Please read the nrpe.cfg file. It states:
ALLOWED HOST ADDRESSES
This is a comma-delimited list of IP address of hosts that are allowed
to talk to the NRPE daemon.
NOTE: The daemon only does rudimentary checking of the client’s IP
address. I would highly recommend adding entries in your
/etc/hosts.allow file to allow only the specified host to connect
to the port you are running this daemon on.
NOTE: This option is ignored if NRPE is running under either inetd or xinetd
I have to assume that you are in fact using inetd or xinetd.
I would comment out that line, if in fact, you are using inetd or xinetd.