Short answer: BGP NEXT_HOP identifies the address a router must resolve to forward traffic. A route may appear in BGP but be unusable if its next hop is unreachable; iBGP often uses next-hop-self. [1]
NEXT_HOP provides a forwarding target; it does not select the complete end-to-end path.
How NEXT_HOP works
RFC 4271 defines NEXT_HOP as a BGP path attribute. The receiving router must resolve the next-hop address before using the route. Distinguish “BGP learned the prefix” from “the next hop is reachable.” [1]
With eBGP, the peer commonly becomes the next hop. Across iBGP, the existing next hop is commonly preserved. If Edge-1 learns 203.0.113.0/24 from peer 192.0.2.1 and advertises it to Core-1, Core-1 may still need a route to 192.0.2.1. Without one, the BGP path is unusable.
Using next-hop-self
Cisco-style example: router bgp 65000; neighbor 10.0.0.2 remote-as 65000; neighbor 10.0.0.2 next-hop-self. This makes the advertising router the next hop for routes sent to that neighbor. Alternatively, distribute reachability to the original next hop through the IGP. Confirm syntax and address-family behavior for your platform.
Traffic engineering: capabilities and limits
- Outbound: NEXT_HOP determines the immediate forwarding target for the selected route. Rewriting it can steer traffic to an edge or fabric exit, subject to resolution and best-path policy.
- Inbound: It is not reliable control for remote networks' path selection; their routing policy determines forwarding.
- Cannot do: guarantee symmetry, override firewall policy, or make an unreachable address reachable. [1]
Modern data-center and cloud use
In BGP EVPN/VXLAN, control-plane routes and the underlay are distinct but dependent: the receiving VTEP must be reachable through the underlay. A valid EVPN route cannot deliver packets if VTEP reachability is broken. At cloud and dual-ISP edges, inspect next-hop reachability separately for each address family.
Verification
On Cisco-style platforms: show ip bgp 203.0.113.0, show ip route 192.0.2.1, and show ip bgp neighbors 10.0.0.2 advertised-routes. Confirm the prefix, expected NEXT_HOP, and active recursive route. FRRouting examples: show bgp ipv4 unicast 203.0.113.0/24 and show ip route 192.0.2.1; syntax varies by version.
Troubleshooting checklist
- Inspect the received prefix and NEXT_HOP.
- Check routing-table reachability to that address.
- Verify IGP/underlay advertisements include required loopbacks and transit subnets.
- Check route maps for unexpected rewriting.
- Inspect advertised routes at the receiving peer.
- For EVPN/VXLAN, test underlay reachability between VTEPs separately.
- After changes, perform supported route refresh and verify convergence.
Interview answer
BGP NEXT_HOP is the forwarding address associated with a route. The route is usable only when that address resolves in the local routing table. eBGP commonly sets the peer as next hop, while iBGP commonly preserves it, so designs use next-hop-self or provide IGP reachability.
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