The answer is that the route-map is missing a match statement, which is the most likely cause of the BGP as-path prepend failure. Without a match statement, the route-map has no condition to select which routes to modify, so the set as-path prepend command is never applied to any routes, leaving the AS-path unchanged on the neighbor. This scenario tests your understanding of how BGP route-maps process routes sequentially: a match clause is required to identify the routes, and only then does the set clause execute. On the Cisco CCNP ENARSI 300-410 exam, this is a common trap where engineers focus on the set command or direction but overlook the fundamental requirement of a match statement, such as matching an IP prefix-list or as-path access-list. A reliable memory tip is “no match, no patch”—without a match, the route-map will not patch the AS-path with the prepended value.
300-410 Route Maps and Route Filtering Practice Question
This 300-410 practice question tests your understanding of route maps and route filtering. 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 network engineer is troubleshooting a BGP route-map that is supposed to prepend AS-path to routes from a specific neighbor. The engineer configures a route-map with 'set as-path prepend 65001' and applies it outbound to the neighbor. After the configuration, the engineer checks the BGP table on the neighbor and sees that the AS-path does not include the prepended AS. What is the most likely 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
✓
The route-map is missing a 'match' statement; without it, the set command is not applied to any routes.
The 'set as-path prepend' command must be used with 'ip as-path access-list' or in a route-map, but the route-map must be applied in the correct direction. If the route-map is applied outbound, it modifies the AS-path before sending. However, if the neighbor is an eBGP neighbor, the router will not prepend its own AS unless the AS is different from the neighbor's AS. Also, the route-map must have a 'match' statement that matches the routes.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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-map is missing a 'match' statement; without it, the set command is not applied to any routes.
Why this is correct
Correct because a route-map without a match statement will not match any routes, so the set command is not executed.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
The AS 65001 is the same as the neighbor's AS, so BGP ignores the prepend.
Why it's wrong here
Incorrect because BGP allows prepending the same AS; it is a common practice.
✗
The route-map is applied inbound instead of outbound.
Why it's wrong here
Incorrect because the scenario says it is applied outbound.
✗
The neighbor has 'soft-reconfiguration inbound' which prevents AS-path changes.
Why it's wrong here
Incorrect because soft-reconfiguration does not affect outbound AS-path manipulation.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Trap categories for this question
Scenario analysis trap
Incorrect because the scenario says it is applied outbound.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 300-410 question in full detail.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
Route Maps and Route Filtering — This question tests Route Maps and Route Filtering — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The route-map is missing a 'match' statement; without it, the set command is not applied to any routes. — The 'set as-path prepend' command must be used with 'ip as-path access-list' or in a route-map, but the route-map must be applied in the correct direction. If the route-map is applied outbound, it modifies the AS-path before sending. However, if the neighbor is an eBGP neighbor, the router will not prepend its own AS unless the AS is different from the neighbor's AS. Also, the route-map must have a 'match' statement that matches the routes.
What should I do if I get this 300-410 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 300-410 OSPF questions on adjacency and route selection.
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?
OSPF neighbours must agree on key parameters.
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