HP-UX Mobile IPv4 A.03.01 Administrator's Guide
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Chapter 1
3
Base Functionality
This section describes the features included in the Base Functionality for the HP-UX
Mobile IPv4 product. It also provides an overview of Mobile IPv4 technology.
Home Address
In most IP networks, the IP routers require nodes to use IP addresses that are
topologically correct: all nodes attached to the same physical subnetwork or LAN
segment must have the same IP network or subnetwork address prefix. This means that
without Mobile IPv4, a node must change its IP address each time it moves to a new
network attachment point.
A Mobile IPv4 client node, or Mobile Node (MN), can move to different network
attachment points and use a single home address for extended periods of time,
regardless of its current attachment point.
Care of Address, Home Agent and Foreign Agent
When a Mobile Node is attached to a foreign network (a network other than its home
network), it is associated with a Care-of Address (COA) that is topologically correct for
the foreign network. A node that communicates or corresponds with the Mobile Node, a
Correspondent Node (CN), can still send packets to the Mobile Node using the Mobile
Node’s home address. A Home Agent (HA), a router node on the Mobile Node’s home
network, will capture these packets. The Home Agent encapsulates these packets
addressed to the Mobile Node’s home address in new IP packets with the Care-of
Address as the destination address. (The Home Agent forms a tunnel with the Care-of
Address.)
There are two types of Care-of Addresses:
• Foreign Agent Care-of Addresses (FA COAs)
• Co-located Care-of Addresses (CCOAs)
Foreign Agent Care-of Address
A Foreign Agent (FA) is a router node on a foreign network that receives packets on
behalf of Mobile Nodes temporarily attached to, or “visiting,” its network. The Foreign
Agent Care-of Address is an address of the Foreign Agent. Multiple Mobile Nodes
visiting the foreign network can use the same Foreign Agent Care-of Address.
The Foreign Agent receives packets addressed to the Foreign Agent Care-of Address,
de-capsulates them, and sends them to the Mobile Node.