Daily Archives: October 25, 2010

SMIv2-Structure of Management Information

The Structure of Management Information version 2(SMIv2) is component for network management. Its Functions are:

  1. To name Objects.
  2. To define the type of data that can be stored in an object.
  3. To show how to encode data for transmission over the network.

SMI is a guideline for SNMP. It emphasizes three attributes to handle an object: name, data type, and encoding method.


SMI requires that each managed object (such as a router, a variable in a router, a value, etc.) have a unique name. To name objects globally, SMI uses an object identifier, which is a hierarchical identifier based on a tree structure.

The tree structure starts with an unnamed root. Each object can be defined using a sequence of integers separated by dots. The tree structure can also define an object using a sequence of textual names separated by dots. The integer-dot representation is used in SNMP. The name-dot representation is used by people.

The image shows the same object with two different notations:

iso.org.dod.internet <——–>

The objects that are used in SNMP are located under the mib-2 object, so their identifiers always start with


The second attribute of an object is the type of data stored in it. To define the data type, SMI uses fundamental Abstract Syntax Notation 1 (ASN.1) definitions and adds some new definitions. In other words, SMI is both a subset and a superset of ASN.1.

SMI has two broad categories of data type:


Simple Type – Simple Data Types are atomic data types. SOme of them are taken directly form ASN.1; some are added by SMI.
Structured Type – By combining simple and structured data types we can make new structured dat types. SMI defines two structured data types

  • SEQUENCE – A Sequence data type is a combination of simple data types, not necessarily of the same type. It is similar to the                                                  STRUCTURE used in C.
  • SEQUENCE OF – A Sequence of data type is a combination of simple data types all of the same type or combination of Sequence data                                           types all of same type. It is similar to ARRAY used in C.

I hope you have now understood what SMIv2 is and why, how, and where it is used.


SNMP-Simple Network Management Protocol

Many of my friends asked me to write on SNMP since they didn’t get much information about it from the Internet. So this post is for my friends who want to read about Simple Network Management Protocol (from now on SNMP) .

The SNMP is a framework for managing devices in an Internet using the TCP/IP protocol suite. It provides a set of fundamental operations for monitoring and maintaining the Internet.


SNMP uses the concept of manager and agent. That is, a manager. usually a host,controls and monitors a set of agents, usually routers.

SNMP is an application-level protocol in which a few manager stations control a set of agents. The protocol is designed at application level so that it can monitor devices made by different manufacturers and installed on different physical networks. In other words, SNMP frees management tasks from both the physical characteristics of managed devices and the underlying network technology. It can be used in heterogeneous internet made of different LANs & WANs connected by routers made by different manufacturers.

Managers and Agents

A management station, called a Manager, is a host that runs the SNMP client program. A managed station, called the Agent, is a router (or a host) that runs the SNMP server program. Management is achieved through simple interaction between manager and an agent.

The agent keeps performance information in a database. The manager has access to the values in the database. The manager can also make the router perform certain actions.

Agents can also contribute to management process. The server program running on the agent can check the environment and, if it notices something unusual, it can send a warning message (called a TRAP) to the manager.

In other words. management with SNMP is based on 3 basic ideas:

  1. A manager checks an agent by requesting information that reflects the behavior of the agent.
  2. A manager forces an agent to perform a task by resetting values in the agent database.
  3. An agent contributed to the management process by warning the manager of an unusual situation.

Management Components:

To do  management tasks, SNMP uses to other protocols

  • Structure of Management Information (SMI)
  • Management Information Base (MIB)

In other words, management of Internet is done through the cooperation of 3 protocols: SNMP, SMI, MIB

SMI & MIB discussed in above posts.

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