NSE7 Troubleshooting and Diagnostics Practice Question
A BGP peering between two FortiGates is not establishing. The admin runs 'get router info bgp summary' and sees the neighbor state as 'Idle'. What is the most common cause of a BGP session stuck in Idle?
⚠ Common exam trap
Test-takers frequently confuse the Idle state with the Active state, assuming any misconfiguration (like wrong AS number) causes Idle, but in BGP FSM, an AS mismatch typically results in the Active state or a notification error, not Idle.
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
✓
The neighbor IP is not reachable or the TCP port 179 is blocked
The Idle state in BGP indicates that the session has not started or has been reset, often because the underlying TCP connection cannot be established. The most common cause is that the neighbor IP is unreachable or TCP port 179 is blocked by a firewall or ACL, preventing the three-way handshake. Without TCP connectivity, BGP cannot transition out of Idle, regardless of other configurations.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The BGP update timer is set too high
Why it's wrong here
Update timers affect route advertisement, not session state.
- ✗
The remote AS number is misconfigured
Why it's wrong here
A misconfigured ASN typically results in the OpenConfirm or Active state, not Idle.
- ✓
The neighbor IP is not reachable or the TCP port 179 is blocked
Why this is correct
BGP uses TCP port 179; if the neighbor is unreachable or port is blocked, the session cannot start, staying in Idle.
- ✗
The route advertisement is disabled
Why it's wrong here
Route advertisement does not affect the peering state.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This NSE7 practice question is part of Courseiva's free Fortinet certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the NSE7 exam.