Refer to the exhibit. ISP_A is a Tier-1 ISP that provides private Layer 2 and Layer 3 VPN services across the globe using an MPLS-enabled backbone network. Routers R1, R2, R13, and R14 are PE…

Seamless Segment Routing is a modern routing paradigm that addresses scalability but is a different technology from the traditional MPLS framework implied by RFC 3107 in this context.

Implementing MPLS Traffic Engineering only on PE routers primarily focuses on optimizing specific traffic paths and resource allocation, not on a holistic approach to minimize IGP RIB overflow across the entire backbone.

Hierarchical MPLS VPLS (H-VPLS) is a specific Layer 2 VPN scaling solution for VPLS services, not a general architecture to mitigate IGP RIB overflow throughout an entire MPLS-enabled backbone.

Unified MPLS is a scalable architecture designed to address challenges in large-scale networks, such as IGP RIB overflow, by segmenting the network into multiple IGP domains. It uses BGP with MPLS Label Unicast (RFC 3107) to exchange reachability information and labels between these domains, allowing the core IGP to maintain fewer routes and effectively reducing the burden on local RIBs while supporting end-to-end QoS.