[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 draft-ietf-dnsop-nsec-aggressiveuse

Network Working Group                                        K. Fujiwara
Internet-Draft                                                      JPRS
Intended status: Informational                                   A. Kato
Expires: September 19, 2016                                    Keio/WIDE
                                                          March 18, 2016


                      Aggressive use of NSEC/NSEC3
               draft-fujiwara-dnsop-nsec-aggressiveuse-03

Abstract

   While DNS highly depends on cache, its cache usage of non-existence
   information has been limited to exact matching.  This draft proposes
   the aggressive use of a NSEC/NSEC3 resource record, which is able to
   express non-existence of a range of names authoritatively.  With this
   proposal, it is expected that shorter latency to many of negative
   responses as well as some level of mitigation of random sub-domain
   attacks (referred to as "Water Torture" attacks).  It is also
   expected that non-existent TLD queries to Root DNS servers will
   decrease.

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 http://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 September 19, 2016.

Copyright Notice

   Copyright (c) 2016 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



Fujiwara & Kato        Expires September 19, 2016               [Page 1]


Internet-Draft              NSEC/NSEC3 usage                  March 2016


   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
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Proposed Solution . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Aggressive Negative Caching . . . . . . . . . . . . . . .   4
     4.2.  NSEC  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.3.  NSEC3 . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.4.  NSEC3 Opt-Out . . . . . . . . . . . . . . . . . . . . . .   6
     4.5.  Wildcard  . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.6.  Consideration on TTL  . . . . . . . . . . . . . . . . . .   6
   5.  Additional Considerations . . . . . . . . . . . . . . . . . .   6
     5.1.  The CD Bit  . . . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  Detecting random subdomain attacks  . . . . . . . . . . .   7
   6.  Possible side effect  . . . . . . . . . . . . . . . . . . . .   7
   7.  Additional proposals  . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Partial implementation  . . . . . . . . . . . . . . . . .   7
     7.2.  Aggressive negative caching without DNSSEC validation . .   8
     7.3.  Aggressive negative caching flag idea . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   10. Implementation Status . . . . . . . . . . . . . . . . . . . .   9
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   12. Change History  . . . . . . . . . . . . . . . . . . . . . . .   9
     12.1.  Version 01 . . . . . . . . . . . . . . . . . . . . . . .   9
     12.2.  Version 02 . . . . . . . . . . . . . . . . . . . . . . .   9
     12.3.  Version 03 . . . . . . . . . . . . . . . . . . . . . . .   9
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     13.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Appendix A.  Aggressive negative caching from RFC 5074  . . . . .  11
   Appendix B.  Detailed implementation idea . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   While negative (non-existence) information of DNS caching mechanism
   has been known as DNS negative cache [RFC2308], it requires exact
   matching in most cases.  Assume that "example.com" zone doesn't have
   names such as "a.example.com" and "b.example.com".  When a full-
   service resolver receives a query "a.example.com" , it performs a DNS



Fujiwara & Kato        Expires September 19, 2016               [Page 2]


Internet-Draft              NSEC/NSEC3 usage                  March 2016


   resolution process, and eventually gets NXDOMAIN and stores it into
   its negative cache.  When the full-service resolver receives another
   query "b.example.com", it doesn't match with "a.example.com".  So it
   will send a query to one of the authoritative servers of
   "example.com".  This was because the NXDOMAIN response just says
   there is no such name "a.example.com" and it doesn't tell anything
   for "b.example.com".

   Section 5 of [RFC2308] seems to show that negative answers should be
   cached only for the exact query name, and not (necessarily) for
   anything below it.

   Recently, DNSSEC [RFC4035] [RFC5155] has been practically deployed.
   Two types of resource record (NSEC and NSEC3) along with their RRSIG
   records represent authentic non-existence.  For a zone signed with
   NSEC, it would be possible to use the information carried in NSEC
   resource records to indicate that a range of names where no valid
   name exists.  Such use is discouraged by Section 4.5 of RFC 4035,
   however.

