An Azure Network Security Group (NSG) is a fundamental security tool in Azure used to filter network traffic.
Understanding Azure NSGs is crucial for securing your cloud resources. An Azure Network Security Group (NSG) is a core component of Azure's security fabric. It provides a way to control the flow of network traffic to and from resources deployed within your Azure Virtual Network (VNet).
Core Functionality
At its core, an NSG is effectively a set of access control rules you assign to an Azure resource. These rules determine whether to permit or deny network traffic based on several factors.
- Traffic Filtering: Leveraging an NSG, you can filter traffic to and from Azure resources that you have commissioned on an Azure Virtual Network (VNet). This includes filtering traffic between resources within the same VNet, as well as traffic between the VNet and external networks (like the internet or on-premises networks).
- Rule Definition: Each rule specifies:
- Source and destination IP addresses or ranges.
- Source and destination ports.
- The protocol (TCP, UDP, or *).
- The direction of traffic (Inbound or Outbound).
- An action (Allow or Deny).
- A priority number to determine rule processing order.
Where NSGs are Applied
NSGs are highly flexible and can be associated with different levels within your virtual network:
- Subnets: Applying an NSG to a subnet means the rules affect all resources within that subnet.
- Network Interfaces (NICs): Applying an NSG directly to a resource's network interface means the rules affect only that specific resource.
When an NSG is applied to both a subnet and a NIC, the rules are evaluated cumulatively to determine the final traffic flow.
Practical Benefits
Using Azure NSGs allows you to:
- Enhance Security: Control exactly which traffic is allowed to reach your applications and servers, reducing the attack surface.
- Isolate Resources: Create security boundaries between different types of resources or applications within your VNet.
- Implement Compliance: Meet regulatory requirements by enforcing specific network access policies.
In summary, an Azure NSG is a powerful and essential tool for implementing robust network security within your Azure environment by providing granular control over network traffic through a configurable set of access control rules.
