Bill Stewart wrote:
When I came back, I found this ugly EUI-64 thing instead, so not only was autoconfiguration much uglier, but you needed a /56 instead of a /64 if you were going to subnet.
It's supposed to be a /48 per customer, on the assumption that 16 bits of subnet information is sufficient for virtually anyone; exceptions should be rare enough that they can be handled as special cases.
The /56 monstrosity came about because a US cable company wanted to assign a prefix to every home they passed, regardless of whether it contained a customer, so that they'd never need to renumber anything ever again. However, that would require they get more than the /32 minimum allocation, and ARIN policy doesn't allow _potential_ customers as a justification for getting a larger allocation, so they had to shrink the per-customer prefix down to a /56 to fit them all into a single /32. If all those assignments were to _real_ customers, they could have gotten a /24 and given each customer a /48 as expected. And, after that, many folks who can't wrap their heads around the size of the IPv6 address space appear to be obsessed with doing the same in other cases where even that weak justification doesn't apply...
Does anybody know why anybody thought it was a good idea to put the extra bits in the middle, or for IPv6 to adopt them?
Why the switch from EUI-48 to EUI-64? Someone in the IEEE got worried about running short of MAC (er, EUI-48) addresses at some point in the future, so they inserted 16 bits in the middle (after the OUI) to form an EUI-64 and are now "discouraging" new uses of EUI-48. The IETF decided to follow the IEEE's guidance and switch IPv6 autoconfig from EUI-48 to EUI-64, but FireWire is the only significant user of EUI-64 addresses to date; if you're using a link layer with EUI-48 addresses (e.g. Ethernet), an extra 16 bits (FFFE) get stuffed in the middle to transform it into the EUI-64 that IPv6 expects.
S -- Stephen Sprunk "God does not play dice." --Albert Einstein CCIE #3723 "God is an inveterate gambler, and He throws the K5SSS dice at every possible opportunity." --Stephen Hawking
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