What are the differences between Public URL and Internal URL when configuring Alternate Access Mappings in SharePoint2010
Say for instance your website is:
That is the public url, the url that you want most people to see.
That site may be delivered by two internal servers that are load balanced, people should never see these addresses
Normally, when those sites render links, they would be displayed as
Another possiblity is when you public url is a secure site
And you want your proxy server to terminiate the SSL connection, then pass standard HTTP traffic to the same two internal servers (Off Box SSL/HTTPS termination)
Your Internal and Public URLs should always be the same unless you're using something like a hardware load balancer, or a reverse proxy; something that rewrites URLs. If you haven't got anything in place that's rewriting your URLs, they should be the same.