< draft-ietf-dnsop-glue-is-not-optional-03.txt		draft-ietf-dnsop-glue-is-not-optional-04.txt >
	DNSOP M. Andrews		DNSOP M. Andrews
	Internet-Draft ISC		Internet-Draft ISC
	Updates: 1034 (if approved) S. Huque		Updates: 1034 (if approved) S. Huque
	Intended status: Standards Track Salesforce		Intended status: Standards Track Salesforce
	Expires: 14 April 2022 P. Wouters		Expires: 12 August 2022 P. Wouters
	Aiven		Aiven
	D. Wessels		D. Wessels
	Verisign		Verisign
	11 October 2021		8 February 2022
	Glue In DNS Referral Responses Is Not Optional		DNS Referral Glue Requirements
	draft-ietf-dnsop-glue-is-not-optional-03		draft-ietf-dnsop-glue-is-not-optional-04
	Abstract		Abstract
	The DNS uses glue records to allow iterative clients to find the		The DNS uses referral glue records to allow iterative clients to find
	addresses of nameservers that are contained within a delegated zone.		the addresses of nameservers that are contained within a delegated
	Authoritative Servers are expected to return all available glue		zone. Authoritative Servers are expected to return all available
	records in referrals. If message size constraints prevent the		referral glue records in a referral response. If message size
	inclusion of all glue records in a UDP response, the server MUST set		constraints prevent the inclusion of all in-domain referral glue
	the TC flag to inform the client that the response is incomplete, and		records, the server MUST set the TC flag to inform the client that
	that the client SHOULD use TCP to retrieve the full response. This		the response is incomplete, and that the client SHOULD use another
	document updates RFC 1034 to clarify correct server behavior.		transport to retrieve the full response. This document updates RFC
			1034 to clarify correct server behavior.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on 14 April 2022.		This Internet-Draft will expire on 12 August 2022.
	Copyright Notice		Copyright Notice
	Copyright (c) 2021 IETF Trust and the persons identified as the		Copyright (c) 2022 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
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	provided without warranty as described in the Simplified BSD License.		provided without warranty as described in the Revised BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Reserved Words . . . . . . . . . . . . . . . . . . . . . 3		1.1. Reserved Words . . . . . . . . . . . . . . . . . . . . . 3
	2. Types of Glue . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Types of Referral Glue . . . . . . . . . . . . . . . . . . . 3
	2.1. In-Domain Glue . . . . . . . . . . . . . . . . . . . . . 3		2.1. In-Domain Referral Glue . . . . . . . . . . . . . . . . . 3
	2.2. Sibling Glue . . . . . . . . . . . . . . . . . . . . . . 4		2.2. Sibling Referral Glue . . . . . . . . . . . . . . . . . . 4
	2.3. Sibling Cyclic Glue . . . . . . . . . . . . . . . . . . . 4		2.3. Cyclic Sibling Referral Glue . . . . . . . . . . . . . . 5
	2.4. Missing glue . . . . . . . . . . . . . . . . . . . . . . 5		2.4. Missing Referral Glue . . . . . . . . . . . . . . . . . . 5
	3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 6		3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 6
	3.1. In-Domain Glue . . . . . . . . . . . . . . . . . . . . . 6		3.1. In-Domain Referral Glue . . . . . . . . . . . . . . . . . 6
	3.2. Sibling Glue . . . . . . . . . . . . . . . . . . . . . . 6		3.2. Sibling Referral Glue . . . . . . . . . . . . . . . . . . 7
	3.3. Updates to RFC 1034 . . . . . . . . . . . . . . . . . . . 6		3.3. Updates to RFC 1034 . . . . . . . . . . . . . . . . . . . 7
	4. Security Considerations . . . . . . . . . . . . . . . . . . . 7		4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7		5. Operational Considerations . . . . . . . . . . . . . . . . . 8
	6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
	7. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 7		7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
	8. Normative References . . . . . . . . . . . . . . . . . . . . 8		8. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
	9. Informative References . . . . . . . . . . . . . . . . . . . 8		9. Normative References . . . . . . . . . . . . . . . . . . . . 9
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9		10. Informative References . . . . . . . . . . . . . . . . . . . 9
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
	1. Introduction		1. Introduction
	The Domain Name System (DNS) [RFC1034], [RFC1035] uses glue records		The Domain Name System (DNS) [RFC1034], [RFC1035] uses referral glue
	to allow iterative clients to find the addresses of nameservers that		records to allow iterative clients to find the addresses of
	are contained within a delegated zone. Glue records are added to the		nameservers that are contained within a delegated zone. Referral
	parent zone as part of the delegation process and returned in		glue records are added to the parent zone as part of the delegation
	referral responses, otherwise a resolver following the referral has		process and returned in referral responses, otherwise a resolver
	no way of finding these addresses. Authoritative servers are		following the referral has no way of finding these addresses.
