# Enable NAT
iptables -t nat -A POSTROUTING -s 172.16.42.0/24 ! -d 172.16.42.0/24 -j MASQUERADE
# Accept incoming packets for existing connections
iptables -A FORWARD -o docker0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
# Accept all non-intercontainer outgoing packets
iptables -A FORWARD -i docker0 ! -o docker0 -j ACCEPT
# By default allow all outgoing traffic
iptables -A FORWARD -i docker0 -o docker0 -j ACCEPT