Chapter 6. Virtual Networking

Table of Contents

6.1. Virtual Networking Hardware
6.2. Introduction to Networking Modes
6.3. Network Address Translation (NAT)
6.3.1. Configuring Port Forwarding with NAT
6.3.2. PXE Booting with NAT
6.3.3. NAT Limitations
6.4. Network Address Translation Service
6.5. Bridged Networking
6.6. Internal Networking
6.7. Host-Only Networking
6.8. UDP Tunnel Networking
6.9. VDE Networking
6.10. Limiting Bandwidth for Network Input/Output
6.11. Improving Network Performance

As mentioned in Section 3.9, “Network Settings”, Oracle VM VirtualBox provides up to eight virtual PCI Ethernet cards for each virtual machine. For each such card, you can individually select the following:

Four of the network cards can be configured in the Network section of the Settings dialog in the graphical user interface of Oracle VM VirtualBox. You can configure all eight network cards on the command line using VBoxManage modifyvm. See Section 8.8, “VBoxManage modifyvm”.

This chapter explains the various networking settings in more detail.

6.1. Virtual Networking Hardware

For each card, you can individually select what kind of hardware will be presented to the virtual machine. Oracle VM VirtualBox can virtualize the following types of networking hardware:

  • AMD PCNet PCI II (Am79C970A)

  • AMD PCNet FAST III (Am79C973), the default setting

  • Intel PRO/1000 MT Desktop (82540EM)

  • Intel PRO/1000 T Server (82543GC)

  • Intel PRO/1000 MT Server (82545EM)

  • Paravirtualized network adapter (virtio-net)

The PCNet FAST III is the default because it is supported by nearly all operating systems, as well as by the GNU GRUB boot manager. As an exception, the Intel PRO/1000 family adapters are chosen for some guest operating system types that no longer ship with drivers for the PCNet card, such as Windows Vista.

The Intel PRO/1000 MT Desktop type works with Windows Vista and later versions. The T Server variant of the Intel PRO/1000 card is recognized by Windows XP guests without additional driver installation. The MT Server variant facilitates OVF imports from other platforms.

The Paravirtualized network adapter (virtio-net) is special. If you select this adapter, then Oracle VM VirtualBox does not virtualize common networking hardware that is supported by common guest operating systems. Instead, Oracle VM VirtualBox expects a special software interface for virtualized environments to be provided by the guest, thus avoiding the complexity of emulating networking hardware and improving network performance. Oracle VM VirtualBox provides support for the industry-standard virtio networking drivers, which are part of the open source KVM project.

The virtio networking drivers are available for the following guest operating systems:

  • Linux kernels version 2.6.25 or later can be configured to provide virtio support. Some distributions have also back-ported virtio to older kernels.

  • For Windows 2000, XP, and Vista, virtio drivers can be downloaded and installed from the KVM project web page:

    http://www.linux-kvm.org/page/WindowsGuestDrivers.

Oracle VM VirtualBox also has limited support for jumbo frames. These are networking packets with more than 1500 bytes of data, provided that you use the Intel card virtualization and bridged networking. Jumbo frames are not supported 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.

6.2. Introduction to Networking Modes

Each of the networking adapters can be separately configured to operate in one of the following modes:

  • Not attached. In this mode, Oracle VM VirtualBox reports to the guest that a network card is present, but that there is no connection. This is as if no Ethernet cable was plugged into the card. Using this mode, it is possible to "pull" the virtual Ethernet cable and disrupt the connection, which can be useful to inform a guest operating system that no network connection is available and enforce a reconfiguration.

  • Network Address Translation (NAT). If all you want is to browse the Web, download files, and view email inside the guest, then this default mode should be sufficient for you, and you can skip the rest of this section. Please note that there are certain limitations when using Windows file sharing. See Section 6.3.3, “NAT Limitations”.

  • NAT Network. A NAT network is a type of internal network that allows outbound connections. See Section 6.4, “Network Address Translation Service”.

  • Bridged networking. This is for more advanced networking needs, such as network simulations and running servers in a guest. When enabled, Oracle VM VirtualBox connects to one of your installed network cards and exchanges network packets directly, circumventing your host operating system's network stack.

