--append  -A chain        Append to chain
  --delete  -D chain        Delete matching rule from chain
  --delete  -D chain rulenum
                Delete rule rulenum (1 = first) from chain
  --insert  -I chain [rulenum]
                Insert in chain as rulenum (default 1=first)
  --replace -R chain rulenum
                Replace rule rulenum (1 = first) in chain
  --list    -L [chain [rulenum]]
                List the rules in a chain or all chains
iptables，顾名思义，是针对IP层的处理，用来管理网络层数据包的流动和转送

https://wiki.archlinux.org/index.php/Iptables_(%E7%AE%80%E4%BD%93%E4%B8%AD%E6%96%87)