Over the weekend, my ML1400 with a static IP suddenly disconnected from the network, displaying an IP conflict with a MAC address on the screen. Initially, I thought the displayed MAC address was from the problematic device. However, upon checking, I realized that the MAC address matched that of the ML1400. I was able to resolve the issue by disconnecting and reconnecting the Ethernet cable. During the disconnection, I couldn't ping the static IP, implying that any conflicting device was currently offline. Can it be concluded that there was a misunderstanding, or is there a potential bug affecting the device's functionality?
I am uncertain if the MicroLogix 1400 displays the MAC ID of the conflicting device or its own MAC ID. Have you considered trying another device to troubleshoot? The Duplicate IP Address packets are sent out every 2 minutes after the initial startup, making it a quick process. False Duplicate IP faults may occur with the MicroLogix 1400, particularly when used with Stratix switches that have the IP Tracking feature enabled. This issue is discussed in the Knowledgebase, and it is worth noting that the v21 firmware potentially allows users to disable Duplicate IP checking.
In the midst of troubleshooting networking issues with a PLC, it was discovered that the MAC address displayed on the ARP entry did not match the MAC address shown in the Ethernet Status on the PLC's LCD screen. This discrepancy was not a one-time occurrence but had happened multiple times with different MAC addresses being reported. Upon closer inspection, it was determined that the conflict was with the PLC itself, as the network setup did not involve a Cisco or Stratix switch, but rather a managed Planet IGS-801M switch connected via Ubiquiti wireless radios. The original PLC had gone offline after three years, prompting its replacement. However, the new PLC was also experiencing similar issues, with IP conflicts attributed to a self-MAC address conflict displayed on the front panel. Despite changing the switch three months prior, the problem persisted, leading to concerns about the PLC's ethernet hardware layer. The discrepancy between the MAC address in the conflict message and the Wireshark ARP entry raised questions about the PLC's behavior during ARP processes. The investigation into the mismatched MAC addresses highlighted the need for a deeper understanding of how the PLC handles network requests and ARP resolutions, especially in cases where conflicts arise unexpectedly. It was essential to consider the possibility of the PLC's software manipulating the MAC address dynamically, resulting in discrepancies observed during network troubleshooting.
In response to the issue with the PLC, it was discovered that there was an IP conflict with the self MAC address, as indicated on the front panel. The problem initially occurred with the original PLC, which went offline after three years of service. Despite attempts to troubleshoot, including replacing the PLC and changing the switch, the issue persists. Wireshark analysis revealed ARP announcements, indicating that the PLC recognizes its IP address but refuses to respond to network requests. This recurring problem, now also affecting the new PLC, suggests a deeper network issue that needs to be addressed promptly.
I encountered a situation with an AC powered ML1400 PLC that initially reported an IP conflict, which was resolved by power cycling the device. However, the PLC eventually malfunctioned and had to be replaced. This particular PLC was connected to a residential-grade UPS system installed by someone else. I have also worked on other systems using AC powered ML1400s connected to UPS units from big box stores, which experienced temporary issues due to brownouts when the UPS batteries were low during a power outage. In contrast, I have found DC powered ML1400s and DC UPS systems to be more reliable. If you have ruled out a genuine IP conflict, my personal experience suggests considering alternative power sources for better performance.
breshead mentioned the following: TLDR: * Issue with MAC address not limited to a specific switch brand * Repeated occurrence of the problem * Discrepancy between MAC address in ARP entry and Ethernet->Status on LCD Thank you for the response. It's interesting how I overlook obvious solutions when low on mental energy. I tested another PLC by setting my laptop to the same address and connecting directly to the Ethernet port. I found that it reported a different MAC address for another device. Considering I don't have a Cisco or Stratix switch (using a managed Planet IGS-801M with Ubiquiti wireless radios), the issue seems to be with the PLC itself. I recently replaced the original PLC that went offline after 3 years of service, which seemed like a network problem. Despite the PID loops running, there were no indicators on the HMI and SCADA system. Even after various troubleshooting methods, including connecting directly to my laptop, the PLC wouldn't come online fully. When analyzed with Wireshark, it showed a Rockwell ARP but no further response. Although the new PLC is now displaying a conflict with itself on the front panel. In February, I switched from a Cisco to a Planet switch, but the original PLC issue surfaced only a week ago. The new PLC experienced a similar problem within a week with conflicting MAC addresses. Upon inspection, the MAC address displayed doesn't match the one in the Wireshark ARP entry. I mistakenly compared the MAC addresses of two different PLCs. Upon verification, the MAC address in the ARP entry matches the one on the LCD display.
It definitely sounds like a strange situation. I've come across similar network issues before, and generally, it seems like it could be a bug or perhaps intermittent poor network quality causing the system to incorrectly flag your device as conflicting. Also, it is always worthwhile to double-check for any potential device network conflicts, and possibly consult with your service provider about the issue. They might have more detailed logs that can shed light on these peculiar incidents. However, if the problem's rectified itself after reconnecting and there's no conflict anymore, it might be nothing to worry about. Just monitor the situation and seek professional help if it happens recurrently.
I'm not convinced that there's a bug with your device. It seems like the issue is with the network configuration. The fact that you were unable to ping the static IP during the disconnection indicates that the IP conflict could be due to an offline device previously configured with the same static IP which came online or reconnected to the network momentarily. I would suggest checking your network for any device that could potentially be set with the same static IP. Also, make sure your DHCP range, if you're using one, doesn't include this static IP to avoid possible clashes.
It sounds like you had quite the puzzling experience! It’s possible that the ML1400 was experiencing a temporary glitch that caused it to misreport its own MAC address during the conflict. Network devices can sometimes get confused, especially if there's a momentary hiccup or a duplicate IP address somewhere in the mix. Since you were able to resolve it by cycling the Ethernet cable, it leans more toward a brief fault rather than a systemic bug. If it continues to happen, it might be worth digging deeper into your network configuration or updating the firmware, just to rule out any underlying issues.
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Answer: Answer: The displayed MAC address matched that of the Micrologix 1400 itself, indicating a self-conflict issue rather than an external device causing the problem.
Answer: Answer: The issue was resolved by disconnecting and then reconnecting the Ethernet cable, which seemed to reset the connection and resolve the IP conflict.
Answer: Answer: The inability to ping the static IP while the cable was disconnected suggests that any conflicting device causing the issue was offline at that time.
Answer: Answer: Based on the information provided, it seems that the issue was resolved by reconnecting the Ethernet cable, indicating a possible temporary glitch rather than a bug affecting the device's functionality.
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