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What is the point of having more than a single public IP address for a dedicated server with a single network interface? I see a lot of dedicated server hosting offers that show something like "public IPs: 8". What am I missing? Thanks!

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2 Answers 2

up vote 10 down vote accepted

One reason is to provision multiple SSL encrypted services on the same port. SSL starts before the application layer which leads to certificate errors when accessing the host on a hostname that doesn't match the CN value on the certificate.

Using HTTP virtual hosting as an example:

The SSL layer sits between the client and the webserver. Once the client has issued the GET request (and hence transmitted the hostname it was expecting) the server has already started SSL. At that point its too late to specify a different certificate.

If you implement IP-based virtual hosting then each hostname can have it's own IP and subsequently its own certificate. Of course, wildcard certificates are another way around the problem, but they're often more expensive than just allocating another ip.

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Thanks! Perfectly clear. –  z8000 Feb 24 '10 at 6:35
    
Almost all major web browsers already support TLS Server Name Indication extension, allowing the use of hostname-based virtual hosts with SSL. –  grawity Feb 24 '10 at 14:01
    
True, although plenty of older browsers are still kicking about without support. Certain elements within the university I work for still develop for IE 6 exclusively so I end up having to support it more than I'd like to. –  Frenchie Feb 24 '10 at 14:29

VM's? Multiple websites with their own certs? There are lots of things you could use 'em for.

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