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:  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)


Turns out the script is checking for OID . 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:


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.


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

While checking the Kemp LB MIBs (accessible here: I found out that OID . 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:


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

Feedback appreciated.


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

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