Agent Discovery

A mobile node uses a method known as agent discovery to determine the following information:

• When the node has moved from one network to another

• Whether the network is the node's home or a foreign network

• What is the foreign agent care-of address offered by each foreign agent on that network

Mobility agents transmit agent advertisements to advertise their services on a network. In the absence of agent advertisements, a mobile node can solicit advertisements. This is known as agent solicitation.

Agent Advertisement

Mobile nodes use agent advertisements to determine their current point of attachment to the Internet or to an organization's network. An agent advertisement is an Internet Control Message Protocol (ICMP) router advertisement that has been extended to also carry a mobility agent advertisement extension.

A foreign agent can be too busy to serve additional mobile nodes. However, a foreign agent must continue to send agent advertisements. This way, mobile nodes that are already registered with it will know that they have not moved out of range of the foreign agent and that the foreign agent has not failed.

Also, a foreign agent that supports reverse tunnels must send it's advertisements with the reverse tunnel flag set on.

Agent Solicitation

Every mobile node should implement agent solicitation. The mobile node uses the same procedures, defaults, and constants for agent solicitation, as specified for ICMP router solicitation messages.

The rate at which a mobile node sends solicitations is limited by the mobile node. The mobile node can send three initial solicitations at a maximum rate of one per second while searching for an agent. After registering with an agent, the rate at which solicitations are sent is reduced, to limit the overhead on the local network.