On 2008-11-11 at 16:39 -0800, Phil Pennock wrote:
[ IPv6 ]
> Anything less than a /64 is asinine as it breaks stateless
> autoconfiguration on ethernet (64-bit node identifier), it breaks the
> privacy extensions (64-bit node identifier from MD5) and so has just
> blocked use of the most commonly deployed client implementations in the
> end-user OSes.

RFC 5375 is now out, "IPv6 Unicast Address Assignment Considerations",
informational.  It contains more data points to back this assertion of
mine.

Most pertinent is this paragraph from section 3:
   Using a subnet prefix length other than a /64 will break many
   features of IPv6, including Neighbor Discovery (ND), Secure Neighbor
   Discovery (SEND) [RFC3971], privacy extensions [RFC4941], parts of
   Mobile IPv6 [RFC4866], Protocol Independent Multicast - Sparse Mode
   (PIM-SM) with Embedded-RP [RFC3956], and Site Multihoming by IPv6
   Intermediation (SHIM6) [SHIM6], among others.  A number of other
   features currently in development, or being proposed, also rely on
   /64 subnet prefixes.

Surrounding context adds exceptions for special address-space (loopback,
mapped IPv4 addresses) and cautiously allows for manually-configured
nodes on point-to-point links using prefices longer than /64.

-Phil
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