350-501 Question #561: Real Exam Question with Answer & Explanation

Question

What is the feature of the Unified MPLS architecture?

Options

• AIt uses a flat Level 2 or backbone area network throughout the entire IGP domain
• BABR routers are part of the iBGP mesh design and participate in exchange of all VPN prefixes
• CIt exchanges label information using BGP
• DThe MPLS label stack reqquires 8bytes of overhead between the ingress and egress PEs

Explanation

A key feature of the Unified MPLS architecture is its use of BGP to exchange MPLS label information, enabling scalable and hierarchical MPLS deployments.

Common mistakes.

• A. Unified MPLS aims to avoid a flat network, instead using a hierarchical design, often with multiple IGP levels to improve scalability and reduce IGP database size.
• B. While ABRs are crucial, Unified MPLS's scalability with BGP means not all routers need to be part of a full iBGP mesh exchanging all VPN prefixes; route reflectors are typically used.
• D. A single MPLS label is 4 bytes, so a label stack requires 4 bytes per label; 8 bytes implies two labels, which is common but not a defining or unique feature of Unified MPLS itself.

Concept tested. Unified MPLS architecture features, BGP label distribution

Reference. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/xe-3s/asr1000/irg-xe-3s-asr1k-book/irg-unified-mpls.html

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