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

[Simon Hobson <linux@xxxxxxxxxxxxxxxx>]

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
    netmask 255.255.255.0
    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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