To enable SNMP on CentOS
yum install net-snmp-utils -y
yum install net-snmp -y
mv /etc/snmp/snmpd.conf /etc/snmp/snmpd.conf.org
vi /etc/snmp/snmpd.conf
rocommunity public
Save and Exit
/etc/init.d/snmpd start
chkconfig snmpd on
Make sure you configured your Firewall