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Re: [Xen-users] Xen 4.0 Bridged Networking MAC Rewrite?

  • To: xen-users@xxxxxxxxxxxxxxxxxxx
  • From: Andrew Sorensen <andrewx192@xxxxxxxxx>
  • Date: Thu, 09 Jun 2011 19:53:54 -0700
  • Delivery-date: Thu, 09 Jun 2011 19:55:19 -0700
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On Thu, 2011-06-09 at 08:53 +0100, Simon Hobson wrote:
> Fajar A. Nugraha wrote:
> >Where is that written? You should be able to put any mac you want
> >(well, any mac valid for a NIC anyway), so you could impersonate (e.g)
> >a Cisco router if you want.
> >
> >The recommendation to use xen prefix is more of a best-practice to
> >prefent mac address conflict.
> Indeed, and I know someone who's had a MAC address conflict which was 
> apparently "quite interesting" ! This was in a University and they 
> had a desktop refresh - it seems Dell had an "off by one" bug in 
> their config system and for every 257 machines, there would be two 
> with the same MAC. Of course, this would only show up if someone 
> bought sufficiently large numbers all in one go ...
> If you stick to using the Xen prefix, it just means you that you can 
> only conflict with other Xen VMs - thus narrowing the target a bit.
> >At this point I highly suggest you ask your ISP. Probably they only
> >allow one IP address on that port. If they don't know, then I guess
> >the best option would be to look at ebtables.
> I believe they vary considerably. Some may require you to register 
> the (singular) MAC address that you'll be connecting. I believe most 
> common is that (as you say) you'll be limited to one IP address (or 
> more if you've paid for them). But, this is usually given out by DHCP 
> or similar, and the address cannot be reissued to another device 
> until the previous lease expires. You can either wait (a problem if 
> the lease tiem is in hours or days), or you may have to get your ISP 
> to reset the lease.
It turns out my issue was a simple need to restart my modem. Everything
started working as expected after a reboot!

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