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tc-pfifo(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
          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 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>



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