A care-of address (usually referred to as ''CoA'') is a temporary

IP address An Internet Protocol address (IP address) is a numerical label such as that is assigned to a device connected to a computer network that uses the Internet Protocol for communication. IP addresses serve two main functions: network interface i ...

for a

mobile device A mobile device or handheld device is a computer small enough to hold and operate in hand. Mobile devices are typically battery-powered and possess a flat-panel display and one or more built-in input devices, such as a touchscreen or keypad. ...

used in Internet routing. This allows a home agent to forward messages to the mobile device. A separate address is required because the IP address of the device that is used as host identification is topologically incorrect—it does not match the network of attachment. The care-of address splits the dual nature of an IP address, that is, its use is to identify the host and the location within the global IP network.

Address assignment

The care-of address can be acquired by the mobile

node In general, a node is a localized swelling (a "knot") or a point of intersection (a vertex). Node may refer to: In mathematics * Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two or more curves, lines ...

in two different ways: * ''Foreign agent care-of address'' (FACoA): The mobile node receives the same CoA as the

foreign agent A foreign agent is any person or entity actively carrying out the interests of a foreign principal while located in another host country, generally outside the Diplomatic immunity, protections offered to those working in their official capacity fo ...

. All mobile nodes in the foreign network are given the same CoA. * ''Co-located care-of address'': Each mobile node in the foreign network is assigned its own CoA, usually by a DHCP server. This might happen in a network where the foreign agent has not been deployed yet. Given the imminent IPv4 address exhaustion, the first solution is more frequently chosen, because it does not waste a public IP address for every mobile node when changing network location, as the collocated CoA does. The ''care-of address'' has to be a valid IP address within the foreign network, so that it allows the mobile node to receive and make connections with any host in the outside. To send outgoing packets, the mobile node may as well use its home address but, since it is not a connected IP address for the current network attachment, some routers in the way might prevent the packets from reaching the destination. That is why, in

IPv4 Internet Protocol version 4 (IPv4) is the first version of the Internet Protocol (IP) as a standalone specification. It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. ...

, the outgoing information is transported to the home agent (which is in the home network) by means of an

IP tunnel An IP tunnel is an Internet Protocol (IP) network communications channel between two networks. It is used to transport another network protocol by Encapsulation (networking), encapsulation of its packet (information technology), packets. IP tun ...

. From the Home Network, the packets of the Mobile Node can be sent using its original Home Address, without any routing problem. The Correspondent Node will send its information again to the Home Network. Thus, it has to be sent on through the tunnel to the foreign agent and then to the Mobile Node. When all mobile nodes share the same IP address with the foreign agent, this is implemented by the foreign agent acting as a proxy ARP.Cisco IOS local-area mobility
/ref>

References

{{DEFAULTSORT:Care-Of Address Network addressing

Address assignment

See also

References