Azure Virtual Network IP Addressing

Introduction to IP Addressing in Azure Virtual Networks

Azure Virtual Network (VNet) provides a flexible and robust platform for deploying and managing your cloud resources. A crucial aspect of VNet configuration is IP addressing. This document will guide you through the concepts and considerations for assigning IP addresses to resources within your Azure VNets.

IP Address Types

Azure supports two primary types of IP addresses for resources within a VNet:

• Private IP Addresses: These are used for communication within your VNet and with other connected VNets or on-premises networks. Private IP addresses are not routable on the internet. Azure allocates a private IP address from the address space you define for your VNet.
• Public IP Addresses: These are used to communicate with resources on the internet. Resources like Virtual Machines, Load Balancers, and NAT Gateways can be assigned public IP addresses.

Private IP Address Allocation

When you deploy a resource that supports IP addressing (like a Virtual Machine) into a subnet within a VNet, Azure assigns it a private IP address. You have two options for how this assignment occurs:

• Dynamic Allocation: In this mode, Azure assigns an available IP address from the subnet to the resource. When the resource is stopped (deallocated), the IP address is released back into the subnet's pool and may be reassigned to another resource later. This is the default method.
• Static Allocation: With static allocation, you specify a particular IP address within the subnet's range for the resource. This IP address remains assigned to the resource until you explicitly change it or remove the resource. Static IP addresses are crucial for scenarios where predictable IP addresses are required, such as for domain controllers or services that rely on specific IP bindings.

Subnet Considerations

Every subnet within a VNet is allocated a block of IP addresses. Azure reserves the first four and the last IP address in each subnet for protocol conformance. For example, a subnet with the address range 10.0.1.0/24 (256 addresses) has 251 usable IP addresses.

Public IP Address Assignment

Public IP addresses in Azure can be assigned to various resources to enable internet connectivity. There are two SKU types for Public IP addresses:

• Basic SKU: Offers core public IP address functionality. These are not associated with Availability Zones and have specific limitations.
• Standard SKU: Provides enhanced features, including Availability Zone support, faster routing, and more robust security features. Standard SKU is generally recommended for production workloads.

Public IP addresses can also be allocated dynamically or statically, similar to private IP addresses.

Use Cases for Public IPs

• Directly exposing a Virtual Machine to the internet.
• Assigning to a Load Balancer for distributing incoming internet traffic.
• Enabling outbound internet connectivity for resources that only have private IPs using NAT Gateways.

IP Addressing Best Practices

• Plan Your Address Space: Carefully design your VNet and subnet address spaces to avoid conflicts and ensure scalability.
• Use Private IPs by Default: Only assign public IP addresses when internet connectivity is strictly necessary for a resource.
• Leverage Static IPs for Critical Resources: Use static private IP addresses for services that require a fixed IP address.
• Consider Address Overlap: If peering VNets or connecting to on-premises networks, ensure no overlapping IP address ranges exist.
• Utilize NAT Gateways for Outbound Connectivity: For resources that only need outbound internet access, NAT Gateways provide a scalable and secure solution using public IP addresses without directly exposing the resources.