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How do I open a link via a proxy sever?

What is a proxy server?

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migrated from stackoverflow.com Jul 30 '09 at 19:54

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6 Answers

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When you attempt to access, say, google, your browser goes through several steps:

Firstly, it doesn't really know what google.com is, so it asks it's more knowledgeable friend, the DNS server. He/She knows who google is (they know EVERYBODY. Life of a party, seriously), so they check their records and give the browser google's 'number' (their IP address (74.125.53.100, in this case)

Right, now you know their number, so 'ring them' (make a connection), and say hello (ask for some content). Google then sends you their homepage, which your browser looks at, then sends off to the HTML rendering guys. They put all the tags and words and stuff together into something that looks like it should. (Sometimes the HTML guys come across some javascript, they ignore that and don't put it in the page, then the Javascript guys deal with it later).

When you use a proxy server, instead of asking the DNS server who google is, you tell the proxy you want to speak to google, so THEY ask who google are, ring them up, and get their details, and then just send you the data for the HTML and javascript guys. The upshot of this is that if your DNS server really doesn't like google, and you don't know any other DNS servers, or can't ask another DNS server for whatever reason, Mr. Proxy can still find google for you.

How you use a proxy depends on what it is. Web-Based proxy services have a form for you to type in the URL, then they go and get the content, but other proxy servers are configured in your browser, and it automatically asks the proxy instead of the DNS guys without you having to do any more configuration. Step one to using one is finding one, a web-based one is straightforward, and in FF you'd go to options/advanced/network/configure how firefox connects to the internet/ to set up a different proxy.

In many workplaces you may already be using a proxy service without you knowing, these could be used to reduce the number of times the DNS server is queried (500 PCs all trying to reach google? Why not cut your DNS requests by 500 by getting the proxy to remember who google is?), filter dangerous or inappropriate content (Can't get viruses as easily if they're blocked from contacting you, and you can't slack off if your favourite flash games site is blocked :)), or as Arjan correctly states below, to trick region-locked services such as Hulu into thinking you live somewhere it can be used. Privacy is another concern, but you're better off using a service that allows you to encrypt the content with SSL in that case (Though there is a lot of overlap, there).

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Nice! Minor detail: unless you're in a country like China or Iran, I doubt proxy servers are used because a DNS server might not (want to) know some domain. DNS has been designed to delegate such questions to other DNS servers when needed. Instead, proxy servers are used to do some caching, for some additional security (like to allow filtering), for some extra privacy, or to fake the location from which you're requesting a web site. (When your DNS is bad, then rather than using a proxy server one might as well use a better DNS server instead.) – Arjan Oct 18 '09 at 13:53
I was trying to skirt around the issue of work and school blocking proxies, but that's an equally valid point. – Phoshi Oct 18 '09 at 13:58
Updated the answer, thanks :) – Phoshi Oct 18 '09 at 14:03
I guess schools and offices that filter actually don't do that in some DNS, but explicitly intercept HTTP traffic (if only to intercept plain IP addresses as well), either by explicitly requiring usage of a proxy server they control, or by using a transparent proxy? But I've never suffered filtering so you may indeed be right. – Arjan Oct 18 '09 at 14:08
At least in my experience it's been a mix of the two. Mainly DNS filtering, but does indeed also filter the HTML (My own blog was blocked for a while because it used too many "bloggy" words. Removing the post that contained said words also unblocked the page), but in both cases a standard webbased proxy bypasses it (which doesn't make much sense if they're filtering the HTML - unless the proxy I used happened to be doing some sort of encryption somehow) – Phoshi Oct 18 '09 at 14:13
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up vote 0 down vote

You could use the WebBrowser object to link to a proxy server, here is an example using VB .NET.

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A proxy server is generally system which offers a system's service representatively. This may be used for example to gain more performance (caching), to have full control over the data which passes to the service (maybe a reverse proxy or ALG) or to balance the load of a network.

You can use your web browser to surf a web site through a web proxy (HTTP or SOCKS, I guess). The exact configuration depends on the web browser. Which web browser do you want to use?

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Wikipedia provides a good explanation of a Proxy Server here. It is basically a machine on the local network acting as a gateway to the internet and caches parts of the pages browsed locally to reduce the amount of traffic going out on the line.

Proxy settings is specified differently depending on the browser you use. In Safari and Firefox it is under Preferences/Advanced or Preferences/Network Settings and in IE it is under Options/Connections

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If you look up proxy in a dictionary you'll likely see: "A person authorized to act for another"

A proxy server does a similar thing for computers. There are lots of types of proxy servers but the most common is a caching web proxy. When a browser requests a web page, a caching proxy looks in its cache to see if it already has the requested page. If it does it sends it to the browser. If it doesn't, it gets it from the server, saves a copy in its cache and passes it to the browser.

If you want to experiment with using a proxy and how to set one up try downloading Proxomitron. Its a small proxy server that you can run on your computer and configure your browser to use it. Its not a caching proxy but a filtering proxy designed to block advertisments. Its no longer updated (Sadly, the author died) but it is simple to install and setup so it is a great introduction to proxy servers.

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Is this a one-off problem, or do you need to access certain sites via proxy?

PAC files were created for this. Please comment w/ more info, and I will explain further.

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