Would it be possible to have two separate RADIUS servers on the same 4400 WLC, assuming a wireless user would only be accessing them one at a time? If it's, how would a user select the RADIUS server he would like to authenticate to?
The wlc will only use the 1st radius server that it can communicate with. If that radius server later becomes unavailable, then the wlc will use the second radius server configured. The bad part is that if the primary or first radius server comes back online, the wlc will not use it until the second radius server becomes unavailable.
The only way to force it is to reboot the wlc or palce the secondary radius in the primary spot and hit apply then add the primary radius server back in its spot along with the secondary.
You have to watch out for that and might want to test it. I believe even though you have a ssid's using separate radius servers, which ever is the first radius the wlc communicates with, it will use. So in this case.... no matter what radius server you choose to point to, it will use the first one.
It is like if you have an ssid configured for peap using radius 1 and then you have an ssid using webauth and no radius servers configured..... users will still be able to use their AD username and password to authenticate via WebAuth.