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Editorial Team
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Asked: 2026-06-14T17:06:39+00:00

I’m writing a local Proxy server. It already works for the majority of the

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I’m writing a local Proxy server. It already works for the majority of the requests. But sometimes I have Problems when I want to resolve the Host-name. Here is what I do:

When the header of the request is received, I filter the first line out. Then I take the Request-URL (which is between the two spaces) out of that line and store it into an Uri object. After that I extract the hostname with: string host= uri.host;
At least I do the DNS-call: IPAddress[] ips = Dns.GetHostAddresses(host)[0];
(How do I know here, which IP of the array I should take. Whats the difference between those IP’s)

Like I said, for the majority of the Requests that works fine. But there are some adresses, that cannot be resolved. Here an example: When I want to open http://www.gmx.net, I first get the HTML-File ( this works fine ). After that, the Browser reloads a couple of Web-Objects like pics, javascript and so on. Those Object of course have some URL. And one of those URLs, that cannot be resolved is: ipv4-cout.gmx.net .
The attempt to resolve this URL results in the warning: The stated Host is unknown.

Another thing I need to know is: How to handle Alias-Host-names? For example: When I enter the hostname gmx.de into the Browser, it automaticaly resolves it into http://www.gmx.net. I know, there are Recource Reccords on a DNS-Server with type CNAME, but I dont know how to implement this.

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1 Answer

  1. Editorial Team

    I would say that they come back in the order that the DNS server sends them, I can no find no reference to any particular ordering.

    Dns.GetHostAddresses Method

    In most cases, there would only be a single IP address. In the case of http://www.gmx.net, they do have 2 and in theory, this would mean that you would round-robin the requests.

    www.gmx.net has address 212.227.223.5
www.gmx.net has address 212.227.223.4

    For your information. pv4-cout.gmx.net does not resolve on my machine and would result in a 404 when accessed any other way.

    gmx.de does not resolve to http://www.gmx.net, there is a URL redirect on the web server.

    Connecting to www.gmx.de|212.227.223.10|:80... connected.
HTTP request sent, awaiting response... 301 Moved Permanently
Location: http://www.gmx.net/ [following]
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