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Re: [Xen-users] network-bridge breaks networking when eth0:1 is added

r A. Nugraha wrote on Mon, 27 Apr 2009 19:51:55 +0700:

> Didn't you say Xen version is different?

But the network-bridge script is the same. I even copied over the one from 
3.2.1 to the 3.3.1 setup, just to be sure. But comparing them didn't reveal 
any big difference, anyway. The main difference is some extra code for 
detecting NFS.

> > So for example
> >> you can have these files
> >>
> >> /etc/sysconfig/network-scripts/ifcfg-eth0
> >> /etc/sysconfig/network-scripts/ifcfg-xenbr0
> >
> > This looks like the old way it was done in Xen 3.0.
> RHEL5/Centos still uses the same thing. So does Xen 3.3.1 port from
> Gitco repository.

No, not here. On this machine I installed the rpms from gitco right away. 
There weren't any self-made or xen.org supplied rpms and I think I even didn't 
install the CentOS xen. I applied the gitco stuff right-away.
The network-bridge script is dated 5. 1.2009.
Are you having xenbr on a gitco setup? By simply installing the gitco rpms and 
starting xend?

> >> Let me know if you need more detail on this setup (like what those
> >> file's contents look like).

I'm reluctant to post long scripts where most people might not be interested 
in. As I said, the network-bridge script (in /etc/xen/scripts) is identical in 
the relevant areas to the older script and if I copy the older network-bridge 
script and also the xen-network-common.sh script over I get the exact same 

> >
> > Yes, I'm not experienced in bridging. If you could tell me a sample config
> > I could try that.
> Something like this should work

Ok, thanks, that looks easy, I will check that out as an alternative!
Still, I would like to know why the normal ways fails on that machine :-(
It's not so easy to capture the output from the various commands in the 
script, but it sure gets the same initial input for the inet interfaces from
ip addr show dev eth0.

> > I would also need to tell xen to use xenbr0 for the vifs then.
> If I remember correctly Xen would use the first bridge it found by
> default. Since I have lots of bridges (for different vlans), I like to
> specify the bridge explicitly.

Aha, ok, let's try that first :-)

> > The reason why
> > I want to add another IP address to eth0 is that I want to be able to
> > access the domUs on eth0 from eth1 and eth2 which are in a different non-
> > routable subnet.
> I'm not following you here. If you mean you want to create a private,
> non-routeable network between dom0 and domU, you could simply create
> another bridge.
> /etc/sysconfig/network-scripts/ifcfg-brdummy0 :
> DEVICE=brdummy0
> ONBOOT=yes
> TYPE=Bridge
> BOOTPROTO=static

But how do the domU's recognize that? I'm just using eth0 in there and as I 
understand that independant of any bridge names on the dom0, anyway?

> But if you want to create another bridge with eth1 or eth2 as the
> physical device (thus domU would have two or more NICs, each connected
> to a different bridge), you can copy the eth0/xenbr0 config above and
> modify them accordingly.

Ok. That actually sounds like the "real thing". I'm going to check out the 
simple, one-bridge thing from above and then build upon it once that works.

The situation is as follows.
Three machines. All in the same rack to the same switch, 100 MBit links, in 
the same datacenter. All eth0 are on the same routable subnet. Two of the 
machines are cross-over-cabled to the third machine via the additional ports. 
These ports are all on a non-routable subnet of their own, no gateway set. I 
want to access the domUs via these extra 1 Gig links for instance for backup 
purposes. Going thru the direct cable link would be much faster. So, I need 
something to "bridge" from eth1 to eth0 on the source machines. If I add an IP 
address from the same subnet as eth1 to eth0:1 and to each of the running 
domUs I can access them (I guess by way of broadcasting).


Kai Schätzl, Berlin, Germany
Get your web at Conactive Internet Services: http://www.conactive.com

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