Starting with VirtualBox 4.1, VirtualBox ships a new network filter driver that utilizes Solaris 11's Crossbow functionality. By default, this new driver is installed for Solaris 11 hosts (builds 159 and above) that has support for it.
To force installation of the older STREAMS based network filter driver, execute as root the following command before installing the VirtualBox package:
touch /etc/vboxinst_vboxflt
To force installation of the Crossbow based network filter driver, execute as root the following command before installing the VirtualBox package:
touch /etc/vboxinst_vboxbow
To check which driver is currently being used by VirtualBox, execute:
modinfo | grep vbox
If the output contains "vboxbow", it indicates VirtualBox is using the Crossbow network filter driver, while the name "vboxflt" indicates usage of the older STREAMS network filter.