Archive for July, 2024

How to use Nagios and NRPE to monitor remote OPNSense HA secondary routers

by on Jul.19, 2024, under Linux, Networking, Software

Network diagram image showing Nagios Server monitoring OPNSense Secondary Router via the use of a NRPE Reflector

In this article, I’ll be discussing how to use the Nagios NRPE (Nagios Remote Program Executor) service to monitor the remote secondary OPNSense firewall in a high availability configuration to overcome a VPN routing limitation where the secondary instance is not reachable. The root cause is due to the way the VPN routing is performed in OPNSense where the incoming traffic flow won’t communicate due to a routing conflict. While this issue isn’t an OPNSense specific issue (it affects pfSense and other firewalls that use HA/CARP with VPN).

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