	expected to return all available glue records in referrals. If		Authoritative servers are expected to return all available in-domain
	message size constraints prevent the inclusion of all glue records in		referral glue records in a referral response. If message size
	a UDP response, the server MUST set the TC (Truncated) flag to inform		constraints prevent the inclusion of all in-domain glue records over
	the client that the response is incomplete, and that the client		the chosen transport, the server MUST set the TC (Truncated) flag to
	SHOULD use TCP to retrieve the full response. This document		inform the client that the response is incomplete, and that the
	clarifies that expectation.		client SHOULD use another transport retrieve the full response. This
			document clarifies that expectation.
	DNS responses sometimes contain optional data in the additional		DNS responses sometimes contain optional data in the additional
	section. Glue records however are not optional. Several other		section. In-domain referral glue records, however, are not optional.
	protocol extensions, when used, are also not optional. This includes		Several other protocol extensions, when used, are also not optional.
	TSIG [RFC2845], OPT [RFC6891], and SIG(0) [RFC2931].		This includes TSIG [RFC2845], OPT [RFC6891], and SIG(0) [RFC2931].
			At the time of this writing, referral glue is the only type of glue
			defined for the DNS. Referral glue records are always addresses (A
			or AAAA records) of a delegation's authoritative name servers. New
			work underway in the IETF may lead to definitions for other types of
			glue data, with requirements that differ from referral glue. This
			document only describes requirements for referral glue. Unless
			stated otherwise, "glue" in the remainder of this document always
			means "referral glue."
	Note that this document only clarifies requirements of name server		Note that this document only clarifies requirements of name server
	software implementations. It does not place any requirements on data		software implementations. It does not place any requirements on data
	placed in DNS zones or registries.		placed in DNS zones or registries.
	1.1. Reserved Words		1.1. Reserved Words
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in [RFC2119].		document are to be interpreted as described in [RFC2119].
	2. Types of Glue		2. Types of Referral Glue
	This section describes different types of glue that may be found in		This section describes different types of glue that may be found in
	DNS referral responses. Note that the type of glue depends on the		DNS referral responses. Note that the type of glue depends on the
	QNAME. A particular record can be in-domain glue for one response		QNAME. A particular record can be in-domain glue for one response
	and sibling glue for another.		and sibling glue for another.
	2.1. In-Domain Glue		2.1. In-Domain Referral Glue
	The following is a simple example of glue records present in the		The following is a simple example of glue records present in the
	delegating zone "test" for the child zone "foo.test". The		delegating zone "test" for the child zone "foo.test". The
	nameservers for foo.test (ns1.foo.test and ns2.foo.test) are both		nameservers for foo.test (ns1.foo.test and ns2.foo.test) are both
	below the delegation point. They are configured as glue records in		below the delegation point. They are configured as glue records in
	the "test" zone:		the "test" zone:
	foo.test. 86400 IN NS ns1.foo.test.		foo.test. 86400 IN NS ns1.foo.test.
	foo.test. 86400 IN NS ns2.foo.test.		foo.test. 86400 IN NS ns2.foo.test.
	ns1.foo.test. 86400 IN A 192.0.2.1		ns1.foo.test. 86400 IN A 192.0.2.1
	skipping to change at page 4, line 5 ¶		skipping to change at page 4, line 16 ¶
	;www.foo.test. IN A		;www.foo.test. IN A
	;; AUTHORITY SECTION:		;; AUTHORITY SECTION:
	foo.test. 86400 IN NS ns1.foo.test.		foo.test. 86400 IN NS ns1.foo.test.
	foo.test. 86400 IN NS ns2.foo.test.		foo.test. 86400 IN NS ns2.foo.test.
