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 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 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  txqueuelen,  as  specified
              with 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>