URL Redirection

Currently I have 2 port in my IIs, which was port 80 and port 81. And the default port was port 80. How can I configure my server to make a redirection to both of my IIs port. Let say if I type the URL http://www.any.com/ it will go to my port 80 and if I type URL http://web.any.com/ it will go to my port 81.

PS:) Besides having IIs server, I’m also running my own DNS Server. Thanks In Advance.