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

[Joshua West <jwest@xxxxxxxxxxxx>]

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.

-- 
Joshua West
Systems Engineer
Brandeis University
http://www.brandeis.edu

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