pfifo - Packet limited First In, First Out queue

       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'.

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

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

iproute2                                         10 January 2002                                       PBFIFO(8)

       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.

       pfifo - Packet limited First In, First Out queue

       bfifo - Byte limited First In, First Out queue

       The  output  of tc-sqdiscls 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.

       limit  Maximum queue size. Specified in bytes for bfifo, in packets for pfifo. For pfifo, defaults to the
              interface txqueuelen, as specified with 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.

tc(8)

tcqdisc...addpfifo[limit packets ]tcqdisc...addbfifo[limit bytes ]