By default, Neutron applies anti-spoofing rules to all ports to ensure that unexpected or undesired traffic cannot originate from or pass through a port. This includes rules that prohibit instances from running DHCP servers or from acting as routers. To address the latter, the allowed-address-pairs extension can be used to allow additional IPs, subnets, and MAC addresses through the port. However, additional functionality may be required that cannot be addressed by the allowed-address-pairs extension.

In the Kilo release of OpenStack, the port security extension was introduced for the ML2 plugin, which allows all packet filtering to be disabled on a port. This includes default rules that prevent IP and MAC spoofing as well as security group functionality. This extension is especially useful when deploying instances for use as a router or a load balancer...