mediumMultiple 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 in AS 65001 is configured to redistribute connected routes into BGP. The route 10.10.10.0/24 is learned via BGP on R2 (AS 65002), but R2's iBGP neighbor R3 (AS 65002) does not receive this route. R2 and R3 have a full iBGP mesh, and the BGP session is established. The output of 'show ip bgp' on R2 shows the route with the 'r' flag (RIB-failure). 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 route is marked as RIB-failure because a route with a lower administrative distance already exists in the routing table for the same prefix.
RIB-failure indicates that BGP learned a route but it was not installed in the routing table because a better route (e.g., from an IGP or static) already exists. This prevents the route from being advertised to iBGP peers.
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 route is marked as RIB-failure because a route with a lower administrative distance already exists in the routing table for the same prefix.
Why this is correct
Correct because RIB-failure occurs when another routing source (e.g., OSPF, EIGRP, static) has a better route, preventing BGP from installing its route.
- ✗
The route is marked as RIB-failure because the next-hop is unreachable.
Why it's wrong here
Incorrect because next-hop unreachability would show the route as valid but not best, not as RIB-failure.
- ✗
The route is marked as RIB-failure because BGP synchronization is enabled and the IGP does not have the route.
Why it's wrong here
Incorrect because synchronization would prevent the route from being considered best, not cause RIB-failure.
- ✗
The route is marked as RIB-failure because the prefix is being filtered by an outbound route map.
Why it's wrong here
Incorrect because filtering would cause the route to be absent from the BGP table, not marked as RIB-failure.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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