Open Stack

We are having a firewalling/networking problem with our Openstack, running folsom with quantum and openvswitch, some ports become inaccessible with some instances.
For example: the Nagios Check_MK port 6556 is not accessible from the the Nagios server for a few of the instances, but other instances within the same subnet/vlan are fine.
I can reach the same port 6556 from some tenants and externally fine.
 
Its not limited to the above port, it has also happened with rabbitmq instances, while other ports on the same instance are accessible. it happens with different instance OS's (windows/ubuntu), not limited to any particular vlan/subnet/tenant.
When I run a tcpdump I can only see ICMP packets coming through from the nagios server, i.e. at the check_mk agent side but nothing hits 6556
It has worked previously and the security groups all look to be setup fine.

We create our vlans/subnets externally and realise them through into openstack, has anybody come across something similar or point me in the correct direction to help solve this, is there any known bugs that could be contributing to this, let me know what logs/configs I need to gather to help solve this.
thanks, conor

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