kvm bridging problem on ubuntu 11.04

Hello, my problem my Ubuntu 11.04 with KVM is that I just can't get the
bridge between my VMs and my host working.

I've been reading the information in and following the instructions in:

https://help.ubuntu.com/11.04/serverguide/C/network-
configuration.html#bridging

https://help.ubuntu.com/community/NetworkAdmin

http://www.howtoforge.com/virtualiza...n-ubuntu-11.04

https://help.ubuntu.com/11.04/serverguide/C/network-
configuration.html#bridging


KVM automatically installs its own bridge: virbr0, to which the VMs
virtual NICs vnet0 and vnet1 are connected.

I am able to make an additional bridge, br0, to which the physical NICs
eth0 and eth1 (currently unused) are connected as ports.

What I get form 'brctl show' is:

----------- start quote
bridge name bridge id STP enabled interfaces
br0 8000.1c6f653005e6 yes eth0
eth1
virbr0 8000.fe54003c4d1d yes vnet0
vnet1
----------- end quote


and ifconfig gives me (leaving out the traffic data):

----------- start quote
br0 Link encap:Ethernet HWaddr 1c:6f:65:30:05:e6
inet addr:192.168.193.223 Bcast:255.255.255.255
Mask:255.255.255.0
inet6 addr: fe80::1e6f:65ff:fe30:5e6/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1

eth0 Link encap:Ethernet HWaddr 1c:6f:65:30:06:07
inet6 addr: fe80::1e6f:65ff:fe30:607/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1

eth1 Link encap:Ethernet HWaddr 1c:6f:65:30:05:e6
UP BROADCAST MULTICAST MTU:1500 Metric:1

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1

virbr0 Link encap:Ethernet HWaddr fe:54:00:3c:4d:1d
inet addr:192.168.122.1 Bcast:192.168.122.255
Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1

vnet0 Link encap:Ethernet HWaddr fe:54:00:3c:4d:1d
inet6 addr: fe80::fc54:ff:fe3c:4d1d/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1

vnet1 Link encap:Ethernet HWaddr fe:54:00:99:b7:61
inet6 addr: fe80::fc54:ff:fe99:b761/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
----------- end quote

and the structure is apparently:

lo
br0 <--> eth0 eth1
virbr0 <--> vnet0 vnet1

Both bridges are STP enabled.
I was thinking that maybe the virtual interfaces should be connected to
br0, giving:

lo
br0 <--> eth0 eth1 vnet0 vnet1
virbr0

but I can't get it working that way.
I tried to remove vnet0 and vnet1 from the bridge virbr0 using brctl and
added them to the br0 bridge, but at the next restart they were not
listed anymore, so I put them back.

I have flushed the iptables on the physical host and on one of the
virtual hosts and set hosts.allow to ALL: ALL.

I'm almost there, because I'm able to ping the virbr0, just not the
clients that are connected on vnet0 and vnet1.

If someone could give me a clue of what's lacking, then I'd appreciate
that very much.

Thanks,
ario