Hi All, We have some RHEL 7.9, SUSE sles 15 and Windows 2016 servers in our environment where we recently changed the DNS servers in Azure vnet. After DNS change Windows servers get update automatically. Linux servers don't get the update. I found this https://learn.microsoft.com/en-us/troubleshoot/azure/virtual-machines/linux/custom-dns-configuration-for-azure-linux-vms?tabs=RHEL . Following this I ran "sudo netconfig update" and "sudo systemctl restart wicked.service". It change the records in SUSE servers. But RHEL servers is not getting the updates after running "sudo systemctl restart NetworkManager". I see the old DNS only /etc/resolv.conf. Then I checked /run/NetworkManager/resolv.conf it's having the correct DNS. And I ran "nmcli dev show" it's also having the correct ones. Should I need to link /run/NetworkManger/resolv.conf and /etc/resolv.conf or should I leave them as it is?

Hi Arunprasad K , Welcome to the Microsoft Q&A Platform. Thank you for posting your query here. As per my understanding, linking /run/NetworkManager/resolv.conf and /etc/resolv.conf is generally may not be necessary if your system is already managing DNS resolution correctly. I have reproduced your scenario and tried to update the dns of RHEL 9.4 server by following the steps in the documentation mentioned and it worked. The initial configuration of the /etc/resolv.conf file in an Azure Linux VM is as shown Configured custom DNS servers at the Azure virtual network or network interface level. Restart the NetworkManager service,and then check the /etc/resolv.conf file. This file reflects the new DNS settings configured in the VNet Can you please confirm if you have followed above steps and can you please confirm If dhclient is responsible for DNS management or NetworkManager to manage DNS. To check this open the NetworkManager.conf file and check [main] dns=default. If the comment is helpful, please click "upvote" to let us know. Let me know if you have any further queries!

How to update the DNS records on Azure RHEL VM?

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Mounika Reddy Anumandla 2,180 Reputation points Microsoft Vendor

2025-01-27T07:08:12.2166667+00:00

Hi Arunprasad K,

Welcome to the Microsoft Q&A Platform. Thank you for posting your query here.

As per my understanding, linking /run/NetworkManager/resolv.conf and /etc/resolv.conf is generally may not be necessary if your system is already managing DNS resolution correctly.
I have reproduced your scenario and tried to update the dns of RHEL 9.4 server by following the steps in the documentation mentioned and it worked.

The initial configuration of the /etc/resolv.conf file in an Azure Linux VM is as shown

Configured custom DNS servers at the Azure virtual network or network interface level.

Restart the NetworkManager service,and then check the /etc/resolv.conf file. This file reflects the new DNS settings configured in the VNet

Can you please confirm if you have followed above steps and can you please confirm If dhclient is responsible for DNS management or NetworkManager to manage DNS.

To check this open the NetworkManager.conf file and check [main] dns=default.

If the comment is helpful, please click "upvote" to let us know.

Let me know if you have any further queries!
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1 person found this answer helpful.
Mounika Reddy Anumandla 2,180 Reputation points Microsoft Vendor

2025-01-29T03:58:11.0166667+00:00

Hi Arunprasad K,

Thank you for providing additional information. I have checked my NetworkManager.conf file and below is the entry.

sudo vim /etc/NetworkManager/NetworkManager.conf

Since I have dhclient=dhclient, dhclient it means that NetworkManager is being configured to use dhclient as the DHCP client for that system.

On the other hand, an empty NetworkManager.conf simply means the system is relying on NetworkManager's default configuration, which may or may not explicitly mention dhclient. Without additional configurations in the NetworkManager.conf file, NetworkManager will operate with its default settings. It will use dhclient for DHCP (as specified). Other settings like DNS management (unless configured elsewhere) will fall back to NetworkManager’s defaults or other tools like dhclient or /etc/resolve.conf.

In the absence of NetworkManager and systemd, you can manually check the contents of this file: cat /etc/resolv.conf

Hope the information helps!

Let me know if you have any further queries!

If the information provided is helpful, please click "Accept answer". Accepted answer will help other community members navigate to the appropriate solutions.

Arunprasad K 20 Reputation points

2025-01-29T07:03:55.27+00:00

Hi @Mounika Reddy Anumandla

I didn't own those server. That's why I am little hesitant to put any screenshots. Let me give you screenshots of another server with same issue. In this server Network Manager is running and etc/resolve.conf is not saying "Generated by dhclient-script " as well.

Please see content of my /etc/NetworkManager/NetworkManager.conf.

Content of /etc/resolv.conf before restarting the Network Manager.

#domain nameserver 10.155.17.69 nameserver 10.5.2.7 nameserver 139.69.73.5 nameserver 10.5.2.8 nameserver 139.69.73.6

I issue I am currently dealing with is that restarting the Network Manager is not updating the /etc/resolv.conf from the Azure Vnet DNS servers list.

My DNS

Content of /etc/resolv.conf after restarting the Network Manager.

#domain nameserver 10.155.17.69 nameserver 10.5.2.7 nameserver 139.69.73.5 nameserver 10.5.2.8 nameserver 139.69.73.6

Please know how can I update this DNS records. Once again thanks for your time.