   This document proposes to make a minor change to RFC 4035 and a full-
   service resolver can use NSEC/NSEC3 resource records aggressively so
   that the resolver responds with NXDOMAIN immediately if the name in
   question falls into a range expressed by a NSEC/NSEC3 resource
   record.

   Aggressive Negative Caching was first proposed in Section 6 of DNSSEC
   Lookaside Validation (DLV) [RFC5074] in order to find covering NSEC
   records efficiently.  Unbound [UNBOUND] has aggressive negative
   caching code in its DLV validator.  Unbound TODO file contains "NSEC/
   NSEC3 aggressive negative caching".

   Section 3 of [I-D.vixie-dnsext-resimprove] ("Stopping Downward Cache
   Search on NXDOMAIN") proposed another approach to use NXDOMAIN
   information effectively.

2.  Terminology

   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 RFC 2119 [RFC2119].

   Many of the specialized terms used in this specification are defined
   in DNS Terminology [RFC7719].







Fujiwara & Kato        Expires September 19, 2016               [Page 3]


Internet-Draft              NSEC/NSEC3 usage                  March 2016


3.  Problem Statement

   Random sub-domain attacks (referred to as "Water Torture" attacks or
   NXDomain attacks) send many non-existent queries to full-service
   resolvers.  Their query names consist of random prefixes and a target
   domain name.  The negative cache does not work well and target full-
   service resolvers result in sending queries to authoritative DNS
   servers of the target domain name.

   When number of queries is large, the full-service resolvers drop
   queries from both legitimate users and attackers as their outstanding
   queues are filled up.

   For example, BIND 9.10.2 [BIND9] full-service resolvers answer
   SERVFAIL and Unbound 1.5.2 full-service resolvers drop most of
   queries under 10,000 queries per second attack.

   The countermeasures implemented at this moment are rate limiting and
   disabling name resolution of target domain names in ad-hoc manner.

4.  Proposed Solution

4.1.  Aggressive Negative Caching

   If the target domain names are DNSSEC signed, aggressive use of NSEC/
   NSEC3 resource records mitigates the problem.

   Section 4.5 of [RFC4035] shows that "In theory, a resolver could use
   wildcards or NSEC RRs to generate positive and negative responses
   (respectively) until the TTL or signatures on the records in question
   expire.  However, it seems prudent for resolvers to avoid blocking
   new authoritative data or synthesizing new data on their own.
   Resolvers that follow this recommendation will have a more consistent
   view of the namespace".

   To reduce non-existent queries sent to authoritative DNS servers, it
   is suggested to relax this restriction as follows:

   +--------------------------------------------------------------+
   |  DNSSEC enabled full-service resolvers MAY use               |
   |  NSEC/NSEC3 resource records to generate negative responses  |
   |  until their effective TTLs or signatures on the records     |
   |  in question expire.                                         |
   +--------------------------------------------------------------+

   If the full-service resolver's cache have enough information to
   validate the query, the full-service resolver MAY use NSEC/NSEC3/




Fujiwara & Kato        Expires September 19, 2016               [Page 4]


Internet-Draft              NSEC/NSEC3 usage                  March 2016


   wildcard records aggressively.  Otherwise, the full-service resolver
   MUST fall back to send the query to the authoritative DNS servers.

   Necessary information to validate are matching/covering NSEC/NSEC3 of
   the wildcards which may match the query name, matching/covering NSEC/
   NSEC3 of non-terminals which derive from the query name and matching/
   covering NSEC/NSEC3 of the query name.

   If the query name has the matching NSEC/NSEC3 RR and it shows the
   query type does not exist, the full-service resolver is possible to
   respond with NODATA (empty) answer.

4.2.  NSEC

   A full-service resolver implementation SHOULD support aggressive use
   of NSEC and enable it by default.  It SHOULD provide a configuration
   knob to disable aggressive use of NSEC.

   The validating resolver need to check the existence of matching
   wildcards which derive from the query name, covering NSEC RRs of the
   matching wildcards and covering NSEC RR of the query name.

   If the full-service resolver's cache contains covering NSEC RRs of
   matching wildcards and the covering NSEC RR of the query name, the
   full-service resolver is possible to respond with NXDOMAIN error
   immediately.

