This information only pertains to those systems that have more than one IP feeding the same box simultaneously. Do not confuse this with DYNAMIC IPs (where your IP changes over a given range periodically).
If your server has more than one IP, you may utilize multiple IP rolling to distribute your data traffic across them.

* You can not use multi-IP rolling in private IP environment (192.168.x.x) to serve outside users from internet

First, open the FTPD configuration menu by selecting FTP-SERVER from the SETUP menu. Open the server you wish to edit. In the SERVER IP box, enter the primary IP you wish to use. In the EXTRA IP box, ADD the additional IPs you want RaidenFTPD to use for rolling.

Check USE MULTI-IP TO OFFER DATA CONNECTIONS AUTOMATICALLY. Save and exit.

Now, as a user connects to your server, the server will automatically make use of the additional IPs you entered for file transfers.

* RaidenFTPD will always use the IP with an instaneously minimal traffic to serve the data transfers.