Quality of Service on Cisco 3850

[dvag-nsafe]

Hi there!

I have some questions about configuring QoS on the 3850's. We use them as Access-Switches and have a pair of 6840's to aggregate them. We only have L2 on the 3850, routing is done on the 6840's.

Now, i need to configure QoS in the LAN and want to trust/remark the DSCP-values coming in from the Laptops, who also have softphones (Skype for Business) installed. So i need to classify traffic coming from the Laptops.

I can configure a policy for the DSCP-values, but my question is, will the switch even be able to look at them since it is only operating on L2? The traffic to the Aggregation will be L2 so i need to create a class-map to translate them to COS values, right?

Thanks for any help,

Christian

[Joseph W. Doherty · Accepted solution]

I can configure a policy for the DSCP-values, but my question is, will the switch even be able to look at them since it is only operating on L2?

I don't have experience with the 3850, but since the earlier 3560/3750 could do that, I think it likely the 3650/3850 can too.

The traffic to the Aggregation will be L2 so i need to create a class-map to translate them to COS values, right?

I believe the answer to that is yes too.  However, you need VLAN frame tags to use L2 CoS, and since most modern QoS capable switches, even "L2" switches, can "see" the L3 ToS, you might find you only need to use DSCP.