Creating a Redirect from old url to root
Assuming this question is about D7, you can use the Rules module for this, with a custom rule that looks like so:

{ "rules_redirect_some_path_to_the_frontpage" : {
    "LABEL" : "Redirect some path to the frontpage",
    "PLUGIN" : "reaction rule",
    "ACTIVE" : false,
    "OWNER" : "rules",
    "REQUIRES" : [ "rules" ],
    "ON" : { "init" : [] },
    "IF" : [
      { "text_matches" : {
          "text" : [ "site:current-page:path" ],
          "match" : "Default.aspx?id=index",
          "operation" : "starts"
        }
      }
    ],
    "DO" : [
      { "drupal_message" : { "message" : "Sorry, the old path is no longer in use, you will be redirected automatically to the homepage" } },
      { "redirect" : { "url" : "[site:url]" } }
    ]
  }
}


If you have the Rules UI module enabled, you should be able to just import the above rule, then "enable" it, and that's all you'd need to do.

What this rule actually does:


Check if the current path is Default.aspx?id=index
If that's indeed the path, then a redirect to your frontpage will be performed.


Note: feel free to adapt the first Rules Action (to display a message), or if you don't want such message at all, just remove that Rules Action.