Provided by: iproute2_4.15.0-2ubuntu1.3_amd64 bug


       pfifo - Packet limited First In, First Out queue

       bfifo - Byte limited First In, First Out queue


       tc qdisc ... add pfifo [ limit packets ]

       tc qdisc ... add bfifo [ limit bytes ]


       The pfifo and bfifo qdiscs are unadorned First In, First Out queues. They are the simplest
       queues possible and therefore have no  overhead.   pfifo  constrains  the  queue  size  as
       measured in packets.  bfifo does so as measured in bytes.

       Like  all  non-default  qdiscs, they maintain statistics. This might be a reason to prefer
       pfifo or bfifo over the default.


       A list of packets is maintained, when a packet is enqueued it gets inserted at the tail of
       a  list.  When  a packet needs to be sent out to the network, it is taken from the head of
       the list.

       If the list is too long, no further packets are allowed on. This is called 'tail drop'.


       limit  Maximum queue size. Specified in bytes for bfifo, in packets for pfifo. For  pfifo,
              defaults  to the interface txqueuelen, as specified with ifconfig(8) or ip(8).  The
              range for this parameter is [0, UINT32_MAX].

              For bfifo, it defaults to the txqueuelen multiplied  by  the  interface  MTU.   The
              range for this parameter is [0, UINT32_MAX] bytes.

              Note: The link layer header was considered when counting packets length.


       The  output  of  tc -s qdisc ls contains the limit, either in packets or in bytes, and the
       number of bytes and packets actually sent. An  unsent  and  dropped  packet  only  appears
       between braces and is not counted as 'Sent'.

       In  this example, the queue length is 100 packets, 45894 bytes were sent over 681 packets.
       No packets were dropped, and as the pfifo queue does not slow  down  packets,  there  were
       also no overlimits:

       # tc -s qdisc ls dev eth0
       qdisc pfifo 8001: dev eth0 limit 100p
        Sent 45894 bytes 681 pkts (dropped 0, overlimits 0)

       If a backlog occurs, this is displayed as well.




       Alexey N. Kuznetsov, <>

       This manpage maintained by bert hubert <>