Only A records that are automatically registered by the service are supported (no manual registration of records)Īs you can see from the above the negatives far outweigh the positives.You’re stuck with the namespace assigned to the VNet.Solution doesn’t scale with multiple VNets.VMs within a VNet can resolve each other’s IP addresses out of the box.DNS service provided by Azure automatically scales.No need to provision your own DNS servers and worry about high availability or scalability.Let’s sum up the positives and negatives of Azure-provided DNS. Take note that if you wanted to resolve these host names from on-premises you could use a similar conditional forwarder pattern. You can see as the number of VNets increases the scalability of this solution quickly breaks down. Notes the DHCP Server and DNS Server settings in the ipconfig output of the azuredns vm shown below. Azure has assigned the a namespace of r0b5mqxog0hu5nbrf150v3iuuh.bx. to the VNet. Two Windows Server 2016 VMs have been created named azuredns and azuredns1 with the IP addresses 10.101.0.4 and 10.101.0.5. I’ve assigned the CIDR block of 10.101.0.0/16 and created a single subnet assigned the 10.101.0.0/24 block. Let’s look at an example with a single VNet. and each VM in the VNet can resolve IP addresses of one another. This namespace is pushed to the machine via DHCP Option 15 thus each VM has an fully qualified domain name of. Each time you spin up a virtual network Azure assigns it a unique private DNS namespace using the format. This brings us to the first option for DNS resolution in Azure, Azure-provided name resolution. If you run a route print on a Windows machine, you can see this route defined in the routing table of the VM. Traffic is routed to and from this virtual IP address through the subnet gateway. Fun fact, some geolocation services will report this IP as being based out of Hong Kong and I’m sure you can imagine how that works when something like a WAF is in place with regional IP restrictions. The address is static and is the same for any VNet you create in every Azure region. It provides functionality such as virtual machine (VM) agent communication of the VM’s ready state, health state, enables the VM to obtain an IP address via DHCP, and you guessed it, enables the VM to leverage Azure DNS services. This public IP address is owned by Microsoft and is presented as a virtual IP address serving as a communication channel to the host node for a number of platform resources. If you’ve ever done anything even basic in Azure, you’ve probably run into this address or used it without knowing it. If any of those are unfamiliar to you, take some time to review the basics then come back to this post.īefore we jump into the DNS options in Azure, I first want to cover the 168.63.129.16 address. I’m going to go into this assuming you have a basic knowledge of DNS and understand the namespaces, various record types, forward and reverse lookup zones, recursive and iterative queries, DNS forwarding and conditional forwarding, and other core DNS concepts. Specifically, we’re going to look at the options for private DNS in Microsoft Azure and what the positives and negatives are of each pattern. Yes folks, we’re going to cover Domain Naming System (DNS). In this series of posts I’m going to talk about a technology, that while old, still provides a critical foundational service.
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