1. SNMP Management Information
J. Won-Ki Hong
Dept. of Computer Science and Engineering
POSTECH
Tel: 1 1

2. Table of Contents Structure of Management Information Overview
Meanings of MIB
SNMP MIB Structure
MIB Object Syntax
Defining MIB Objects
Defining MIB Tables 3

3. 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 4

4. 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 4

5. MIB Structure all MOs are structured hierarchically
Leaf objects in the tree are real MOs
Each MO has an OBJECT IDENTIFIER (OID)
root
ccitt(0)
iso(1)
joint-iso-ccitt(2)
org(3)
dod(6)
internet(1)
mgmt(2)
experimental(3)
snmpv2(6)
private(4)
mib-2(1)
enterprises(1) 4

6. Object Identifier (OID)
uniquely identifies an MO in the MIB
internet OBJECT IDENTIFIER : =
{ iso(1) org(3) dod(6) 1}
can be written as { } or
OID for tcpConnTable is
iso org dod internet mgmt mib-2 tcp tcpConnTable
What is the OID for the object ifInOctets? (Hint: see MIB-II interfaces group, Fig 5.1 & 6.2) 4

7. 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 4

8. 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) 4

9. 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) 4

10. Encoding MOs
Objects in the MIB are encoded using the basic encoding rules (BER)
BER is a widely used and standard encoding scheme 4