Why is there a “reddog” DNS Suffix for my VM’s?

Depending on how you are using Azure to host your virtual machines (VM’s), there will most likely be the need for communication between the different VM’s or services. Although this communication is done using IP addresses, it’s still much simpler to use names that can be easily remembered and do not change. Along with the computer name, there is the add-on of the DNS suffix. When you deploy a new server and join it to an Active Directory domain, the primary DNS suffix of the computer’s fully qualified domain name (FQDN), is the same as the name of the Active Directory domain name. You probably wouldn’t assume any difference from a VM running in Azure… Well, have you noticed the additional DNS suffix “reddog.microsoft.com” in your VM’s network configuration?

Let me provide some background information on how the Azure virtual network (VNet) works. By default, every Azure VM automatically receives an IP address from the subnet they are connected to. An Azure provided DHCP service is taking care of the assignment of those dynamic IP addresses. The same procedure also applies to VM’s which have to be configured for static IP address. To phrase it differently, there is no requirement to configure anything within the operating system (OS); everything happens from the Azure-side. This design brings some advantages as the design allows the entire network configuration to be managed from the Azure Portal or using PowerShell. The Azure DHCP server then creates a DHCP reservation for the required static IP addresses.

Along with the IP address assignment, Azure also provides internal name resolution for VMs that reside within the same VNet. To enable name resolution for non-domain-joined machines, an internal DNS suffix called *.internal.cloudapp.net is provided. This DNS suffix enables hostname resolution, as all hostname records are in the internal.cloudapp.net zone. In the case where the servers are part of an Active Directory domain, this DNS suffix is not applied, to avoid interferences with the customers DNS architectures. However, there is still a DNS suffix being applied. The mysterious reddog.microsoft.com DNS suffix; which is used as a non-functioning placeholder. Unfortunately, the Azure-created DNS suffix names cannot be modified. However, this is by-design, and no further actions are required

The official Azure Docs provide helpful details on how the name resolution in Azure works, and also how static IP addresses have to be configured. Moving forward, Azure DNS will also be available for private zones.

The Azure DNS Private Zone feature is currently in Public Preview (as of April 2018). This preview version is provided without a service level agreement, and it is not recommended for production workloads. Certain features might not be supported or might have constrained capabilities.

There’s just one more thing…

Ever wondered why the DNS suffix is called “reddog”? Interestingly, “Red Dog” was the codename used by Microsoft before the public cloud service launched in 2008 as Microsoft Azure.