alt Hacker NewsWild guess: packet forward is implemented in hardware while arp/nd is software, with probably some things (think "hardware interrupt" or something alike) that allows hardware to "call" the software stack (for instance, when the link-layer addr is unknown)
So, to implement what you said, we need more than a simple router upgrade: we'd need to change the hardware, so that when a packet is forwarded from a source that's not in the mac table, the software can (asynchronously) perform an arp/nd lookup
There is probably a world of issue behind that behavior, but I do not know
Great guess, not sure why it's at the bottom of the responses so far :).
You can either have the hardware do additional lookups for every packet it processes or you can just follow the normal process for the very first packet from that IP. Or, exactly what this article is about for the best of both worlds.
Advanced ASICs usually go down a different path of offering the ability to validate the ND process (to prevent spoofing) rather than doing even more to trust whatever is sent. This is compatible with the way GRAND works, making it a win-win-win approach.