An Object Identifier or OID is used to identify a node in a hierarchy. An Object Identifier consists of a sequence of numbers, where the first number identifies the root node and subsequent numbers identify subnodes. For example, the object identifier 1.3.6.1.2.1.1.1 represents the sysDescr property of an SNMP Agent. The numbers in this sequence represent: iso(1), org(3), dod(6), internet(1), mgmt(2), mib-2(1), system(1), sysDescr(1).
The most common object identifier prefixes are 1.3.6.1.2.1 (mib-2) and 1.3.6.1.4.1 (enterprises).
The Internet Engineering Task Force document RFC1213 defines the hierarchy below 1.3.6.1.2.1 (mib-2). Examples of mib-2 object identifiers include:
| Object Identifier Name | Description |
|---|---|
| 1.3.6.1.2.1.1.1 sysDescr | The description of the SNMP Agent |
| 1.3.6.1.2.1.1.3 sysUpTime | The elapsed time since the SNMP agent was started |
| 1.3.6.1.2.1.4.3 ipInReceives | The total number of received IP datagrams |
| 1.3.6.1.2.1.4.7 ipInUnknownProtos | The total number of discarded IP datagrams due an unknown protocol |
| 1.3.6.1.2.1.6.10 tcpInSegs | The total number of TCP segments received |
| 1.3.6.1.2.1.6.11 tcpOutSegs | The total number of TCP segments sent |
Any organization can define their own custom hierarchy to identify data not defined in the mib-2 standard. Each organization is allocated a unique private enterprise number (PEN) by the Internet Assigned Numbers Authority (IANA). Examples of some private enterprise numbers (PEN) include:
| Organization | PEN | Object Identifier |
|---|---|---|
| IBM | 2 | 1.3.6.1.4.1.2 |
| Cisco | 9 | 1.3.6.1.4.1.9 |
| Xerox | 253 | 1.3.6.1.4.1.253 |
| Siemens AG Automation & Drives | 4196 | 1.3.6.1.4.1.4196 |
| TP-Link | 11863 | 1.3.6.1.4.1.11863 |
| Omron Corporation | 16838 | 1.3.6.1.4.1.16838 |
Organizations are free to define their own hierarchy below their private enterprise object identifier. Organizations define their own hierarchy using MIB files, and usually make these available on their product support website.
You can view MIB files in any text editor. As an alternative you can use a MIB browser, for example SnmpB.
For an overview of the SNMP Client Driver.
For information about other drivers available in Fernhill SCADA.
For the meaning of terms used in Fernhill SCADA.