Modify your Registry to resolve common IPX-based RAS problems

In October, I covered NetBEUI-based RAS clients and discussed the RAS NetBIOS gateway, the RAS RemoteListen parameter, and how to modify your RAS server's configuration to extend networking functionality to your RAS clients. This issue, I discuss the Registry values that affect the behavior of another RAS-supported protocol—NWLink IPX/SPX.

Several problems are common to IPX-based RAS scenarios. To understand these problems, you first need to understand how Windows NT treats RAS clients in NetBIOSover-IPX (i.e., Type 20 packets) broadcast traffic. Two Registry entries affect this configuration. The HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\ Services\NwlnkIpx\Parameters\DisableDialinNetbios subkey is an IPX-specific value of type REG_DWORD that defaults to 1, which means that RAS broadcasts NetBIOS packets from only remote clients to the internal network and the RAS server, but RAS doesn't forward the packets back to the remote clients. Table 1 lists possible values for this setting.

The second Registry value that affects NetBIOS-over-IPX broadcast traffic is the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NwlnkRip\ Parameters\NetBiosRouting subkey of type REG_DWORD with a default value of 2. Table 2 lists the possible values for this Registry subkey. This Registry value is a global IPX setting that isn't RAS specific, so it affects the behavior of IPX on all adapters. You can use this value in a cumulative fashion to combine various packet-forwarding behaviors. For example, if you want a RAS server to forward Type 20 NetBIOS packets not only from the RAS client to the LAN but also from the LAN to the RAS client, you set this value to 6.

If the RAS server is a multihomed server acting as an IPX router, you can set the RAS server to propagate Type 20 packets between various LAN segments by adding 1 to the existing value. For example, if you want RAS to forward broadcasts between the client and the LAN and between multiple LAN segments, you set the value of NetBiosRouting to 7. This value guarantees that RAS forwards all IPX NetBIOS broadcast traffic between all network interfaces on the RAS server.

Although the DisableDialinNetbios and the NetBiosRouting values seem redundant at first glance, they complement rather than overlap each other. Depending on your situation, you might need to modify one or both values to support IPX-based RAS clients' applications. The downside of making these changes is decreased performance, because any setting that causes RAS clients to receive broadcast traffic can consume significant bandwidth. Whether changing these values significantly affects users' connections depends on the speed of the link and the amount of broadcast traffic your network generates.