If there's an artical on this, please direct me to it. I have a requirement to control which IP is given opportunity to authenticate to my VPN 3000-series concentrator. I also have RADIUS available, if that can be used in any way, using vendor-specific attributes / classes.
Obviously a firewall on the "Outside" side of the concentrator would do this, but I'm in a large organization, and we don't have timely control of the firewall that's in place, so we can't control access to our VPN Concentrator using this firewall; we have to put the control in place on the concentrator itself.
Example: If Joe wants to authenticate, he has to be coming from his hardened workstation at 10.10.10.10. However, if Joe tries to authenticate using his laptop on the McDonalds WiFi at 192.168.1.1, then he'll be denied. RFC1918 addresses used as examples.