[libvirt-users] Starting libvirtd cuts off host access to external network

[PLD]

I've spent some hours on this without success - any help greatly 
appreciated.

I've just done a new RHEL6 setup, with a KVM guest (first time). The 
basic installation works fine until I start libvirtd; at this point, the 
host machine loses access to the external network:

step 1: ping from host to network works; external machine on network can 
ping both eth0 and br1 on the host

step 2: /sbin/service libvirtd start

step 3: ping from host to network fails; external machine on the network 
can't ping either eth0 or br1 on the host

Stopping libvirtd (/sbin/service libvirtd stop) makes no difference - 
the network remains unreachable.

Any idea why this would happen? I have installed a kvm guest, using the 
default network script at /etc/libvirtd/qemu/networks/default.xml 
(although I've changed the IP addresses to be on my subnet, and the DHCP 
server returns only one address).

I have also configured a bridge; I've attached ifcfg-eth0, ifcfg-eth1, 
and ifcfg-br1 below. I haven't changed any iptables configuration. If I 
run the guest (also RHEL6) the guest can talk to the host, but it can't 
see the outside world.

Thanks -

Paul

================================================

ifcfg-eth0:
-----------

NM_CONTROLLED="no"
DEVICE="eth0"
HWADDR=00:16:E6:8A:C7:20
ONBOOT=yes
TYPE=Ethernet
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME="System eth0"
NETMASK=255.255.255.0
BOOTPROTO=dhcp

ifcfg-eth1:
-----------

NM_CONTROLLED="no"
DEVICE="eth1"
HWADDR=00:16:E6:8A:C7:21
ONBOOT=yes
TYPE=Ethernet
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME="System eth1"
BRIDGE=br1
NETMASK=255.255.255.0

ifcfg-br1:
----------

NM_CONTROLLED="no"
DEVICE=br1
BOOTPROTO=dhcp
ONBOOT=yes
TYPE=Bridge
DELAY=0