The goal is to enable Bidirectional Forwarding Detection (BFD) for eBGP neighbors 10.10.10.2 and
10.10.20.2 on the AOS-CX VSF stack (AS 65000). Global BFD settings are already configured. We need the specific commands to link BFD state to the BGP neighbor relationship.
* BFD for BGP Configuration:Requires enabling the fall-over bfd parameter for the specific neighbor within the router bgp <asn> configuration hierarchy.
* Analyzing the Options (New Image):
* Option 1 (Top):
router bgp 65000
address-family ipv4 unicast
neighbor 10.10.10.2 fall-over bfd
neighbor 10.10.20.2 fall-over bfd
This enables BFD specifically within the ipv4 unicast address family context for both neighbors. This is a valid configuration location.
* Option 2 (Second):
router bgp 65000
neighbor 10.10.10.2 fall-over bfd
neighbor 10.10.20.2 fall-over bfd
This enables BFD directly under the main neighbor <ip> configuration lines within router bgp 65000. This typically applies BFD to all address families configured for that neighbor relationship (including IPv4 unicast). This is also a valid and common configuration location.
* Option 3 (Third):
int 1/1/1-1/1/2, 2/1/1-2/1/2
fall-over-bfd
Incorrect. Applies BFD configuration under an interface range context, which is not how BFD is linked to BGP sessions.
* Option 4 (Bottom):
interface lag1-2
fall-over bfd
Incorrect. Applies BFD configuration under an interface LAG range context, which is not how BFD is linked to BGP sessions.
* Comparing Valid Options (1 vs 2):Both Option 1 and Option 2 correctly use the fall-over bfd command under router bgp. Option 1 provides per-address-family granularity, while Option 2 applies it to the neighbor generally. Without a specific requirement to enable BFDonlyfor IPv4, applying it at the neighbor level (Option 2) is often simpler and sufficient. Both achieve the goal for the required IPv4 peering. In many documentation examples, the configuration is shown at the neighbor level unless per- AF control is explicitly needed.
* Conclusion:Both Option 1 and Option 2 show valid configuration methods. Option 2 is arguably slightly more common/general when BFD is desired for the overall neighbor relationship.
References:AOS-CX BFD Guide, AOS-CX BGP Guide (neighbor commands, fall-over bfd option). This relates to "Routing" (16%) and "Network Resiliency and virtualization" (8%) objectives.
