FQ_CoDel(8)                         Linux                        FQ_CoDel(8)

NAME         top

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

SYNOPSIS         top

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

DESCRIPTION         top

       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 provide 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         top

       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.

       is the number of flows into which the incoming packets are
       classified. Due to the stochastic nature of hashing, 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

       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.

       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.

       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

EXAMPLES         top

       #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)
          backlog 0b 0p requeues 0
           maxpacket 256 drop_overlimit 0 new_flow_count 0 ecn_mark 0
           new_flows_len 0 old_flows_len 0

       #tc qdisc add dev eth0 root fq_codel limit 2000 target 3ms interval
       40ms noecn
       #tc -s qdisc show
       qdisc fq_codel 8003: dev eth0 root refcnt 2 limit 2000p flows 1024
       quantum 1514 target 3.0ms interval 40.0ms
        Sent 2588985006 bytes 1783629 pkt (dropped 0, overlimits 0 requeues
        backlog 0b 0p requeues 34869
         maxpacket 65226 drop_overlimit 0 new_flow_count 73 ecn_mark 0
         new_flows_len 1 old_flows_len 3

SEE ALSO         top

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

AUTHORS         top

       FQ_CoDel was implemented by Eric Dumazet. This manpage was written by
       Vijay Subramanian. Please report corrections to the Linux Networking
       mailing list <>.

COLOPHON         top

       This page is part of the iproute2 (utilities for controlling TCP/IP
       networking and traffic) project.  Information about the project can
       be found at 
       If you have a bug report for this manual page, send it to,  This page was obtained
       from the project's upstream Git repository 
       on 2017-09-15.  If you discover any rendering problems in this HTML
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       manual page), send a mail to

iproute2                         4 June 2012                     FQ_CoDel(8)

Pages that refer to this page: tc(8)