A method and arrangement for connecting an ad-hoc communication network (101) to a permanent communication network (102), e.g. to a cellular mobile communication network. The ad-hoc communication network is established between communication devices (103-106) and a gateway device (107) using a routing protocol that is run in the gateway device and in the communication devices. A protocol address that is associated in a communication device with a protocol data unit is determined on the basis of a control action given by a user of the communication device. In a gateway device, the protocol data unit is relayed to the permanent communication network if the protocol data unit is provided with a pre-determined protocol address. The user of the communication device can determine with the aid of the control action whether he is communicating only inside the ad-hoc communication network or via the permanent communication network.