1. A method comprising: receiving, by a network device, a first general packet radio service (GPRS) tunneling protocol (GTP) tunnel packet that includes tunnel identification information corresponding to a GTP tunnel; determining, by the network device, that the tunnel identification information of the first GTP tunnel packet matches information in a list of interception identifiers; intercepting, by the network device, the first GTP tunnel packet after determining that the tunnel identification information of the first GTP tunnel packet matches the information in the list of interception identifiers; tracking, by the network device, a start time for the GTP tunnel based on a time of receiving the first GTP tunnel packet; transmitting, by the network device, the first GTP tunnel packet to an endpoint of the GTP tunnel; and tracking, by the network device, a stop time for the GTP tunnel based on a time of transmitting a final GTP tunnel packet to the endpoint of the GTP tunnel, the first GTP tunnel packet being the final GTP tunnel packet until the network device receives a second GTP tunnel packet, and the second GTP tunnel packet being the final GTP tunnel packet after the network device transmit the second GTP tunnel packet and until the network device receives a third GTP tunnel packet.