1246		Default: 0
1247	
1248	autoconf - BOOLEAN
1249		Autoconfigure addresses using Prefix Information in Router
1250		Advertisements.
1251	
1252		Functional default: enabled if accept_ra_pinfo is enabled.
1253				    disabled if accept_ra_pinfo is disabled.
1254	
1255	dad_transmits - INTEGER
1256		The amount of Duplicate Address Detection probes to send.
1257		Default: 1
1258	
1259	forwarding - INTEGER
1260		Configure interface-specific Host/Router behaviour.
1261	
1262		Note: It is recommended to have the same setting on all
1263		interfaces; mixed router/host scenarios are rather uncommon.
1264	
1265		Possible values are:
1266			0 Forwarding disabled
1267			1 Forwarding enabled
1268	
1269		FALSE (0):
1270	
1271		By default, Host behaviour is assumed.  This means:
1272	
1273		1. IsRouter flag is not set in Neighbour Advertisements.
1274		2. If accept_ra is TRUE (default), transmit Router
1275		   Solicitations.
1276		3. If accept_ra is TRUE (default), accept Router
1277		   Advertisements (and do autoconfiguration).
1278		4. If accept_redirects is TRUE (default), accept Redirects.
1279	
1280		TRUE (1):
1281	
1282		If local forwarding is enabled, Router behaviour is assumed.
1283		This means exactly the reverse from the above:
1284	
1285		1. IsRouter flag is set in Neighbour Advertisements.
1286		2. Router Solicitations are not sent unless accept_ra is 2.
1287		3. Router Advertisements are ignored unless accept_ra is 2.
1288		4. Redirects are ignored.
1289	
1290		Default: 0 (disabled) if global forwarding is disabled (default),
1291			 otherwise 1 (enabled).
1292	
1293	hop_limit - INTEGER
1294		Default Hop Limit to set.
1295		Default: 64
1296	
1297	mtu - INTEGER
1298		Default Maximum Transfer Unit
1299		Default: 1280 (IPv6 required minimum)
1300	
1301	router_probe_interval - INTEGER
1302		Minimum interval (in seconds) between Router Probing described
1303		in RFC4191.
1304	
1305		Default: 60
1306	
1307	router_solicitation_delay - INTEGER
1308		Number of seconds to wait after interface is brought up
1309		before sending Router Solicitations.
1310		Default: 1
1311	
1312	router_solicitation_interval - INTEGER
1313		Number of seconds to wait between Router Solicitations.
1314		Default: 4
1315	
1316	router_solicitations - INTEGER
1317		Number of Router Solicitations to send until assuming no
1318		routers are present.
1319		Default: 3
1320	
1321	use_tempaddr - INTEGER
1322		Preference for Privacy Extensions (RFC3041).
1323		  <= 0 : disable Privacy Extensions
1324		  == 1 : enable Privacy Extensions, but prefer public
1325		         addresses over temporary addresses.
1326		  >  1 : enable Privacy Extensions and prefer temporary
1327		         addresses over public addresses.
1328		Default:  0 (for most devices)
1329			 -1 (for point-to-point devices and loopback devices)
1330	
1331	temp_valid_lft - INTEGER
1332		valid lifetime (in seconds) for temporary addresses.
1333		Default: 604800 (7 days)
1334	
1335	temp_prefered_lft - INTEGER
1336		Preferred lifetime (in seconds) for temporary addresses.
1337		Default: 86400 (1 day)
1338	
1339	max_desync_factor - INTEGER
1340		Maximum value for DESYNC_FACTOR, which is a random value
1341		that ensures that clients don't synchronize with each
1342		other and generate new addresses at exactly the same time.
1343		value is in seconds.
1344		Default: 600
1345	
1346	regen_max_retry - INTEGER
1347		Number of attempts before give up attempting to generate
1348		valid temporary addresses.
1349		Default: 5
1350	
1351	max_addresses - INTEGER
1352		Maximum number of autoconfigured addresses per interface.  Setting
1353		to zero disables the limitation.  It is not recommended to set this
1354		value too large (or to zero) because it would be an easy way to
1355		crash the kernel by allowing too many addresses to be created.
1356		Default: 16
1357	
1358	disable_ipv6 - BOOLEAN
1359		Disable IPv6 operation.  If accept_dad is set to 2, this value
1360		will be dynamically set to TRUE if DAD fails for the link-local
1361		address.
1362		Default: FALSE (enable IPv6 operation)
1363	
1364		When this value is changed from 1 to 0 (IPv6 is being enabled),
1365		it will dynamically create a link-local address on the given
1366		interface and start Duplicate Address Detection, if necessary.
