In order to access Sitefinity on an IP or domain different than the one it is hosted on you need a set of rewrite rules that modify the request both inbound and outbound. This is referred as reverse proxy and can be achieved by following the steps in the following KB article: http://www.sitefinity.com/developer-network/knowledge-base/details/host-sitefinity-under-reverse-proxy
Please note that even with every rewrite rule implemented correctly there are still several places in the application's backend where URLs will be generated incorrectly. The only 2 currently known are for preview links and embed links of images. Images will work correctly on the frontend though.
Other than that it is also important to configure authentication correctly. The first step is to modify the wsFederation element in web.config file and specify the issuer and realm correctly.
After that you need to add entries in the SecurityConfig.config file for each token issuer and relying party explicitly. Make sure they use the same keys as the default entries for localhost.
Please note that if you are using SSL you need to also add separate entries for https as well.
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