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Step 2 : Create a Map Descriptor (MD) to catch the Trap
Pay special consideration to the following parameters;
•SNMP_OID: Specify the OID of the event state. The field must contain an integer value which is the value that will be stored. When the trap is received the driver extracts the contents and takes the 1st OID in the message and looks for a MD whose ‘SNMP_OID’ matches. If it doesn’t find one then the trap is discarded.
•SNMP_Trap_Store_Method: Set the value of this parameter to ‘Lookup’. This tells the driver to use the lookup table and also to use
the following two parameters;
o SNMP_OID_Index1: Specify the OID of the field that contains the 1st part of the search/lookup string. Once the driver sees that a ‘Lookup’ store is to be done it extracts the string contents of this OID to form the 1st part of the search string.
o SNMP_OID_Index2: Specify the OID of the field that contains the 2nd part of the search/lookup string. Once the driver sees
that a ‘Lookup’ store is to be done it extracts the string contents of this OID to form the search string by adding a colon to the 1st part and then appending the string found in this OID.
Map_Descriptor_Name, | Data_Array_Name, | Data_Array_Offset, | Function, | Node_Name, | SNMP_OID, | SNMP_Trap_Store_Method, | SNMP_OID_Index1, | SNMP_OID_Index2 |
MD1, | DA_TRAPS, | 0, | Passive_Client, | Agent 1, | 1.3.6.1.4.1.290.1.0, | Lookup, | 1.3.6.1.4.1.290.2, | 1.3.6.1.4.1.290.3 |
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The following notes refer to the decoded SNMP trap message shown above in this section.
•Driver receives trap and starts extracting data from the message
•Driver finds OID= 1.3.6.1.4.1.290.1, extracts the Integer value=4 and searches for an MD with SNMP_OID= 1.3.6.1.4.1.290.1
•The MD specifying Storage Method=Lookup and Data Array Name = DA_TRAPS is found. (If not found, the message is discarded.)
•Driver finds IOD = 1.3.6.1.4.1.290.2 and extracts a string = CROSSTWN_KDA
•Driver compares the extracted OID to the OID specified by ‘SNMP_OID_Index1’. If it matches then it forms the 1st fragment of the search string, otherwise the driver continues extracting OID’s from the trap.
•Driver finds IOD = 1.3.6.1.4.1.290.3 and extracts a string = EMS_84_900MHZ_RADIO_B
•Driver compares the extracted OID to the OID specified by ‘SNMP_OID_Index2’. If it matches then it forms the 2nd fragment of the search string, otherwise the driver continues extracting OID’s from the trap.
•Once a complete search string is formed, the driver starts searching the lookup table defined in step1. The search is case insensitive. A match is made with offset 3 and the driver stores the value 4 at offset 3 in DA_TRAPS. (If the search fails – there is no matching entry then the driver uses offset zero). The offsets are relative to the offset specified by ‘Data_Array_Offset’.
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