- Implement a managed interface for each external telecommunication service;
- Establish a traffic flow policy for each managed interface;
- Protect the confidentiality and integrity of the information being transmitted across each interface;
- Document each exception to the traffic flow policy with a supporting mission or business need and duration of that need;
- Review exceptions to the traffic flow policy [Assignment: organization-defined frequency] and remove exceptions that are no longer supported by an explicit mission or business need;
- Prevent unauthorized exchange of control plane traffic with external networks;
- Publish information to enable remote networks to detect unauthorized control plane traffic from internal networks; and
- Filter unauthorized control plane traffic from external networks.
External telecommunications services can provide data and/or voice communications services. Examples of control plane traffic include Border Gateway Protocol (BGP) routing, Domain Name System (DNS), and management protocols. See SP 800-189 for additional information on the use of the resource public key infrastructure (RPKI) to protect BGP routes and detect unauthorized BGP announcements.