PBFIFO(8)                                                              Linux                                                             PBFIFO(8)

NAME

       pfifo - Packet limited First In, First Out queue

       bfifo - Byte limited First In, First Out queue

SYNOPSIS

       tc qdisc ... add pfifo [ limit packets ]

       tc qdisc ... add bfifo [ limit bytes ]

DESCRIPTION

       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 measured 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.

ALGORITHM

       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'.

PARAMETERS

       limit  Maximum  queue  size. Specified in bytes for bfifo, in packets for pfifo. For pfifo, defaults to the interface txqueuelen, as speci-
              fied 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 counting packets length.

OUTPUT

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

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                                                        PBFIFO(8)