Re: [Xen-users] quick question about bonding with vlans and Xen

["Fajar A. Nugraha" <fajar@xxxxxxxxx>]

On Tue, May 25, 2010 at 4:25 AM, Donny Brooks <dbrooks@xxxxxxxxxxxxxxxx> wrote:
> Ok, so far I have followed up till this point with eth2 and eth3 (third and 
> fourth ports in the server) leaving eth0 and eth1 alone for now.

... which you can add to the bridge as well later, if you like.

> So when I pass the domu "bridge=br1" (changed it to br1 from 9) and it is a 
> dhcp host, how does it know where to get it's IP?

I think you're still missing the basics. Here's an analogy to make
things easier. When using the above setup (bonding + vlan + bridge),
Xen dom0 behaves the same way as an L2 switch with vlans enabled and
multiple bonded ports for uplink trunk.

For simplicity sake lets assume the bridge names is the same as vlan
numbers. I wouldn't recommend using vlan1 (and thus br1), as vlan1 is
usually the default management vlan/default vlan for untagged traffic.
So lets assume we'll be using vlan9/br9. eth2 and eth3 (which is the
uplink trunk interface) must be connected to a switch as trunk,
possibly requiring special bonding setup on the switch side as well
(depends on which bonding mode you use). The switch must already have
an existing vlan9, which is connected to an existing network with an
existing DHCP server.

So in that sense, a domU connected to br9 behaves just like another
physical machine connected to the switch directly and assigned vlan9.
It can get IP address from an existing DHCP server on that vlan. If no
DHCP server exists, you have to create one first :D


> I have 18 VLAN's I need to pass to Xen, VLAN 2-19. Is it that br1 needs only 
> setup with one vlan? So if I did a ifcfg-bond0.2 I would make a br2 and point 
> the domu to that? Just trying to clarify since I think that's how I would 
> need to do it.

You'd need 18 vlan interface, from bond0.2 to bond0.19, and 18
bridges, from br2 to br19.

>
>
>> >
>> > But do I have to assign an IP to each "interface"? Would I need to 
>> > designate one specific NIC to handle Dom0 and it's static IP or would Dom0 
>> > still be able to have a static IP with all 4 bonded together with vlans on 
>> > them?

Again, think L2 switch. Usually it will only have one management IP
address, no matter how many vlans it has. Let's assume your dom0
management IP address will be on vlan9, so on
/etc/sysconfig/network-scripts/ifcfg-br9 you can put IP address
settings, and leave all other bridges WITHOUT IP address setting. This
setup has the advantage that dom0 will also benefit from the bonding
setup.

Another approach that you can use is to have a dedicated NIC for dom0
management IP address. Let's assume eth0. You can connect it to a
different switch. This setup has the advantage that you'd get an
out-of-band management network (think HP's ILO or Sun's rsc), but you
don't have the benefit of bonding.

> For simplicity sake, I might just leave dom0 on eth0 for now and just use 
> eth1 thru eth3 for the bond. That way if I foobar something I can still get 
> to dom0 remotely. Thank you for taking the time to explain this. Now I just 
> need to figure out the switch portion of the bond :)

In my example above, "mode=balance-alb" means you don't have to do
much on the switch side. Just make sure the ports eth1-3 uses are set
as trunk, not access. If you use  "mode=802.3ad" or 4, you'd need to
setup bonding on the switch side as well. This page has a good
explanation: 
http://wiki.oracle.com/page/Cisco+Systems+IOS-based+switches-+interface+bonding+and+trunking

-- 
Fajar

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