PBFIFO(8)                           Linux                          PBFIFO(8)

NAME         top

       pfifo - Packet limited First In, First Out queue

       bfifo - Byte limited First In, First Out queue

SYNOPSIS         top

       tc qdisc ... add pfifo [ limit packets ]

       tc qdisc ... add bfifo [ limit bytes ]

DESCRIPTION         top

       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.

ALGORITHM         top

       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'.

PARAMETERS         top

       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.

OUTPUT         top

       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.

SEE ALSO         top


AUTHORS         top

       Alexey N. Kuznetsov, <>

       This manpage maintained by bert hubert <>

COLOPHON         top

       This page is part of the iproute2 (utilities for controlling TCP/IP
       networking and traffic) project.  Information about the project can
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iproute2                       10 January 2002                     PBFIFO(8)