Support Classes for MIB Objects

When a routing instance is specified, all routing-related MIB objects return data maintained by the routing instance in the request. For all other MIB objects, the data returned is segregated according to that routing instance. For example, only those interfaces assigned to that routing instance (for example, the logical interfaces [ifls] as well as their corresponding physical interfaces [ifds]) are exposed by the SNMP agent. Similarly, objects with an unambiguous attachment to an interface (for example, addresses) are segregated as well.

For those objects where the attachment is ambiguous (for example, objects in sysApplMIB), no segregation is done and all instances are visible in all cases.

Another category of objects is visible only when no logical system is specified (only within the default logical system) regardless of the routing instance within the default logical system. Objects in this category are Chassis MIB objects, objects in the SNMP group, RMON alarm, event and log groups, Ping MIB objects, configuration management objects, and V3 objects.

In summary, to support routing instances, MIB objects fall into one of the following categories:

• Class 1—Data is segregated according to the routing instance in the request. This is the most granular of the segregation classes.
• Class 2—Data is segregated according to the logical system specified in the request. The same data is returned for all routing instances that belong to a particular logical system. Typically, this applies to routing table objects where it is difficult to extract routing instance information or where routing instances do not apply.
• Class 3—Data is exposed only for the default logical system. The same set of data is returned for all routing instances that belong to the default logical system. If you specify another logical system (not the default), no data is returned. Typically this class applies to objects implemented in subagents that do not monitor logical system changes and register their objects using only the default context (for example, Chassis MIB objects).
• Class 4—Data is not segregated by routing instance. The same data is returned for all routing instances. Typically, this applies to objects implemented in subagents that monitor logical system changes and register or deregister all their objects for each logical system change. Objects whose values cannot be segregated by routing instance fall into this class.

See MIB Support Details for a list of the objects associated with each class.

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