[j-nsp] Confusion about DSCP marking and rewrite rules

[Per Granath]

Note that "marking" is not word used in Junos...

On ingress you do "classification", and on the class assigned you do queuing, etc. The class does not change any bit in the packet header - the class is assigned "outside" the packet header internally in the router.

On egress you may apply a rewrite rule to a class (on an interface). Essentially, this means you cannot rewrite on ingress.

So, your IRB "marking filter", which in Junos is called "multi field classifier", does not change any bit in the packet headers - it only assigns the internal class - when packets ingress on the IRB.

The rewrite rules on the IRB only rewrite bits when a packet egress on the IRB.


On some other vendor you may be used to doing rewrite/marking on ingress...