If you wanted to trust the CoS value, you would use this command
Switch(config-if)# mls qos trust cos
Rate Limiting
You can configure the 3550 switch to limit traffic just like you can on a router with the 損olice,?command entered in policy-map configuration mode. For example if you wanted to limit traffic to an average rate of 5mb with burst capability to 2mb, and drop exceeding traffic, you would use this command: police 5000000 2000000 exceed-action drop
Class Maps and Policy Maps
QoS configuration is modular in fashion, meaning you configure different modules of your policy and then pull it all together under the interface. Class maps are used to define the traffic that will be policed, or manipulated. Under class map configuration you can specify an access-list to match, IP precedence, CoS or DSCP values. This example classifies traffic that came from the IP address 10.1.1.1:
access-list 10 permit 10.1.1.1 class-map xxxxxx match access-group 10
This is the first module of our QoS configuration, now we can create a policy map to specify what we want to do to our classified traffic.
Policy Maps
Policy maps are the next module of this whole puzzle. They are used to police and mark the classified traffic. For example:
policy-map xxxxxx class xxxxxx set ip dscp 56 police 2500000 200000 exceed-action drop
These modules are all pulled together under the preferred interface with the command:
service policy [inputoutput] xxxxxx
Between the above two examples you learned how to classify, police, and mark using policy maps. Now we will show how to classify, police, and mark using Aggregate policers. Aggregate policers allow the switch to use the same policer for multiple flows, and are recommended for a smaller number of combined flows.
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