Install the SNMP service on Centos

Install the SNMP service
#yum install net-snmp
then
#mv /etc/snmp/snmpd.conf /etc/snmp/snmpd.conf.org
#vim /etc/snmp/snmpd.conf
and insert
rocommunity public 192.168.x.x
then replace 192.168.x.x with the IP address of the server that you want to allow SNMP lookups from:
Start the service
#/etc/init.d/snmpd start
and configure to start automatically
#chkconfig snmpd on
Run the command in order to open firewall
#system-config-firewall-tui
in shell console and open UDP port 161 to your SNMP lookup server.
Finally test it as follows:
#snmpwalk -v 2c -c public 192.168.x.x