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 connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...

for a

mobile device A mobile device (or handheld computer) is a computer small enough to hold and operate in the hand. Mobile devices typically have a flat LCD or OLED screen, a touchscreen interface, and digital or physical buttons. They may also have a physical ...

used in Internet routing. This allows a

home agent Mobile IP (or MIP) is an Internet Engineering Task Force (IETF) standard communications protocol that is designed to allow mobile device users to move from one network to another while maintaining a permanent IP address. Mobile IP for IPv4 is desc ...

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 country while located in another host country, generally outside the protections offered to those working in their official capacity for a diplomatic missio ...

. 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 The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on Internet Protocol (IP) networks for automatically assigning IP addresses and other communication parameters to devices connected to the network using a cli ...

server. This might happen in a network where the foreign agent has not been deployed yet. Given the imminent

IPv4 address exhaustion IPv4 address exhaustion is the depletion of the pool of unallocated IPv4 addresses. Because the original Internet architecture had fewer than 4.3 billion addresses available, depletion has been anticipated since the late 1980s, when the Interne ...

, 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 fourth version of the Internet Protocol (IP). It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. IPv4 was the first version de ...

, 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 of its packets. IP tunnels are often used for connecting two disjoint IP networks ...

. 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 Proxy ARP is a technique by which a proxy server on a given network answers the Address Resolution Protocol (ARP) queries for an IP address that is not on that network. The proxy is aware of the location of the traffic's destination and offers its ...

.Cisco IOS local-area mobility
/ref>

References

Network addressing {{Compu-network-stub

Address assignment

See also

References