350-501 MPLS and Segment Routing Practice Question
Which TWO types of SIDs are defined in Segment Routing? (Select two.)
⚠ Common exam trap
Cisco often tests the distinction between Node-SID and Prefix-SID, where candidates mistakenly treat Node-SID as a separate SID type, but it is actually a Prefix-SID assigned to the router's loopback address.
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
✓
Adjacency-SID
Segment Routing (SR) defines two primary types of Segment Identifiers (SIDs): the Prefix-SID and the Adjacency-SID. A Prefix-SID is a global or local label associated with an IGP prefix (e.g., a loopback), enabling shortest-path forwarding toward that prefix. An Adjacency-SID is a local label associated with a specific adjacency (link) between two routers, forcing traffic out that exact interface regardless of the IGP shortest path.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Adjacency-SID
Why this is correct
Identifies a link adjacency.
- ✗
TI-LFA SID
Why it's wrong here
TI-LFA is fast reroute, not a SID type.
- ✗
Service-SID
Why it's wrong here
Not a standard SR SID type.
- ✓
Prefix-SID
Why this is correct
Identifies an IP prefix.
- ✗
Node-SID
Why it's wrong here
Node-SID is a subset of prefix-SID for the router's loopback.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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