Tag Archives: VPN

Windows 7 Can’t Connect to Mac OS X VPN Server

How To Connect Windows 7 To Mac VPN Server behind Firewall

Background of problem:

I had a Mac OS X VPN Server set up at a school district that was behind a firewall. It was set up with a static 1 to 1 NAT so that it could be reached publicly. I was able to connect to the Mac VPN with all of my mac devices and had no issues. However, my boss – a windows user – wanted access. Her Windows 7 machine was not able to connect to the VPN Server. No matter what settings we tried it just would not connect.

I spend hours googling and searching the internet for a solution to my problem. I figured that it must be something incompatible between the Mac server and Windows 7. As it turns out – it really had nothing to do with the fact that it was a Mac server. According to Microsoft, Windows by default does not support IPSec over NAT. What this means is that no matter how hard your try to connect to an IPSec VPN that is behind NAT – Windows is not going to connect.

How To Fix:

  1. Log on to the Windows Vista client computer as a user who is a member of the Administrators group.
  2. Click Start Start button, point to All Programs, click Accessories, click Run, type regedit, and then click OK. If the User Account Control dialog box is displayed on the screen and prompts you to elevate your administrator token, clickContinue.
  3. Locate and then click the following registry subkey:
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\PolicyAgent
     Note: You can also apply the
    AssumeUDPEncapsulationContextOnSendRule
    DWORD value to a Microsoft Windows XP Service Pack 2 (SP2)-based VPN client          computer. To do this, locate and then click the following registry subkey:     HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\IPSec
  4. On the Edit menu, point to New, and then click DWORD (32-bit) Value.
  5. Type AssumeUDPEncapsulationContextOnSendRule, and then press ENTER.
  6. Right-click AssumeUDPEncapsulationContextOnSendRule, and then click Modify.
  7. In the Value Data box, type one of the following values:
    • 0
      A value of 0 (zero) configures Windows so that it cannot establish security associations with servers that are located behind NAT devices. This is the default value.
    • 1
      A value of 1 configures Windows so that it can establish security associations with servers that are located behind NAT devices.
    • 2
      A value of 2 configures Windows so that it can establish security associations when both the server and the Windows Vista-based or Windows Server 2008-based VPN client computer are behind NAT devices.
  8. Click OK, and then exit Registry Editor.
  9. Restart the computer.