Method for protecting the time synchronization in a network against unauthorized changes to the grandmaster clock of a base time domain, comprising: - monitoring the physical communication interfaces of a first network device for the arrival of messages relating to time synchronization from a second network device, which messages are used to disseminate information relating to the best clock in the network, - performing first checking to determine whether the messages relating to time synchronization apply to the initially set-up and synchronized base time domain and, if this is the case: - performing second checking to determine whether the messages relating to time synchronization announce a new grandmaster clock having better clock parameters than those of the present grandmaster clock, and, if this is the case: - the first network device starting a virtual base time domain, wherein the first network device forwards no messages relating to time synchronization that are based on the messages relating to time synchronization of the second network device to the remainder of the network, and wherein only for the necessary requests are responses sent from the first network device to the second network device in relation to the virtual base time domain, - verifying the clock parameters sent by the second network device, wherein, if the verification reveals that the grandmaster clock proposed by the second network device is trustworthy or valid, the first network device discontinues the virtual base time domain , updates its stored information concerning the grandmaster clock , and, from this time onward, sends messages relating to time synchronization that are based on the new clock parameters to the network, or otherwise declines the clock as the new grandmaster clock for the base time domain . - monitoring the physical communication interfaces of a first network device for the arrival of messages relating to time synchronization from a second network device, which messages are used to disseminate information relating to the best clock in the network, - performing first checking to determine whether the messages relating to time synchronization apply to the initially set-up and synchronized base time domain and, if this is the case: - performing second checking to determine whether the messages relating to time synchronization announce a new grandmaster clock having better clock parameters than those of the present grandmaster clock, and, if this is the case: - the first network device starting a virtual base time domain, wherein the first network device forwards no messages relating to time synchronization that are based on the messages relating to time synchronization of the second network device to the remainder of the network, and wherein only for the necessary requests are responses sent from the first network device to the second network device in relation to the virtual base time domain, - verifying the clock parameters sent by the second network device, wherein, if the verification reveals that the grandmaster clock proposed by the second network device is trustworthy or valid, the first network device discontinues the virtual base time domain , updates its stored information concerning the grandmaster clock , and, from this time onward, sends messages relating to time synchronization that are based on the new clock parameters to the network, or otherwise declines the clock as the new grandmaster clock for the base time domain . <EOS>