Azure VM DNS not using the correct order

Chau Le 96

Hi Team,

We have a strange situation here. We moved an Azure VM to an ISOLATED network...

We RE-IP'ed the VM

The VM now has DNS servers configured that are in the production network

We added a new DNS server and moved it to the TOP of the DNS list (VNET settings).

However the VM is NOT using the primary DNS, it keeps using 2ndary and 3rd DNS.

Doesn't look like the setting is applying when we add a new DNS server to the VM and move to the top of the list...

Where can we check about this?

GitaraniSharma-MSFT 48,011 Reputation points Microsoft Employee

2022-02-03T10:34:04.67+00:00
Hello @Chau Le ,

Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well.

As mentioned in this doc, DNS server lists are used in the order that they are specified. They do not work as a round-robin setup. If the first DNS server in the list can be reached, the client uses that DNS server, regardless of whether the DNS server is functioning properly.

I would request you to check the below:

Could you please check if the primary DNS server is reachable?

What is the DNS server assigned to the network interface of the VM - Is it inheriting the DNS settings from virtual network or using custom DNS servers? If it is inheriting the DNS settings from virtual network, then it is fine but if it is using custom DNS server, make sure that primary DNS server is at the top of the list.

Did you restart the VMs that are connected to the virtual network, so they are assigned the new DNS server settings? VMs continue to use their current DNS settings until they are restarted.

Refer :
https://learn.microsoft.com/en-us/azure/virtual-network/manage-virtual-network#change-dns-servers
https://learn.microsoft.com/en-us/azure/virtual-network/virtual-network-network-interface#change-dns-servers

Regards,
Gita
Chau Le 96 Reputation points

2022-02-03T15:56:29.737+00:00

Hello

Yes the DNS server is reachable and just fine - we confirmed with ping and nslookup
For some reason it ignores the primary DNS and keeps trying to use the 2nd DNS
Yes we also did reboot for the changes to happen and we confirm using ipconfig /all
For this one we used "Custom DNS"
GitaraniSharma-MSFT 48,011 Reputation points Microsoft Employee

2022-02-04T08:52:37.123+00:00

Hello @Chau Le ,

What is DNS server setting in the NIC of the VM? Could you please confirm if it is inheriting the DNS settings from virtual network or using custom DNS servers? If it is inheriting the DNS settings from virtual network, then it is fine but if it is using custom DNS server, make sure that primary DNS server is at the top of the list.

Refer : https://learn.microsoft.com/en-us/azure/virtual-network/virtual-network-network-interface#change-dns-servers

Also, could you please confirm if you have configured any DNS settings manually within the VM guest OS?

Regards,
Gita
GitaraniSharma-MSFT 48,011 Reputation points Microsoft Employee

2022-02-09T06:03:15.933+00:00

Hello @Chau Le ,

I'm following up on my above comment. Could you please provide an update on this issue?

Regards,
Gita
GitaraniSharma-MSFT 48,011 Reputation points Microsoft Employee

2022-02-14T04:44:29.937+00:00

Hello @Chau Le , do you have any further updates on this issue?

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Azure VM DNS not using the correct order