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I'm trying to setup a public DNS server in Azure IaaS. I have successfully created the server, installed DNS and configured my authoritative zones. I have configured endpoints for both TCP and UDP ports 53. Windows firewall is currently off for testing purposes.

When I do an nslookup, specifying localhost, everything works fine. However, when I do an nslookup specifying the public IP Address , the request times out.

What steps should I take to diagnose the issue?

Wayne Yang
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S. Walker
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    What does your NSG look like? – joeqwerty Sep 06 '17 at 01:13
  • Inbound endpoints for 3389, TCP 53 and UDP 53 are open. – S. Walker Sep 06 '17 at 01:14
  • I can telnet to port 53 from the internet – S. Walker Sep 06 '17 at 01:14
  • So rDNS (reverse DNS) is not working. Have you setup your rDNS Looup Zone? See: https://technet.microsoft.com/en-us/library/cc961414.aspx – SamAndrew81 Sep 06 '17 at 01:59
  • @S.Walker, I think you need an SOA in your rDNS Lookup Zone and your issue will be resolved. – SamAndrew81 Sep 06 '17 at 02:04
  • What does a reverse lookup zone do for me if I am on another network? For example, how will a reverse lookup zone on the authoritative server help if i am on my personal computer? I will try though. – S. Walker Sep 06 '17 at 02:13
  • You said if you specify localhost it works, if you specify the public IP it fails. So, I assume you did both of these on the server? You also said you can telnet to port 53 from the internet. So, what happens when you do an nslookup specifying the public IP from an internet connected computer? Technicalities of Azure aside, it is not uncommon to not be able to connect to yourself on a public IP if the network is NATd in anyway. – Appleoddity Sep 06 '17 at 06:00

3 Answers3

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If I understand correctly , you nslookup your VM’s Public IP address though your DNS server and get the error ”DNS request timed out”. I suggest you can take following steps to troubleshtoot:

  1. Ensure there is no 3rd party firewall software on your VM.
  2. Ensure that you had setup your DNS Server correctly.
  3. You can use the Debug function of nslookup to check hwo nslookup on your machine to find it whether a network issue.

Exmaple: 

C:\Administrator>nslookup
                >set debug
                >[Your test IP address]
  1. If your network configuration is correct, this issue may caused by the nslookup Tools problem. You can use 'nosearch' and ‘srchlist=’

Exmaple:

C:/>nslookup -nosearch <Test IP address>

C:/>nslookup -srchlist= <Test IP address>

If all above does not help you resolve this issue, you can offer me more details about How you test, the How did you setup your DNS server and Error information so that I can troubleshoot it clearly.

Notice: you can also to refer to this link to setup public DNS Server on Azure VM.

Wayne Yang
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I presume that the public IP is set on Azure firewall not on the VMs vNIC. nslookup, when running on the VM itself, cannot go to the outside network and then loop back to the VM if network is not correctly configured. Does it work if you execute it on another indipendent host (neither in Azure nor in your LAN)?

MaCae
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I ended up resolving this issue by removing the Network Security Group and re-assigning it to the Network Card.

S. Walker
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