Similar to "secure" (SSL) web admin interfaces on various systems, which are by now so outdated that modern browsers refuse to talk to them, it now gets increasingly difficult to get OpenSSH to connect to old ssh servers... For the web stuff, it's useful to keep an old version of Portable Firefox available...
For ssh, I've seen this hint on IRC today:
That should work with everything, unless you're trying to connect to a server that only supports ssh1 - which is usually disabled in current OpenSSH builds, and will go away completely later this year: "In approximately August 2017, removing remaining support for the SSH v.1 protocol (client-only and currently compile-time disabled)." (From the OpenSSH 7.4 release notes).
Well, I guess PuTTY can still do that.
For ssh, I've seen this hint on IRC today:
alias oldssh='ssh -o '\''HostKeyAlgorithms=+ssh-dss'\'' -o '\''KexAlgorithms=+diffie-hellman-group1-sha1'\'''
That should work with everything, unless you're trying to connect to a server that only supports ssh1 - which is usually disabled in current OpenSSH builds, and will go away completely later this year: "In approximately August 2017, removing remaining support for the SSH v.1 protocol (client-only and currently compile-time disabled)." (From the OpenSSH 7.4 release notes).
Well, I guess PuTTY can still do that.