350-501 Question #556: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. IS-IS is configured in the service provider network. Data is shared between the customer branch offices via CE1 and CE2. The service provider engineering team is implementing MPLS to assist packet switching through the customer VPN. The team must ensure there is no packet loss due to synchronization conflicts. Which action meets the requirement?

Options

• AImplement IS-IS between the PEs and CEs to share VPN routes.
• BImplement LDP sync so that IGP and LDP must be up simultaneously.
• CImplement static routes to CE1 and CE2 from their respective connected PEs.
• DImplement mutual redistribution between BGP and the service provider IGP.

Explanation

To prevent packet loss due to synchronization conflicts when implementing MPLS in an IS-IS network, LDP synchronization must be implemented.

Common mistakes.

• A. Implementing IS-IS between PEs and CEs would typically be for IGP routing within a VPN (VPNv4/VPNv6) and not directly related to preventing LDP/IGP synchronization issues in the service provider core.
• C. Implementing static routes to CE1 and CE2 from their respective connected PEs would fix reachability but bypass the dynamic nature and benefits of IGP and LDP for MPLS, and would not inherently solve synchronization issues for other dynamically learned routes.
• D. Implementing mutual redistribution between BGP and the service provider IGP (IS-IS) would introduce routing complexity and potential for loops, and is not the specific mechanism to prevent LDP/IGP synchronization conflicts in an MPLS environment.

Concept tested. MPLS LDP synchronization with IGP

Reference. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mpls/configuration/xe-3s/mpls-xe-3s-book/mp-ldp-sync.html

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