how can I block a proxy servers on my network?. What is the proxy ports or proxy IPs?

Question

I am using Firewall, I can providing safety area for my clients. But some clients are using proxy for illegal search.

Answer 1

Depending on the type of firewall you are using filtering out proxies can be difficult since (i'm assuming this is an http proxy) proxy traffic can look just like http traffic. You'd need to know which proxy (IP address) they are using and block the particular IP. As for port it's usuaully the http port (80) since most corp firewalls don't block outgoing http traffic.

One thing you may want to do is setup your own proxy and force everyone to use that and block all outgoing traffic to everyone since proxies can run on any port the only way to know for sure is to block everything :) (you'd need to setup a proxy for every outgoing service your network may need) If you really need this much security within your own network you'll have to take drastic measures such as this.

Answer 2

It's going to be almost impossible without some type of third party software. If you close port 80 (http), you block all internet access. If you open port 80 for the internet, any proxy server can be accessed. There are thousands of them and their IPs change constantly. You can't block them successfully without a constantly updating list (hence the third party software).
You need some type of surfware. Otherwise... flat-out hopeless.