Question 1,468 of 2,152

MPLS L3VPN →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the `next-hop-self` command is ignored for routes reflected by a route reflector to its clients. This occurs because BGP’s route reflection logic is designed to preserve the original next-hop attribute when reflecting routes from one iBGP speaker to another, even if `neighbor x.x.x.x next-hop-self` is explicitly configured on the route reflector for the client session. The command only modifies the next-hop for routes learned via eBGP or for iBGP sessions where the neighbor is not a route-reflector client, making it a common pitfall in MPLS L3VPN designs. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding of BGP route reflection behavior and the limitations of `next-hop-self` in a service provider context. The trap is assuming the command works universally; instead, remember that a route reflector is a “pass-through” for the next-hop attribute. Memory tip: “Reflectors reflect, they don’t redirect.”

300-410 MPLS L3VPN Practice Question

This 300-410 practice question tests your understanding of mpls l3vpn. 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 configures iBGP between two PE routers in an MPLS L3VPN. The PE routers are in the same AS and are directly connected. The engineer configures 'neighbor x.x.x.x next-hop-self' on the route reflector (RR) but notices that the RR is not sending the VPNv4 routes to the client PE with the next-hop set to itself. The client PE receives the routes but the next-hop remains the original PE. 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.

Question 1hardmultiple choice

Open the full BGP breakdown →

A
The 'next-hop-self' command is not applied to the route-reflector client session; it must be applied to the client's neighbor statement on the RR, but it is ignored for reflected routes.
Correct. 'next-hop-self' is not effective for routes reflected by a route reflector; the RR preserves the original next-hop.
B
The 'next-hop-self' command is only applicable to eBGP sessions, not iBGP.
Why wrong: Incorrect. 'next-hop-self' works for iBGP sessions as well, but not for route-reflector reflected routes.
C
The 'next-hop-self' command requires the 'soft-reconfiguration inbound' to be configured to take effect.
Why wrong: Incorrect. Soft reconfiguration is not required for 'next-hop-self' to take effect.
D
The 'next-hop-self' command is overridden by the 'next-hop-unchanged' command on the route reflector.
Why wrong: Incorrect. 'next-hop-unchanged' is used in MPLS VPN to preserve the next-hop across the core, but it is not configured by default and would not override 'next-hop-self' if both were present.

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

✓

The 'next-hop-self' command is not applied to the route-reflector client session; it must be applied to the client's neighbor statement on the RR, but it is ignored for reflected routes.

In BGP, the 'next-hop-self' command is only effective for eBGP sessions or for iBGP sessions when the neighbor is not a route-reflector client. When a route reflector sends a route to a client, it does not change the next-hop attribute by default, even if 'next-hop-self' is configured. This is because the route reflector is expected to preserve the next-hop as learned from the original router. To change the next-hop on a route reflector, the engineer must use 'neighbor x.x.x.x next-hop-self' on the RR for the client, but this command is ignored for routes that are reflected from another iBGP speaker. This is a known edge case that can cause reachability issues if the client cannot reach the original next-hop.

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 is not applied to the route-reflector client session; it must be applied to the client's neighbor statement on the RR, but it is ignored for reflected routes.
Why this is correct
Correct. 'next-hop-self' is not effective for routes reflected by a route reflector; the RR preserves the original next-hop.
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 only applicable to eBGP sessions, not iBGP.
Why it's wrong here
Incorrect. 'next-hop-self' works for iBGP sessions as well, but not for route-reflector reflected routes.
✗
The 'next-hop-self' command requires the 'soft-reconfiguration inbound' to be configured to take effect.
Why it's wrong here
Incorrect. Soft reconfiguration is not required for 'next-hop-self' to take effect.
✗
The 'next-hop-self' command is overridden by the 'next-hop-unchanged' command on the route reflector.
Why it's wrong here
Incorrect. 'next-hop-unchanged' is used in MPLS VPN to preserve the next-hop across the core, but it is not configured by default and would not override 'next-hop-self' if both were present.

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.

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 L3VPN — This question tests MPLS L3VPN — OSPF neighbours must agree on key parameters..

What is the correct answer to this question?

The correct answer is: The 'next-hop-self' command is not applied to the route-reflector client session; it must be applied to the client's neighbor statement on the RR, but it is ignored for reflected routes. — In BGP, the 'next-hop-self' command is only effective for eBGP sessions or for iBGP sessions when the neighbor is not a route-reflector client. When a route reflector sends a route to a client, it does not change the next-hop attribute by default, even if 'next-hop-self' is configured. This is because the route reflector is expected to preserve the next-hop as learned from the original router. To change the next-hop on a route reflector, the engineer must use 'neighbor x.x.x.x next-hop-self' on the RR for the client, but this command is ignored for routes that are reflected from another iBGP speaker. This is a known edge case that can cause reachability issues if the client cannot reach the original next-hop.

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

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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