I want to block the packets whose source ip is not localhost(172.17.7.1) when sending out. how to do this ? I write a rule like this
iptables -A OUTPUT -s !172.17.7.1 -J DROP
it does not work`
iptables -A OUTPUT -s ! 172.17.7.1 -j DROP
Use small caps "j" and append space after "!" sign, else it will be interpreted like a command from your shell history. Pay attention that you do apppend with A and not insert on the beginning of the chain.