From Wikipedia article on EtherNet/IP http://en.wikipedia.org/wiki/EtherNet/IP
EtherNet/IP was developed in the late 1990s by Rockwell Automation as part of Rockwell's industrial Ethernet networking solutions. Rockwell gave EtherNet/IP its moniker and handed it over to ODVA, which now manages the protocol and assures multi-vendor system interoperability by requiring adherence to established standards whenever new products that utilize the protocol are developed today.
EtherNet/IP is most commonly used in industrial automation control systems, such as for water processing plants, manufacturing facilities and utilities. Several control system vendors have developed programmable automation controllers and I/O capable of communicating via EtherNet/IP.
An EtherNet/IP device is positively identified by querying TCP/44818 with a list Identities Message (0x63). The response messages will determine if it is a EtherNet/IP device and parse the information to enumerate the device. From here
Default port: 44818 UDP/TCP
PORT STATE SERVICE44818/tcp open EtherNet/IP
nmap -n -sV --script enip-enumerate -p 44818 <IP>