PFIFO_FAST(T)                 Linux                 PFIFO_FAST(T)



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 auto-
       matically 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(o)  qdisc.   pfifo_fast  is  like  three  tc-pfifo(o)
       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 traf-
       fic or penalize 'lowest cost' traffic.

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

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

PARAMETERS
       txqueuelen
              The length of the three bands depends on the inter-
              face  txqueuelen,  as specified with ifconfig(g) or
              ip(p).


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(c)


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

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





iproute2                 10 January 2002            PFIFO_FAST(T)