 the CN is outside the network protected by the firewall and the MN is in the network protected by the firewall. Therefore, the five elements in the entry item includes a source home address 0, a destination home address, a source port, a destination port and a protocol number. Step 000: Match the replaced destination address of the data packet, i.e. the home address of the MN with the destination home address in the entry item; if the home address of the MN matches the destination home address in the entry item, Step 000 is performed; otherwise, Step 000 is performed. In this step, the replaced destination address of the data packet, i.e. the home address of the MN matches the destination home address in the entry item; if the home address of the MN matches the destination address in the entry item, the matching is successful; otherwise, the matching is unsuccessful. Step