	;; ADDITIONAL SECTION:		;; ADDITIONAL SECTION:
	ns1.foo.test. 86400 IN A 192.0.2.1		ns1.foo.test. 86400 IN A 192.0.2.1
	ns2.foo.test. 86400 IN AAAA 2001:db8::2:2		ns2.foo.test. 86400 IN AAAA 2001:db8::2:2
	2.2. Sibling Glue		2.2. Sibling Referral Glue
	Sibling glue are glue records that are not contained in the delegated		Sibling glue are glue records that are not contained in the delegated
	zone itself, but in another delegated zone from the same parent. In		zone itself, but in another zone delegated from the same parent. In
	many cases, these are not strictly required for resolution, since the		many cases, these are not strictly required for resolution, since the
	resolver can make follow-on queries to the same zone to resolve the		resolver can make follow-on queries to the other zone to resolve the
	nameserver addresses after following the referral to the sibling		nameserver addresses after following the referral to the sibling
	zone. However, most nameserver implementations today provide them as		zone. However, most nameserver implementations today provide them as
	an optimization to obviate the need for extra traffic from iterative		an optimization to obviate the need for extra traffic from iterative
	resolvers.		resolvers.
	Here the delegating zone "test" contains 2 sub-delegations for the		Here the delegating zone "test" contains two delegations for the
	subzones "bar.test" and "foo.test":		child zones "bar.test" and "foo.test":
	bar.test. 86400 IN NS ns1.bar.test.		bar.test. 86400 IN NS ns1.bar.test.
	bar.test. 86400 IN NS ns2.bar.test.		bar.test. 86400 IN NS ns2.bar.test.
	ns1.bar.test. 86400 IN A 192.0.2.1		ns1.bar.test. 86400 IN A 192.0.2.1
	ns2.bar.test. 86400 IN AAAA 2001:db8::2:2		ns2.bar.test. 86400 IN AAAA 2001:db8::2:2
	foo.test. 86400 IN NS ns1.bar.test.		foo.test. 86400 IN NS ns1.bar.test.
	foo.test. 86400 IN NS ns2.bar.test.		foo.test. 86400 IN NS ns2.bar.test.
	A referral response from "test" for "foo.test" with sibling glue		A referral response from "test" for "foo.test" with sibling glue
	skipping to change at page 4, line 41 ¶		skipping to change at page 5, line 5 ¶
	;www.foo.test. IN A		;www.foo.test. IN A
	;; AUTHORITY SECTION:		;; AUTHORITY SECTION:
	foo.test. 86400 IN NS ns1.bar.test.		foo.test. 86400 IN NS ns1.bar.test.
	foo.test. 86400 IN NS ns2.bar.test.		foo.test. 86400 IN NS ns2.bar.test.
	;; ADDITIONAL SECTION:		;; ADDITIONAL SECTION:
	ns1.bar.test. 86400 IN A 192.0.2.1		ns1.bar.test. 86400 IN A 192.0.2.1
	ns2.bar.test. 86400 IN AAAA 2001:db8::2:2		ns2.bar.test. 86400 IN AAAA 2001:db8::2:2
	2.3. Sibling Cyclic Glue		2.3. Cyclic Sibling Referral Glue
	The use of sibling glue can introduce cyclic dependencies. This		The use of sibling glue can introduce cyclic dependencies. This
	happens when one domain specifies name servers from a sibling domain,		happens when one domain specifies name servers from a sibling domain,
	and vice versa. This type of cyclic dependency can only be broken		and vice versa. This type of cyclic dependency can only be broken
	when the delegating name server includes the sibling glue in a		when the delegating name server includes the sibling glue in a
	referral response.		referral response.
