man/man8/tc-red.8 - maze/iproute2 - Git at Google

 .TH RED 8 "13 December 2001" "iproute2" "Linux"
 .SH NAME
 red \- Random Early Detection
 .SH SYNOPSIS
 .B tc qdisc ... red
 .B limit
 bytes
 .B [ min
 bytes
 .B ] [ max
 bytes
 .B ] avpkt
 bytes
 .B [ burst
 packets
 .B ] [ ecn ] [ harddrop] [ bandwidth
 rate
 .B ] [ probability
 chance
 .B ] [ adaptive ]

 .SH DESCRIPTION
 Random Early Detection is a classless qdisc which manages its queue size
 smartly. Regular queues simply drop packets from the tail when they are
 full, which may not be the optimal behaviour. RED also performs tail drop,
 but does so in a more gradual way.

 Once the queue hits a certain average length, packets enqueued have a
 configurable chance of being marked (which may mean dropped). This chance
 increases linearly up to a point called the
 .B max
 average queue length, although the queue might get bigger.

 This has a host of benefits over simple taildrop, while not being processor
 intensive. It prevents synchronous retransmits after a burst in traffic,
 which cause further retransmits, etc.

 The goal is to have a small queue size, which is good for interactivity
 while not disturbing TCP/IP traffic with too many sudden drops after a burst
 of traffic.

 Depending on if ECN is configured, marking either means dropping or
 purely marking a packet as overlimit.
 .SH ALGORITHM
 The average queue size is used for determining the marking
 probability. This is calculated using an Exponential Weighted Moving
 Average, which can be more or less sensitive to bursts.

 When the average queue size is below
 .B min
 bytes, no packet will ever be marked. When it exceeds
 .B min,
 the probability of doing so climbs linearly up
 to
 .B probability,
 until the average queue size hits
 .B max
 bytes. Because
 .B probability
 is normally not set to 100%, the queue size might
 conceivably rise above
 .B max
 bytes, so the
 .B limit
 parameter is provided to set a hard maximum for the size of the queue.

 .SH PARAMETERS
 .TP
 min
 Average queue size at which marking becomes a possibility. Defaults to
 .B max
 /3

 .TP
 max
 At this average queue size, the marking probability is maximal. Should be at
 least twice
 .B min
 to prevent synchronous retransmits, higher for low
 .B min.
 Default to
 .B limit
 /4
 .TP
 probability
 Maximum probability for marking, specified as a floating point
 number from 0.0 to 1.0. Suggested values are 0.01 or 0.02 (1 or 2%,
 respectively). Default : 0.02
 .TP
 limit
 Hard limit on the real (not average) queue size in bytes. Further packets
 are dropped. Should be set higher than max+burst. It is advised to set this
 a few times higher than
 .B max.
 .TP
 burst
 Used for determining how fast the average queue size is influenced by the
 real queue size. Larger values make the calculation more sluggish, allowing
 longer bursts of traffic before marking starts. Real life experiments
 support the following guideline: (min+min+max)/(3*avpkt).
 .TP
 avpkt
 Specified in bytes. Used with burst to determine the time constant for
 average queue size calculations. 1000 is a good value.
 .TP
 bandwidth
 This rate is used for calculating the average queue size after some
 idle time. Should be set to the bandwidth of your interface. Does not mean
 that RED will shape for you! Optional. Default : 10Mbit
 .TP
 ecn
 As mentioned before, RED can either 'mark' or 'drop'. Explicit Congestion
 Notification allows RED to notify remote hosts that their rate exceeds the
 amount of bandwidth available. Non-ECN capable hosts can only be notified by
 dropping a packet.  If this parameter is specified, packets which indicate
 that their hosts honor ECN will only be marked and not dropped, unless the
 queue size hits
 .B limit
 bytes. Recommended.
 .TP
 harddrop
 If average flow queue size is above
 .B max
 bytes, this parameter forces a drop instead of ecn marking.
 .TP
 adaptive
 (Added in linux-3.3) Sets RED in adaptive mode as described in http://icir.org/floyd/papers/adaptiveRed.pdf
 .nf
 Goal of Adaptive RED is to make 'probability' dynamic value between 1% and 50% to reach the target average queue :
 .B (max - min) / 2
 .fi

 .SH EXAMPLE

 .P
 # tc qdisc add dev eth0 parent 1:1 handle 10: red
  limit 400000 min 30000 max 90000 avpkt 1000
  burst 55 ecn adaptive bandwidth 10Mbit

 .SH SEE ALSO
 .BR tc (8),
 .BR tc-choke (8)

 .SH SOURCES
 .TP
 o
 Floyd, S., and Jacobson, V., Random Early Detection gateways for
 Congestion Avoidance. http://www.aciri.org/floyd/papers/red/red.html
 .TP
 o
 Some changes to the algorithm by Alexey N. Kuznetsov.
 .TP
 o
 Adaptive RED  : http://icir.org/floyd/papers/adaptiveRed.pdf

 .SH AUTHORS
 Alexey N. Kuznetsov, <kuznet@ms2.inr.ac.ru>,  Alexey Makarenko
 <makar@phoenix.kharkov.ua>, J Hadi Salim <hadi@nortelnetworks.com>,
 Eric Dumazet <eric.dumazet@gmail.com>.
 This manpage maintained by bert hubert <ahu@ds9a.nl>
	.TH RED 8 "13 December 2001" "iproute2" "Linux"
	.SH NAME
	red \- Random Early Detection
	.SH SYNOPSIS
	.B tc qdisc ... red
	.B limit
	bytes
	.B [ min
	bytes
	.B ] [ max
	bytes
	.B ] avpkt
	bytes
	.B [ burst
	packets
	.B ] [ ecn ] [ harddrop] [ bandwidth
	rate
	.B ] [ probability
	chance
	.B ] [ adaptive ]

	.SH DESCRIPTION
	Random Early Detection is a classless qdisc which manages its queue size
	smartly. Regular queues simply drop packets from the tail when they are
	full, which may not be the optimal behaviour. RED also performs tail drop,
	but does so in a more gradual way.

