CCNP SP MPLS FAQ: Forwarding Labeled Packets
Q1. What does the push operation do on a labeled packet?
Q2. Which Cisco IOS command do you use to see what the swapped label is and which labels are pushed onto a received packet for a certain prefix?
Q3. What does the outgoing label entry of “Aggregate” in the LFIB of a Cisco IOS LSR mean?
Q4. What label value signals the penultimate LSR to use penultimate hop popping (PHP)?
Figure: Penultimate Hop Popping
Q5. What are the value and the function of the Router Alert label?
Q6. Why does an LSR forward the ICMP message “time exceeded” along the LSP of the original packet with the TTL expiring instead of returning it directly?
Q7. Is using Path MTU Discovery a guarantee that there will be no MTU problems in the MPLS network?
Q8. Why is MTU or MRU such an important parameter in MPLS networks?