In IPv4 world, when you want to talk to another computer, you ask which MAC address claims a given IPv4 address, the
arp who-has ... tell ... exchange as per
tcpdump, and a cache of such mappings from IPv4 to MAC addresses is usually available though
What about IPv6, with manual configuration? IPv6 addresses don't show up on
How does one computer discover another one over IPv6 within the same prefix?