I’ve been battling this problem for a while.
I opened all firewalls, killed ufw, killed iptables, still I was unable to get any connections to work. Ping / dig / external DNS / all failed.
tcpdump showed incoming connections failing but “something” was making it here.
Turns out the problem was… an incorrect value in my /etc/network/interfaces file for my eth0.
Make sure that your IP address is listed in ifconfig.
ifconfig | grep my_ip_address
My static IP was missing a few digits.
Set the correct value, restart networking, and we’re good to go.