	Once the queue hits a certain average length, packets enqueued have a
	configurable chance of being marked (which may mean dropped). This chance
	increases linearly up to a point called the
	.B max
	average queue length, although the queue might get bigger.

	This has a host of benefits over simple taildrop, while not being processor
	intensive. It prevents synchronous retransmits after a burst in traffic,
	which cause further retransmits, etc.

	The goal is to have a small queue size, which is good for interactivity
	while not disturbing TCP/IP traffic with too many sudden drops after a burst
	of traffic.

	Depending on if ECN is configured, marking either means dropping or
	purely marking a packet as overlimit.
	.SH ALGORITHM
	The average queue size is used for determining the marking
	probability. This is calculated using an Exponential Weighted Moving
	Average, which can be more or less sensitive to bursts.

	When the average queue size is below
	.B min
	bytes, no packet will ever be marked. When it exceeds
	.B min,
	the probability of doing so climbs linearly up
	to
	.B probability,
	until the average queue size hits
	.B max
	bytes. Because
	.B probability
	is normally not set to 100%, the queue size might
	conceivably rise above
	.B max
	bytes, so the
	.B limit
	parameter is provided to set a hard maximum for the size of the queue.

	.SH PARAMETERS
	.TP
	min
	Average queue size at which marking becomes a possibility. Defaults to
	.B max
	/3

	.TP
	max
	At this average queue size, the marking probability is maximal. Should be at
	least twice
	.B min
	to prevent synchronous retransmits, higher for low
	.B min.
	Default to
	.B limit
	/4
	.TP
	probability
	Maximum probability for marking, specified as a floating point
	number from 0.0 to 1.0. Suggested values are 0.01 or 0.02 (1 or 2%,
	respectively). Default : 0.02
	.TP
	limit
	Hard limit on the real (not average) queue size in bytes. Further packets
	are dropped. Should be set higher than max+burst. It is advised to set this
	a few times higher than
	.B max.
	.TP
	burst
	Used for determining how fast the average queue size is influenced by the
	real queue size. Larger values make the calculation more sluggish, allowing
	longer bursts of traffic before marking starts. Real life experiments
	support the following guideline: (min+min+max)/(3*avpkt).
	.TP
	avpkt
	Specified in bytes. Used with burst to determine the time constant for
	average queue size calculations. 1000 is a good value.
	.TP
	bandwidth
	This rate is used for calculating the average queue size after some
	idle time. Should be set to the bandwidth of your interface. Does not mean
	that RED will shape for you! Optional. Default : 10Mbit
	.TP
	ecn
	As mentioned before, RED can either 'mark' or 'drop'. Explicit Congestion
	Notification allows RED to notify remote hosts that their rate exceeds the
	amount of bandwidth available. Non-ECN capable hosts can only be notified by
	dropping a packet. If this parameter is specified, packets which indicate
	that their hosts honor ECN will only be marked and not dropped, unless the
	queue size hits
	.B limit
	bytes. Recommended.
	.TP
	harddrop
	If average flow queue size is above
	.B max
	bytes, this parameter forces a drop instead of ecn marking.
	.TP
	adaptive
	(Added in linux-3.3) Sets RED in adaptive mode as described in http://icir.org/floyd/papers/adaptiveRed.pdf
	.nf
	Goal of Adaptive RED is to make 'probability' dynamic value between 1% and 50% to reach the target average queue :
	.B (max - min) / 2
	.fi

	.SH EXAMPLE

	.P
	# tc qdisc add dev eth0 parent 1:1 handle 10: red
	limit 400000 min 30000 max 90000 avpkt 1000
	burst 55 ecn adaptive bandwidth 10Mbit

	.SH SEE ALSO
	.BR tc (8),
	.BR tc-choke (8)

	.SH SOURCES
	.TP
	o
	Floyd, S., and Jacobson, V., Random Early Detection gateways for
	Congestion Avoidance. http://www.aciri.org/floyd/papers/red/red.html
	.TP
	o
	Some changes to the algorithm by Alexey N. Kuznetsov.
	.TP
	o
	Adaptive RED : http://icir.org/floyd/papers/adaptiveRed.pdf

	.SH AUTHORS
	Alexey N. Kuznetsov, <kuznet@ms2.inr.ac.ru>, Alexey Makarenko
	<makar@phoenix.kharkov.ua>, J Hadi Salim <hadi@nortelnetworks.com>,
	Eric Dumazet <eric.dumazet@gmail.com>.
	This manpage maintained by bert hubert <ahu@ds9a.nl>