Previous Table of Contents Next


Chapter 3
Management Information Bases

This chapter is the second of three to discuss Internet network management standards. Chapter 2 discussed the SMI, which defines the syntax that retrieves and communicates information, the ways information is placed into logical groups, and the naming mechanisms, known as the object identifiers, that identify each managed object.

This chapter extends the discussion of naming mechanisms to include management information bases (MIBs), which store management information. Chapter 4 considers the protocol mechanisms, including SNMP, the User Datagram Protocol (UDP), the Internet Protocol (IP), and the Internet Control Message Protocol (ICMP), that communicate management information.

You can think of a MIB as a virtual information warehouse. Like a physical warehouse with specific floors, aisles, and bins, the MIB must implement an inventory control scheme. SMI defines the scheme for the MIBs. Just as a large company can have several warehouses, there are several different types of MIBs. Some, such as Internet standards, are for public use; specific organizations have developed others for private use for their products.

Network managers must understand the concepts underlying the SMI and learn to apply them to the available MIBs.

3.1 MIBs within the Internet Object Identifier Subtree

Section 2.6 discussed the Internet network management naming structure. A tree represents the management structure, with branches and leaves representing the managed objects (Figure 3-1). This discussion focuses on the Internet subtree, designated {1.3.6.1}. In the figure, you can see seven subtrees under Internet: directory (1), mgmt (2), experimental (3), private (4), security (5), snmpV2 (6), and mail (7).


Figure 3-1.  The Internet OID tree

The directory (1) subtree is reserved for future use of the OSI directory within the Internet. The mgmt (2) subtree handles Internet-approved documents, such as the Internet standard MIBs, which are MIB-I (see RFC 1156) and MIB-II (see RFC 1213). An object identifier (OID) with a prefix of {1.3.6.1.2.1} denotes managed objects within MIB-I and MIB-II.

Internet experiments use the experimental subtree (3). The Internet Assigned Numbers Authority (IANA) at the USC-Information Sciences Institute (e-mail iana@isi.edu) administers this subtree.

The private subtree (4) allows vendors to register a MIB for their equipment. The enterprise subtree, whose branches are private organizations, falls under the private subtree. The IANA assigns “enterprise codes” to branches representing private organizations and publishes them in the current assigned numbers RFC (currently RFC 1700). Enterprise OIDs begin with the prefix {1.3.6.1.4.1}. Appendix F lists the currently assigned enterprise codes.

This chapter focuses primarily on the mgmt MIBs. MIB-I was the first version of the mgmt MIBs and was defined in RFC 1156 ([reference 3-1]). MIB-II (RFC 1213) {3.2} replaced the earlier version. This chapter also discusses the remote network monitoring (RMON) MIBs for Ethernet and token ring networks, which are also under the mgmt subtree. Other subtrees contain objects for security, SNMP version 2 (which will be discussed in Chapter 5), and mail.

3.2. MIB Development

As noted previously, MIBs address the need for a standard network management platform by the Internet as a whole and by private enterprises. These MIBs require a consistent objective and format to realize this objective. Let’s begin by discussing the history of various MIBs so you can see the basis of these developments.

3.2.1 MIB-I—RFC 1156

The first MIB, MIB-I (RFC 1156), was published in May 1990. MIB-I divided managed objects into eight groups in order to simplify OID assignment and implementation (that is, the SMI “structure”). Those groups were System, Interfaces, Address Translation, IP, ICMP, TCP, UDP, and EGP. Elements from RFC 1212, The Concise MIB Definitions, and RFC 1213, known as MIB-II and published in March 1991, have replaced MIB-I.

3.2.2 Concise MIB Definitions—RFC 1212

With different private enterprises developing MIBs, it’s necessary to develop a consistent format for MIB modules. RFC 1212, entitled “Concise MIB Definitions,” addresses this issue [3-3]. Prior to the publication of RFC 1212, there were two ways to define objects: a textual definition and the ASN.1 OBJECT-TYPE macro, which is discussed in Section 2.4.1. RFC 1212 embedded the textual definition within the OBJECT-TYPE macro, reducing the amount of documentation. The Concise SMI Definition includes this macro (review Section 2.7).


Previous Table of Contents Next