ILMI is a protocol based loosely on SNMP commands used for automagically configuring ATM edge devices.

Described and defined in ATM Forum specifications UNI 3.0 and UNI 4.1 and RFCs 115, 1213, and 1157, ILMI typically communicates using VPI/VCI 0/16. It is used solely on UNI (User-Network Interface) connections -- which exist between an edge device and an ATM cloud -- and not PNNI connections between ATM network devices.

The chief advantage of ILMI is that it can be used to create ATM virtual circuits on the fly. Similar to D-channel signalling in ISDN, ILMI can be used to set up "calls" over the ATM network and establish end-to-end temporary (SVC) or permanent (PVC) circuits.

Trivia about ILMI: Like many Internet and telecommunications related protocols, ILMI was designed as a temporary solution. When it was defined in the ATM Forum's UNI 3.0 specification, it was explicitly referred to as an interim protocol. However, the convenience ILMI quickly outweighed the need to develop a successor and when the UNI specification was revised, ILMI was re-dubbed to hide it's "experimental" nature.