	Here the delegating zone "test" contains 2 sub-delegations for the		Here the delegating zone "test" contains two delegations for the
	subzones "bar.test" and "foo.test", and each use name servers under		child zones "bar.test" and "foo.test", and each use name servers
	the other:		under the other:
	bar.test. 86400 IN NS ns1.foo.test.		bar.test. 86400 IN NS ns1.foo.test.
	bar.test. 86400 IN NS ns2.foo.test.		bar.test. 86400 IN NS ns2.foo.test.
	ns1.bar.test. 86400 IN A 192.0.2.1		ns1.bar.test. 86400 IN A 192.0.2.1
	ns2.bar.test. 86400 IN AAAA 2001:db8::2:2		ns2.bar.test. 86400 IN AAAA 2001:db8::2:2
	foo.test. 86400 IN NS ns1.bar.test.		foo.test. 86400 IN NS ns1.bar.test.
	foo.test. 86400 IN NS ns2.bar.test.		foo.test. 86400 IN NS ns2.bar.test.
	ns1.foo.test. 86400 IN A 192.0.2.3		ns1.foo.test. 86400 IN A 192.0.2.3
	ns2.foo.test. 86400 IN AAAA 2001:db8::2:4		ns2.foo.test. 86400 IN AAAA 2001:db8::2:4
	skipping to change at page 5, line 29 ¶		skipping to change at page 5, line 41 ¶
	;www.bar.test. IN A		;www.bar.test. IN A
	;; AUTHORITY SECTION:		;; AUTHORITY SECTION:
	bar.test. 86400 IN NS ns1.foo.test.		bar.test. 86400 IN NS ns1.foo.test.
	bar.test. 86400 IN NS ns2.foo.test.		bar.test. 86400 IN NS ns2.foo.test.
	;; ADDITIONAL SECTION:		;; ADDITIONAL SECTION:
	ns1.foo.test. 86400 IN A 192.0.2.3		ns1.foo.test. 86400 IN A 192.0.2.3
	ns2.foo.test. 86400 IN AAAA 2001:db8::2:4		ns2.foo.test. 86400 IN AAAA 2001:db8::2:4
	2.4. Missing glue		In late 2021 the authors analyzed zone file data available from
			ICANN's Centralized Zone Data Service [CZDS] and found 222 out of
			approximately 209,000,000 total delegations that had only sibling NS
			RRs in a cyclic dependency as above.
	An example of missing glue is included here, even though it is not		2.4. Missing Referral Glue
	really a type of glue. While not common, real examples of responses
	that lack required glue, and with TC=0, have been shown to occur and		An example of missing glue is included here, even though it can not
	cause resolution failures.		be considered as a type of glue. While not common, real examples of
			responses that lack required glue, and with TC=0, have been shown to
			occur and cause resolution failures.
	The example below is based on a response observed in June 2020. The		The example below is based on a response observed in June 2020. The
	names have been altered to fall under documentation domains. It		names have been altered to fall under documentation domains. It
	shows a case where none of the glue records present in the zone fit		shows a case where none of the glue records present in the zone fit
	into the available space of the UDP respose, and TC=1 was not set.		into the available space of the UDP response, and the TC flag was not
	While this example shows a referral with DNSSEC records [RFC4033],		set. While this example shows a referral with DNSSEC records
	[RFC4034], [RFC4035], this behaviour has been seen with plain DNS		[RFC4033], [RFC4034], [RFC4035], this behavior has been seen with
	responses as well. Some records have been truncated for display		plain DNS responses as well. Some records have been truncated for
	purposes. Note that at the time of this writing, the servers		display purposes. Note that at the time of this writing, the servers
	originally responsible for this example have been updated and now		originally responsible for this example have been updated and now
	correctly set the TC=1 flag.		correctly set the TC flag.
