On Wed, Jan 12, 2022 at 07:19:07PM -0500, Brian J. Murrell wrote:
> Looks like Google has upped the ante with Chromecasts and it's no
> longer sufficient to just block external DNS queries and expect the
> Chromecast devices to fall-back to the DHCP supplied local DNS
> resolvers.
> 
> Looks like we are going to have to up the game to redirecting DNS
> requests to the internal server and forging the responses as being from
> the external server the queries were directed at.
> 
> So I have added a rules entry:
> 
> DNS/DNAT loc:!10.75.22.247 $INT_DNS
> 
> where 10.75.22.247 is the internal DNS server.
> 
> That seems to result in local queries that were going to say, 8.8.8.8
> being redirected to the internal server.  But the problem is that the
> replies are coming back from the internal server's address and being
> rejected by the originator.  The replies need to forge the request
> destination address.

You need to make sure the reply is coming by way of the shorewall system.
Which can then apply SNAT rules.
https://shorewall.org/FAQ.htm#faq1f

-- 
Justin


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