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350-501 · Question #474

Under which circumstance does BGP ignore the best-path algorithm after receiving multiple routes to a destination?

The correct answer is C. when the route's next hop is unreachable. BGP ignores the best-path algorithm if the next hop of a route is unreachable. BGP relies on the IGP to verify the reachability of the next hop. If the next hop is not reachable, the route is not considered for selection, regardless of the other attributes. This ensures that…

Networking

Question

Under which circumstance does BGP ignore the best-path algorithm after receiving multiple routes to a destination?

Options

  • Awhen the routes have local-preference values less than 100
  • Bwhen the route's first hop has a different AS number
  • Cwhen the route's next hop is unreachable
  • Dwhen the routes are synchronized

How the community answered

(36 responses)
  • A
    6% (2)
  • C
    92% (33)
  • D
    3% (1)

Explanation

BGP ignores the best-path algorithm if the next hop of a route is unreachable. BGP relies on the IGP to verify the reachability of the next hop. If the next hop is not reachable, the route is not considered for selection, regardless of the other attributes. This ensures that the router does not advertise or attempt to use routes that are invalid due to an unreachable next hop.

Topics

#BGP best-path#BGP route validity#Next-hop reachability

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