With 'no bgp default ipv4-unicast' set at the router level, VRF gold
eBGP/iBGP neighbors were establishing but not exchanging any IPv4
prefixes, breaking inter-fabric transit between DC and Campus. Add an
explicit 'address-family ipv4' block with 'neighbor X activate' under
'vrf gold' on both cores and all four border leafs.
Also drop 'redistribute learned' from the border leaf VRF gold stanza:
it is not a valid command in that context and was silently stripped by
EOS.
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.