4.3.  NSEC3

   NSEC3 aggressive negative caching is more difficult.  If the zone is
   signed with NSEC3, the validating resolver need to check the
   existence of non-terminals and wildcards which derive from query
   names.

   If the full-service resolver's cache contains covering NSEC3 RRs of
   matching wildcards, the covering NSEC3 RRs of the non-terminals and
   the covering NSEC3 RR of the query name, the full-service resolver is
   possible to respond with NXDOMAIN error immediately.

   If the validating resolver proves the non-exisence of the non-
   terminal domain name of the query name, the query name does not
   exist.

   To identify signing types of the zone, validating resolvers need to
   build separated cache of NSEC and NSEC3 resource records for each
   signer domain name.





Fujiwara & Kato        Expires September 19, 2016               [Page 5]


Internet-Draft              NSEC/NSEC3 usage                  March 2016


   When a query name is not in the regular cache, find closest enclosing
   NS RRset in the regular cache.  The owner of the closest enclosing NS
   RRset may be the longest signer domain name of the query name.  If
   there is no entry in the NSEC/NSEC3 cache of the signer domain name,
   aggressive negative caching is not possible at this moment.
   Otherwise, there is at least one NSEC or NSEC3 resource records.  The
   record shows the signing type.

   A full-service resolver implementation MAY support aggressive use of
   NSEC3.  It SHOULD provide a configuration knob to disable aggressive
   use NSEC3 in this case.

4.4.  NSEC3 Opt-Out

   If the zone is signed with NSEC3 and with Opt-Out flag set to 1, the
   aggressive negative caching is not possible at the zone.

4.5.  Wildcard

   Even if a wildcard is cached, it is necessary to send a query to an
   authoritative server to ensure that the name in question doesn't
   exist as long as the name is not in the negative cache.

   When aggressive use is enabled, regardless of description of
   Section 4.5 of [RFC4035], it is possible to send a positive response
   immediately when the name in question matches a NSEC/NSEC3 RRs in the
   negative cache.

4.6.  Consideration on TTL

   This function needs care on the TTL value of negative information
   because newly added domain names cannot be used while the negative
   information is effective.  RFC 2308 states the maximum number of
   negative cache TTL value is 10800 (3 hours).  So the full-service
   resolver SHOULD limit the maximum effective TTL value of negative
   responses (NSEC/NSEC3 RRs) to 10800 (3 hours).  It is reasonably
   small but still effective for the purpose of this document as it can
   eliminate significant amount of DNS attacks with randomly generated
   names.

5.  Additional Considerations

5.1.  The CD Bit

   The CD bit disables signature validation.  It is one of the basic
   functions of DNSSEC protocol and it SHOULD NOT be changed.  However,
   attackers may set the CD bit to their attack queries and the
   aggressive negative caching will be of no use.



Fujiwara & Kato        Expires September 19, 2016               [Page 6]


Internet-Draft              NSEC/NSEC3 usage                  March 2016


   Ignoring the CD bit function may break the DNSSEC protocol.

   This draft proposes that the CD bit may be ignored to support
   aggressive negative caching when the full-service resolver is under
   attacks with CD bit set.

5.2.  Detecting random subdomain attacks

   Full-service resolvers should detect conditions under random
   subdomain attacks.  When they are under attacks, their outstanding
   queries increase.  If there are some destination addresses whose
   outstanding queries are many, they may contain attack target domain
   names.  Existing countermeasures may implement attack detection.

6.  Possible side effect

   Aggressive use of NSEC/NSEC3 resource records may decrease queries to
   Root DNS servers.

   People may generate many typos in TLD, and they will result in
   unnecessary DNS queries.  Some implementations leak non-existent TLD
   queries whose second level domain are different each other.  Well
   observed TLDs are ".local" and ".belkin".  With this proposal, it is
   possible to return NXDOMAIN immediately to such queries without
   further DNS recursive resolution process.  It may reduces round trip
   time, as well as reduces the DNS queries to corresponding
   authoritative servers, including Root DNS servers.

