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

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