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BGP Troubleshooting →hardMultiple ChoiceObjective-mapped

300-410 BGP Troubleshooting Practice Question

This 300-410 practice question tests your understanding of bgp troubleshooting. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

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?

A
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.
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.
B
R2's MED comparison is incorrect; lower MED should be preferred, but R2 should have chosen R3.
Why wrong: Lower MED is preferred, so R2 correctly chose R1.
C
R2 is missing a static route to 192.168.1.0/24.
Why wrong: BGP provides the route; the issue is on R1.
D
R1 should use next-hop-self when advertising to R2.
Why wrong: R1 already uses its own IP as next-hop; that is not the issue.

Full breakdown with real-world context →

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.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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.
Related concept
Read the scenario before looking for a memorised answer.
✗
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.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.

Detailed technical explanation

How to think about this question

This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.

TExam Day Tips

Underline the problem statement mentally.
Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.

What to study next

Got this wrong? Here's your next step.

Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.

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FAQ

Questions learners often ask

What does this 300-410 question test?

BGP Troubleshooting — This question tests BGP Troubleshooting — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: 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.

What should I do if I get this 300-410 question wrong?

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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