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I have got an on-premise AD-DC which I am trying to extend to Azure. This server hosts the DNS services as well. I created a VNet on Azure and set its DNS server property to point to my on-premise server. Now from the Vms within the Vnet I can ping my on-premise server and domain join with it. However when I look into the DNS setting section for the VM using the command Get-AzureRmNetworkInterface I still see .fx.cloudapp.net. I am not sure why this is not set to reddog.microsoft.com which should be the case as per the documentation. Any help highly appreciated.

Update on infrastructure details:
1. A Hub network on Azure connected to on-premise over S2S (in future to be converted to Express Route)
2. The Hub network hosts an Azure VM which is hosting ADDC/DNS replicated with on-premise AD. This VM is domain joined with on-premise AD This also hosts a windows jump box
3. The Hub network has its VNet DNS setting pointing to the Azure ADDC/DNS VM IP
4. There is a spoke network connected to the hub over VNet peering which is hosting SAP VMs. The Spoke network is having its DNS setting pointing to the Azure ADDC/DNS VM IP.

Current Issue: None of the VMs on hub/spoke network are showing reddog.microsoft.com as its DNS. Instead some of the VMs are showing .fx.cloudapp.net while others are showing blank when I use Get-AzureRmNetworkInterface command

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I guess you have seen this doc.

When you are using Azure-provided name resolution, Azure Dynamic Host Configuration Protocol (DHCP) provides an internal DNS suffix (.internal.cloudapp.net) to each VM. This suffix enables hostname resolution because the hostname records are in the internal.cloudapp.net zone. When you are using your own name resolution solution, this suffix is not supplied to VMs because it interferes with other DNS architectures (like domain-joined scenarios). Instead, Azure provides a non-functioning placeholder (reddog.microsoft.com).

By default, reddog.microsoft.com will be the specific DNS suffix for the ethernet adapter for Azure VM. When a VM joins an AD domain however the primary DNS suffix will automatically be changed for the IP configuration to that of the AD domain which overrides others and adapter DNS suffix ignored.

In this case, even though you see reddog.microsoft.com as the DNS suffix for the adapter as long as the IP configuration primary suffix is that of the domain there is no further action needed. Make sure you joined the domain and added the AD domain suffix correctly. Also, you can restart your Azure VM to take the domain changing effect. You can refer to this similar case.

  • Thank you for your response. I had already searched and found the two links you mentioned - but that doesn't help my case. My problem is I donot see reddog.microsoft.com for the domain joined VM. It still shows .internal.cloudapp.net. In between I created a number of Windows and Linux VMs in the VNet, but these are not domain joined. The VNet points to my custom AD DNS server. Since I am not using Azure DHCP I was expecting my machines to get reddog.Microsoft.com as DNS suffix, however I see some of the VMs having .internal.cloudapp.net while others are showing blank. This is really puzzling. – shaswata pal Oct 23 '18 at 7:44
  • By default, if VMs have not joined a domain, you only see the .internal.cloudapp.net suffix, Can you check the DNS servers of the network interface? Once you specify the custom AD DNS server of the vNet, the VMs inside the vNet should restart. – Nancy Xiong Oct 23 '18 at 8:04
  • I checked the DNS Entry for NIC for one of the machines. It is set to "Inherit from virtual network" . There is no entry under Applied DNS servers. As per documentation "When you are using your own name resolution solution, this suffix is not supplied to VMs because it interferes with other DNS architectures (like domain-joined scenarios). Instead, Azure provides a non-functioning placeholder (reddog.microsoft.com)." => I thought by setting the DNS server at VNet level I am indicating that I am not using Azure DNS but using my own name resolution mechanism. Is this not true then? – shaswata pal Oct 23 '18 at 8:16
  • The nic setting is correct, you can only set the DNS setting on the vnet level. How do you connect the on-premise net to your Azure vnet? via VPN? I mean what is custom AD DNS server? public or private IP of DNS server? – Nancy Xiong Oct 23 '18 at 8:22
  • I have updated the original question to add more details on the infrastructure. Please let me know if this answers your question. Thanks again for all your help – shaswata pal Oct 23 '18 at 8:32

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