Re: [netmod] rfc6991bis: inet:host

Ladislav Lhotka <ladislav.lhotka@nic.cz> Mon, 27 July 2020 08:51 UTC

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From: Ladislav Lhotka <ladislav.lhotka@nic.cz>
To: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>, tom petch <ietfc@btconnect.com>, "netmod\@ietf.org" <netmod@ietf.org>
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Date: Mon, 27 Jul 2020 10:51:31 +0200
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Subject: Re: [netmod] rfc6991bis: inet:host
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Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> writes:

> So would the following do the right thing?

The invert-match pattern also needs to be added in order to avoid reserved labels:

>
>     typedef host-name {
>       type domain-name {
> 	pattern	'[a-zA-Z0-9\-\.]+';
	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 labels consisting of letters, digits
>        	 and hyphens separated by dots (see RFC1123 and RFC 952).";
>       reference
>         "RFC  952: DoD Internet Host Table Specification
> 	"RFC 1123: Requirements for Internet Hosts: Application and Support";
>     }

I am also not convinced that deriving host-name from domain-name is a good thing to do. Apart from being somewhat complicated, this coupling can also cause problems, e.g. if domain-name was to be obsoleted in the future.

Lada

>
> /js
>
> On Sun, Jul 26, 2020 at 03:11:15PM +0200, Ladislav Lhotka wrote:
>> 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
>
> -- 
> 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/>
>
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> netmod@ietf.org
> https://www.ietf.org/mailman/listinfo/netmod

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