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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.

   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 October 18, 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   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
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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



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   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  . . . . . . . . . . . . . . . . . . . . .   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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