pfifo_fast - three-band first in, first out queue
pfifo_fast is the default qdisc of each
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
In this sense this qdisc is magic, and unlike other
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
See tc-prio(8) for complete details on how TOS bits
are translated into bands.
The length of the three bands depends on the interface
txqueuelen, as specified with ifconfig(8) or
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.
Alexey N. Kuznetsov,
This manpage maintained by bert hubert