So I know that COS only is available in a trunk connection. My question is when configuring a trunk between two switches should I trust the COS or DSCP on the link? I would think you would trust the COS value but I have been questioning myself lately. If I have a device that only generates DSCP values such as Unity or Call Manger and it goes over this trunk how it will place the voice traffic in the correct priority queue on the interface if it is only concerned with COS values and Unity only marks DSCP.
OK but according to my previous post I should not have to configure the DSCP-TO-COS mapping as it is alreayd there on the 6500. Also still using my Unity example. It maks the correct DSCP value on it's port. I trust the DSCP mapping of Unity. It now goes accross the 802.1q trunk to the other switch. I have the below commands configure for queuing on the Trunk link and the port for Unity.
Now as Unit generates the traffic it will only generate DSCP markings. I trust the DSCP but will the switch conver the DSCP to COS and perform the correct queueing on the port that Unity is connected to? Also as it travels over the Layer 2 link to the other 6500 will it convert the DSCP to COS and perform the apropriate queueing? On the other side of the trunk link I am mapping the COS to DSCP and trusting the COS value so as it goes over the link it should still be correct.
You don't have to configure the DSCP-to-CoS map if you are happy with the current settings.
The switch will indeed convert the DSCP to a CoS value because otherwise it couldn't queue it on egress. So to travel over the L2 link it has to use a CoS value to queue it on the outbound trunk port.