This guy returns an array of URI, not necessarily network addresses; a better name might be in order. resolved_uris perhaps?

Also, we should probably just raise if the template uri is nil, or if any of the resolved addresses is not a host. (In cases where a DNS name resolved to IPNets, it simply doesn't make sense for someone to ask "could you turn that into some URIs for me?" We could end up with thousands and thousands of distinct URIs...)