Re: [netmod] rfc6991bis: inet:host

Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> Sun, 26 July 2020 20:24 UTC

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Date: Sun, 26 Jul 2020 22:24:27 +0200
From: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>
To: tom petch <ietfc@btconnect.com>, "netmod@ietf.org" <netmod@ietf.org>
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References: <20200717191717.u5a3wv4nbajjdcaj@anna.jacobs.jacobs-university.de> <87ft9mzhe0.fsf@nic.cz> <20200721194434.pvekzgxaus43iihg@anna.jacobs.jacobs-university.de> <AM7PR07MB62482ED4917241DBCD08E7B7A0790@AM7PR07MB6248.eurprd07.prod.outlook.com> <20200722110030.6c7r6utxgjbsilkq@anna.jacobs.jacobs-university.de> <ff42e4cb-957c-a4f0-a88b-333a6565ed8e@nic.cz> <20200724083617.u3wkr34ehjezmusq@anna.jacobs.jacobs-university.de> <87a6zmifpo.fsf@nic.cz>
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Archived-At: <https://mailarchive.ietf.org/arch/msg/netmod/n1Q3HHYH17YQSoh3F5jdT-U7NVk>
Subject: Re: [netmod] rfc6991bis: inet:host
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So would the following do the right thing?

    typedef host-name {
      type domain-name {
	pattern	'[a-zA-Z0-9\-\.]+';
        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";
    }

/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/>