You must have a data or wireless internet connection in order to receive a push. However, with the Duo Mobile app on your phone, you can tap the green key button to receive a 6-digit passcode.
This option will work even without an internet connection and/or cellular service.
2FA on Cisco AnyConnect VPN
On the Cisco AnyConnect VPN, you will type this information into the password field on Cisco AnyConnect VPN.
For example: password,725495
2FA on CAS
On the CAS 2FA page, you will select Enter a Passcode and type the passcode from the Duo Mobile app.