reverse proxy identification

[sami ghourabi <sami.ghourabi () icn com tn>]

I'm currently pentesting C class subnet.
It seems that it hosts webservers, as a large number of IP @ replied OK 
to port 80 scan.
However I dont think that for each IP adress there is a physical server, 
but perhaps a multiplexing device that also does application firewalling.
According to nmap it may be a Blue Coat SG4.
When I browse to the IPs with firefox, I recieve several messages "No 
web site is configured at this address." for some IP.
Does anybody here know if this message is specific to a given reverse 
proxy/web server product ?
Any other experiences similar to this situation are welcome.

Sami.

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