Explanation/Reference:
Explanation:
The following security models exist: SNMPv1, SNMPv2, SNMPv3. The following security levels exits:
noAuthNoPriv (no authentiation and no encryption noauth keyword in CLI), AuthNoPriv (messages are authenticated but not encrypted auth keyword in CLI), AuthPriv (messages are authenticated and encrypted priv keyword in CLI). SNMPv1 and SNMPv2 models only support the noAuthNoPriv model since they use plain community string to match the incoming packets. The SNMPv3 implementations could be configured to use either of the models on per-group basis (in case if noAuthNoPriv is configured, username serves as a replacement for community string).
Reference: http://blog.ine.com/2008/07/19/snmpv3-tutorial/