VBoxNetNAT refuses connections for port-forwarding after one day or two

[Steve Sun]

I started using NAT network since several months ago. My setup is quite simple: Linux host (CentOS 7.3) running two Windows 7 guests. All guests use NAT network with static IPs. Port-forwarding is configured on the NAT network.

NAT network: 10.0.2.1/24
Guest 1 IP: 10.0.2.11
Guest 2 IP: 10.0.2.12
Forward 1: <host_ip>:5911 <--> 10.0.0.11:5900
Forward 2: <host_ip>:5912 <--> 10.0.0.12:5900

Everything work great, until, after some time, maybe one day or two, connections to host port 2211/2212 got rejected. One solution I find is to restart guest OS, sometime more than once, until the port-forward is normal again.

During the whole process (good --> bad --> restart --> good again), I can see that port 2211/2212 are always bound by process /usr/lib/virtualbox/VBoxNetNAT, and its pid never changed.

When connections are rejected on port 5911 and 5912, guests can connect to each other's 5900 port, which rules out guests failures.

Another observation is, sometimes the restart of one guest OS can solve problems for all guests.

[Valery Ushakov]

When it gets into that state, can you make outbound connections from guests to the outside world?