How can I share Internet Connection among two Linux computers using firewire running Ubuntu 14.04?

Question

I have two computers (let say "A" and "B") that are already pinging and sshing each other via firewire, both with static ip. Computer A is connected to the Internet and I want it to share its internet connection to computer B. I have no idea of how this can be done via firewire interface. Any ideas? thanks a lot.

Answer 1

Computer [A]:

• enable IP forwarding
  • temporarily by running echo 1 > /proc/sys/net/ipv4/ip_forward
  • or permanently by adding net.ipv4.ip_forward=1 in /etc/sysctl.conf
• iptables rules, assuming eth0 is your interface to the internet and firewire0 the internal connection to comp [B] (to make them permanent, add them to /etc/rc.local before the "exit 0":

/sbin/iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE /sbin/iptables -A FORWARD -i eth0 -o firewire0 -m state --state RELATED,ESTABLISHED -j ACCEPT /sbin/iptables -A FORWARD -i firewire0 -o eth0 -j ACCEPT

Computer [B]:

• check for a valid DNS server in /etc/resolv.conf, if not add a line with nameserver 8.8.8.8
• make sure the default route is through comp [A] (route -n shows computer [A] IP's on the line with destination 0.0.0.0). if not, run route del default; route add default gw COMPUTER_A_IP_ON_firewire0