Locating a frequency deviation in a communication network is provided. A node clock frequency is assigned to each internal clock of each network node. Messages are transmitted synchronizing the internal clocks. The synchronization messages are transmitted from one node to another in succession based on a reference clock frequency predefined by a reference clock. The synchronization messages include a reference clock count state of the reference clock. Synchronization deviations are calculated at predefined intervals of time. If the synchronization deviation of the middle network node exceeds a threshold value, a change in the reference clock frequency is detected if the synchronization deviations of adjacent nodes. Otherwise, a change in the node clock frequency of the middle network node is detected.