How to find out if a server is acting as a reverse proxy?

Question

As far as I know some webhosting companies use reverse proxies as some sort of load balancer, so all the HTTP requests go to one one physical server, but behind this there are several other webservers. For example if you visit http://www.yougetsignal.com/tools/web-sites-on-web-server/ and type in the IP 213.239.234.111 you will see that this machine hosts more than 700 domains.

Now my question is:

Is there a possibility to find out, if a server acts as a reverse proxy, maybe through HTTP headers or other fingerprinting methods?

Answer 1

The fact that the machine hosts more than 700 domains on one IP has nothing to do with a reverse proxy.

1. Since IP address is a scarce commodity, it is a common practice to host several (many) web sites on one IP address. Web hosting companies do it all the time, and 700 websites on one server is not uncommon, if these web sites are not particularly high-traffic. There is no reverse proxy involved.

2. Reverse proxy existence may or may not be revealed in HTTP headers. Usually not. Also, reverse proxy application may be on the same server as the web application itself. Also, this is done quite often.

3. Sometimes, if you can "fingerprint" a particular piece of hardware or software as being a specialized load balancer, you can be pretty sure it acts as a reverse proxy. But in case of a general purpose software (Apache, etc.) that can act as a proxy also, this is impossible.