easyMultiple ChoiceObjective-mapped
300-410 Practice Question: Is troubleshooting a BGP route advertisement issue
A network engineer is troubleshooting a BGP route advertisement issue. Router R1 (AS 65001) is an eBGP peer of R2 (AS 65002). R1 is advertising the prefix 10.0.0.0/8 to R2. R2 has an iBGP session with R3 (AS 65002). R3's BGP table shows the prefix 10.0.0.0/8 with next-hop 10.1.1.1 (R1's interface). However, R3 does not install this route in its routing table. The output of 'show ip route 10.0.0.0' on R3 shows no route. The engineer checks the routing table on R3 and sees that the interface connected to 10.1.1.0/24 is down. What is the most likely cause?
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 10.1.1.1 is not reachable because the directly connected interface is down.
For BGP to install a route, the next-hop must be reachable. If the interface to the next-hop is down, the route is considered unreachable and will not be 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 next-hop 10.1.1.1 is not reachable because the directly connected interface is down.
Why this is correct
Correct because BGP requires the next-hop to be reachable; a down interface makes the next-hop unreachable.
- ✗
The route is not installed because BGP synchronization is enabled.
Why it's wrong here
Incorrect because synchronization is disabled by default and would not cause this issue.
- ✗
The route is not installed because the prefix is being filtered by an inbound route-map on R3.
Why it's wrong here
Incorrect because if the route were filtered, it would not appear in the BGP table at all.
- ✗
The route is not installed because the administrative distance of the route is too high.
Why it's wrong here
Incorrect because administrative distance does not prevent installation; it only affects preference among multiple routes.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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