Scalability
When designing for scalability, use the following best practice:
For a large amount of authentication traffic within an Active Directory forest, use a layer of RADIUS proxies running Windows Server 2003 IAS between the wireless APs and the RADIUS servers.
By default, an IAS RADIUS proxy balances the load of RADIUS traffic across all the members of a remote RADIUS server group on a per-authentication basis and uses failover and failback mechanisms. Members of a remote RADIUS server group can also be individually configured with priority and weight settings so that the IAS RADIUS proxy favors specific RADIUS servers.