Techniques are described for providing virtual networking functionality for managed computer networks. In some situations, a user may configure or otherwise specify a logical network topology for a managed computer network with multiple computing nodes that includes one or more virtual networking devices each associated with a specified group of the multiple computing nodes. Corresponding networking functionality may be provided for communications between the multiple computing nodes by emulating functionality that would be provided by the networking devices if they were physically present and configured to support the specified network topology. In some situations, the managed computer network is a virtual computer network overlaid on a substrate network, and the networking device functionality emulating includes receiving routing communications directed to the networking devices and using included routing information to update the specified network topology for the managed computer network.