Re: [Xen-users] domU network has sleeping sickness

[Rudi Ahlers <Rudi@xxxxxxxxxxx>]

Joshua West wrote:
> Rudi Ahlers wrote:
>   
> > Joshua West wrote:
> >     
> > > The symptoms you describe sound similar to whats found when there's a
> > > MAC address conflict.  Make sure that the MAC addresses of your virtual
> > > machines are completely unique and not used anywhere else in your
> > > network.
> > >  
> > >       
> > < -- snip -->
> >
> > Joshua, what will happen if the network aliases (eth0:0, eth0:1, eth0:2,
> > etc) all have same MAC address?
> >
> > and how do I know what MAC address to give to the dom_U's?
> >
> >     
> Sub-interfaces (eth0:0, eth0:1, etc) should and do have the same MAC
> address.  Its when one gets into assigning MAC addresses to different
> virtual interfaces for your domU (i.e. eth0 in your VM and eth1 in your
> VM) that you need different MAC addresses.
>
> Additionally, unless you have a really good reason, each virtual
> interface in your domU (eth0, eth1, etc) should be in a different
> network.  Meaning, if eth0 is in a 192.168.100.0/24 network, then eth1
> should not also be in 192.168.100.0/24.  You can run into asynchronous
> routing issues that way... as well as some fun when using stateless
> protocols like UDP and ICMP.  This is all not even considering what
> happens when you're also leveraging a stateful/connection-tracking
> firewall like a Cisco FWSM (they don't like to see asynchronous routing).
>
> You configure the MAC address of your domU's virtual interface's (VIF's)
> in your domU configuration file.  For example, the following line gives
> a domU two network interfaces:
>
> vif = [ 'bridge=xenbr20, mac=aa:bb:cc:00:00:80', 'bridge=xenbr50,
> mac=aa:bb:cc:00:00:81' ]
>
> The first interface, aka eth0 in the domU, gets attached to xenbr20 in
> the dom0.  The second interface, aka eth1 in the domU, gets attached to
> xenbr50 in the dom0.
>
> Regarding knowing what MAC address to give your domU's, I believe you
> can have Xen automatically assign one for you (but last time I checked,
> it can change upon reboot of a VM).  IMHO its better to just keep a list
> of MAC addresses that you've assigned to individual specific interfaces
> in your domU's.  Additionally, prefix the MAC address with an OUI (the
> first three bytes) that you'll never find on a vendor's network card,
> such as "aa:bb:cc".
>
> Hope this helps.
>
>   
Thanx, that helps. I already know about not using two different NIC's on 
the same IP subnet, but using different virtual / alias NIC's on the 
same physical NIC is a bit new to me.

So, if dom0 is on 192.168.10.0/24, then would it be a problem if vm01 is 
on .10/24 - .19/24, vm02 on .20/24 - .29/24, etc - all on the same IP 
subnet?
How is a MAC address calculated? i.e in hex / dec / binary etc?
Is aa.bb.cc safe to use for the 1st 3 octets?

--

Kind Regards
Rudi Ahlers
CEO, SoftDux

Web:   http://www.SoftDux.com
Check out my technical blog, http://blog.softdux.com for Linux or other 
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