You have the Azure virtual network named VNet1 that contains a subnet named Subnet1. Subnet1 contains three Azure virtual machines. Each virtual machine has a public IP address. The virtual machines host several applications that are accessible over port 443 to users on the Internet. Your on-premises network has a site-to-site VPN connection to VNet1. You discover that the virtual machines can be accessed by using the Remote Desktop Protocol (RDP) from the Internet and from the on-premises network. You need to prevent RDP access to the virtual machines from the Internet, unless the RDP connection is established from the on-premises network. The solution must ensure that all the applications can still be accessed by the Internet users. What should you do? 

Answer options:

A. Modify the address space of the local network gateway
B. Create a deny rule in a network security group (NSG) that is linked to Subnet1
C. Remove the public IP addresses from the virtual machines
D. Modify the address space of Subnet1

B

You can use a site-to-site VPN to connect your on-premises network to an Azure virtual network. Users on your on-premises network connect by using the RDP or SSH protocol over the site-to-site VPN connection. You don`t have to allow direct RDP or SSH access over the internet. Reference: https://docs.microsoft.com/en-us/azure/security/fundamentals/network-best-practices