It's hard to find the documentaion for --sport and --dport by using "iptables --help" or "man iptables".
iptables --help | grep port
man iptables | grep port
But I can find it from Internet:
https://linux.die.net/man/8/iptables
--source-port,--sport [!] port[:port]
--destination-port,--dport [!] port[:port]
What's the command for checking the iptables docs for --sport and --dport in offline?
man ?
man iptables-extensionshas what you are looking for?man -k iptablesandman -a iptables.manpage documents the option you're looking for (in this case steeldriver has it right I think, but in general you can use waltinator's method), you can type/while reading the man page, type down stuff and search for strings (in this case--sport/--dport) within the manpage and (hopefully) quickly get to the relevant section instead ofgrepping stuff.nfor the next result,Nfor the previous result andgto go back at the start.