Re: [netmod] rfc6991bis: inet:host

Ladislav Lhotka <ladislav.lhotka@nic.cz> Sun, 26 July 2020 13:11 UTC

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From: Ladislav Lhotka <ladislav.lhotka@nic.cz>
To: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>
Cc: tom petch <ietfc@btconnect.com>, "netmod\@ietf.org" <netmod@ietf.org>
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Subject: Re: [netmod] rfc6991bis: inet:host
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Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> writes:

> On Wed, Jul 22, 2020 at 01:46:38PM +0200, Ladislav Lhotka wrote:
>> 
>> 
>> On 22. 07. 20 13:00, Juergen Schoenwaelder wrote:
>> > Tom,
>> > 
>> > my understanding is that Lada is now proposing something slightly
>> > different but I am not sure what exactly, hence I asked again.
>> 
>> Oh yes, I messed it up by mixing different things together, sorry. I
>> checked again the ML archive, and the message that is relevant to this
>> thread is this:
>> 
>> https://mailarchive.ietf.org/arch/msg/netmod/PISOifrtow4oWLGW7meBBSri7nM/
>> 
>> The aim of that proposal was to limit the "inet:host" type to DNS names
>> that are reasonable as host names, i.e. eliminate values like "." or "_".
>
> You are proposing to change the length restriction from 1..253 to
> 2..253 following RFC 952:
>
>    [...] Single character names
>    or nicknames are not allowed.
>
> And you add
>
>         pattern '(.*\.)?..\-\-.*' {
>           modifier invert-match;
>         }
>
> to restrict things to non-reserved letter-digit-hyphen labels as per
> RFC 5890. Is it clear that this second restriction applies to host
> names? How do you represent internationalized host names? Perhaps we
> need a collection of examples? And is the pattern correct? RFC 5890
> says:
>
>    Reserved LDH labels, known as "tagged domain names" in some other
>    contexts, have the property that they contain "--" in the third and
>    fourth characters but which otherwise conform to LDH label rules.
>
> What is the '(.*\.)?' part doing in your pattern?
>
> Finally, would it be useful to derive a host-name type from the
> domain-name type (if host-names are really a strict subset of what
> domain-name allows), e.g.:

The current definition of "inet:domain-name" in 6991bis also permits the underscore character in labels, so it is not LDH.

Lada

>
>   typedef host-name {
>     type domain-name {
>       pattern '(.*\.)?..\-\-.*' {
>         modifier invert-match;
>       }
>       length "2..max";
>     }
>     description
>       "Host names  must be at least two characters long (see RFC 952)
>        and they are restricted to non-reserved letter-digit-hyphen
>        (NR-LDH) labels (see RFC ????).";
>     reference
>       "RFC  952: DoD Internet Host Table Specification
>        RFC ????: ????";
>   }
>
> /js
>
> -- 
> Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
> Fax:   +49 421 200 3103         <https://www.jacobs-university.de/>

-- 
Ladislav Lhotka 
Head, CZ.NIC Labs
PGP Key ID: 0xB8F92B08A9F76C67