Detecting duplicate IPs on a network

Is there a way in LibreNMS to detect a duplicate IP address and set up an alert in PagerDuty?

If your LibreNMS instance contains only routers it shouldn’t be so hard to do.
You need to compare all arp tables and look for duplicates. You have to look for:

  • same ip address, but different mac addresses

It may be not that obvious on a complicated infrastructure and a LibreNMS instance with many devices. Some devices (like Mikrotik) use bridge which would confuse the ARP table. Moreover - many devices (in my case) have more than one ip addresses on the same interface.

Try this SQL query and check on your own. First column: number of occurances, Second column: mac address.

select count(*) ipv4_address,mac_address from ipv4_mac group by mac_address having ipv4_address > 1;

I am sure it is possible to filter all unwanted results and find decent solution for this, but this needs some effort in my opinion and it depends on many things. Maybe this will lead you to right direction.