350-401 Network Assurance Practice Question
A network administrator is troubleshooting a BGP routing issue where routes from an eBGP neighbor are not being installed in the routing table. The 'show ip bgp' output shows the routes are received but not valid. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the distinction between routes being received in the BGP table versus being installed in the routing table, and the trap here is that candidates confuse synchronization (a deprecated feature) with the next-hop reachability requirement, which is the immediate cause of the 'not valid' status.
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 next-hop IP address is not reachable.
For a BGP route to be considered valid and installed in the routing table, the next-hop IP address must be reachable via an IGP or a static route. If the next hop is not reachable, the route will appear in the 'show ip bgp' output but will be marked as not valid (often with a 'r' for received but not valid). This is the most common cause when routes are received from an eBGP neighbor but not installed.
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 AS-path contains the local AS number.
Why it's wrong here
This is incorrect. While an AS-path containing the local AS number can cause routes to be rejected due to loop prevention, the typical symptom is routes not being received at all or being marked as invalid, not the specific 'received but not valid' status. The most common cause for 'not valid' is next-hop unreachability.
- ✓
The next-hop IP address is not reachable.
Why this is correct
Correct. For a BGP route to be considered valid and installed in the routing table, the next-hop IP address must be reachable via an IGP or static route. If the next hop is not reachable, the route will appear in the 'show ip bgp' output but be marked as not valid.
- ✗
BGP synchronization is enabled.
Why it's wrong here
This is incorrect. BGP synchronization is a legacy feature that requires the route to be in the IGP before it is advertised. In modern networks, synchronization is disabled by default. Even if enabled, it affects advertisement, not the validity of received routes in the BGP table.
- ✗
The maximum-prefix limit has been exceeded.
Why it's wrong here
This is incorrect. Exceeding the maximum-prefix limit typically causes the BGP session to reset or routes to be withdrawn, not to be marked as 'not valid' in the BGP table. Routes would likely be removed entirely, not just marked invalid.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 practice question is part of Courseiva's free Cisco 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 350-401 exam.