Loss of DSCP Marking when routing between VLAN's

[russell.sage]

I have a 3750G switch running 12.2(44)SE6 my customer has some Cisco EX90 and ex-Tandberg VC units connected to the switch in a dedicated VLAN 600. The switch is then connected to the WAN router which has its own VLAN 6

From sh mls qos interface x/x/x statistics I can see that the traffic is marked by the VC units as DSCP 34 however when I run this command on the interface to the CE router the marking has been lost.

Similarly in the opposite direction incoming from the CE router I can see the marking coming from across the MPLS ok but when I check the output to the VC unit the marking has been lost.

This would indicate that in the process of routing between VLAN's the DSCP marking has been lost.

Can anyone advise on how to correct this issue. Because my interfaces are in different VLAN's do I need to VLAN based QoS?

[Joseph W. Doherty]

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Posting

On a 3750G, if mls qos is disabled, DSCP markings should be left alone.  However, if mls qos is enabled, DSCP markings are reset to zero unless you trust them (or have an input policy that trusts).

[russell.sage]

MLS QoS is enabled. mls qos trust dscp in configured on all interfaces.

[paul driver]

Hello

On all switches in between scr/dest can you show mls qos maps cos-dscp & dscp-cos

Also set a extended ping to dest with tos value of 126 and post the output from the dscp marking on dst interface ( sh policy-map interface xx )

Res
Paul

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