I have users running Win2000 Pro on laptops, as members of an NT 4.0 domain. When these people go home and connect to a cable modem or home network, they experience timeouts of about a minute when they either open a new browser window, or try to save a file like a new spreadsheet they have just created. Once the browser is open, searching for new URLs does not produce this problem again. But, if a new instance of the browser is launched, it does happen. This doesn't happen on our LAN. People who go home and connect to the Internet via modems also don't have this problem. People who have NT 4.0 on their laptops don't have this problem, either. The common denominator seems to be Win2000 and a network card that's plugged into something that isn't the usual network. Can you shed any light on this?
Windows 2000 does a "slow network" calculation via a series of pings to determine the average bandwidth of a connection. If the speed is less than 512K bytes/s, the system tags the connection as "slow." Quite a few networking applications use this information to determine if they should use locally cached information or download new information from the network. The cable modem connection is probably faster than 512K bytes/s (unless everyone on the same neighborhood interface box is downloading the latest Napster rips at the same time) so the network applications fall back on their usual chatty, connection-oriented behavior. The dial-up connections get the "slow" flag and avoid the bad behavior.
Because you're experiencing the timeout when you touch a server for the first time, it could be the NetBIOS-over-TCPIP helper that's causing the problem. It's trying to find the subnet master browser via Windows Internet Naming Service (WINS) or its broadcasting a name resolution message or engaging in some other obnoxious behavior. Because you probably don?t expose your WINS server outside the firewall, the clients are timing out.
You can test this theory by putting two or three of your server names in LMHOSTS then see how long it takes to make the initial connection. (Be sure to use the #PRE switch and preload the addresses using NBTSTAT -R.) If the connection works immediately, you've got it solved. Either put a WINS server outside the firewall or use a VPN or put a centrally managed LMHOSTS file on your laptops.
If that doesn't solve the problem, look for other possible timeout sources. You might want to put a packet sniffer on a hub along with the machine to look for the queries that are timing out or delayed.
This was first published in February 2001