SNMP technical overview
Simple Network Management Protocol (SNMP) was proposed in 1988 as a set of Requests for Comments (RFCs) defining the basic principles and implementation for a protocol that would establish a standard for Internet monitoring and management, as a replacement for the myriad of vendor-specific network management solutions available at the time.
Since then, SNMP has gained considerable popularity. Although it hasn’t replaced all proprietary solutions, it has become a widely accepted standard for network management. Subsequent RFCs for SNMP have corrected problems and supplemented the original standard Management Information Base (MIB).
The standard MIB, defined by RFC1213, defines numerous objects in ten groups—system, interfaces, address translation, IP, ICMP, TCP, UDP, EGP, transmission, and SNMP.
However, manufacturers are constantly adding capabilities to their products, and some of them are not covered by the standard objects and groups. To bring the benefits of SNMP monitoring and control to additional features, software and hardware vendors have developed proprietary MIBs.
Most major computer hardware manufacturers now offer lines of networking products that support SNMP, including network cards, hubs, bridges, routers, switches, and printers. Because adding an SNMP agent to network hardware often increases the price of the product, manufacturers usually offer versions with and without SNMP support.
Most operating systems, including UNIX and Microsoft Windows systems, implement SNMP agents in their architecture.
In early 1990, the original SNMP specifications were revised and updated. New MIB groups were added and some old MIB objects became obsolete. In general, the new MIB specification, called MIB II (or MIB-2) is compatible with the original MIB, now called MIB I.
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.