Cisco VPN Client Error 51 – Open Your Firewall

Annoying!  How Annoying!

This very simple, very typical error message, but it is so hard to find a quick solution.

Symptoms: You are starting a Cisco VPN Client and immediately you are getting this error message:

Error 51: Unable to communicate with the VPN subsystem.
Please make sure that you have at least one network interface that is currently active
and has an IP address and start this application again.

Most of Internet discussions on this error message revolve around MAC OS.  But this error I was able to fix on Windows XP.

Quickly – What to Do?

Quickly – Open your firewall.  Each firewall solution is different, but find, where to open your firewall settings.

On McAfee Enterprise client I found a list of blocked applications under “View Application List”:

Each firewall interface looks and behaves differently.  Here is a procedure for McAfee SaaS Endpoint Protection 5.2.0.	I selected those two VPN lines and clicked on Approve button.  You might need to add them to your application list.

I hope this article will save you several painful minutes at the control board.  Especially, if you are in a  hurry to connect, and  start a” real-problem-solving”.

Note about PPTP connection (Windows Built-In VPN)

If you are connecting to multiple clients networks, you might have several different VPN solutions installed on your laptop.  This trick bellow applies to Windows own built-in VPN software.

If you need to connect to a client VPN from work, and you are using Windows PPTP (build-in VPN), you need to open TCP port 1723 on your local or corporate Firewall.  See Microsoft article “How to configure a connection to a VPN in Windows XP”  (http://support.microsoft.com/kb/314076).

To open this port on McAfee SaaS Endpoint Protection 5.2.0 you need to go to Action Menu –> Set Connection Type –> Custom –> Add Approved Service and add/specify TCP port 1723.

Do not Move Cisco Shortcuts

Shortly after Cisco VPN install I moved the icon group away from the Start Menu – Programs folder.  Later I’ve noticed that Cisco VPN is trying to repair or install something on every restart.  It turns out that you shouldn’t move those icons.  If you did, move them back to resolve the issue.