- A
It defines a contiguous block of labels used for global SIDs such as Node SIDs.
Correct definition.
- B
It defines the range of labels for Adjacency SIDs.
Why wrong: Adjacency SIDs are local.
- C
It is used to reserve labels for RSVP-TE tunnels.
Why wrong: RSVP-TE uses different label space.
- D
It is the set of labels allowed for MPLS VPNs.
Why wrong: VPN labels are separate.
Question 851 of 1,000
350-501 MPLS and Segment Routing Practice Question
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.
What is the purpose of the SRGB (Segment Routing Global Block) in SR-MPLS?
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
✓
It defines a contiguous block of labels used for global SIDs such as Node SIDs.
The SRGB defines a range of labels reserved for global segment routing SIDs (e.g., Node SIDs). It ensures that the same label value represents the same prefix across the domain, avoiding label conflicts.
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.
- ✓
It defines a contiguous block of labels used for global SIDs such as Node SIDs.
Why this is correct
Correct definition.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
It defines the range of labels for Adjacency SIDs.
Why it's wrong here
Adjacency SIDs are local.
- ✗
It is used to reserve labels for RSVP-TE tunnels.
Why it's wrong here
RSVP-TE uses different label space.
- ✗
It is the set of labels allowed for MPLS VPNs.
Why it's wrong here
VPN labels are separate.
Common exam traps
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.
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FAQ
Questions learners often ask
What does this 350-501 question test?
MPLS and Segment Routing — This question tests MPLS and Segment Routing — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: It defines a contiguous block of labels used for global SIDs such as Node SIDs. — The SRGB defines a range of labels reserved for global segment routing SIDs (e.g., Node SIDs). It ensures that the same label value represents the same prefix across the domain, avoiding label conflicts.
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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Last reviewed: Jul 4, 2026
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