Users may get the “A VPN connection will not be established” while trying to connect to the corporate VPN using Cisco AnyConnect.
The below error message is somewhat misleading, it points to the internet/cable provider. however, there is an easy fix that works all the time.
“The VPN client was unable to successfully verify the ip forwarding table modification. A VPN connection will not be established”
This is also documented that it is a known bug by Cisco
Cisco Bug: CSCvf16310 – IPv6 Addresses intermittently assigned to AnyConnect clients
Known Affected Releases
Below is the screenshot of the error message you may get.
Here is what you will need to to.
- Go to “start” “run” and “cmd” and type the command “ncpa.cpl” to launch the network connections window.
2. This is just a quick way to get to your network connections screen and you can also launch the network connection window by navigating to the control panel.
3. Right-click the connection and choose properties and un-check the “Internet Protocol Version 6(TCP/IPv6)”
Now right-click the Cisco AnyConnect client and choose “Network Repair” and this should fix the problem.
Try connecting again and this time it will and should work, the reason behind this is that your adapter chooses IPV6 which may a preferred path by the service provider.
Thanks for reading and I hope it provided some value