350-501 MPLS and Segment Routing Practice Question
Which TWO statements about SR-MPLS compared to LDP are correct? (Choose two.)
⚠ Common exam trap
Cisco often tests the misconception that SR-MPLS is dependent on LDP or RSVP-TE, when in fact SR-MPLS is designed to replace these protocols by leveraging IGP for label distribution and SR-TE policies for traffic engineering.
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
✓
SR-MPLS uses a global label block (SRGB) that is consistent across the domain.
SR-MPLS uses a Segment Routing Global Block (SRGB), which is a reserved label range (e.g., 16000–23999 per RFC 8660) that is configured consistently across all routers in the SR domain. This global consistency allows any router to interpret a label from the SRGB as the same topological or service instruction, eliminating the need for per-hop label negotiation.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
SR-MPLS uses a global label block (SRGB) that is consistent across the domain.
Why this is correct
Correct. SRGB is configured consistently.
- ✗
SR-MPLS requires LDP for label distribution.
Why it's wrong here
SR-MPLS uses IGP extensions, not LDP.
- ✗
SR-MPLS supports only dynamic label allocation.
Why it's wrong here
SR-MPLS uses pre-allocated SIDs.
- ✓
SR-MPLS allocates a per-prefix label (Node SID) for each router's loopback.
Why this is correct
Correct. Node SID is a prefix SID.
- ✗
SR-MPLS requires RSVP-TE for TE tunnels.
Why it's wrong here
SR-TE does not need RSVP.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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