The goal was to ust ssh-keyscan for hosts behind ssh jumpbox.

My ssh_config has ProxyJump defined for each host behind jumpbox.

But it seems `ssh-keyscan' does not consult the ssh_config at all (checked with `strace'). It reported:

---%>---
# ssh-keyscan -v foo-host
getaddrinfo foo-host: Name or service not known
---%<---

ssh_config was something like that

---%>---
Host foo-host
    Hostname 10.72.8.4
    ProxyJump backup@jumpbox.example.com
---%<---