tmichels,
A sample would go along way in terms of providing configuration details, but I can speak in generalities.
Splunk can easily extract both src/dest IP and calculate unique (distinct) counts for these extracted fields. For example: | stats dc(src_ip) as unique_src_ips
It is possible to add additional information based on an IP Address lookup. The integration depends on your data source. Is this information in a CSV? If yes, you can use a standard Splunk lookup. If it's accessible via an API or DB, you can use a scripted (custom) lookup
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