SNMP (Simple Network Management Protocol) uses Object Identifiers (OIDs) to uniquely identify managed objects within a Management Information Base (MIB). OIDs are hierarchical in nature and follow a standardized notation. Let’s explore the concept of SNMP OID values and provide some examples:
- Structure of OID:
- OIDs are represented as a series of numbers separated by dots (periods).
- Each number represents a node in the OID tree structure.
- The first arc in the OID denotes the organization or standards body that defines the object.
- The subsequent arcs represent subidentifiers within that organization’s subtree.
- Example OID: iso.org.dod.internet.mgmt.mib-2.system.sysDescr
- iso (1). org (3). dod (6). internet (1). mgmt (2). mib-2 (1). system (1). sysDescr (1)
- In this example, the OID represents the system description object in the SNMP MIB-2 subtree.
- MIB-2:
- The MIB-2 subtree is a commonly used OID tree defined in the SNMP standard (RFC 1213) and contains commonly monitored objects.
- Examples of MIB-2 OIDs include:
- sysDescr (1.3.6.1.2.1.1.1): System description.
- sysUpTime (1.3.6.1.2.1.1.3): System uptime.
- ifDescr (1.3.6.1.2.1.2.2.1.2): Interface description.
- ifInOctets (1.3.6.1.2.1.2.2.1.10): Input octets on an interface.
- Vendor-Specific OIDs:
- Vendors often define their own OIDs to represent specific objects within their devices’ MIBs.
- Examples of vendor-specific OIDs include:
- Cisco’s ciscoEnvMonTemperatureStatusValue (1.3.6.1.4.1.9.9.13.1.3.1.3): Environmental temperature status on Cisco devices.
- Juniper’s jnxOperatingTemp (1.3.6.1.4.1.2636.3.1.13.1.7): Operating temperature on Juniper devices.
- OID Subidentifiers:
- OID subidentifiers can be numeric (e.g., 1, 2, 3) or textual (e.g., “sysDescr”, “ifDescr”).
- Textual subidentifiers are typically defined in MIB files, which provide human-readable descriptions of the objects.
- OID Value Retrieval:
- SNMP managers can retrieve the value of an OID by querying SNMP agents using GET or GETNEXT operations.
- SNMP agents respond with the value associated with the requested OID.
- SNMP managers can recursively retrieve the values of entire OID trees by using GETBULK or GETNEXT operations.
OIDs play a crucial role in SNMP-based network management, enabling the identification and retrieval of specific objects within a managed network device. They provide a standardized way to reference and monitor network parameters, performance metrics, and device status.
