Explanation
The Trusted IPs feature of Azure Multi-Factor Authentication is used by administrators of a managed or federated tenant. The feature bypasses two-step verification for users who sign in from the company intranet.
The feature is available with the full version of Azure Multi-Factor Authentication, and not the free version for administrators.
References:
https://docs.microsoft.com/en-us/azure/active-directory/authentication/howto-mfa-mfasettings#trusted-ips