How can I know which Internet proxies servers are avaliable in a LAN?

Question

How can I know which Internet proxies servers are available in a LAN? The computer I'm using is running Windows.

Answer 1

In general, a scan of port 53 (tcp should be okay), for the entire LAN would show you which computers are running the DNS service. You can get nmap for Windows to do this.

If you suspect a computer might be a DNS server, you can telnet <ip> 53 and see if the sessions starts. You could of course also use nslookup.

Edit:
So you want to scan for tcp ports 80,8080,8081, using nmap you could nmap -sT -pT:80,8080,8081 192.168.1.1/24 to scan the 192.168.1.1 255.255.255.0 network, and look for 'open' ports.

Answer 2

You can't.

A proxy server could be listening on any TCP port, and although 80, 8080, 8081 and similar ones are quite common, there's no guarantee that if one of such ports is open on a given host, that is actually a proxy server.

Answer 3

seems like a pretty simple question.

there are a number of windows clients that look like they will find proxies

try

http://www.google.com/search?q=windows+proxy+scanner