How do I clear System.Net client DNS cache?

Question

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?

I have a number o

Answer 1

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

ServicePointManager.DnsRefreshTimeout = 0;

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;

Answer 2

you could use System.Diagnostics.Process to launch ipconfig /flushdns

Answer 3

If you want to keep the DnsRefreshTimeout > 0 then you can update the cache by making a call to:

System.Net.Dns.GetHostEntry("example.com");

Answer 4

A late answer to be sure, but I found this solution worked better than the accepted answer. In my scenario I am testing SQL connections, and I couldn't apply the existing answer since I have no request.KeepAlive to set.

This page by Brian Mancini ("derp turkey") details his adventure in clearing the DNS cache. Full props to him, I'm just adding his solution here:

public class DnsUtils  
{        
    [DllImport("dnsapi.dll", EntryPoint="DnsFlushResolverCache")]
    static extern UInt32 DnsFlushResolverCache();

    [DllImport("dnsapi.dll", EntryPoint = "DnsFlushResolverCacheEntry_A")]
    public static extern int DnsFlushResolverCacheEntry(string hostName);

    public static void FlushCache()
    {
        DnsFlushResolverCache();
    }

    public static void FlushCache(string hostName)
    {
        DnsFlushResolverCacheEntry(hostName);
    }
}