350-501 Networking Practice Question
An engineer is deploying Segment Routing in an MPLS network. To ensure that routers can forward packets based on SR-MPLS labels without requiring LDP, which requirement must be met?
⚠ Common exam trap
Cisco often tests the misconception that LDP is always required for MPLS forwarding, but SR-MPLS bypasses LDP by using the IGP to distribute labels, so candidates must recognize that the IGP SR extension is the enabling requirement.
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
✓
IS-IS or OSPF must have the SR extension enabled.
Segment Routing (SR) can operate without LDP by encoding the forwarding path as a list of MPLS labels derived from the IGP. For routers to allocate and advertise these SR-MPLS labels, the IGP (IS-IS or OSPF) must have the Segment Routing extension enabled. This allows the IGP to distribute prefix-SIDs (labels) that routers use to forward packets, eliminating the need for LDP.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
IS-IS or OSPF must have the SR extension enabled.
Why this is correct
Correct. The IGP distributes prefix-SIDs for SR-MPLS label forwarding.
- ✗
MPLS LDP must be enabled on all interfaces.
Why it's wrong here
Incorrect. SR-MPLS is designed to replace LDP.
- ✗
All routers must run BGP-LU.
Why it's wrong here
Incorrect. BGP-LU is an alternative but not required for SR-MPLS.
- ✗
The IGP must have the overload bit set.
Why it's wrong here
Incorrect. The overload bit is used to prevent transit traffic.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.