Webpage on subnet only

Webpage on subnet only

How do I lock down the webpage interface where users can login, reset their password, and unlock their accounts only to computers in my subnet?  For example, we want only computers in 255.255.248.0 to be able to hit http://<servername>:8888

Thanks,
Dereatha Cross
College of Architecture Planning + Design
Kansas State University
Manhattan, Kansas 66506]