Industrial Ethernet Design

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Industrial Ethernet Design
Sean
12-03-2007

Sean posted on
December 3, 2007, 1:27 am

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I'm a network admin in a small manufacturing plant, and as part of my
responsibilities, I oversee all the Ethernet in the plant.  During a
recent network issue (a loop caused by a maintenance tech plugging
both ends of a patch cable into the same switch), it was discovered
that our Ethernet-enabled PLCs were connected to the same physical
network infrastructure as our IT-Ethernet network and given a
separate, non-routeable IP address space.

I don't know when this occurred, but it was done years before I was
hired and I suspect that it was done the way it was to keep costs
down.  However, I do need to clean this up as I clean up the rest of
the facility's network.

Do PLCs and any terminals that communicate with them need to be on a
separate physical network (not plugged into my switches), and are
there any good sources/best practices that I can read up on how to
implement an industrial network?  Are there any products available
that would allow me to restrict access to the network based on their
login credentials?

pnachtwey posted on
December 3, 2007, 2:45 am
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Re: Industrial Ethernet Design

OOOh, that will be a problem.  It is best that you take the attitude
that you help whom ever is in charge of the plant floor.   If not
there will  be resentment.

Yes. This has been discussed many times on www.plcs.net.

Yes.  I am not sure about login credentials.  From the plant floor
stand point it means having access to a laptop that has access to
wireless network.  One must separate the office network from the plant
floor network using a router.  The PLCs on the plant floor should have
an Ethernet address such as 192.168.XXX.YYY where XXX is the machine
center and yyy is the controller IP address within the machine
center.  There should be a router that keeps the traffic from one
machine center from interfering with another machine center.  In
addition the plant floor must be separated from the office by a
router.  Sometimes managed switches will do but it is imperatives that
copying a file in the office does not interfere with the plant floor
or traffic on the plant floor traffic does not interfere with the
office.   However, the office should be able to access a specific
machine and the plant floor should have wireless Ethernet so the PLC
programmers can program their PLC from anywhere on the plant floor.

If you are using Rockwell Automation PLCs then understanding routers
and localizing traffic is very important because Ethernet/IP allows
all the slave device to transmit their status a specific intervals.
The default is 10 ms.  This can swamp a network that doesn't localize
traffic.

Cooperate, separate, don't try to dominate you will have much more
success.

Peter Nachtwey