CompactLogix 5370 lost IP address

We have some vendor supplied machinery that runs on a CompactLogix 5370 (1769-L24ER-EBFC1B, FW rev. 28.011) that wasn't communicating with the local HMI nor the supervisory PLC when power was restored after an unexpected outage. When I went online directly with the unit via USB cable, the processor was in Run mode but the IP settings were all 0.0.0.0. I re-entered the IP settings but they immediately cleared out again after clicking "OK" or "Apply".

Our troubleshooting led to a suspected duplicate IP address. IT confirmed this and corrected the issue. However, I'm wondering if there's a way to prevent this from happening in the future.

Is there a setting in the controller that maintains the IP settings, even if a duplicate node is detected?

Also, I noticed there's no way to view the IP settings in the offline program; lots of previous forum posts indicate there's no way to do so. I went through the supervisory PLC's I/O Configuration to confirm the settings. Short of placing a sticker inside the enclosure door, is there a better method for readily accessing these settings?

Thanks in advance.

If the controller has a static ip address then You should be able to view it offline.

Double click the controller then look at the network tab. Or, simply hover your mouse cursor over the plc and the ip address will appear in a small window by your cursor.

_Dock_ said:

If the controller has a static ip address then You should be able to view it offline.

Double click the controller then look at the network tab. Or, simply hover your mouse cursor over the plc and the ip address will appear in a small window by your cursor.

Click to expand...

That may work with some processors but apparently not this flavor. The network tab contains no IP information. The Internet Protocol tab is shown below in offline mode. The IP is Manually configured on all of our processors - not DHCP.

DHCP Persistence...

RonJohn said:

That may work with some processors but apparently not this flavor. The network tab contains no IP information. The Internet Protocol tab is shown below in offline mode. The IP is Manually configured on all of our processors - not DHCP

Click to expand...

That would be correct for the 5370 CompactLogix controllers. Under the Ethernet port properties, they do not display their current online network configuration when offline.

What I've often done is write the IP address on the sticker provided on the controller. Our enclosures are all under lock and key for Security and Safety reasons.

But to add more determinism, all our 5370 controllers are connected to Stratix 8000 switches where we (I) deploy DHCP Persistence. The controllers are left configured for DHCP and are automatically assigned their network configuration based on the preconfigured switch port they are connected to. As the only place to connect to each VLAN segment on the network is via a DHCP Persistence switch port, there is little or no chance of a duplicate IP address. The pool of IP addresses dedicated to the VLAN is exactly the number of ports on the switch and no more. Enabling DHCP Snooping further helps in preventing other possible DHCP Servers (switches, etc.) from attempting to service the local VLAN devices i.e. only the local switch will dynamically assign the configuration for its connected devices.

All this wonderful talk of switches - have you any managed switches in play here? There is a known anomaly concerning switch based networks and false duplicate IP detection, but I won't elaborate upon that unless necessary.

Regards,
George

Thanks George,

We do use VLAN switches to segregate our networks, although I must admit the guy who set them up had better knowledge of control system networks than our current IT folks. I am by no means a VLAN or IT expert. I will pass on the concept of DHCP persistence. I do know that the switch hardware was upgraded very recently and they found some DCHP settings that were incorrect after our issue the other day; these may have been a factor.

Hopefully their remedy will prevent the IP address reset issue from occurring but I am curious if there was a way to maintain the 5370's IP address in the event of a conflict so that we wouldn't be at the mercy of such external hardware/software changes.

Switches abound!

If they are using Cisco architecture...

568750 - False Duplicate IP detection on Ethernet modules when used with Cisco switches
Access Level: Everyone

I'll let you read that one yourself. But if unsure, then pass it on to the "Gods". If the current configuration permits (and we are talking Cisco based switches) then they could execute some of the command line workarounds mentioned to help prevent false duplicate IP detections in the future.

If "anyone" is considering using DHCP Persistence, then please make sure they read up a lot on it before attempting to implement it. If you've ever any questions on it then feel free to ask on the Forum and I'd be more than happy to further advise, if I'm about. Although, I think I've written a "little" on it here somewhere before?

G.

Many thanks George! They are using Cisco and while the technote appears to be quite helpful, I'm not able to fully decipher & digest on my own so it's getting passed on up the ladder.

Am I to understand correctly that the switch may have been the one to change the PLC's IP address and not the CompactLogix itself? If so, that would be scary!