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I’m pretty sure this is useless on most versions of Linux because the default DHCP plugin that comes with the Nagios Plugins distribution has this functionality and seems to work just fine everywhere except on RedHat-based distros like RHEL, Centos and Fedora Core. On these systems the default plugin does not seem to work and fails to detect any DHCP servers. This plugin is different to the one I gave instructions for before which tests whether a particular DHCP server is answering requests, this plugin finds rogue servers, it will not alert you if any of your actual DHCP servers are down. Hence, you should probably install both. This plugin is not very polished, it is rough and ready but I know it works on RHEL4. If you’re running a different system you may have to do some minor tweaks but this should serve as an excellent starting point none-the-less.

[tags]Nagios, DHCP, RedHat, RHEL, CentOS, Fedora, Linux[/tags]

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Tagged with: DHCP • RHEL • tutorial • software release • Linux • open source • Perl

One of my current projects in work is to set up a Nagios install to monitor our network. We have been monitoring with the free version of BigBrother for a while now but BB isn’t as good so we’re switching to Nagios. I had plenty of problems getting Nagios running on RHEL 4 because in work we try to do as much as possible using only RPMs. I’m working on simple how-to for setting up Nagios on RHEL4 which I’ll publish here soon but the base install does not give you DHCP monitoring. I tried to look for RHEL rpms that provide check_dhcp but I couldn’t find any. There were lots for Fedora but they don’t work on RHEL (I tried FC4 and 5 rpms). I tried to manually build the latest version of the Nagios plugins which do contain a check_dhcp binary but there is a problem with that binary that results in it always showing your DHCP server as down. I know the problem is with the binary because if I watch the logs on the DHCP server I see it issuing an offer and tcpdump on my Nagios server shows the offer arriving, yet the plugin still insists that the service is down. The solution is to use this Perl script. However, if you follow the instructions on that page it won’t work on RHEL. I spent an entire day beating this script into submission but in the end I got it working.

[tags]Nagios, RedHat Enterprise Linux, RHEL, RHEL4, DHCP[/tags]

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Tagged with: DHCP • RHEL • tutorial • Linux • open source