System information

SNMP Technical Overview 389
By the end of 1991, the standard SNMP MIB specification was extended by the Remote
Network Monitoring MIB (RMON). RMON provides a set of SNMP objects related to
network analysis and monitoring. Information provided by RMON is somewhat different
in scope from the typical SNMP information provided by network devices. Usually, a
device collects information about the device itself, in connection to either operation of the
device or its relationship to the network. The RMON agent, on the other hand, attempts to
collect information about network traffic to and from other devices on the network (aside
from the agent device), including network statistics, history, information about hosts on
the network, connections, and events. An RMON agent can set filters and capture traffic to
and from specific devices on the network.
Security concerns related to SNMP prompted development of a secure SNMP called S-
SNMP, and the first S-SNMP RFCs appeared in mid-1992. S-SNMP adds security
enhancements to the original SNMP protocol but does not offer any additional
functionality. S-SNMP is not compatible with the original SNMP.
About the same time, a considerable design effort focused on enhancing the SNMP
protocol, incorporating the security features provided by S-SNMP and adding new MIB
functionality. The result of this effort is SNMP Version 2, or SNMPv2.
SMNPv2 was not received enthusiastically by many software and hardware vendors.
Many had devoted considerable effort to the development of SNMP MIB I and MIB II
agents, and in many cases security was not important for users. Most agents currently
provided by vendors are SNMP MIB II, not SNMPv2.
SNMP MIB II with proprietary functionality is currently the defacto standard among
SNMP users. This overview addresses the general principles of SNMP without addressing
the details of SNMPv2.
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.