DNSOP M. Andrews
Internet-Draft ISC
Updates: 1034 (if approved) S. Huque
Intended status: Standards Track Salesforce
Expires: 12 January 2022 P. Wouters
Aiven
D. Wessels
Verisign
11 July 2021
Glue In DNS Referral Responses Is Not Optional
draft-ietf-dnsop-glue-is-not-optional-01
Abstract
The DNS uses glue records to allow iterative clients to find the
addresses of nameservers that are contained within a delegated zone.
Servers are expected to return available glue records in referrals.
If message size constraints prevent the inclusion of 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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 12 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 . . . . . . . . . . . . . . . . . . . . . 2
2. Clarifying modifications to RFC1034 . . . . . . . . . . . . . 2
3. Why glue is required . . . . . . . . . . . . . . . . . . . . 3
3.1. Example one: Missing glue . . . . . . . . . . . . . . . . 3
3.2. Example two: sibling glue . . . . . . . . . . . . . . . . 4
3.3. Promoted (or orphaned) glue . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Normative References . . . . . . . . . . . . . . . . . . . . 5
7. Informative References . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
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. Servers are expected
to return available glue records in referrals. If message size
constraints prevent the inclusion of 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 clarifies that
expectation.
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. Clarifying modifications to RFC1034
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 glue RRs do not fit set TC=1 in
the header. Go to step 4."
3. Why glue is required
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.
3.1. Example one: Missing glue
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 ...
;; Query time: 226 msec
;; SERVER: 69.36.157.30#53(69.36.157.30)
;; WHEN: Wed Apr 15 13:34:43 AEST 2020
;; MSG SIZE rcvd: 500
%
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].
3.2. Example two: sibling glue
A zone's sibling glue is glue in another zone that is required for
proper resolving. While the example below is obvious, real life
examples can be more complex and not obvious.
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example.com. 86400 IN NS ns1.example.net.
example.com. 86400 IN NS ns2.example.net.
ns1.example.com. 86400 IN A 192.0.1.1
ns2.example.com. 86400 IN A 192.0.1.2
example.net. 86400 IN NS ns1.example.com.
example.net. 86400 IN NS ns2.example.com.
ns1.example.net. 86400 IN A 198.51.100.1
ns2.example.net. 86400 IN A 198.51.100.2
This situation is harder to detect if the sibling zones are nog
hosted on the same nameservers.
3.3. 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 NS records
are no longer glue records, but authorative data of the parent zone,
and should be added to the DNS response similarly to regular glue
records.
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. 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>.
7. Informative References
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[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>.
[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
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Duane Wessels
Verisign
Email: dwessels@verisign.com
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