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300-410 Practice Question: An engineer configures iBGP between two PE…
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?
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.
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.
- ✗
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.
Go deeper
Related to this question
Learn chapter
OSPF Neighbor Adjacency and Basics
Key term
LDP Protocol
LDP, or Label Distribution Protocol, is a protocol that routers use to automatically exchange labels that enable MPLS (Multiprotocol Label Switching) to create fast, efficient paths for data packets across a network.
Key term
BGP Route Reflector
A BGP Route Reflector is a networking device that reduces the number of BGP peer connections needed in a large network by allowing routers to share routing information without needing to connect to every other router directly.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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