Since no one seems to have mentioned it (or my spam filter
blocked it),
the ARIN policy recommends both /56 and /64 allocations.
From the ARIN
Number Policy Manual:
6.5.4.1. Assignment address space size
End-users are assigned an end site assignment from their LIR
or ISP. The
exact size of the assignment is a local decision for the LIR
or ISP to
make, using a minimum value of a /64 (when only one subnet
is
anticipated for the end site) up to the normal maximum of
/48, except in
cases of extra large end sites where a larger assignment can
be
justified.
The following guidelines may be useful (but they are only
guidelines):
* /64 when it is known that one and only one subnet is
needed
* /56 for small sites, those expected to need only a few
subnets
over the next 5 years.
* /48 for larger sites
For end sites to whom reverse DNS will be delegated, the
LIR/ISP should
consider making an assignment on a nibble (4-bit) boundary
to simplify
reverse lookup delegation.
RIRs/NIRs are not concerned about which address size an
LIR/ISP actually
assigns. Accordingly, RIRs/NIRs will not request the
detailed
information on IPv6 user networks as they did in IPv4,
except for the
cases described in Section 6.4.4 and for the purposes of
measuring
utilization as defined in this document.
--
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley
Lab)
E-mail: oberman es.net Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4 EADA 927D EBB3
987B 3751
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