On Mon, Sep 19, 2011 at 7:02 PM, Brian E Carpenter
<brian.e.carpen...@gmail.com> wrote:
> On 2011-09-20 09:23, Nathan Ward wrote:
>> On 20/09/2011, at 9:19 AM, Iljitsch van Beijnum wrote:
>>
>>> My position is that prefixes should always end in :: so the address part is
>>> a valid address and the same code can be used to parse addresses, prefixes
>>> and addresses with a prefix length.
>>
>> Agreed. Shortening IPv4 addresses to things like 10/8 makes sense because we
>> don't have another way to do shortening. If we did (i.e. 10../8 or
>> something) then we'd use that.
>
>
> It's unfortunate, I think, that RFC 4291 just says:
>
> The use of "::" indicates one or more groups of 16 bits of zeros.
> The "::" can only appear once in an address. The "::" can also be
> used to compress leading or trailing zeros in an address.
>
> It would better if it also specified where to use :: if there
> is more than one run of zeros. As in
>
> If an address contains more than one group of zeros where "::"
> could be used, only the {least|most} significant such group
> may be represented by "::".
>
> Take your pick between "least" and "most".
>
> If we don't have such a rule, I fear that the only unambiguous rule for
> prefixes is to avoid abbreviation.
>
The errata to RFC 4291 offer more clarity in the use of :: in an address
http://www.rfc-editor.org/errata_search.php?rfc=4291
I believe the convention when more than one sequence of zeros meets
the criteria is to compress the longest such sequence.
-K-
> Brian
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