Basic lxc allows you to spin up lightweight system containers for testing. But if you're running a host firewall you may find it prevents your containers from acquiring an IP address over DHCP for networking, and from connecting to external hosts (like distro package servers).
NOTE: I don't use lxc in production, and have purged it from all my machines after some experimentation. Diving deeper into Docker seemed a better use of my time.
If running ufw on Ubuntu you should be able to fix that with the following command: