| dnsop | D. Crocker |
| Internet-Draft | Brandenburg InternetWorking |
| Updates: 2782, 3263, 3529, 3620, 3832, | November 20, 2018 |
| 3887, 3958, 4120, 4227, 4386, | |
| 4387, 4976, 5026, 5328, 5389, | |
| 5415, 5518, 5555, 5617, 5679, | |
| 5766, 5780, 5804, 5864, 5928, | |
| 6120, 6186, 6376, 6733, 6763, | |
| 7208, 7489, 8145 (if approved) | |
| Intended status: Standards Track | |
| Expires: May 24, 2019 |
DNS Attrleaf Changes: Fixing Specifications with Underscored Node Name Use
draft-ietf-dnsop-attrleaf-fix-07
Original uses of an underscore character as a domain node name prefix, which creates a space for constrained interpretation of resource records, were specified without the benefit of an IANA registry. This produced an entirely uncoordinated set of name-creation activities, all drawing from the same namespace. A registry now has been defined. However the existing specifications that use underscore naming need to be modified, to be in line with the new registry. This document specifies those changes. The changes preserve existing software and operational practice, while adapting the specifications for those practices to the newer underscore registry model.
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This Internet-Draft will expire on May 24, 2019.
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Original uses of an underscore character as a domain node name prefix, which creates a space for constrained interpretation of resource records, were specified without the benefit of an [IANA-reg] registry. This produced an entirely uncoordinated set of name-creation activities, all drawing from the same namespace. A registry has been now defined, and that document discusses the background for underscored domain name use [Attrleaf].
The basic model for underscored name registration, as specified in [Attrleaf], is to have each registry entry be unique in terms of the combination of a resource record type and a 'global' (highest-level) underscored name; that is, the node name beginning with an underscore, which is the closest to the DNS root.
The existing uses of underscored naming have specifications that do not reflect the existence of this integrated registry. For the new reader or the new editor of one of those documents, there is currently nothing signaling that the underscore name(s) defined in the document are now processed through an IANA registry. This document remedies that, by marking such a published document with an update, indicating the nature of the change.
Further, the documents that define the SRV and URI DNS resource records provide a meta-template for underscored name assignments, partially based on separate registries [RFC6335]. For the portion that selects the global (highest-level) underscored name, this perpetuates uncoordinated assignment activities by separate technical specifications, out of the same name space. This document remedies that by providing detail for revisions to the SRV and URI specifications, to bring their use in line with the single, integrated global underscore registry.
The result of these changes preserves existing software and operations practices, while adapting the technical specifications to the newer underscore registry model.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
The use of underscored node names is specific to each RRTYPE that is being scoped. Each name defines a place, but does not define the rules for what appears underneath that place, either as additional underscored naming or as a leaf node with resource records. Details for those rules are provided by specifications for individual RRTYPEs. The sections below describe the way that existing underscore labels are used with the RRTYPEs that they name.
This section provides a generic approach for changes to existing specifications that define straightforward use of underscored node names, when scoping the use of a TXT RRset. The approach provides the information needed for adapting such specifications to the use of the IANA DNS Underscore Global Scoped Entry Registry. Hence the approach is meant both as an update to these existing specifications, and as guidance for changes when those documents are revised.
For any document that specifies the use of a TXT RRset under one or more underscored names, the 'global' name is expected to be registered in the IANA DNS Underscore Global Scoped Entry Registry. An effort has been made to locate existing drafts that do this, register the global underscored names, and list them in the initial set of names added to the registry.
If a public specification defines use of a TXT RRset and calls for the use of an underscore-prefixed domain name, here is a template of suggested text for registering the global underscored name -- the one closest to the root -- through the IANA Considerations section of the specification:
| RR Type | _NODE NAME | REFERENCE |
|---|---|---|
| TXT | _{DNS node name} | {citation for the document making the addition.} |
Specification of the SRV resource record provides a template for use of underscored node names. The global name is characterised as referencing the 'protocol' that is associated with SRV RRset usage.
This section provides a generic approach for changes to existing specifications that define the use of an SRV RRset. The approach provides the information needed for adapting such specifications to the use of the IANA DNS Underscore Global Scoped Entry Registry. Hence the approach is meant both as an update to these existing specifications, and as guidance for changes when those documents are revised.
For any document that specifies the use of an SRV RRset, the global ('protocol') underscored name is expected to be registered in the IANA DNS Underscore Global Scoped Entry Registry. An effort has been made to locate existing drafts that do this, register the global underscored names, and list them in the initial set of names added to the registry.
If a public specification defines use of a SRV RRset and calls for the use of an underscore-prefixed domain name, here is a template of suggested text for registering the global underscored name -- the one closest to the root -- through the IANA Considerations section of the specification:
| RR Type | _NODE NAME | REFERENCE |
|---|---|---|
| SRV | _{DNS 'protocol' node name} | {citation for the document making the addition.} |
Specification of the URI resource record provides a template for use of underscored node names. The global name is characterised as naming the 'protocol' that is associated with URI RR usage or by reversing an Enumservice sequence [RFC6117].
