A junior penetration tester at your firm is using a non-transparent proxy for the first time to test a web server. He sees the web site In his browser but nothing shows up In the proxy. He tells you…

Changing the port value alone is insufficient if the proxy host address field is still blank or set to a wrong value, so traffic will still not route through the proxy.

The 'use this proxy server for all protocols' checkbox only controls which protocols are proxied, not whether the proxy can be reached - a missing or incorrect proxy address means no traffic reaches the proxy regardless of that setting.

A non-transparent (explicit) proxy does not intercept traffic automatically - the browser must be told exactly where to send proxied requests. Because the proxy is installed on the same machine as the browser, the HTTP Proxy address must be set to 127.0.0.1 (the loopback address for localhost) so the browser routes requests through it. Without this address configured, the browser sends requests directly to the web server, completely bypassing the proxy.

Selecting 'No Proxy' explicitly disables proxy use in the browser, causing all traffic to bypass the proxy entirely and defeating the purpose of the penetration test.