Saturday, October 7, 2017

Conflicting Use of TCP Port 102 for IEC 61850 and Simatic S7

IEC 61850-8-1 defines how the abstract IEC 61850 services (ACSI) are mapped to MMS (ISO 9506). The MMS protocol runs on ISO/OSI Transport Layer, ISO/OSI Session Layer, ... For IEC 61850 it has been decided to use TCP/IP as transport protocol.

TCP has to be "extended" by some definitions to get the same services and protocol features as provided by ISO/OSI Transport Layer class 0: The IETF RFC 1006 defines how to use TCP for MMS. RFC 1006 defines among other issues to use TCP Port number 102 for the MMS Server role. Any IEC 61850 Server role has to run on port 102 - independent of the platform it is running on: protection device, control device or a Windows PC.

Siemens SIMATIC S7 PLCs use RFC 1006 entitled "ISO Transport Service on top of the TCP" (ISO-on-TCP) as a protocol extension for the TCP protocol for connection between two systems.

RFC 1006 (and thus Port 102) is used for standard connections in the SIMATIC environment.

  • STEP 7 remote programming via LAN
  • ISO-on-TCP connections
  • S7 connections via Industrial Ethernet

I have come across situations where PCs are running SIMATIC S7 tools that are using Port 102! In that case you cannot run an IEC 61850 Server role on the same PC (with the same IP address) - because Port 102 is already in use!!

If you have trouble running an IE 61850 Server role on your computer - check also if Port 102 is already in use. In one case we figured out this situation with a server model (SCL) that we tried to simulate with the Omicron IED Scout! IED Scout reported an error: TCP Port 102 already in use. We stopped the SIMATIC S7 application to free the Port 102.

This is another use case where the IEDScout reports very useful error information!

Here is an example of the command "netstat -a" (may use as well "netstat -a -b") to figure out, if the port 102 is used or not: Waiting for port "102": 

Click HERE for the Server demo (shown on the right).

Click HERE for a list of ports used by Siemens SIMATIC S7.

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