COS marking - Layer 2

[awoog]

I plan to have a router connected on a VPLS network, a CISCO 2951, connected via one of two the standard Ethernet port. I need to set the Layer 2 COS to the right priority for Voice. How can I do that ? Does the DSCP EF marking automatically reflects in the COS via a default map - or alternatively do I need to set explicitely the CoS via a policay map "set cos" command ?  Is the "set cos" command accepted on a router, standard Ethernet ports ?

[Jon Marshall]

As far as i know only L3 switches have default mapping tables from DSCP to CoS so you will need to explicitly mark it.

Couple of caveats -

1) you can only do this on an outbound service policy because it doesn't make any sense to mark the packet inbound but it sounds like that is what you are going to do ie. outbound

2) more importantly the CoS field is only present in an 802.1q tagged frame because the CoS markings are contained within the 802.1q tag. So you cannot do this on the main interface because those frames will be untagged and therefore cannot carry CoS markings.  You would have to run 802.1q on the interface ie. create a subinterface for that vlan, use dot1q encapsulation and then you can set the CoS value.

Jon

[awoog]

Thanks for your answer. So you can do that on a Cisco 2951 with "set cos" in a policy map on a VLAN subinterface of the Ethernet port  Gi0/0 ? Is that correct ?

[Jon Marshall]

awoog wrote:
Thanks for your answer. So you can do that on a Cisco 2951 with "set cos" in a policy map on a VLAN subinterface of the Ethernet port  Gi0/0 ? Is that correct ?

Yes, it should work fine if you create the subinterface.

Jon