Here's the rundown. Our LAN system was running fine until we changed from an ISDN internet service to a Fractional T1. When we changed from our original router for ISDN to the Siemens T1 router DHCP forced IP address changes from 128.x.x.x to 65.xxx.xx.xxx, after the change the internet will work, but our accounting system AS400 will not. DHCP is now and always has been enabled on all pc's. If I manually set the IP back to 128.x.x.x the accounting software will work but the internet will not. Note: I have one PC that is not connected to the LAN but is connected to the T1 router I had to manually set the DNS server for the internet connection to work. I hope this is enough info. Any help will be appreciated.

Try the networking forum http://www.computing.net/networking/wwwboard/wwwboard.html Jimi_l

From what you've said it's difficult to determine, but it sounds like all your computers on the LAN still have the 128.x.x.x IP address range. When you manually set the accounting machine to that range, it connects to the other machines since they are still using that same IP range. Based on the information provided here, the educated guess would then be that your T1 router is not doing NAT (network address translation), therefore your local computers have nothing to pull new IP addresses from. The choice is to either re-program the T1 router to do NAT (if capable), or purchase a router that will do NAT like the Linksys BEFSR41, or for more security get a SonicWall SOHO3. I'd recommend the linksys since it's a breeze to administrate. Incidentally, for security reasons you need something like the LinkSys or Sonicwall installed. It sounds like you've been running with your accounting system exposed to the public internet. Breif NAT explanation: Your T1 provider provides the 65.x.x.x PUBLIC ip address, but you should have a router that converts that to a LOCAL PRIVATE ip address range, like 192.168.1.1 to 192.168.255.255. Essentially, creating a barrier or 'wall' between the public internet and your private LAN. This process is usually called NAT. Once NAT is used, every computer on your network will display the same PUBLIC IP when you visit ipchicken.com. Hope I didnt wander too far off course here :-) --YM