[EXTERNAL] DNS filtering in practice, Re: Charter DNS servers returning malware filtered IP addresses

Wed Nov 1 20:28:34 UTC 2023

On 10/28/23 3:13 AM, John Levine wrote:
> It appears that Michael Thomas <mike at mtcc.com> said:
>>> If you're one of the small minority of retail users that knows enough
>>> about the technology to pick your own resolver, go ahead.  But it's
>>> a reasonable default to keep malware out of Grandma's iPad.
>> How does this line up with DoH? Aren't they using hardwired resolver
>> addresses? I would hope they are not doing anything heroic.
> Generally, no.  I believe that Chrome probes whatever resolver is configured
> into the system and uses that if it does DoH or DoT.
>
> At one point Firefox was going to send everything to their favorite
> DoH resolver but they got a great deal of pushback from people who
> pointed out that they had policies on their networks and they'd have
> to ban Firefox.  Firefox responded with a lame hack
> where you can tell your cache to respond to some name and if so
> Firefox will use your resolver.

That's probably what I'm remembering with Firefox. But doesn't probing 
the local resolver sort of defeat the point of DoH? That is, I really 
don't want my ISP to be able to snoop on my DNS history. Sending it off 
to one of the well known resolvers at least gives me a chance to know 
whether they are evil or not because there aren't very many of them vs 
every random ISP out there. Since nobody but people like us know about 
those resolvers it seems to me that without preconfiguration meaningful 
DoH is pretty limited?

Or maybe I just don't understand what problem they were trying to solve?

Mike