Title text: I think the IETF hit the right balance with the 128 bits thing. We can fit MAC addresses in a /64 subnet, and the nanobots will only be able to devour half the planet.
Megan and Ponytail are in orbit while nanobots are devouring the earth in a swarm. The nanobots stop after devouring 40% of the planet. This is a take on the "Grey goo" scenario in which self-replicating nanobots destroy the earth while creating more and more of themselves non-stop.
However, the nanobots are only able to destroy 40% of the planet because 40% of the earth volume = (# of IPv6 addresses) x (A few cubic microns). Without more IP addresses, the nanobots cannot continue to replicate (assuming that each nanobot must be individually addressable).
IPv6 supports approximately 3.4×1038 addresses while the Earth's volume is around 1.08321×1012 km3 or 1.08321×1039 µm3(cubic micrometre). Randall's guess on 40% of the planet would mean each nanobot is about 1.27331 µm3 - which is still less than "a few cubic microns" according to 1070: Words for Small Sets. Note however, that the nanobot density might be different than Earth density, so "a few microns" might still be correct.
1998 is when the IPv6 Specification (RFC 2460) was published and IETF is the Internet Engineering Task Force.
Note that an April fool joke for IPV9 exists and would have guaranteed Earth's doom in this comic's scenario.
- [Megan and commander are on a space station.]
- Megan: Commander! Come quick! It's the nanobots—they've STOPPED!
- Megan: They devoured 40% of the Earth, and then just... quit! They're just sitting there! Why?!
- Ponytail: It's a mystery. ...unless... What's the volume of each nanobot?
- Megan: A few cubic microns. Why?
- Ponytail: I think the year 1998 just bought us some time.
- [Earth's surface, covered in mountains of nanobots.]
- In the swarm:
- Nanobot: What do you mean, "Run out of addresses?"
- Other Nanobot: Look, we should've migrated away from IPv6 AGES ago...
- On the website, the space above the comic says "xkcd.com now has IPv6 connectivity. If you can't reach it, you or your ISP have misconfigured equipment. Sadly, I now have no way to tell you."
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