using Nagios to detect rogue DHCP servers?

[Brian A. Seklecki]

> What about writing a custom plugin that uses this GPL prog to return the
> warning/critical/ok/pending values?

That sounds very reasonable; there's always the possibility that you won't 
see, within your run time threshold, offers from a rouge server due to 
race conditions or other crud (slow networks, etc.).

Of course, then you have a lot of proactive bogus DHCP Client activity 
coming from your Nagios system.

The best solution of course, but not always the most feasible, is a SPAN 
port in your core:

Simply:

$ sudo tcpdump -n -e -vvv 'src port bootps && !ether src 0:50:da:28:37:62'

Replace the MAC with your know DHCP server.  Matches are rouge.  If you 
see them, get out the jumper cables.

~BAS


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