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> let me open my big yellow pages of globally unique MAC addresses

Yeah, well, you've basically described IPv6.

How do networks manage the larger number of IPv6 addresses?

My cursory digging indicates that the secret sauce is to grant large IPv6 prefixes and delegate routing to the prefix. An informative-looking Reddit comment says there are 100k IPv6 prefixes (as of Oct. 2020), and each active route takes 1 KiB. [1]

So, IPv6 differs significantly from MAC addresses because you only need to track prefixes.

[1]: https://old.reddit.com/r/networking/comments/j9twgq/how_much...

Prefixes are routed. ARP, in IPv6, is replaced by a function of Neighbor Discovery Protocol (NDP) called Neighbor Advertisment (NA) and Neighbor Solicitation (NS) where L2 MAC is sent in it's messaging. The NS messaging leverages multicast to communicate with the broader set of hosts for discovery. Basically it sends a message to the multicast address containing the IPv6 address such that it can discover it's MAC. So the flooding/broadcasting for MAC of v4 is replaced by a much more efficient L3 to L2 lookup in v6.

rfc4941 is from 2011 if you use an OS that isn't using it you have bigger problems.

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