Re: Fix IPV6 literal notation?

[tom petch <[e-mail]>]

From: ipv6 <[e-mail]> on behalf of Alexandre Petrescu <[e-mail]>
Sent: 29 December 2020 11:27

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.

> 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)?

<tp>
Augmented Backus Naur 
RFC5234 (which seems like a good enough reason to me)
Tom Petch




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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