Choice of network space when numbering interfaces with IPv6

[Zaid Ali <zaid () zaidali com>]

SO I have been turning up v6 with multiple providers now and notice that
some choose /64 for numbering interfaces but one I came across use a /126. A
/126 is awfully large (for interface numbering) and I am curious if there is
some rationale behind using a /126 instead of a /64.

Zaid