Comment # 9 on bug 1027742 from jean-christophe baptiste

Frankly, I am not understanding your setup either.

Cross guest communication is not the purpose, and network-manager is not the
topic (either on the host or the guest). Your test may not work for a variety
of reasons, including firewalling, and it is too complicated for the purpose of
this report.

Here would be a quick test :

1. Fire up a simple guest with a vboxnet0 interface and start a listener (after
obtaining a DCHP address with dhclient or network-manager) :

netcat -l -p9999 -v

2. From the host, try :

netcat <guest IP> 9999 -v

If the hosts gets an IP address in vboxnet0 and can reach the guest over the
192.168.56.0/24 network, then problem solved.

Otherwise, still an issue.