350-501 MPLS and Segment Routing Practice Question
A service provider is migrating from LDP-based MPLS to Segment Routing (SR-MPLS) with IS-IS. After enabling SR on all routers, the adjacency segment IDs (ADJ-SIDs) are not being advertised. Which configuration is missing?
⚠ Common exam trap
Cisco often tests the distinction between global SR enablement (`segment-routing mpls` under global config) and IGP-specific activation (`segment-routing mpls` under the IS-IS or OSPF process), leading candidates to assume global configuration is sufficient.
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 `segment-routing mpls` command is not enabled under the IS-IS process
In IS-IS, Segment Routing (SR-MPLS) requires explicit activation under the IS-IS routing process with the `segment-routing mpls` command. Without this, the router will not generate or advertise adjacency SIDs (ADJ-SIDs) even if SR is enabled globally. This command ties the SR-MPLS data plane to the IS-IS control plane, enabling IS-IS to allocate and distribute SIDs for adjacencies.
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 `segment-routing mpls` command is not enabled under the IS-IS process
Why this is correct
IS-IS requires the segment-routing mpls command under the IS-IS process to advertise SR capabilities.
- ✗
The router is running OSPF instead of IS-IS
Why it's wrong here
The question states IS-IS is used, so that's not the issue.
- ✗
The interface has the `isis adjacency-sid` command incorrectly configured
Why it's wrong here
ADJ-SIDs are automatically generated; explicit configuration is not required.
- ✗
The loopback interface does not have an ip address configured
Why it's wrong here
Loopback is needed for prefix-SID but not for ADJ-SID advertisement.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-501 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-501 exam.