350-501 MPLS and Segment Routing Practice Question
A service provider is deploying MPLS in their core network and wants to ensure that all routers in the MPLS domain can dynamically exchange label bindings. Which protocol should be enabled on all routers to meet this requirement?
⚠ Common exam trap
Cisco often tests the distinction between protocols that distribute labels for all routes (LDP) versus protocols that only distribute labels for specific routes (e.g., iBGP for BGP routes) or are used for traffic engineering (RSVP-TE), leading candidates to mistakenly choose iBGP or RSVP-TE when the question asks for dynamic label exchange across the entire MPLS domain.
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
✓
LDP
LDP (Label Distribution Protocol) is the correct choice because it is the standard protocol used in MPLS networks to dynamically distribute label bindings for all routes in the routing table. It operates by establishing LDP sessions between directly connected LSRs and exchanging label mappings for each prefix, ensuring every router in the MPLS domain has the necessary labels to forward labeled packets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
LDP
Why this is correct
LDP dynamically distributes labels for all prefixes in the IGP.
- ✗
OSPF
Why it's wrong here
OSPF is an IGP that does not distribute MPLS labels.
- ✗
iBGP
Why it's wrong here
iBGP carries VPNv4 routes and labels for Layer 3 VPNs, not transport labels.
- ✗
RSVP-TE
Why it's wrong here
RSVP-TE is used for traffic engineering tunnels, not for general label distribution.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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