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I found that the behavior of Firefox on proxy server side is quite different from what I expected.

I thought that you can bypass local traffic by putting local address range, such as 192.168. But I discovered that it is not enough, you have to put DNS names of the server also.

Say that I have a local server testwww. If I don't out testwww into the bypass list, the traffic will go through proxy server.

Is this by design?

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8 Answers

Proxy rules work on what you enter into URL field of the browser.

If you enter "testwww.intranet.com", nobody knows that whether it's in 192.168.0.0/16 or not.

The domain name will get resolved only by the one who actually connects to the server: if proxied, it will be proxy, if not, it will be your browser.

This is why you have to use patterns that will match your input into URL field for proxy config (i.e. testwww, *.intranet.com, ...), and not what comes out as a result of domain name resolution.

I hope this answers your question.

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After struggling through mozilla bug 72444, I discovered that you can add <local> as the name of a host to exclude in the list of proxy exceptions. That will exclude all hostnames that does not contain a dot.

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You put in the local address range like this 192.168.0.0/16 ?

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Yes. It is by design. AFAIK, this is true for any service/software that uses proxy.

If you follow a proper FQDN structure while naming your hosts/virtual hosts, then you can easily circumvent this by adding your sub-domain name to the no-proxy list. For example adding the domain suffic '.intranet.example.com' will ensure that access will be made locally, and NOT via the proxy server for all hosts sitting under .intranet.example.com. (host1.intranet.example.com, host2.example.com).

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for more flexible control, use the foxyproxy plugin which supports whitelists and other advanced pattern matching to decide when and which proxies to use.

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IE performs differently. I just checked and found that IE connects to the local server directly.

We currently enter machine name in the location bar without domain name - for example testwww not testwww.company.com. And we have an internal DNS and an external DNS for our company domain.

Is the Firefox implement standard defined (whitelist domain names instead of IP ranges)?

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Yes. Put simply, this feature matches the string of the hostname or IP address. It does not lookup the hostname and do comparison of the found IP address.

That is a feature request that has been around for some time. See bug 136789

The actual documentation for this is pretty comprehensive.

http://kb.mozillazine.org/No%5Fproxy%5Ffor

or

https://developer.mozilla.org/en/No%5FProxy%5FFor%5Fconfiguration

should answer a lot of the detailed questions. NOTE: I wrote the original www.mozilla.org article that the source for these.

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I would like to add little more to the topic. In IE, when we bypass a domain like *.xyz.com; we can access any machine abc(whose entry is there in local dns). In case of forefox, .xyz.com is supposed to do the trick ,but it fails. This is the case for last many versions of firefox.

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