7.  Additional proposals

   There are additional proposals to the aggressive negative caching.

7.1.  Partial implementation

   It is possible to implement aggressive negative caching partially.

   DLV aggressive negative caching [RFC5074] is an implementation of
   NSEC aggressive negative caching which targets DLV domain names.

   NSEC only aggressive negative caching is easier to implement NSEC/
   NSEC3 aggressive negative caching (full implantation) because NSEC3
   handling is hard to implement.

   Root only aggressive negative caching is possible.  It uses NSEC and
   RRSIG resource records whose signer domain name is root.

   An implementation without detecting attacks is possible.  It cannot
   ignore the CD bit and the effectiveness may be limited.



Fujiwara & Kato        Expires September 19, 2016               [Page 7]


Internet-Draft              NSEC/NSEC3 usage                  March 2016


7.2.  Aggressive negative caching without DNSSEC validation

   Aggressive negative caching may be applicable to full-service
   resolvers without DNSSEC validation.  They can set DNSSEC OK bit in
   query packets to obtain corresponding NSEC/NSEC3 resource records.
   While the full-service resolvers SHOULD validate the NSEC/NSEC3
   resource records, they MAY use the records to respond NXDOMAIN error
   immediately without DNSSEC validation.

   However, it is highly recommended to apply DNSSEC validation.

7.3.  Aggressive negative caching flag idea

   Authoritative DNS servers that dynamically generate NSEC records
   normally generate minimally covering NSEC Records [RFC4470].
   Aggressive negative caching does not work with minimally covering
   NSEC records.  Most of DNS operators don't want zone enumeration and
   zone information leaks.  They prefer NSEC resource records with
   narrow ranges.  When there is a flag that show a full-service
   resolver support the aggressive negative caching and a query have the
   aggressive negative caching flag, authoritative DNS servers can
   generate NSEC resource records with wider range under random
   subdomain attacks.

   However, changing range of minimally covering NSEC Records may be
   implemented by detecting attacks.  Authoritative DNS servers can
   answer any range of minimally covering NSEC Records.

8.  IANA Considerations

   This document has no IANA actions.

9.  Security Considerations

   Newly registered resource records may not be used immediately.
   However, choosing suitable TTL value will mitigate the problem and it
   is not a security problem.

   It is also suggested to limit the maximum TTL value of NSEC resource
   records in the negative cache to, for example, 10800 seconds (3hrs),
   to mitigate the issue.  Implementations which comply with this
   proposal is suggested to have a configurable maximum value of NSEC
   RRs in the negative cache.

   Aggressive use of NSEC/NSEC3 resource records without DNSSEC
   validation may cause security problems.





Fujiwara & Kato        Expires September 19, 2016               [Page 8]


Internet-Draft              NSEC/NSEC3 usage                  March 2016


10.  Implementation Status

   Unbound has aggressive negative caching code in its DLV validator.
   The author implemented NSEC aggressive caching using Unbound and its
   DLV validator code.

11.  Acknowledgments

   The authors gratefully acknowledge DLV [RFC5074] author Samuel Weiler
   and Unbound developers.  Olafur Gudmundsson and Pieter Lexis proposed
   aggressive negative caching flag idea.  Valuable comments were
   provided by Bob Harold, Tatuya JINMEI, Shumon Huque, Mark Andrews,
   and Casey Deccio.

12.  Change History

   This section is used for tracking the update of this document.  Will
   be removed after finalize.

12.1.  Version 01

   o  Added reference to DLV [RFC5074] and imported some sentences.

   o  Added Aggressive Negative Caching Flag idea.

   o  Added detailed algorithms.

12.2.  Version 02

   o  Added reference to [I-D.vixie-dnsext-resimprove]

   o  Added considerations for the CD bit

   o  Updated detailed algorithms.

   o  Moved Aggressive Negative Caching Flag idea into Additional
      Proposals

12.3.  Version 03

   o  Added "Partial implementation"

   o  Section 4,5,6 reorganized for better representation

   o  Added NODATA answer in Section 4

   o  Trivial updates




Fujiwara & Kato        Expires September 19, 2016               [Page 9]


Internet-Draft              NSEC/NSEC3 usage                  March 2016


   o  Updated pseudo code

13.  References

13.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2308]  Andrews, M., "Negative Caching of DNS Queries (DNS
              NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,
              <http://www.rfc-editor.org/info/rfc2308>.

