350-501 Architecture Practice Question
In a Carrier Supporting Carrier (CSC) architecture, which condition is necessary for the customer carrier's BGP routes to be carried over the provider carrier's MPLS backbone?
⚠ Common exam trap
Cisco often tests the misconception that route-target matching (Option B) is required for CSC, when in fact the critical requirement is IGP reachability to the BGP next-hop, not VRF route-target alignment.
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
✓
The BGP next-hop on the customer carrier's routes must be reachable via IGP in the provider carrier.
In a Carrier Supporting Carrier (CSC) architecture, the provider carrier's MPLS backbone must be able to forward packets toward the BGP next-hop of the customer carrier's routes. For this to happen, the BGP next-hop (typically a loopback interface on the customer carrier's PE router) must be reachable via an IGP (e.g., OSPF or IS-IS) running within the provider carrier's core. Without IGP reachability to that next-hop, the provider carrier's P routers cannot perform MPLS label switching to deliver traffic to the customer carrier's egress router, breaking end-to-end connectivity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The BGP next-hop on the customer carrier's routes must be reachable via IGP in the provider carrier.
Why this is correct
For the provider carrier to switch MPLS packets, the BGP next-hop must be reachable via the IGP and have a label binding.
- ✗
The provider carrier's VRF must have the route-target matching the customer carrier's.
Why it's wrong here
CSC often uses no VRF on the provider carrier; instead, the customer carrier's routes are treated as standard BGP routes.
- ✗
The provider carrier must be in the same AS as the customer carrier.
Why it's wrong here
Different AS numbers are typical; the provider carrier uses BGP to carry VPN routes.
- ✗
The customer carrier must use LDP for label distribution.
Why it's wrong here
LDP is used inside the customer carrier network, but the provider carrier does not require LDP from the customer carrier.
Visual reference
Go deeper
Related to this question
About these practice questions
This 350-501 question is part of Courseiva's 971-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
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.