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I've 3 Web Server with 2 main websites on each with domain name registered

http://mycompanycrm.internal and

http://mycompanyportal.internal

each IIS server has two website ie. crm and portal.

Question:

How does Load balancer knows where to redirect based on above request so that relevant websites are shown.

Update

Infrastructure guys have told me that both the above domain name are pointing to IP Address of Load Balancer.

Thanks

flybyte
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  • you don't say which load balacing technology are going to be used. Microsoft NLB work at IP level, but others like F5 can work up to level 7 (http level, modifying url and cookie) – Mathieu Chateau Mar 01 '12 at 22:25

2 Answers2

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A load balancer only cares about IP addresses, not site names. So it basically spreads client requests between the three web servers, regardless of the request contents.

Each server, which hosts both web sites, then uses the HTTP headers in the request to know which site the client actually asked for, and serve it accordingly.

The mapping between client requests and web sites is done by the web server(s), and it would work in exactly the same way if there was only one server and no load balancer was involved.

Massimo
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  • Thanks @Massimo, both domain names I mentioned are pointing to same IP Address of Load Balancer. – flybyte Mar 01 '12 at 21:37
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As defined in the HTTP/1.1 RFC, the Host: request header tells the web server which site is requested.

DNS, load balancing, puppies, or dolphins have nothing to do with it.

adaptr
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  • Thanks @adaptr, if both http://mycompanycrm.internal & http://mycompanyportal.internal are pointing to same IP Address of Load balancer, what would the request header look like and how will IIS handle request? – flybyte Mar 01 '12 at 21:41
  • As indicated above, none of this is related to DNS. The HTTP/1.1 Host: header is set by the client. – adaptr Mar 02 '12 at 09:07