Ethernet
From Wikipedia:
Ethernet is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3. Ethernet has since been refined to support higher bit rates, a greater number of nodes, and longer link distances, but retains much backward compatibility.
Setup
When installing setup-alpine should give you the option to easily setup Ethernet or if you need to setup Ethernet after installation you can use setup-interfaces.
setup-interfaces
start by running this command:
# setup-interfaces
Contents of setup-interfaces
choose eth0
(or your Ethernet device)
if asked:
Ip address for eth0? (or 'dhcp', 'none', '?') [dhcp]
choose dhcp
Now it will ask Do you to do any manual network configuration? (y/n) [n]
unless you have a reason to choose n, if you need to do manual network configuration choose y and it will open the interfaces file.