Need quick help with networking question

TonysControls · Jun 23, 2022

So the quick and short of the situation is that I designed an axle press that was sent to one of my company's other facilities. That facility just implemented a local network that is on 11.11.41.XXX. The plc for the press was on 11.11.41.11. I am trying to change the IP from a distance and I used RSLinx to do so by remoting into a coworkers computer. The thing is I changed the IP on the device in RSLinx and now I cannot connect to the PLC and it has the red x.

The IP it was: 11.11.41.11 default gateway: 11.11.41.1

IP I assigned new: 11.11.40.60 (what IT gave me)

I changed the IP but forgot to change the default gateway before I clicked OK and now the device isn't at either IP.

I don't know if it is not showing up because the default gateway doesn't match the IP or what. Any help would be greatly appreciated.

MikeyN · Jun 23, 2022

This sounds like a potential subnet issue. What subnet mask are you using? If 255.255.255.0 you will not see anything on 11.11.40.0/24.

TonysControls · Jun 23, 2022

I was using 255.255.255.0

Curious though, in my mind the current settings in that plc now are
IP: 11.11.40.60
Subnet Mask: 255.255.255.0
Gateway: 11.11.41.1

Ken Roach · Jun 23, 2022

What make and model of controller is it ?

The Default Gateway is not, by itself, as important as the Subnet Mask.

If the Subnet Mask is 255.255.0.0 then both of those devices are on the same IP subnet. If it's something different, they might not be.

You need to start by figuring out the IP address and subnet mask of the network that the PC you're using to configure this device are set for.

The other problem is that "11.xxx.yyy.zzz" is a public Internet-facing address, not a private one like "10.xxx.yyy.zzz". 11.11.40.11 is actually part of a network address block that belongs to the US Department of Defense.

If that facility has built its internal enterprise network with addresses that also exist on or are reserved to the public Internet, you can expect frequent problems with their network and routers.

TonysControls · Jun 23, 2022

I greatly appreciate the replies. In an attempt to 'mask sensitive' information I said 11.11 the IP is actually 10.10.41.11. Didn't know that about the DOD and obviously reveals my limited networking knowledge.

So quick redo:

Previous IP: 10.10.41.11
IP I changed to in RSLinx: 10.10.40.60

Subnet mask for both is 255.255.255.0

Before I changed it I set my coworkers Ethernet adapter IPv4 setting to 10.10.41.230 and was able to see the connection. After I changed the IP in RSLinx I could no longer see it, so I changed my coworkers ethernet adapter to 10.10.40.230 and have yet to be able to see the device still.

Very sorry for the confusion

TonysControls · Jun 23, 2022

And the controller is a CompactLogix 1769-l16er-bb1b

MikeyN · Jun 23, 2022

Have you tried to ping the device? At one time Ken Roach linked to a program called TCPing that runs within the command prompt similar to the stock ping ccommand, but it lets you choose a specific port to ping. I have found to be incredibly helpful.

Ken Roach said:
Try also TCPING, which simply opens a TCP connection on a specific Port number. Port 502 is standard for Modbus/TCP, but sometimes folks use Port 503 and up.

https://www.elifulkerson.com/projects/tcping.php

Running Wireshark at the same time as you try those tools sometimes gives you insight into the device's basic connectivity as well.

Did you verify that no other devices were using 10.10.40.230 before you changed? I am not sure what you would see if there was an IP address conflict.

TonysControls · Jun 23, 2022

I should also say that the 10.10.41.11 still appears in the active connections in RSLinx

harryting · Jun 23, 2022

Well, that's not going to work. They are in different subnet.

You shown up two different subnet, call it A and B.

Subnet A is 10.10.40.x/24, host range from 10.10.40.1 to 10.10.40.254

Subnet B is 10.10.41.x/24, host range from 10.10.41.1 to 10.10.41.254

Subnet A can not see or talk to B without a router (gateway) but you left your gateway in the OTHER subnet. I would check with your IT, but I'm quite sure you also have to change your gateway to 10.10.40.x range.

ETA: which subnet if your PC at? A or B? If your computer is in a different subnet from the PLC then the Ethernet/IP driver will not work since that depends on the broadcast function of CIP, use the Ethernet Device driver.

TonysControls · Jun 23, 2022

Hmm I'm not 100% sure I understand.

Presently the gateway is 10.10.41.1
But the IP is (I'm assuming the IP did actually change when I set it): 10.10.40.60

Do I need to set the PLC gateway to 10.10.40.X or leave it? Or do I change the PC that my coworker is using?

I am going to have my coworker get a USB-B cable so that hopefully I'll be able to see the PLC again.

harryting · Jun 23, 2022

Exactly, this "Presently the gateway is 10.10.41.1
But the IP is (I'm assuming the IP did actually change when I set it): 10.10.40.60"

is NOT going to work. you can't have a gateway outside your subnet.

Put it this way, you mail letter from New York to Chicago but your letter need to get to New York Post office first before "routed" to another PO but you set up your local post office as Chicago. The gateway is the LOCAL address of your router, who knows how to properly route the message outside of your local subnet.

TonysControls · Jun 23, 2022

Ok perfect I assumed I was going to have to change the default gateway so that it would work, the thing I don't quite understand is how I will be able to find the device with these current settings?

I couldn't ping it while the PC's IP was 10.10.41.230 or 10.10.40.230. Do you have a suggestion for how I could reach the PLC so that I can change the default gateway?

I am kind of just hoping that I'll be able to find and change the settings via USB but I am not 100% sure.

EDIT: I see on the bottom you said to use just the Ethernet Device Driver. That will be able to find the PLC you think?

harryting · Jun 23, 2022

USB cable is the best option. I would also check your PC's IP, if it's in a different subnet than you need to use the Ethernet Device driver to see it in RSLinx. However, you should still be able to ping it.

drbitboy · Jun 23, 2022

you might be able to get away with temporarily setting the PC mask to 10.10.40.0/23 i.e. 10.10.40.0/255.255.254.0 and keep its IP of 10.10.41.x. It will think it is on a bigger subnet, but everything else on 10.10.41.0/24 i.e. 10.10.41.0/255.255.255.0 should be able to communicate with it, and it should be able to see the PLC on 10.10.40.0/24 i.e. 10.10.40.0/255.

QvixoteRoux · Jun 23, 2022

Quick reference info

IP is formed by 4 octets (4 groups of numbers)

AAA.BBB.CCC.XXX

the simplest network use subnet class C, this means that all values in AAA, BBB and CCC must be the same across all devices. To indicate the type/class of subnet is used the mask is configures
255.000.000.000 for Class A
255.255.000.000 for Class B
255.255.255.000 for Class C

Class C is the simple one, you just asign mask class C, the first 3 groups of numbers must be equal always and the last 3 (the XXX) should be different

The other 2 type of subnets are a bit more complicated and require specialist hardware and knowledge. All machine sin 8 years I have built use class C

I hope this help you understand a bit better

Need quick help with networking question

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