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Old 08-13-2009, 09:35 AM   #1
Registered: Aug 2006
Posts: 609

Rep: Reputation: 79
Xen virtual using bridging

Hi all,

A year ago I installed CentOS and configured Xen.

Recently I upgraded to 3.3.x

First my network wouldnt work and after a long time of trying I seem to have it fixed (I used the libvirtd networking guide to fix this)

Now, a few months later, I reboot my server and networking is again not working anymore.

The setup is as follows:
1 Dom0
1 DomU
1 Laptop
1 Router

The goal is to have all these accessible from/to any of these devices

I need a bridge for this so I configured it.
The Dom0 I want to be accessible trough and the DomU through
There is no dhcp needed.
I added a ifcfg-br0 config (with "Bridge" and not "bridge"/"BRIDGE" in it)
ifcfg-eth0 I configured to use br0.
In example configs I have seen that the bridge IP was assigned through dhcp. But I dont want to assign it through dhcp. So I configured the address for it.
When I restart the networking service the Dom0 is accessible through and can ping any other except the DomU.

If I do arp -n then I see that the HWaddress for the DomU is incomplete (aka no answer?).
If I do the same on the DomU (through the console) I see a HWaddress for the Dom0 (, however this is the address of the br0 interface.

Now I wonder if eth0 is the physical interface, or br0.
I would think some interface in ifconfig should have an HWaddress that accepts all traffic.

The interface of the DomU (vifx.0 or something) and eth0 is added to the br0.

Does anyone knows what I do/understand wrong and explain to me?
Maybe I do not understand the bridge workings correctly.

THanks alot in advance!

EDIT: in the output of arp -n on the DomU I meant that the mac was shown of a tap interface instead of the br0 interface

Last edited by deadeyes; 08-13-2009 at 02:15 PM.
Old 08-13-2009, 04:18 PM   #2
Registered: Aug 2006
Posts: 609

Original Poster
Rep: Reputation: 79
I couldn't seem to find what was causing the problem but I fixed it as explained below.

The only thing weird for me was that I couldn't see a "Source Device" in virtmanager. And there is no way to select anything.
So I added a new NIC and had the possibilty to select a bridge, br0. I selected this one and created it.
After rebooting the DomU and configuring an IP on that interface, I was able to connect it.

So deleting the old one and adding a new one on the bridge interface should solve this.

I think this might be a bug as no Source Device was selected.

for anyone trying to solve this instead of using the previous workaround, you can try to edit the config file in: /usr/lib/xend/domains/

Last edited by deadeyes; 08-14-2009 at 04:14 AM.


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