Quick Answer
The answer is an IGP with Segment Routing extensions (OSPF or IS-IS), Node-SID and Adj-SID, and the MPLS forwarding plane. These three components form the non-negotiable foundation for deploying Segment Routing in an MPLS network because the IGP must be extended to distribute the SID information, the Node-SID and Adj-SID are the basic label types that define the topology, and the MPLS data plane is required to actually forward packets based on those labels. On the Cisco SPCOR 350-501 exam, this question tests your ability to distinguish mandatory building blocks from optional features like SR-TE or RSVP-TE, which are common distractors. A frequent trap is assuming that a centralized controller or traffic engineering policy is required, but those are only needed for advanced path optimization. To lock in the answer, remember the "three pillars" of SR-MPLS: the routing protocol (IGP), the label types (Node/Adj-SID), and the forwarding mechanism (MPLS).
This 350-501 practice question tests your understanding of mpls and segment routing. 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.
Which three are required components for deploying Segment Routing in an MPLS network? (Choose three.)
RSVP-TE signaling protocol
Why wrong: SR uses IGP for signaling, not RSVP-TE.
MPLS forwarding capability on routers
Routers must support MPLS forwarding to process labels.
Node-SID and Adj-SID assignments
These SIDs are the foundation of SR-MPLS paths.
IGP with Segment Routing extensions (OSPF or IS-IS)
IGP distributes SIDs and topologies.
LDP for label distribution
Why wrong: SR replaces LDP; LDP is not required.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
MPLS forwarding capability on routers
A correct: IGP must be extended with Segment Routing extensions (OSPF or IS-IS). C correct: Node-SID and Adj-SID are the basic SID types. D correct: MPLS forwarding plane is needed to forward labeled packets. B is optional for traffic engineering. E is not an SR component; it's for RSVP-TE.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
RSVP-TE signaling protocol
Why it's wrong here
SR uses IGP for signaling, not RSVP-TE.
MPLS forwarding capability on routers
Why this is correct
Routers must support MPLS forwarding to process labels.
Related concept
OSPF neighbours must agree on key parameters.
Node-SID and Adj-SID assignments
Why this is correct
These SIDs are the foundation of SR-MPLS paths.
Related concept
OSPF neighbours must agree on key parameters.
IGP with Segment Routing extensions (OSPF or IS-IS)
Why this is correct
IGP distributes SIDs and topologies.
Related concept
OSPF neighbours must agree on key parameters.
LDP for label distribution
Why it's wrong here
SR replaces LDP; LDP is not required.
Common exam traps
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
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.
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
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
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.
MPLS and Segment Routing — study guide chapter
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FAQ
MPLS and Segment Routing — This question tests MPLS and Segment Routing — OSPF neighbours must agree on key parameters..
The correct answer is: MPLS forwarding capability on routers — A correct: IGP must be extended with Segment Routing extensions (OSPF or IS-IS). C correct: Node-SID and Adj-SID are the basic SID types. D correct: MPLS forwarding plane is needed to forward labeled packets. B is optional for traffic engineering. E is not an SR component; it's for RSVP-TE.
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.
OSPF neighbours must agree on key parameters.
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Last reviewed: Jun 24, 2026
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