The correct answer is that Prefix-SIDs are bound to node loopbacks, as this fundamental characteristic of SR-MPLS ties a specific label to the router’s loopback interface for unique node identification within the IGP domain. This binding allows the network to forward traffic along the shortest path to that node without requiring signaling protocols like LDP or RSVP-TE, which SR-MPLS eliminates entirely. On the Cisco SPCOR 350-501 exam, this concept tests your understanding of how Segment Routing simplifies MPLS by using IGP extensions (OSPF or IS-IS) to distribute labels, and a common trap is confusing Prefix-SIDs with Adjacency-SIDs—the latter are locally significant and not bound to loopbacks. Remember that the SRGB (Segment Routing Global Block) must be globally unique across the domain, while Prefix-SIDs are globally significant and typically assigned to loopbacks for stable routing. A helpful memory tip: “Prefix points to the node, Adjacency to the link.”
350-501 Architecture Practice Question
This 350-501 practice question tests your understanding of architecture. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A service provider is implementing Segment Routing (SR) with MPLS. Which three statements are true regarding SR-MPLS? (Choose three.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
SR-MPLS does not require LDP or RSVP-TE
SR-MPLS does not require LDP or RSVP-TE (A). The SRGB should be globally unique (B). Prefix-SIDs are typically bound to node loopbacks (D). Option C is false: Adjacency SIDs are advertised via IGP, not BGP-LS exclusively. Option E is false: SR supports distributed TE via TI-LFA and explicit paths without a central controller.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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 supports traffic engineering only with a central controller
Why it's wrong here
SR-MPLS supports distributed traffic engineering using TI-LFA and explicit paths.
✓
SR-MPLS does not require LDP or RSVP-TE
Why this is correct
SR uses IGP to distribute labels, eliminating the need for LDP or RSVP-TE.
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-501 OSPF questions on adjacency and route selection.
Architecture — This question tests Architecture — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: SR-MPLS does not require LDP or RSVP-TE — SR-MPLS does not require LDP or RSVP-TE (A). The SRGB should be globally unique (B). Prefix-SIDs are typically bound to node loopbacks (D). Option C is false: Adjacency SIDs are advertised via IGP, not BGP-LS exclusively. Option E is false: SR supports distributed TE via TI-LFA and explicit paths without a central controller.
What should I do if I get this 350-501 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-501 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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