Using IPv6 link-local addressing for the underlay enables point-to-point links to function without requiring globally assigned interface addresses, while still maintaining BGP reachability between directly connected devices. The underlay relies solely on IPv6 link-local peering, while IPv4 loopback addresses are used for VXLAN tunnel endpoints and EVPN next-hop resolution. This auto-assigned, unnumbered IPv6 underlay reduces the risk of human configuration errors and streamlines the underlay configuration process.

In this test, we reused the previous symmetric VLAN-based IRB, as the overlay was still IPv4. We sent full-mesh unicast traffic with Keysight IxNetwork and observed no packet loss, confirming the unnumbered IPv6 underlay worked as expected.