Glue In DNS Referral Responses Is Not Optional
draft-ietf-dnsop-glue-is-not-optional-03
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (dnsop WG) | |
|---|---|---|---|
| Authors | Mark P. Andrews , Shumon Huque , Paul Wouters , Duane Wessels | ||
| Last updated | 2021-10-11 | ||
| Replaces | draft-andrews-dnsop-glue-is-not-optional | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text html xml htmlized pdfized bibtex | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-dnsop-glue-is-not-optional-03
DNSOP M. Andrews
Internet-Draft ISC
Updates: 1034 (if approved) S. Huque
Intended status: Standards Track Salesforce
Expires: 14 April 2022 P. Wouters
Aiven
D. Wessels
Verisign
11 October 2021
Glue In DNS Referral Responses Is Not Optional
draft-ietf-dnsop-glue-is-not-optional-03
Abstract
The DNS uses glue records to allow iterative clients to find the
addresses of nameservers that are contained within a delegated zone.
Authoritative Servers are expected to return all available glue
records in referrals. If message size constraints prevent the
inclusion of all glue records in a UDP response, the server MUST set
the TC flag to inform the client that the response is incomplete, and
that the client SHOULD use TCP to retrieve the full response. This
document updates RFC 1034 to clarify correct server behavior.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 14 April 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Reserved Words . . . . . . . . . . . . . . . . . . . . . 3
2. Types of Glue . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. In-Domain Glue . . . . . . . . . . . . . . . . . . . . . 3
2.2. Sibling Glue . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Sibling Cyclic Glue . . . . . . . . . . . . . . . . . . . 4
2.4. Missing glue . . . . . . . . . . . . . . . . . . . . . . 5
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. In-Domain Glue . . . . . . . . . . . . . . . . . . . . . 6
3.2. Sibling Glue . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Updates to RFC 1034 . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Normative References . . . . . . . . . . . . . . . . . . . . 8
9. Informative References . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The Domain Name System (DNS) [RFC1034], [RFC1035] uses glue records
to allow iterative clients to find the addresses of nameservers that
are contained within a delegated zone. Glue records are added to the
parent zone as part of the delegation process and returned in
referral responses, otherwise a resolver following the referral has
no way of finding these addresses. Authoritative servers are
expected to return all available glue records in referrals. If
message size constraints prevent the inclusion of all glue records in
a UDP response, the server MUST set the TC (Truncated) flag to inform
the client that the response is incomplete, and that the client
SHOULD use TCP to retrieve the full response. This document
clarifies that expectation.
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DNS responses sometimes contain optional data in the additional
section. Glue records however are not optional. Several other
protocol extensions, when used, are also not optional. This includes
TSIG [RFC2845], OPT [RFC6891], and SIG(0) [RFC2931].
Note that this document only clarifies requirements of name server
software implementations. It does not place any requirements on data
placed in DNS zones or registries.
1.1. Reserved Words
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Types of Glue
This section describes different types of glue that may be found in
DNS referral responses. Note that the type of glue depends on the
QNAME. A particular record can be in-domain glue for one response
and sibling glue for another.
2.1. In-Domain Glue
The following is a simple example of glue records present in the
delegating zone "test" for the child zone "foo.test". The
nameservers for foo.test (ns1.foo.test and ns2.foo.test) are both
below the delegation point. They are configured as glue records in
the "test" zone:
foo.test. 86400 IN NS ns1.foo.test.
foo.test. 86400 IN NS ns2.foo.test.
ns1.foo.test. 86400 IN A 192.0.2.1
ns2.foo.test. 86400 IN AAAA 2001:db8::2:2
A referral response from "test" for "foo.test" with in-domain glue
looks like this:
;; QUESTION SECTION:
;www.foo.test. IN A
;; AUTHORITY SECTION:
foo.test. 86400 IN NS ns1.foo.test.
foo.test. 86400 IN NS ns2.foo.test.
;; ADDITIONAL SECTION:
ns1.foo.test. 86400 IN A 192.0.2.1
ns2.foo.test. 86400 IN AAAA 2001:db8::2:2
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2.2. Sibling Glue
Sibling glue are glue records that are not contained in the delegated
zone itself, but in another delegated zone from the same parent. In
many cases, these are not strictly required for resolution, since the
resolver can make follow-on queries to the same zone to resolve the
nameserver addresses after following the referral to the sibling
zone. However, most nameserver implementations today provide them as
an optimization to obviate the need for extra traffic from iterative
resolvers.
Here the delegating zone "test" contains 2 sub-delegations for the
subzones "bar.test" and "foo.test":
bar.test. 86400 IN NS ns1.bar.test.
bar.test. 86400 IN NS ns2.bar.test.
ns1.bar.test. 86400 IN A 192.0.2.1
ns2.bar.test. 86400 IN AAAA 2001:db8::2:2
foo.test. 86400 IN NS ns1.bar.test.
foo.test. 86400 IN NS ns2.bar.test.
A referral response from "test" for "foo.test" with sibling glue
looks like this:
;; QUESTION SECTION:
;www.foo.test. IN A
;; AUTHORITY SECTION:
foo.test. 86400 IN NS ns1.bar.test.
foo.test. 86400 IN NS ns2.bar.test.
;; ADDITIONAL SECTION:
ns1.bar.test. 86400 IN A 192.0.2.1
ns2.bar.test. 86400 IN AAAA 2001:db8::2:2
2.3. Sibling Cyclic Glue
The use of sibling glue can introduce cyclic dependencies. This
happens when one domain specifies name servers from a sibling domain,
and vice versa. This type of cyclic dependency can only be broken
when the delegating name server includes the sibling glue in a
referral response.
