Internet DRAFT - draft-andrews-dnsop-glue-is-not-optional
draft-andrews-dnsop-glue-is-not-optional
Network Working Group M. Andrews
Internet-Draft ISC
Updates: 1034 (if approved) April 16, 2020
Intended status: Standards Track
Expires: October 18, 2020
Glue In DNS Referral Responses Is Not Optional
draft-andrews-dnsop-glue-is-not-optional-01
Abstract
The DNS uses glue records to allow iterative clients to find the
addresses of nameservers that live within the delegated zone. Glue
records are expected to be returned as part of a referral and if they
cannot be fitted into the UDP response, TC=1 MUST be set to inform
the client that the response is incomplete and that TCP SHOULD be
used 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.
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This Internet-Draft will expire on October 18, 2020.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
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the Trust Legal Provisions and are provided without warranty as
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Reserved Words . . . . . . . . . . . . . . . . . . . . . 4
2. Modifications to RFC1034 . . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Normative References . . . . . . . . . . . . . . . . . . 4
5.2. Informative References . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
The DNS [RFC1034], [RFC1035] uses glue records to allow iterative
clients to find the addresses of nameservers that live within the
delegated zone. Glue records are expected to be returned as part of
a referral and if they cannot be fitted into the UDP response, TC=1
MUST be set to inform the client that the response is incomplete and
that TCP SHOULD be used to retrieve the full response.
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 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.
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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
%
This is almost certainly due a wide spread misbelief that all
additional section records are optional. This has never been the
case with respect to glue records and later protocol extension have
added more cases where records in the additional section are not
optional in the response. This includes TSIG [RFC2845], OPT
[RFC6891], and SIG(0) [RFC2931].
Glue records are added to the parent zone as part of the delegation
process. They are expected to be returned as part of a referral and
if they can't fit in a UDP response TC=1 MUST be set to signal to the
client to retry over TCP. This document reinforces that expectation.
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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. Modifications to RFC1034
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 glue RRs do not fit set TC=1 in
the header. Go to step 4."
3. Security Considerations
This document reinforces DNS server behaviour expectations and does
not introduce new security considerations.
4. IANA Considerations
There are no actions for IANA.
5. References
5.1. 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>.
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5.2. 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>.
[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>.
Author's Address
M. Andrews
Internet Systems Consortium
PO Box 360
Newmarket, NH 03857
US
Email: marka@isc.org
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