SNMP, MIBs and OIDs – an Overview


In general, the RA for a sub-node operates independently in allocating further sub-arcs to other organizations, but can be constrained by rules imposed by its superior, should the superior so wish.

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There are two types of MIBs: Scalar objects define a single object instance whereas tabular objects define multiple related object instances grouped in MIB tables. MIBs are collections of definitions which define the properties of the managed object within the device to be managed. The typical objects to monitor on a printer are the different cartridge states and maybe the number of printed files, and on a switch the typical objects of interest are the incoming and outgoing traffic as well as the rate of package loss or the number of packets addressed to a broadcast address.

OIDs stands for O bject Id entifiers. This can be depicted as a tree, the levels of which are assigned by different organizations. These numbers are the ones used in PRTG when setting up custom sensors, in order to access the appropriate elements of the device that you want to monitor. That means that it monitors a selected device and its specific OID. More information about PRTG SNMP v1 is considered the de facto network management protocol in the Internet community. SNMP works on the basis that network management systems send out a request and the managed devices return a response.

This is implemented using one of four operations: Get, GetNext, Set, and Trap. The headers consist of the SNMP version number and the community name. The community name is used as a form of security in SNMP. The PDU depends on the type of message that is being sent. MIBs are a collection of definitions which define the properties of the managed object within the device to be managed such as a router, switch, etc.

Each managed device keeps a database of values for each of the definitions written in the MIB. As such, it is not actually database but implementation dependant. In order for all of this to be properly organized, all of the manageable features of all products from each vendor are arranged in this tree. This is the OID. Nodes near the top of the tree are extremely general I nature. For example, to get to the Internet, one has to reach to the fourth tier. As one moves further down, the names get more and more specific, until one gets to the bottom, where each node represents a particular feature on a specific device or agent.

A managed device is a node that has an SNMP agent and resides on a managed network. It is not intended to be used for transient naming. It is based on a hierarchical name structure based on the " OID tree ". This naming structure uses a sequence of names, of which the first name identifies a top-level "node" in the OID tree, and the next provides further identification of arcs leading to sub-nodes beneath the top-level, and so on to any depth.

A critical feature of this identification mechanism is that it makes OIDs available to a great many organizations and specifications for their own use including countries, ITU-T Recommendations, ISO and IEC International Standards, specifications from national, regional or international organizations, etc.

At each node, including the root, there is a requirement for some organization or standard to be responsible for allocating arcs to sub-nodes and recording that allocation together with the organization the subordinate node has been allocated to , not necessarily publicly.

This activity is called a Registration Authority RA. In general, the RA for a sub-node operates independently in allocating further sub-arcs to other organizations, but can be constrained by rules imposed by its superior, should the superior so wish. The registration tree is indeed managed in a completely decentralized way a node gives full power to its children.

Initially, it was left for each Registration Authority RA in the hierarchy to maintain its own record of allocation beneath that RA, and to keep those allocations private if it so chose. There was never any policing of this.

An RA in the hierarchy was its own master and operated autonomously. In the early s Orange developed software for their internal use which was generic enough to provide a publicly available repository of OID allocations.

Information on OIDs is often buried inside the databases perhaps sometimes paper maintained by an immense number of RAs. The information can be hard to access and is sometimes private. Today this OID repository is regarded as the easiest way to access a large amount of the publicly available information on OIDs: