What is IP address 168.63.129.16?

IP address 168.63.129.16 is a virtual public IP address that is used to facilitate a communication channel to Azure platform resources. Customers can define any address space for their private virtual network in Azure. Therefore, the Azure platform resources must be presented as a unique public IP address. This virtual public IP address facilitates the following things:

  • Enables the VM Agent to communicate with the Azure platform to signal that it is in a "Ready" state.
  • Enables communication with the DNS virtual server to provide filtered name resolution to the resources (such as VM) that do not have a custom DNS server. This filtering makes sure that customers can resolve only the hostnames of their resources.
  • Enables health probes from Azure load balancer to determine the health state of VMs.
  • Enables the VM to obtain a dynamic IP address from the DHCP service in Azure.
  • Enables Guest Agent heartbeat messages for the PaaS role.

Scope of IP address 168.63.129.16

The public IP address 168.63.129.16 is used in all regions and all national clouds. This special public IP address is owned by Microsoft and will not change. It is allowed by the default network security group rule. We recommend that you allow this IP address in any local firewall policies. The communication between this special IP address and the resources is safe because only the internal Azure platform can source a message from this IP address. If this address is blocked, unexpected behavior can occur in a variety of scenarios.

Azure Load Balancer health probes originates from this IP address. If you block this IP address, your probes will fail.

In a non-virtual network scenario (Classic), the health probe is sourced from a private IP and 168.63.129.16 is not used.

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