IP Addresses in Azure

Private IP addresses in Azure 

Private IP addresses enable communication among resources in Azure.

Resources can be:

• In a virtual network.
• Azure Services such as:
  • Virtual machine network interfaces
  • Internal load balancers (ILBs)
  • Application gateways
• On-premise network via a VPN gateway or ExpressRoute circuit.

Private IP addresses enable communication with these resources without the usage of a public IP address.

IP Address Assignment

Private IP addresses are assigned to resources from the address range of the virtual network subnet where the resource is by Azure.

Azure reserves the first 4 addresses in each subnet address range. The addresses can not be allocated to resources. IP addresses within the address range of a subnet can only be assigned to one resource at a time.

There are two ways through which a private IP address is given:

• Dynamic: Azure assigns the next available unreserved or unassigned IP address in the address range of the subnet. For example, Azure assigns 10.0.0.8 to a new resource, if addresses 10.0.0.3-10.0.0.7 are already assigned to other resources.
• Dynamic is the default allocation method. Once assigned, dynamic IP addresses are resolved if a network interface is:
  • Deleted
  • within the same virtual network, reassigned to a different subnet.
  • The allocation method is switched to static, and a different IP address is mentioned.

By default, Azure allocates the previous dynamically assigned address as the static address when the user changes the allocation method from dynamic to static.

• Static: The user selects and assigns any unreserved or unassigned IP address in the subnet's address range of the subnet.
• For example, an address range of a subnet is 10.0.0.0/16, and addresses 10.0.0.3-10.0.0.6 are assigned to other resources. The user can assign any address between 10.0.0.7 - 10.0.255.254. Static addresses are only given if a network interface is deleted.
• Azure offers the static IP as the dynamic IP when the allocation method is changed. The reassignment takes place even if the address is not the next available in the subnet. The address changes if the network interface is assigned to another subnet.
• To assign the network interface to another subnet, the user needs to change the allocation method from static to dynamic. He needs to assign the network interface to a different subnet, then change the allocation method back to static, then assign an IP address from the new subnet's address range.

Internal DNS hostname resolution (for Virtual Machines)

By default, Azure Virtual Machines are configured with Azure-managed DNS servers. Users can configure custom DNS servers explicitly. These DNS servers offer internal name resolution for virtual machines that are within the same virtual network.

A mapping for the hostname to a private IP address of the virtual machine is added to the Azure-managed DNS servers.

A hostname is mapped to the primary IP of the main network interface if a virtual machine has:

• Multiple IP Addresses
• Multiple Network Interfaces
• Both

Azure-managed DNS which are configured with virtual machines resolve the hostnames within the same virtual network. 

Frequently Asked Questions 

What is an IP address?

The IP address is short for the internet protocol address. It is an identifying figure that is related to a specific computer or computer network. When connected to the internet, the IP address enables the computers to pass information.

What is DNS?  

The Domain Name System (DNS) resolves domain names into IP addresses, which browsers use to load internet pages. Each device connected to the internet has its own IP address, that is used by other devices to locate the device.

Mention a few features of the public IP addresses. 

Some features of the public IP addresses are:

• The Global Tier enables a public IP address to be used with cross-region load balancers.
• The Internet Routing Preference option optimizes the time that traffic spends on the Microsoft network, decreasing the egress data transfer cost. 

Conclusion

This article extensively discusses the concept of IP Addresses in Azure in detail.

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