  • Internal networking. This can be used to create a different kind of software-based network which is visible to selected virtual machines, but not to applications running on the host or to the outside world.

  • Host-only networking. This can be used to create a network containing the host and a set of virtual machines, without the need for the host's physical network interface. Instead, a virtual network interface, similar to a loopback interface, is created on the host, providing connectivity among virtual machines and the host.

  • Generic networking. Rarely used modes which share the same generic network interface, by allowing the user to select a driver which can be included with Oracle VM VirtualBox or be distributed in an extension pack.

    The following sub-modes are available:

    • UDP Tunnel: Used to interconnect virtual machines running on different hosts directly, easily, and transparently, over an existing network infrastructure.

    • VDE (Virtual Distributed Ethernet) networking: Used to connect to a Virtual Distributed Ethernet switch on a Linux or a FreeBSD host. At the moment this option requires compilation of Oracle VM VirtualBox from sources, as the Oracle packages do not include it.

The following table provides an overview of the most important networking modes.

Table 6.1. Overview of Networking Modes

Mode

VM→Host

VM←Host

VM1↔VM2

VM→Net/LAN

VM←Net/LAN

Host-only

+

+

+

Internal

+

Bridged

+

+

+

+

+

NAT

+

Port forward

+

Port forward

NATservice

+

Port forward

+

+

Port forward

The following sections describe the available network modes in more detail.

6.3. Network Address Translation (NAT)

Network Address Translation (NAT) is the simplest way of accessing an external network from a virtual machine. Usually, it does not require any configuration on the host network and guest system. For this reason, it is the default networking mode in Oracle VM VirtualBox.

A virtual machine with NAT enabled acts much like a real computer that connects to the Internet through a router. The router, in this case, is the Oracle VM VirtualBox networking engine, which maps traffic from and to the virtual machine transparently. In Oracle VM VirtualBox this router is placed between each virtual machine and the host. This separation maximizes security since by default virtual machines cannot talk to each other.

The disadvantage of NAT mode is that, much like a private network behind a router, the virtual machine is invisible and unreachable from the outside internet. You cannot run a server this way unless you set up port forwarding. See Section 6.3.1, “Configuring Port Forwarding with NAT”.

The network frames sent out by the guest operating system are received by Oracle VM VirtualBox's NAT engine, which extracts the TCP/IP data and resends it using the host operating system. To an application on the host, or to another computer on the same network as the host, it looks like the data was sent by the Oracle VM VirtualBox application on the host, using an IP address belonging to the host. Oracle VM VirtualBox listens for replies to the packages sent, and repacks and resends them to the guest machine on its private network.

The virtual machine receives its network address and configuration on the private network from a DHCP server integrated into Oracle VM VirtualBox. The IP address thus assigned to the virtual machine is usually on a completely different network than the host. As more than one card of a virtual machine can be set up to use NAT, the first card is connected to the private network 10.0.2.0, the second card to the network 10.0.3.0 and so on. If you need to change the guest-assigned IP range, see Section 9.10, “Fine Tuning the Oracle VM VirtualBox NAT Engine”.

6.3.1. Configuring Port Forwarding with NAT

As the virtual machine is connected to a private network internal to Oracle VM VirtualBox and invisible to the host, network services on the guest are not accessible to the host machine or to other computers on the same network. However, like a physical router, Oracle VM VirtualBox can make selected services available to the world outside the guest through port forwarding. This means that Oracle VM VirtualBox listens to certain ports on the host and resends all packets which arrive there to the guest, on the same or a different port.

To an application on the host or other physical or virtual machines on the network, it looks as though the service being proxied is actually running on the host. This also means that you cannot run the same service on the same ports on the host. However, you still gain the advantages of running the service in a virtual machine. For example, services on the host machine or on other virtual machines cannot be compromised or crashed by a vulnerability or a bug in the service, and the service can run in a different operating system than the host system.

To configure port forwarding you can use the graphical Port Forwarding editor which can be found in the Network Settings dialog for network adaptors configured to use NAT. Here, you can map host ports to guest ports to allow network traffic to be routed to a specific port in the guest.

Alternatively, the command line tool VBoxManage can be used. See Section 8.8, “VBoxManage modifyvm”.