	% dig +norec +dnssec +bufsize=512 +ignore @ns.example.net \		% dig +norec +dnssec +bufsize=512 +ignore @ns.example.net \
	rh202ns2.355.foo.example		rh202ns2.355.foo.example
	; <<>> DiG 9.15.4 <<>> +norec +dnssec +bufsize +ignore \		; <<>> DiG 9.15.4 <<>> +norec +dnssec +bufsize +ignore \
	@ns.example.net rh202ns2.355.foo.example		@ns.example.net rh202ns2.355.foo.example
	; (2 servers found)		; (2 servers found)
	;; global options: +cmd		;; global options: +cmd
	;; Got answer:		;; Got answer:
	;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 8798		;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 8798
	skipping to change at page 6, line 34 ¶		skipping to change at page 6, line 45 ¶
	foo.example. 86400 IN NS rh120ns1.368.foo.example.		foo.example. 86400 IN NS rh120ns1.368.foo.example.
	foo.example. 86400 IN NS rh202ns1.355.foo.example.		foo.example. 86400 IN NS rh202ns1.355.foo.example.
	foo.example. 3600 IN DS 51937 8 1 ...		foo.example. 3600 IN DS 51937 8 1 ...
	foo.example. 3600 IN DS 635 8 2 ...		foo.example. 3600 IN DS 635 8 2 ...
	foo.example. 3600 IN DS 51937 8 2 ...		foo.example. 3600 IN DS 51937 8 2 ...
	foo.example. 3600 IN DS 635 8 1 ...		foo.example. 3600 IN DS 635 8 1 ...
	foo.example. 3600 IN RRSIG DS 8 2 3600 ...		foo.example. 3600 IN RRSIG DS 8 2 3600 ...
	3. Requirements		3. Requirements
	3.1. In-Domain Glue		This section describes updated requirements for including glue in
			referral responses.
			3.1. In-Domain Referral Glue
	This document clarifies that when a name server generates a referral		This document clarifies that when a name server generates a referral
	response, it MUST include all available in-domain glue records in the		response, it MUST include all available in-domain glue records in the
	additional section. If all in-domain glue records do not fit in a		additional section, or MUST set TC=1 if constrained by message size.
	UDP response, the name server MUST set TC=1.
	3.2. Sibling Glue		At the time of writing, most iterative clients send initial queries
			over UDP and retry over TCP upon receiving a response with the TC
			flag set. UDP responses are generally limited to between 1232 and
			4096 bytes, due to values commonly used for the EDNS0 UDP Message
			Size field [RFC6891], [FLAGDAY2020]. TCP responses are limited to
			65,536 bytes.
			3.2. Sibling Referral Glue
	This document clarifies that when a name server generates a referral		This document clarifies that when a name server generates a referral
	response, it MUST [SHOULD] include available sibling glue records in		response, it SHOULD include all available glue records in the
	the additional section. If all sibling glue records do not fit in a		additional section. If after adding all in-domain glue records, not
	UDP response, the name server MUST [is NOT REQUIRED to] set TC=1.		all sibling glue records fit due to message size constraints, the
			name server is NOT REQUIRED to set TC=1.
	3.3. Updates to RFC 1034		Note that users may experience resolution failures for domains with
			only sibling glue when a name servers chooses to omit them in a
			referral response. As described in Section 2.3, such domains are
			rare.
	[this doesn't really account for SHOULD on sibling glue...]		3.3. Updates to RFC 1034
	Replace		Replace
	"Copy the NS RRs for the subzone into the authority section of the		"Copy the NS RRs for the subzone into the authority section of the
	reply. Put whatever addresses are available into the additional		reply. Put whatever addresses are available into the additional
	section, using glue RRs if the addresses are not available from		section, using glue RRs if the addresses are not available from
	authoritative data or the cache. Go to step 4."		authoritative data or the cache. Go to step 4."
	with		with
	"Copy the NS RRs for the subzone into the authority section of the		"Copy the NS RRs for the subzone into the authority section of the
	reply. Put whatever addresses are available into the additional		reply. Put whatever NS addresses are available into the additional
	section, using glue RRs if the addresses are not available from		section, using glue RRs if the addresses are not available from
	authoritative data or the cache. If all glue RRs do not fit, set		authoritative data or the cache. If all in-domain glue RRs do not
	TC=1 in the header. Go to step 4."		fit, set TC=1 in the header. Go to step 4."
