Simple Network Management Protocol (SNMP) is used by administrators to monitor and control remote hosts and gateways on an internetwork. The Windows NT SNMP service allows a Windows NT computer to be monitored remotely but does not include an application to monitor other SNMP systems on the network.
Note You must install the SNMP service to use the TCP/IP performance counters in Performance Monitor, as described in Chapter 17, "Using Performance Monitor with TCP/IP Services."
SNMP is a network management protocol widely used in TCP/IP networks. These kinds of protocols are used to communicate between a management program run by an administrator and the network management agent running on a host or gateway. These protocols define the form and meaning of the messages exchanged, the representation of names and values in the messages, and administrative relationships among hosts being managed. SNMP defines a set of variables that the host must keep and specifies that all operations on the gateway are side effects of getting, putting, or setting the data variables. Because different network-management services are used for different types of devices or for different network-management protocols, each service has its own set of objects. The entire set of objects that any service or protocol uses is referred to as its management information base (MIB).
The Windows NT SNMP service includes MIB II (based on RFC 1213) and LAN Manager MIB II plus MIBs for DHCP and WINS servers, as described in Appendix A, "MIB Object Types for Windows NT." The SNMP service allows SNMP-based managers to perform standard SNMP commands, such as reading the counters in the standard MIBs included with the service. Windows NT SNMP has an extensible architecture, so it can be used to create custom functionality on a Windows NT computer, such as starting and stopping specific services or shutting down the system.
The SNMP service works with any computer running Windows NT and the TCP/IP protocol. With the SNMP service, a Windows NT computer can report its current status to an SNMP management system on a TCP/IP network. The service sends status information to a host in the following two cases:
The SNMP service can handle requests from one or more hosts, and it can also report network-management information to one or more hosts, in discrete blocks of data called traps.
The SNMP service uses the unique host names and IP addresses of devices to recognize the host(s) to which it reports information and from which it receives requests.
When a network manager requests information about a device on the network, SNMP management software can be used to determine object values that represent network status. MIB objects represent various types of information about the device. For example, the management station might request an object called SvStatOpen, which would be the total number of files open on the Windows NT computer.
The SNMP service for Windows NT supports multiple MIBs through an agent Application Programming Interface (API) extension interface. At SNMP service startup time, the SNMP service loads all of the extension-agent dynamic link libraries (DLLs) that are defined in the Windows NT Registry. Two extension-agent DLLs come with Windows NT; others might be developed and added by users.