user manual

6-6
Cisco Aironet 1200 Series Access Point Software Configuration Guide
OL-2159-05
Chapter 6 Configuring Proxy Mobile IP
Introduction to Mobility in IP
Proxy Mobile IP supports Mobile IP for wireless nodes without requiring specialized software for those
devices. The wireless access point acts as a proxy on behalf of wireless clients that are not aware of the
fact that they have roamed onto a different Layer 3 network. The access point handles the IRDP
communications to the foreign agent and handles registrations to the home agent. This scheme offers less
cost, less administration, and a faster time to deployment.
There are three primary states of operation for proxy Mobile IP:
• Agent discovery
• Updating the subnet map table
• Device registration
The following paragraphs offer a high-level view of how proxy Mobile IP operates.
The IRDP handles agent discovery in proxy Mobile IP. This protocol must be enabled on the home agent
and foreign agent router interfaces on which access points reside. The protocol enables the access point
to identify services being offered by local Mobile IP entities and provides some necessary information
to be used when an access point must register a mobile node.
Any access point in the network may be designated as an authoritative access Point (AAP), which means
that it updates all other access points in the network about networks that have mobile nodes on them.
The protocol used for this interaction is UDP-based (port 6500) and is enabled when proxy Mobile IP is
enabled.
An access point that has discovered a foreign agent on its network and has received an updated subnet
map from the authoritative access point is ready to service mobile nodes, which roam to it from other
subnets. The mobile node decides to roam to a new access point based on criteria such as signal strength,
traffic load on the access point, and so forth. Once associated, the mobile node eventually sends traffic
to the access point. The access point recognizes that the source address in use is from a different Layer
3 network than its own and checks its subnet map table for an entry. If the subnet matches one of the
entries in the table, the access point sends a registration request to the local foreign agent requesting that
the mobile node be registered with the proper home agent. The foreign agent in turn forwards the
registration request to the home agent.
The home agent verifies that the mobile node is valid (either through its local security associations or
through associations housed on a AAA server). If it is valid, the home agent binds the mobile node to
the foreign agent’s care-of address and builds a tunnel between the foreign agent and the home agent.
Traffic can then flow from the home agent to foreign agent, from foreign agent to access point, and from
access point to mobile node. The mobile node can send traffic to directly to the node to which it is
intended.
Before Deploying Proxy Mobile IP
Before deploying proxy Mobile IP, you should ask some fundamental questions of the network design
and implementation engineers:
• Is there an alternative to using proxy Mobile IP?
• What is the corporate policy regarding device roaming?
• Should you use static or dynamic IP address assignments?
• Do I have an operational Mobile IP network or do I need to build one from scratch?
• If I build a network from scratch, do I have the right software revision and feature set on my routers?
The answers to these questions may vary. For further information, see the Proxy Mobile IP Deployment
Guide.