Abstract: A middlebox and method of operating the middlebox to provide an interface between first and second IP networks. An entity within the first IP network allocates IP addresses to one or more entities in the second IP network. The middlebox routes IP traffic within and between the networks based on the IP addresses, implements at least one IP address dependent service other than routing, and dynamically informs each service of the IP addresses allocated to the network entities and of changes to these addresses.