LibreNMS is an open source auto-discovering network monitoring tool for servers and network hardware. It supports a wide range of network hardware like Cisco, Juniper, Brocade, Foundry, HP and operating systems including Linux and Windows. LibraNMS is a community-based fork of Network monitoring tool “Observium“, released under GPLv3.
LibreNMS can discover your entire network using CDP, FDP, LLDP, OSPF, BGP, SNMP and ARP protocols. It’s alerting system can be highly customized to receive alerts via email, IRC, slack and more.

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