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MPLS Fundamentals: Forwarding Labeled Packets

Chapter Description

Forwarding labeled packets is quite different from forwarding IP packets in that not only is the IP lookup replaced with a lookup of the label in the label forwarding information base (LFIB), but different label operations are also possible. This chapter specifically focuses on how labeled packets are forwarded in an MPLS network.

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Chapter Review Questions

  1. What does the push operation do on a labeled packet?
  2. 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?
  3. What does the outgoing label entry of "Aggregate" in the LFIB of a Cisco IOS LSR mean?
  4. What label value signals the penultimate LSR to use penultimate hop popping (PHP)?
  5. What are the value and the function of the Router Alert label?
  6. 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?
  7. Is using Path MTU Discovery a guarantee that there will be no MTU problems in the MPLS network?
  8. Why is MTU or MRU such an important parameter in MPLS networks?