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SNMP Configuration 173
Software Configuration Guide Release 2.10, Revision 1.00
operations and associated protocol data unit (PDU) formats is described in RFC 1157. The
second set of protocol operations and associated PDU formats is described in RFC 1905
An NMS executes applications that monitor and control managed devices. NMSs provide the bulk of
the processing and memory resources required for network management. One or more NMSs must
exist on any managed network.
20.1.3 SNMP Basic Commands
Managed devices are monitored and controlled using four basic SNMP commands: read, write, trap,
and traversal operations.
• The read command is used by an NMS to monitor managed devices. The NMS examines
different variables that are maintained by managed devices.
•
The write command is used by an NMS to control managed devices. The NMS changes the
values of variables stored within managed devices.
• The trap command is used by managed devices to asynchronously report events to the NMS.
When certain types of events occur, a managed device sends a trap to the NMS.
• Traversal operations are used by the NMS to determine which variables a managed device
supports and to sequentially gather information in variable tables, such as a routing table.
20.1.4 SNMP Management Information Base (MIB)
A Management Information Base (MIB) is a collection of information that is organized hierarchically.
MIBs are accessed using a network-management protocol such as SNMP. They are comprised of
managed objects and are identified by object identifiers.
Managed objects are accessed via a virtual information store, termed the Management Information
Base or MIB. Objects in the MIB are defined using the subset of abstract syntax notation one (ASN.1)
defined in the SMI. In particular, an
object identifier , an administratively assigned name, names each
object type. The object type together with an object instance serves to uniquely identify a specific
instantiation of the object. For human convenience, a textual string, termed the descriptor, to refer to
the object type, is often used.
An object identifier (OID) world-wide identifies a managed object in the MIB hierarchy. The MIB
hierarchy can be depicted as a tree with a nameless root, the levels of which are assigned by different
organizations.
20.1.5 Network Management Framework
This section provides a brief overview of the current SNMP management framework. An overall
architecture is described in RFC 2571 “An Architecture for Describing SNMP Management
Frameworks”. The SNMP management framework has several components:
• Mechanisms for describing and naming objects and events for the purpose of management.
The first version, Structure of Management Information (SMIv1) is described in RFC 1155
“Structure and Identification of Management Information for TCP/IP-based Internets”, RFC
1212 “Concise MIB Definitions”, RFC 1213 “Management Information Base for Network
Management of TCP/IP-based Internets: MIB-II”, and RFC 1215 “A Convention for Defining
Traps for use with the SNMP”. The second version, SMIv2, is described in RFC 2233 “The
Interfaces Group MIB using SMIv2”, RFC 2578 “Structure of Management Information
Version 2 (SMIv2)”, RFC 2579 “Textual Conventions for SMIv2”, and RFC 2580
“Conformance Statements for SMIv2”.
• Message protocols for transferring management information. The first version, SNMPv1, is
described in RFC 1157 “A Simple Network Management Protocol (SNMP).” The second
version, SNMPv2, which is not an Internet standards track protocol, is described in RFC 1901
“Introduction to Community-Based SNMPv2” and RFC 1906 “Transport Mappings for
Version 2 of the Simple Network Management Protocol (SNMPv2)”.
• Protocol operations for accessing management information. The first set of protocol