Re: [DNSOP] DNS Delegation Requirements

["Darcy Kevin (FCA)" <[e-mail]>]

That’s a very good catch. Restrictions on *hostnames* are different than restrictions on *domain*names*. The language below, from RFC 2181, Section 11 (incorrectly cited as RFC 2182, Section 11, in the draft; but RFC 2182 has no Section 11), should be controlling, and the other references (to RFCs 1035, 1123) should be discarded, since they refer specifically to *hostname* (not *domain*name*) restrictions, and/or are ambiguous as to whether they apply to hostnames or domain names. The reference to RFC 3696 should be discarded also, since it is only an Informational RFC, and defers to the others (1035, 1123 and 2181) as “authoritative” (and in any case, makes an explicit exception for “names that are normally not seen by users”).

--- RFC 2181, SECTION 11 ---
Occasionally it is assumed that the Domain Name System serves only
   the purpose of mapping Internet host names to data, and mapping
   Internet addresses to host names.  This is not correct, the DNS is a
   general (if somewhat limited) hierarchical database, and can store
   almost any kind of data, for almost any purpose.

   The DNS itself places only one restriction on the particular labels
   that can be used to identify resource records.  That one restriction
   relates to the length of the label and the full name.  The length of
   any one label is limited to between 1 and 63 octets.  A full domain
   name is limited to 255 octets (including the separators).  The zero
   length full name is defined as representing the root of the DNS tree,
   and is typically written and displayed as ".".  Those restrictions
   aside, any binary string whatever can be used as the label of any
   resource record.  Similarly, any binary string can serve as the value
   of any record that includes a domain name as some or all of its value

   (SOA, NS, MX, PTR, CNAME, and any others that may be added).
--- END QUOTE ---

(Nota bene the reference to “any binary string” being legal “as the value” of an NS record – how can that be compatible with subjecting delegations to “hostname” rules?).

Now, if a particular *registry* wants to put additional restrictions on the names it will delegate, then that’s another matter, but IMO outside the scope of this draft.

In practice, it is quite common to delegate subzones whose only contained “leaf” RRs are of type SRV and thus *must*, according to the naming conventions of SRV, contain underscores in their FQDNs. As long as those zones contain no “hostname” records, this is perfectly legal and acceptable, according to current standards, and I see no compelling reason to disparage or mark as “defective”, the delegation of such domains. Although much rarer, some zones might only contain MX records, and/or some other record type(s) which is/are not considered to represent a “hostname”, _per_se_.

                                                                                                                                                                - Kevin

From: DNSOP [mailto:[e-mail]] On Behalf Of Jacques Latour
Sent: Tuesday, February 09, 2016 12:00 PM
To: Warren Kumari; Darcy Kevin (FCA); dnsop
Subject: Re: [DNSOP] DNS Delegation Requirements


Hi,



Sent something relating to this on DNS-OARC this morning, but it seems to be legit to have delegation for a “_tcp.example.ca”, which fails the syntax requirements defined in section  “8.1.  Illegal characters MUST NOT be in the domain name".



A delegation can happen to a valid domain name, not necessarily a valid hostname.



Zonemaster fails on delegations like “_sips._tcp.cam.ac.uk”



# dig _sips._tcp.cam.ac.uk  ns +short

rnb-uls2-jabber.phone.cam.ac.uk.

cnh-uls2-jabber.phone.cam.ac.uk.

wolf-uls2-jabber.phone.cam.ac.uk.





Jack




From: DNSOP [mailto:[e-mail]] On Behalf Of Warren Kumari
Sent: February-08-16 6:51 PM
To: Darcy Kevin (FCA); dnsop
Subject: Re: [DNSOP] DNS Delegation Requirements


On Mon, Feb 8, 2016 at 3:38 PM Darcy Kevin (FCA) <[e-mail]<mailto:[e-mail]>> wrote:
My 2 cents…

I don’t think any DNS RFC should be tied to any specific element of Internet routing technology. Keep it relatively generic and avoid mention of “ASes” and the like, since this RFC may outlive the use of ASes for Internet routing. ”Path diversity”, “link diversity”, “network-level redundancy”, those are all fine.

That works too -- RFC 2182, 3.1. ? :-)

W



                                                                                                                        - Kevin

From: DNSOP [mailto:[e-mail]<mailto:[e-mail]>] On Behalf Of Warren Kumari
Sent: Monday, February 08, 2016 9:21 AM
To: Ralf Weber; Jakob Schlyter
Cc: dnsop; Patrik Wallström
Subject: Re: [DNSOP] DNS Delegation Requirements


On Mon, Feb 8, 2016 at 2:00 AM Ralf Weber <[e-mail]<mailto:[e-mail]>> wrote:
Moin!

On 8 Feb 2016, at 9:57, Jakob Schlyter wrote:
> At this point, we're seeking more public comments - on this mailing
> list (unless the chairs disapproves), on the our issue tracker [4] or
> via email to the authors.
Thanks a lot for this work. I certainly would like dnsop to work on
this.

I would soften some of language and have a question.

5.1. There are use cases where the serial number rarely if ever is the
same on all servers and it's only really used inside communication for a
given domain and not during resolution. So the only people who know if a
divergent serial number is a problem are the domain owners. So we
shouldn't tell the public that this is a problem. I would say that a
different SOA serial number could be seen as an indicator of an
inconsistent setup, but that further analysis is required to really
conclude that.

6.2 The name servers SHOULD NOT belong to the same AS
I would drop that requirement altogether or make it a MAY. We really
should not tell people how to build networks from the DNS world.


I think that the SHOULD NOT is actually correct here -- from RFC1771: The use of the term Autonomous System
here stresses the fact that, even when multiple IGPs and metrics are
used, the administration of an AS appears to other ASs to have a
single coherent interior routing plan and presents a consistent
picture of what destinations are reachable through it.

An AS is a "network", run by one organization. This means that there is a monkey sitting somewhere making all of the routing decisions, and sometimes monkeys screw up. Having a nameserver in an AS that is run by a different monkey means that you need multiple monkeys messing up at the same time[0]. Also, a significant amount of routing and traffic engineering decisions are made at the AS level ("Meh, I'll local-pref AS 42 down to move this traffic $there") - this means that sometimes folk screw up and accidentally block access to some set of ASes - SIDR may or may not make this more likely :-)

This is *not* telling people how to build their network - it is simply *suggesting* that they consider putting some net of nameservers in a network run by someone else.  If you understand the implications of putting all of your nameservers in one AS, good for you. If not, chances are it's safer to put at least some elsewhere...

W
[0]: This (obviously) isn't really true, both ASs could share the same upstream, router, etc. RFC 2182, 3.1. says it best:
"They should also be connected to
the net via quite diverse paths.  This means that the failure of any
one link, or of routing within some segment of the network (such as a
service provider) will not make all of the servers unreachable."






8.7 We should point out here that neither an MX nor an A record are
required at the zone apex or do you want either of them mandatory?

On the SOA settings I do have a question. Would the following SOA be
legitimate according to this draft?
        localhost. root.localhost. 1115106304 16384 2048 1048576 2560
If not why not, as my spot checking didn't find anything that made it
invalid.

So long
-Ralf

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