First, set the default policies for each of the built-in chains to ACCEPT. The main reason to do this is to ensure that you won’t be locked out from your server via SSH:
iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT
Then flush the nat and mangle tables, flush all chains (-F), and delete all non-default chains (-X):
iptables -t nat -F
iptables -t mangle -F
iptables -F
iptables -X
