Test Center Rx: When Good Subnets Go Bad

SAN MATEO (04/10/2000) - Our company just upgraded to Microsoft Corp.'s Windows NT Server and changed our network protocol to TCP/IP. Since the upgrade I can no longer access (through my dial-up Internet connection) any Web site with an IP address that begins with 192. I noticed that our clients, our server, and our print servers all start with 192. Is there a conflict here? Is the browser perhaps looking for those sites through my network connection and not the dial-up connection?

Aaron Watson

Brooks: Well, there are two possibilities here, but my main thought is that this looks like a classic case of subnetting gone wrong. It's important to understand that the combination of your IP address and subnet mask tells your system which IP addresses are local and which need to be sent through a router.

The first thing I'd check is that your subnet mask isn't set to 255.0.0.0, which would tell your computer that every IP address that starts with 192 is a local address and does not need to be routed. This sounds as if it's the most likely problem if other Web sites are working fine and only those that start with 192 are not, regardless of their later digits. Other funky subnet masks could do similar things (for example, 255.0.255.0).

Another possibility is that you're behind a proxy server -- if all of your internal addresses start with 192.168 this is almost certain. But that should affect all Web sites, not just those with 192 in the first octet.

(Each of the four "numbers" in an IP address is an octet. In reality, an IP address is a 32-bit number. But people aren't so good at remembering single big numbers. To computers, IP addresses are really just a string of 32 1's and 0's.

But humans are even worse at remembering those. So by convention we break the 32 bits into four decimal numbers, each one representing eight bits of that big 32-bit number.)Going with the more likely problem, and because this is a dial-up connection, you may need to reconfigure the RAS (remote access server) and/or DHCP (Dynamic Host Configuration Protocol) if they are giving out erroneous subnet masks to dial-up clients. Odds are, every dial-up user is experiencing this problem and most aren't familiar enough with the server to track down the IP addresses and figure out the common symptom.

If the subnets look right, the last thing I can think of is to check your machine's routing table and see if an incorrect entry for 192.0.0.0 has crept in and managed to be saved. I can't get static routes to stick unless I put batch files in the start-up group, but I've been told that other people have the opposite problem and can't get them to go away.

Lori: I agree that you most likely have a subnet configuration problem. Your best bet is to verify your configuration setup to rule out any misconfigurations with your subnet masks or possibly reconfigure RAS and/or DHCP. Another slim possibility is that a server or internal machine may be configured as a default router. All the packets may be reaching this machine and thus not getting to the proper destination.

If you haven't already tried using the tracert (trace route) command in NT, you should do so. This will help you determine where the problem lies. By typing in tracert and the IP address, the trace route utility will return a list of hops (or routers) that are encountered along the way to the IP address' destination and where the packet stops. Because this is likely an internal problem, you will be pointed to the machine that is holding things up.

Saving Web pages with IE 5

Joseph Becker wrote a helpful response to our Feb. 28 column regarding difficulties saving Web pages in Internet Explorer (see "How to work around IE 5.0's defaults while saving Web pages," www.infoworld.com/printlinks). He found a handy way to delete the "Save Web Page, complete" option that causes so much grief. The simple fix is in the registry: In the "Current_User/Software/Policies/Microsoft/Internet Explorer/Infodelivery/Restrictions" key, create a new DWORD value called "NoBrowserSaveWebComplete" and set its value to "1." Thanks, Joseph!

Brooks Talley is senior business and technology architect for InfoWorld.com.

Lori Mitchell is a senior analyst in the Test Center. Send your questions for them to testcenter_rx@infoworld.com.

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