The answer is that the three correct characteristics of Segment Routing (SR-MPLS) compared to traditional MPLS with LDP are that it eliminates the need for LDP or RSVP-TE for label distribution, uses the IGP to distribute labels, and supports traffic engineering via segment lists. This is because SR-MPLS encodes the path as an ordered list of segment identifiers directly into the packet header, allowing the IGP—such as OSPF or IS-IS—to flood these SIDs, which removes the dependency on separate label distribution protocols like LDP or RSVP-TE. On the Cisco SPCOR 350-501 exam, this topic tests your understanding of how SR-MPLS simplifies the control plane while enabling advanced traffic engineering; a common trap is confusing LDP’s multicast discovery with SR-MPLS’s IGP flooding, which is unicast-based. Remember the memory tip: “No LDP, just IGP flooding and segment lists for TE.”
350-501 Networking Practice Question
This 350-501 practice question tests your understanding of networking. 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 of the following are characteristics of Segment Routing (SR-MPLS) compared to traditional MPLS with LDP?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The IGP (IS-IS or OSPF) is used to advertise prefix SIDs.
Options A, C, and E are correct. SR-MPLS does not require LDP (A), uses IGP to distribute labels (C), and supports traffic engineering via segment lists (E). Option B is incorrect; LDP uses multicast for discovery, but SR-MPLS uses IGP flooding, not multicast. Option D is incorrect; LDP can be used for both transit and egress.
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 can only be used for transit, not for egress routers.
Why it's wrong here
Incorrect. Egress routers can also use SR.
✓
The IGP (IS-IS or OSPF) is used to advertise prefix SIDs.
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.
Networking — This question tests Networking — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The IGP (IS-IS or OSPF) is used to advertise prefix SIDs. — Options A, C, and E are correct. SR-MPLS does not require LDP (A), uses IGP to distribute labels (C), and supports traffic engineering via segment lists (E). Option B is incorrect; LDP uses multicast for discovery, but SR-MPLS uses IGP flooding, not multicast. Option D is incorrect; LDP can be used for both transit and egress.
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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Question Discussion
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