   [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,
              <http://www.rfc-editor.org/info/rfc4035>.

   [RFC4470]  Weiler, S. and J. Ihren, "Minimally Covering NSEC Records
              and DNSSEC On-line Signing", RFC 4470, DOI 10.17487/
              RFC4470, April 2006,
              <http://www.rfc-editor.org/info/rfc4470>.

   [RFC5074]  Weiler, S., "DNSSEC Lookaside Validation (DLV)", RFC 5074,
              DOI 10.17487/RFC5074, November 2007,
              <http://www.rfc-editor.org/info/rfc5074>.

   [RFC5155]  Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
              Security (DNSSEC) Hashed Authenticated Denial of
              Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,
              <http://www.rfc-editor.org/info/rfc5155>.

   [RFC7719]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", RFC 7719, DOI 10.17487/RFC7719, December
              2015, <http://www.rfc-editor.org/info/rfc7719>.

13.2.  Informative References

   [BIND9]    Internet Systems Consortium, Inc., "Name Server Software",
              2000, <https://www.isc.org/downloads/bind/>.

   [I-D.vixie-dnsext-resimprove]
              Vixie, P., Joffe, R., and F. Neves, "Improvements to DNS
              Resolvers for Resiliency, Robustness, and Responsiveness",
              draft-vixie-dnsext-resimprove-00 (work in progress), June
              2010.



Fujiwara & Kato        Expires September 19, 2016              [Page 10]


Internet-Draft              NSEC/NSEC3 usage                  March 2016


   [UNBOUND]  NLnet Labs, "Unbound DNS validating resolver", 2006,
              <http://www.unbound.net/>.

Appendix A.  Aggressive negative caching from RFC 5074

   Imported from Section 6 of [RFC5074].

   Previously, cached negative responses were indexed by QNAME, QCLASS,
   QTYPE, and the setting of the CD bit (see RFC 4035, Section 4.7), and
   only queries matching the index key would be answered from the cache.
   With aggressive negative caching, the validator, in addition to
   checking to see if the answer is in its cache before sending a query,
   checks to see whether any cached and validated NSEC record denies the
   existence of the sought record(s).

   Using aggressive negative caching, a validator will not make queries
   for any name covered by a cached and validated NSEC record.
   Furthermore, a validator answering queries from clients will
   synthesize a negative answer whenever it has an applicable validated
   NSEC in its cache unless the CD bit was set on the incoming query.

   Imported from Section 6.1 of [RFC5074].

   Implementing aggressive negative caching suggests that a validator
   will need to build an ordered data structure of NSEC records in order
   to efficiently find covering NSEC records.  Only NSEC records from
   DLV domains need to be included in this data structure.

Appendix B.  Detailed implementation idea

   Section 6.1 of [RFC5074] is expanded as follows.

   Implementing aggressive negative caching suggests that a validator
   will need to build an ordered data structure of NSEC and NSEC3
   records for each signer domain name of NSEC / NSEC3 records in order
   to efficiently find covering NSEC / NSEC3 records.  Call the table as
   NSEC_TABLE.

   The aggressive negative caching may be inserted at the cache lookup
   part of the full-service resolvers.

   If errors happen in aggressive negative caching algorithm, resolvers
   MUST fall back to resolve the query as usual.  "Resolve the query as
   usual" means that the full-resolver resolve the query in Recursive-
   mode as if the full-service resolver does not implement aggressive
   negative caching.





