SLC Ethernet issue

[ScottyH 0]

On a SLC processor 1747-L553. What sort of fault would happen if two computers were to use the same IP address and connect through a Ethernet switch to the PLC? What would happen if you had one pc and another device with the same IP address? Can you provide any information? Background I would like to get a better understanding of the Ethernet communication on the 1747-L553 SLC processor. This morning I had an incident when I plugged in my laptop pc Ethernet cable to the switch that also linked to the PLC. Within a minute I had maintenance people calming I took the plant down. My question - is this possible? I did not get the driver for RSLinx configured yet, and I did not even go on line with the PLC. The only thing I may of did would be to have my pc using the same IP address as a device on the network. Would this cause a processor shut down? I did not get to look at the fault and I suspect when maintenance man opened the door for me he pulled on a DH+ cable from the PLC. On resetting the cable the card, then the processor it all came up and working fine. But still I have the question

[Ken Roach 194]

Anyone who has used industrial networking has made this exact mistake, most of us more than once. Duplicate IP addresses on Ethernet are bad news; they tend to make both devices "blind" to the network and can confuse switches and routers that try to deal with two devices with the same IP address but different hardware identifiers (called MAC IDs, used at a low level by switches). It shouldn't fault the SLC-5/05 controller, but it will definitely make any message instructions or HMI/SCADA instructions fail. That could have an interaction with other systems, and thus the "you took down the plant" cascading set of failures. Some devices will recover from a duplicate IP when they are unplugged and replugged into the network, but some require a power cycle. You could test this with an SLC-5/05 on a benchtop setup if you're interested improving your understanding of the failure mechanism, but I'd say it's 50/50 that it was a dragged cable versus a duplicate IP. Get into the habit of opening a Command window and issuing an IPCONFIG command before plugging into a new system, to be sure you know what IP address your computer has and take a moment to consider whether or not you want to switch to a different static IP or to a dynamic IP.

[Cookie Monster 2]

I have made that mistake only once before. Luckly it was a non time critical MSG to another controller. I have since gotten into the habit of setting up an alternate configuration within IPv4. This is a static address that has been dedicated to our "Plant Floor" IP structure so I know that no other equipment will be using that IP.

[ScottyH 0]

All Good advice and I should know better at this time as I have been doing this work for a while now. I guess I do not need any more information and It really does not matter if the processor faults out if 2 devices have the same IP address as it is best practice to be sure and use a unique IP address. Thanks!

[Conor 4]

In reply to Cookie Monsters reply: A while back someone told me about Netset man. http://www.netsetman.com. I have used it ever since for setting my IP address on my Engineering Laptop. It is very handy as you can set up to 6 different IP configurations. I think that I have 5 set up. It speeds up the process great.