from what i understnd
o on the left is cernet2, which has goof ipv6 connectivity and tunneled
ipv4
o on the right we have a commercial isp with good ipv4 connectivity
and tunneled ipv6
so i suggest
o taking full bgp from both, ipv4 and ipv6
o downpreffing v6 prefixes heard from the isp
o downpreffing v4 prefixes heard from cernet2
randy