Ask HN: With all the talk of alternate DNS; How does IP resolving work?

How is it fundamentally different to block an IP (or subnet, etc) from "the internet" as opposed to a domain name? edit: I should add, the wiki's for Internet Protocol Suite, and Internet Protocol do not address the issue. Also, I found this shortly after submitting: www.3com.com/other/pdfs/infra/corpinfo/en_US/501302.pdf which says it's "Everything you ever wanted to know about IP addressing"