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

Adam Roach <> Thu, 10 January 2019 18:22 UTC

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To: Dave Crocker <>, Kent Watsen <>, Alexey Melnikov <>
Cc: The IESG <>, "" <>, "" <>, "" <>, Benjamin Kaduk <>
References: <> <> <> <> <> <> <> <> <> <>
From: Adam Roach <>
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Date: Thu, 10 Jan 2019 12:22:03 -0600
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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 
<> [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").


[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 ->