如何清除System.Net客户端DNS缓存？ [英] How do I clear System.Net client DNS cache?

问题描述

我使用的是.NET的WebRequest而改变我的HOSTS文件。我观察到System.Net不接受这些变化？ - 我怎么可以把它做这样

I'm using the .NET WebRequest while changing my HOSTS file. I'm observing that System.Net doesn't honor those changes - how can I make it do so?

我公司拥有一批服务器后面的单主机负载平衡的，让我们说'example.com'。我想针对其中几个独立，所以我计划将硬code在我的HOSTS机器特定的IP地址将请求发送到example.com之前文件：

I have a number of servers load-balanced behind a single hostname, let's say 'example.com'. I want to target several of them individually, so my program will hard-code the machine-specific IP address in my HOSTS file before sending a request to example.com:

163.56.0.34  example.com

对于第一个服务器，并第一个请求，这工作正常。然后，我的计划再次改变HOSTS文件：

For the first server and first request, this works fine. Then my program changes the HOSTS file again:

163.56.0.48  example.com

和我创建一个新的HttpWebRequest。当我把这个的时候，我可以在NETMON观察到它去，而不是预期的第二个到第一个IP地址（163.56.0.34）。

And I create a new HttpWebRequest. When I send this one off, I can observe in NETMON that it goes to the first IP address (163.56.0.34) instead of the expected second one.

使用断点和调试的痕迹，我已经验证了正确的值不会被写入到主机每次文件。当我试图从一个浏览器或其他程序访问example.com，它确实兑现了HOSTS文件，然后进入第二个IP地址。

Using breakpoints and debug traces, I've verified that the correct value does get written to the HOSTS file each time. When I attempt to access example.com from a browser or other program, it does honor the HOSTS file and go to the second IP address.

使用NETMON我验证请求直接将显示的IP地址;没有HTTP代理

Using NETMON I've verified that requests are going directly to the IP address shown; there is no HTTP proxy.

因为其他一切都尊重改变HOSTS文件，我强烈怀疑System.Net基础设施缓存example.com的DNS主机IP关联。但是，我找不到任何参考这个缓存，并没有什么别的方法来冲洗，或将其关闭。

Since everything else is honoring the changed HOSTS file, I strongly suspect that the System.Net infrastructure has cached the DNS host-IP association for example.com. However, I can find no reference to this caching, and know of no way to flush it or turn it off.

我欢迎指令处理缓存，还有什么可能会引起这些症状，或者其他提出的诊断步骤的建议，可能是有益的。

I would welcome instructions for dealing with the cache, suggestions for what else might be causing these symptoms, or other proposed diagnostic steps that might be useful.

推荐答案

我终于挖出了从MSDN晦涩的命令，修复这样的：

I finally dug up the obscure command from MSDN that fixes this:

ServicePointManager.DnsRefreshTimeout = 0;

当我解开所有的奇怪的事情我已经试过previously，我发现一个，我需要与上面的另一个设置;请求对象上，关闭保活：

As I unwound all the weird things I'd tried previously, I discovered one other setting that I need along with the one above; on the request object, turn off keep-alive:

request.KeepAlive = false;

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