SNMP Management Information

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SNMP ManagementInformation

• J. Won-Ki Hong
• Dept. of Computer Science and Engineering
• POSTECH
• Tel [phone]
• Email jwkhong_at_postech.ac.kr

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Table of Contents

• Structure of Management Information
• Overview
• Meanings of MIB
• SNMP MIB Structure
• MIB Object Syntax
• Defining MIB Objects
• Defining MIB Tables

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Overview of SNMP SMI

• Structure of Management Information (SMI)
• RFC 1155 (Full Standard)
• defines the general framework for defining SNMP
  MIBs
• describes how the managed objects (MOs) can be
  defined in the MIB, data types and values MOs can
  have and how MOs are named
• SNMP SMI uses a subset of ASN.1
• SNMP MIB can store only simple data types
• scalars
• 2-dimensional arrays of scalars

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Meanings of MIB

• a MIB - a single MO definition
• the MIB - the union of all MO definitions
• MIB - the actual values of management
  information in a system

a system's MIB
MIB document
1
2
3
the MIB
MIB module
a MIB
a document containing definitions of management
information
management information
a module written in a computer parsable form
containing definitions
a managed system
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MIB Structure

• all MOs are structured hierarchically
• Leaf objects in the tree are real MOs
• Each MO has an OBJECT IDENTIFIER (OID)

root
joint-iso-ccitt(2)
iso(1)
ccitt(0)
org(3)
dod(6)
internet(1)
mgmt(2)
experimental(3)
snmpv2(6)
private(4)
mib-2(1)
enterprises(1)
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Object Identifier (OID)

• uniquely identifies an MO in the MIB
• internet OBJECT IDENTIFIER
• iso(1) org(3) dod(6) 1
• can be written as 1 3 6 1 or 1.3.6.1
• OID for tcpConnTable is 1.3.6.1.2.1.6.13
• iso org dod internet mgmt mib-2 tcp tcpConnTable
• 1 3 6 1 2 1
  6 13
• What is the OID for the object ifInOctets? (Hint
  see MIB-II interfaces group, Fig 5.1 6.2)

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Managed Object Syntax

• ASN.1 notation is used to define MOs and the
  entire MIB structure

• Universal Types
• INTEGER
• OCTET STRING
• NULL
• OBJECT IDENTIFIER
• SEQUENCE
• SEQUENCE-OF

• Application-wide Types
• Networkaddress
• Ipaddress
• Counter
• Gauge
• Timeticks
• Opaque

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Defining Managed Objects

• the macro definition used for SNMP MIBs was
  initially defined in RFC 1155 (SMI) and later
  expanded in RFC 1212 (Concise MIB Definition)
• RFC 1155 is used for defining MOs in MIB-I
• RFC 1212 is used for defining MOs in MIB-II which
  is implemented in most SNMP agents today
• OBJECT TYPE MACRO definition is used to define
  MOs
• see Figure 5.3 (Macro for Managed Objects - RFC
  1212)
• see Figure 5.4 (SMI - RFC 1155)

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Defining MO Tables

• SNMP MIB structure is a simple 2-dimensional
  table with scalar-valued entries
• A table typically consists of a SEQUENCE OF some
  entries
• A table entry typically consists of a SEQUENCE
  that includes a number of scalar elements
• See Figure 5.6 (MIB-II Specification of TCP
  Connection Table - RFC 1213)

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Encoding MOs

• Objects in the MIB are encoded using the basic
  encoding rules (BER)
• BER is a widely used and standard encoding scheme
• READING Read Chapter 5