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    Command:

    tc-red

    
    
    

    SYNOPSIS

           tc  qdisc  ...  red  limit  bytes min bytes max bytes avpkt bytes burst
           packets [ ecn ] [ bandwidth rate ] probability chance
    
    
    

    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  per-
           forms 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 max average queue
           length, although the queue might get bigger.
    
           This has a host of benefits over simple taildrop, while not being  pro-
           cessor  intensive. It prevents synchronous retransmits after a burst in
           traffic, which cause further retransmits, etc.
    
           The goal is the have a small queue size, which is good for  interactiv-
           ity  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.
    
    
    

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

    PARAMETERS

           min    Average queue size at which marking becomes a possibility.
    
           max    At this average queue size, the marking probability is  maximal.
                  Should be at least twice min to prevent synchronous retransmits,
                  higher for low min.
    
           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).
    
                  This rate is used for calculating the average queue  size  after
                  some  idle  time.  Should be set to the bandwidth of your inter-
                  face. Does not mean that RED will shape for you! Optional.
    
           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 limit bytes. Needs a tc binary with RED  support
                  compiled in. Recommended.
    
    
    

    SEE ALSO

           tc(8)
    
    
    

    SOURCES

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

    AUTHORS

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

    iproute2 13 December 2001 RED(8)

    
    
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