I have 2 Windows Server 2019 VMs. Both of them run Hamachi to allow them to access an off-site PC behind a firewall and NAT. When I restart the servers everyone is able to connect to the server's HTTP site.
After a while (ranging from a few hours to 6 or so), I get clients complaining that they can't access the website on the server. At that point, they can't even ping the server. All ping requests fail completely.
But from my internet connection, I can access the websites and ping the server. On one VM, I have 2 public IPs, on the one IP the ping would work, but on the other, the ping would fail from this location that lost connection to the sites.
Then when I simply Disable the Hamachi NIC, all the pings start working and the sites are accessible. Then when I Enable the adaptor again, the client continues to have access. After an hour or so, the client starts having the same problem.
Things I have tried
I've disabled the firewall, to see if the firewall is involved, but this didn't do anything. In all cases, the Firewall is already set to allow pings and HTTP ports. So this is no surprise.
I've completely uninstalled Hamachi and removed the user settings, and installed it again. Once installed the problem starts again.
As long as I keep Hamachi "offline" (this also disables the NIC) the problem stays away, as soon as I enable Hamachi the problem returns after a while.
The location from where the traffic is blocked are not always the same.
I've restarted the 2 VMs last night, the one is stable today, but the other one started having problems again.
Confusing Parts
The traffic is only blocked on my public IP. This is not the Hamachi IP. I've got the understanding that Hamachi work as any other VPN, by simply creating a virtual NIC, and any traffic through it are encrypted and send to the VPN server over the public IP/NIC. In the case of Hamachi, it could be P2P where it sends it to the other Hamachi clients. Why would Hamachi have an influence on any other traffic than its own port's traffic?
Why would only some traffic be blocked from some IPs?
Why is this only a problem on Windows Server 2019! I have used this setup on Windows 2008 R2 up to Windows Server 2012 with nothing like this happening?
Question
What can I look at to figure this one out? What tools can I use? (I don't have access to any routers or "man in the middle" hardware to "see" what is happening on the LAN side)
Edit (2021-07-04): Workaround
I have worked out that this problem started after I enabled Windows Server 2019's built-in VPN server. I disabled/removed the Windows Server 2019 VPN, and the problem went away.
I have the exact same setup on the Windows Server 2012 VM and there it is working up to this day still fine. So it is only the Windows Server 2019 VPN server that is interfering with Hamachi.
I still don't have a fix for how to concurrently run Hamachi and Windows Server 2019 VPN together.
Real-World Application
Hamachi is used to set up a tunnel to an offsite backup server, behind a NAT. The Windows VPN is used to create a P2P VPN connection to the VM to allow for RDP, as a public IP RDP is being bruted all the time.
