1 .TH RED 8 "13 December 2001" "iproute2" "Linux"
3 red \- Random Early Detection
16 .B ] [ ecn ] [ harddrop] [ bandwidth
23 Random Early Detection is a classless qdisc which manages its queue size
24 smartly. Regular queues simply drop packets from the tail when they are
25 full, which may not be the optimal behaviour. RED also performs tail drop,
26 but does so in a more gradual way.
28 Once the queue hits a certain average length, packets enqueued have a
29 configurable chance of being marked (which may mean dropped). This chance
30 increases linearly up to a point called the
32 average queue length, although the queue might get bigger.
34 This has a host of benefits over simple taildrop, while not being processor
35 intensive. It prevents synchronous retransmits after a burst in traffic,
36 which cause further retransmits, etc.
38 The goal is to have a small queue size, which is good for interactivity
39 while not disturbing TCP/IP traffic with too many sudden drops after a burst
42 Depending on if ECN is configured, marking either means dropping or
43 purely marking a packet as overlimit.
45 The average queue size is used for determining the marking
46 probability. This is calculated using an Exponential Weighted Moving
47 Average, which can be more or less sensitive to bursts.
49 When the average queue size is below
51 bytes, no packet will ever be marked. When it exceeds
53 the probability of doing so climbs linearly up
56 until the average queue size hits
60 is normally not set to 100%, the queue size might
61 conceivably rise above
65 parameter is provided to set a hard maximum for the size of the queue.
70 Average queue size at which marking becomes a possibility. Defaults to
76 At this average queue size, the marking probability is maximal. Should be at
79 to prevent synchronous retransmits, higher for low
86 Maximum probability for marking, specified as a floating point
87 number from 0.0 to 1.0. Suggested values are 0.01 or 0.02 (1 or 2%,
88 respectively). Default : 0.02
91 Hard limit on the real (not average) queue size in bytes. Further packets
92 are dropped. Should be set higher than max+burst. It is advised to set this
93 a few times higher than
97 Used for determining how fast the average queue size is influenced by the
98 real queue size. Larger values make the calculation more sluggish, allowing
99 longer bursts of traffic before marking starts. Real life experiments
100 support the following guideline: (min+min+max)/(3*avpkt).
103 Specified in bytes. Used with burst to determine the time constant for
104 average queue size calculations. 1000 is a good value.
107 This rate is used for calculating the average queue size after some
108 idle time. Should be set to the bandwidth of your interface. Does not mean
109 that RED will shape for you! Optional. Default : 10Mbit
112 As mentioned before, RED can either 'mark' or 'drop'. Explicit Congestion
113 Notification allows RED to notify remote hosts that their rate exceeds the
114 amount of bandwidth available. Non-ECN capable hosts can only be notified by
115 dropping a packet. If this parameter is specified, packets which indicate
116 that their hosts honor ECN will only be marked and not dropped, unless the
122 If average flow queue size is above
124 bytes, this parameter forces a drop instead of ecn marking.
127 (Added in linux-3.3) Sets RED in adaptive mode as described in http://icir.org/floyd/papers/adaptiveRed.pdf
129 Goal of Adaptive RED is to make 'probability' dynamic value between 1% and 50% to reach the target average queue :
136 # tc qdisc add dev eth0 parent 1:1 handle 10: red
137 limit 400000 min 30000 max 90000 avpkt 1000
138 burst 55 ecn adaptive bandwidth 10Mbit
147 Floyd, S., and Jacobson, V., Random Early Detection gateways for
148 Congestion Avoidance. http://www.aciri.org/floyd/papers/red/red.html
151 Some changes to the algorithm by Alexey N. Kuznetsov.
154 Adaptive RED : http://icir.org/floyd/papers/adaptiveRed.pdf
157 Alexey N. Kuznetsov, <kuznet@ms2.inr.ac.ru>, Alexey Makarenko
158 <makar@phoenix.kharkov.ua>, J Hadi Salim <hadi@nortelnetworks.com>,
159 Eric Dumazet <eric.dumazet@gmail.com>.
160 This manpage maintained by bert hubert <ahu@ds9a.nl>