You will need to know which ports on the guest the service uses and to decide which ports to use on the host. You may want to use the same ports on the guest and on the host. You can use any ports on the host which are not already in use by a service. For example, to set up incoming NAT connections to an ssh server in the guest, use the following command:

VBoxManage modifyvm "VM name" --natpf1 "guestssh,tcp,,2222,,22"

In the above example, all TCP traffic arriving on port 2222 on any host interface will be forwarded to port 22 in the guest. The protocol name tcp is a mandatory attribute defining which protocol should be used for forwarding, udp could also be used. The name guestssh is purely descriptive and will be auto-generated if omitted. The number after --natpf denotes the network card, as with other VBoxManage commands.

To remove this forwarding rule, use the following command:

VBoxManage modifyvm "VM name" --natpf1 delete "guestssh"

If for some reason the guest uses a static assigned IP address not leased from the built-in DHCP server, it is required to specify the guest IP when registering the forwarding rule, as follows:

VBoxManage modifyvm "VM name" --natpf1 "guestssh,tcp,,2222,10.0.2.19,22"

This example is identical to the previous one, except that the NAT engine is being told that the guest can be found at the 10.0.2.19 address.

To forward all incoming traffic from a specific host interface to the guest, specify the IP of that host interface as follows:

VBoxManage modifyvm "VM name" --natpf1 "guestssh,tcp,127.0.0.1,2222,,22"

This example forwards all TCP traffic arriving on the localhost interface at 127.0.0.1 through port 2222 to port 22 in the guest.

It is possible to configure incoming NAT connections while the VM is running, see Section 8.14, “VBoxManage controlvm”.

6.3.2. PXE Booting with NAT

PXE booting is now supported in NAT mode. The NAT DHCP server provides a boot file name of the form vmname.pxe if the directory TFTP exists in the directory where the user's VirtualBox.xml file is kept. It is the responsibility of the user to provide vmname.pxe.

6.3.3. NAT Limitations

There are some limitations of NAT mode which users should be aware of, as follows:

  • ICMP protocol limitations. Some frequently used network debugging tools, such as ping or tracerouting, rely on the ICMP protocol for sending and receiving messages. While ICMP support has been improved with Oracle VM VirtualBox 2.1, meaning ping should now work, some other tools may not work reliably.

  • Receiving of UDP broadcasts. The guest does not reliably receive UDP broadcasts. In order to save resources, it only listens for a certain amount of time after the guest has sent UDP data on a particular port. As a consequence, NetBios name resolution based on broadcasts does not always work, but WINS always works. As a workaround, you can use the numeric IP of the desired server in the \\server\share notation.

  • Some protocols are not supported. Protocols other than TCP and UDP are not supported. GRE is not supported. This means some VPN products, such as PPTP from Microsoft, cannot be used. There are other VPN products which use only TCP and UDP.

  • Forwarding host ports below 1024. On UNIX-based hosts, such as Linux, Oracle Solaris, and Mac OS X, it is not possible to bind to ports below 1024 from applications that are not run by root. As a result, if you try to configure such a port forwarding, the VM will refuse to start.

These limitations normally do not affect standard network use. But the presence of NAT has also subtle effects that may interfere with protocols that are normally working. One example is NFS, where the server is often configured to refuse connections from non-privileged ports, which are those ports not below 1024.

6.4. Network Address Translation Service

The Network Address Translation (NAT) service works in a similar way to a home router, grouping the systems using it into a network and preventing systems outside of this network from directly accessing systems inside it, but letting systems inside communicate with each other and with systems outside using TCP and UDP over IPv4 and IPv6.

A NAT service is attached to an internal network. Virtual machines which are to make use of it should be attached to that internal network. The name of internal network is chosen when the NAT service is created and the internal network will be created if it does not already exist. The following is an example command to create a NAT network:

VBoxManage natnetwork add --netname natnet1 --network "192.168.15.0/24" --enable

Here, natnet1 is the name of the internal network to be used and 192.168.15.0/24 is the network address and mask of the NAT service interface. By default in this static configuration the gateway will be assigned the address 192.168.15.1, the address following the interface address, though this is subject to change. To attach a DHCP server to the internal network, modify the example command as follows:

VBoxManage natnetwork add --netname natnet1 --network "192.168.15.0/24" --enable --dhcp on

To add a DHCP server to an existing network, use the following command:

VBoxManage natnetwork modify --netname natnet1 --dhcp on

To disable the DHCP server, use the following command:

VBoxManage natnetwork modify --netname natnet1 --dhcp off

A DHCP server provides a list of registered nameservers, but does not map servers from the 127/8 network.

