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<H1>PFIFO_FAST</H1>
Section: Linux (8)<BR>Updated: 10 January 2002<BR><A HREF="#index">Index</A>
<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
<A NAME="lbAB">&nbsp;</A>
<H2>NAME</H2>
pfifo_fast - three-band first in, first out queue
<P>
<A NAME="lbAC">&nbsp;</A>
<H2>DESCRIPTION</H2>
pfifo_fast is the default qdisc of each interface.
<P>
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.
<P>
In this sense this qdisc is magic, and unlike other qdiscs.
<P>
<A NAME="lbAD">&nbsp;</A>
<H2>ALGORITHM</H2>
The algorithm is very similar to that of the classful
<B><A HREF="/cgi-bin/man/man2html?8+tc-prio">tc-prio</A></B>(8)
qdisc.
<B>pfifo_fast</B>
is like three
<B><A HREF="/cgi-bin/man/man2html?8+tc-pfifo">tc-pfifo</A></B>(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.
<P>
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.
<P>
Each band can be txqueuelen packets long, as configured with
<B><A HREF="/cgi-bin/man/man2html?8+ifconfig">ifconfig</A></B>(8)
or
<B><A HREF="/cgi-bin/man/man2html?8+ip">ip</A></B>(8).
Additional packets coming in are not enqueued but are instead dropped.
<P>
See
<B><A HREF="/cgi-bin/man/man2html?8+tc-prio">tc-prio</A></B>(8)
for complete details on how TOS bits are translated into bands.
<A NAME="lbAE">&nbsp;</A>
<H2>PARAMETERS</H2>
<DL COMPACT>
<DT id="1">txqueuelen<DD>
The length of the three bands depends on the interface txqueuelen, as
specified with
<B><A HREF="/cgi-bin/man/man2html?8+ifconfig">ifconfig</A></B>(8)
or
<B><A HREF="/cgi-bin/man/man2html?8+ip">ip</A></B>(8).
<P>
</DL>
<A NAME="lbAF">&nbsp;</A>
<H2>BUGS</H2>
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.
<P>
<A NAME="lbAG">&nbsp;</A>
<H2>SEE ALSO</H2>
<B><A HREF="/cgi-bin/man/man2html?8+tc">tc</A></B>(8)
<P>
<A NAME="lbAH">&nbsp;</A>
<H2>AUTHORS</H2>
Alexey N. Kuznetsov, &lt;<A HREF="mailto:kuznet@ms2.inr.ac.ru">kuznet@ms2.inr.ac.ru</A>&gt;
<P>
This manpage maintained by bert hubert &lt;<A HREF="mailto:ahu@ds9a.nl">ahu@ds9a.nl</A>&gt;
<P>
<HR>
<A NAME="index">&nbsp;</A><H2>Index</H2>
<DL>
<DT id="2"><A HREF="#lbAB">NAME</A><DD>
<DT id="3"><A HREF="#lbAC">DESCRIPTION</A><DD>
<DT id="4"><A HREF="#lbAD">ALGORITHM</A><DD>
<DT id="5"><A HREF="#lbAE">PARAMETERS</A><DD>
<DT id="6"><A HREF="#lbAF">BUGS</A><DD>
<DT id="7"><A HREF="#lbAG">SEE ALSO</A><DD>
<DT id="8"><A HREF="#lbAH">AUTHORS</A><DD>
</DL>
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