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300-410 R1 and R2 are eBGP peers Practice Question
R1 and R2 are eBGP peers. R1 advertises a prefix 192.168.1.0/24 with MED 50. R2 also receives the same prefix from another eBGP peer R3 with MED 100. R2's BGP best path selection chooses the path via R1 because of lower MED. However, R2's routing table shows the next-hop for 192.168.1.0/24 as 10.1.1.1 (R1), but R2 cannot ping 192.168.1.1. R2 has: interface GigabitEthernet0/0, ip address 10.1.1.2 255.255.255.0, and no ip route to 192.168.1.0/24 other than BGP. R1's interface to R2 has ip address 10.1.1.1 255.255.255.0. R1's BGP table shows the prefix with next-hop 10.1.1.1 (self). What is the root 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
✓
R1 does not have the prefix 192.168.1.0/24 in its routing table because the next-hop for that prefix in R1's BGP table is unreachable.
The issue is that R1 is advertising the prefix with next-hop 10.1.1.1, which is the interface IP of R1 towards R2. R2 installs the route with that next-hop, and since it is directly connected, R2 can reach it. However, R1 may not have a route to 192.168.1.0/24 in its routing table (e.g., it learned it via iBGP but did not install it due to next-hop unreachable or other issue). R1's BGP table shows the prefix, but if the next-hop is not reachable in R1's routing table, R1 will not install it in the routing table, and thus cannot forward packets. The root cause is that R1 does not have a valid route to the next-hop of the prefix it is advertising, so it cannot forward traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
R1 does not have the prefix 192.168.1.0/24 in its routing table because the next-hop for that prefix in R1's BGP table is unreachable.
Why this is correct
R1's BGP table may have the prefix, but if the next-hop is not reachable (e.g., due to missing route), R1 will not install it in the routing table, causing forwarding failure.
- ✗
R2's MED comparison is incorrect; lower MED should be preferred, but R2 should have chosen R3.
Why it's wrong here
Lower MED is preferred, so R2 correctly chose R1.
- ✗
R2 is missing a static route to 192.168.1.0/24.
Why it's wrong here
BGP provides the route; the issue is on R1.
- ✗
R1 should use next-hop-self when advertising to R2.
Why it's wrong here
R1 already uses its own IP as next-hop; that is not the issue.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 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 300-410 exam.