Blog Post

Tech Talk

A DataSource to Troubleshoot ERI Merging

Chris_Wallis's avatar
Icon for LM Champion rankLM Champion
2 years ago

One of the most common behaviours noticed in topology maps is ERI Merging. This is caused when two or more devices share the same identifier (ERI). 

The example I always like to give when I’m teaching Topology Mapping is the word “football”. 

To a European like myself this is a game played with your feet, however in other parts of the world this is an altogether different game. 

Now let’s imagine we have a Topology Map connecting various sports together; what would show up if the map connects “football” to “basketball” - would it be the kicking game or the throwing game? Well, in LogicMonitor, it would be effectively indeterministic to tell. The two games would merge into a single object in the map (they merge into one of the resources at “random”). A key indicator of merging is one device showing as another device in the topology map.

Luckily, there are a few out of the box ways to overcome this merging - the topo.blacklist and topo.namespace properties. If you’re interested in finding out more about merging how these are used, I have created a LearningByte which you can watch for free in LM Academy here - you will need a free Academy account created first.

In order to use the blacklist property, you must know which ERIs are being merged. This can be discovered in the UI through a manual comparison of ERIs between resources (you can export to excel and process there if you’d like), however this can be a cumbersome process and doesn’t reveal how many resources are merged. 

That’s where my new ERIMergeTroubleshooter comes in.

Using the LogicMonitor API to run the !erimergelist and !erimergedetail collector debug commands, it creates one instance for each merged ERI and a subsequent instance level property listing which other resources merge with that ERI. For example, we can see that this “Router” resource has merged with a “Server” resource. Applying the troubleshooter DataSource, it immediately reveals which particular ERI has merged, and which resource it has merged with (this is a trivial example, although most situations are often more complex).

If you’d like to try out this custom Logicmodule, it can be imported now from the LMExchange (locator: F26PEJ); it will be great to hear some feedback from real world testing!


  • By default, this applies to all resources in the portal, so users should modify the appliesto if they require testing on specific devices only
  • The module has not been tested against or developed for chained ERI merging
  • API credentials are to be added as device properties based on the technical notes


Published 2 years ago
Version 1.0