Let's start with the question: What is an NVA? The answer consists of several parts as follows:

• An NVA is usually a third-party solution and is distributed over the Azure Marketplace
• An NVA is offered in the form of a VM
• An NVA is part of its own VNet subnet and stands apart from the rest of the VNet

Examples of using a NVA are:

• Firewall
• Intrusion detection/intrusion prevention
• Management of security risks
• Application control
• Network-based detection of anomalies
• Web filtering
• Virus protection
• Bot protection

One example of using an NVA in a VNet architecture, is to set up a DMZ using firewall solutions, such as offered by Barracuda, Palo Alto, Fortinet or Sophos.