NSE7 Advanced Networking and SD-WAN Practice Question
An administrator runs 'get router info bgp summary' and sees that the BGP session to a neighbor is in the 'Idle' state. The neighbor IP is reachable via ping. The BGP configuration uses loopback interfaces with 'update-source loopback1'. What is the MOST likely reason for the Idle state?
⚠ Common exam trap
Many candidates assume ping reachability to the neighbor IP guarantees BGP session establishment, but they overlook that BGP packets are sourced from the loopback interface, requiring the neighbor to have a return route to that specific source IP.
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
✓
There is no route on the neighbor back to the FortiGate's loopback IP
The 'Idle' state in BGP indicates that the session cannot start, often due to a missing route to the neighbor's update-source IP. Since the neighbor IP is reachable via ping but the session uses loopback interfaces with 'update-source loopback1', the FortiGate's BGP packets will source from its loopback1 IP. If the neighbor does not have a route back to that loopback IP, it cannot respond to the TCP handshake, leaving the session stuck in Idle. This is a classic BGP loopback peering issue where reachability of the source IP is required, not just the physical interface IP.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
There is no route on the neighbor back to the FortiGate's loopback IP
Why this is correct
BGP uses TCP; if the neighbor cannot reach the update-source IP, the TCP handshake fails, keeping the session in Idle.
- ✗
The loopback interface is down or has no IP address assigned
Why it's wrong here
If the loopback is down, the update-source would fail, but the BGP session might show Idle; however, ping to neighbor works, so local loopback is likely up.
- ✗
The BGP neighbor's remote-as is misconfigured
Why it's wrong here
Misconfigured remote-as usually leads to Active state, not Idle.
- ✗
The BGP timer values (keepalive/hold) are mismatched
Why it's wrong here
Timer mismatch typically causes session flapping, not persistent Idle.
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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.