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Cisco VPN Client on OSX

I’ve had a few problems with the Cisco VPN Client for Mac OS X  (release 4.9.01 (100) ) recently.
I’d get intermittent “Error 51: Unable to contact the VPN subsystem” when opening the VPNClient appliaction.
Some times a reboot would fix it, sometimes it wouldn’t.
I can’t reliably reproduce it either, sometimes coming out of sleep breaks it, sometimes restarting breaks it.

I think I’ve worked out how to resolve this now from a command line:

Firstly take the fw0 interface down and bring it up again:
Sudo ifconfig fw0 down
Sudo ifconfig fw0 up

Then restart the VPN SS:
Sudo /System/Library/StartupItems/CiscoVPN/CiscoVPN restart

That has resolved it for me the last 5 times it happened, without needing to reboot again.

Hope that helps someone else out.


  1. Hey Mate. I also have to use the cisco 3000 vpn client at the moment. I didnt know about the first 2 terminal commands, but I have been using the last command on its own with equal success. It may save you a little time. Of course the next logical step is to turn it into either a script or an automator task.

  2. […] at Ian Talks Tech my friend Macca recently posted a fix for the “Error 51 : Unable to communicate with the VPN […]

  3. Macca says:

    I found that just restarting the VPN subsystem didn’t solve the issue – I’m guessing that there is something funky in iptables that is causing this, certainly for me.

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