Here the delegating zone "test" contains 2 sub-delegations for the
subzones "bar.test" and "foo.test", and each use name servers under
the other:
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bar.test. 86400 IN NS ns1.foo.test.
bar.test. 86400 IN NS ns2.foo.test.
ns1.bar.test. 86400 IN A 192.0.2.1
ns2.bar.test. 86400 IN AAAA 2001:db8::2:2
foo.test. 86400 IN NS ns1.bar.test.
foo.test. 86400 IN NS ns2.bar.test.
ns1.foo.test. 86400 IN A 192.0.2.3
ns2.foo.test. 86400 IN AAAA 2001:db8::2:4
A referral response from "test" for "bar.test" with sibling glue
looks like this:
;; QUESTION SECTION:
;www.bar.test. IN A
;; AUTHORITY SECTION:
bar.test. 86400 IN NS ns1.foo.test.
bar.test. 86400 IN NS ns2.foo.test.
;; ADDITIONAL SECTION:
ns1.foo.test. 86400 IN A 192.0.2.3
ns2.foo.test. 86400 IN AAAA 2001:db8::2:4
2.4. Missing glue
An example of missing glue is included here, even though it is not
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
cause resolution failures.
The example below is based on a response observed in June 2020. The
names have been altered to fall under documentation domains. It
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.
While this example shows a referral with DNSSEC records [RFC4033],
[RFC4034], [RFC4035], this behaviour has been seen with plain DNS
responses as well. Some records have been truncated for display
purposes. Note that at the time of this writing, the servers
originally responsible for this example have been updated and now
correctly set the TC=1 flag.
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% dig +norec +dnssec +bufsize=512 +ignore @ns.example.net \
rh202ns2.355.foo.example
; <<>> DiG 9.15.4 <<>> +norec +dnssec +bufsize +ignore \
@ns.example.net rh202ns2.355.foo.example
; (2 servers found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 8798
;; flags: qr; QUERY: 1, ANSWER: 0, AUTHORITY: 9, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags: do; udp: 4096
;; QUESTION SECTION:
;rh202ns2.355.foo.example. IN A
;; AUTHORITY SECTION:
foo.example. 86400 IN NS rh120ns2.368.foo.example.
foo.example. 86400 IN NS rh202ns2.355.foo.example.
foo.example. 86400 IN NS rh120ns1.368.foo.example.
foo.example. 86400 IN NS rh202ns1.355.foo.example.
foo.example. 3600 IN DS 51937 8 1 ...
foo.example. 3600 IN DS 635 8 2 ...
foo.example. 3600 IN DS 51937 8 2 ...
foo.example. 3600 IN DS 635 8 1 ...
foo.example. 3600 IN RRSIG DS 8 2 3600 ...
3. Requirements
3.1. In-Domain Glue
This document clarifies that when a name server generates a referral
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
UDP response, the name server MUST set TC=1.
3.2. Sibling Glue
This document clarifies that when a name server generates a referral
response, it MUST [SHOULD] include available sibling glue records in
the additional section. If all sibling glue records do not fit in a
UDP response, the name server MUST [is NOT REQUIRED to] set TC=1.
3.3. Updates to RFC 1034
[this doesn't really account for SHOULD on sibling glue...]
Replace
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"Copy the NS RRs for the subzone into the authority section of the
reply. Put whatever addresses are available into the additional
section, using glue RRs if the addresses are not available from
authoritative data or the cache. Go to step 4."
with
"Copy the NS RRs for the subzone into the authority section of the
reply. Put whatever addresses are available into the additional
section, using glue RRs if the addresses are not available from
authoritative data or the cache. If all glue RRs do not fit, set
TC=1 in the header. Go to step 4."
4. Security Considerations
This document clarifies correct DNS server behaviour and does not
introduce any changes or new security considerations.
5. IANA Considerations
There are no actions for IANA.
6. Acknowledgements
The authors wish to thank Joe Abley, Brian Dickson, Geoff Huston,
Jared Mauch, George Michaelson, Benno Overeinder, John R Levine,
Shinta Sato, Puneet Sood, Ralf Weber, Tim Wicinski, Suzanne Woolf,
and other members of the DNSOP working group for their input.
7. Changes
RFC Editor: Please remove this section before publication.
This section lists substantial changes to the document as it is being
worked on.
From -01 to -02:
* Clarified that "servers" means "authoritative servers".
* Clarified that "available glue" means "all available glue".
* Updated examples and placed before RFC 1034 update.
From -02 to -03:
* Clarified scope to focus only on name server responses, and not
zone/registry data.
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* Reorganized with section 2 as Types of Glue and section 3 as
Requirements.
* Removed any discussion of promoted / orphan glue.
* Use appropriate documentation addresses and domain names.
* Added Sibling Cyclic Glue example.
8. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
9. Informative References
[RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
Wellington, "Secret Key Transaction Authentication for DNS
(TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000,
<https://www.rfc-editor.org/info/rfc2845>.
[RFC2931] Eastlake 3rd, D., "DNS Request and Transaction Signatures
( SIG(0)s )", RFC 2931, DOI 10.17487/RFC2931, September
2000, <https://www.rfc-editor.org/info/rfc2931>.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC4033, March 2005,
<https://www.rfc-editor.org/info/rfc4033>.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, DOI 10.17487/RFC4034, March 2005,
<https://www.rfc-editor.org/info/rfc4034>.
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[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
<https://www.rfc-editor.org/info/rfc4035>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013,
<https://www.rfc-editor.org/info/rfc6891>.
Authors' Addresses
M. Andrews
ISC
Email: marka@isc.org
Shumon Huque
Salesforce
Email: shuque@gmail.com
Paul Wouters
Aiven
Email: paul.wouters@aiven.io
Duane Wessels
Verisign
Email: dwessels@verisign.com
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