Open Stack

Hello everyone.
I found out that openstack router drops packets going from it's internal 
network into the Internet if the source IP address in the packet does 
not belong to router's internal subnet.

I tried to disable security groups globally and set 
port_security_enabled to False on the router's port but this did not help.
tcpdump on router's internal interface shows packets arriving fine, but 
nothing goes outside. Packets are probably dropped somewhere within 
router's iptables rules but I couldn't find exact rule that does this.

Is there a way around this behavior? Or maybe someone can direct me to 
the exact iptables rule?