Re: [Xen-users] Wired and Wireless with Etables

[Simon Hobson <linux@xxxxxxxxxxxxxxxx>]

On 1 Jul 2017, at 13:16, Ray Joseph <ray3960852@xxxxxxxxx> wrote:

> I would like to determine how to configure dom0 to use either wireless or 
> wired connections automatically depending upon which are available. 
> 
> The machine will come up in Xen when configured as either wired or wireless.  
> This may not be relevant, but Xen will not boot if wireless is configured and 
> no wireless is available, nor if both are configured and set to the bridge 
> set to wired and wireless is not available.

Does it give any clues as to what the problem may be ? It doesn't sound right, 
because the networking isn't done by Xen.

> It seems the way to do this is to bond wlan0 and eth0 as bond0, then build a 
> bridge for domus with bond0.

No, just no. Do not try introducing bonding as it just isn't what you need.

> Etables requires the bridge MAC to be defined in the rules.  I do not know 
> how to assign a MAC to the bridge since I don't know which interface came up.

As I said to you in reply to your off-list response - for ETHERNET networking 
you do **NOT** need to do any of that ebtables stuff. Really, you do NOT need 
to do anything.

> How can I set up bridging without knowing which interface is up?

Lets get some basics in first.
The bridge can exist without any devices attached to it. Devices can be 
dynamically added and removed as needed - and this the default action by Xen as 
guests are created (VIF created and added to bridge)/destroyed (VIF removed 
from bridge and destroyed).
You can assign an IP to the bridge regardless of whether any devices are 
attached to it.
You can attach an ethernet interface without it being connected to anything (ie 
cable unplugged).
I don't know if that is the case with a WiFi interface - try it and see.

So it should be sufficient to create a bridge and add both the ethernet and 
WiFi interfaces to it. The host should then be able to network using either 
interface depending on which is connected. You should leave STP turned on, 
otherwise you'll find a network loop that will kill your network if you have 
both WiFi and Ethernet connected to the same network.

Now, back to running Xen over that bridge.

Over ethernet, you do NOT need any ebtable rules - it just works out of the box 
as it were.
You *may* need the ebtables rules when using WiFi (you may find you don't) - 
but it's safe to leave these in place as they won't have any effect on traffic 
over the ethernet interface.
So it should be perfectly safe to configure the bridge with the ebtables rules 
for using WiFi whichever interface is in use. Furthermore, it should be safe to 
configure the MAC address of the bridge to be that of the WiFi interface even 
when using ethernet.


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