To start the NAT service, use the following command:

VBoxManage natnetwork start --netname natnet1

If the network has a DHCP server attached then it will start together with the NAT network service.

To stop the NAT network service, together with any DHCP server:

VBoxManage natnetwork stop --netname natnet1

To delete the NAT network service:

VBoxManage natnetwork remove --netname natnet1

This command does not remove the DHCP server if one is enabled on the internal network.

Port-forwarding is supported, using the --port-forward-4 switch for IPv4 and --port-forward-6 for IPv6. For example:

VBoxManage natnetwork modify \
  --netname natnet1 --port-forward-4 "ssh:tcp:[]:1022:[192.168.15.5]:22"

This adds a port-forwarding rule from the host's TCP 1022 port to the port 22 on the guest with IP address 192.168.15.5. Host port, guest port and guest IP are mandatory. To delete the rule, use the following command:

VBoxManage natnetwork modify --netname natnet1 --port-forward-4 delete ssh

It is possible to bind a NAT service to specified interface. For example:

VBoxManage setextradata global "NAT/win-nat-test-0/SourceIp4" 192.168.1.185

To see the list of registered NAT networks, use the following command:

VBoxManage list natnetworks

6.5. Bridged Networking

With bridged networking, Oracle VM 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 enables Oracle VM 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 interface, 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.

Note

Even though TAP interfaces are no longer necessary on Linux for bridged networking, you can still use TAP interfaces for certain advanced setups, since you can connect a VM to any host interface.

To enable bridged networking, 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. Select a 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.

Note

Bridging to a wireless interface is done differently from bridging to a wired interface, because most wireless adapters do not support promiscuous mode. All traffic has to use the MAC address of the host's wireless adapter, and therefore Oracle VM VirtualBox needs to replace the source MAC address in the Ethernet header of an outgoing packet to make sure the reply will be sent to the host interface. When Oracle VM VirtualBox sees an incoming packet with a destination IP address that belongs to one of the virtual machine adapters it replaces the destination MAC address in the Ethernet header with the VM adapter's MAC address and passes it on. Oracle VM VirtualBox examines ARP and DHCP packets in order to learn the IP addresses of virtual machines.

Depending on your host operating system, the following limitations apply:

  • Mac OS X hosts. Functionality is limited when using AirPort, the Mac's wireless networking system, for bridged networking. Currently, Oracle VM VirtualBox supports only IPv4 and IPv6 over AirPort. For other protocols, such as IPX, you must choose a wired interface.

  • Linux hosts. Functionality is limited when using wireless interfaces for bridged networking. Currently, Oracle VM VirtualBox supports only IPv4 and IPv6 over wireless. For other protocols, such as 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.

    Some adapters strip VLAN tags in hardware. This does not allow you to use VLAN trunking between VM and the external network with pre-2.6.27 Linux kernels, or with host operating systems other than Linux.

  • Oracle 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 Oracle Solaris networking subsystem. These issues may be addressed in later releases of Oracle Solaris 11.

    On Oracle Solaris 11 hosts build 159 and above, it is possible to use Oracle Solaris Crossbow Virtual Network Interfaces (VNICs) directly with Oracle VM VirtualBox without any additional configuration other than each VNIC must be exclusive for every guest network interface.

    When using VLAN interfaces with Oracle VM VirtualBox, they must be named according to the PPA-hack naming scheme, such as e1000g513001. Otherwise, the guest may receive packets in an unexpected format.

6.6. Internal Networking

Internal Networking is similar to bridged networking in that the VM can directly communicate with the outside world. However, the outside world is limited to other VMs on the same host which connect to the same internal network.

