SNMP Version 2

SNMP version 2 (SNMPv2) is an evolution of the intial, SNMPv1. Originally, SNMPv2 was published as a set of proposed Internet standards in 1993; currently, it is a draft standard. As with SNMPv1, SNMPv2 functions within the specifications of the Structure of Management Information (SMI). In theory, SNMPv2 offers a number of improvements to SNMPv1, including additional protocol operations.

The structure of Management Information (SMI) defines the rules for describing management information, using ASN.1. The SNMPv2 SMI is described in RFC 1902. It makes certain additions and enhancements to the SNMPv1 SMI-specific data types, such as including bit strings, network addresses and counters. Bit strings are defined only in SNMPv2 and comprise zero or more named bits that specify a value. Network addresses represent an address from a particular protocol family. SNMPv1 supports only 32-bit IP addresses, but SNMPv2 can support other types of addresses as well. Counters are non-negative integers that increase until they reach a maximum value and then return to zero. In SNMPv1, a 32-bit counter size is specified. In SNMPv2, 32-bit and 64-bit counters are defined.

The SNMPv2 SMI also specifies information modules, which specify a group of related definitions. Three types of SMI information modules exists: MIB modules, compliance statements, and capability statements. MIB modules contain definitions of interrelated managed objects. Compliance statements provide a systematic way to describe a group of managed objects that must be implemented for conformance to standard. Capability statements are used to indicate the precise level of support that an agent claims with respect to a MIB group. An NMS can adjust its behavior toward agents according to the capabilities statements associated with each agent.