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Re: [moonv6] /120 prefix length at UNH

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From: Alain Durand (Alain.Durand@Sun.COM)
Date: 10/15/03


moonv6 post from Alain Durand <Alain.Durand@Sun.COM>

Bound, Jim wrote:

>
>
>I do not interpret 2.5.1 as you do. A /120, /115, or /64 prefix does not
>preclude that a EUI-64 format for the low order bits exist. If UNH had used
>a /58 then that would be a violation of 3513.
>
>From 3513:
>
>2.5.4 Global Unicast Addresses
>
> The general format for IPv6 global unicast addresses is as follows:
>
> | n bits | m bits | 128-n-m bits |
> +------------------------+-----------+----------------------------+
> | global routing prefix | subnet ID | interface ID |
> +------------------------+-----------+----------------------------+
>
> where the global routing prefix is a (typically hierarchically-
> structured) value assigned to a site (a cluster of subnets/links),
> the subnet ID is an identifier of a link within the site, and the
> interface ID is as defined in section 2.5.1.
>
> All global unicast addresses other than those that start with binary
> 000 have a 64-bit interface ID field (i.e., n + m = 64), formatted as
> described in section 2.5.1. Global unicast addresses that start with
> binary 000 have no such constraint on the size or structure of the
> interface ID field.
>
>A /120 prefix does not say that n+m != 64. It simply states that the high
>order bits of n == 8 and m == 58, which == 64 leaving 64 for EUI-64.
>
>/120 prefix is not a violation of 3513.
>

Yes it is. Wich ever way you cut it, with /120, m+n == 120, and this by definition of the prefix length.

RFC3513, section 2.3: 

      prefix-length   is a decimal value specifying how many of the
                      leftmost contiguous bits of the address comprise
                      the prefix.
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