eth0 on my Arch Linux box is connected directly to a cable modem.
ip a shows the following info. openvpn has established one tunnel. All traffic should flow over the openvpn tunnel only. What are all these other connections for? Do they pose security concerns?
eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000 link/ether c4:d4:64:34:b4:94 brd ff:ff:ff:ff:ff:ff inet 10.0.0.181/24 brd 10.0.0.255 scope global eth0 valid_lft forever preferred_lft forever inet6 2601:343:380:1f6::3c84/128 scope global dynamic noprefixroute valid_lft 566296sec preferred_lft 566296sec inet6 2601:343:380:1f6:d609:189b:cf5b:bb8e/64 scope global dynamic mngtmpaddr noprefixroute valid_lft 196684sec preferred_lft 196684sec inet6 fe80::2e4d:54ff:fe53:8b92/64 scope link valid_lft forever preferred_lft forever
Changed title from "Understanding ethernet connections on one interface" to "Understanding ethernet addresses on one interface" as per dirkt's answer.