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FQ_CoDel(8)                                             Linux                                             FQ_CoDel(8)



NAME
       CoDel - Fair Queuing (FQ) with Controlled Delay (CoDel)

SYNOPSIS
       tc qdisc ... fq_codel [ limit PACKETS ] [ flows NUMBER ] [ target TIME ] [ interval TIME ] [ quantum BYTES ] [
       ecn | noecn ]


DESCRIPTION
       FQ_Codel (Fair Queuing Controlled Delay) is queuing discipline that combines Fair Queuing with the  CoDel  AQM
       scheme. FQ_Codel uses a stochastic model to classify incoming packets into different flows and is used to pro‐
       vide a fair share of the bandwidth to all the flows using the queue. Each such flow is managed  by  the  CoDel
       queuing discipline. Reordering within a flow is avoided since Codel internally uses a FIFO queue.


PARAMETERS
   limit
       has  the  same  semantics  as codel and is the hard limit on the real queue size.  When this limit is reached,
       incoming packets are dropped. Default is 10240 packets.


   flows
       is the number of flows into which the incoming packets are classified. Due to the stochastic nature  of  hash‐
       ing,  multiple  flows  may  end up being hashed into the same slot. Newer flows have priority over older ones.
       This parameter can be set only at load time since memory has to be allocated  for  the  hash  table.   Default
       value is 1024.


   target
       has  the  same  semantics as codel and is the acceptable minimum standing/persistent queue delay. This minimum
       delay is identified by tracking the local minimum queue delay that packets experience. Default value is 5ms.


   interval
       has the same semantics as codel and is used to ensure that the measured minimum  delay  does  not  become  too
       stale.   The  minimum  delay must be experienced in the last epoch of length .B interval.  It should be set on
       the order of the worst-case RTT through the bottleneck to give endpoints sufficient  time  to  react.  Default
       value is 100ms.


   quantum
       is  the  number  of  bytes used as 'deficit' in the fair queuing algorithm. Default is set to 1514 bytes which
       corresponds to the Ethernet MTU plus the hardware header length of 14 bytes.


   ecn | noecn
       has the same semantics as codel and can be used to mark packets instead of dropping  them.  If  ecn  has  been
       enabled, noecn can be used to turn it off and vice-a-versa. Unlike codel, ecn is turned on by default.


EXAMPLES
       #tc qdisc add   dev eth0 root fq_codel
       #tc -s qdisc show
       qdisc fq_codel 8002: dev eth0 root refcnt 2 limit 10240p flows 1024 quantum 1514
        target 5.0ms interval 100.0ms ecn
          Sent 428514 bytes 2269 pkt (dropped 0, overlimits 0 requeues 0)


SEE ALSO
       tc(8), tc-codel(8), tc-red(8)


AUTHORS
       FQ_CoDel was implemented by Eric Dumazet. This manpage was written by Vijay Subramanian. Please report correc‐
       tions to the Linux Networking mailing list <[email protected]>.



iproute2                                             4 June 2012                                          FQ_CoDel(8)