Techniques are described for providing managed virtual computer networks that have a configured logical network topology with virtual networking devices, such as by a network-accessible configurable network service, 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 virtual networking devices if they were physically present. In some situations, the networking functionality provided for a managed computer network of a client includes receiving routing communications directed to the virtual networking devices, and using included routing information to identify and initiate external actions whose effects are not related to how network communications between computing nodes of the managed computer network are configured to be routed or otherwise forwarded through the managed computer network, such as external actions that affect devices that are not part of the managed computer network, or other types of external actions.