Re: [Netconf] Benjamin Kaduk's Discuss on draft-ietf-netconf-zerotouch-25: (with DISCUSS and COMMENT)

Adam Roach <adam@nostrum.com> Thu, 10 January 2019 18:22 UTC

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To: Dave Crocker <dcrocker@bbiw.net>, Kent Watsen <kwatsen@juniper.net>, Alexey Melnikov <aamelnikov@fastmail.fm>
Cc: The IESG <iesg@ietf.org>, "draft-ietf-netconf-zerotouch@ietf.org" <draft-ietf-netconf-zerotouch@ietf.org>, "netconf-chairs@ietf.org" <netconf-chairs@ietf.org>, "netconf@ietf.org" <netconf@ietf.org>, Benjamin Kaduk <kaduk@mit.edu>
References: <154390493154.31734.13025584839857369253.idtracker@ietfa.amsl.com> <F526DA60-77EC-45D6-ADE0-B345020A89BF@juniper.net> <20181230003002.GC57547@kduck.kaduk.org> <5DCD6C74-7918-45AB-BEA7-2C1A020B4411@juniper.net> <20190106050255.GJ28515@kduck.kaduk.org> <35A436B3-5D57-4015-A51E-5F9A1E349D31@juniper.net> <DAC627AC-8453-41D2-B95C-BC25746E66C1@juniper.net> <cc5adc78-6751-fabf-03d2-e0c65f8a6c91@bbiw.net> <F844EDFB-3E15-47FB-A714-06363B996FC2@juniper.net> <42cddba1-9f59-f19f-176f-197f0c0c0c96@bbiw.net>
From: Adam Roach <adam@nostrum.com>
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Subject: Re: [Netconf] Benjamin Kaduk's Discuss on draft-ietf-netconf-zerotouch-25: (with DISCUSS and COMMENT)
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On 1/10/19 11:26 AM, Dave Crocker wrote:
> On 1/9/2019 1:12 PM, Kent Watsen wrote:
> ...
>> To clarify, the draft uses DNS in two ways:
>>
>> 1) the first is for traditional SRV records, for which being under 
>> _tcp makes sense.
>
> +1
>> 2) the second is for TXT records that, of and in themselves, are not 
>> describing a TCP service, so much as providing bootstrapping data, 
>> that may or may not cause the device to initiate a subsequent 
>> connection (TCP or otherwise). For this case, we also have the _sztp 
>> record under _tcp, but *should* it be under the TLD instead?
>
> Absent deep involvement in the work of the spec, and just basing my 
> view on the small bits of the spec I've read, I'd suggest dropping use 
> of _tcp for the TXT and just using _sztp as a globally-scoped attrleaf 
> node name, registering it in the new attrleaf registry. 


I don't think this is right. Draft-ietf-netconf-zerotouch is explicitly 
using DNS-SD procedures [1]. In turn, DNS-SD absolutely mandates the 
presence of both SRV and TXT records with the same name [2]. So the 
names need to match.

Dave's assertion that the use of _sztp._tcp... is not under the purview 
of draft-ietf-dnsop-attrleaf is correct [3]. The assumption in attrleaf 
is that whatever document ends up registering a global underscored name 
will provide guidance for those name elements that precede (are lower 
down in the tree than) the global underscored name.

In the case of DNS-SD, both the SRV and TXT _tcp global leaf namespace 
is clearly spelled out to be governed by 
<http://www.iana.org/assignments/port-numbers> [4][5][6][7].

In short, unless we're making radical changes to zerotouch so that it no 
longer uses RFC 6763, there is no valid path forward other than 
registering a corresponding service in the IANA table cited above (such 
as "sztp").

/a

____
[1] draft-ietf-netconf-zerotouch §4.2.1: "Devices claiming to support 
DNS as a source of bootstrapping data MUST first query for 
device-specific DNS records using DNS-SD [RFC6763]"

[2] RFC 6763 §6: "Every DNS-SD service MUST have a TXT record in 
addition to its SRV record, with the same name"

[3] draft-ietf-dnsop-attrleaf §2: "Only global underscored names are 
registered in the IANA Underscore Global table."

[4] draft-ietf-dnsop-attrleaf §4.3 defers authority for SRV/_tcp to RFC 
2782 and authority for TXT/_tcp to RFC 6763.

[5] RFC 6763 §7: "The first label of the pair is an underscore character 
followed by the Service Name [RFC6335]."

[6] RFC 6335 §10, which is too long too reasonably quote here.

[7] RFC2782 §"The format of the SRV RR"; see definition of "Service", 
with STD 2/RFC 1700 -> RFC 3232 -> iana.org