[CentOS] Setup multiple bridges for use with KVM

Eduardo Grosclaude eduardo.grosclaude at gmail.com
Sun Jan 10 23:51:51 UTC 2010

On Sat, Jan 9, 2010 at 11:15 PM, Jacob Hydeman <jhydeman at gmail.com> wrote:
> Running CentOS 5.4 x64.
> Have successfully bridged eth2 with br2 by following the instructions here:
> http://wiki.libvirt.org/page/Networking (under the RHEL section)
> Have been running several KVM VMs successfully via this bridge.
> I am now trying to bridge additional interfaces by using the same routine.
> Each bridge is named to correspond with the ethX device its bridged with.
> Example of ifcfg-eth0 script:
> DEVICE=eth0
> HWADDR=00:16:76:D6:C9:45
> ONBOOT=yes
> BRIDGE=br0
> then of ifcfg-br0 script:
> DEVICE=br0
> TYPE=Bridge
> ONBOOT=yes
> This is repeated 3 times for eth0-eth2 and br0-br2.
> I've read somewhere that STP needs to be enabled when using multiple
> bridges. I've tried adding STP=on to the ifcfg-brX scripts but with the same
> result. Yes, brctl shows that STP is on.
> The original bridge eth2-br2 continues to work but I can't get any traffic
> across any other bridge. Either by dhcp or static ips.
> Is multiple bridges a possibility?
> Previous to moving to KVM I was running Xen Server on the same hardware. I
> am just trying to recreate the network setup I had. I believe Xen Server
> runs on top of a linux platform so such a thing should be possible.

I am curious as to what exactly is your topology and which is its
intended use. I have found no issues wrt STP but you seemingly need to
assign different vlans to your VM interfaces, depending on which
bridge they are attached to (i.e. roughly 1 bridge = 1 vlan).
I am confused about what interfaces are attached to which bridge in
your setup, would like to see the scripts you are using to start your
Thank you in advance

Eduardo Grosclaude
Universidad Nacional del Comahue
Neuquen, Argentina

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