The answer is that the next-hop is not reachable from the upstream provider. BGP will mark a prefix as valid in its table but will not advertise it to a neighbor if the next-hop IP is not reachable via the routing table on the PE router, because the upstream router would have no path to forward traffic. This is a fundamental BGP path-selection rule: a route must have a resolvable next-hop to be considered for advertisement, unless the `neighbor x.x.x.x next-hop-self` command overrides it. On the Cisco SPCOR 350-501 exam, this scenario tests your understanding of BGP route advertisement mechanics and the common pitfall where a route-map permits the prefix but the next-hop remains unresolved. A frequent trap is assuming a valid BGP table entry guarantees advertisement, but the "not advertised" status points directly to a reachability issue. Remember the mnemonic: "Valid but not sent? Next-hop is bent."
350-501 Architecture Practice Question
This 350-501 practice question tests your understanding of architecture. 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.
A service provider is troubleshooting a BGP route advertisement issue. Routes from a customer are not being advertised to the upstream provider. The PE router is configured with 'neighbor 10.0.0.1 route-map RMAP out'. The route-map RMAP permits the customer prefix. However, the BGP table on the PE shows the prefix as valid but not advertised. What is a likely cause?
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 is not reachable from the upstream provider
The BGP table shows the prefix as valid but not advertised, which indicates that BGP has the route but is not sending it to the upstream neighbor. A common cause is that the next-hop for the customer prefix is not reachable from the PE router via the interface used to reach the upstream provider. BGP will not advertise a route if the next-hop is not reachable in the routing table (unless 'neighbor x.x.x.x next-hop-self' is configured), because the upstream router would be unable to forward traffic to that next-hop.
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.
✓
The next-hop is not reachable from the upstream provider
Why this is correct
If next-hop-self is not used, the next-hop might be a customer-facing interface not reachable upstream.
Related concept
Read the scenario before looking for a memorised answer.
✗
The BGP session to the upstream provider is flapping
Why it's wrong here
If flapping, the route might appear and disappear, but the scenario indicates stable.
✗
The prefix is not in the global routing table
Why it's wrong here
It is in the BGP table, so it is in the routing table.
✗
The route-map is applied inbound instead of outbound
Why it's wrong here
The configuration shows outbound, so that is not the issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the subtle distinction between a prefix being 'valid' (next-hop reachable in the global routing table) and 'advertised' (next-hop reachable from the specific neighbor's perspective), leading candidates to overlook next-hop reachability as the root cause.
Trap categories for this question
Command / output trap
The configuration shows outbound, so that is not the issue.
Scenario analysis trap
If flapping, the route might appear and disappear, but the scenario indicates stable.
Detailed technical explanation
How to think about this question
BGP's 'valid' status in 'show ip bgp' means the prefix has a resolvable next-hop in the routing table, but 'not advertised' means the route fails outbound policy or next-hop reachability checks. The 'neighbor x.x.x.x next-hop-self' command can override this by setting the next-hop to the PE's own IP, ensuring reachability. In real-world scenarios, this often occurs when redistributing connected interfaces or using unnumbered links without proper next-hop resolution.
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.
TExam Day Tips
→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 network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Architecture — This question tests Architecture — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The next-hop is not reachable from the upstream provider — The BGP table shows the prefix as valid but not advertised, which indicates that BGP has the route but is not sending it to the upstream neighbor. A common cause is that the next-hop for the customer prefix is not reachable from the PE router via the interface used to reach the upstream provider. BGP will not advertise a route if the next-hop is not reachable in the routing table (unless 'neighbor x.x.x.x next-hop-self' is configured), because the upstream router would be unable to forward traffic to that next-hop.
What should I do if I get this 350-501 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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