Aruba Networks Version 3.3 manual Mobility Controller Physical Placement and Connectivity

When the client roams off of its ‘home’ network to another network, the network is said to be attached to a ‘foreign’ network. The foreign network is defined as a network controlled by a different Mobility Controller than the one controlling the home network, but still within the same Mobility Domain. The IP address of the Mobility Controller on the foreign network becomes the client’s ‘care-of address’. This address is passed to the Mobility Controller on the home network, where the Home Agent keeps a map of clients and care-of addresses. The Home Agent learns the care-of address from a similar process on the foreign network known as the Foreign Agent.

All of this is necessary to ensure proper traffic delivery to the client. From an IP perspective, the client still appears to be attached to its home network, so all data bound for that client will be routed to its home network. When the Home Agent sees packets bound for the client, it will tunnel those packets to the foreign network for delivery to the client. Any traffic generated by the client is sent directly from the foreign network using standard IP routing and delivery mechanisms. Routing tables remain intact, and the client can continue to use the IP address acquired in its home network.

Mobility Domains take some amount of planning, but generally follow the physical layout of the network. For a centralized network that is located in a single building or campus, it may be possible to design a network that has only a single Mobility Domain. The main design consideration should always be “can the user realistically roam between the subnets and controllers in a single session?” This is possible in the same building or on a campus with coverage between buildings; however, roaming between an office in Los Angeles and an office in New York is not going to occur.

Los Angeles

MD1

Home

Agent

LAN

Foreign

Agent

New York
LAN	Foreign
MD2	Agent
Home
Agent

				Client travels
172.16.20.1	Client travels	172.16.20.1	10.100.2.1	10.100.2.1
	172.16.20.2		Client travels	10.100.2.10

To plan a Mobility Domain, begin by taking a look at the network map, with a special focus on the access points and controllers. Generally, this will provide the information you need to develop a logical grouping of Mobility Domains. You should also examine heat maps of your network, and determine if the coverage areas provide enough connectivity and overlap to allow your clients to transition networks. Outdoor APs may extend this coverage between buildings providing you with a larger Mobility Domain.

Mobility Controller Physical Placement and Connectivity

Physical deployment of the Mobility Controllers is typically in two areas, the data center and the distribution layer of the network. The data center contains the Master Controllers that comprise the Management layer, while the distribution layer switches will connect to the Local Controllers that make up the Aggregation layer.

Master Controller Placement

The Master Controller should be given adequate bandwidth connections to the network, preferably a minimum of a Gigabit Ethernet LAN connection. Using the MMC-3600 appliance, Aruba recommends at

Campus Wireless Networks Validated Reference Design Version 3.3 Design Guide Mobility Controller and Access Point Deployment 33