Problem solved: Monitoring Kemp Loadbalancers with Check_MK (kemplb_real_servers, kemplb_rsvs and kemp_virtual_server)

About two weeks ago I found a plug-in for monitoring Kemp loadbalancers on Check_MK Exchange (go here: http://exchange.check-mk.org/index.php?option=com_remository&Itemid=59&func=fileinfo&id=135).  Until today it was working absolutely flawless on two loadbalancers and was a really big help on monitoring all the services (including connection and pool data).

Unfortunately, it would not recognize the services on a third Kemp loadbalancer. That´s when I went CLI and checked the snmp_scan_function. (Note: The plug-in consist of three different checks: kemplb_real_servers, kemplb_rsvs and kemp_virtual_server)

kemplb0

Turns out the script is checking for OID .1.3.6.1.4.1.12196.12.8.1.2.1 in order to inventory the servers. So I decided to compare the output from the working and faulty Kemp LBs when doing a snmpget for this OID:

kemplb1

Turns out that the working LB is giving back a value, while the other Loadbalancer does not. This is quite interesting since both LBs are on same firmware version and platform (virtual machines).

Then I used a MIB-Browser to investigate which values in this OID tree would be available.

kemplb3

As we can see from the screenshot there is no OID .1.3.6.1.4.1.12196.12.8.1.2.1. Instead there are a couple other OIDS like .1.3.6.1.4.1.12196.12.8.1.2.4. and .18 etc in the subtree.

While checking the Kemp LB MIBs (accessible here: http://kemptechnologies.com/files/downloads/documentation/7.0/LM_mibs.zip) I found out that OID .1.3.6.1.4.1.12196.12.8 is “a table containing Totals for Real Server (RS) specific information.”

So it seems that there is no Real Server “1” on the faulty LB. Thereforet Check_MK is not doing an inventory (even though it would find services on the LB).

So here is a solution that worked for me: I changed the last lines of the three check scripts as following:

kemplb4

So basically it is checking OID .1.3.6.1.2.1.1.2.0 (“The vendor’s authoritative identification of the network management subsystem contained in the entity”)  and validates if the returned value starts with .1.3.6.1.4.1.12196 (because in that case it is a Kemp LB and we want the plug-in to start the inventory).

Feedback appreciated.

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About sitweak
Monitoring, Network, Firewall, Mobile Security. I´m totally into that stuff!

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