Mobile nodes that have private addresses that are not globally routeable through the Internet require reverse tunnels. Solaris Mobile IP supports mobile nodes that are privately addressed. See Overview of the Solaris Mobile IP Implementation for the functions that Solaris Mobile IP does not support.
Enterprises employ private addresses when external connectivity is not required. Private addresses are not routeable through the Internet. When a mobile node has a private address, the mobile node can only communicate with a correspondent node by having its datagrams reverse-tunneled to its home agent. The home agent then delivers the datagram to the correspondent node in whatever manner the datagram is normally delivered when the mobile node is at home. The following figure shows a network topology with two mobile nodes that are privately addressed. The two mobile nodes use the same care-of address when they are registered to the same foreign agent.
The care-of address and the home agent address must be globally routeable addresses if these addresses belong to different domains that are connected by a public Internet.
The same foreign network can include two mobile nodes that are privately addressed with the same IP address. However, each mobile node must have a different home agent. Also, each mobile node must be on different advertising subnets of a single foreign agent. The following figure shows a network topology that depicts this situation.