Which of the following do you need to take into account when designing IS-IS for an MPLS-VPN environment? (Select two.)

Question

Options

• ARoute leaking is required from L2 to L1 for MPLS (LDP) to work.
• BIf MPLS-TE is used, it is simpler to use a single area/Level IS-IS design.
• CIf MPLS-TE is used, it is recommended to use a multiarea/Level IS-IS design to achieve more
• DFor MPLS to work over IS-IS, IS-IS wide metric must be enabled.
• ERoute leaking should be avoided when MPLS and MP-BGP is used.

• A
  67% (14)
• C
  5% (1)
• D
  10% (2)
• E
  19% (4)

Explanation

A is correct: In a multi-level IS-IS design, L1-only routers do not learn L2 prefixes by default. LDP must establish label bindings for all prefixes in the network. Without route leaking from L2 into L1, L1-only routers lack the routing entries needed for LDP to build complete label-switched paths (LSPs), breaking MPLS forwarding. B is correct: MPLS-TE uses CSPF (Constrained Shortest Path First), which requires a full view of the network topology including link attributes (bandwidth, delay, TE metric). IS-IS TE extensions (TLVs) do not automatically cross level boundaries in a multi-level design, so a single-level (flat) IS-IS design is far simpler for MPLS-TE deployments. C is false because multi-level IS-IS actually complicates MPLS-TE, not simplifies it. D is false because basic MPLS/LDP does not require wide metrics - wide metrics are needed for MPLS-TE extensions. E is false because route leaking is necessary (not something to avoid) when MPLS is used in a multi-level IS-IS design.

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