How to link back –

I would like to have subdomains link to my wordpress site and the wordpress site be able to find its way back to the right subdomain with a home button. I know I need to pass in some value to the main site just not sure how. I.E. http://www.1.site.com, http://www.2.site.com, http://www.3.site.com, will all go into http://www.site.com/page1, http://www.site.com/page2 , http://www.site.com/page3 and then when you want to go home (home button, not the back button) it will find its way back to the right starter subdomain.

Thanks for any help,
BH–