.TH PBFIFO 8 "10 January 2002" "iproute2" "Linux"

.SH NAME

pfifo \- Packet limited First In, First Out queue

.P

bfifo \- Byte limited First In, First Out queue

.SH SYNOPSIS

.B tc qdisc ... add pfifo

.B [ limit

packets

.B ]

.P

.B tc qdisc ... add bfifo

.B [ limit

bytes

.B ]

.SH DESCRIPTION

The pfifo and bfifo qdiscs are unadorned First In, First Out queues. They are the

simplest queues possible and therefore have no overhead.

.B pfifo

constrains the queue size as measured in packets.

.B 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.

.SH 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'.

.SH PARAMETERS

.TP

limit

Maximum queue size. Specified in bytes for bfifo, in packets for pfifo. For pfifo, defaults

to the interface txqueuelen, as specified with

.BR ifconfig (8)

or

.BR 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.

.SH OUTPUT

The output of

.B 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:

.P

.nf

# tc -s qdisc ls dev eth0

qdisc pfifo 8001: dev eth0 limit 100p

 Sent 45894 bytes 681 pkts (dropped 0, overlimits 0)

.fi

If a backlog occurs, this is displayed as well.

.SH SEE ALSO

.BR tc (8)

.SH AUTHORS

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

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