1. A virtual machine manager to host one or more virtual machines that form part of a segmented virtual network and to receive outgoing messages from the one or more virtual machines, at least a given one of the outgoing messages having a part allocated for an intermediate destination address representing an intermediate node in a local segment of the segmented virtual network, the intermediate node being suitable for passing the given outgoing message on towards a destination node in another of the segments, the virtual machine manager comprising: a router configured to determine a new intermediate destination address outside the local segment, and to route the given outgoing message according to the new intermediate destination address; wherein the router is configured to change the intermediate destination address of the given outgoing message from an address in the virtual network to an address of a node in a physical communications network; and wherein the virtual machine manager is configured to receive an incoming message from the physical communications network destined for one or more of the one or more hosted virtual machines, and wherein the router is configured to change an intermediate destination address of the incoming message from an address in the physical communications network to an address in the virtual network.