Network topology information is determined in a network-based communication system by generating communications between, for example, selected pairs of endpoint devices each associated with a network. A given one of the communications is sent from a first one of the endpoint devices to a second one of the endpoint devices and returned from the second endpoint device to the first endpoint device. Information contained in the communication as received at the first endpoint device from the second endpoint device is processed to determine network topology information characterizing at least a portion of the network.