Cisco Tips & Tricks

May 20, 2006

QoS-Rate-Limiting Tip

Filed under: Access-lists, QOS, Router, Switching, Technology and Software — ciscotips @ 7:17 am

QOS feature that performs rate-limiting and packet classification is called CAR-Committed Access Rate.

Here is a quick tip that limits an Internet based traffic
(primarily http and FTP) to 512K, with a nice, fat burst.

First create the access lists.

access-list 100 permit tcp any any eq www
access-list 100 permit tcp any any eq ftp

Then apply rate limiting rules to the appropriate interface:

interface Serial1/0
bandwidth 2048
ip address 172.16.100.2 255.255.255.252
rate-limit input access-group 100 512000 1024000 2048000 conform-action transmit exceed-action drop
rate-limit output access-group 100 512000 1024000 2048000 conform-action transmit exceed-action drop

It will limit only http and ftp trafic, for other corporate web applications running on different ports, it will still get full E1 bandwidth.

Warning:-If, in a rate-limit rule, you reference an access list that does not exist, the rule will match all traffic. Usually not good.

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