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POSTECH DP&NM Lab

SNMP ManagementInformation

J. Won-Ki Hong

Dept. of Computer Science and Engineering

POSTECH

Tel: 054-279-2244

Email: jwkhong@postech.ac.kr

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POSTECH DP&NM Lab

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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POSTECH DP&NM Lab

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 th

e 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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POSTECH DP&NM Lab

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 document containing definitions of management information

a module written in a computer parsable form containing definitions

MIB module

the MIB a MIB

a managed system

a system's MIB

management information

1 2 3MIB document

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POSTECH DP&NM Lab

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) private(4) snmpv2(6)

mib-2(1) enterprises(1)

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POSTECH DP&NM Lab

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: s

ee MIB-II interfaces group, Fig 5.1 & 6.2)

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POSTECH DP&NM Lab

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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POSTECH DP&NM Lab

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 whic

h is implemented in most SNMP agents today• OBJECT TYPE MACRO definition is used to defin

e MOs– see Figure 5.3 (Macro for Managed Objects - RFC 1212)– see Figure 5.4 (SMI - RFC 1155)

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POSTECH DP&NM Lab

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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POSTECH DP&NM Lab

Encoding MOs• Objects in the MIB are encoded using the basic

encoding rules (BER)• BER is a widely used and standard encoding

scheme