Both border leafs share VTEP Loopback1 10.0.255.15 and peer with DC
spines in eBGP IPv4 + EVPN. Uplinks to core1/core2 use dot1q
subinterfaces (.100 default underlay, .200 VRF gold) with OSPF area 0
and eBGP to AS 65500. VRF gold extended via vxlan vrf gold vni 100001
with RD <Lo0>:1 and RT 1:100001.