Nagios Support Forum

Login to the remote system and verify that the snmpd daemon is running and check the /var/log/messages log file for any errors for that.
Also, Centos7 uses another firewall daemon called firewalld , try stopping that if it is running.

Also, take a look at this link for installing snmpd on a Centos7 system.
http://mvcp007.blogspot.com/2015/12/how ... mp-on.html

The problem was only firewalld, I stopped. How do I do not reoccur. I stop this service? Will be detrimental to my system? Or I can open a door in the arquivo.conf Firewalld. And what file?

The link shows how to add an exception to the firewalld daemon, do that and you should be good.