6.5 How the DMI Mapper Works

The subagent registers the DMI components in the system with the SNMP Master Agent. Proper mapping on the part of the mapper requires that the MIF structure of a component be identified in a mapping file used by the subagent when it is processing requests from the SNMP agent. The mapping file contains a unique SNMP OID for the component. The OID is used as a registration point for the Master Agent.

To generate the mapping file, perform one of the following tasks:

• Create the file manually using a text editor.

• Use the miftomib utility to generate the mapping file and a corresponding SNMP MIB file for the component MIF.

The operational process of the subagent has the following states:

• Initialization

• Normal operation

• Exception reporting

• Termination

These states provide a general operational flow. The mapper snmpXdmid runs as a daemon. Normally, it waits for SNMP requests. On arrival of the request, it processes the request, returns the response, then continues to wait for further SNMP requests. This mapper also receives indications from the DMI SP. These are then forwarded by default as SNMP traps.

6.5.1 Initializing and Reinitializing the Subagent

The mapper normally starts at the system boot time through startup scripts. The mapper startup must be performed in the later stages of system startup. This enables the SNMP Master Agent and DMI (SP) to be initialized. Dynamic registration then takes place between snmpXdmid and both the Master Agent and the DMI SP.

1. The mapper uses the Management Interface (MI) registration call to register itself with the Service Provider (SP) before any other management activity may be initiated.

   This enables the SP to provide services (such as access to the MIF database). The mapper also adds an entry in the subscription table/filter table on the SP to receive indications.

2. The mapper builds the translation table.

   The translation table retains a Master Agent registration point for each unique pair of SNMP OID prefix and component names it finds in the .MAP files. When constructing these translation tables, the mapper searches all .MAP files in the /var/dmi/map directory.

   Identifiers for these components, along with group identifiers associated with each component, are retained for translation. Attributes of installed components not found in a .MAP file by the program are inaccessible by the SNMP agent. Whenever a component is installed or uninstalled, the translation tables are appropriately adjusted.

   The mapper re-reads all the map files when a new component is registered with the SP to insure that the translation tables are always current.

3. The mapper connects to the Master Agent.

   Before the communication may take place for this connection, the mapper must establish a connection and register with the Master Agent.

   Registration is achieved by using the following definitions:

   • Subagent ID

   • Agent status = ACTIVE

   • Timeout value

   • Subagent name

   • Subagent address

4. At this point, the agent registers the object ID for the MIB for which it is responsible.

   The MIB OID prefixes that have been retrieved from the .MAP files are used for registration. OID prefixes associated with component names for which there are no installed components may also be registered.

   On initialization, if the DMI and its interfaces are functional, and the translation table is correct, a cold-start trap is sent to the agent. Refer to "6.6.1 Exception Reporting" for more information on trapping.

   Reinitialization occurs upon detection of a severe or potentially severe error. This may be an error in communicating with either DMI or the Master Agent. On reinitializing DMI, Master Agent, and table initialization, a warm-start trap is sent to the Master Agent.