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Reid L Stidolph or Gene Shtirmer might have some information for you.
Hey Brian K Berry , typically when the config is set for traffic to be (re-)marked on ingress (say at a LAN GW or something), and the route is to a peer, naturally the traffic is going egress SVR with the prescribed markings. So if the network/neighborhood you are peering across can be trusted to carry those markings all the way through, you should be good to go.
That said, I've definitely run into cases where the network did NOT preserve my markings (it was over public broadband). In that case, I had to set my waypoints in that neighborhood to re-write DSCP values as well. That had the overall effect of ensuring the traffic was consistently marked when it left my data-center router, even if my markings got messed up in flight from when they were first marked at my branch. The nice part about the service and it's service-policy being global, is that even if both routers are re-marking, they'll always set it the same.
I believe that the re-writing of DSCP works independently of the prioritization modes. In other words, no matter what you have set there, if you have rewrite-dscp true, it is going to mark to what is set in the session's service-class.
I suppose that you could have a config where you are prioritizing based on incoming DSCP (`prioritization-mode dscp`) AND re-writing the DSCP values (`rewrite-dscp true`)...in which case I think you'd see the router place the packets into it's own queues based on the ingress markings, and then egress the packets with whatever markings were in the service-class. I'd want to check with Sarah V Jaffer for sure though, on exactly how that would behave.
You are correct, Reid. Our prioritization-mode dscp is all about traffic engineering of incoming packets and using the markings they are coming in with. The other configuration option, rewrite-dscp is about how packets are marked when they are sent out. The two features do not interact directly. Determining priority from incoming DSCP is done before the value is rewritten and is unaffected by what we're rewriting the value to.
Reid L Stidolph I appreciate the quick response and have a follow up question. Does rewrite DSCP work for both local and DSCP prioritization modes?