Even though technically, everything that can be done using internal networking can also be done using bridged networking, there are security advantages with internal networking. In bridged networking mode, all traffic goes through a physical interface of the host system. It is therefore possible to attach a packet sniffer such as Wireshark to the host interface and log all traffic that goes over it. If, for any reason, you prefer two or more VMs on the same machine to communicate privately, hiding their data from both the host system and the user, bridged networking therefore is not an option.

Internal networks are created automatically as needed. There is no central configuration. Every internal network is identified simply by its name. Once there is more than one active virtual network card with the same internal network ID, the Oracle VM VirtualBox support driver will automatically wire the cards and act as a network switch. The Oracle VM VirtualBox support driver implements a complete Ethernet switch and supports both broadcast/multicast frames and promiscuous mode.

In order to attach a VM's network card to an internal network, set its networking mode to Internal Networking. There are two ways to accomplish this:

  • Use the VM's Settings dialog in the Oracle VM VirtualBox graphical user interface. In the Networking category of the settings dialog, select Internal Networking from the drop-down list of networking modes. Select the name of an existing internal network from the drop-down list below, or enter a new name into the Name field.

  • Use the command line, for example:

    VBoxManage modifyvm "VM name" --nic<x> intnet

    Optionally, you can specify a network name with the command:

    VBoxManage modifyvm "VM name" --intnet<x> "network name"

    If you do not specify a network name, the network card will be attached to the network intnet by default.

Unless you configure the virtual network cards in the guest operating systems that are participating in the internal network to use static IP addresses, you may want to use the DHCP server that is built into Oracle VM VirtualBox to manage IP addresses for the internal network. See Section 8.39, “VBoxManage dhcpserver”.

As a security measure, by default, the Linux implementation of internal networking only allows VMs running under the same user ID to establish an internal network. However, it is possible to create a shared internal networking interface, accessible by users with different user IDs.

6.7. Host-Only Networking

Host-only networking is another networking mode that was added with version 2.2 of Oracle VM VirtualBox. It can be thought of as a hybrid between the bridged and internal networking modes. As with bridged networking, the virtual machines can talk to each other and the host as if they were connected through a physical Ethernet switch. As with internal networking, a physical networking interface need not be present, and the virtual machines cannot talk to the world outside the host since they are not connected to a physical networking interface.

When host-only networking is used, Oracle VM VirtualBox creates a new software interface on the host which then appears next to your existing network interfaces. In other words, whereas with bridged networking an existing physical interface is used to attach virtual machines to, with host-only networking a new loopback interface is created on the host. And whereas with internal networking, the traffic between the virtual machines cannot be seen, the traffic on the loopback interface on the host can be intercepted.

Host-only networking is particularly useful for preconfigured virtual appliances, where multiple virtual machines are shipped together and designed to cooperate. For example, one virtual machine may contain a web server and a second one a database, and since they are intended to talk to each other, the appliance can instruct Oracle VM VirtualBox to set up a host-only network for the two. A second, bridged, network would then connect the web server to the outside world to serve data to, but the outside world cannot connect to the database.

To change a virtual machine's virtual network interface to Host Only mode, do either of the following:

  • Go to the Network page in the virtual machine's Settings dialog and select Host-Only Networking.

  • On the command line, enter VBoxManage modifyvm "VM name" --nic<x> hostonly. See Section 8.8, “VBoxManage modifyvm”.

Before you can attach a VM to a host-only network you have to create at least one host-only interface. You can use the GUI for this. Choose File, Preferences, Network, Host-Only Network, (+)Add Host-Only Network.

Alternatively, you can use the command line:

VBoxManage hostonlyif create

See Section 8.38, “VBoxManage hostonlyif”.

For host-only networking, as with internal networking, you may find the DHCP server useful that is built into Oracle VM VirtualBox. This can be enabled to then manage the IP addresses in the host-only network since otherwise you would need to configure all IP addresses statically.

  • In the Oracle VM VirtualBox graphical user interface, you can configure all these items in the global settings by choosing File, Preferences, Network. This lists all host-only networks which are presently in use. Click on the network name and then on Edit. You can then modify the adapter and DHCP settings.

  • Alternatively, you can use VBoxManage dhcpserver on the command line. See Section 8.39, “VBoxManage dhcpserver”.

