You won't be able to directly connect to an
SSH server if it's in a private network or if it's behind a
NAT or firewall. A host could also be configured to only allow connection from a specific host or network and deny connection from everywhere else. For this you would have to first either connect to the specific host or network via a
VPN, or to connect via a proxy.
PuTTY could be configured to tunnel its connection via a proxy. The supported proxy types for
Steps to connect to SSH server using PuTTY via proxy:
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