The answer is that the neighbor IP is not reachable or TCP port 179 is blocked. This is the most common cause of a BGP neighbor stuck in Idle state on FortiGate because the Idle state indicates the BGP process has not initiated a TCP connection, and without Layer 3 reachability or an open port 179, the three-way handshake cannot begin. On the Fortinet NSE 7 Advanced Security NSE7 exam, this concept tests your understanding of BGP state machine fundamentals and basic network troubleshooting—often appearing in scenario-based questions where a misconfigured static route or firewall policy silently drops BGP traffic. A common trap is assuming the issue lies in BGP configuration itself, such as incorrect AS numbers or authentication, when the root cause is simpler. Remember the memory tip: “Idle means no TCP dial—check the route and firewall rule.”
NSE7 Troubleshooting and Diagnostics Practice Question
This NSE7 practice question tests your understanding of troubleshooting and diagnostics. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
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
Idle state usually means the BGP process has not started or is waiting for a start event. The most common cause is that the neighbor IP is unreachable or the TCP connection cannot be established.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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.
Route advertisement does not affect the peering state.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related NSE7 OSPF questions on adjacency and route selection.
Troubleshooting and Diagnostics — This question tests Troubleshooting and Diagnostics — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The neighbor IP is not reachable or the TCP port 179 is blocked — Idle state usually means the BGP process has not started or is waiting for a start event. The most common cause is that the neighbor IP is unreachable or the TCP connection cannot be established.
What should I do if I get this NSE7 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related NSE7 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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Question Discussion
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