When you're connected to the net Your device(computer, phone, server) has two IP addresses. One is private between your device and internet server. That address is isolated between your computer and the internet access server. The other is public and it is between the internet access server and internet. This is the address you get when you type IP address in your search bar or address bar.
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Anyway if you flagged based on IP address you will be restricting every body on the COX network in the city of Tulsa, OKC or some other location tied to that address.
To find out who owns an IP address type in the unix command whois and the address. "whois 12.345.678.901"
I figure flagging is tied to your email address and the post in question.