Definitely yes. The robots.txt file of your sudomain.domain.com should be visible at http ://subdomain.domain.com/robots.txt. I do not mean that all domains and subdomains need a robots.txt. It is useful only when you want to avoid the visit of robots in some parts of the domain or subdomain. Jean-Luc
if we dont have robots.txt in our site, will it cause problems ? ( not getting indexed by google , etc )
If there is no robots.txt, Google and the other search engines will consider they are allowed to visit and index all your pages. robots.txt is only useful to disallow access to some addresses. Jean-Luc