[closed] VM only accessible from VM hosts

I have setup 2 UCS 4.3 servers (both migrated from 4.2). First one is PDC with Univention Virtual Machine Manager, the second one is a UCS member server and hosting KVM.

When I create a new VM via UVMM on the KVM host I cannot access this VM from the network. The VM can access the network without problems. I have tested with Windows 10 Pro and LinuxMint 18 VM Guest.
Network setup of the VM is briged to br0.
The VM has its own IP on the subnet. I can ping the IP. But all other services do not respond.
From the KVM host I can SSH into the Linux VM. I have checked the fingerprint to verify I am really on the VM.

Disabling firewalls on host and/or guest did not have any effect. Neither on Linux nor Windows.
Therefor I assume that KVM nwfilter might not be configured correctly.

I have invested 2 full days on investigation already and I am somewhat desperate now.



if I understand you correctly, the VM is bridged into your subnet, any connections (to subnet IPs outside the KVM host) initiated by the VM are fully functional, but initiating communication from outside the KVM host to the VM fails apart from ping.

What does ssh -vv towards the VM say? Test both directions with nc, use tcpdump on both hosts while performing the tests.

Aaaarrrrrgh, shame on me :frowning:
Routing of a sub-net wasn’t configured correctly in the VM. So it did not know how to send packets back to the client calling.