DNS Flag Day: I had to open the TCP/53 port

[Roberto Carna]

Dear, I have a BIND 9.10 public server and I have delegated some public
domains.

When I test these domains with the EDNS tool offered in the DNS Flag Day
webpage, the test was wrong wit just UDP/53 port opened to Internet.

After that, when I opened also TCP/53 port, the test was succesful.

Please can you explain me the reason I have to open TCP/53 port to Internet
from February 1st to the future???

Really thanks, regards.
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