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If you try to establish a virtual private network (VPN) connection to an enterprise network using a PPTP (point to point tunneling protocol) client, the connection to the Microsoft Windows Server remote access server may fail. You can receive the following error message:
Error 721: The remote computer is not responding.
Note that the description of error 721 may vary.
This problem can occur if the network firewall does not allow GRE (Generic Routing Encapsulation) protocol traffic. GRE is the IP 47 protocol, PPTP uses GRE for tunnelized data.
What is the cause of this error?
This problem can occur if the network firewall does not allow GRE (Generic Routing Encapsulation) protocol traffic. GRE is the IP 47 protocol, PPTP uses GRE for tunnelized data.
The point-to-point tunneling protocol uses generic routing encapsulation (GRE) for tunnel data. The VPN 721 error may occur if the network firewall does not allow GRE protocol traffic. The generic routing encapsulation protocol is used in conjunction with the point-to-point tunneling protocol to create virtual private networks between server and client or between clients.
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Use the registry editor
1. click on “Start” and then on “Run”.
2. in the “Open” field, type “regedit” (without quotation marks).
then press ENTER.
3. In the Registry Editor, locate the following subkey in the registry:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325
-11CE-BFC1-08002bE10318}\000x , where 000x represents the network.
Interface used to establish the VPN connection.
4. On the “Edit” menu, point to “New” and then click “DWORD Value”.
5. type ValidateAddress (without quotation marks), and then Press ENTER.
6. Exit the registry editor.
7. Restart your computer.
Other ways to solve this problem
To correct this error, you can do this solutions:
- Configure the network firewall to allow the GRE 47 protocol.
- Make sure that the network firewall allows TCP traffic on port 1723.
- These two conditions must be met to establish VPN connectivity via PPTP.
- Disable your security program/firewall application on the system and test the VPN.
- If you are using a wireless connection, switch to Cable mode.
- Close the VPN, perform a network diagnostic, make sure your Internet connection is working, and then turn the VPN back on.
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