If you use RFC-5424 formatted (IETF-syslog) messages, you can also create custom fields in the `SDATA` part of the message (For details on the `SDATA` message part, see The STRUCTURED-DATA message part).

According to RFC-5424, the name of the field (its SD-ID) must not contain the @ character for reserved SD-IDs. Custom SDATA fields must be in the following format: .SDATA.group-name@<private enterprise number>.field-name, for example, .SDATA.mySDATA-field-group@18372.4.mySDATA-field. (18372.4 is the private enterprise number of One Identity LLC, the developer of syslog-ng OSE.)

Example: Rewriting custom SDATA fields

The following example sets the sequence ID field of the RFC-5424 formatted (IETF-syslog) messages to a fixed value. This field is a predefined SDATA field with a reserved SD-ID, therefore its name does not contain the @ character.

rewrite r_sd {
    set("55555" value(".SDATA.meta.sequenceId"));
};

It is also possible to set the value of a field that does not exist yet, and create a new, custom name-value pair that is associated with the message. The following example creates the .SDATA.groupID.fieldID@18372.4 field and sets its value to yes. If you use the ${.SDATA.groupID.fieldID@18372.4} macro in a template or SQL table, its value will be yes for every message that was processed with this rewrite rule, and empty for every other message.

The next example creates a new SDATA field-group and field called custom and sourceip, respectively:

rewrite r_rewrite_set {
    set("${SOURCEIP}" value(".SDATA.custom@18372.4.sourceip"));
};

If you use the ${.SDATA.custom@18372.4.sourceip} macro in a template or SQL table, its value will be that of the ${SOURCEIP} macro (as seen on the machine where the SDATA field was created) for every message that was processed with this rewrite rule, and empty for every other message.

You can verify whether or not the format is correct by looking at the actual network traffic. The SDATA field-group will be called custom@18372.4, and sourceip will become a field within that group. If you decide to set up several fields, they will be listed in consecutive order within the field-group's SDATA block.

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