Nagios reports its own host as DOWN

[Alnis Morics]

Hi,

I installed nagios4-4.1.1_5,1 on a FreeBSD 10.3 jail. (It's my first 
time with Nagios)

I managed the core to show up as working, and the system now lists its 
first host (the one it is installed on) -- as DOWN.

Small wander, because the way it checks this is by pinging "localhost" 
(/sbin/ping -n -c 5 127.0.0.1 ), although ping is disabled in my jail 
(as per default), and its localhost address is changed to 127.0.0.3.

How can I correct this checking? I found there is a script for checking 
FreeBSD jails 
(https://exchange.nagios.org/components/com_mtree/attachment.php?link_id=1859&cf_id=24) 
but, again, I can't find any hint of how to use it or whether it can 
help me at all. Will I be able to check services on jails of other 
machines?

Thanks for any advice,

-Alnis