DSCP marking

Unanswered Question
Feb 9th, 2009

I have a network with several routers/switches and with an edge router at the border to the internet.

I'm interested to mark some traffic with DSCP=26.

In uplink I will ensure this by performing the DCSP marking inside the L3 switches where the hosts are directly connected, whereas in downlink inside the edge router. Also in the routers/L3 switches/L2 switches in-between edge router and hosts I need to configure them to let pass the DSCP=26.

My question is how can I get this practically done,meaning:

- what criteria is the best to use for defining the traffic that is to be marked with DSCP=26 (host IP@ only ? TCP/UDP port only? both IP@ and TCP/UDP port? etc)

- what to type in the edge router CLI (cisco 3845) to have this marking done

- what to type in the CLI of the routers/switches in-between in order to make them pass the traffic with DSCP=26 and not strip it off to DSCP=0 nor remark it.

I have this problem too.
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lejoe.thomas Mon, 02/09/2009 - 18:53

Hi

- what criteria is the best to use for defining the traffic that is to be marked with DSCP=26 (host IP@ only ? TCP/UDP port only? both IP@ and TCP/UDP port? etc)

There a various methods for classifying traffic. In the above case, it could be an ACL, the more specific, the better it is.

- what to type in the edge router CLI (cisco 3845) to have this marking done

The three steps to classifying traffic

Classify Traffic [class-maps and match statements]

Mark Traffic [Policy-map and set statements]

Apply the policy inbound or outbound direction to the interface. [service-policy command]

Example is provided below

http://www.cisco.com/en/US/docs/ios/qos/configuration/guide/clsfy_netwk_traffic_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1095198

- what to type in the CLI of the routers/switches in-between in order to make them pass the traffic with DSCP=26 and not strip it off to DSCP=0 nor remark it.

If you're doing classification and marking at the switches, as long you're not re-classifying and marking at the devices in between, the DSCP value in the DS field will remain the same.

Try to classify traffic as close to the ingress as possible. (i.e if you're classifying and marking at L3 switch, you wont need do anything at the edge router or you could just classify and mark at the edge router).

HTH

Lejoe

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Posted February 9, 2009 at 3:25 PM
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