PFIFO_FAST(8)                       Linux                      PFIFO_FAST(8)

NAME         top

       pfifo_fast - three-band first in, first out queue

DESCRIPTION         top

       pfifo_fast is the default qdisc of each interface.

       Whenever an interface is created, the pfifo_fast qdisc is
       automatically used as a queue. If another qdisc is attached, it
       preempts the default pfifo_fast, which automatically returns to
       function when an existing qdisc is detached.

       In this sense this qdisc is magic, and unlike other qdiscs.

ALGORITHM         top

       The algorithm is very similar to that of the classful tc-prio(8)
       qdisc.  pfifo_fast is like three tc-pfifo(8) queues side by side,
       where packets can be enqueued in any of the three bands based on
       their Type of Service bits or assigned priority.

       Not all three bands are dequeued simultaneously - as long as lower
       bands have traffic, higher bands are never dequeued. This can be used
       to prioritize interactive traffic or penalize 'lowest cost' traffic.

       Each band can be txqueuelen packets long, as configured with
       ifconfig(8) or ip(8).  Additional packets coming in are not enqueued
       but are instead dropped.

       See tc-prio(8) for complete details on how TOS bits are translated
       into bands.

PARAMETERS         top

              The length of the three bands depends on the interface
              txqueuelen, as specified with ifconfig(8) or ip(8).

BUGS         top

       Does not maintain statistics and does not show up in tc qdisc ls.
       This is because it is the automatic default in the absence of a
       configured qdisc.

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                 PFIFO_FAST(8)