Agents

An agent is an SNMP program that must be installed on each managed computer in an SNMP-managed network. The Windows NT-based SNMP service includes an SNMP agent.

The agent program provides an interface to the MIBs and managed-objects installed on the computer. SNMP management programs send management requests to the computers on the network. The agent program on the computer receives the requests and processes them by retrieving information from the MIBs on the computer. The agent then sends the requested information back to the SNMP manager program that initiated the request.

The Windows NT-based SNMP service is an optional service that is installed after TCP/IP is installed on a Windows NT-based computer. After the SNMP service is installed on a computer, it automatically starts each time the computer is started.

When the agent program is started on a computer, it waits for SNMP requests from a manager program on the network management console (computer). When an agent program receives an SNMP message, it performs the requested get, get-next, and set operations.

The only operation that an agent spontaneously starts is a trap operation to alert the SNMP manager program that the computer has started, stopped, or is experiencing an extraordinary event (such as disk-full) on some managed-object on the computer.

In summary, the agent program performs the following operations:

• The get operation retrieves a specific value about a managed-object, such as available hard disk space, from the host MIB.
• The get-next operation returns the "next" value by traversing the MIB database of managed-object variables.
• The set operation changes the value of a managed-object variable. Only variables whose object definitions allow read/write access can be set.
• The trap operation sends messages to the SNMP management console when a change or error occurs in a managed-object.

Note

By installation default, the computer software port 161 is used to listen for SNMP messages and port 162 is used listen for SNMP traps. If you need to run multiple SNMP agents, you can change these port settings in the \systemroot\ System32\Drivers\Etc\Service\Service file.