Ask Dr. Intranet

FRAMINGHAM (03/17/2000) - My company has an IP network address of 192.168.x.x.

Our service provider reserved the IP address of 204. x.x.x for our use. I have an Exchange server, a firewall and a registered domain name. I don't know what to do with the IP addresses so the outside world can e-mail me at

Which IP address should I use to set up the Exchange server? Which address should I have my service provider point its DNS to? Do I need a proxy server to connect to the Internet instead of changing everybody's IP address?

Your 192.168.x.x IP network uses private IP addresses that are not routable over the Internet, so you will need to use the public addresses provided by your service provider to set up your public services and use either a proxy, firewall or router to perform network address translation (NAT) between your private net-work and the Internet.

Your firewall should be able to provide this functionality. Point your domain name to the public address, configure NAT on your gateway and the mail should go through. RFC 1597 describes the use of private IP addresses.

One useful tutorial is available at Your firewall and/or router

documentation is another good place to look for configuration information.

Blass is a network architect at Sprint Paranet in Houston. He can be reached at

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