Langue: en

Autres versions - même langue

Version: 361773 (ubuntu - 24/10/10)

Section: 4 (Pilotes et protocoles réseau)

BSD mandoc


ng_car - Commited Access Rate netgraph node type


In netgraph/ng_car.h


The car node type limits traffic flowing through it using:


This node type supports the following hooks:
Hook leading to upper layer protocols.
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.


Each hook can operate in one of the following modes:
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.
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.
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.

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.


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 Vt struct ng_car_bulkconf
NGM_CAR_GET_CONF (getconf )
Return current node configuration as Vt struct ng_car_bulkconf
 struct ng_car_hookconf {
         u_int64_t cbs;          /* Committed burst size */
         u_int64_t ebs;          /* Exceeded/Peak burst size */
         u_int64_t cir;          /* Committed information rate */
         u_int64_t pir;          /* Peak information rate */
         u_int8_t green_action;  /* Action for green packets */
         u_int8_t yellow_action; /* Action for yellow packets */
         u_int8_t red_action;    /* Action for red packets */
         u_int8_t mode;          /* operation mode */
         u_int8_t opt;           /* mode options */
 /* possible actions (..._action) */
 enum {
 /* operation modes (mode) */
 enum {
 /* mode options (opt) */
 #define NG_CAR_COUNT_PACKETS    2
 struct ng_car_bulkconf {
         struct ng_car_hookconf upstream;
         struct ng_car_hookconf downstream;
NGM_CAR_GET_STATS (getstats )
Return node statistics as Vt struct ng_car_bulkstats
 struct ng_car_hookstats {
         u_int64_t passed_pkts;
         u_int64_t droped_pkts;
         u_int64_t green_pkts;
         u_int64_t yellow_pkts;
         u_int64_t red_pkts;
         u_int64_t errors;
 struct ng_car_bulkstats {
         struct ng_car_hookstats upstream;
         struct ng_car_hookstats downstream;
NGM_CAR_CLR_STATS (clrstats )
Clear node statistics.
NGM_CAR_GETCLR_STATS (getclrstats )
Atomically return and clear node statistics.


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


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 } }


netgraph(4), ngctl(8)
J. Heinanen "A Single Rate Three Color Marker" RFC 2697
J. Heinanen "A Two Rate Three Color Marker" RFC 2698


An Nuno Antunes Aq An Alexander Motin Aq


At this moment only DROP and FORWARD actions are implemented.