Note

On Linux and Mac OS X hosts the number of host-only interfaces is limited to 128. There is no such limit for Oracle Solaris and Windows hosts.

6.8. UDP Tunnel Networking

This networking mode enables you to interconnect virtual machines running on different hosts.

Technically this is done by encapsulating Ethernet frames sent or received by the guest network card into UDP/IP datagrams, and sending them over any network available to the host.

UDP Tunnel mode has the following parameters:

  • Source UDP port: The port on which the host listens. Datagrams arriving on this port from any source address will be forwarded to the receiving part of the guest network card.

  • Destination address: IP address of the target host of the transmitted data.

  • Destination UDP port: Port number to which the transmitted data is sent.

When interconnecting two virtual machines on two different hosts, their IP addresses must be swapped. On a single host, source and destination UDP ports must be swapped.

In the following example, host 1 uses the IP address 10.0.0.1 and host 2 uses IP address 10.0.0.2. To configure using the command-line:

        VBoxManage modifyvm "VM 01 on host 1" --nic<x> generic
        VBoxManage modifyvm "VM 01 on host 1" --nicgenericdrv<x> UDPTunnel
        VBoxManage modifyvm "VM 01 on host 1" --nicproperty<x> dest=10.0.0.2
        VBoxManage modifyvm "VM 01 on host 1" --nicproperty<x> sport=10001
        VBoxManage modifyvm "VM 01 on host 1" --nicproperty<x> dport=10002
        VBoxManage modifyvm "VM 02 on host 2" --nic<y> generic
        VBoxManage modifyvm "VM 02 on host 2" --nicgenericdrv<y> UDPTunnel
        VBoxManage modifyvm "VM 02 on host 2" --nicproperty<y> dest=10.0.0.1
        VBoxManage modifyvm "VM 02 on host 2" --nicproperty<y> sport=10002
        VBoxManage modifyvm "VM 02 on host 2" --nicproperty<y> dport=10001

Of course, you can always interconnect two virtual machines on the same host, by setting the destination address parameter to 127.0.0.1 on both. It will act similarly to an internal network in this case. However, the host can see the network traffic which it could not in the normal internal network case.

Note

On UNIX-based hosts, such as Linux, Oracle Solaris, and Mac OS X, it is not possible to bind to ports below 1024 from applications that are not run by root. As a result, if you try to configure such a source UDP port, the VM will refuse to start.

6.9. VDE Networking

Virtual Distributed Ethernet (VDE) is a flexible, virtual network infrastructure system, spanning across multiple hosts in a secure way. It enables L2/L3 switching, including spanning-tree protocol, VLANs, and WAN emulation. It is an optional part of Oracle VM VirtualBox which is only included in the source code.

VDE is a project developed by Renzo Davoli, Associate Professor at the University of Bologna, Italy.

The basic building blocks of the infrastructure are VDE switches, VDE plugs, and VDE wires which interconnect the switches.

The Oracle VM VirtualBox VDE driver has a single parameter: VDE network. This is the name of the VDE network switch socket to which the VM will be connected.

The following basic example shows how to connect a virtual machine to a VDE switch.

  1. Create a VDE switch:

    vde_switch -s /tmp/switch1
  2. Configure VMs using the command-line:

    VBoxManage modifyvm "VM name" --nic<x> generic
    VBoxManage modifyvm "VM name" --nicgenericdrv<x> VDE

    To connect to an automatically allocated switch port:

    VBoxManage modifyvm "VM name" --nicproperty<x> network=/tmp/switch1

    To connect to a specific switch port n:

    VBoxManage modifyvm "VM name" --nicproperty<x> network=/tmp/switch1[<n>]

    This command can be useful for VLANs.

  3. (Optional) Map between a VDE switch port and a VLAN.

    Using the switch command line:

    vde$ vlan/create <VLAN>
    vde$ port/setvlan <port> <VLAN>

VDE is available on Linux and FreeBSD hosts only. It is only available if the VDE software and the VDE plugin library from the VirtualSquare project are installed on the host system.

Note

For Linux hosts, the shared library libvdeplug.so must be available in the search path for shared libraries.

