iptables

linuxnature

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   MATCH EXTENSIONS
       iptables can use extended packet matching modules.  These are loaded in two ways: implicitly, when -p or --protocol is specified, or with the -m or --match options, followed by the matching module name; after these, various extra command   line  options  become available, depending on the specific module.  You can specify multiple extended match modules in one line, and you can use the -h or --help options after the module has been specified to  receive  help  specific  to that module.

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