L2 network

[nilantha liyanage]

Hi All,
I have configured an advanced zone with security groups on KVM and would like 
to use L2 network between two VM's as private heartbeat network, I cannot ping 
between them unless I flush iptables on the nodes or set 
net.bridge.bridge-nf-call-iptables = 0.need some advice as I'm new to 
cloudstack?.
Thanks,Nilantha