The /64 is really only a requirement if you want to
support SLAAC.
Which is not to say a /64 is only required if you need
SLAAC. Just that if you need SLAAC, not other prefix length
will work.
I know lots of networks that use a /64 for point-to-point
links. I don't, but many do, and it works.
FWIW, I've had to look into this lately and went trawling through the
RFCs for guidance.
The IETF is very firmly on the side of always using a /64 for subnets.
At least RFCs 3177, 3315, 3627, 3736, 3956, 3971, 4291, 4862, 4866,
4872, 4941, 5375 either mandate, recommend, specify, or rely on, the use
of /64 for *all* subnets with hosts.
This goes so far as language in the RFCs that reads like "...however,
not all IPv6 implementations prevent the use of longer subnet prefixes
at this time...". (Quoting from memory, might not be 100% accurate.)
There's only one exception I've found and that's
DRAFT-KOHNO-IPV6-PREFIXLEN-P2P, which AFAIK has not been accepted and is
now ineligible to become a standards-track RFC.
I firmly agree with previous posts that outline why this allocation
policy is suboptimal.
However, I do *not* want to be renumbering my IPv6 hosts down the road
simply because I wanted to be the most efficient guy on the block. Nor
do I want to be the guy who can't run protocol XYZ because I didn't use
/64s.
--
-Adam Thompson
[email protected]
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