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Re: [Xen-users] XEN - networking and performance

D. Duckworth wrote:

A vitriolic rant !

Right now I just care about creating my ideal networking solution, i.e.
routing, bridging and firewall stuff for vms with different roles.


... and Xen may not change networking in any way unless specified.

All that is trivial to do. The network-script is (I believe) deprecated anyway as the developers realise it's not very good AND OS native tools for things like managing bridges have improved somewhat. It probably made sense when they were first written, and making bridges and/or flexible setups that can survive booting in or out of Xen, required more script voodoo than most users could muster. It's one thing to say these scripts are rubbish, but you have to realise the historical context from when they were written.

So comment out any network-script in your Xen config. You are now no longer using the Xen supplied scripts for setting up your host networking.

In your host config, get it to create the bridge - this is trivially easy in Debian and multiple posts have been made here recently. This is an extract from my own system at home :
  auto eth0
  iface eth0 inet static
    bridge_ports peth0
    address 192.168.nn.nn
    gateway 192.168.nn.nn
You see, that really is all it takes to configure a bridge in Debian these days !

My preference is to have Udev name my physical interfaces as things like pethint, pethext, and so on. This is one simple edit in something like /etc/udev/rules.d/<something>persistent-net-rules where you simply change "eth<n>" for the interface to something else. You don't have to do this, but IMO it makes things much easier as you don't have to keep remembering whether eth0 is the outside, inside, something else network !

These two changes will mean you have a network in Dom0 that works the same whether booted natively or with Xen, where the Dom0 uses one (or more) bridge(s) for it's own networking, and the physical interface(s) are connected to the bridge(s) you want.

Now, if you want a DomU to act as a router for the rest of the network, that's easy too - I do that at home. There are two ways of doing it.

1) You can use pci passthrough to hide a NIC from the host and make it available natively to the guest. Then just configure the guest to do whatever you want with the traffic.

2) You can create another bridge but don't configure an IP address on it in Dom0. Connect the guest to this bridge as well as the other internal networks, and it can route traffic in the same way. This is logically the same as option 1 but having installed a (software) switch between the guest and the outside world.

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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