Hi Ilan, what kind of datasource are you using? I just tried it with a few I had around with abundant ip addresses (an xls and a SQL Server database) and in both instances Tableau recognized it as a text string and just brought it over as-is.
I've seen this happen with IP addresses in a CSV file. The JET engine sees numbers and the first dot and just truncates at the second dot and turns it into a number ("192.168.0.1" would become 192.168).
To get around that you need to convince JET to treat it as a string in the first place - the data is already mangled before Tableau gets its hands on it. Options are to wrap the IP address in quotes in the CSV file or define a schema.ini file to tell JET that it's a string field.
I think you can just put quotes around the IP address in the first row of the CSV file and that should be enough to convince JET to treat them all as strings. I'm not quite sure about that.
Or have a fake first line where that column is just text.