What I really like about this calculator is the fact that when you type in a full blown IPv6 address it shows you the compressed version of the IPv6 address provided. Really cool. Download & enjoy :)
In order to build resiliency in your network you absolutely have to have redundant DHCP LAN servers. You can use your Cisco routers or switches as DHCP servers to provide this capability.
There are multiple ways of influencing Inbound vs. Outbound Traffic flow in BGP.