LoopBack port Err disabled

[IT Researcher]

We have Cisco 350X and Dlink 1210-28 switches working together in our network.

Both these switches are inter-operating together and LACP is configured between them.

Dlink 1210-28 switch:

Firmware: 6.10.007

Hardware Version: F1

Loopback detect setting

enabled.

LACP mode: Active

Cisco 350X switch:

Firmware: 2.5.0.83

Loopback detect, Spanning Tree State enabled and Link Flap Prevention are enabled.

The switches are connected in Star Topology.

We are seeing frequent Loopback detect messages on Dlink and the Cisco switches and the ports get disabled. There are no physical connection loops in our network.

 Also when we re-enable the ports from Error recovery settings page they start to work without needing any physical changes in our Network or on the switches whose ports were disabled.

Since the informational logs on Cisco and Dlink do not provide any info on what device caused the Loopback error and the reason. So is there any way to get more details in the logs? 

Also is there any way to find out what is actually causing these Loopback detect logs?

[marce1000]

  - What is the full model-name of the Cisco switch ? Also post the complete log-entries you are seeing (from dlink too)

 M.

[Georg Pauwen]

Hello,

--> The switches are connected in Star Topology

How many switches are in your topology ? If you are sure there are no physical or logical loops, you might as well turn off loopback detection on the 350 switch altogether...

https://www.cisco.com/c/en/us/support/docs/smb/switches/cisco-250-series-smart-switches/smb5794-enable-loopback-detection-on-a-switch.html

[IT Researcher]

We are not sure about logical loops.

Will Cisco by default log the exact reason of the "loopback detect" in logs like whether the ports were blocked due to a physical loop or logical loop or any such info. Also It would be helpful if you can point us to such setting so that we may get some more information about the type of loopback.