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

[Simon Hobson <linux@xxxxxxxxxxxxxxxx>]

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.
--
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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