Mounika Reddy Anumandla 2,180 Reputation points Microsoft Vendor

2025-01-29T08:00:14.04+00:00

Hi Arunprasad K,

Can you try rebooting the virtual machine and see if the DNS record gets updated.

And also, please note: In Azure, you can set custom DNS servers at the virtual network level or the network interface level. If you set custom DNS servers at the network interface level, it will override the custom DNS server's configuration in the virtual network. https://learn.microsoft.com/en-us/troubleshoot/azure/virtual-machines/linux/custom-dns-configuration-for-azure-linux-vms?tabs=RHEL

Let me know if you have any further queries!

Mounika Reddy Anumandla 2,180 Reputation points Microsoft Vendor

2025-01-30T05:40:52.8366667+00:00

Hi Arunprasad K,
Just wanted to check the status of this case. Please let us know if you would like further assistance.

Meanwhile, if the reply is helpful to you, please click "Upvote" on the post to let us know.

Arunprasad K 20 Reputation points

2025-01-30T08:50:02.6866667+00:00

Hi @Mounika Reddy Anumandla

I tried restarting also, nothing changed. I also tired manually adding dns=default in NetworkManager and restarting it, no change happened. I think I need to work on dhclient-script. Please let me know your comments.

Mounika Reddy Anumandla 2,180 Reputation points Microsoft Vendor

2025-01-30T15:36:37.35+00:00

Hi Arunprasad K,

I would like to know if you have checked the if you set custom DNS servers at the network interface level. Azure DHCP assigns the DNS server to the NIC within the VM operating system. The NIC can inherit the settings from the virtual network, or use its own unique settings that override the setting for the virtual network. For more information about name resolution settings for a NIC, see Name resolution for virtual machines.https://learn.microsoft.com/en-us/azure/virtual-network/virtual-network-network-interface?tabs=azure-portal#add-or-change-dns-servers

It has overwritten the DNS Configuration set at the vnet level.

Hope this helps!

Please let me know if you have verified the above. Let me know if you have any further queries!

Arunprasad K 20 Reputation points

2025-01-30T15:50:11.45+00:00

Hi @Mounika Reddy Anumandla

I checked and it's inherit from v-net in our configuration.

Mounika Reddy Anumandla 2,180 Reputation points Microsoft Vendor

2025-02-03T02:28:32.59+00:00

Hi Arunprasad K,

Thank you for providing more information.

The above-mentioned document works well for RHEL 8.X/9.X. The issue you are facing might be due the version differences.

Let me know if you have any further queries!

Arunprasad K 20 Reputation points

2025-02-04T11:07:23.27+00:00

Hi @Mounika Reddy Anumandla

Yes, you are correct. Our Linux VM is RHEL 7.9. I am trying to update the DHCP with the right DNS servers. It is not possible to deploy custom DHCP server in Azure like provisioning a custom DNS server, is it? It's automatically managed by Azure.

Mounika Reddy Anumandla 2,180 Reputation points Microsoft Vendor

2025-02-04T11:32:33.3533333+00:00

Hi Arunprasad K,

Azure natively provides DHCP services to all virtual networks created within an Azure subscription. The DHCP service is automatically enabled for each virtual network.

Previously, different workarounds were proposed to customers who required custom DHCP solutions in Azure due to the lack of support for such solutions.
Reference: https://techcommunity.microsoft.com/blog/azurenetworkingblog/custom-dhcp-support-in-azure/4089674

Hope the answer is helpful, please click "Accept Answer" and "Upvote it."

Mounika Reddy Anumandla 2,180 Reputation points Microsoft Vendor

2025-02-05T07:31:00.4866667+00:00

Hi Arunprasad K,

Just checking in to see if you had a chance to review my comment on your question. Please let us know if it was helpful and feel free to reach out if you have any further queries.

If you found the information useful, please click "Accept Answer" and "Upvote" on the post as a token of appreciation.

Thank You.

anashetty 2,040 Reputation points Microsoft Vendor

2025-02-06T02:20:21.7033333+00:00

Hi Arunprasad K,

I am checking the status of this case. Please let us know if you would like further assistance. Meanwhile, if the reply is helpful to you, please accept answer and click "Upvote" on the post to let us know.

Thank you for your understanding and patience!

Arunprasad K 20 Reputation points

2025-02-06T18:01:44.3233333+00:00

Hi @Mounika Reddy Anumandla ,

I am still trying to overcome the issue with dhclient. I tried to run renew, it's showing some crazy numbers. I am good with Network Manager output for the DNS records. Thank you so much for your time.

Mounika Reddy Anumandla 2,180 Reputation points Microsoft Vendor

2025-02-07T02:06:41.3966667+00:00

Hi Arunprasad K,

As per my understanding, Azure do not provide support for custom DHCP solutions although some work arounds are provided in the above document suggested. The DHCP service is automatically enabled for each virtual network.
I request you to kindly open another case with details of what you actually would like to do and your expectation with right tags. The team will be able to assist you better!

If the answer is helpful, please consider accepting the answer and click "upvote" as a token of appreciation.
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How to update the DNS records on Azure RHEL VM?

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