multiple compact logix's on dynamic network

[spoonsc1]

hello all. i must say this is a great site! i am currently helping the college i am about to graduate from to finally, after years of having them, get the compactlogix(l23e) connected and running. so far the six plc's have been flashed with the firmware and i can use the rslinx/rs500 to hook up to the ethernet using the serial cord. i felt like a hero at first since they have not been able to do so. but the next night i had found the schools computers run on a dynamic network and the first three octets change. that wont work with a static ip in the plc and also the serial cords are limited to 2 homemade ones! how can i enable a dynamic address on the plc that will connect to the SAME computer it is assigned to? if i get this straight i am moving on to the panelview setup. oh, an i have only 2 weeks! thanks for any help
scott

 

[The Plc Kid]

So you say your college network is setup so that the entire subnet changes? The first 3 octets? I really doubt that and it would be stupid to do so as you would gain nothing but problems.

You need a better understanding of networking. This sounds like homework so do some research on subnetting and DHCP and you will understand how to make it work.

 

[Ken Roach]

Welcome to the Forum !

I'll bet you mean that the last three octets can change. This is the way the first few large networks were done, like ARPA in the 1970's.

In Classful Network lingo, that's a Class A network, so the first octet is the Network number and the other three are the Host.

10.1.1.4, for example, could talk to 10.200.38.121. The Subnet Mask would be 255.0.0.0.

This is the opposite of the usual method of using Class C networks for small networks, where the first three octets are the Network Number and the last octet is the Host.

The very common format is "192.168.1.x", with a Subnet Mask of 255.255.255.0

 

[spoonsc1]

lets put it this way, i set up 2 or 3 of the plc's on one day, first three octets on one computer was 10.7.65 next 169.254.59 and finally 169.254.197. i originally bypassed the ethernet switch to ensure i was setting the proper plc's static ip. after the address was set we has rs5000 connected and working. the instructor 2 days later told me he could not get it connected again. i showed him how to go throught the linx and there was the problem, it showed the computer as a different ip. so i changed the plc;s static to match and we connected. so if the plc was to be a dynamic address, how would it know to connect the correct pc? while on the network i can pic any plc thats with the same first three octets, but it may be located 2 stations away. thanks again, i am probably suggesting a usb to ethernet adapter for this application to make it easier. oh the subnet is 255.255.0.0

 

[Ken Roach]

The easiest way around this problem is to get the campus IT administration to give you a set of reserved static IP addresses.

The lab computers can then get any IP address they want, but they can specifically connect to a particular PLC via its Static IP address.

The second-easiest way around the problem is to install a separate physical network for the lab. New Ethernet NIC cards for each computer, separate network switches for the lab.

When you use dynamic IP addressing, you need some other way to identify devices, and that's the Host Name. Host Names are controlled by the Domain Name Services (DNS) Server on your network.

You can put a Host Name into the A-B Ethernet driver configuration, and RSLinx Classic will browse to it.

But if you cannot configure the DNS server to specifically give names to specific hardware, it's a non-starter.

Connecting PLCs to a network that includes a general-purpose DHCP Server will always put them in a random address. And connecting more than one DHCP Server to a network is a recipe for losing your campus computer privileges. Don't try either one.

 

[Ken Roach]

OK, thanks for posting those clarifications.

You're actually looking at two different scenarios.

In the first scenario, your lab PC connected to the campus network and was assigned an address of 10.7.x.y by the DHCP server on the campus network.

In the second scenario, your lab PC was disconnected from the campus network and tried in vain to get an IP address from a DHCP server. Eventually it fell back to the default mechanism of using an Automatic Private IP Address. These always fall into the 169.254.x.y range.

 

[Ken Roach]

Adding a USB/Ethernet adapter and giving it a Static IP address that you use only in the lab is not only a practical workaround, but also a very common method used in real-world industrial practice.

The fellowship of guys who have bought USB/Ethernet converters at retail outlets in far-flung cities to work around messed up campus or machine networks includes.. well, many of us here on the Forum !

 

[spoonsc1]

guys i appreciate all the comments and advice, i did fail to mention the "deep freeze" the technical college employs. it will wipe all computers clean at midnight. anything saved as you are logged in will be gone including when save to what one thinks is the "hard drive". (even with the computer off) i am a Quality Control Analyst for Schneider Electric and i work closing with our High Tech group and they recommended the usb idea. thanks again to all, have a good holiday!

 

[The Plc Kid]

guys i appreciate all the comments and advice, i did fail to mention the "deep freeze" the technical college employs. it will wipe all computers clean at midnight. anything saved as you are logged in will be gone including when save to what one thinks is the "hard drive". (even with the computer off) i am a Quality Control Analyst for Schneider Electric and i work closing with our High Tech group and they recommended the usb idea. thanks again to all, have a good holiday!

If your college is using Deep Freeze your IT Admin can provide a Thawed space on the HD that does not get reverted. if they do not wish to do that your only choice is to save things to a network drive or a thumb drive, etc.

Using Deep Freeze in the manner that they are doing means you would need to setup your RS Linx driver and Path each time the machine is restarted which should not be a big issue.

As far as the PLC's I agree with Ken I would set a static IP in the private range and employ a second NIC on the PC's which could be internal or an external USB to NIC unit like Ken mentioned.

The second Internal NIC would likely involve working with IT but the USB version is something you could do in the Lab. The only possible caveat maybe that you need to setup the driver for the USB to Ethernet NIC device each time and that could be fast or very slow depending on the model you choose and the driver it needs.