A computer-readable medium having stored contents that, upon execution, cause one or more computing systems to perform a method, the method comprising: configuring, for an indicated computing node that is one of multiple computing nodes in a virtual network spanning multiple physical networks and that is executing a software program, a communication manager module (215a - 215c) associated with the indicated computing node to manage outgoing communications from the executing software program by associating the outgoing communications with the virtual network while the outgoing communications are forwarded in a first physical network of the multiple physical networks that uses a first networking protocol, wherein the managing of each of the outgoing communications includes modifying the outgoing communication to include a first networking identifier based on the first networking protocol, and includes forwarding the modified outgoing communication from the indicated computing node over the first physical network, wherein the first networking identifier is associated with the virtual network in a mapping maintained in network configuration information for the virtual network; and configuring a physical networking device (225a - 225c) in the first physical network to further manage the outgoing communications from the executing software program that are being forwarded in the first physical network so as to associate the outgoing communications with the virtual network while the outgoing communications are forwarded in a second physical network of the multiple physical networks that uses a second networking protocol, wherein the further managing of each of the outgoing communications includes further modifying the outgoing communication to include a second networking identifier based on the second networking protocol, and includes forwarding the further modified outgoing communication over the second physical network, wherein the second networking identifier is associated with the virtual network in a mapping maintained in the network configuration information for the virtual network. configuring, for an indicated computing node that is one of multiple computing nodes in a virtual network spanning multiple physical networks and that is executing a software program, a communication manager module (215a - 215c) associated with the indicated computing node to manage outgoing communications from the executing software program by associating the outgoing communications with the virtual network while the outgoing communications are forwarded in a first physical network of the multiple physical networks that uses a first networking protocol, wherein the managing of each of the outgoing communications includes modifying the outgoing communication to include a first networking identifier based on the first networking protocol, and includes forwarding the modified outgoing communication from the indicated computing node over the first physical network, wherein the first networking identifier is associated with the virtual network in a mapping maintained in network configuration information for the virtual network; and configuring a physical networking device (225a - 225c) in the first physical network to further manage the outgoing communications from the executing software program that are being forwarded in the first physical network so as to associate the outgoing communications with the virtual network while the outgoing communications are forwarded in a second physical network of the multiple physical networks that uses a second networking protocol, wherein the further managing of each of the outgoing communications includes further modifying the outgoing communication to include a second networking identifier based on the second networking protocol, and includes forwarding the further modified outgoing communication over the second physical network, wherein the second networking identifier is associated with the virtual network in a mapping maintained in the network configuration information for the virtual network.