care-of address

In Internet routing, a care-of address is a temporary IP address for a mobile node (mobile device) that enables message delivery when the device is connecting from somewhere other than its home network. The care-of address identifies a mobile node's current point of attachment to the Internet and makes it possible to connect from a different location without changing the device's home address (permanent IP address). This works similarly to the way the postal system might forward letters through a care-of address: messages sent to the known permanent address are rerouted to the care-of address while the recipient can be reached there. Thus, the recipient avoids having to change their official address to the temporary one when they change their location, and change it back again when they return home.

When a mobile device is away from its home network, it is assigned a care-of address. This may be a foreign agent care-of address, which is the static IP address of a foreign agent on a visited network, or a colocated care-of address, which is a temporary IP address assigned to the mobile node. A colocated care-of address may be acquired through some means such as Dynamic Host Configuration Protocol (DHCP), or may be a longer-term address assigned a device for connecting through a specific foreign network. Mobile IP, as defined in the Internet Engineering Task Force (IETF) RFC 2002 specifications, registers the care-of address with a home agent, which resides on the home network. When a message for the mobile node is delivered to the home network, the home agent intercepts the message and tunnels it to the recipient at the care-of address.

This was last updated in September 2005

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