[CentOS-virt] xenbr0 isn't created anymore

Fri Mar 28 13:44:44 UTC 2008
Ross S. W. Walker <rwalker at medallion.com>

Kai Schaetzl wrote:
> Somehow I managed to disable the creation of xenbr0 on boot-up of the host 
> system. CentOS 5 with standard CentOS Xen. 
> I changed all Xen VMs to use xenbr0 instead of virbr0 and disabled 
> virtlibd. Works fine. But when I later restarted the machine I found that 
> all networking for guests had gone. On inspection there's no xenbr0 
> created anymore. I can get it up by stopping network (or eth0) and then 
> running /etc/xen/scripts/network-bridge start
> xend-config.sxp still has (network-script network-bridge), logging shows 
> no problems. It seems that the network-bridge script simply doesn't run, 
> but why? I can't see any init script or so that might run it, so I assume 
> it's xend doing that, but there's no error in any log.


Snooping around I found this in /etc/xen/qemu-ifup:

# Old style bridge setup with netloop, used to have a bridge name
# of xenbrX, enslaving pethX and vif0.X, and then configuring
# eth0.
# New style bridge setup does not use netloop, so the bridge name
# is ethX and the physical device is enslaved pethX
# So if...
#   - User asks for xenbrX
#   - AND xenbrX doesn't exist
#   - AND there is a ethX device which is a bridge
# ..then we translate xenbrX to ethX
# This lets old config files work without modification

So it turns out Xen networking changed in current releases and they never
updated their Wiki.

Now I am not sure how the vif0.X and vethX interfaces fit into the
picture here... Maybe these are no longer used?

vifX.Y interfaces are still used though for linking domU interfaces
with the physical interface.


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