If a device on a private network needs to communicate with other networks, a ""mediating gateway"" (in-between gateway) is needed to ensure that the outside network is presented with an address that is "real" (or publicly reachable) so that Internet routers allow the communication. This gateway is typically a NAT device or a proxy server. Public Internet Routers by default will not forward packets with RFC 1918 addresses. Unlike public Internet routers that need additional configuration to forward these packets, internal routers do not need any additional configuration to forward these packets.