Network-to-network interface

In telecommunications, a network-to-network interface (NNI) is an interface that specifies signaling and management functions between two networks. An NNI circuit can be used for interconnection of signalling (e.g., SS7), (IP) (e.g., ) or ATM networks.

In networks based on MPLS or GMPLS, NNI is used for the interconnection of core Provider Routers (class 4 or higher). In the case of GMPLS, the type of interconnection can vary across Back-to-Back, EBGP or mixed NNI connection scenarios, depending on the type of VRF exchange used for interconnection. 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, P routers are taught how to dynamically exchange VRF records without VLAN creation. NNI also can be used for interconnection of two VoIP nodes. In cases of mixed or full-mesh scenarios, other NNI types are possible.

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

...
Wikipedia