A network interface in a MAC-based network always requires a MAC address, virtual or physical. However, there are networks that are not MAC-based.
lo as a virtual network interface?
ifconfig doesn't show its MAC address, does it mean
lo has no MAC address, and the network of loopback IP addresses is not MAC-based?
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 inet6 ::1 prefixlen 128 scopeid 0x10<host> loop txqueuelen 1000 (Local Loopback) RX packets 2403613 bytes 138542051 (138.5 MB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 2403613 bytes 138542051 (138.5 MB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0