[j-nsp] MPLS and QoS at penultimate hop ?

[Chris Kawchuk]

It was my understanding that the label was "logically" popped on Egress (in terms of how one would envision the packet flow); hence the outer label EXP bits were evaluated by the BA classifier on ingress properly. (Whether it's popped on ingress, yet evaluated prior-to-pop is a mechanics thing..)

But yes, I have no documentation I can point to; off the top of my head that the above is indeed true. I would be interested to know for future information sake that the JNPR box is indeed "doing the right thing" so to speak… i.e. since the PIC/MPC pops the Layer-2 information as well, it needs to be able to read the 802.1P bits, if there is a 1p-VLAN tag BA applied to the interface. Hopefully we're also reading the outer EXP label at the same time; as this would make sense.

i.e. if you're doing VLAN pop/swapping, you'd need to retain any BA-p-tag specific classification there as well, prior to any tag manipulation.

400 quatloos says it's done on ingress before the label is popped.

- Ck.


> 
> Simple question I'm not able to find answer for: what is the order 
> of label pop operation and BA classification on penultimate router ? 
> 
> I have a gut feeling that label is stripped first and then BA 
> classification is done on a "naked" packet, f.e., ipprec-based
> in case of IP packet, without taking (already stripped) EXP bits into 
> account, but I can't find any documentation proving or disproving it...