using Nagios to detect rogue DHCP servers?

Hari Sekhon hpsekhon at googlemail.com
Wed Jul 11 12:43:00 CEST 2007


err, that is not at all nagios or automatic or anything.

I am not personally going to __manually__ check for rogue dhcp servers, 
don't have the time for that.

I check my dhcp servers anyway, if I get an extra offer, an alarm is raised.

This is automatic, has no extra overhead as I check my dhcp servers 
anyway as part of my monitoring.

I have never seen a dhcpoffer being missed, but at the very least I run 
the check every 3 minutes so you're not going to get away with it here 
for more than that.


I think the wrapper to check_dhcp is quick and effective with no overhead.

The best solution would be to extend the check_dhcp plugin, get into the 
C and add the functionality.
Maybe if it's not done in the future I will come back and do it.

Until then, the wrapper does exactly what I need.

-h

Hari Sekhon



Brian A. Seklecki wrote:
>> 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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