Fujiwara & Kato        Expires September 19, 2016              [Page 11]


Internet-Draft              NSEC/NSEC3 usage                  March 2016


   To implement aggressive negative caching, resolver algorithm near
   cache lookup will be changed as follows:

   QNAME = the query name;
   QTYPE = the query type;
   if ({QNAME,QTYPE} entry exists in the cache) {
       // the resolver responds the RRSet from the cache
       resolve the query as usual;
   }

   // if NSEC* exists, QTYPE existence is proved by type bitmap
   if (matching NSEC/NSEC3 of QNAME exists in the cache) {
       if (QTYPE exists in type bitmap of NSEC/NSEC3 of QNAME) {
           // the entry exists, however, it is not in the cache.
           // need to iterate QNAME/QTYPE.
           resolve the query as usual;
       } else {
           // QNAME exists, QTYPE does not exist.
           the resolver can generate NODATA response;
       }
   }

   // Find closest enclosing NS RRset in the cache.
   // The owner of this NS RRset will be a suffix of the QNAME
   //    - the longest suffix of any NS RRset in the cache.
   SIGNER = closest enclosing NS RRSet of QNAME in the cache;

   // Check the SOA RR of the SIGNER
   if (SOA RR of SIGNER does not exist in the cache
       or SIGNER zone is not signed or not validated) {
      Resolve the query as usual;
   }

   if (SIGNER zone does not have NSEC_TABLE) {
       Resolve the query as usual;
   }

   if (SIGNER zone is signed with NSEC) { // NSEC mode

       // Check the non-existence of QNAME
       CoveringNSEC = Find the covering NSEC of QNAME;
       if (Covering NSEC doesn't exist in the cache) {
           Resolve the query as usual.
       }

       // Select the longest existing name of QNAME from covering NSEC
       LongestExistName = common part of both owner name and
                           next domain name of CoveringNSEC;



Fujiwara & Kato        Expires September 19, 2016              [Page 12]


Internet-Draft              NSEC/NSEC3 usage                  March 2016


       if (*.LongestExistName entry exists in the cache) {
           the resolver can generate positive response
           // synthesize the wildcard *.TEST
       }
       if covering NSEC RR of "*.LongestExistName" at SIGNER zone exists
            in the cache {
           the resolver can generate negative response;
       }
       //*.LongestExistName may exist. cannot generate negative response
       Resolve the query as usual.

   } else
   if (SIGNER zone is signed with NSEC3 and does not use Opt-Out) {
       // NSEC3 mode

       TEST = SIGNER;
       while (TEST != QNAME) {
           // if any error happens in this loop, break this loop
           UPPER = TEST;
           add a label from the QNAME to the start of TEST;
             // TEST = label.UPPER
           if (TEST name entry exist in the cache
               || matching NSEC3 of TEST exist in the cache) {
               // TEST exist
               continue; // need to check rest of QNAME
           }
           if (covering NSEC3 of TEST exist in the cache) {
               // (non-)terminal name TEST does not exist
               if (*.UPPER name entry exist in the cache) {
                   // TEST does not exist and *.UPPER exist
                   the resolver can generate positive response;
               } else
               if (covering NSEC3 of *.UPPER exist in the cache) {
                   // TEST does not exist and *.UPPER does not exist
                   the resolver can generate negative response;
               }
               break; // Lack of information (No *.UPPER information)
           }
           break; // Lack of information (No TEST information)
       }
       // no matching/covering NSEC3 of QNAME information
       Resolve the query as usual
   }








Fujiwara & Kato        Expires September 19, 2016              [Page 13]


Internet-Draft              NSEC/NSEC3 usage                  March 2016


Authors' Addresses

   Kazunori Fujiwara
   Japan Registry Services Co., Ltd.
   Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda
   Chiyoda-ku, Tokyo  101-0065
   Japan

   Phone: +81 3 5215 8451
   Email: fujiwara@jprs.co.jp


   Akira Kato
   Keio University/WIDE Project
   Graduate School of Media Design, 4-1-1 Hiyoshi
   Kohoku, Yokohama  223-8526
   Japan

   Phone: +81 45 564 2490
   Email: kato@wide.ad.jp































Fujiwara & Kato        Expires September 19, 2016              [Page 14]


Html markup produced by rfcmarkup 1.123, available from https://tools.ietf.org/tools/rfcmarkup/