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A use of "2" type of redirect would be where you have a substantial amount of changes and you may want to redirect the user to a page that alerts them about changes, i.e. http://oldsite.cornell.edu -> http://newsite.cornell.edu/welcome-oldsite-users.html
Note that it is not NOT possible to automatically create a redirect by pointing the DNS for siteA to siteB. In some cases this may simply cause both siteA and siteB urls to work without a redirect or it may not work at all. For a redirect to be setup it requires that a webserver be configured to perform the redirect.
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