NSE4 High Availability and Diagnostics Practice Question
An administrator runs 'diagnose debug flow' for a specific policy and sees the following output: id=20085 trace_id=10 func=vf_ip_route_in msg='No matching interface to route packet' What does this indicate?
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 destination IP address has no matching route in the routing table
The trace indicates that FortiGate cannot find a route to forward the packet, meaning the destination is unreachable.
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 packet is being blocked by a firewall policy
Why it's wrong here
Policy blocking generates explicit deny or drop messages naming the policy; this trace fails earlier, during route lookup. It tempts because administrators debugging traffic commonly suspect policy, but no matching route exists, so the packet never reaches policy evaluation.
- ✗
The source interface is down
Why it's wrong here
The message concerns route lookup failing to find an outgoing interface, not interface operational state; a down source interface produces different diagnostics. It tempts because interface problems commonly cause drops, but here the route table lacks a matching entry for the destination.
- ✓
The destination IP address has no matching route in the routing table
Why this is correct
The debug flow message 'No matching interface to route packet' means the FortiGate found no route entry for the destination IP, so the packet cannot be forwarded. The routing table lookup failed, indicating a missing or incorrect route rather than a policy or interface issue.
- ✗
The session table is full
Why it's wrong here
Session table exhaustion produces messages about session allocation or memory limits, not route lookup failure. It tempts because full session tables do drop traffic under load, but this trace shows the route lookup stage failing before any session could be created.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This NSE4 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 NSE4 exam.