On /etc/nagios/nrpe.cfg, (remote server) comment out the following line:

• #allowed_hosts=

They say it ignores this config line if you use xinet.d, but they are totally wrong. I used to get the “Host <blah> is not allowed to talk to us!” error because of this.

The command I used to test the connection (on the host server) is:

• /usr/lib/nagios/plugins/check_nrpe -H <remote_server_ip>