(MPLS) Flashcards

Which MPLS label operation replaces an existing label with a new label?

Answer: Swap

The Swap operation replaces the top label in the MPLS stack with a new label at each transit LSR.

What is the default MPLS label value reserved for the IPv4 explicit null label?

Answer: 0

Label value 0 is the IPv4 Explicit Null label, signaling the egress PE to pop the label and forward based on the IPv4 header.

In an MPLS network, what does the term 'LSP' stand for?

Answer: Label Switched Path

LSP stands for Label Switched Path, which is the unidirectional path from ingress to egress LSR that packets follow.

Which protocol can be used to signal MPLS LSPs and also carries QoS traffic engineering constraints?

Answer: RSVP-TE

RSVP-TE (Resource Reservation Protocol - Traffic Engineering) signals LSPs and carries bandwidth and constraint information for TE tunnels.

What is the role of a P (Provider) router in an MPLS VPN architecture?

Answer: Performs label swap operations in the core

P routers are core MPLS routers that only perform label swap operations and have no knowledge of VPN or customer routes.

Which label is used in MPLS OAM to perform a router-alert function similar to IP router-alert?

Answer: Label 1

Label 1 is the Router Alert label, which causes each transit LSR to examine the packet more closely rather than just switching it.

In MPLS, what does 'penultimate hop popping' (PHP) accomplish?

Answer: Removes the top label one hop before the egress

PHP removes the outermost MPLS label at the penultimate LSR, reducing the egress PE's processing burden to a single lookup.