ng_car

NAME

ng_car — Committed Access Rate netgraph node type

DESCRIPTION

The car node type limits traffic flowing through it using:

Single rate three color marker as described in RFC 2697,
Two rate three color marker as described in RFC 2698,
RED-like rate limit algorithm used by Cisco,
Traffic shaping with RED.

HOOKS

This node type supports the following hooks:

upper: Hook leading to upper layer protocols.
lower: Hook leading to lower layer protocols.

Traffic flowing from upper to lower is considered downstream traffic. Traffic flowing from lower to upper is considered upstream traffic.

MODES OF OPERATION

Each hook can operate in one of the following modes:

NG_CAR_SINGLE_RATE: Single rate three color marker as described in RFC 2697. Committed burst packets are counted as green, extended burst packets are counted as yellow and exceeding packets are counted as red. Committed burst getting refilled with CIR (Committed Information Rate) speed. When it is full, exceeded burst getting refilled.
NG_CAR_DOUBLE_RATE: Two rate three color marker as described in RFC 2698. Committed burst packets are counted as green, peak burst packets are counted as yellow and exceeding packets are counted as red. Committed burst getting refilled with CIR speed. Peak burst getting refilled with PIR (Peak Information Rate) speed at the same time.
NG_CAR_RED: Similar to NG_CAR_SINGLE_RATE, but with different understanding of extended burst. When normal burst exceeded and extended burst is used, packets are counted red with probability equal to part of extended burst consumed. Extended burst getting refilled first. When it is full, committed burst getting refilled. This behavior is similar to RED active queue management algorithm.
This algorithm is more polite to the TCP traffic than NG_CAR_SINGLE_RATE.
NG_CAR_SHAPE: Committed burst packets are counted as green, exceeding packets are delayed by queue with RED management and counted as yellow. Packets dropped by queue counted as red. Queue parameters are hardcoded: length 99 packets, min_th 8 packets, max_p 100%.
Traffic shaping is much more polite to the TCP traffic than rate limit on links with bandwidth * delay product less than 6-8 TCP segments, but it consumes additional system resources for queue processing.

By default, all information rates are measured in bits per second and bursts are measured in bytes. But when NG_CAR_COUNT_PACKETS option is enabled, rates are measured in packets per second and bursts are in packets.

CONTROL MESSAGES

This node type supports the generic control messages and the following specific messages.

NGM_CAR_SET_CONF (setconf): Set node configuration to the specified at struct ng_car_bulkconf
NGM_CAR_GET_CONF (getconf): Return current node configuration as struct ng_car_bulkconf
NGM_CAR_GET_STATS (getstats): Return node statistics as struct ng_car_bulkstats
NGM_CAR_CLR_STATS (clrstats): Clear node statistics.
NGM_CAR_GETCLR_STATS (getclrstats): Atomically return and clear node statistics.

SHUTDOWN

This node shuts down upon receipt of a NGM_SHUTDOWN control message, or when all hooks have been disconnected.

EXAMPLES

Limit outgoing data rate over fxp0 Ethernet interface to 20Mbit/s and incoming packet rate to 5000pps.

/usr/sbin/ngctl -f- <<-SEQ 
	mkpeer fxp0: car lower lower 
	name fxp0:lower fxp0_car 
	connect fxp0: fxp0_car: upper upper 
	msg fxp0_car: setconf { downstream={ cir=20000000 cbs=2500000 ebs=2500000 greenAction=1 yellowAction=1 redAction=2 mode=2 } upstream={ cir=5000 cbs=100 ebs=100 greenAction=1 yellowAction=1 redAction=2 mode=2 opt=2 } } 
SEQ

AUTHORS

Nuno Antunes <[email protected]>
Alexander Motin <[email protected]>

BUGS

At this moment only DROP and FORWARD actions are implemented.

November 13, 2012

Debian