draft-ietf-6man-prefixlen-p2p-01 clarification

[Michael Sinatra]

Hi,

I am trying to properly interpret draft-ietf-6man-prefixlen-p2p-01 
(http://tools.ietf.org/html/draft-ietf-6man-prefixlen-p2p-01), which I 
believe has been advanced to proposed standard.  In section 6 of the 
draft, it says:

    Routers MUST support the assignment of /127 prefixes on point-to-
    point inter-router links.  Routers MUST disable subnet-router anycast
    for the prefix when /127 prefixes are used.

    When assigning and using any /127 prefixes, the following
    considerations apply.  Some addresses have special meanings, in
    particular addresses corresponding to reserved anycast addresses.
    When assigning prefixes (and addresses) to links, care should be
    taken to ensure that addresses reserved for such purposes aren't
    inadvertently assigned and used as unicast addresses.  Otherwise,
    nodes may receive packets that they are not intended to receive.
    Specifically, assuming that a number of point-to-point links will be
    numbered out of a single /64 prefix:

       a) Addresses with all zeros in the rightmost 64 bits SHOULD NOT be
       assigned as unicast addresses, to avoid colliding with the Subnet-
       Router anycast address [RFC4291].


Okay, so I understand the point about the routers must turn off 
subnet-router anycast; otherwise /127s could never be used.  However, it 
appears that the second paragraph is trying to recommend what prefix the 
operator assigns as a /127 point-to-point link.  If that's the case, 
then it further seems that "a)" requires that I not assign the zeroth 
/127 prefix carved out of a /64.  But if subnet-router anycast is turned 
of, should that matter?  RFC 4291 only states that the zeroth host bits 
*of a given prefixlen* not be used (i.e. the last 128-prefixlen bits 
cannot be zero).  Of course, if that's the case, then no /127 would 
work, which is why we need section 6 of the draft as quoted above.  So 
is it really the case that we can't assign the zeroth /127 out of a 
given /64?

This certainly doesn't matter from an addressing point of view, as there 
are way too many /127s in a /64 for this to be a remote worry.  However, 
I have heard people say that you can't use the zeroth /127 and I have 
experienced other people say "Why the heck are you skipping the first 
/127 and instead using 2001:db8:1:2::2/127 (or whatever)?"  So it's more 
of a confusion thing for me.  Any interpretations of what the draft is 
trying to say?

thanks,
michael