Understanding SNMP

Simple Network Management Protocol (SNMP) is a vendor-independentprotocol for transporting management data between networked devices andapplications and the systems that control and monitor those devices andapplications. The Internet community first developed SNMP in 1987 to augmentexisting TCP/IP network management tools (e.g., ping). SNMP is based on Internetstandards. Several Internet Engineering Task Force (IETF) Request for Comments(RFCs) define SNMP (notably RFC 1157). Because of SNMP's origins, many usersimplement it over IP. In fact, User Datagram Protocol (UDP) ports 161 and 162identify SNMP agents and managers, respectively. However, you can deliver SNMPmessages using other protocols such as SNA.

MIBs, Agents, and Traps
SNMP-compliant hardware and software ship with agent software to help trackrelevant information about network traffic and device or application statistics.These hardware and software resources store up-to-date information in managementinformation bases (MIBs--see IETF RFCs 1213 and 1573). MIBs are hierarchicalname spaces that contain relevant information about the device or applicationthat you are monitoring with SNMP.

Agent software generally waits to be polled by the SNMP-monitoring softwareand then returns the current values for the requested MIB objects. In additionto receiving information from devices and applications with built-in MIBs,several agent-building toolkits let you define custom MIBs and agents.

SNMP primarily uses two types of commands: get (to retrieveinformation) and set (to change it). Another command, trap,sends an alarm to a management station under predefined conditions.

SNMP's primary goal is simplicity, so it contains only three getcommands: GetRequest, GetResponse, and GetNextRequest. A new getcommand, GetBulk (which will let you retrieve information from more than one MIBat a time), is part of the proposed SNMPv2* (V2 star) specification in IETF RFCs1441 through 1452.

SNMPv2* is emerging to address problems of scalability--because of thenature of the simple manager and agent model, SNMP doesn't scalewell--manager-to-manager communications, and security. Be aware, however, thatmany individuals in the computer industry do not support the adoption of SNMPv2*because it isn't a simple superset of SNMP and it doesn't support backwardcompatibility. For more information about SNMP, check the following Web sitesand USENET newsgroup: