Which of the following descriptions about the next-hop application of routing in BGP are correct? (Multiple choice)

Question

Options

• ABy default, no next-hop iteration routing policy is configured
• BThe BGP speaker does not modify the next-hop attribute, not necessarily the IP address of the adjacent device
• CYou can use the peer x.x.x.xnext-hop-local command to modify the next-hop address when advertising routes to IBGP peers
• DBy default, when BGP advertises imported IGP routes to IBGP peers, it changes the next hop attribute to its own interface address

• A
  7% (3)
• B
  77% (34)
• D
  16% (7)

Explanation

B is correct because BGP preserves the next-hop attribute when re-advertising routes from EBGP into IBGP by default - meaning an IBGP peer may receive a next-hop address that belongs to a remote EBGP peer, several hops away, not the directly adjacent BGP speaker. C is correct because peer x.x.x.x next-hop-local is the explicit command used to override this behavior, forcing the advertising router to substitute its own address as the next-hop when sending routes to IBGP peers - this is the standard fix for IBGP reachability problems.

A is wrong because BGP does perform next-hop reachability validation (called next-hop iteration) by default - it checks whether the next-hop address is reachable via the routing table before installing or advertising the route. D is wrong because it describes behavior that is not the default - BGP does not automatically change the next-hop to its own interface address when advertising imported IGP routes to IBGP peers; that is precisely why the next-hop-local command in option C exists and must be configured explicitly.

Memory tip: IBGP = "I Don't Break Paths" by default - it preserves whatever next-hop it received and passes it along unchanged, which is why you must use next-hop-local to fix reachability when IBGP peers can't reach that original next-hop.

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