Abnormality detection apparatus and abnormality detection method

An abnormality detection apparatus for a mobility entity and for detecting an abnormality in a network system, the network system including a first network and a second network that use different communication protocols, the abnormality detection apparatus comprising:

• a first communication circuit that receives state information indicating a state of the mobility entity, the state information being acquired from the second network;
• a second communication circuit that transmits and receives a first frame according to a communication protocol used in the first network;
• a memory that stores an abnormality detection rule;
• and
• a processor that, in operation, performs operations including:
• detecting, based on the state information and the abnormality detection rule, whether a control command included in the first frame received by the second communication circuit is abnormal, and
• in a case where the processor detects that the control command is abnormal, prohibiting the control command from being transmitted,
• wherein the abnormality detection rule associates the control command with a plurality of states of the mobility entity, and
• the processor detects that the control command is abnormal in response to the state of the mobility entity, which is received by the first communication circuit, not being one of the plurality of states, which is associated with the control command.