The problem occurs when the laptop is running Windows NT or Windows 2000 and the LAN consists of Windows 95/98/Me machines in a peer-to-peer network. Larger businesses, of course, are likely to have at least one Windows NT or Windows 2000 server running as a DC (domain controller), in which case the problem I'm describing doesn't occur. But small businesses or branch offices often set up their own peer networks using a few Windows 9x machines. Everything seems to run fine, and co-workers can share files and printers -- until that roamin' laptop plugs into the network.
In that case, the Windows NT or Windows 2000 portable can assert itself as a "master browser" on the network. This confusing term has nothing to do with "browsing the internet" or "using a web browser". Instead, the master browser on a Microsoft peer network is responsible for maintaining a list of resources -- servers, file shares, shared printers and so on -- across a workgroup.
A Windows NT or Windows 2000 machine has a higher priority than Windows 9x when it joins such a network. So it becomes the "master browser", but it initially has no information about all the other resources on the LAN. The traffic created by the resulting data-collection process can slow the network down for several minutes.
As reader Kent England said when he wrote to me about this situation, "If you have a Win2K [or NT] laptop periodically joining a Win 9x desktop network, then the plugging and unplugging of the laptop will disrupt the Network Neighborhood view each time and generate an excessive amount of traffic as the new browser master learns of all the nodes on the network."
A different but related problem occurs when a master browser is multihomed (using more than one network adapter). In this case, only a portion of the shares on a network will be visible to other machines.
The solution in both cases is to change Registry values that are at Hkey_Local_Machine\System\CurrentControlSet\Services\Browser\Parameter. To keep a machine from becoming a master, change the value of MaintainServerList to false for Windows NT or no for Windows 2000. To encourage a single-homed computer to become the master, change the value of IsDomainMaster to yes.
To see Microsoft articles that describe this, go to search.support.microsoft.com/kb/c.asp and search for article ID numbers Q191611, Q188001 and Q188305. A scenario for Windows 9x machines is at www.help.com/cat/1/106/hto/3311/3.html.
Reader England will receive a free copy of Windows Me Secrets for sending a tip I printed.
Brian Livingston's latest book is Windows Me Secrets (IDG Books). Send tips to firstname.lastname@example.org.