Also known as seamless MPLS, or hierarchical MPLS. It’s a way to scale to a very large network with multiple IGP domains. Let’s get started exploring this feature. I’ll use the below topology as we go along.Unified MPLS Topology What’s new here is the RFC 3107 BGP IPv4 + label and the fact that we have multiple IGP domains. In this topology we have both an OSPF domain to the left between R2-R3-R4.