SNMP Management Information J. Won-Ki Hong Dept. of Computer Science and Engineering POSTECH Tel: 054-279-2244 Email: jwkhong@postech.ac.kr 1 1

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

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

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

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) 4

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

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

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

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