A set of commands to setup iptables for the firewall host

set_iptable_rules.bash

cat <<EOF | sudo bash
# Flush existing rules and set default policies
iptables -F
iptables -t nat -F
iptables -t mangle -F
iptables -t raw -F
iptables -X

iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT

# Allow SSH
iptables -A INPUT -p tcp --dport 22 -j ACCEPT

# Forward Telnet traffic to BBS
iptables -t nat -A PREROUTING -p tcp --dport 23 -j DNAT --to-destination 192.168.1.99:23

# Masquerade outgoing traffic
iptables -t nat -A POSTROUTING -s 192.168.1.0/24 -o enp4s0 -j MASQUERADE

# Allow forwarding of established connections and all traffic from the local network
iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -s 192.168.1.0/24 -j ACCEPT

# Enable IP forwarding
sysctl -w net.ipv4.ip_forward=1
echo "net.ipv4.ip_forward=1" >> /etc/sysctl.conf
sysctl -p

# Save iptables rules
iptables-save > /etc/iptables/rules.v4
netfilter-persistent save
EOF