2FA/MFA, Configure Duo Mobile for Salesforce

Salesforce requires multifactor authentication (MFA/2FA) to sign in to the system. Two authenticator apps are supported: Salesforce Authenticator and Duo Mobile, both free apps in the Apple App Store and Google Play Store. The University of Illinois uses Duo Mobile for most MFA/2FA security, and it will likely be the most familiar and comfortable to use. Follow this guide to configure Duo Mobile for use with Salesforce.

Sign into Salesforce
When prompted to connect Salesforce Authenticator, select "Choose Another Verification Method"
Select "Use verification codes from an authenticator app" and click "Continue"
Open "Duo Mobile" on your mobile device (phone, tablet)
Tap "+ Add"
Select "Use QR code"
Scan the QR code presented on the Salesforce page
Confirm that the account name looks correct and tap "Save"
You’ll receive a confirmation that your account is linked
You’ll then be prompted to enter your Salesforce password. Once you do this, you’ll receive confirmation that your password is saved and ready to be used. 
Return to Salesforce. The prompt to verify your identity should include your Salesforce login name.  
Return to the Duo Mobile app on your mobile device to find the 6-digit code displayed underneath the new account you’ve added. 
On the Salesforce page, type the confirmation code and choose "Connect"