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NetBSD 6.1.5 - man page for tbrconfig (netbsd section 8)

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TBRCONFIG(8)			   BSD System Manager's Manual			     TBRCONFIG(8)

NAME
     tbrconfig -- configure a token bucket regulator for an output queue

SYNOPSIS
     tbrconfig interface [tokenrate [bucketsize]]
     tbrconfig -d interface
     tbrconfig -a

DESCRIPTION
     tbrconfig configures a token bucket regulator for the output network interface queue.  A
     token bucket regulator limits both the average amount and instantaneous amount of packets
     that the underlying driver can dequeue from the network interface within the kernel.

     Conceptually, tokens accumulate in a bucket at the average tokenrate, up to the bucketsize.
     The driver can dequeue packets as long as there are positive amount of tokens, and the
     length of the dequeued packet is subtracted from the remaining tokens.  Tokens can be nega-
     tive as a deficit, and packets are not dequeued from the interface queue until the tokens
     become positive again.  The tokenrate limits the average rate, and the bucketsize limits the
     maximum burst size.

     Limiting the burst size is essential to packet scheduling, since the scheduler schedules
     packets backlogged at the network interface.  Limiting the burst size is also needed for
     drivers which dequeues more packets than they can send and end up with discarding excess
     packets.

     When the tokenrate is set to higher than the actual transmission rate, the transmission com-
     plete interrupt will trigger the next dequeue.  On the other hand, when the tokenrate is set
     to lower than the actual transmission rate, the transmission complete interrupt would occur
     before the tokens become positive.  In this case, the next dequeue will be triggered by a
     timer event.  Because the kernel timer has a limited granularity, a larger bucketsize is
     required for a higher tokenrate.

     The interface parameter is a string of the form ``name unit'', for example, ``en0''.

     The tokenrate parameter specifies the average rate in bits per second, and ``K'' or ``M''
     can be appended to tokenrate as a short hand of ``Kilo-bps'' or ``Mega-bps'', respectively.
     When tokenrate is omitted, tbrconfig displays the current parameter values.

     The bucketsize parameter specifies the bucket size in bytes, and ``K'' can be appended to
     bucketsize as a short hand of ``Kilo-bytes''.  When bucketsize is omitted, tbrconfig assumes
     the regulator is driven by transmission complete interrupts and, using heuristics, assigns a
     small bucket size according to the tokenrate.  When the keyword ``auto'' is given as
     bucketsize, tbrconfig assumes the regulator is driven by the kernel timer, and computes the
     bucket size from tokenrate and the kernel clock frequency.

     If the -d flag is passed before an interface name, tbrconfig will remove the token bucket
     regulator for the specified interface.

     Optionally, the -a flag may be used instead of an interface name.	This flag instructs
     tbrconfig to display information about all interfaces in the system.

EXAMPLES
     To configure a token bucket regulator for the interface en0 with 10Mbps token rate and 8KB
     bucket size,

	   # tbrconfig en0 10M 8K

     To rate-limit the interface en0 up to 3Mbps,

	   # tbrconfig en0 3M auto

SEE ALSO
     altq.conf(5), altqd(8)

HISTORY
     The tbrconfig command first appeared in WIDE/KAME IPv6 protocol stack kit as part of ALTQ
     tools.

BSD					  July 25, 2000 				      BSD
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