Abstract: A method and a node for associating an IP address of a device with its MAC address, where the network parts of the device and the node are different. The device receives an ARP response comprising the device's IP address and MAC address, accepts the response regardless of a difference between the network parts, and associates the IP address with the MAC address. There is further a method and a node in an IP network where the node receives a message for the device, determines that it does not have the MAC address corresponding to the IP address, and broadcasts an ARP request. The method and node is particularly useful for mobile IP, where a device roams between various sub-nets.