Click the exhibit. Router R6 is a route reflector with clients R1, R2 and R5 with local preferences 100, 200 and 500 respectively. Router R3 advertises prefix 192.168.1.0/27 and R2 and R5 which are…

Question

Options

• AThe routes from routers R1, R2 and R5.
• BThe routes from routers R1 and R2.
• CThe routes from routers R2 and R5.
• DTwo routes are chosen at random and advertised to router R4.

• A
  23% (6)
• B
  12% (3)
• C
  62% (16)
• D
  4% (1)

Explanation

Option C is correct because R2 and R5 both have direct eBGP connections to R3, and their advertise-external configuration causes each to advertise its best external (eBGP-learned) path to the route reflector R6 - even though R5's route (local pref 500) beats R2's (local pref 200). R6, configured with add-paths send 2, then forwards exactly 2 paths to R4: R5's best path and R2's advertise-external path.

A is wrong because R1 has no eBGP session with R3 - it only learns the prefix via iBGP reflection from R6, so it contributes no additional path for R6 to reflect. B is wrong because R5 holds the highest local preference (500) and its path is definitively included; R1 is still excluded for the same reason above. D is wrong because BGP add-paths selection is deterministic, following the standard BGP best-path algorithm - there is nothing random about it.

Memory tip: "Only routers with eBGP skin in the game can play." Only R2 and R5 have external paths to advertise (advertise-external only matters if you have an external path), and add-paths send 2 means the RR picks the top 2 - the best (R5) and the best-external-from-a-loser (R2).

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