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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Network Configuration and Management Protocols (BOOTP, DHCP, SNMP and RMON)            9  TCP/IP Network Management Framework and Protocols (SNMP and RMON)

SNMP Version 3 (SNMPv3) Message Format 1 2 3 TCP/IP Key Applications and Application Protocols

The Simple Network Management Protocol (SNMP) defines both a framework and a specific protocol for exchanging network information on a TCP/IP internetwork. The general model used by SNMP is that of a network management station (NMS) that sends requests to SNMP agents running on managed devices. The SNMP agents may also initiate certain types of communication by sending trap messages to tell the NMS when particular events occur.

This model works well, which is why SNMP has become so popular. However, one fundamental limitation of the protocol and the model it uses is that it is oriented around the communication of network information from SNMP agents that are normally part of regular TCP/IP devices, such as hosts and routers. The amount of information gathered by these devices is usually somewhat limited, because obviously hosts and routers have “real work to do”—that is, doing the jobs of being hosts and routers. They can't devote themselves to network management tasks.

Thus, in situations where more information is needed about a network than is gathered by traditional devices, administrators often use special hardware units called network analyzers, monitors or probes. These are dedicated pieces of equipment that are connected to a network and used strictly for the purpose of gathering statistics and watching for events of interest or concern to the administrator. It would obviously be very useful if these devices could use SNMP to allow the information they gather to be retrieved, and to let them generate traps when they notice something important.

To enable this, the Remote Network Monitoring (RMON) specification was created. RMON is often called a protocol, and you will sometimes see SNMP and RMON referred to as “the TCP/IP network management protocols”. However, RMON really isn't a separate protocol at all—it defines no protocol operations. RMON is in fact part of SNMP, and the RMON specification is simply a management information base (MIB) module that defines a particular set of MIB objects for use by network monitoring probes. Architecturally, it is just one of the many MIB modules that comprise the SNMP Framework.

The first standard documenting RMON was RFC 1271, Remote Network Monitoring Management Information Base, published in 1991. RFC 1271 was replaced by RFC 1757 in 1995, which made a couple of changes to the specification. RFC 2819, May 2000, updates RMON to use the new Structure of Management Information version 2 (SMIv2) specification that is part of SNMPv2 but is functionally the same as RFC 1757.

SNMP Version 3 (SNMPv3) Message Format 1 2 3 TCP/IP Key Applications and Application Protocols