Glue In DNS Referral Responses Is Not Optional
draft-ietf-dnsop-glue-is-not-optional-01

DNSOP                                                         M. Andrews
Internet-Draft                                                       ISC
Updates: 1034 (if approved)                                     S. Huque
Intended status: Standards Track                              Salesforce
Expires: 13 January 2022                                      P. Wouters
                                                                   Aiven
                                                              D. Wessels
                                                                Verisign
                                                            12 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 13 January 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Andrews, et al.          Expires 13 January 2022                [Page 1]
Internet-Draft  Glue In DNS Referral Responses Is Not Op       July 2021

   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 . . . . . . . . . . . . .   3
   3.  Why glue is required  . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Example one: Missing glue . . . . . . . . . . . . . . . .   3
     3.2.  Example two: Sibling Glue from the same delegating
           zone  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.3.  Example three: Cross Zone Sibling Glue  . . . . . . . . .   5
     3.4.  Promoted (or orphaned) glue . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   7.  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.  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].

Andrews, et al.          Expires 13 January 2022                [Page 2]
Internet-Draft  Glue In DNS Referral Responses Is Not Op       July 2021

2.  Clarifying 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.  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.

Andrews, et al.          Expires 13 January 2022                [Page 3]
Internet-Draft  Glue In DNS Referral Responses Is Not Op       July 2021

      % 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 from the same delegating zone

   Sibling glue are glue records that are not contained in the
   delegating zone itself, but in another delegated zone.  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 provide them as an
   optimization to obviate the need for extra traffic.

Andrews, et al.          Expires 13 January 2022                [Page 4]
Internet-Draft  Glue In DNS Referral Responses Is Not Op       July 2021

 Here the delegating zone "test" contains 2 delegations for the
 subzones "bar.test" and "foo.test". The nameservers for "foo.test"
 consist of sibling glue for "bar.test" (ns1.bar.test and ns2.bar.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 should include the sibling
 glue:

    ;; 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

   Question: if sibling glue from the same delegating zone does not fit
   into the response, should we also recommend or require that TC=1 be
   set?

3.3.  Example three: Cross Zone Sibling Glue

   Here is a more complex example of sibling glue that lives in another
   zone, but is required to resolve a circular dependency in the zone
   configuration.

      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

Andrews, et al.          Expires 13 January 2022                [Page 5]
Internet-Draft  Glue In DNS Referral Responses Is Not Op       July 2021

3.4.  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 authoritative 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

   [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>.

Andrews, et al.          Expires 13 January 2022                [Page 6]
Internet-Draft  Glue In DNS Referral Responses Is Not Op       July 2021

   [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

Andrews, et al.          Expires 13 January 2022                [Page 7]