Sure, you can hook an Ethernet cable to the BBB, and talk to the outside world. But, since we've already set up an Ethernet connection to a host computer, shouldn't that second connection be redundant? And yet, with the default setup, you can only reach the host, not the outside world at large. Life doesn't have to be that way, at least if your host computer is running Linux (and why would you hook it to anything else? Hmmmm??).
I've documented here the additional steps, on both the host and the BBB, that are necessary to really network through the USB.
First, on the host Linux system, we need to make three changes:
sudo ifconfig eth1 192.168.7.1 netmask 255.255.255.252
echo 1 | sudo tee /proc/sys/net/ipv4/ip_forward > /dev/null
sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
sudo iptables -A FORWARD -i eth0 -o eth1 -m state --state RELATED,ESTABLISHED -j ACCEPT
sudo iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT
Now... On the Beaglebone Black, you need the following two commands to complete the setup:
route add default gw 192.168.7.1
echo "nameserver 184.108.40.206" >> /etc/resolv.conf
That's it! Now you can find Google, download software directly to the Beaglebone from various websites, and use opkg to install and upgrade packages in Angstrom Linux, or whatever flavor you have running on your BBB.