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DSCP vs CoS

I need to think outloud here, just to make sure I have my barings right.

CoS is stored in the vlan tag, DSCP is stored in the IP header.  So, if I have a phone or an app that can insert a DSCP value into the IP header and then trust all of the uplinks to my destination, when, how or why would CoS ever come into the picture?  Looking into deploying QoS on both wired and wireless networks and want to solidify my understanding.

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Silver

DSCP vs CoS

If you have the option it's better to set DSCP because that can traverse the network without being rewritten. Some devices only know how to set CoS which means you don't have a choice.

Switches use CoS to DSCP mapping for queuing internally though.

Daniel Dib
CCIE #37149

Daniel Dib CCIE #37149 Please rate helpful posts.
Super Bronze

Re: DSCP vs CoS

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So, if I have a phone or an app that can insert a DSCP value into the IP header and then trust all of the uplinks to my destination, when, how or why would CoS ever come into the picture?

If L3 ToS is supported, the only reason to really used L2 Cos is when L3 ToS is not supported.  (E.g. "pure" L2 switches.)

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