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Appendix A. Advanced Topics |
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Appendix A.1. Receiving SNMP TRAPS |
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A trap can reveal the causal event in two ways:
•The cause can be indicated by the OID number inside the trap with the event state reported by the associated data value.
•The cause can be indicated by the value of one OID field and the event state by the value of another OID field.
Appendix A.1.1. Trap Source IP Address
When a trap is received it contains its source IP address information within the UDP packet header. It is possible for a trap to reveal its source IP address by coding an IP_ADDRESS field inside the trap.
To catch a trap it is necessary to define Map Descriptors containing the OID’s of the trap. Map Descriptors are associated with a Node. A Node is defined by its IP address amongst other parameters. When a trap is received the source of the IP address must match the IP address of the Node associated with the Map Descriptor.
A trap may originate from one IP address, and contain an alternative source IP Address within the message. In this case, the FieldServer will use the IP_Address contained within the message as the source rather than the IP address of the sending device. When this situation occurs the driver prints a message to the error log so that you know why, perhaps, the trap was ignored/processed differently from your expectations."
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