Open Stack

Hello,

I'm getting an important problem after deleting an instance. I'm running 
Openstack Juno in a server that acts as controller and network node 
(with 3 nics). Computes have 2 nics. Because of computes are in an 
student laboratory, each compute has a local iptables with its rules. 
Then, when I launch an instance, some rules from neutron are 
automatically added. However, when I terminate that instaces, that rules 
are not automatically deleted, what it is causing me the problem because 
rule "neutron-openvswi-input" is added as first rule (like an "iptables 
-I", not an "iptables -A"), so some rules I had added are not executed...

How can I solve this problem? How can I reconfigure openstack for 
deleting automatically that neutron rules?

Thanks.