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