man/man8/tc-bfifo.8

   1 .TH PBFIFO 8 "10 January 2002" "iproute2" "Linux"
   2 .SH NAME
   3 pfifo \- Packet limited First In, First Out queue
   4 .P
   5 bfifo \- Byte limited First In, First Out queue
   6
   7 .SH SYNOPSIS
   8 .B tc qdisc ... add pfifo
   9 .B [ limit
  10 packets
  11 .B ]
  12 .P
  13 .B tc qdisc ... add bfifo
  14 .B [ limit
  15 bytes
  16 .B ]
  17
  18 .SH DESCRIPTION
  19 The pfifo and bfifo qdiscs are unadorned First In, First Out queues. They are the
  20 simplest queues possible and therefore have no overhead.
  21 .B pfifo
  22 constrains the queue size as measured in packets.
  23 .B bfifo
  24 does so as measured in bytes.
  25
  26 Like all non-default qdiscs, they maintain statistics. This might be a reason to prefer
  27 pfifo or bfifo over the default.
  28
  29 .SH ALGORITHM
  30 A list of packets is maintained, when a packet is enqueued it gets inserted at the tail of
  31 a list. When a packet needs to be sent out to the network, it is taken from the head of the list.
  32
  33 If the list is too long, no further packets are allowed on. This is called 'tail drop'.
  34
  35 .SH PARAMETERS
  36 .TP
  37 limit
  38 Maximum queue size. Specified in bytes for bfifo, in packets for pfifo. For pfifo, defaults
  39 to the interface txqueuelen, as specified with
  40 .BR ifconfig (8)
  41 or
  42 .BR ip (8).
  43 The range for this parameter is [0, UINT32_MAX].
  44
  45 For bfifo, it defaults to the txqueuelen multiplied by the interface MTU.
  46 The range for this parameter is [0, UINT32_MAX] bytes.
  47
  48 Note: The link layer header was considered when counting packets length.
  49
  50 .SH OUTPUT
  51 The output of
  52 .B tc -s qdisc ls
  53 contains the limit, either in packets or in bytes, and the number of bytes
  54 and packets actually sent. An unsent and dropped packet only appears between braces
  55 and is not counted as 'Sent'.
  56
  57 In this example, the queue length is 100 packets, 45894 bytes were sent over 681 packets.
  58 No packets were dropped, and as the pfifo queue does not slow down packets, there were also no
  59 overlimits:
  60 .P
  61 .nf
  62 # tc -s qdisc ls dev eth0
  63 qdisc pfifo 8001: dev eth0 limit 100p
  64  Sent 45894 bytes 681 pkts (dropped 0, overlimits 0)
  65 .fi
  66
  67 If a backlog occurs, this is displayed as well.
  68 .SH SEE ALSO
  69 .BR tc (8)
  70
  71 .SH AUTHORS
  72 Alexey N. Kuznetsov, <kuznet@ms2.inr.ac.ru>
  73
  74 This manpage maintained by bert hubert <ahu@ds9a.nl>
  75
  76