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 negative 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.  Limit-
     ing 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 complete 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 gran-
     ularity, 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