Which of the following descriptions of BGP Next_Hop attributes is incorrect?

Question

Options

• AThe BGP first check whether the next hop of the route is reachable before selecting a route. Routes whose next hop is unreachable are inactive routes and cannot participate in BGP route selection.
• BThe BGP next-hop is not allowed and it is necessary to modify the next hop.
• CThe address of Next Hop must be the IP address of the neighbor device interface.
• DThe next hop is a recognized mandatory attribute

• A
  8% (2)
• B
  4% (1)
• C
  85% (22)
• D
  4% (1)

Explanation

Option C is incorrect because the BGP NEXT_HOP attribute does not have to be the IP address of the directly connected neighbor's interface. In iBGP scenarios, the next-hop is typically preserved as the original eBGP peer's address (which is not the iBGP neighbor), and in third-party next-hop cases, it can point to a completely different device. This is why next-hop-self is often required in iBGP full-mesh or route-reflector setups.

Why the distractors are valid (correct) statements:

• A is correct - BGP performs next-hop reachability validation; routes with unreachable next-hops are marked inactive and excluded from best-path selection.
• B is correct - there are scenarios (e.g., iBGP peering over eBGP-learned routes) where the next-hop must be explicitly modified using next-hop-self to ensure reachability.
• D is correct - NEXT_HOP is a well-known mandatory path attribute, meaning it must be present in every BGP UPDATE message.

Memory tip: Remember "iBGP doesn't touch the next hop" - when a route learned via eBGP is re-advertised to iBGP peers, the next-hop stays as the original eBGP neighbor's address, not the iBGP neighbor's address. This directly disproves option C and is a classic BGP exam trap.

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