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RE: [Xen-users] 'Wandering' eth interface - Xen 3.0.4 + linux

  • To: "TMC" <tmciolek@xxxxxxxxx>, "Xen users mailing list" <xen-users@xxxxxxxxxxxxxxxxxxx>
  • From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
  • Date: Mon, 30 Apr 2007 17:18:30 +0200
  • Delivery-date: Mon, 30 Apr 2007 08:18:47 -0700
  • List-id: Xen user discussion <xen-users.lists.xensource.com>
  • Thread-index: AceLObyk/sl4wp0qTZyx2NqEisdlkQAAH+gA
  • Thread-topic: [Xen-users] 'Wandering' eth interface - Xen 3.0.4 + linux


> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of TMC
> Sent: 30 April 2007 16:10
> To: Xen users mailing list
> Subject: [Xen-users] 'Wandering' eth interface - Xen 3.0.4 + 
> linux
> I have a Xen 3.0.4 with Debian Etch (4.0) running quite 
> successfully...
> except for an annoying problem, which i have not observed in other
> DomU instances, nor have I observed it with my test server...
> The problem I am observing in that one domain is that on reboot, the
> eth interface seems to "wander" - that is  monotonically increase the
> index value...

You can probably fix this by setting a fixed MAC address. This isn't
Xen's fault, it's because your distro believes that a particular device
should always be given the same ethN number, and it records the MAC
address to remember which interface has which MAC. Since Xen's
auto-numbering is pseudo-random, each time you start a domain again, it
will have a different MAC-address (unless you do it many enough times to
find a collision, but that's not going to happen very often with 2^24
possible combinations). [Note, only some distros do this]. 

I think there are other possible "fixes" (e.g. modifying the script that
figures out which MAC address corresponds to which ethN device name),
but giving a fixed MAC address is a good practice anyways if you are
planning to use your domains for anything serious. 


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