virtualbox bridged adaptor works only guest->host but not host->guest

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http://serverfault.com – I have virtualbox 4.1 on a ubuntu 12.04 host. On my host I have a virtual interface eth0:1 configurend as I have a few virtual machines using bridged adapters, configured in the net which I can reach (ping, ssh, ...) from my host via the virtual interface. Now I installed an ubuntu server 12.04 in a virtual box, again using bridged adapter, but I can not reach that host. The strange thing is I can reach my host from my guest, e.g. ssh from guest to host works well. So I am sure the virtual cable is pluged. But my host does not even know about the mac of that virtual machin (HowTos)