Glue In DNS Referral Responses Is Not Optional
draft-ietf-dnsop-glue-is-not-optional-02

Document Type Active Internet-Draft (dnsop WG)
Authors Mark 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
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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
   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 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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