There seems to be a bug where DNS PTR (Reverse DNS lookup) checks do not work in Xymon (4.3.7, but I don't recall seeing any fixes in the commits). The man page for hosts.cfg says the format to use is: dns=TYPE:lookup and one of the examples underneath for TYPE is PTR (reverse). I have tried this in small and capitals and neither work (the result is Name not found). Using A does work though. I wonder if it could be related to the fact that DiG needs to be invoked with -x for PTR checks. A quick look at the DiG man page suggests you could use either:

dig -t PTR my.ip.ad.dr.ess

Or:

dig my.ip.ad.dr.ess PTR

However, this is not the case. A closer looks reveals you have to use:

dig -x my.ip.ad.dr.ess

So what I am saying is that the treatment for type PTR differs from the other types, and that the parameters supplied to DiG (if Xymon uses DiG ) differ for PTR.

Tested manually with DiG 9.2.4 and the latest RHEL5: 9.3.6-P1-RedHat-9.3.6-20.P1.el5_8.6.

Kind regards,

SebA