Network devices, systems, and methods are described that perform network service monitoring. One method includes examining a number of packets received by a first network device to determine whether a protocol of a packet corresponds to a given network service, forwarding an event to a second network device in response to a determination that the protocol of the packet corresponds to the network service, determining whether the network service is an authorized service by comparing the network service to a list of network services, and executing a remedial action in response to a determination that the network service is an unauthorized service.