ubuntu ufw

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      First, ufw needs to be enabled. From a terminal prompt enter:

      sudo ufw enable

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      To open a port (ssh in this example):

      sudo ufw allow 22

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      Similarly, to close an opened port:

      sudo ufw deny 22

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      To remove a rule, use delete followed by the rule:

      sudo ufw delete deny 22

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      It is also possible to allow access from specific hosts or networks to a port. The following example allows ssh access from host 192.168.0.2 to any ip address on this host:

      sudo ufw allow proto tcp from 192.168.0.2 to any port 22

      Replace 192.168.0.2 with 192.168.0.0/24 to allow ssh access from the entire subnet.
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      ufw can be disabled by:

      sudo ufw disable