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> If the answer is too big for UDP, DNS falls back to TCP and this fall-back is used more often these days. With the emergence of DNSSEC and TXT records, large answers are more common than they used to be.

I did not know that was a thing!

https://serverfault.com/questions/698251/how-does-the-dns-pr...

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It’s a tricky issue to track down because it only adds latency on the first request to a new domain.

And the wonderful issues that can come with it sometimes. Although I suspect much less now that large responses are more common.

Back in the day a very popular registrar that included DNS service would have random issues with the size of DNS response when it switched over to TCP, returning servfail instead of answer.

I'm guessing it was a load balanced cluster and some of the servers were broken. We reported the issue a few times but never heard back, as expected.

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