Hello everyone.

I want to create a gateway out of my laptop and connect it to a Beaglebone Black. The goal is to ssh into the Beagle and also to connect the Beagle to the net.

Laptop:
What i did is create a DHCP server on the network 192.168.0.0/24 using the interface card eth0
On wlan0 i have my wifi connection to the LAN router at 192.168.1.1

Now i tried to write a routing script, on my laptop, to route the packets from eth0 to wlan0 but it didnt work: "bad argument eth0".

# Always accept loopback traffic
iptables -A INPUT -i lo -j ACCEPT


# Allow established connections, and those not coming from the outside
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A INPUT -m state --state NEW -i ! eth0 -j ACCEPT
iptables -A FORWARD -i eth0 -o wlan0 -m state --state ESTABLISHED,RELATED -j ACCEPT

# Allow outgoing connections from the LAN side.
iptables -A FORWARD -i eth0 -o wlan0 -j ACCEPT

# Masquerade.
iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE

# Don't forward from the outside to the inside.
iptables -A FORWARD -i eth0 -o wlan0 -j REJECT

I also set the kernel to forward the packets like this
emacs /etc/sysctl.conf
net.ipv4.ip_forward=1 //i uncommented this line in the sample file

Can anyone tell me what am i doing wrong?
Why can is the iptables giving me this error and also am I going about this in a correct way?

Thanks in advance.
Jenia

Well, one thing i noticed is you have an errant exclamation point in your commands.

iptables -A INPUT -m state --state NEW -i ! eth0 -j ACCEPT

i am not sure if that is just a typo but i dont think the exclamation point should be there and that probably would cause the error you were experiencing.

i also think you have the same line twice.

# Allow outgoing connections from the LAN side.
iptables -A FORWARD -i eth0 -o wlan0 -j ACCEPT

# Don't forward from the outside to the inside.
iptables -A FORWARD -i eth0 -o wlan0 -j REJECT

that would not cause an error but is conflicting code.

also, one last thing, if you are using this as a script for the firewall controls, it would be a good idea with starting by flushing all rules prioir to yours. it might not cause a problem and usually doesnt but it is usually a good idea.

one thing i would suggest is switching to shorewall for your firewall. once you sit down and look at it, it is A LOT easier to configure and is just a secure.

Accept all traffic from eth0.
i.e iptables -I INPUT -i eth0 -j ACCEPT

Thanks
Sharan