MEF 26.2 is a specification document developed by the Technical Committee of the MEF that defines the External Network Network Interface (ENNI)
"The Metro Ethernet Network Architecture Framework – Part 1: Generic Framework (MEF 4) specifies a reference point that is the interface between two Carrier Ethernet Networks (CENs), where each Operator CEN is under the control of a distinct administrative authority. This reference point is termed the External Network Network Interface or ENNI. The ENNI isintended to support the extension of Ethernet services across multiple Operator CENs. ThisTechnical Specification specifies:
The requirements at the ENNI reference point as well as the interface functionalityin sufficient detail to ensure interoperability between two Operator CENs.
The connectivity attributes UNI to UNI, UNI to ENNI, and ENNI to ENNI suchthat multiple Operator CENs can be interconnected and the Ethernet services andService Attributes in MEF 6.2 , MEF 10.3 , and MEF 51  can be realized.
The concept of the Super Operator which allows an Operator, acting as a SuperOperator, to combine multiple Operator CENs together and make them appear asa single Operator CEN to a Service Provider or another Super Operator."