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
       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>

iproute2			10 January 2002			 PFIFO_FAST(8)