350-501 Architecture Practice Question
You are a network architect for a large service provider. The network consists of multiple core routers (P routers) and edge routers (PE routers) supporting both L3VPN and L2VPN services. The network currently uses LDP for label distribution and has a flat IGP (OSPF) design. Recently, there have been scalability issues: the IGP convergence time has increased significantly, and the OSPF link-state database (LSDB) has grown large, causing high CPU utilization on core routers. Additionally, the LDP sessions are taking longer to establish after a router reboot. You are tasked with redesigning the network to improve scalability and convergence. The budget allows for significant changes but cannot replace all hardware. Which approach best addresses the scalability issues while minimizing disruption?
⚠ Common exam trap
Cisco often tests the misconception that adding a second IGP or upgrading to OSPFv3 will improve scalability, when in fact the real issue is the overhead of a separate label distribution protocol (LDP) and the LSDB size, which Segment Routing directly addresses by integrating label distribution into the IGP.
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
✓
Implement Segment Routing (SR-MPLS) to replace LDP and reduce IGP overhead
Segment Routing (SR-MPLS) eliminates the need for LDP by encoding MPLS labels directly in the IGP (OSPF or IS-IS) using extensions, which reduces control-plane overhead and speeds up convergence. This directly addresses the large OSPF LSDB and slow LDP session establishment because SR-MPLS does not require a separate label distribution protocol and can leverage a single IGP for both routing and label information, improving scalability without hardware replacement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Upgrade OSPF to OSPFv3 to support IPv6 and improve performance
Why it's wrong here
OSPFv3 is for IPv6 and does not inherently reduce LSDB size or improve convergence.
- ✓
Implement Segment Routing (SR-MPLS) to replace LDP and reduce IGP overhead
Why this is correct
SR-MPLS eliminates LDP and reduces IGP LSDB size because SIDs are advertised as TLV extensions, reducing the number of LSA types.
- ✗
Introduce IS-IS as a second IGP to offload traffic from OSPF, and use route redistribution between the two protocols
Why it's wrong here
Running two IGPs increases complexity and does not reduce the LSDB size; redistribution can cause loops.
- ✗
Replace OSPF with BGP as the core IGP to reduce link-state overhead
Why it's wrong here
BGP is not designed as an IGP; it would require a full mesh or route reflectors and would not improve convergence.
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JA
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.