How can I configure a second radius server as backup in http://splunk-base.splunk.com/apps/47339/radius-authentication ?
This app doesn't currently support a backup RADIUS server. However, I can modify the app to support it relatively easily.
For reference, I have a ticket opened regarding this feature at http://lukemurphey.net/issues/405.
I just uploaded a new version that supports a backup server. Re-run the setup to add the backup server or add it manually via the radius.conf file.
See the following for details: http://lukemurphey.net/projects/splunk-radius-auth/wiki/Using_a_Backup_Server
Let me know if you have any issues with it.