ERROR: MTU Size Error with VPN View The Full Article Sometimes when connecting to the VPN, an error occurs referencing a problem with MTU size. Below is a guide to fix this problem to ensure the Anyconnect VPN client connects correctly. 1 Ensure that the AnyConnect program is not running then open the start menu and go to All ProgramsAccessories then rightclick on Command Prompt and select Run as Administrator 2 From the command prompt window, type the following command and press enter. netsh interface ipv6 show subinterfaces It will display a list. Under Interface you will see an entry for each network device including a loopback which is fake device. Take a note of the interface name by the one that have a lot of Bytes In and Bytes Out. They will likely say Local Area Connection or Wireless Interface. 3 Type the following command into the command prompt window where LOCAL AREA CONNECTION matches the name from the previous step. If there were multiple names listed, run this command for each of them. Note the quotation marks around the interface name need to be entered into the command. netsh interface ipv6 set subinterface LOCAL AREA CONNECTION mtu1500 storepersistent 4 To ensure that all connections have the correct MTU size we will run both of the commands in the previous steps for the ipv4 interface as well. To do this, run the following command: netsh interface ipv4 show subinterfaces This will show a list of connections with the ipv4 interface. Make sure to take note of all the names of the connections listed and then run the following command for each of them where LOCAL AREA CONNECTION matches the name of each connection. netsh interface ipv4 set subinterface LOCAL AREA CONNECTION mtu1500 storepersistent 5 Once this process is completed, all connections will have the proper MTU size and AnyConnect will be able to establish a VPN connection to Clemsonand39s campus.