350-501 · Question #623
350-501 Question #623: Real Exam Question with Answer & Explanation
The correct answer is B: Establish an LDP neighbor relationship with P1 and P3.. To enable a new P router to participate in an MPLS Layer 3 VPN, it must establish Label Distribution Protocol (LDP) neighbor relationships with its directly connected P and PE routers.
Question
Refer to the exhibit. A service provider is running MPLS in the core to support Layer 3 VPN. OSPF is configured to support dynamic routing, and BGP is enabled throughout the network. A network engineer is adding a new P router to the infrastructure and is connecting it to P1 and P3. Which task must the engineer perform on the new router to allow it to participate in the Layer 3 VPN?
Options
- AEnable LDP sync under the OSPF routing process.
- BEstablish an LDP neighbor relationship with P1 and P3.
- CConfigure OSPF and BGP to support MPLS.
- DEnable LDP and establish an OSPF adjacency in a new area.
Explanation
To enable a new P router to participate in an MPLS Layer 3 VPN, it must establish Label Distribution Protocol (LDP) neighbor relationships with its directly connected P and PE routers.
Common mistakes.
- A. Enabling LDP sync under OSPF is used to ensure LDP convergence before IGP convergence, preventing blackholes, but it's not the fundamental step for LDP functionality itself.
- C. While OSPF and BGP are configured in the network, a P router's primary role in L3VPN is MPLS label switching, which is enabled by LDP, not directly by configuring OSPF or BGP to 'support MPLS'.
- D. While LDP needs to be enabled and an OSPF adjacency established, simply enabling LDP and establishing OSPF in a 'new area' doesn't specify the critical step of forming LDP neighbor relationships with existing adjacent MPLS routers, which is crucial for label distribution.
Concept tested. MPLS P router configuration in L3VPN
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