Virtual Machine Networking Options

3Q12 10:01 Derby RTC - Carlisle Wapping Sidings

I am frequently asked to help people setup virtual machines. One of the most common questions is about how to setup networking properly, so I thought I’d share that information here.

Virtual machines have a variety of networking setups available. In addition there are also many options for the underlying OS, such as Windows, OSX, or Linux. Before you can make real use of a virtual machine, it will be necessary to make sure that you have a proper IP address. Enterprise deployments should be on a dedicated hypervisor, such as
vSphere / ESXi from VMware, VirtualBox, Hyper-V, etc. For them you setup networking as you would any other machine.

The VM can use either a static IP address or DHCP. By default virtual machines are often preset for DHCP or dynamic setup. If you want to use a static address you will need to set it to an appropriate value. For more details on linux networking, check the Ubuntu Network Configuration guide.

Desktop VM Network Configuration
VMware provides three types of networking configurations: Nat, Bridged, and Private or host-only. I expect most desktop hypervisors to have similar options.

NAT addressing
NAT means that the VM is running on a private network confined to the host machine. It can see external machines, but is generally unavailable to other machines on the network – they cannot see it. The IP address for the VM is supplied from the VM server itself, using DHCP. This setup is well suited to normal, personal use or a demo, but is usually inappropriate for an actual deployment.

Bridged addressing
Bridged lets your virtual machine share the network adapter from the host machine. In
this setup, your machine gets a “normal” IP address on your network. Typically this
is something like DHCP, and may require you to give the MAC address of the VM to your system administrator. This is a good setup if you need others to be able to access the VM. You can find your MAC address by following the instructions above under “Getting the MAC address”. If you know the correct range of IP addresses, you can also assign a fixed address this way, but you’ll need to have all the necessary information for a static network configuration.

Host-only addressing
Host-only mode lets your VM ONLY see your host machine. The VM has no access to
the network or the world at large. This is ok for certain demos, but not useful for general purpose use. It is very secure.

Your Address
You can find your network address and mac address either by using the ifconfig command from a prompt for linux, (described above under “Getting the MAC address”), or from the user menu when logged in you can select “System – Preferences – Network Connections”. For windows you can using the ipconfig command or right-click your networking icon.

Getting the MAC address
If you want to use DHCP for the address, you will probably need to give the MAC address for the VM to your system administrator. Some networks may require the MAC address for any access at all. From the VM terminal (see “logging in” for details) you can run the command: “ifconfig”. You will see two or more entries. One is “lo” which is for the loopback and can be ignored. The other should be eth followed by some number, such as eth1 or eth2. Take note of this value as you will use it later on in the configuration. On the same line as the ethx you should see a label that says “HWaddr” – the value following that label is your mac address for that network interface.

If there are others tricks you know, please share them. If there are other topics you’d like me to cover, let me know.

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