Where to buy Internet IP addresses

Stephen Sprunk stephen at sprunk.org
Mon May 4 16:36:16 CDT 2009

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.


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

-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/x-pkcs7-signature
Size: 3241 bytes
Desc: S/MIME Cryptographic Signature
URL: <http://mailman.nanog.org/pipermail/nanog/attachments/20090504/3855de38/attachment.bin>

More information about the NANOG mailing list