Access Switch: Trust CoS or DSCP?

[bruce.thornton]

For an Access Point(3802i) switch port configuration, should I used trust COS or trust DSCP.  My uplink  to the core is L2 and I'm trusting COS.

[Jhosbell Verdesca De Aguiar]

You could do both, it depends on how the AP is deployed. But I would always recommend using DSCP for a couple of reasons:

1. You can only trust CoS if you have a VLAN tag (trunk links) because the 802.1p tag goes in the 802.1q header. So, If you have FlexConnect Local Switching, you will be tagging the users VLANs and then you can trust CoS for the Users traffic.
2. However, the CAPWAP traffic from/to the AP is on the Native VLAN if it is a trunk or on the Access VLAN if it is an access port. By default those ports do not have any 802.1q header, therefore there is no CoS to trust.

3. DSCP is at the IP Header, so it does not get lost over the path, unless any device re-writes the value.

Hope that helps.