The answer is that Segment Routing eliminates the need for label distribution protocols like LDP or RSVP. This is correct because Segment Routing encodes the forwarding path as an ordered list of segment identifiers (SIDs) pushed onto a label stack at the source router, a source-routing paradigm that allows the ingress node to specify the exact path without requiring intermediate routers to maintain per-flow state. On the Cisco SPCOR / CCNP Service Provider Core 350-501 exam, this question tests your understanding of how Segment Routing characteristics differ from traditional MPLS, often appearing as a trap where candidates mistakenly think SR still relies on LDP or RSVP for label distribution. A key memory tip is to remember that SR is “stateful at the edge, stateless in the core”—the source router does all the work, so no signaling protocols are needed in the middle.
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.
Which TWO statements correctly describe Segment Routing characteristics? (Select two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The path is encoded as a label stack at the source router
Option B is correct because Segment Routing (SR) encodes the forwarding path as an ordered list of segment identifiers (SIDs) pushed onto a label stack at the source router. This source-routing paradigm allows the ingress node to specify the exact path through the network without requiring intermediate routers to maintain per-flow state.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
All routers must be configured with the same SRGB value
Why it's wrong here
SRGB must be same only if using the same block; but can be different with mapping.
✓
The path is encoded as a label stack at the source router
Why this is correct
SR uses a label stack to specify the path.
Related concept
Read the scenario before looking for a memorised answer.
✓
Label distribution does not rely on LDP or RSVP
Why this is correct
Labels are derived from IGP SIDs.
Related concept
Read the scenario before looking for a memorised answer.
✗
SR eliminates all per-prefix state from core routers
Why it's wrong here
SR still requires per-prefix label forwarding entries.
✗
Traffic engineering policies are distributed via BGP without any IGP extension
Why it's wrong here
IGP extensions are needed to advertise prefix-SIDs and adjacency-SIDs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that SR eliminates all per-prefix state from core routers, but in reality, core routers still maintain IGP per-prefix state and may hold SR-MPLS labels for those prefixes.
Detailed technical explanation
How to think about this question
In SR-MPLS, the source router pushes a label stack where each label corresponds to a segment (e.g., prefix-SID or adjacency-SID). The stack can be built using a controller or PCE, and the path is enforced hop-by-hop via label swapping, eliminating the need for LDP or RSVP-TE signaling. A real-world scenario is traffic engineering in a large service provider network where SR-TE policies are computed centrally and pushed as label stacks to edge routers, reducing complexity and improving scalability.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
MPLS and Segment Routing — This question tests MPLS and Segment Routing — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The path is encoded as a label stack at the source router — Option B is correct because Segment Routing (SR) encodes the forwarding path as an ordered list of segment identifiers (SIDs) pushed onto a label stack at the source router. This source-routing paradigm allows the ingress node to specify the exact path through the network without requiring intermediate routers to maintain per-flow state.
What should I do if I get this 350-501 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which TWO are characteristics of Segment Routing (SR-MPLS)? (Choose two.)
easy
✓ A.It relies on source routing
B.It requires a centralized controller for traffic engineering
C.It forwards packets based on destination IP address at each hop
D.It requires MPLS LDP for label distribution
✓ E.It supports both MPLS and IPv6 data planes
Why A: Segment Routing uses source routing where the source specifies the path as a list of segments. It does not require LDP or RSVP-TE. It can use both MPLS and IPv6 data planes. Option C is wrong because SR does not require a centralized controller by default (though it can be used with one). Option D is wrong because SR allows intermediate nodes to forward based on the top segment, not IP address.
Last reviewed: Jun 25, 2026
Question Discussion
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