RAS Server Cannot Use DHCP to Assign Addresses w/ PPTP Filtering

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This article was previously published under Q158387

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SYMPTOMS

PPTP clients are unable to connect to your PPTP server with the TCP/IP protocol. The following error message is logged in the Event Viewer on the PPTP server:

Event ID: 20091
Source: RemoteAccess
Description: The Remote Access Server was unable to acquire an IP Address from the DHCP Server to be used on the Server Adapter. Incoming users will be unable to connect using IP.

This problem will occur if you have two network interfaces on your PPTP server, one connected to your internal network and the other connected to the Internet, and PPTP filtering is enabled on the interface with a connection to the Internet.

You enable PPTP filtering on the interface connected to the Internet to disable this interface for non-PPTP traffic. The interface connected to your internal network does not have PPTP filtering enabled; however, the RAS Server service running on this machine is still unable to obtain an IP address from the DHCP server for the RAS Server PPTP adapter.

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CAUSE

DHCP traffic is sent via broadcast. On a computer with more than one network interface, the Tcpip.sys driver incorrectly discards broadcast packets when one of the network interfaces has PPTP filtering enabled. Tcpip.sys should forward the broadcast packets to the non-PPTP filtering interfaces instead of discarding the broadcasts.

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RESOLUTION

To correct this problem, install Windows NT 4.0 service pack 2 or later.

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STATUS

Microsoft has confirmed this to be a problem in Windows NT version 4.0. This problem was corrected in the latest Microsoft Windows NT 4.0 U.S. Service Pack. For information on obtaining the service pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

S E R V P A C K

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