Subject: Re: Patch for fixing the slow DNS lookup issue

Re: Patch for fixing the slow DNS lookup issue

From: Brad House <>
Date: Tue, 04 Nov 2014 13:27:38 -0500

On 5/22/14, 1:43 AM, Lei Shi wrote:
> Hello, everyone
> This patch include two major change groups. one is fixing the dns lookup issue due to dummy dns information of a
> disconnected adapter(in my case is a bluetooth adapter). I changed the dns lookup policy to try GetNetworkParams first
> because the GetNetworkParams provides the most reliable dns information(lots of checks were done by system).
> I also filter out inoperable adapter in DNS_AdaptersAddresses in case GetNetworkParams fail.
> the other is explicit invoke ANSI version Win32 API in case compile c-ares in unicode environment.
> Best Wishes
> Lei Shi.

I just had a report of a similar issue from a customer complaining that DNS lookups were slow across multiple
machines running c-ares 1.10.0, but not from machines running much older versions of c-ares 1.5.3. I haven't
fully investigated since I don't have access to their machines, but it is very likely in their environment that
they could have some disabled interfaces with bogus server addresses which this patch appears to address. I
know c-ares completely changed the way windows DNS servers are looked up between those versions.

I checked the Git repo and it doesn't appear a patch similar to this ever made it upstream. Did this get
dropped? Has anyone else tested this patch and found it to be improper, or if there was a better way
to handle it?

Received on 2014-11-04