Slackware server as a gateway

 TBC

Assumptions:

Internet gateway: 10.28.12.2

Slackware box:

   eth0: 10.28.12.102

   eth1: 23.128.16.1

Client:

   eth0: 10.28.12.101

   Default Gateway: 10.28.12.102

Server Steps:

1) Add default gateway:

ip route add default via 10.28.16.2 dev eth0

2) Enable IP forwarding:

sysctl -w net.ipv4.ip_forward=1

3) Make it permanent TBA

4) Set up iptables rules:

# 1. Allow new connections coming from 10.x (eth0) into the 23.x network (eth1)

iptables -A FORWARD -i eth0 -o eth1 -j ACCEPT

# 2. Allow return traffic for those established/related sessions to flow back out to 10.x (eth0)

iptables -A FORWARD -i eth1 -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT

# 3. Explicitly DROP any new connections initiated from the 23.x network trying to go anywhere else

iptables -A FORWARD -i eth1 -o eth0 -j DROP

# 4. Masquerade traffic leaving out the upstream interface (for the 10.x-initiated traffic)

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

5) Save the rules:

iptables-save > /etc/sysctl.iptables

6) Make them permanent, add the rolling to rc.local:

# Restore iptables routing rules

if [ -x /sbin/iptables-restore -a -f /etc/sysctl.iptables ]; then

    /sbin/iptables-restore < /etc/sysctl.iptables

fi

Client Steps:

TBA