Red Hat OpenStack Platform introduces additional functionality to control access to external networks via the RBAC framework.

From the engineering bug:

"This allows access to external networks to be controlled via the RBAC framework added during Liberty with a new 'access_as_external' action. A migration adds all current external networks to the RBAC policies table with a wildcard indicating that all tenants can access the network as RBAC. Unlike the conversion of shared networks to RBAC, the external table is left in the DB to avoid invasive changes throughout the codebase to calculate the flag relative to the caller. So the current 'external' flag is used throughout the code base as it previously was for wiring up floating IPs, router gateway ports, etc. Then the RBAC entries are only referenced when determining what networks to show the tenants."