Using /126 for IPv6 router links

Valdis.Kletnieks at Valdis.Kletnieks at
Sun Jan 24 23:26:14 UTC 2010

On Sun, 24 Jan 2010 17:01:21 EST, Steven Bellovin said:

> Actually, Scott Bradner and I share most of the credit (or blame) for
> the change from 64 bits to 128.
> During the days of the IPng directorate, quite a number of different
> alternatives were considered.  At one point, there was a compromise
> proposal known as the "Big 10" design, because it was propounded at the
> Big Ten Conference Center near O'Hare.  One feature of it was addresses
> of length 64, 128, 192, or 256 bits, determined by the high-order two
> bits.  That deal fell apart for reasons I no longer remember;

I don't remember the details of Big 10, but I do remember the general objection
to variable-length addresses (cf. some of the OSI-influenced schemes) was the
perceived difficulty of building an ASIC to do hardware handling of the
address fields at line rate.  Or was Big 10 itself the compromise to avoid
dealing with variable-length NSAP-style addresses ("What do you mean, the
address can be between 7 and 23 bytes long, depending on bits in bytes 3, 12,
and 17?" :)
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