Yes - most webservers can allow/deny a list/range of ip addresses.
Also, any firewall worth using will allow you to block specific ip/port combinations.
POrtSentry is more about scan detection and auto-blocking etc. I think you should look at something like IPTables if this is the route you want to take (PortSentry can use IPtables as a defense action - but this is based on the detection process)
Any of these methods will prevent the request from reaching the webserver's page delivery engine - so no page request will even exist - only a connection attempt and subsequent block.
If you did the check through the server side scripting (JSP/ASP/PHP/Ruby etc) this would connect successfully, then request the page succesfully, but the response could either show a graceful rejection page, or it could send a relevant HTTP header code, rejecting the request.
None of them would load the actual page's contents.
If you are the IP that is blocked - then it is very possible that it is PortSentry, but it could be a variety of other things too.
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