General principles
SNMP is designed around the concept of a relationship between a management station and managed agents.
A management station is the location where a network administrator can view, analyze, and even manage local network devices. A management station can be a dedicated computer or workstation, or software running on a general-purpose workstation—like a personal computer running SNMP Extension on Windows 2000/XP.
An SNMP agent is a program that runs on the managed device. It collects information about device operation. For example, if the object is a TCP/IP router, the agent can collect information about network traffic passing through the router and information about the behavior of the router itself under different load conditions.
The SNMP agent maintains a database called the Management Information Base (MIB). The agent uses the MIB to track and systematically update data. Information in a MIB is organized in a tree structure. Each piece of data can be considered a leaf on various branches of the tree. Individual pieces of data are called data objects.
When the management station needs information from an SNMP agent, it sends an SNMP request. SNMP specifications allow the station to ask for more than one MIB object in a single request.
When the SNMP agent receives the request, it searches its local MIB, finds the current values of the requested data, forms a response packet (PDU), and sends the PDU back to the management station.
The management station receives the PDU, decodes it from the SNMP PDU format, and displays the information as a list or in a graphical format that allows the network manager to view, analyze, and modify the information.
The following sections review the concepts above in more detail.