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As briefly mentioned in Sectioná3.7.5, “Network settings”, VirtualBox provides up to four virtual PCI Ethernet cards for each virtual machine. For each such card, you can individually select
the hardware that will be virtualized as well as
the virtualization mode that the virtual card will be operating in with respect to your physical networking hardware on the host.
For each card, you can individually select what kind of hardware will be presented to the virtual machine. VirtualBox can virtualize the following four types of networking hardware:
AMD PCNet PCI II;
AMD PCNet FAST III (the default);
Intel PRO/1000 MT Desktop;
Intel PRO/1000 T Server.
The PCNet FAST III is the default because it is supported by nearly all operating systems out of the box, as well as the GNU GRUB boot manager. However, support for the Intel PRO/1000 MT type was added with VirtualBox 1.6 because Microsoft dropped support for the AMD PCNet cards with Windows Vista, and Vista guests therefore have no networking without manual driver installation otherwise. See Sectioná4.2.4, “Windows Vista networking” for details. The Server variant of the Intel PRO/1000 card was added with VirtualBox 1.6.2 because this one is recognized by Windows XP guests without additional driver installation.
VirtualBox has limited support for so-called jumbo frames, i.e. networking packets with more than 1500 bytes of data, provided that you use the Intel card virtualization and Host Interface Networking. In other words, jumbo frames are not supported in NAT mode or with the AMD networking devices; in those cases, jumbo packets will silently be dropped for both the transmit and the receive direction. Guest operating systems trying to use this feature will observe this as a packet loss, which may lead to unexpected application behavior in the guest. This does not cause problems with guest operating systems in their default configuration, as jumbo frames need to be explicitly enabled.