PBFIFO(8)               (10 January 2002)               PBFIFO(8)

          pfifo - Packet limited First In, First Out queue

          bfifo - Byte limited First In, First Out queue

          tc qdisc ... add pfifo [ limit packets ]

          tc qdisc ... add bfifo [ limit bytes ]

          The pfifo and bfifo qdiscs are unadorned First In, First Out
          queues. They are the simplest queues possible and therefore
          have no overhead.  pfifo constrains the queue size as mea-
          sured in packets.  bfifo does so as measured in bytes.

          Like all non-default qdiscs, they maintain statistics. This
          might be a reason to prefer pfifo or bfifo over the default.

          A list of packets is maintained, when a packet is enqueued
          it gets inserted at the tail of a list. When a packet needs
          to be sent out to the network, it is taken from the head of
          the list.

          If the list is too long, no further packets are allowed on.
          This is called 'tail drop'.

               Maximum queue size. Specified in bytes for bfifo, in
               packets for pfifo. For pfifo, defaults to the interface
               txqueuelen, as specified with ifconfig(8) or ip(8).
               The range for this parameter is [0, UINT32_MAX].

               For bfifo, it defaults to the txqueuelen multiplied by
               the interface MTU.  The range for this parameter is [0,
               UINT32_MAX] bytes.

               Note: The link layer header was considered when count-
               ing packets length.

          The output of tc -s qdisc ls contains the limit, either in
          packets or in bytes, and the number of bytes and packets

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     PBFIFO(8)               (10 January 2002)               PBFIFO(8)

          actually sent. An unsent and dropped packet only appears
          between braces and is not counted as 'Sent'.

          In this example, the queue length is 100 packets, 45894
          bytes were sent over 681 packets.  No packets were dropped,
          and as the pfifo queue does not slow down packets, there
          were also no overlimits:

          # tc -s qdisc ls dev eth0
          qdisc pfifo 8001: dev eth0 limit 100p
           Sent 45894 bytes 681 pkts (dropped 0, overlimits 0)

          If a backlog occurs, this is displayed as well.


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

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

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