This protocol is used by network admin to monitor network equipment.
Use community strings to identify machines. Public and Private access are the default configuration. SNMP use plaintext community strings, encryption and authent are added on SNMP V3.
Useful tools
snmpv3brute snmpwalk onesixtyone braa
snmpwalk -v2c -c public $iponesixtyone -c /opt/useful/seclists/Discovery/SNMP/snmp.txt $ipbraa $community_string@$ip:.1.3.6.*