Learn how to properly implement BFD to detect forwarding path failures when using OSPF routing in your data center. Configuring BFD between each adjacent router is key.
Table of Contents
Question
An engineer configured OSPF on all routers in the data center in the same exchange as other routers. Layer 2 connectivity was established. Now, the engineer plans to implement BFD to detect failures in the forwarding path. Which action must the engineer take?
A. Configure IS-IS routing before implementing BFD.
B. Configure BFD between each adjacent router.
C. Configure BFD on any one of the routers.
D. Configure CEF before implementing BFD.
Answer
B. Configure BFD between each adjacent router.
Explanation
To properly implement Bidirectional Forwarding Detection (BFD) for detecting failures in the forwarding path when using OSPF routing, the correct action is to configure BFD between each adjacent router (Option B).
BFD is a protocol that provides fast failure detection times between two adjacent routers, even on high-latency media. It operates independently of any routing protocol and detects faults in the bidirectional path between the two systems, including interfaces, data links, and to the extent possible the forwarding engines themselves.
When BFD is enabled on an interface, a BFD session is created and BFD timers are negotiated between the two endpoints. If a timer expires, the endpoint is declared unavailable. At that point, the BFD state of the interface changes and the routing protocol is notified.
So in this scenario, with OSPF already configured on all routers in the same exchange, the engineer must enable BFD on each interface between adjacent OSPF routers. The other options (configuring IS-IS, configuring BFD on only one router, or configuring CEF) will not properly implement BFD for comprehensive forwarding path failure detection across the OSPF routed network.
In summary, always configure BFD between each pair of adjacent routers to allow the protocol to detect any failures in either direction of the bidirectional forwarding path. This will ensure fast convergence if any component in the data path fails.
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