How can I block Internet to computers that are not using manual proxy

How I can send only by the proxy the internet; if the navegator (firefox) is select NO PROXY the user cant navegate, only can navegate if the proxy es put manually; I think yhe configuration is in the firewall… can any body help me.?

NethServer Version: 7
Module: your_module

“Web Proxy” -> Tab “Proxy”

Enable Proxy: checked
Put the selection on “Transparent” or “Transparent with SSL”

I don´t want transparente… I want manually… can be.?

There is a wpad file released by Nethserver.
Nethserver must be the DHCP and DNS server of your lan.

Then, in your Firefox configuration:
“Options” -> “Advanced” -> tab “Network” -> “Configure how Firefox connect to internet” -> Button “Settings” -> put the choice on “Auto-detect proxy settings for this network”

Or, if you want to enable the proxy to the entire pc:
in your Firefox configuration:
“Options” -> “Advanced” -> tab “Network” -> “Configure how Firefox connect to internet” -> Button “Settings” -> put the choice on "Use system proxy settings"
Then, in Internet Explorer:
“Internet Options” -> tab “Connections” -> Button “Lan Setting” -> check “Find automatically configurations”.
Maybe, if you check “Use automatic configuration script” and put http://ip.of.your.nethserver/wpad.dat in the below field, isn’t necessary that Nethserver is the DNS and the DHCP server of your network.
(please note: I dont have a IE in english language, so the fields name should be a bit differents than my translation)

You can find some info here: http://docs.nethserver.org/es/latest/web_proxy.html

Did I understand right, that you only want to let users to the internet that have manually proxy-settings in their Firefox?

So Nethserver has to be the gateway, than you can only access internet with proxy settings.

thats right… I want to set manually the proxy and all the internet conection cross on the proxy

You only have to setup your clients using nethserver as Gateway. If you use DHCP you can do the setup at DHCP Server.