DNS entry for the form a.i.p.i:port/folder?

Question

Domain Name System

Good afternoon. There is WIn7 with IIS 7. It has 2 sites. One is standard on port 80, the other is on port 81, and it's still in the folder.
How can I make sure that users don't have to write domain.org:81/ when typing in the domain browser? That is, what would DNS tell the browser which web port or something like that?