After installing Ubuntu server 15.10, I am unable to reach the Internet and do not have an IPv4 address. ifconfig only shows lo, but if I type in ifconfig -a, it also shows enp1s0f0, which matches up to the internal ethernet port, but it doesn't have an IP address. I skipped around the steps in the installer, though I did auto-configure DHCP...
As far as I can tell, "enp1s0f0" seems to correspond to virtual machines, on CentOS/Red Hat, and I'm not sure why it's this instead of eth0...
I have tried renaming it to eth0 (fwiw), but a reboot wiped that out. I also tried adding auto-config code to /etc/network/interfaces, but no luck with that, either.
EDIT: Here's the interfaces file, more or less:
"# The loopback..."
iface inet loopback
iface enp1s0f0 inet dhcp
Also, I unplugged the Ethernet and plugged it into a Thunderbolt to Ethernet adapter, which Ubuntu recognizes, still no Internet... Plugged it back into internal Ethernet port, now Internet works. I don't know why. I'd still like to know about the enp1s0f0 interface, why it's not "en0" and how it's different.