This section provides a generic approach for changes to existing specifications that define use of a URI RRset. The approach provides the information needed for adapting such specifications to the use of the IANA DNS Underscore Global Scoped Entry Registry. Hence the approach is meant both as an update to these existing specifications, and as guidance for changes when those documents are revised.
For any document that specifies the use of a URI RRset, the global ('protocol' or highest-level enumservice) underscored name is expected to be registered in the IANA DNS Underscore Global Scoped Entry Registry. An effort has been made to locate existing drafts that do this, register the global underscored names, and list them in the initial set of names added to the registry.
If a public specification defines use of a URI RRset and calls for the use of an underscore-prefixed domain name, here is a template of suggested text for registering the global underscored name -- the one closest to the root -- through the IANA Considerations section of the specification:
| RR Type | _NODE NAME | REFERENCE |
|---|---|---|
| URI | _{DNS 'protocol' or Enumservice node name} | {citation for the document making the addition.} |
The specification for a domain name, under which an SRV resource record appears, provides a template for use of underscored node names. The global underscored name is characterised as indicating the 'protocol' that is associated with SRV RR usage.
The format of the SRV RR
Here is the format of the SRV RR, whose DNS type code is 33:
_Service._Proto.Name TTL Class SRV Priority Weight Port Target
...
Proto
The symbolic name of the desired protocol, with an underscore
(_) prepended to prevent collisions with DNS labels that occur
in nature. _TCP and _UDP are at present the most useful values
for this field, though any name defined by Assigned Numbers or
locally may be used (as for Service). The Proto is case
insensitive.
Text of that existing specification is changed as follows:
Specification for the domain name, under which a URI resource record occurs, is similar to that for the SRV resource record, although the text refers only to 'service' name, rather than distinguishing 'service' from 'protocol'. Further, the URI RR specification permits alternative underscored naming schemes:
4.1. Owner Name, Class, and Type
The URI owner name is subject to special conventions.
Just like the SRV RR [RFC2782], the URI RR has service information
encoded in its owner name. In order to encode the service for a
specific owner name, one uses service parameters. Valid service
parameters are those registered by IANA in the "Service Name and
Transport Protocol Port Number Registry" [RFC6335] or as "Enumservice
---
Registrations [RFC6117]. The Enumservice Registration parameters are
reversed (i.e., subtype(s) before type), prepended with an underscore
(_), and prepended to the owner name in separate labels. The
underscore is prepended to the service parameters to avoid collisions
with DNS labels that occur in nature, and the order is reversed to
make it possible to do delegations, if needed, to different zones
(and therefore providers of DNS).
For example, suppose we are looking for the URI for a service with
ENUM Service Parameter "A:B:C" for host example.com. Then we would
query for (QNAME,QTYPE)=("_C._B._A.example.com","URI").
As another example, suppose we are looking for the URI for a service
with Service Name "A" and Transport Protocol "B" for host
example.com. Then we would query for
(QNAME,QTYPE)=("_A._B.example.com","URI").
Text of that existing specification is changed as follows:
"Signaling Trust Anchor Knowledge in DNS Security Extensions (DNSSEC)" [RFC8145] defines a use of DNS node names that effectively consumes all names beginning with the string "_ta-", when using the NULL RR in the query.
For example, a validating DNS resolver ...
QNAME=_ta-4444.
Text of Section 5.1, "Query Format", of that existing specification, is changed as follows:
Although this document makes reference to IANA registries, it introduces no new IANA registries or procedures.
This memo raises no security issues.
| [Attrleaf] | Crocker, D., "DNS Scoped Data Through 'Underscore' Naming of Attribute Leaves", I-D draft-ietf-dnsop-attrleaf, 2018. |
| [RFC6117] | Hoeneisen, B., Mayrhofer, A. and J. Livingood, "IANA Registration of Enumservices: Guide, Template, and IANA Considerations", RFC 6117, March 2011. |
| [RFC6335] | Cotton, M., Eggert, L., Tpuch, J., Westerlund, M. and S. Cheshire, "Internet Assigned Numbers Authority (IANA) Procedures for the Management of the Service Name and Transport Protocol Port Number Registry", RFC 6335, Aug 2011. |
| [RFC7553] | Falstrom, P. and O. Kolkman, "The Uniform Resource Identifier (URI) DNS Resource Record", RFC 7553, ISSN 2070-1721, June 2015. |
| [RFC8145] | Wessels, D., Kumari, W. and P. Hoffman, "Signaling Trust Anchor Knowledge in DNS Security Extensions (DNSSEC)", RFC 8145, April 2017. |
Thanks go to Bill Fenner, Dick Franks, Tony Hansen, Peter Koch, Olaf Kolkman, and Andrew Sullivan for diligent review of the (much) earlier drafts. For the later enhancements, thanks to: Tim Wicinski, John Levine, Bob Harold, Joel Jaeggli, Ondřej Surý and Paul Wouters.
Special thanks to Ray Bellis for his persistent encouragement to continue this effort, as well as the suggestion for an essential simplification to the registration model.