6 Virtual networking 6.4 Bridged networking With bridged networking, VirtualBox uses a device driver on your host system that filters data from your physical network adapter. This driver is therefore called a “net filter” driver. This allows VirtualBox to intercept data from the physical network and inject data into it, effectively creating a new network interface in software. When a guest is using such a new software inter- face, it looks to the host system as though the guest were physically connected to the interface using a network cable: the host can send data to the guest through that interface and receive data from it. This means that you can set up routing or bridging between the guest and the rest of your network. For this to work, VirtualBox needs a device driver on your host system. The way bridged net- working works has been completely rewritten with VirtualBox 2.0 and 2.1, depending on the host operating system. From the user perspective, the main difference is that complex configuration is no longer necessary on any of the supported host operating systems.3 Note: Even though TAP is no longer necessary on Linux with bridged networking, you can still use TAP interfaces for certain advanced setups, since you can connect a VM to any host interface – which could also be a TAP interface. To enable bridged networking, all you need to do is to open the Settings dialog of a virtual machine, go to the “Network” page and select “Bridged network” in the drop down list for the “Attached to” field. Finally, select desired host interface from the list at the bottom of the page, which contains the physical network interfaces of your systems. On a typical MacBook, for example, this will allow you to select between “en1: AirPort” (which is the wireless interface) and “en0: Ethernet”, which represents the interface with a network cable. Depending on your host operating system, the following limitations should be kept in mind: • On Macintosh hosts, functionality is limited when using AirPort (the Mac’s wireless net- working) for bridged networking. Currently, VirtualBox supports only IPv4 over AirPort. For other protocols such as IPv6 and IPX, you must choose a wired interface. • On Linux hosts, functionality is limited when using wireless interfaces for bridged net- working. Currently, VirtualBox supports only IPv4 over wireless. For other protocols such as IPv6 and IPX, you must choose a wired interface. Also, setting the MTU to less than 1500 bytes on wired interfaces provided by the sky2 driver on the Marvell Yukon II EC Ultra Ethernet NIC is known to cause packet losses under certain conditions. • On Solaris hosts, there is no support for using wireless interfaces. Filtering guest traffic using IPFilter is also not completely supported due to technical restrictions of the Solaris networking subsystem. These issues would be addressed in a future release of Solaris 11. With VirtualBox 2.0.4 and above, it is possible to use Crossbow Virtual Network Interfaces (VNICs) with bridged networking, but with the following caveats: – A VNIC cannot be shared between multiple guest network interfaces, i.e. each guest network interface must have its own, exclusive VNIC. – The VNIC and the guest network interface that uses the VNIC must be assigned iden- tical MAC addresses. 3For Mac OS X and Solaris hosts, net filter drivers were already added in VirtualBox 2.0 (as initial support for Host Interface Networking on these platforms). With VirtualBox 2.1, net filter drivers were also added for the Windows and Linux hosts, replacing the mechanisms previously present in VirtualBox for those platforms especially on Linux, the earlier method required creating TAP interfaces and bridges, which was complex and varied from one distribution to the next. None of this is necessary anymore. Bridged network was formerly called “Host Interface Networking” and has been renamed with version 2.2 without any change in functionality. 87