A care-of address (CoA) is a temporarily assigned IP address that a mobile device receives when it switches from one IP network to another. The mobile device can still send messages even if it is no longer connected to its home network.
The care-of address identifies the connection point to which the mobile device is connected to the Internet and can connect to any possible connection point without changing the IP address of the home network. If messages are sent to the permanent IP address, then they are routed to the care-of address through which the recipient can receive them.
There are two different care-of addresses. The first is that of the foreign agent, which the mobile node receives when it moves to a foreign network. This requires that the foreign agent has at least one interface to the foreign network.
The second care-of address is the collocated care-of address. This is a temporarily assigned address for the mobile node's interface to the foreign network. This address is used when no foreign agent is available.