Open NOIP security settings, main menu - File - Security.
IP filter page, add new IP range.
Select IP range and specify type of connection.
NOIP ports. Use different ports for different type of connections.
Advanced page. Restrict version of the Viewer and Server.
Filters for Server's ID and Viewer's MAC addresses. Main menu - File - Filters.
Use ID filter for connections of Servers or MAC filter for connections of Viewers. Using of the symbol * is possible, for example xp* allow xp1, xp2, xp123.
MAC filter of Viewer. Filter for MAC addresses of Viewers.