Reflecting on IP/Ethernet

"Backstage" - Reflecting on EtherNet / IP / Ethernet

I started out this blog post after reply to a somewhat confused sales person about the use of the trademarked EtherNet/IP protocol with their local telecomms provider. "Could we order a driver for it ? " After several cross-country exchanges we figured out, politely almost, that perhaps the problem was that he was thinking Internet Protocol, best described by DARPA in 1981, but writing EtherNet/IP which refers to the more proprietary Industrial Protocol originated by Rockwell some 20 years later.

How best to explain this .. without being too long suffering about it.

For readers of this blog, the following excerpts from descriptive information found on the web may be a reminder of the difference.

IP --- 1.2. Scope The internet protocol is specifically limited in scope to provide the functions necessary to deliver a package of bits (an internet datagram) from a source to a destination over an interconnected system of networks. There are no mechanisms to augment end-to-end data reliability, flow control, sequencing, or other services commonly found in host-to-host protocols. The internet protocol can capitalize on the services of its supporting networks to provide various types and qualities of service. - DARPA Internet Protocol Specification 1981

EtherNet/IP™ was introduced in 2001 and today is the most developed, proven and complete industrial Ethernet network solution available for manufacturing automation. EtherNet/IP is a member of a family of networks that implements the Common Industrial Protocol (CIP™) at its upper layers. - ODVA.ORG

The Internet Protocol itself is used by everyone and everything with an IP address. Everyone knows somehow that IP runs on the Ethernet. The number of connection points on the overall network and the allocation of IP address ranges has forced the global community to adopt IPv6 which has an address space of 3.4 x 10^38.. close to infinite really.  So almost all technology now supports some kind of IP address and connectivity so we can network with it.

Contrasting that, the ODVA's EtherNet/IP Application Layer protocol is really a set of protocols which makes use of the IP protocol described above. The IP in the moniker refers to "Industrial Protocol". The number of potential users of EtherNet/IP is large but restricted to specific supporting Industrial devices.

All the hard work of the industrial application is done by the application layer of the protocol stack. For SCADA supervision on networks which lack determinism and which suffer from reliability and bandwidth restrictions, the Distributed Network Protocol [IEEE Std 1815-2012 ][ DNP] provides SCADA application connectivity and Security. For manufacturing and industrial automation on tightly coupled networks, EtherNet/IP can be much more appropriate.

The broad simplified stack structure of the protocols is explained in the following diagram.

Diagram 1 - Contrasting the EtherNet/IP stack and the DNP3 Stack

A quick look at Diagram 1 shows the commonality between DNP3 and Ethernet/IP. Generally both protocols use TCP and IP and the Ethernet at the lower layers.  Look therefore at the application layer.  EtherNet/IP draws on the tradition and definition of the CIP [Common Industrial Protocol] whereas DNP draws on the tradition and definition of the Distributed Network Protocol [dnp.org].

For this reason, when told about supporting different protocols, ask for the protocol stack structure. A simple diagram can rapidly show the points of similarity and difference.

Take home points:-

• Ethernet/IP is not the same as IP/Ethernet
• Ethernet/IP depends on IP/Ethernet at its Network and Data Link layers
• Ethernet/IP depends on TCP/UDP and other routing protocols
• The core functionality of Ethernet/IP is built around CIP the Common Industrial Protocol at the higher level application layer.

Still it can be amusing and confusing sometimes when trying to sort these things out by email.  Hence this blog post which hopefully will dispel the confusion and help people looking for an answer in a hurry.

Chris Smith - Feb 2013.

Ethernet/IP from the ODVA.ORG

Ethernet/IP from Wikipedia

Internet Protocol Specification from the DARPA Internet program 1981

Distributed Network Protocol - User Forum dnp.org

Photo: "Backstage" attrib F Decomite [flickr]. Used as background for artwork.