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 spec-
	      ified 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)