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diff --git a/man/man8/tc-red.8 b/man/man8/tc-red.8 new file mode 100644 index 0000000..662e4d8 --- /dev/null +++ b/man/man8/tc-red.8 @@ -0,0 +1,180 @@ +.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 ] [ nodrop ] [ bandwidth +rate +.B ] [ probability +chance +.B ] [ adaptive ] [ qevent early_drop block +index +.B ] [ qevent mark block +index +.B ] + +.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 +nodrop +With this parameter, traffic that should be marked, but is not ECN-capable, is +enqueued. Without the parameter it is early-dropped. +.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 QEVENTS +See tc (8) for some general notes about qevents. The RED qdisc supports the +following qevents: + +.TP +early_drop +The associated block is executed when packets are early-dropped. This includes +non-ECT packets in ECN mode. +.TP +mark +The associated block is executed when packets are marked in ECN mode. + +.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> |