In Manage Database for the tab, create a summary field = Count of IP address. On the layout, add a subsummary part when sorted by IP address. Add the summary field to that part. Show all the records and sort by the IP address.
And if you only want to see each IP address listed a single time with the count of occurrences, follow David's instructions, but then delete the body layout part, leaving just a sub summary part with IP Address field and summary field to list your data and the counts.