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SNMP Fundamentals

This section of the guide is a brief overview of several core SNMP concepts. To start troubleshooting SNMP issues immediately, simply jump ahead.

A Brief History of SNMP

Since its creation in 1988 as a short-term solution to manage elements in the growing Internet and other attached networks, SNMP has achieved widespread acceptance.

SNMP was derived from its predecessor, SGMP (Simple Gateway Management Protocol), and was intended to be replaced by a solution based on the CMIS/CMIP (Common Management Information Service/Protocol) architecture. This long-term solution, however, never received the widespread acceptance of SNMP.

SNMP Architecture

SNMP is based on the manager/agent model, consisting of a manager, an agent, a database of management information, managed objects, and the network protocol. The manager provides the interface between the human network manager and the management system. The agent provides the interface between the manager and the physical device(s) being managed.

The manager and agent use a Management Information Base (MIB) and a relatively small set of commands to exchange information. The MIB is organized in a tree structure with individual variables, such as point status or description, being represented as leaves on the branches. A long numeric tag or object identifier (OID) is used to distinguish each variable uniquely in the MIB and in SNMP messages.

The manager/agent model is very simple on the surface, but it takes many different forms. You have many different devices, each with their own MIB. Sometimes, manufacturers who claim, "Our device is SNMP compatible" will not provide a MIB. That makes it incredibly difficult to actually use SNMP for that device.

Since the original introduction of SNMPv1, architecture has been complicated by the arrival of new SNMP versions. V2c and V3 managers are generally backward-compatible with earlier versions, but security can become a concern. You may not WANT to use SNMP versions earlier than SNMPv3 to make sure that your remote-management traffic is always encrypted.

The different generations of SNMP have created a definite fracturing of what was once a simple architecture. Now, you have to consider the multi-generational SNMP versions you have in play and consider mediation devices to convert older SNMP to SNMPv3.

Next Page: Understanding OID
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