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Chapter 5
SNMP Version 2

The original version of SNMP (SNMPv1) was derived from the Simple Gateway Monitoring Protocol (SGMP) and published as an RFC in 1988. At that time, the industry agreed that SNMP would be an interim solution until OSI-based network management using CMIS/CMIP became more mature. Since then, however, SNMP has become more popular while the OSI solution has been less widely adopted than was anticipated originally. As a result, it became appropriate to revise and improve SNMPv1. This chapter will discuss the development of SNMPv2 and the resulting enhancements to SNMPv1.

5.1 The Development of SNMPv2

In March of 1992, the IETF solicited proposals to enhance SNMPv1. A team consisting of Jeffrey Case, Keith McCloghrie, Marshall Rose, and Steven Waldbusser prepared a proposal called the Simple Management Protocol (SMP). At about the same time, the IETF initiated another effort aimed at enhancing SNMP security. These two research efforts merged and became known as version 2 of the Internet-standard Network Management Framework, or simply the SNMPv2 framework. The new documentation comprised more than 400 pages in twelve documents (RFCs 1441 to 1452). The first document, “An Introduction to SNMPv2” [5-1], provided an overview of the remaining documents.

Unfortunately, the first SNMPv2 design (which is now referred to as Party-based SNMPv2) was not widely accepted in the marketplace. Frequently cited reasons were the complexities of the security enhancements and the administrative framework. The SNMPv2 Working Group reconvened in late 1994 and several simplified approaches for the administrative framework were considered; however, no consensus was reached. As a result, three actions occurred:

  Documents which had the consensus of the SNMPv2 Working Group were published in January 1996 as RFCs 1902–1908.
  Minor modifications to the SNMPv2 Security and Administrative model, called Community-based SNMPv2 (or SNMPv2C), were published in January 1996 as RFC 1901 [5-2].
  Work continues on the unfinished elements: security, administrative framework, a remote configuration MIB, and Manager-to-Manager communication.

The documentation for the April 1993 and January 1996 publications of SNMPv2 can be compared as follows (Obsolete RFCs are noted with an “O” and Historic RFCs are noted with an “H”):

Previous RFC Subject Current RFC

1441 Introduction to SNMPv2 Introduction to Community-based SNMPv2 1901
1442-O Structure of Management Information for version 2 of the Simple Network Management Protocol (SNMPv2) 1902
1443-O Textual Conventions for version 2 of the Simple Network Management Protocol (SNMPv2) 1903
1444-O Conformance Statements for version 2 of the Simple Network Management Protocol (SNMPv2) 1904
1445-H Administrative Model for version 2 of the Simple Network Management Protocol (SNMPv2)
1446-H Security Protocols for version 2 of the Simple Network Management Protocol (SNMPv2)
1447-H Party MIB for version 2 of the Simple Network Management Protocol (SNMPv2)
1448-O Protocol Operations for version 2 of the Simple Network Management Protocol (SNMPv2) 1905
1449-O Transport Mappings for version 2 of the Simple Network Management Protocol (SNMPv2) 1906
1450-O Management Information Base for version 2 of the Simple Network Management Protocol (SNMPv2) 1907
1451-H Manager-to-Manager Management Information Base
1452-O Coexistence between version 1 and version 2 of the Internet-standard Network Management Framework 1908

The major enhancements included in SNMPv2 include: new data types, new macros, textual conventions, protocol operations that facilitate bulk data transfers, richer error codes, and multiprotocol transport support. This chapter will discuss these key enhancements in the SNMPv2C framework and will refer you to the appropriate sources for further details.

5.2 The SNMPv2 Structure of Management Information

As Chapter 2 discussed, MIB modules provide a mechanism for grouping similar objects. The SMI for SNMPv2 [5-3] defines the subset of the ASN.1 language that describes various MIB modules. SNMPv2 has two documents that support the SMI: the Conformance Statements and the Textual Conventions. The Textual Conventions define the data types used within these MIB modules and make it easier to read the modules [5-4]. The conformance statements provide an implementation baseline and include, for example, a lower bound on what agents must support [5-5].

The SMI also defines two new branches of the Internet OID tree: security {1.3.6.1.5} and snmpV2 {1.3.6.1.6}. Under snmpV2 are the Transport domains (snmpDomains); Transport proxies (snmpProxys); and Module identities (snmpModules). Defined under the snmpModules are the SNMPv2 MIB (snmpMIB); the Manager to Manager MIB, (snmpM2M); and the Party MIB (partyMIB). Note that at the time of this writing, the snmpM2M and partyMIB branches are not populated with any objects, pending the outcome of the SNMPv2 security research. (For that matter, it is also possible that entirely new MIBs, having new OIDs, will be developed as replacements for snmpM2M and partyMIB. Make sure to consult the final RFC documents when these issues are settled. Figure 5-1 illustrates the positions of these new elements of the OID tree.


Figure 5-1.  SNMPv2 elements within the OID tree

According to RFC 1901, the SMI is divided into three parts:

  Module definitions which are used to describe information modules, such MIB modules, compliance statements for MIB modules and capability statements for agent implementations
  Object Definitions, which are used to describe managed objects
  Notification definitions, which are used to describe unsolicited transmissions of management information, such as traps.

The next three sections discuss these three elements of the SMI.


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