Abstract: Embodiments of the present invention relate to coordinating address allocation events at a routing device and at a host machine, where the routing device is arranged to route data between the host machine and at least one other host machine. The routing device may be a router and the host machine may be a computer located in a first network, the first network operating in accordance with a first transmission protocol. The other host machine may be a computer, located in a second network, the second network operating in accordance with a second transmission protocol. The method is particularly suited to situations where the host machine is running one or more applications in accordance with the second transmission protocol. Embodiments of the invention are concerned with coordinating address allocation events that are required to enable data of the second transmission protocol to be transmitted through the first network and on to the other host machine.