1367	
1368		When this value is changed from 0 to 1 (IPv6 is being disabled),
1369		it will dynamically delete all address on the given interface.
1370	
1371	accept_dad - INTEGER
1372		Whether to accept DAD (Duplicate Address Detection).
1373		0: Disable DAD
1374		1: Enable DAD (default)
1375		2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
1376		   link-local address has been found.
1377	
1378	force_tllao - BOOLEAN
1379		Enable sending the target link-layer address option even when
1380		responding to a unicast neighbor solicitation.
1381		Default: FALSE
1382	
1383		Quoting from RFC 2461, section 4.4, Target link-layer address:
1384	
1385		"The option MUST be included for multicast solicitations in order to
1386		avoid infinite Neighbor Solicitation "recursion" when the peer node
1387		does not have a cache entry to return a Neighbor Advertisements
1388		message.  When responding to unicast solicitations, the option can be
1389		omitted since the sender of the solicitation has the correct link-
1390		layer address; otherwise it would not have be able to send the unicast
1391		solicitation in the first place. However, including the link-layer
1392		address in this case adds little overhead and eliminates a potential
1393		race condition where the sender deletes the cached link-layer address
1394		prior to receiving a response to a previous solicitation."
1395	
1396	ndisc_notify - BOOLEAN
1397		Define mode for notification of address and device changes.
1398		0 - (default): do nothing
1399		1 - Generate unsolicited neighbour advertisements when device is brought
1400		    up or hardware address changes.
1401	
1402	mldv1_unsolicited_report_interval - INTEGER
1403		The interval in milliseconds in which the next unsolicited
1404		MLDv1 report retransmit will take place.
1405		Default: 10000 (10 seconds)
1406	
1407	mldv2_unsolicited_report_interval - INTEGER
1408		The interval in milliseconds in which the next unsolicited
1409		MLDv2 report retransmit will take place.
1410		Default: 1000 (1 second)
1411	
1412	force_mld_version - INTEGER
1413		0 - (default) No enforcement of a MLD version, MLDv1 fallback allowed
1414		1 - Enforce to use MLD version 1
1415		2 - Enforce to use MLD version 2
1416	
1417	suppress_frag_ndisc - INTEGER
1418		Control RFC 6980 (Security Implications of IPv6 Fragmentation
1419		with IPv6 Neighbor Discovery) behavior:
1420		1 - (default) discard fragmented neighbor discovery packets
1421		0 - allow fragmented neighbor discovery packets
1422	
1423	icmp/*:
1424	ratelimit - INTEGER
1425		Limit the maximal rates for sending ICMPv6 packets.
1426		0 to disable any limiting,
1427		otherwise the minimal space between responses in milliseconds.
1428		Default: 1000
1429	
1430	
1431	IPv6 Update by:
1432	Pekka Savola <pekkas@netcore.fi>
1433	YOSHIFUJI Hideaki / USAGI Project <yoshfuji@linux-ipv6.org>
1434	
1435	
1436	/proc/sys/net/bridge/* Variables:
1437	
1438	bridge-nf-call-arptables - BOOLEAN
1439		1 : pass bridged ARP traffic to arptables' FORWARD chain.
1440		0 : disable this.
1441		Default: 1
1442	
1443	bridge-nf-call-iptables - BOOLEAN
1444		1 : pass bridged IPv4 traffic to iptables' chains.
1445		0 : disable this.
1446		Default: 1
1447	
1448	bridge-nf-call-ip6tables - BOOLEAN
1449		1 : pass bridged IPv6 traffic to ip6tables' chains.
1450		0 : disable this.
1451		Default: 1
1452	
1453	bridge-nf-filter-vlan-tagged - BOOLEAN
1454		1 : pass bridged vlan-tagged ARP/IP/IPv6 traffic to {arp,ip,ip6}tables.
1455		0 : disable this.
1456		Default: 0
1457	
1458	bridge-nf-filter-pppoe-tagged - BOOLEAN
1459		1 : pass bridged pppoe-tagged IP/IPv6 traffic to {ip,ip6}tables.
1460		0 : disable this.
1461		Default: 0
1462	
1463	bridge-nf-pass-vlan-input-dev - BOOLEAN
1464		1: if bridge-nf-filter-vlan-tagged is enabled, try to find a vlan
1465		interface on the bridge and set the netfilter input device to the vlan.
1466		This allows use of e.g. "iptables -i br0.1" and makes the REDIRECT
1467		target work with vlan-on-top-of-bridge interfaces.  When no matching
1468		vlan interface is found, or this switch is off, the input device is
1469		set to the bridge interface.
