How can I exclude users from my internal network from being included in the report? What filtering criteria would I use?

Both our external customers and internal users use our website for their day-to-day applications. I'd like to be able to run separate reports with one report including only our internal users and a second report for only our external customers.

I've been unsuccessful at figuring out the correct filtering criteria to 1) include only our internal network users and 2) exclude our internal network users.