Re: [Xen-users] Please help with network configuration.

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2015-11-24 at 22:36 +0000, Christian-Josef Schrattenthaler wrote:
> Hi!
> Â
> I am confused about the right network configuration for my server.
> Â
> I have a Debian 8 root server with one network card and 4 external ip
> addresses from my provider. I did already the standard network
> configuration (eth0, eth0:0, eth0:1 and eth0:2). So far so good.
>
> Now I want to create the right bridging for Xen andÂthe virtual machines.
> And this is the point where I get confused. Should I create one bridge
> for everything, or should I create a bridge for every external ip address
> I have? I have 4 external ip addresses, and I want to make 4 virtual
> machines. This means, that the server and one virtual machine have to
> share an ip address, which is not a problem, because the server needs
> ssh, and the virtual machines are with Windows.

Have you seenÂhttp://wiki.xen.org/wiki/HostConfiguration/NetworkingÂ;?

You normally want one bridge per virtual subnet which you wish to support,
normally if you want external connectivity then you would want there to be
one "physical" (which might really be a VLAN or even a bonded device etc)
on the bridge. You appear to have a single subnet, on which you have been
assigned 4 IP addresses.

I think you most likely want to put eth0 on the bridge and give the bridge
eth0's IP configuration to form the dom0 host IP address.

Then you need to get rid of eth0:* from dom0 and use those 3 IP addresses
to assign to 3 VMs, using the VMs internal configuration tools.

Which just leaves your 4th VM.

With bridging you can't have the host (dom0) and a VM share an IP in the
way you seem to be suggesting (irrespective of the OSes anything is
running).

You can think of a Linux bridge a lot like a managed switch, your VMs
correspond to physical ports in the switch and dom0's IP address is like
the management IP of the switch itself, you wouldn't consider sharing IP
addresses between hosts and the switch in such a situation I think.

So if you want more VMs than the N-1 IP addresses available you would need
to do something like NAT just like you would with a physical firewall to
put multiple devices with internal IP addresses behind one public IP.

Or you could ask for a 5th IP address, which would obviously be a lot
simpler.

Ian.

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