1470		0: disable bridge netfilter vlan interface lookup.
1471		Default: 0
1472	
1473	proc/sys/net/sctp/* Variables:
1474	
1475	addip_enable - BOOLEAN
1476		Enable or disable extension of  Dynamic Address Reconfiguration
1477		(ADD-IP) functionality specified in RFC5061.  This extension provides
1478		the ability to dynamically add and remove new addresses for the SCTP
1479		associations.
1480	
1481		1: Enable extension.
1482	
1483		0: Disable extension.
1484	
1485		Default: 0
1486	
1487	addip_noauth_enable - BOOLEAN
1488		Dynamic Address Reconfiguration (ADD-IP) requires the use of
1489		authentication to protect the operations of adding or removing new
1490		addresses.  This requirement is mandated so that unauthorized hosts
1491		would not be able to hijack associations.  However, older
1492		implementations may not have implemented this requirement while
1493		allowing the ADD-IP extension.  For reasons of interoperability,
1494		we provide this variable to control the enforcement of the
1495		authentication requirement.
1496	
1497		1: Allow ADD-IP extension to be used without authentication.  This
1498		   should only be set in a closed environment for interoperability
1499		   with older implementations.
1500	
1501		0: Enforce the authentication requirement
1502	
1503		Default: 0
1504	
1505	auth_enable - BOOLEAN
1506		Enable or disable Authenticated Chunks extension.  This extension
1507		provides the ability to send and receive authenticated chunks and is
1508		required for secure operation of Dynamic Address Reconfiguration
1509		(ADD-IP) extension.
1510	
1511		1: Enable this extension.
1512		0: Disable this extension.
1513	
1514		Default: 0
1515	
1516	prsctp_enable - BOOLEAN
1517		Enable or disable the Partial Reliability extension (RFC3758) which
1518		is used to notify peers that a given DATA should no longer be expected.
1519	
1520		1: Enable extension
1521		0: Disable
1522	
1523		Default: 1
1524	
1525	max_burst - INTEGER
1526		The limit of the number of new packets that can be initially sent.  It
1527		controls how bursty the generated traffic can be.
1528	
1529		Default: 4
1530	
1531	association_max_retrans - INTEGER
1532		Set the maximum number for retransmissions that an association can
1533		attempt deciding that the remote end is unreachable.  If this value
1534		is exceeded, the association is terminated.
1535	
1536		Default: 10
1537	
1538	max_init_retransmits - INTEGER
1539		The maximum number of retransmissions of INIT and COOKIE-ECHO chunks
1540		that an association will attempt before declaring the destination
1541		unreachable and terminating.
1542	
1543		Default: 8
1544	
1545	path_max_retrans - INTEGER
1546		The maximum number of retransmissions that will be attempted on a given
1547		path.  Once this threshold is exceeded, the path is considered
1548		unreachable, and new traffic will use a different path when the
1549		association is multihomed.
1550	
1551		Default: 5
1552	
1553	pf_retrans - INTEGER
1554		The number of retransmissions that will be attempted on a given path
1555		before traffic is redirected to an alternate transport (should one
1556		exist).  Note this is distinct from path_max_retrans, as a path that
1557		passes the pf_retrans threshold can still be used.  Its only
1558		deprioritized when a transmission path is selected by the stack.  This
1559		setting is primarily used to enable fast failover mechanisms without
1560		having to reduce path_max_retrans to a very low value.  See:
1561		http://www.ietf.org/id/draft-nishida-tsvwg-sctp-failover-05.txt
1562		for details.  Note also that a value of pf_retrans > path_max_retrans
1563		disables this feature
1564	
1565		Default: 0
1566	
1567	rto_initial - INTEGER
1568		The initial round trip timeout value in milliseconds that will be used
1569		in calculating round trip times.  This is the initial time interval
1570		for retransmissions.
1571	
1572		Default: 3000
1573	
1574	rto_max - INTEGER
1575		The maximum value (in milliseconds) of the round trip timeout.  This
1576		is the largest time interval that can elapse between retransmissions.
1577	
1578		Default: 60000
1579	
1580	rto_min - INTEGER
1581		The minimum value (in milliseconds) of the round trip timeout.  This
1582		is the smallest time interval the can elapse between retransmissions.
1583	
1584		Default: 1000
1585	
1586	hb_interval - INTEGER
1587		The interval (in milliseconds) between HEARTBEAT chunks.  These chunks
1588		are sent at the specified interval on idle paths to probe the state of
1589		a given path between 2 associations.
