Also, DNS round robin won’t work with IPv6. At all. Round robin DNS depends on a client connecting to the first address record it receives in the DNS reply, and the DNS server altering its responses to set different addresses as the first one each time it sends a DNS response. But with IPv6, a client host is required to connect to the address closest to its own (as determined by the longest range of common bits), regardless of the adress’ position in the DNS reply.