CCDE: Cisco Certified Design Expert (Written) — Question 5

A company plans to include Nonstop Forwarding and Bidirectional Forwarding Detection as a part of their network redundancy plan. In which two ways do NSF and BFD work together when different hardware platforms are compared? (Choose two.)

Answer options

• A. During supervisor engine or routing engine failover, the NSF feature will always ensure that the BFD at the peer router will not trigger a link down independent of the used hardware platform.
• B. At some hardware platforms, BFD and NSF are not supported together. During supervisor engine or routing engine failover, the BFD at the peer router will trigger a link down.
• C. To ensure that BFD at the peer router will not trigger a link down during NSF, the BFD packets must be processed fast enough, and, during supervisor engine or routing engine failover, by processing the BFD independent from the supervisor engine or routing engine.
• D. Because BFD is always processed at the line cards (not at the supervisor engine or routing engine), a supervisor engine or routing engine failover will not affect the BFD peer router.
• E. Because BFD is always processed at the supervisor engine or routing engine, a supervisor engine or routing engine failover will always trigger a link down at the peer router.

Correct answer: B, C

Explanation

Option B is correct because it highlights that on some hardware, BFD and NSF cannot operate together, leading to a link down during engine failover. Option C is also correct as it explains the requirement for fast processing of BFD packets independent of the supervisor engine to prevent link down during NSF. The other options are incorrect as they either misrepresent the relationship between BFD, NSF, and hardware processing or incorrectly assert the effects of engine failover.