===== Clearing iptables custom commands prior to applying new ones =====

Let's say, as an example, that you wanted to use some custom iptables commands in a script, such as the firewall script. In fact, the following principles would apply to any recurring script (such as "WAN Up").

 \\ You can remove previously-added iptables directives using a simple approach:

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''nvram get script_fire | grep -E '^iptables*' | sed 's/-A\|-I/-D/' | while read line; do exec ${line} &>/dev/null; done''

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The commands below will check what iptables **-A** (append) or **-I** (insert) directives have been issued previously in the current Script/Firewall text. They will then force a run of the same command, replacing any instance of **-A** or **-I** with a **-D** (Delete) command. In essence, this will reverse/remove any previous user-added iptables directives.

A user might have created custom tables in which to use advanced iptables commands. This is usually performed using the "**-N**" (new) command. The same principles described above will also apply to previously-issued directives which used the **-N command**.

 \\ Here are some rules to remember when using these commands:

  * First, you need to dereference the custom table from the built-in one, using the above method.
  * A table must then be emptied with the **-F** (Flush) switch/parameter (for example, **iptables -F $TABLE_NAME ) **.
  * Only at this point will you be allowed to remove the table with the command:  **iptables -X $TABLE_NAME** .

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