Traffic Management - CCIE Routing and Switching Exam Certification Guide - page 526

but does not shape traffic to a specified rate. CAR typically drops traffic that exceeds the rate;
in contrast, traffic shaping delays traffic in a buffer to delay packets to shape the flow of traffic.
CAR is configured with the interface rate-limit command. The command has the following
syntax:
rate-limit {input | output} [access-group [rate-limit]
acl-index | qos-group number] bps burst-normal burst-max
conform-action action exceed-action action
Example 11-13 configures CAR on a High-Speed Serial Interface (HSSI) to limit the bandwidth
to 25 Mbps, in and out. The interface is also configured to allow bursts up to 30,000 bytes, with
all exceeded packets being dropped.
Example 11-13 CAR Configuration
interface Hssi0/0/0
description 45Mbps Link with CAR
ip address 1.1.1.1 255.255.255.252
rate-limit input 25000000 30000 30000 conform-action transmit
exceed-action drop
rate-limit output 25000000 30000 30000 conform-action transmit
exceed-action drop
To verify the configuration and monitor CAR statistics, use the show interfaces rate-limit
command, as shown in Example 11-14.
Example 11-14 show interfaces rate-limit Command
R4# show interfaces hssi 0/0/0 rate-limit
Hssi0/0/0 45Mbps Link with CAR
Input
matches: all traffic
params: 25000000 bps, 30000 limit, 30000 extended limit
conformed 14 packets, 828 bytes; action: transmit
exceeded 0 packets, 0 bytes; action: drop
last packet: 110ms ago, current burst: 0 bytes
last cleared 00:05:31 ago, conformed 0 bps, exceeded 0 bps
Output
matches: all traffic
params: 25000000 bps, 30000 limit, 30000 extended limit
conformed 0 packets, 0 bytes; action: transmit
exceeded 0 packets, 0 bytes; action: drop
last packet: 110ms ago, current burst: 0 bytes
last cleared 00:05:31 ago, conformed 0 bps, exceeded 0 bps