How let Ubuntu share specific interface over Wire?

Question

I shared my internet over Wire with others devices by Clicking on the network icon > Edit connections > Share to other computer . However, The problem is when I share my VPN connection and that VPN connection drops down/failed for any reasons; Ubuntu keeps shearing my internet which is wireless connection with others!

How do I let Ubuntu stick with vpn interface, once is dropped, the other devices get no internet?

Answer 1

I'm thinking about one way to do what you desired using Network-Manager by having 2 profiles for your wired connection:

1. Profile wire_shared
2. Profile wire_not_shared

And then run some trigger that switches your connection between the two profiles depending on the VPN state. You can use cron job and simple script like this

But more detailed answer need more detailed input from your side:).

Answer 2

I just found it:

1. Don't share your internet, instead of that set the Wired connection getting manual IP.

2. Give Wired connection local IPs such as "10.42.0.1/255.255.255.0"

3. Apply these iptables rules in Terminal:

   sudo apt-get install linux-image-$(uname -r)

   sudo bash -c 'echo 1 > /proc/sys/net/ipv4/ip_forward

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

   sudo iptables -A FORWARD -i eth1 -o eth0 -m state --state ESTABLISHED,RELATED \

   -j ACCEPT

   sudo iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE

4. At other device side, set manual iPs as well such as "10.42.0.15/255.255.255.0/10.42.0.1"

Done. Once eth1 (or whatever your target interface) get disconnected, all others devices get no internet.