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    The article mentions that port 22 was nice because ssh is a cross between ftp (port 21) and telnet (port 23). Why did they take those ports and 22 was left empty in between?

    A good example where HN comments are useful. The TCP predecessor NCP used odd ports for “incoming” data, so the even port 22 was still free.

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      Also regarding the SSH trademark, see this https://www.openssh.com/ssh-dispute/ for history (2001)

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        Just to augment this article: https://www.openssh.com/history.html