ETHER_GEN_ADDR(9)

💖 ETHER_GEN_ADDR(9) 💖

okay so bestie, welcome to the ether_gen_addr era of the Kernel Developer's Manual ✨ this one's all about handing out a MAC address when nobody assigned one, and honestly? it's giving "fairy godmother but for network interfaces" 🧚

✨ NAME ✨

ether_gen_addr — generate an arbitrary MAC address for use 🎀

🦋 SYNOPSIS 🦋

like, include these first, obviously:

#include <sys/types.h>
#include <sys/socket.h>
#include <net/if.h>
#include <net/if_var.h>
#include <net/ethernet.h>

void
ether_gen_addr(struct ifnet *ifp, struct ether_addr *hwaddr);

🌸 DESCRIPTION 🌸

The ether_gen_addr() function generates an arbitrary MAC address for use by an ethernet interface that does not have an assigned address 🫶 like, it's literally the fallback bestie.

By default, ether_gen_addr attempts to generate a stable MAC address using the hostid of the jail that the ifp is being added to 💅 During early boot though, the hostid may not be set on machines that haven't yet populated /etc/hostid, or on machines that do not use loader(8) 😭 (yes, that's a whole thing).

ether_gen_addr can fail to derive a MAC address due to memory allocation failure, or because the hostid has not been populated 💀 In these cases, a locally-administered unicast MAC address will be randomly generated and returned via the hwaddr parameter — no cap, the fallback is still a valid vibe ✨

If ether_gen_addr succeeds, then it will return a MAC address in the FreeBSD Foundation OUI, 58:9c:fc, via the hwaddr parameter 👑

ngl the two paths are: stable-ish and hostid-based, or random-but-still-locally-administered-unicast. both land in hwaddr. that's the whole deal 🍓

👑 AUTHORS 👑

This manual page was written by Kyle Evans <kevans@FreeBSD.org> 💖 iconic of him, fr fr.

and that's the whole page bestie, you ate 🌈✨ this little slice of lore comes to you from Debian, dated June 1, 2021, and it's ETHER_GEN_ADDR(9) all the way down 🎀 bye bestie, go generate some addresses responsibly 💜