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VPN: Error is "mtu size too small"


You may get this error when you are trying to use the software VPN on an IPv6 network. The software will work on these networks, but you must use the IPv4 protocol settings and disable IPv6. This issue primarily affects Windows users.

Follow these steps to turn off IPv6 protocol in the Cisco Anyconnect VPN client.

  1. Select the Start button and then select the Control Panel
  2. Under the Network and Internet category, select the Network and Sharing Center
  3. In the left-hand panel select Change Adapter Settings.
  4. Right click on the "Cisco AnyConnect Secure Mobility Client Connection" and select "Properties"
  5. Uncheck the "Internet Protocol Version 6 (TCP/IP v6)" box and click OK.