Cisco Systems DL-2159-05 manual Registration, Tunneling

Chapter 6 Configuring Proxy Mobile IP

Introduction to Mobility in IP

When a client device associates to an access point and the access point determines that the client is visiting from another network, the access point performs a longest-match lookup on its subnet map table and obtains the home agent address for the visiting client. When the access point has the home agent address, it can proceed to the registration step.

Registration

The access point is configured with the mobility security association of all potential visiting clients with their corresponding home agents. You can enter the mobility security association information locally on the access point or on a RADIUS server on your network, and access points with proxy Mobile IP enabled can access it there.

As an access point on a network with a local home agent, the access point registers mobile nodes with the home agent prior to any roaming taking place. Mobile nodes must be listed by IP address (or address range) in the access point and the home agent along with security information stored either locally, on a AAA server, or both.

On the foreign network, the access point uses the security association information, the visiting client’s IP address, and the information that it learns from the foreign agent advertisements to form a Mobile IP registration request on behalf of the visiting client. It sends the registration request to the visiting client’s home agent through the foreign agent. The foreign agent checks the validity of the registration request, which includes verifying that the requested lifetime does not exceed its limitations and that the requested tunnel encapsulation is available. If the registration request is valid, the foreign agent relays the request to the home agent.

The home agent checks the validity of the registration request, which includes authentication of the visiting client. If the registration request is valid, the home agent creates a mobility binding (an association of the visiting client with its care-of address), a tunnel to the care-of address, and a routing entry for forwarding packets to the home address through the tunnel.

The home agent then sends a registration reply to the access point hosting the visiting client through the foreign agent (because the registration request was received through the foreign agent). The foreign agent verifies the validity of the registration reply, including ensuring that an associated registration request exists in its pending list. If the registration reply is valid, the foreign agent adds the visiting client to its visitor list, establishes a tunnel to the home agent, and creates a routing entry for forwarding packets to the home address. It then relays the registration reply to the visiting client.

Finally, the access point checks the validity of the registration reply. If the registration reply specifies that the registration is accepted, the access point is able to confirm that the mobility agents are aware of the visiting client's roaming. Subsequently, the access point intercepts all packets from the visiting client and sends them to the foreign agent.

The access point reregisters on behalf of the visiting client before its registration lifetime expires. The home agent and foreign agent update their mobility binding and visitor entry, respectively, during reregistration.

A successful Mobile IP registration by the access point on behalf of the visiting client sets up the routing mechanism for transporting packets to and from the visiting client as it roams.

Tunneling

The visiting client sends packets using its home IP address, effectively maintaining the appearance that it is always on its home network. Even while the visiting client is roaming on foreign networks, its movements are transparent to correspondent nodes (other devices with which the visiting client communicates).

Cisco Aironet 1200 Series Access Point Software Configuration Guide

6-10 OL-2159-05