[libvirt] Bug:libvirtd boot up blocked in NAT network setup

Hello, guys I met a strange problem in libvirt+kvm massive deployment case. What shows is that libvirtd will not respond to any virsh calls, with debug I found that libvirtd was blocked at the step to setup default nat network, that is command "iptables -table nat xxxxx". In terminal, I found command "iptables -L" will also block, and "brctl show" shows that about 160 tap devices "vnetXXX" were attached to virbr0. After I deleted these tap devices, things become normal, But when I re-create them and attach these tap device to virbr0, it can't be reproduced. There are too server met this problem in test, so I think it is not a hardware problem. Does someone have experience this before? information: server: RH6.2 libvirt: libvirt-0.9.4 kernel: 2.6.32 -- Best Regards Wenchao Xia