Mobile IP in the WiMAX Environment

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Worldwide Interoperability for Microwave Access (WiMAX) is the international standard for wide area radio access networks. It provides a framework for networks that are implemented in different ways to successfully interoperate with mobile subscribers that roam among the networks. This interoperability enables the subscribers to be authenticated by their home network wherever they roam, and to receive the services for which they are authorized.

The Mobile IP home agent can operate in either of two access modes, generic and WiMAX. The generic access type is appropriate when the home agent is deployed in a generic Mobile IP home network. When deployed as a home agent in a WiMAX home connectivity services network (H-CSN), you must configure the WiMAX access type. The WiMAX access type enables the Mobile IP home agent to receive, process, and send WiMAX vendor-specific attributes (VSAs) that are used by AAA and the RADIUS server to authenticate the mobile subscriber. When the access type is generic, the Mobile IP home agent cannot handle these VSAs.

Note: The Mobile IP configuration for WiMAX requires that AAA be used for the authentication method. For that reason, WiMAX is available only in the default router context.

A WiMAX H-CSN is analogous to the Mobile IP home network for non-WiMAX implementations. When WiMAX is enabled for the Mobile IP home agent in an H-CSN, the Mobile IP home agent triggers subscriber authentication when the agent receives the registration request. The home agent stores WiMAX Forum (vendor ID 24757) vendor-specific attributes (VSAs) listed in Table 24 in the session database based on the registration request.

Table 24: WiMAX Forum VSAs used by Mobile IP

Attribute Number	Attribute Name	Description	Value
26–1	WiMAX-Capability	Identifies the WiMAX capabilities supported by the home agent (sent in the Access-Request message). In an Access-Accept message, Identifies the capabilities selected by the RADIUS server (returned in the Access-Accept message).	string or integer
26–6	hHA-IP-MIP4	IP address of the home home agent (hHA) making the request	octet string: IP address
26–10	MN-HA-MIP4-KEY	MN-hHA key sent by the RADIUS server for validation by the home agent	integer: 2-octet salt followed by 16-octet encrypted MN-hHA hash key
26–11	MN-HA-MIP4-SPI	Security parameter index (SPI) associated with the MN-HA-MIP4 key	integer: 4-octet
26–15	hHA-RK-KEY	Key used by the NAS to generate FA-HA keys	integer: 2-octet salt followed by 16-octet encrypted MN-hHA hash key
26–16	hHA-RK-SPI	SPI associated with the hHA-RK key	integer: 4-octet
26–17	HA-RK-Lifetime	Lifetime of the hHA-RK key and derived keys	integer: 4-octet
26–18	RRQ-HA-IP	IP address of the home agent contained in the Mobile IP registration request or the binding update	octet string: IP address
26–19	RRQ-MN-HA-KEY	The MN-HA key bound to the home agent IP address as reported by the RRQ-HA-IP attribute. Used to validate the MN-HA-AE of the Mobile IP registration request.	integer: 2-octet salt followed by 16-octet encrypted MN-hHA hash key

The home agent requests AAA to fetch the corresponding WiMAX-related information from the RADIUS server. The AAA client sends an Access-Request message to the server. The RADIUS server responds with the necessary WiMAX information, such as the MN-HA key and the HA-RK key, and then the AAA client passes the response to the home agent. The Mobile IP home agent verifies the response received from AAA, processes the registration request, and then grants, extends, or denies subscriber registration.

Figure 7 shows the elements of a sample WiMAX topology.

Figure 7: Sample Mobile IP WiMAX Topology

Image g017281.gif

The Mobile IP subscriber registration flow is a four-step process.

The access service network gateway (ASN-GW) sends the subscriber registration request from the mobile node to the Mobile IP home agent. The registration request is protected by the MN-HA authentication extension and the FA-HA authentication extension.
The home agent requests that the RADIUS server send the cryptographic keys for the Mobile IP session identified by user@realm. The home agent announces to the RADIUS server that it would like to source IP session-based accounting messages.
The RADIUS server agrees to use IP session-based accounting, provides the requested cryptographic keys, and sends the AAA-Session-ID for this session.
The home agent replies to the Mobile IP registration request.

Reauthentication of WiMAX subscribers is not currently supported.

You can configure the Mobile IP home agent for WiMAX access by including the wimax statement at the [edit services mobile-ip access-type] hierarchy level. You can prevent the Mobile IP home agent from being able to process WiMAX VSAs by either removing the wimax statement at the [edit services mobile-ip access-type] hierarchy level or by including the generic statement at the [edit services mobile-ip access-type] hierarchy level. The default access type for Mobile IP home agent is generic.

Mobile IP in the WiMAX Environment

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