QoS on 2950. Service policy and trusted ports

Answered Question
Mar 22nd, 2008
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Probably this question is not very useful in real life enviroments, but is just to understand (I'm studyng for QoS exam)


On a 2950(EI) switch, You can configure classification using:

- trust state (CoS/DSCP) that affects internalDSCP with COS-to-DSCP mapping or directly trusting DSCP of inconming frame

- using a service policy applied to interface with a policy-map configured to "set ip dscp X" that should directly affect internal DSCP value


What happens if both method are used? Which of the 2 commans has higher priority and affect the internalDSCP?


I was looking on Cisco site...but I can't find an answer.

hxxp://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1...


Hope for your comments


THanks


Correct Answer by Jon Marshall about 9 years 3 days ago

Hi


Generally speaking if you have a service-policy on the ingress port and at the same time you trust the marking then the service policy takes precedence. If there is no match in the service policy then the trust is taken into account. From your link


"A policy-map configuration state supersedes any actions due to an interface trust state"


http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_22_ea5/configuration/guide/swqos.html#wp1044930


HTH


Jon

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Correct Answer
Jon Marshall Sat, 03/22/2008 - 12:18
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Hi


Generally speaking if you have a service-policy on the ingress port and at the same time you trust the marking then the service policy takes precedence. If there is no match in the service policy then the trust is taken into account. From your link


"A policy-map configuration state supersedes any actions due to an interface trust state"


http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_22_ea5/configuration/guide/swqos.html#wp1044930


HTH


Jon

Marcofbbr Sat, 03/22/2008 - 13:20
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Thanks Jon,

I missed this one while reading. ;)

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