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Re: [Xen-users] Constructor code in MAC address does matter ?

On Mon, Aug 15, 2005 at 01:09:15PM +0200, Jean-Christophe Guillain wrote:
> I observed a strange networking behaviour of my Debian virtual host in 
> function of the MAC address I use. It seems that when I use an existing 
> constructor code, networking works without any problem, but is impossible 
> in the other case...
> Ex. :
> - vif = [ 'mac=aa:00:00:00:00:55, bridge=xen-br0' ] -> no problem
> - vif = [ 'mac=df:00:00:00:00:55, bridge=xen-br0' ] -> the bridge does not 
> transmit my packets apparently. No DHCP possible, and when I used a static 
> address I can't ping the bridge from the guest... 

Yes, this actually makes sense. Bit 0 of the first hex byte of the MAC
address indicates the packet is going to a broadcast address, but in a
source MAC address, it's nonsensical. I'm not surprised other TCP stacks
would squash it. Provide a MAC address that doesn't have that bit set.
(I.e., de:00:00:00:00:55 should work; df:00:00:00:00:55 won't.)

Note that this has nothing to do with the domain builder, and everything
to do with the behavior of Ethernet networking.

Derrik Pates

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