[Koha] ports and URL

hi i have a simple problem now i can access my opac and staff client from real IP from internet , i have 2 sub domain to my library , i would like to acces opac when type library.mydomain.com , that's no problem and staff when type library-admin.mydomain.com that's my problem i don't want to type 8080 in the end of URL when access staff. any help :)