IP header compression is enabled by default on Windows NT 3.51 and 4.0 Remote Access Service (RAS) servers. However, no option exists in the graphical user interface to enable or disable IP header compression for the RAS server itself. In order to enable IP header compression on the RAS server, you will need to make appropriate changes in the Windows NT Registry.

You should not normally need to disable IP header compression. This should only be disabled on the RAS server if you have many RAS clients that do not correctly negotiate IP header compression.

IP header compression is also known as Van Jacobson or VJ header compression as described in RFC 1144. This feature can be enabled or disabled for the Windows NT RAS client using the TCP/IP settings dialog in Dial-Up Networking for Windows NT 4.0 and the Remote Access Phone Book Entry for Windows NT 3.51.

IP header compression is enabled by default on a Windows NT RAS server, and to disable the feature you need to add one or both of these values:

WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.

To modify the settings on the RAS server that disable IP header compression, perform the following steps:

1.	Run Registry Editor (Regedt32.exe)and find the following key in the registry: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Rasman\PPP\IPCP
2.	On the Edit menu, click Add Value and use the following entries: Value Name: AcceptVJCompression Data Type: REG_DWORD DefaultValue: 1 (enabled, set to 0 to disable) Value Name: RequestVJCompression DataType: REG_DWORD DefaultValue: 1 (enabled, set to 0 to disable)

The above entries will not normally appear in the registry, and will use their default settings (which enables IP header compression). By setting the REG_DWORD data to 0 for these values in the Registry, you will disable IP header compression on the RAS server.

VJ header compression is discussed in the help file for the PPP TCP/IP Settings dialog found in the Dial-Up Networking interface for Windows NT 4.0 and in the Network option of the Edit Phone Book entry dialog for Windows 3.51.

For additional information, please see the following article in the Microsoft Knowledge Base: