Provided is a communication device in which communication between hosts of a layer 2 network is overlaid on a layer 3 network. The communication device manages a first MTU length of each communication path with respect to a plurality of communication paths in the layer 3 network, determines a second MTU length based on information to be added in cases where communication between the hosts of the layer 2 network is overlaid via the plurality of communication paths, and notifies the hosts of the second MTU length.