IPng Networks

A deep technical exploration of SRv6 (Segment Routing for IPv6) implemented in VPP (Vector Packet Processor). Covers SRv6 fundamentals including the Segment Routing Header structure, SR Policies, Source/Transit/Endpoint nodes, and practical L2VPN configuration. The author extends VPP to support SRv6 encap/decap on sub-interfaces (not just physical interfaces), discovers and fixes a quad-loop bug in `sr_policy_rewrite_encaps_l2()` that caused ~75% packet loss when segment lists had length 1, and adds unit tests for PHY and sub-interface encap/decap scenarios. The change (~850 LOC) is submitted for upstream review on fd.io Gerrit.