As you maybe know Google can punish your site for duplicate content
Usually you can get your site as
http://www.yoursite.com/ and http://www.yoursite.com/index.html
It’s maybe also index.php or index.asp or default.aps, etc.
To avoid this, you can act permanent redirect 301 by using the following ModRewrite rules in your .htaccess file:

RewriteEngine on RewriteCond %{THE_REQUEST} ^[A-Z]{3,9} /index.html HTTP/ RewriteRule ^index.html$ http://www.domain.com/ [R=301,L]

The file should be located in your website main folder (web root).

The code will tell to the search engine both that all requests to index.html should be redirected to the “/” (slash only).