Quick Answer
The answer is that segment routing provides source routing capability and eliminates the need for the LDP protocol. This is correct because segment routing, or SR-MPLS, encodes MPLS labels directly into the IGP using extensions like RFC 8665 for OSPF and RFC 8667 for IS-IS, removing the entire LDP control plane and its associated state machine. On the Cisco SPCOR 350-501 exam, this topic tests your understanding of MPLS control plane simplification; a common trap is confusing LDP removal with label distribution elimination—remember that SR still distributes labels, but via the IGP instead of a separate protocol. A key memory tip is "SR = Single Protocol," meaning one less protocol to manage, which directly reduces operational complexity and convergence time.
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.
Which TWO of the following are advantages of segment routing over traditional LDP-based MPLS? (Choose two.)
Reduces the number of BGP peers required
Why wrong: SR does not affect BGP peering.
Eliminates the need for the LDP protocol
SR uses IGP extensions instead of LDP.
Requires RSVP-TE for traffic engineering
Why wrong: SR can do TE without RSVP-TE.
Provides source routing capability
SR allows the source to specify the path via segment lists.
Eliminates the need for IGP
Why wrong: SR still requires IGP for link-state.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Eliminates the need for the LDP protocol
Option B is correct because segment routing (SR-MPLS) eliminates the need for the LDP protocol by encoding MPLS labels directly in the IGP (e.g., OSPF or IS-IS) using extensions like RFC 8665 and RFC 8667. This simplifies the control plane by removing an entire protocol (LDP) and its associated state, reducing operational complexity and convergence time.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Reduces the number of BGP peers required
Why it's wrong here
SR does not affect BGP peering.
Eliminates the need for the LDP protocol
Why this is correct
SR uses IGP extensions instead of LDP.
Related concept
Read the scenario before looking for a memorised answer.
Requires RSVP-TE for traffic engineering
Why it's wrong here
SR can do TE without RSVP-TE.
Provides source routing capability
Why this is correct
SR allows the source to specify the path via segment lists.
Related concept
Read the scenario before looking for a memorised answer.
Eliminates the need for IGP
Why it's wrong here
SR still requires IGP for link-state.
Common exam traps
Cisco often tests the misconception that segment routing eliminates the IGP entirely, but in reality, SR relies on the IGP to distribute SIDs, so the IGP is still required.
Detailed technical explanation
Segment routing leverages the IGP to advertise prefix-SIDs and adjacency-SIDs, which are used to build MPLS labels without LDP. For traffic engineering, SR uses a segment list (stack of labels) encoded in the packet header, enabling source routing where the ingress node specifies the path. In real-world deployments, SR-TE can be combined with a PCE for dynamic path computation, avoiding the per-flow state of RSVP-TE and scaling better in large networks.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
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FAQ
Architecture — This question tests Architecture — Read the scenario before looking for a memorised answer..
The correct answer is: Eliminates the need for the LDP protocol — Option B is correct because segment routing (SR-MPLS) eliminates the need for the LDP protocol by encoding MPLS labels directly in the IGP (e.g., OSPF or IS-IS) using extensions like RFC 8665 and RFC 8667. This simplifies the control plane by removing an entire protocol (LDP) and its associated state, reducing operational complexity and convergence time.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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