Is it possible to set up a firewall on Ubuntu to allow certain applications access to certain subnets, and deny the rest?

Question

ubuntu

What are the options?....................

Answer 1

Look at namespaces. You can do a lot of things there.

Answer 2

Try to run an application that is allowed to access the subnet from a specific user:
sudo -u the application
then in iptables:
sudo iptables -A OUTPUT -p tcp -m owner --uid-owner -o eth1 -j ACCEPT
only instead of -o eth1 you need as- then insert the required subnet, somewhere there may be an answer