When using GhostCasting, either with Multicast or Unicast method, the client machines will try to request an IP address from the GhostCast server. The Client machines will not be able to get the GhostCast servers private IP address because of the NAT Firewall and will be returned an address from the NAT. The client machines will time out as they cannot get the private IP address of the GhostCast Server.
RML (Reliable Multicast Library) across NAT will never work, in either Unicast or Multicast mode. NAT Firewalls do not support multicast across the NAT itself, but furthermore, RML is based on a fixed range of UDP port numbers, and these can’t be changed by the firewall without breaking connectivity.