1590	
1591		Default: 30000
1592	
1593	sack_timeout - INTEGER
1594		The amount of time (in milliseconds) that the implementation will wait
1595		to send a SACK.
1596	
1597		Default: 200
1598	
1599	valid_cookie_life - INTEGER
1600		The default lifetime of the SCTP cookie (in milliseconds).  The cookie
1601		is used during association establishment.
1602	
1603		Default: 60000
1604	
1605	cookie_preserve_enable - BOOLEAN
1606		Enable or disable the ability to extend the lifetime of the SCTP cookie
1607		that is used during the establishment phase of SCTP association
1608	
1609		1: Enable cookie lifetime extension.
1610		0: Disable
1611	
1612		Default: 1
1613	
1614	cookie_hmac_alg - STRING
1615		Select the hmac algorithm used when generating the cookie value sent by
1616		a listening sctp socket to a connecting client in the INIT-ACK chunk.
1617		Valid values are:
1618		* md5
1619		* sha1
1620		* none
1621		Ability to assign md5 or sha1 as the selected alg is predicated on the
1622		configuration of those algorithms at build time (CONFIG_CRYPTO_MD5 and
1623		CONFIG_CRYPTO_SHA1).
1624	
1625		Default: Dependent on configuration.  MD5 if available, else SHA1 if
1626		available, else none.
1627	
1628	rcvbuf_policy - INTEGER
1629		Determines if the receive buffer is attributed to the socket or to
1630		association.   SCTP supports the capability to create multiple
1631		associations on a single socket.  When using this capability, it is
1632		possible that a single stalled association that's buffering a lot
1633		of data may block other associations from delivering their data by
1634		consuming all of the receive buffer space.  To work around this,
1635		the rcvbuf_policy could be set to attribute the receiver buffer space
1636		to each association instead of the socket.  This prevents the described
1637		blocking.
1638	
1639		1: rcvbuf space is per association
1640		0: rcvbuf space is per socket
1641	
1642		Default: 0
1643	
1644	sndbuf_policy - INTEGER
1645		Similar to rcvbuf_policy above, this applies to send buffer space.
1646	
1647		1: Send buffer is tracked per association
1648		0: Send buffer is tracked per socket.
1649	
1650		Default: 0
1651	
1652	sctp_mem - vector of 3 INTEGERs: min, pressure, max
1653		Number of pages allowed for queueing by all SCTP sockets.
1654	
1655		min: Below this number of pages SCTP is not bothered about its
1656		memory appetite. When amount of memory allocated by SCTP exceeds
1657		this number, SCTP starts to moderate memory usage.
1658	
1659		pressure: This value was introduced to follow format of tcp_mem.
1660	
1661		max: Number of pages allowed for queueing by all SCTP sockets.
1662	
1663		Default is calculated at boot time from amount of available memory.
1664	
1665	sctp_rmem - vector of 3 INTEGERs: min, default, max
1666		Only the first value ("min") is used, "default" and "max" are
1667		ignored.
1668	
1669		min: Minimal size of receive buffer used by SCTP socket.
1670		It is guaranteed to each SCTP socket (but not association) even
1671		under moderate memory pressure.
1672	
1673		Default: 1 page
1674	
1675	sctp_wmem  - vector of 3 INTEGERs: min, default, max
1676		Currently this tunable has no effect.
1677	
1678	addr_scope_policy - INTEGER
1679		Control IPv4 address scoping - draft-stewart-tsvwg-sctp-ipv4-00
1680	
1681		0   - Disable IPv4 address scoping
1682		1   - Enable IPv4 address scoping
1683		2   - Follow draft but allow IPv4 private addresses
1684		3   - Follow draft but allow IPv4 link local addresses
1685	
1686		Default: 1
1687	
1688	
1689	/proc/sys/net/core/*
1690		Please see: Documentation/sysctl/net.txt for descriptions of these entries.
1691	
1692	
1693	/proc/sys/net/unix/*
1694	max_dgram_qlen - INTEGER
1695		The maximum length of dgram socket receive queue
1696	
1697		Default: 10
1698	
1699	
1700	UNDOCUMENTED:
1701	
1702	/proc/sys/net/irda/*
1703		fast_poll_increase FIXME
1704		warn_noreply_time FIXME
1705		discovery_slots FIXME
1706		slot_timeout FIXME
1707		max_baud_rate FIXME
1708		discovery_timeout FIXME
1709		lap_keepalive_time FIXME
1710		max_noreply_time FIXME
1711		max_tx_data_size FIXME
1712		max_tx_window FIXME
1713		min_tx_turn_time FIXME
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