If you use the ssl then we can use only the domain and not the port.
Ankit, you would need to use a subdomain or redirection or something else. This isn't something you would be doing with Tableau Server itself.
Hi Ankit - Involve your networking team within the organization and request them to alias the tableau server login URL with the domain based(custom name) URL. As toby mentioned, this cannot be controlled/changed in tableau server.