The answer is an outbound route-map on the neighbor filtering all routes. When a BGP session is established but no routes are received, the TCP and BGP open stages have completed successfully, yet the neighbor is not sending any prefixes because an outbound route-map applied on the sending router is denying all advertisements. This scenario tests your understanding that the BGP established state only confirms session formation, not route exchange; the Prefixes received counter of zero points directly to a filtering or policy issue on the neighbor’s outbound direction. On the Cisco SPCOR 350-501 exam, this is a classic trap—candidates often suspect inbound filters or network reachability problems, but the key is that the session is up, so the issue lies in what the neighbor is allowed to send. Remember the memory tip: “Established but empty means outbound policy is the enemy.”
350-501 Networking Practice Question
This 350-501 practice question tests your understanding of networking. 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.
An engineer is troubleshooting a BGP peering issue between two routers. The peering is established, but routes are not being exchanged. On router R1, 'show bgp neighbors 192.0.2.2' shows the neighbor state as 'Established' but the 'Prefixes received' counter is zero. What is most likely the cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
An outbound route-map on the neighbor is filtering all routes.
The neighbor state is 'Established', confirming that the TCP session and BGP open messages have been successfully exchanged. However, zero prefixes received indicates that R1 is not receiving any routes from the neighbor. An outbound route-map applied on the neighbor (the router sending routes to R1) can filter all prefixes before they are advertised, resulting in zero received prefixes while the session remains up.
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.
✓
An outbound route-map on the neighbor is filtering all routes.
Why this is correct
An outbound route-map on R2 would filter routes sent to R1, causing zero prefixes received on R1.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The 'maximum-prefix' limit is exceeded, causing the session to reset.
Why it's wrong here
The session is Established, so maximum-prefix has not been exceeded.
✗
The BGP session is in the Idle state due to a misconfigured update-source.
Why it's wrong here
The output shows the session is Established, so it is not in Idle state.
✗
The 'next-hop-self' command is missing on R1.
Why it's wrong here
Next-hop-self affects the next-hop attribute, not the number of prefixes received.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between session state and route exchange; the trap here is that candidates assume an Established session guarantees route exchange, overlooking outbound filtering on the neighbor side.
Trap categories for this question
Command / output trap
The output shows the session is Established, so it is not in Idle state.
Detailed technical explanation
How to think about this question
BGP uses outbound route-maps to filter or modify routes before they are sent to a neighbor. When a route-map with a 'deny' statement or no matching permit is applied outbound, all prefixes are filtered, resulting in zero prefixes received on the peer. This is a common troubleshooting scenario where the session is up but no routes are exchanged, often due to a missing 'permit' statement or an implicit deny at the end of the route-map.
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.
Networking — This question tests Networking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: An outbound route-map on the neighbor is filtering all routes. — The neighbor state is 'Established', confirming that the TCP session and BGP open messages have been successfully exchanged. However, zero prefixes received indicates that R1 is not receiving any routes from the neighbor. An outbound route-map applied on the neighbor (the router sending routes to R1) can filter all prefixes before they are advertised, resulting in zero received prefixes while the session remains up.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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