	4. Security Considerations		4. Security Considerations
	This document clarifies correct DNS server behaviour and does not		This document clarifies correct DNS server behavior and does not
	introduce any changes or new security considerations.		introduce any changes or new security considerations.
	5. IANA Considerations		5. Operational Considerations
			At the time of this writing, the behavior of most DNS server
			implementations is to set the TC flag only if none of the available
			glue records fit in a response over UDP transport. The updated
			requirements in this document might lead to an increase in the
			fraction of UDP responses with the TC flag set, and consequently an
			increase in the number of queries to over TCP transport.
			6. IANA Considerations
	There are no actions for IANA.		There are no actions for IANA.
	6. Acknowledgements		7. Acknowledgements
	The authors wish to thank Joe Abley, Brian Dickson, Geoff Huston,		The authors wish to thank Joe Abley, Brian Dickson, Geoff Huston,
	Jared Mauch, George Michaelson, Benno Overeinder, John R Levine,		Jared Mauch, George Michaelson, Benno Overeinder, John R Levine,
	Shinta Sato, Puneet Sood, Ralf Weber, Tim Wicinski, Suzanne Woolf,		Shinta Sato, Puneet Sood, Ralf Weber, Tim Wicinski, Suzanne Woolf,
	and other members of the DNSOP working group for their input.		and other members of the DNSOP working group for their input.
	7. Changes		8. Changes
	RFC Editor: Please remove this section before publication.		RFC Editor: Please remove this section before publication.
	This section lists substantial changes to the document as it is being		This section lists substantial changes to the document as it is being
	worked on.		worked on.
	From -01 to -02:		From -01 to -02:
	* Clarified that "servers" means "authoritative servers".		* Clarified that "servers" means "authoritative servers".
	skipping to change at page 8, line 14 ¶		skipping to change at page 9, line 5 ¶
	* Reorganized with section 2 as Types of Glue and section 3 as		* Reorganized with section 2 as Types of Glue and section 3 as
	Requirements.		Requirements.
	* Removed any discussion of promoted / orphan glue.		* Removed any discussion of promoted / orphan glue.
	* Use appropriate documentation addresses and domain names.		* Use appropriate documentation addresses and domain names.
	* Added Sibling Cyclic Glue example.		* Added Sibling Cyclic Glue example.
	8. Normative References		From -03 to -04:
			* Use "referral glue" on the assumption that other types of glue may
			be defined in the future.
			* Added Operational Considerations section.
			* Note many current implementations set TC=1 only when no glue RRs
			fit. New requirements may lead to more truncation and TCP.
			* Sibling glue can be optional. Only require TC=1 when all in-
			domain glue RRs don't fit.
			* Avoid talking about requirements for UDP/TCP specifically, and
			talk more generically about message size constraints regardless of
			transport.
			9. Normative References
	[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",		[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
	STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,		STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
	<https://www.rfc-editor.org/info/rfc1034>.		<https://www.rfc-editor.org/info/rfc1034>.
	[RFC1035] Mockapetris, P., "Domain names - implementation and		[RFC1035] Mockapetris, P., "Domain names - implementation and
	specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,		specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
	November 1987, <https://www.rfc-editor.org/info/rfc1035>.		November 1987, <https://www.rfc-editor.org/info/rfc1035>.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	9. Informative References		10. Informative References
			[CZDS] ICANN, "Centralized Zone Data Service", January 2022,
			<https://czds.icann.org/>.
			[FLAGDAY2020]
			Various DNS software and service providers, "DNS Flag Day
			2020", October 2020, <https://dnsflagday.net/2020/>.
	[RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.		[RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
	Wellington, "Secret Key Transaction Authentication for DNS		Wellington, "Secret Key Transaction Authentication for DNS
	(TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000,		(TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000,
	<https://www.rfc-editor.org/info/rfc2845>.		<https://www.rfc-editor.org/info/rfc2845>.
	[RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures		[RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures
	( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September		( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September
	2000, <https://www.rfc-editor.org/info/rfc2931>.		2000, <https://www.rfc-editor.org/info/rfc2931>.
End of changes. 39 change blocks.
	86 lines changed or deleted		150 lines changed or added
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