If ES loaded the data into the data models before you installed the splunk_TA_cisco-asa on the ES Search Head, these values will show as unknown.
You need to rebuild the data model for this to be corrected.
You should browse the data model and confirm that the data is tagged correctly however. Follow the ES documentation based on your datamodel and dashboard :
http://docs.splunk.com/Documentation/ES/3.1.1/User/AdditionalNetworkdashboards
http://docs.splunk.com/Documentation/CIM/latest/User/Howtousethesereferencetables
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