DNS port 53 forwarded over NAT modem for working BIND9 server

Those who "serve root@home" on a BIND9 named server according to RTF 7706 will need to forward port #53 across their modem, such as a NAT dsl router/modem.

This may be a bit tricky, as some cobinations of modems and ISP may not allow that to fully work.

On a "works for me" basis, it may be pointed out, however, that contrary to what some others say, BIND9 will work if both UDP port 53 as well as TCP port 53 are being forwarded to the home PC host machine’s ports 53

With only UDP #53 forwarded but not TCP #53, dig works mostly but AXFR zone transfers keep failing!

In contrast, port-triggering forwarding did not work for me. Regular, non-dynamic port forwarding instead does the trick. This multitude of options may seem confusing at first glance, as one sees stuff working halfway and breaking halfway rather than an outright 100% FAIL.

Quick AXFR diagnosis is being delivered e.g. by web-dig tool in this manner.