Techniques are described for providing managed virtual computer networks that may have a configured logical network topology with one or more virtual networking devices, with corresponding networking functionality provided for communications between multiple computing nodes of the virtual computer network by emulating functionality that would be provided by the networking devices if they were physically present. In some situations, the emulating of networking device functionality includes receiving routing communications directed to the networking devices and using included routing information to update the configured network topology for the managed computer network. In addition, the techniques may further include supporting interactions with devices that are external to the virtual computer network, including remote physical networking devices that are part of a remote computer network configured to interoperate with the virtual computer network, and/or specialized network devices that are accessible via a substrate network on which the virtual computer network is overlaid.