also known as URL Forwarding or Domain Redirection. Its a technique of making webpage available through many URLs.

Checkout wikipedia article on URL redirection for uses of redirection.

• Client Side Fowarding : URL in client browser changes.
• Server Side Redirection : URL in client browser does NOT change. User remains on same website/domain.
• Server Side Forwarding or DNS Forwarding : URL in client browser does NOT change. User is moved to NEW website.

All the above methods are explained below in detail. I will be using Ruby on Rails for illustration.

The server sends a 301 or 302 redirect response with a Location: header containing the new URL. The client browser makes another request to the new URL. This is the most common form of domain forwarding.

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# 302 is default response status of redirect_to
# in controller latest
def index
  redirect_to "article/356"
end


# or redirect to another website
def index
redirect_to "http://www.newsite.com"
end

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def index
  headers["Status"] = "301 Moved Permanently"
  redirect_to "http://www.newsite.com"
end

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##<strong>Two ways</strong>
# 1. Use routes.rb
# in routes.rb write following to redirect incoming request to 'your_controller/create_new'
map.connect 'my_controller/create', :controller => 'your_controller', :action => 'create_new' 

# 2. render :action
# in my_controller
def create
  render :controller => 'your_controller', :action => 'create_new'
end

The server transparently rewrites the requrest URL to another URL. The user is moved to a NEW website and the URL on the client browser does not change. Also known as url masking or url cloaking or url shadowing. The most common method is by Frame Redirects

Note : Apache "core" does NOT perform ANY sort of redirection. Add on modules like mod_redirect to get Client-Side Redirection, mod_rewrite to get Server-Side Redirection, and mod_proxy to get Server-Side Forwarding. So, the ability to redirect is NOT built-in; the modules happen to be in common distros and configuration is baked into httpd.config and .htaccess.

(shamelessly copied from Domain Forwarding in IIS)

DNS Forwarding
The output is exactly similar to Server side Forwarding but approach is different. The user is moved to NEW website and the URL on the client browser does not change. You need to set appropiate CNAME entry in your domainname record at your DNS server. Many hosting service providers or registrars provide you with this service by the name 'Domainname forwarding'. If you have your own DNS server, you can easily set CNAME entry. For example :

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; my website is www.mysite.com. I want to redirect blog.mysite.com to www.myblog.com
; I will add following record in the DNS setting of www.mysite.com
blog       IN      CNAME  www.myblog.com.
; NOTE : do not forget to put '.' in the end

• Wikipedia on URL Redirection
• Domain Forwarding in IIS
• http://railsforum.com/viewtopic.php?id=1340