On Monday, September 19, 2011 05:35:11 PM ar wrote: > Thanks. I dont want to apply policy on all ingress > interface of the PE to remark traffic. That's why I want > to be sure on this TOS reflection..
Well, I always think it's best to mark on ingress because that's the closest interface toward downstream customers. in deployments where you have a router that is both a P and PE device (such as in a Metro-E ring, e.t.c.), it can be difficult to differentiate transit (P) from terminating (PE) traffic. This is why I've never liked Juniper's egress rewriting/remarking policy in earlier line cards, as it really limits the kinds of topologies you can have with certain platforms. Suffice it to say, this is now changing in later line cards, but leaves much to be desired. Anyway... > If this is the case, is it safe enough to just do a > policy-map on the PE-to-P interface matching for the > reflected EXP bits? In theory, yes, as the first 3 bites of the DSCP value will be mapped to the EXP bit. But in order to ensure that you get the right mapping from DSCP to EXP, you may end up marking DSCP traffic on ingress. If you do that, you might as well just mark EXP bits on ingress :-). Otherwise, I can't promise that the values you're matching upstream on the PE-P link will always mirror what was set as the packets came into the PE router in the first place. Cheers, Mark.
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