1. A non-transitory computer-readable medium whose contents upon execution configure a computing system to perform a method, the method comprising: performing configurations to enable a software program executing on an indicated computing node to communicate with other computing nodes that are part of a virtual network spanning multiple physical networks, the performing of the configurations including: configuring a communication manager module associated with the indicated computing node to manage outgoing communications from the indicated computing node by associating the outgoing communications with the virtual network and by sending the outgoing communications over a first physical network using a first networking protocol, the first physical network being one of the multiple physical networks; and configuring at least one networking device of the first physical network to manage incoming communications that are received over the first physical network using the first networking protocol and are associated with the indicated virtual network, the managing of the incoming communications including forwarding the incoming communications using a distinct second networking protocol to at least one other of the multiple physical networks; wherein the at least one networking device is one of one or more physical networking devices that are part of the first physical network and that are configured to use the first networking protocol, wherein the configuring of the communication manager module associated with the indicated computing node includes identifying a first networking identifier based on the first networking protocol so that the sending of the outgoing communications over the first physical network includes modifying the outgoing communications to include the first networking identifier, and wherein the configuring of the at least one networking device includes identifying a second networking identifier based on the second networking protocol so that the forwarding of the received communications includes modifying the forwarded communications to include the second networking identifier.