Re: [netmod] rfc6991bis: inet:host

Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> Fri, 24 July 2020 08:36 UTC

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Date: Fri, 24 Jul 2020 10:36:17 +0200
From: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>
To: Ladislav Lhotka <ladislav.lhotka@nic.cz>
Cc: tom petch <ietfc@btconnect.com>, "netmod@ietf.org" <netmod@ietf.org>
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Mail-Followup-To: Ladislav Lhotka <ladislav.lhotka@nic.cz>, 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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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.:

  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/>