SRv6 and MPLS interworking

This document describes interworking between SRv6 and MPLS domains to provide end to end path. Interworking problem is generalized into various interworking scenarios. These scenarios are stitched either by transport interworking or service interworking. New SRv6 SID endpoint behaviors are defined for the purpose. These new SRv6 SID behaviors and MPLS labels stitch end to end path across different data plane.