Не стоит делать iptables-ом то, что можно корректно сделать настройкой демона.$ man sshd_config
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AllowUsers
This keyword can be followed by a list of user name patterns, separated by spaces. If specified, login is allowed only for user names that
match one of the patterns. Only user names are valid; a numerical user ID is not recognized. By default, login is allowed for all users. If
the pattern takes the form USER@HOST then USER and HOST are separately checked, restricting logins to particular users from particular hosts.
The allow/deny directives are processed in the following order: DenyUsers, AllowUsers, DenyGroups, and finally AllowGroups.
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