Home agents play an active role in the registration process. The home agent receives registration requests from the mobile node. The registration request might be relayed by the foreign agent. The home agent updates its record of the mobility bindings for this mobile node. The home agent issues a suitable registration reply in response to each registration request. The home agent also forwards packets to the mobile node when the mobile node is away from the home network.
A home agent might not have to have a physical subnet configured for mobile nodes. However, the home agent must recognize the home address of the mobile node through the mipagent.conf file or some other mechanism when the home agent grants registration. For more information about mipagent.conf, refer to Creating the Mobile IP Configuration File.
A home agent can support private addressed mobile nodes by configuring the private addressed mobile nodes in the mipagent.conf file. The home addresses that are used by the home agent must be unique.