Hostresolver: Treat AAAA queries as A queries when IPv6 is disabled

[jandubois]

A "correct" answer would be to set handled = true and return a NODATA response.

Unfortunately some older resolvers use a slow random source to set the transaction id.

This creates a problem on M1 computers, which are too fast for that implementation:

Both the A and AAAA queries might end up with the same id. Returning NODATA for AAAA is faster, so would arrive first, and be treated as the response to the A query.

To avoid this, we will treat an AAAA query as an A query when IPv6 has been disabled.

This way it is either a valid response for an A query, or the A records will be discarded by a genuine AAAA query, resulting in the desired NODATA response.

Packet capture with the old implementation:

    1   0.000000 192.168.5.15 → 192.168.5.2  DNS 81 Standard query 0x0edd A mirrorlist.centos.org
    2   0.000020 192.168.5.15 → 192.168.5.2  DNS 81 Standard query 0x0edd AAAA mirrorlist.centos.org
    3   0.000288  192.168.5.2 → 192.168.5.15 DNS 81 Standard query response 0x0edd AAAA mirrorlist.centos.org
    4   0.003276  192.168.5.2 → 192.168.5.15 DNS 303 Standard query response 0x0edd A mirrorlist.centos.org A 67.219.148.138 A 18.225.36.18 A 35.180.43.213 A 85.236.43.108 A 147.75.69.225 A 147.75.83.237

You can see both queries use the same transaction id 0x0edd, so the NODATA response in frame 3 is treated as the answer to the query in frame 1. Getting a second answer in frame 4 with different content is then considered an error:

curl#6 - "Could not resolve host: mirrorlist.centos.org; Unknown error"

With the changes in the PR the packet capture looks like this:

    1   0.000000 192.168.5.15 → 192.168.5.2  DNS 81 Standard query 0x8064 A mirrorlist.centos.org
    2   0.000011 192.168.5.15 → 192.168.5.2  DNS 81 Standard query 0x8064 AAAA mirrorlist.centos.org
    3   0.172135  192.168.5.2 → 192.168.5.15 DNS 303 Standard query response 0x8064 A mirrorlist.centos.org A 147.75.83.237 A 18.225.36.18 A 35.180.43.213 A 67.219.148.138 A 85.236.43.108 A 147.75.69.225
    4   0.172158  192.168.5.2 → 192.168.5.15 DNS 303 Standard query response 0x8064 AAAA mirrorlist.centos.org A 147.75.83.237 A 18.225.36.18 A 35.180.43.213 A 67.219.148.138 A 85.236.43.108 A 147.75.69.225

So the A and AAAA queries still use the same transaction id, but since both responses contain the same requested data, the query succeeds and no error is reported.

Fixes rancher-sandbox/rancher-desktop#1788 (and probably a couple of other DNS issues on M1 machines)

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Shoutout to fellow packet log connoisseurs @chancez, @jsoref, and @Nino-K for their help and the 570 message discussion on Slack! 😄

[AkihiroSuda]

Thanks

[carlosonunez]

Alright, I've built the latest version of lima and am putting it through the paces. I'll let you know how it fares in a few days when I have more data!

Thank you so much for looking into this.

[carlosonunez]

sorry; posted into the wrong thread. i've deleted this.