Azure Subnet (VNet)

A Subnet is a subdivision of an Azure Virtual Network (VNet). Azure subnets are used to segment and organize IP address spaces within a VNet. They allow you to logically isolate and group resources based on specific networking requirements or security considerations. Each Azure VNet can be divided into one or more subnets, and resources deployed within the same subnet can communicate with each other directly, without the need for any additional configuration.

Here are the key points to understand about Azure subnets:

1. **Address Space:** When you create an Azure VNet, you must define an IP address range, also known as the address space, for the VNet. This address space represents the range of IP addresses that can be used within the VNet. Subnets are then created within this address space.

2. **Subnet Address Prefix:** A subnet is associated with a specific address prefix, which is a subset of the VNet's address space. Each subnet's address prefix must be a contiguous range of IP addresses that falls within the VNet's address space.

3. **Resource Isolation:** Subnets provide resource isolation within a VNet. By placing resources in different subnets, you can control the communication between resources based on your network security and access control requirements.

4. **Default Subnet:** When you create a new VNet, Azure automatically creates a default subnet with the entire VNet's address space. You can further divide this default subnet into smaller subnets based on your needs.

5. **Network Security Group (NSG) Association:** Each subnet can be associated with a Network Security Group (NSG). NSGs allow you to control inbound and outbound network traffic to and from resources within the subnet.

6. **Service Endpoints:** Subnets can be configured with service endpoints, allowing resources within the subnet to access specific Azure services (e.g., Azure Storage or Azure SQL Database) directly without using public internet access.

7. **Azure Firewall and Network Virtual Appliances:** Subnets can be used to deploy Azure Firewall or third-party network virtual appliances, which provide advanced network security and routing capabilities for resources within the subnet.

8. **Peering:** VNets can be peered together, allowing resources in one VNet to communicate with resources in another VNet. Subnets within the peered VNets can communicate with each other as well.

By effectively designing and utilizing subnets within an Azure Virtual Network, you can achieve better network organization, resource isolation, and enhanced security for your Azure resources. Properly defining subnets based on your application's needs and security requirements is crucial for establishing a robust and well-structured network infrastructure in Azure.