When you try to establish a virtual private network (VPN) connection from your Windows XP or Windows 2000 PPTP client to your corporate network, the connection may not work, and you may receive the following error message:
Error 721: Remote PPP peer is not responding
This problem occurs when a Windows XP Service Pack 1 (SP1) or Windows 2000 Service Pack 3 (SP3) PPTP client tries to establish a VPN connection to a Windows 2000 server that participates in a cluster that is using the cluster's virtual IP address on TCP port 1723. When the server responds by using Generic Routing Encapsulation (GRE) packets, it uses the source IP address of the first IP address that is bound on the network adapter. However, this address is different from the virtual IP address that is requested by the Windows XP client. The Windows XP client drops these response packets because they originate from a different source IP address from the address that it tried to connect to.
Service Pack Information
To resolve this problem, obtain the latest service pack for Microsoft Windows 2000. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
260910 How to Obtain the Latest Windows 2000 Service Pack
A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.
If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.
Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site:
Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.The English version of this hotfix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.
Date Time Version Size File name ------------------------------------------------------- 03-Dec-2002 11:57 5.0.2195.6150 47,088 Raspptp.sys 13-Nov-2002 15:36 22.214.171.124 4,096 Spmsg.dll 13-Nov-2002 15:37 126.96.36.199 87,040 Spuninst.exe 15-Nov-2001 15:27 n/a 5,149 Empty.cat Update Folder Date Time Version Size File name --------------------------------------------------- 03-Dec-2002 15:20 n/a 7,409 Q810839.cat 13-Nov-2002 15:37 188.8.131.52 18,432 Spcustom.dll 13-Nov-2002 15:36 184.108.40.206 409,088 Update.exe
Note This fix should be applied to your Windows 2000 PPTP server.
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 How to back up and restore the registry in Windows
If you want your PPTP client that is running Windows XP SP1 or Windows 2000 SP4 or later to allow connections to a PPTP server that replies by using a different IP address, follow these steps to disable PPTP address validation: