Network lost connection after enabling Proxmox Mail Gateway and encountering DNS issues

[ngocbi]

Hi everyone,

I recently installed and enabled Proxmox Mail Gateway, but right after doing so, my network lost connection. When I try to ping google.com from a client machine in the network, it returns the error: "Ping request could not find host google.com. Please check the name and try again."

I have configured to route from a DrayTek router into Proxmox Mail Gateway via port 25, and then from PMG, it forwards to a Mail Exchange server within the same network segment. However, I’m unable to resolve the DNS issue after enabling Proxmox Mail Gateway.

Has anyone experienced a similar issue or can help me troubleshoot and resolve this? What should I do to ensure DNS and network functionality after deploying Proxmox Mail Gateway?

Thank you very much!

 

[sw-omit]

I fail to be able to see how activating the PMG would block dns, so let's check a few basic things first:

If your client is a windows PC, please open a commandprompt and do the following commands and post the output of it (photo is fine)

nslookup google.com
nslookup google.com 8.8.8.8
nslookup google.com 1.1.1.1
ping 8.8.8.8 -n 2
ping google.com -n 2

 

[ngocbi]

I fail to be able to see how activating the PMG would block dns, so let's check a few basic things first:

If your client is a windows PC, please open a commandprompt and do the following commands and post the output of it (photo is fine)

nslookup google.com
nslookup google.com 8.8.8.8
nslookup google.com 1.1.1.1
ping 8.8.8.8 -n 2
ping google.com -n 2

Hi Omit.
I NAT PMG port 25 for a while then lost network connection. Ping test will appear as shown below. You help me. Thank you.

 

[sw-omit]

It looks like internet-connections itself is working, as a ping to 8.8.8.8 is working, but it looks like DNS specifically is being blocked, as requests to that same IP are not working.
Have you tried restarting your draytek-router?

Also, it might be this (problem and possible solution):
https://serverfault.com/questions/654169/any-suggestions-on-why-dns-is-failing-over-draytek-2820

 

[ngocbi]

It looks like internet-connections itself is working, as a ping to 8.8.8.8 is working, but it looks like DNS specifically is being blocked, as requests to that same IP are not working.
Have you tried restarting your draytek-router?

Also, it might be this (problem and possible solution):
https://serverfault.com/questions/654169/any-suggestions-on-why-dns-is-failing-over-draytek-2820

I updated the firmware and rebooted but the problem persists. I have to turn off NAT PMG and switch to Server Mail again for it to work.

 

[sw-omit]

Did you also try to disable the "UDP flood defense" as suggested in that topic above?

And just to confirm, the only change you're making is to change the target-IP in your port-forward? (Not creating a new/different one or anything else)

Still, it's more likely that the draytek itself is to blame, since that is your "gateway" to the internet, and it seems to be selectively blocking or allowing some of the traffic going out, judging by the difference in ping and nslookup. (Although why it is when you enable PMG I'm still very confused about)

 

[ngocbi]

Did you also try to disable the "UDP flood defense" as suggested in that topic above?

And just to confirm, the only change you're making is to change the target-IP in your port-forward? (Not creating a new/different one or anything else)

Still, it's more likely that the draytek itself is to blame, since that is your "gateway" to the internet, and it seems to be selectively blocking or allowing some of the traffic going out, judging by the difference in ping and nslookup. (Although why it is when you enable PMG I'm still very confused about)

Yes I did but it didn't get any better.