Router R6 is a route reflector with clients R1, R2, R4 and R5. Router R4 receives three routes from router R6 and is configured with ECMP 3. Given the following BGP configuration on routerR4, how…

Question

Options

• AThree primary paths.
• BTwo primary paths and one backup path.
• COne primary path and two backup paths.
• DOne primary path and one backup path.

• A
  2% (1)
• B
  80% (40)
• C
  6% (3)
• D
  12% (6)

Explanation

Option B is correct because the multipath 2 statement explicitly caps the number of primary (equal-cost) BGP paths at 2, regardless of the ECMP 3 setting mentioned in the question or the 3 routes received from R6. The backup-path ipv4 statement then installs 1 additional backup path, giving a total of 2 primary + 1 backup in R4's BGP table.

Why the distractors fail:

• A (Three primary): While 3 routes arrive and ECMP 3 is mentioned, the multipath 2 BGP statement is the binding constraint - it overrides the broader ECMP setting and limits primary paths to 2.
• C (One primary, two backup): Inverts the multipath logic; multipath 2 grants 2 primary paths, not 1, and backup-path only ever installs a single backup.
• D (One primary, one backup): Ignores multipath 2 entirely; without that statement you might get 1 primary, but with it you get 2.

Memory tip: Think of multipath N as a hard ceiling on primary paths that BGP enforces before backup-path adds its one extra slot. The formula is simply: primary = multipath value, backup = 1 (if backup-path is configured). When in doubt, the explicit BGP statement beats the interface-level ECMP setting.

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