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List:       ipng
Subject:    Re: Fix IPV6 literal notation?
From:       Brian E Carpenter <brian.e.carpenter () gmail ! com>
Date:       2020-12-31 3:47:32
Message-ID: 75dbb983-b40c-1782-6fcf-682f9e2a504e () gmail ! com
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On 30-Dec-20 00:27, Alexandre Petrescu wrote:
> 
> 
> Le 27/12/2020 à 00:25, Brian E Carpenter a écrit :
>> Tim,
>>
>> On 27-Dec-20 11:16, Tim Bray wrote:
>>> See https://twitter.com/dave_universetf/status/1342685822286360576 
>>> to which I heartily concur. IPV6 addresses are neither easy for 
>>> humans to read, nor easy for software to parse.
>>>
>>> *If* someone has a better idea, there's no good reason not to 
>>> standardize it, the old approach would still work.   Does anyone 
>>> have a better idea?
>>
>> I have no idea if there's a proposal in that sequence of Twitter 
>> messages, but if there is, it should be written up as an I-D aimed
>> at the 6man WG and discussed there. (Hence I have changed the IETF
>> list to a Bcc: and added the 6man list in Cc:.)
>>
>> I can say that this much is wrong:
>>
>>> Oh, and the leading zero debate also infects IPv6, to some extent! 
>>> The specs tried to specify the textual representation of IPv6, but 
>>> it failed to be complete. So it's unclear if 
>>> 000001::00001.00002.00003.00004 is a valid IPv6 address
>>
>> It's quite clear that it is invalid. RFC4291 section 2.2 says:
>>
>> "1. The preferred form is x:x:x:x:x:x:x:x, where the 'x's are one to
>>  four hexadecimal digits of the eight 16-bit pieces of the address."
> 
> But there is also that notation in a certain RFC which says that
> 1::1.1.1.1 is a valid notation too.
> 
> So combining the two might indeed lead to 1::01.1.1.1 being a
> potentially valid notation as well.

The parsers that I have convenient access to all treat that leading 0
as invalid, which is no surprise if you study the URI ABNF.

   Brian
> 
>> As for writing a parser, I'd expect the starting point to be the
>> ABNF in RFC3986 (where the limitation to 4 hex digits is also
>> clear).
> 
> One might wonder why ABNF (A Backus Naur Form) and not other notations
> for grammar descriptions, such as ASN.1 (Abstract Syntax Notation number 1)?
> 
> But the idea of a reference parser would be great.  One might start with
> the parsers that are open source in BSD and in linux.
> 
> A reference parser implementation might help avoid incompatible IP
> literal address notations.
> 
> Alex
> 
>>
>> Regards Brian Carpenter
>>
>>
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