Why do so many iptables examples specify both “-p tcp” and “-m tcp”?

Question

The manual isn't very clear, and the online articles & tutorials don't bother to explain it.

What's the significance of -m tcp and -p tcp used together? It seems so redundant, it bothers me...

Thanks

Answer 1

If using -p tcp, -m tcp shouldn't be necessary. From the manual page for iptables:

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.