[chromium-discuss] Chrome's configuration of the Windows DNS Client

[Liam Brown]

Hello,

I would like to request information on how Chrome chooses to configure the
Windows DNS Client. I observe that the behavior of the Windows DNS Client
changes drastically once Chrome (the browser) is booted on my Windows 10
machine with its internal DNS client OFF. Notably, affected behaviors
include DNS server timeouts and fail-over behavior. After observing
Chrome's interactions with Windows API through Procmon and Apimonitor, and
after extensive review of Chrome's open source code, I am still unable to
determine the means by which Chrome configures the DNS Client.

My only lead on this issue was obtained with Procmon. When I
modified(added) a registry key at
HKLM\System\CurrentControlSet\Services\Dnscache\Parameters, I observed
chrome.exe query the values of a TON of keys in this directory. Most of
these reqistry keys are COMPLETELY UNDOCUMENTED by Microsoft, and none of
them are present by default (therefore the queries all returned
NAME_NOT_FOUND). Surprisingly, I was unable to find reference to these
keys withing the Chrome source code. Can anyone shed light on what is
going on here? I will provide the image I obtained from Procmon.

[PhistucK]

If you cannot find them in the source code <http://cs.chromium.org>, then
they are probably queried indirectly (by Windows, as a result of a Windows
API call by Chrome).

☆*PhistucK*

Post by Liam Brown
Hello,
I would like to request information on how Chrome chooses to configure the
Windows DNS Client. I observe that the behavior of the Windows DNS Client
changes drastically once Chrome (the browser) is booted on my Windows 10
machine with its internal DNS client OFF. Notably, affected behaviors
include DNS server timeouts and fail-over behavior. After observing
Chrome's interactions with Windows API through Procmon and Apimonitor, and
after extensive review of Chrome's open source code, I am still unable to
determine the means by which Chrome configures the DNS Client.
My only lead on this issue was obtained with Procmon. When I
modified(added) a registry key at
HKLM\System\CurrentControlSet\Services\Dnscache\Parameters, I observed
chrome.exe query the values of a TON of keys in this directory. Most of
these reqistry keys are COMPLETELY UNDOCUMENTED by Microsoft, and none of
them are present by default (therefore the queries all returned
NAME_NOT_FOUND). Surprisingly, I was unable to find reference to these
keys withing the Chrome source code. Can anyone shed light on what is
going on here? I will provide the image I obtained from Procmon.
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[Liam Brown]

Ok, that makes sense.

Do you know anything about Chrome changing the timeouts/failover behavior of the DNS Client?

Somehow, the timeout for giving up on the primary server and querying the secondary is only 0.15 seconds instead of 1, and the DNS Client is also unwilling to fall back to temporarily only use the secondary. Any thoughts?

Thanks,
Liam.

[PhistucK]

net-dev <https://groups.google.com/a/chromium.org/forum/#!forum/net-dev> might
be more helpful.

☆*PhistucK*

Post by Liam Brown
Ok, that makes sense.
Do you know anything about Chrome changing the timeouts/failover behavior
of the DNS Client?
Somehow, the timeout for giving up on the primary server and querying the
secondary is only 0.15 seconds instead of 1, and the DNS Client is also
unwilling to fall back to temporarily only use the secondary. Any thoughts?
Thanks,
Liam.
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