Turns out this seems to be a never ending story and you might have found a comeback of that issue for your particular configuration as you say this worked on 18.04 but fails on 20.04.
Multiple of the above and some other references refer to requiring ldns support.
That clearly is in openssh since ~v6 but we don't enable it at build time libldns support: no
Is that required and is it now more required than before - I don't know :-/
Sorry, all that I could provide so far was a collection of a (disturbing) history of that feature.
Turns out this seems to be a never ending story and you might have found a comeback of that issue for your particular configuration as you say this worked on 18.04 but fails on 20.04.
This goes way back /bugzilla. mindrot. org/show_ bug.cgi? id=1455 /trac.macports. org/ticket/ 49007 /bugs.debian. org/cgi- bin/bugreport. cgi?bug= 618863 /bugzilla. mindrot. org/show_ bug.cgi? id=2119
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Or half way back
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Other more recent similar issues were around "options edns0" being required to be set for this to work now: /github. com/NixOS/ nixpkgs/ issues/ 12470 /exanames. typepad. com/blog/ 2009/06/ one-more- thing-to- do-with- dnssec- ssh.html /bugzilla. redhat. com/show_ bug.cgi? id=1630180 /bugzilla. redhat. com/show_ bug.cgi? id=1878166
https:/
https:/
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Note: that option was the default for /etc/resolv.conf on Bionic/Focal for me.
Various working setups seem to have been affected by 7.5 /lists. mindrot. org/pipermail/ openssh- bugs/2017- April/017631. html /lists. mindrot. org/pipermail/ openssh- unix-dev/ 2018-January/ 036600. html /bugzilla. mindrot. org/show_ bug.cgi? id=2708
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But Bionic -> Focal is openssh version 7.6 -> 8.3
Multiple of the above and some other references refer to requiring ldns support.
libldns support: no
That clearly is in openssh since ~v6 but we don't enable it at build time
Is that required and is it now more required than before - I don't know :-/
Sorry, all that I could provide so far was a collection of a (disturbing) history of that feature.