Network-to-network interface

An NNI circuit can be used for interconnection of signalling (e.g., SS7), Internet Protocol (IP) (e.g., MPLS) or ATM networks.

[1] In networks based on MPLS or GMPLS, NNI is used for the interconnection of core provider routers (class 4 or higher).

In case of Back-to-Back, VRF is necessary to create VLANs and subsequently sub-interfaces (VLAN headers and DLCI headers for Ethernet and Frame Relay network packets) on each interface used for the NNI circuit.

In the case of eBGP NNI interconnection, IP routers are taught how to dynamically exchange VRF records without VLAN creation.

[2] NNI interconnection is encapsulation independent, but Ethernet and Frame Relay are commonly used.