Simple Network Management Protocol (SNMP) is a protocol for gathering data about the operation of networking devices.  The protocol has undergone three major revisions to enhance functionality and security.  The basic premise of SNMP is to use a Management Information Base (MIB) to GET or SET parameters within the device.

A MIB provides a format for getting the data and is configured in tree like structure.

There is a very nice MIB navigator at Cisco SNMP Object Navigator 

A Network Management Station (NMS) or device would conduct an snmpwalk to gather data via a poll of the network device.  The request (POLL) was verfied by a password known as a community string.  The community string is actually a password with either read-only privileges (GETs only) or read-write (GETs and SETs).   SNMP has three versions-

• SNMPv1    Community String was in the “Clear”/ unencrypted
  • GET gathers information based on the Object ID (OID) from the MIB
  • GETNEXT iterative requests to gather OID info
  • SET define the parameter based on the Object ID
  • TRAP send unsolicited information to the Network Monitoring Device
• SNMPv2c enhanced efficency, but still lacked security
  • GETBULK allows for a single poll to gather several GET
  • INFORM response to TRAP from NMS
• SNMPv3 enabled security with both Authentication and Privacy based on a User-based Security Model (USM)
  • NoAuthNoPriv Communication without authentication and privacy
  • AuthNoPriv Communication with authentication and without privacy
  • AuthPriv Communication with authentication and privacy 

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