Catalyst 4948 QoS configuration (IOS 122-46.SG)

Answered Question
Apr 29th, 2009

I have some Catalyst 4948-10GE switches configured for QoS with COS to DSCP mapping commands. On each interface "qos cos 1" and "qos trust cos" are configured. A WireShark monitor of any port reveals that the packet DSCP value is "0x00". Have tried trust dscp with dscp default of 10 and configuring a Service Policy to tag "any" traffic with a DSCP value of "af", but the packets still have a DSCP value of "0x00".

Any solutions available?

Correct Answer by Giuseppe Larosa about 7 years 9 months ago

Hello Rob,

basic check:

1)

have you configured mls qos in global config mode ?

conf t

qos

see

http://cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/46sg/configuration/guide/qos.html#wp1207227

2) cos settings apply to L2 trunk ports where an 802.1p CoS field is present in the 802.1Q header if the ports are access ports this setting is not effective for them.

3) are you using an monitor session or capturing traffic directed to the PC ?

Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Thu, 04/30/2009 - 00:47

Hello Rob,

basic check:

1)

have you configured mls qos in global config mode ?

conf t

qos

see

http://cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/46sg/configuration/guide/qos.html#wp1207227

2) cos settings apply to L2 trunk ports where an 802.1p CoS field is present in the 802.1Q header if the ports are access ports this setting is not effective for them.

3) are you using an monitor session or capturing traffic directed to the PC ?

Hope to help

Giuseppe

robj Thu, 04/30/2009 - 17:39

Giuseppe,

Was using a monitor session to check the QoS value. Have found out that the QoS settings cannot be seen via a monitor port. Need to analyze the data from another device on the same switch, or monitor a trunk link.

RobJ

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