Mobile IP - Tunneling
Mobile IPs are often used when external workers have to connect to their corporate-intranet.
The connection between both is built up by a "home agent" (a router in the "home network" which manages current locations of its mobile nodes) and a "foreign agent" (a router which allows coupling between foreign networks and mobile nodes).
To hide information of source in the corporate-intranet and mobile nodes, home and foreign agents use "tunneling".
The IP-header of the original message is hidden in the content data and the new IP-header only contains IP-adresses of home and foreign agents as source and destination.