NSE7 Advanced Networking and SD-WAN Practice Question
A FortiGate is using BFD for BGP fast failure detection. The administrator wants to ensure that if the BFD session goes down, the BGP neighbor is removed and routes are withdrawn immediately. Which configuration is necessary?
⚠ Common exam trap
Many candidates think setting low BFD timers alone (Option D) is sufficient, but they forget that BFD must be explicitly enabled on the BGP neighbor configuration to link the BFD session to the BGP session and trigger route withdrawal.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable BFD on the BGP neighbor and ensure BFD timers are set lower than BGP hold time
BFD provides sub-second failure detection independent of BGP's hold timer. When BFD is enabled on a BGP neighbor and the BFD session goes down, the BGP neighbor is immediately declared dead and all routes from that neighbor are withdrawn, without waiting for the BGP hold timer to expire. This ensures rapid convergence as requested by the administrator.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Enable BFD on the BGP neighbor and ensure BFD timers are set lower than BGP hold time
Why this is correct
BFD must be enabled for the BGP neighbor; when BFD detects a failure, it notifies BGP to tear down the session.
- ✗
Configure BGP graceful restart
Why it's wrong here
Graceful restart would actually preserve routes during a restart, not withdraw them immediately.
- ✗
Set BGP hold time to 0
Why it's wrong here
Setting hold time to 0 disables keepalives, but BFD still works only if enabled.
- ✗
Use 'set bfd-desired-min-tx 100' on the interface
Why it's wrong here
This sets the BFD transmission interval, but BFD must be enabled for the BGP neighbor separately.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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