Adding a Rule

When you add a rule proper, you need to specify as much information as possible to have full control over the TCP/IP packets you are allowing into the trusted network.

At a minimum, you need the chain, protocol, and destination port. With just this information, you do not have a very good rule because it does not specify the interface you are allowing the SSH connection to. You can also set the connection type:

■ NEW: This is a new connection; no other traffic is associated with this packet.

■ ESTABLISHED: This packet is from a machine you already have a connection to (remember, you both send and receive data when a connection exists).

■ RELATED: This packet is related to an existing connection. The FTP protocol, for example, makes a connection to the FTP server, and the FTP server actually makes a separate connection to the client. This separate connection from the server to the client is a RELATED connection.

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