A system and method provides network address translation as an external service for private networks. Give the fact that local office networks (i.e., stub networks) are typically assigned only one globally unique IP address (or a small set of addresses), the invention presents a novel service provider access server (e.g., router) which performs basic network address translation (NAT) and network address port translation (NAPT) for such networks. The system allows NAT and NAPT features to be removed from stub network routers, thereby significantly reducing the cost of Internet infrastructure to individual companies and organizations. NAT features on service provider's access servers provide the ability for multiple hosts in disparate private (unregistered) networks to utilize the services of a service provider, using a single global address for each private network and allow private networks to avoid renumbering with access to each new service provider.