An Internet connection for the server is required.
A single IP address suffices. It must be a public, routeable IP address - network address translation will not suffice.
If any firewalling is provided outside of the coordinators control, it should permit TCP port 21,22,25,53,80,443, and ports above 49152 through, UDP ports 53 and 500.
In addition, IP protocol 50 (ESP) will be used to protect the backups.