PFIFO_FAST(8)                        Linux                       PFIFO_FAST(8)

NAME
       pfifo_fast - three-band first in, first out queue

DESCRIPTION
       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
       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  Ser-
       vice 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 ifcon-
       fig(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
       txqueuelen
              The length of the three bands depends on the interface  txqueue-
              len, as specified with ifconfig(8) or ip(8).

BUGS
       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
       tc(8)

AUTHORS
       Alexey N. Kuznetsov, <kuznet@ms2.inr.ac.ru>

       This manpage maintained by bert hubert <ahu@ds9a.nl>

iproute2                        10 January 2002                  PFIFO_FAST(8)

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