Click the exhibit. AS 65540 is using MPLS to provide BGP shortcuts for its iBGP routing. Which routers must be configured with the "configure router bgp igp-shortcuts rsvp-te" command?

Question

Options

• ARouters R0, R1, R4 and R5.
• BRouters R1and R4.
• CRouters R1, R2, R3 and R4.
• DRouters R2 and R3.

• A
  9% (2)
• B
  74% (17)
• C
  13% (3)
• D
  4% (1)

Explanation

Option B is correct because igp-shortcuts rsvp-te must be configured on the ingress PE (Provider Edge) routers - R1 and R4 - which are the iBGP speakers at the edge of AS 65540 that need to resolve BGP next-hops via RSVP-TE LSPs instead of the IGP. Option A is wrong because R0 and R5 are external to AS 65540 (they are CE or external-AS routers) and have no role in the AS's iBGP shortcut mechanism. Option C is wrong because R2 and R3 are core P (Provider) routers that simply switch MPLS labels along the LSP - they do not participate in BGP next-hop resolution and require no BGP shortcut configuration. Option D fails for the same reason: R2 and R3 are transit routers, not BGP speakers making forwarding decisions.

Memory tip: "Shortcuts are chosen at the door, not in the hallway." Only the routers entering the MPLS domain (the PE edge routers) decide to use an RSVP-TE shortcut; the core P routers just carry the labeled packets through.

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