For more information on setting up VDE networks, please see the documentation accompanying the software. See also http://wiki.virtualsquare.org/wiki/index.php/VDE_Basic_Networking.

6.10. Limiting Bandwidth for Network Input/Output

Oracle VM VirtualBox supports limiting of the maximum bandwidth used for network transmission. Several network adapters of one VM may share limits through bandwidth groups. It is possible to have more than one such limit.

Note

Oracle VM VirtualBox shapes VM traffic only in the transmit direction, delaying the packets being sent by virtual machines. It does not limit the traffic being received by virtual machines.

Limits are configured through VBoxManage. The following example creates a bandwidth group named Limit, sets the limit to 20 Mbps and assigns the group to the first and second adapters of the VM:

VBoxManage bandwidthctl "VM name" add Limit --type network --limit 20m
VBoxManage modifyvm "VM name" --nicbandwidthgroup1 Limit
VBoxManage modifyvm "VM name" --nicbandwidthgroup2 Limit

All adapters in a group share the bandwidth limit, meaning that in the example above the bandwidth of both adapters combined can never exceed 20 Mbps. However, if one adapter does not require bandwidth the other can use the remaining bandwidth of its group.

The limits for each group can be changed while the VM is running, with changes being picked up immediately. The following example changes the limit for the group created in the previous example to 100 Kbps:

VBoxManage bandwidthctl "VM name" set Limit --limit 100k

To completely disable shaping for the first adapter of VM use the following command:

VBoxManage modifyvm "VM name" --nicbandwidthgroup1 none

It is also possible to disable shaping for all adapters assigned to a bandwidth group while VM is running, by specifying the zero limit for the group. For example, for the bandwidth group named Limit:

VBoxManage bandwidthctl "VM name" set Limit --limit 0

6.11. Improving Network Performance

Oracle VM VirtualBox provides a variety of virtual network adapters that can be attached to the host's network in a number of ways. Depending on which types of adapters and attachments are used the network performance will be different. Performance-wise the virtio network adapter is preferable over Intel PRO/1000 emulated adapters, which are preferred over the PCNet family of adapters. Both virtio and Intel PRO/1000 adapters enjoy the benefit of segmentation and checksum offloading. Segmentation offloading is essential for high performance as it allows for less context switches, dramatically increasing the sizes of packets that cross the VM/host boundary.

Note

Neither virtio nor Intel PRO/1000 drivers for Windows XP support segmentation offloading. Therefore Windows XP guests never reach the same transmission rates as other guest types. Refer to MS Knowledge base article 842264 for additional information.

Three attachment types: Internal, Bridged, and Host-Only, have nearly identical performance. The Internal type is a little bit faster and uses less CPU cycles as the packets never reach the host's network stack. The NAT attachment type is the slowest and most secure of all attachment types, as it provides network address translation. The generic driver attachment is special and cannot be considered as an alternative to other attachment types.

The number of CPUs assigned to VM does not improve network performance and in some cases may hurt it due to increased concurrency in the guest.

Here is a short summary of things to check in order to improve network performance:

  • Whenever possible use the virtio network adapter. Otherwise, use one of the Intel PRO/1000 adapters.

  • Use a Bridged attachment instead of NAT.

  • Make sure segmentation offloading is enabled in the guest OS. Usually it will be enabled by default. You can check and modify offloading settings using the ethtool command on Linux guests.

  • Perform a full detailed analysis of network traffic on the VM's network adaptor using a third party tool such as Wireshark. To do this, a promiscuous mode policy needs to be used on the VM's network adaptor. Use of this mode is only possible on the following network types: NAT Network, Bridged Adapter, Internal Network, and Host-Only Adapter.

    To setup a promiscuous mode policy, either select from the drop down list located in the Network Settings dialog for the network adaptor or use the command line tool VBoxManage. See Section 8.8, “VBoxManage modifyvm”.

    Promiscuous mode policies are as follows:

    • deny, which hides any traffic not intended for the VM's network adaptor. This is the default setting.

    • allow-vms, which hides all host traffic from the VM's network adaptor, but allows it to see traffic from and to other VMs.

    • allow-all, which removes all restrictions. The VM's network adaptor sees all traffic.