VPN Won't Stay Connected Over AT&T LTE Home Internet

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If you find that the University's Cisco AnyConnect VPN client isn't staying connected reliably and you have AT&T's LTE home Internet service, you may need to adjust a network setting on your computer to fix this problem.

AT&T LTE Modem

Before You Begin:

  1. Right-click the Windows flag in the bottom left of your screen
  2. Select "Network Connections"
  3. Under Change your network settings click Change adapter options
  4. Make note of the name of your wireless adapter. It may be called "Wi-Fi" or "Wireless Network Connection"

Create the Fix File (a technician can do this):

  1. Click in the Search box in Windows and type "Notepad" without the quotes
  2. Click to open the Notepad program
  3. In Notepad cut and paste the following text:
  4. netsh interface ipv4 set subinterface "Wireless Network Connection" mtu=1304 store=persistent 
  5. Change the name in quotes after the word subinterface to match the name of your wireless adapter.
  6. Click File at the top of Notepad and choose Save
  7. Navigate to your Desktop and click the "Save as type" option and select "All Files (*.*)"
  8. Click in the "File name" box and type "attfix.bat" without the quotes
  9. Click Save

Activate the Fix File (the customer does this):

  1. Minimize any open windows and look for the attfix.bat file on your desktop
  2. Right-click and choose "Run as administrator"
  3. Click YES in the permission box that appears
  4. A black window should appear with the results of your command:
    • If the results are Ok. hit spacebar to continue
    • If the results are "The filename, directory name, or volume label syntax is incorrect." then check the name of the wireless adapter in the command. It may need to be adjusted
    • If the results are "The requested operation requires elevation (Run as administrator)." then make sure to right-click and run the attfix.bat file as administrator
  5. Hit spacebar to dismiss the window and make any necessary changes to the attfix.bat file before starting at Step 2.

Try your Cisco AnyConnect VPN again. It should now connect through your AT&T LTE service and stay connected.


This process can be accomplished using Teams Screensharing with the help of the customer. The technician cannot activate an Administrator-level window or program over a remote screensharing session.  The same MTU settings should work for an Ethernet adapter if the customer is wired directly to their AT&T LTE modem. Just be sure to use the name of whichever network adapter is in use.

Undoing this Change:

To restore the network adapter to its original setting, change the MTU value from 1304 to 1500 in the attfix.bat file above, save it, and then run it as administrator. That will restore the default setting.

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Article ID: 1628
Tue 4/7/20 3:28 PM
Tue 5/14/24 11:28 AM