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I've configured my browser(firefox) to use proxy ,but I find that it's still looking up the dns when I visit, why is that still necessary?

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migrated from Apr 19 '11 at 10:08

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HTTP or SOCKS proxy? – grawity Apr 19 '11 at 14:14

Even when connecting via a proxy your browser needs to get the IP address for the web site domain. Generally it will directly query the DNS servers. If you are using a Socks 5 proxy, you can have the DNS queries go through your proxy. There is a check box for that in the Proxies option panel in Firefox.

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Why does the browser need to know the IP address for the web site domain when it's using proxy?I don't think it's necessary at all... – wireshark Apr 19 '11 at 9:53
As explained: DNS queries are not performed by the proxy. If you want DNS queries to be performed by the proxy, then you have to use a proxy protocol that tells the proxy to do that, eg. SOCKS 5. – Rushyo Apr 19 '11 at 12:14
More generally what people think is necessary, in the context of browser internals, is very rarely correct. – Rushyo Apr 19 '11 at 12:15
@Rushyo: HTTP proxy servers always perform DNS queries (confirmed by watching raw traffic), as do SOCKS 4a and optionally SOCKS 5 proxies. It's only SOCKS 4 that requires the browser to do it. – grawity Apr 19 '11 at 14:16
Ok let me put it another way: It's based on the implementation - shorthand for what I wrote. – Rushyo Apr 19 '11 at 15:20

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