Network security typically falls into three areas:

• Secure/manage traffic flow between applications, their tiers, between different environments, and other services
• Secure/manage traffic flow between users and the application
• Secure/manage traffic flow between the applications and the Internet

Azure Network security is about building a defense in depth approach.

The usual type of services that need to be protected from the network perspective, can be categorized into those types:

• IaaS services connected to subnets
• PaaS services connected to subnets
• Public facing PaaS services with security lockdown
• Public facing PaaS services with TLS access restrictions