Install through yum:

[root@system ~]# yum -y install net-snmp net-snmp-libs net-snmp-utils

Install through apt-get:

[root@system ~]# apt-get install snmp

For manual installation:

Download the .rpm or .deb file(s) and save it to disk.
Binary Distributions: http://sourceforge.net/projects/net-snmp/files/net-snmp binaries/

Install:

[root@system ~]# rpm -ivh net-snmp-<version>.rpm net-snmp-libs-<version>.rpm net-snmp-utils-<version>.rpm

or

[root@system ~]# dpkg -i snmp-<version>.deb