Quick Answer
IS-IS is the correct choice because it natively supports MPLS Traffic Engineering (TE) through IS-IS TE extensions defined in RFC 5305, and it delivers fast convergence via mechanisms like IS-IS Fast Flooding and LSP throttling. Unlike OSPF, IS-IS operates directly over Layer 2, making it more scalable and robust in large service provider core networks while avoiding the need for a separate flooding domain for TE. On the Cisco SPCOR 350-501 exam, this question tests your understanding of routing protocol selection for MPLS TE environments, often appearing as a scenario where you must choose between IS-IS and OSPF; the common trap is assuming OSPF is equally suitable, but IS-IS is preferred for its native TE support and superior convergence in SP cores. A helpful memory tip: think of IS-IS as the “I Spy” protocol—it sees directly over Layer 2, so it spies TE extensions without extra flooding domains.
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.
A service provider is designing a new MPLS core network and needs to choose a routing protocol that supports traffic engineering and fast convergence. Which protocol should be used?
RIP
Why wrong: RIP is not suitable for large SP networks and lacks TE support.
EIGRP
Why wrong: EIGRP is a Cisco proprietary protocol not typically used in SP core networks.
OSPF
Why wrong: OSPF can be used but IS-IS is preferred for TE and scalability in SP cores.
IS-IS
IS-IS supports MPLS TE and provides fast convergence, making it ideal for SP core.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
IS-IS
IS-IS is the correct choice because it natively supports MPLS Traffic Engineering (TE) via IS-IS TE extensions (RFC 5305) and offers fast convergence through mechanisms like IS-IS Fast Flooding and LSP throttling. Unlike OSPF, IS-IS operates directly over Layer 2, making it more scalable and robust in large service provider core networks, and it avoids the need for a separate flooding domain for TE.
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.
RIP
Why it's wrong here
RIP is not suitable for large SP networks and lacks TE support.
EIGRP
Why it's wrong here
EIGRP is a Cisco proprietary protocol not typically used in SP core networks.
OSPF
Why it's wrong here
OSPF can be used but IS-IS is preferred for TE and scalability in SP cores.
IS-IS
Why this is correct
IS-IS supports MPLS TE and provides fast convergence, making it ideal for SP core.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Cisco often tests the misconception that OSPF is the only link-state protocol suitable for MPLS TE, but the trap is that IS-IS is actually the more common choice in service provider cores due to its native TE support and superior scalability in hierarchical designs.
Detailed technical explanation
IS-IS uses a two-level hierarchical structure (Level 1 and Level 2) that naturally scales in large core networks, and its TLVs (Type-Length-Values) allow flexible TE extensions without changing the protocol core. In real-world deployments, IS-IS is often chosen over OSPF for MPLS TE because it can carry TE information in the same LSPs as routing information, reducing convergence time and complexity. Additionally, IS-IS supports wide metrics (up to 2^24-1) which are essential for TE path calculations, whereas OSPF requires the use of the TE metric sub-TLV for similar granularity.
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.
What to study next
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FAQ
Architecture — This question tests Architecture — Read the scenario before looking for a memorised answer..
The correct answer is: IS-IS — IS-IS is the correct choice because it natively supports MPLS Traffic Engineering (TE) via IS-IS TE extensions (RFC 5305) and offers fast convergence through mechanisms like IS-IS Fast Flooding and LSP throttling. Unlike OSPF, IS-IS operates directly over Layer 2, making it more scalable and robust in large service provider core networks, and it avoids the need for a separate flooding domain for TE.
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
This 350-501 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 350-501 exam.
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