Glue In DNS Referral Responses Is Not Optional
draft-ietf-dnsop-glue-is-not-optional-02
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 | 2021-08-09 (Latest revision 2021-07-26) | ||
| 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-02
DNSOP M. Andrews
Internet-Draft ISC
Updates: 1034 (if approved) S. Huque
Intended status: Standards Track Salesforce
Expires: 27 January 2022 P. Wouters
Aiven
D. Wessels
Verisign
26 July 2021
Glue In DNS Referral Responses Is Not Optional
draft-ietf-dnsop-glue-is-not-optional-02
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 27 January 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
extracted from this document must include Simplified BSD License text
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. Glue record example . . . . . . . . . . . . . . . . . . . . . 3
2.1. Missing glue . . . . . . . . . . . . . . . . . . . . . . 3
3. Updates to RFC 1034 . . . . . . . . . . . . . . . . . . . . . 4
4. Sibling Glue . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Sibling Glue example . . . . . . . . . . . . . . . . . . 5
5. Promoted (or orphaned) glue . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Normative References . . . . . . . . . . . . . . . . . . . . 6
9. Informative References . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
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.
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].
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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. Glue record example
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 192.0.1.1
ns2.foo.test. 86400 IN A 192.0.1.2
Referral responses from "test" for "foo.test" must include the glue
records in the additional section (and set TC=1 if they do not fit):
;; 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 192.0.1.1
ns2.foo.test. 86400 IN A 192.0.1.2
2.1. Missing glue
While not common, real life examples of servers that fail to set TC=1
when glue records are available, exist and they do cause resolution
failures.
The example below from June 2020 shows a case where none of the glue
records, present in the zone, fitted into the available space and
TC=1 was not set in the response. While this example shows an DNSSEC
[RFC4033], [RFC4034], [RFC4035] referral response, this behaviour has
also been seen with plain DNS responses as well. The records have
been truncated for display purposes. Note that at the time of this
writing, this configuration has been corrected and the response
correctly sets the TC=1 flag.
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% dig +norec +dnssec +bufsize=512 +ignore @a.gov-servers.net \
rh202ns2.355.dhhs.gov
; <<>> DiG 9.15.4 <<>> +norec +dnssec +bufsize +ignore \
@a.gov-servers.net rh202ns2.355.dhhs.gov
; (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.dhhs.gov. IN A
;; AUTHORITY SECTION:
dhhs.gov. 86400 IN NS rh120ns2.368.dhhs.gov.
dhhs.gov. 86400 IN NS rh202ns2.355.dhhs.gov.
dhhs.gov. 86400 IN NS rh120ns1.368.dhhs.gov.
dhhs.gov. 86400 IN NS rh202ns1.355.dhhs.gov.
dhhs.gov. 3600 IN DS 51937 8 1 ...
dhhs.gov. 3600 IN DS 635 8 2 ...
dhhs.gov. 3600 IN DS 51937 8 2 ...
dhhs.gov. 3600 IN DS 635 8 1 ...
dhhs.gov. 3600 IN RRSIG DS 8 2 3600 ...
3. Updates to RFC 1034
Replace
"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."
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4. 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.
This document clarifies that sibling glue (being part of all
available glue records) MUST be returned in referral responses, and
that the requirement to set TC=1 applies to sibling glue that cannot
fit in the response too.
4.1. Sibling Glue example
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 192.0.1.1
ns2.bar.test. 86400 IN A 192.0.1.2
foo.test. 86400 IN NS ns1.bar.test.
foo.test. 86400 IN NS ns2.bar.test.
Referral responses from "test" for "foo.test" must include the
sibling glue (and set TC=1 if they do not fit):
;; 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 192.0.1.1
ns2.bar.test. 86400 IN A 192.0.1.2
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5. Promoted (or orphaned) glue
When a zone is deleted but the parent notices that its NS glue
records are required for other zones, it MAY opt to take these (now
orphaned) glue records into its own zone to ensure that other zones
depending on this glue are not broken. Technically, these address
records are no longer glue records, but authoritative data of the
parent zone, and should be added to the DNS response similarly to
regular glue records.
6. Security Considerations
This document clarifies correct DNS server behaviour and does not
introduce any changes or new security considerations.
7. IANA Considerations
There are no actions for IANA.
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>.
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[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>.
[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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