- A
The 'next-hop-self' command was applied under the wrong address-family.
In BGP, 'next-hop-self' can be configured per address-family. If it is applied under the IPv4 unicast address-family but the routes are being exchanged in a different address-family (e.g., VPNv4), it will not take effect.
- B
The 'next-hop-self' command is not supported for iBGP peers.
Why wrong: 'next-hop-self' is fully supported for iBGP peers and is commonly used to ensure reachability.
- C
The 'synchronization' command is enabled, causing the next-hop to be preserved.
Why wrong: BGP synchronization is disabled by default in modern IOS and does not affect next-hop processing.
- D
The 'bgp bestpath as-path multipath-relax' command is interfering.
Why wrong: This command affects multipath selection, not next-hop modification.
Quick Answer
The answer is that the next-hop-self command was applied under the wrong address-family. In BGP, next-hop-self is an address-family-specific configuration, meaning it must be enabled under the correct IPv4 or IPv6 address-family sub-mode for the neighbor, not under the global router BGP configuration or a different address-family. When an engineer configures next-hop-self on the neighbor statement outside the proper address-family, the router ignores the command for routes exchanged within that address-family, leaving the original next-hop unchanged and potentially unreachable for iBGP peers. This scenario directly tests your understanding of BGP address-family hierarchy on the Cisco CCNP ENARSI 300-410 exam, where a common trap is assuming that neighbor-level commands apply universally across all address-families. A reliable memory tip is to remember that next-hop-self lives inside the address-family, just like network statements—if it’s not under the right family, it’s not working.
300-410 MPLS Operations Practice Question
This 300-410 practice question tests your understanding of mpls operations. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 configures BGP between two iBGP peers in the same AS. The engineer sets 'next-hop-self' on the neighbor statement. However, the routes received from the iBGP peer still show the original next-hop as unreachable. What is the most likely explanation?
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 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
The 'next-hop-self' command was applied under the wrong address-family.
The 'next-hop-self' command in BGP modifies the next-hop attribute for routes advertised to the neighbor. However, if the route is received from an eBGP peer and then advertised to an iBGP peer, the next-hop is changed only for the iBGP peer if 'next-hop-self' is configured. But if the iBGP peer is also a route reflector client, the route reflector does not change the next-hop unless 'next-hop-self' is configured on the route reflector itself. The edge case here is that the engineer may have configured 'next-hop-self' on the wrong router or the command is applied to the wrong address-family.
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 'next-hop-self' command was applied under the wrong address-family.
Why this is correct
In BGP, 'next-hop-self' can be configured per address-family. If it is applied under the IPv4 unicast address-family but the routes are being exchanged in a different address-family (e.g., VPNv4), it will not take effect.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
The 'next-hop-self' command is not supported for iBGP peers.
Why it's wrong here
'next-hop-self' is fully supported for iBGP peers and is commonly used to ensure reachability.
- ✗
The 'synchronization' command is enabled, causing the next-hop to be preserved.
Why it's wrong here
BGP synchronization is disabled by default in modern IOS and does not affect next-hop processing.
- ✗
The 'bgp bestpath as-path multipath-relax' command is interfering.
Why it's wrong here
This command affects multipath selection, not next-hop modification.
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
Command / output trap
This command affects multipath selection, not next-hop modification.
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.
What to study next
Got this wrong? Here's your next step.
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.
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FAQ
Questions learners often ask
What does this 300-410 question test?
MPLS Operations — This question tests MPLS Operations — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The 'next-hop-self' command was applied under the wrong address-family. — The 'next-hop-self' command in BGP modifies the next-hop attribute for routes advertised to the neighbor. However, if the route is received from an eBGP peer and then advertised to an iBGP peer, the next-hop is changed only for the iBGP peer if 'next-hop-self' is configured. But if the iBGP peer is also a route reflector client, the route reflector does not change the next-hop unless 'next-hop-self' is configured on the route reflector itself. The edge case here is that the engineer may have configured 'next-hop-self' on the wrong router or the command is applied to the wrong address-family.
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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Last reviewed: Jun 18, 2026
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