Basic iptables configuration for Linux
What is a good basic iptables config?
Basic rules needed:
- Allow incoming TCP to 22 for SSH but blocks all others.
- Allow outgoing TCP/UDP connections.
You may consider using the following rules as a start:
for tables in iptables ip6tables ; do
# Flush existing rules
$tables -F
# Default policy
$tables -P INPUT DROP
$tables -P FORWARD ACCEPT
$tables -P OUTPUT ACCEPT
# Allow established inbound connections
$tables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
# Allow icmp
$tables -A INPUT -p icmp -j ACCEPT
# Allow all loopback traffic
$tables -A INPUT -i lo -j ACCEPT
# Allow inbound SSH connection
$tables -A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
done