The Virtualization Room

Jul 2 2008   12:09PM GMT

Dissecting bridged-network functionality on Sun xVM VirtualBox for Windows

Rick Vanover Rick Vanover Profile: Rick Vanover


If you have not noticed, I have been on a Sun xVM VirtualBox kick recently. I think it is beneficial to virtualization administrators and managers to be familiar with at least two hypervisors — so why not learn more about xVM?

VirtualBox has a smooth interface for a version 1 release, but the one area that would require the most adjustment is the virtual networking. Let’s take a closer look at network functionality in VirtualBox.

Virtual networking on VirtualBox has a few key differences that VMware users would need to develop an understanding about before fully utilizing the potential of the product. The first difference is the concept of the virtual networking hardware. VirtualBox allows a virtual machine (VM) to have one of four network interface cards virtually assigned. These are the AMD PCNet PCI II, AMD PCNet FAST III, Intel Pro/1000 T and the Intel Pro/1000 MT. This array of virtual adapters allows a VM to have broad support for multiple operating systems, but the corresponding bridging functionality may make network administrators a little uneasy.

Spanning Tree
For Windows systems, VirtualBox uses a spanning tree algorithm from the native operating system bridging that may cause issues on systems with multiple interfaces in managed network environments. The bridged network functionality puts the VMs on the same physical network as the VirtualBox host system. In this fashion, a VM would be able to retrieve a DHCP network from the physical network and interact as if it were placed on the network parallel to the host. Windows XP and Server 2003 products’ bridging functionality is explained on the TechNet website.

Another key difference is that in order for a VM to use the bridged network is the addition of a bridging interface. Adding an interface is fairly straight forward with the use of the VBoxManage command. The following command would add a bridging interface named “VM-Bridge”:

VBoxManage createhostif "VM-Bridge"

Once this command is completed, the VM-Bridge interface is now present in the network connections inventory of the Windows control panel. Then a VM can be configured to use bridged networking with the newly created interface as shown in the figure below:

VirtualBox Bridging

At this point, the VM-Bridge interface can transparently place the VM on the same network as the host when the Windows bridged connections are correctly configured. Note also that in the network configuration you can fully edit the MAC address of the VM. While exceptionally convenient, this can introduce risk for some environments and situations.

Now that we have gone through a quick look at VirtualBox’s implementation of bridging network connections for VMs, I would have to nudge the VMware products to be a little more seamless in the category of bridged networking. By having the VMware bridge protocol binding used instead of a separate series of adapters for the same purpose, VMware’s bridging fits better for most environments.

Make no mistake, the comprehensive VirtualBox networking implementation is fully competitive with VMware. There is much more to the VirtualBox networking implementation available for download in the online user guide in section 6.

3  Comments on this Post

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  • Chris Melville
    Maybe I just dont understand something, but I find VirtualBox's networking to be far inferior to VMware's, so far. Say you are a Windows house and have a multihomed Windows server (using RRAS and/or ISA), and you want to reimplement it as a VM under a Windows "hypervisor" (eg. WS2003 with VirtualBox), working exactly as before in terms of it's network presence. You can't. There is no way to map each physical NIC to a virtual counterpart inside your server VM. But you can do this easily with VMWare. And, in principle, with VirtualBox+Linux as your "hypervisor". Score one (a big one imho, for Windows shops) to VMWare!
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  • Rick Vanover
    I agree with you that VMware's networking is better, it clearly is. You can put the VMs up transparently on the network, it requires the bridging, however with VirtualBox. As for the host being multi-homed, I think that puts VirtualBox in the "one or the other category" as for Windows hosts with 1.6.2 or 1.6.4, I don't believe you can put two bridges in place.
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  • James
    Heres an odd thing, VMware had host-only network mode where you could access the hosts system easilly. With virtualbox I've been able to add a vmware interface but this is less than idea. Is there any way to have a bridged network yet still get access to the host ? Going the NAT route and running CIFS over it is painfully slow with 1.6.4..
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