[Dnsmasq-discuss] dnsmaq on OpenWRT, configuration question

Art Greenberg art at artg.tv
Sun Jul 28 12:46:42 BST 2019

On Sun, Jul 28, 2019, at 02:41, Geert Stappers wrote:
> I think that "aren't so happy" needs elaboration.

I don't know if you're familiar with the Roku. Its a streaming platform, and service providers like Netflix and HBO have written applications that run on the platform to play their "entertainment" content. Some of those applications insert advertising into that content in real time - the advertisements are not embedded in the content. When the application detects that its unable to source advertising, it refuses to play the content.
> > Yet when they make a DNS request, its being processed by dnsmasq
> That is _not supposed_ to happen.
> > and the add-hosts files are being consulted,
> Because the "red" hosts are on the wrong track ...

> > Is there a simpler way to deal with this?
> Yes and you are almost there.
> Explore why red hosts resolve via, they shouldn't.


>> I cannot tell what the Roku streamers have assigned. The UI doesn't expose that information.
> Report that annoying inconvenience at https://support.roku.com/en-gb/

Hahaha. I'll certainly try that. If there isn't already a hidden way to get that information, don't have any expectation that asking for something like that to be implemented will do much good in the short term, at least.

>> I don't know enough about how DNS works, but ... maybe they have
>> accepted that assignment, but the first DNS server in the request chain
>> is dnsmasq - and it answers rather than relays the request to Google's
>> servers because dnsmasq "knows" the answer - its in the addn-hosts file.
>> Does that make sense?

> No, something is misbehaving.
> It is plain wrong to "explain" broken behaviour.

Perhaps you can improve my understanding. What happens, exactly, when a host on a (small) network resolves a DNS request, and a resolver is running on the host and on the gateway? What happens when I run nslookup or dig on the host and specify a DNS server outside the network? (I assume that's a fair analog to my problem.)

> Right now we don't know which device has a "special" feature.
> We do need to dig deeper. Networksniff the DNS traffic
> of the Roku streamer for starters.

Thanks. I've been playing with Wireshark, learning how to capture and filter to see just what I want to see has been a bit of a challenge. That runs on a Linux box on my network, where maybe not everything I want to see is visible.

I have also turned on DNS logging in dnsmasq, and I can capture logs. And I can perhaps instrument some things inside the router as well, perhaps even run a capture in there.

I can also use a Linux box as a stand-in for the Roku to at least work with a platform where I can see everything that happens and make some inference about what should take place.

I'll get back to the list when I have useful results. In the meantime, its simple enough to disable the ad blocking when I want to run a stream that demands advertising.

Art Greenberg
art at artg.tv

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