INTERNET-DRAFT                                      Mark Andrews (CSIRO)
   <draft-ietf-dnsind-ncache-00.txt>                           January 1997
   
   Updates: RFC 1034
   
   
                 Negative Caching of DNS Queries (DNS NCACHE)
   
   
   Status of This Memo
   
           This document is an Internet-Draft.  Internet-Drafts are working
           documents of the Internet Engineering Task Force (IETF), its
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           ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast).
   
   
   Abstract
   
           When [RFC1034] was written there were no DNS servers that imple-
           mented negative caching [RFC1034 Section 4.3.4]. This document
           replaces [RFC1034 Section 4.3.4] in the light of experience.
   
           Negative caching is a optional part of the DNS specification and
           deals with the caching of the non-existence of a RRset or
           domainname.
   
    - Negative Caching
   
   A server MAY add a SOA RR to the additional section of a response. The
   SOA record is that of the containing zone, or a cached RR. If it is from
   the containing zone on a authoritative server the TTL is initialised to
   the MINIMUM field otherwise it is the cached TTL value decremented by
   
   
   
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   INTERNET-DRAFT                 DNS NCACHE                   January 1997
   
   
   the time in the cache.
   
   This SOA record MAY NOT be used to answer a SOA query.
   
   A negative response MAY be cached if there is a SOA record in the
   authority section of the the response. When the SOA record is cached it
   must be cached such that it can only be retrieved by reference to the
   <query name, QTYPE, QCLASS> tuple or <query name, QCLASS> in the case of
   a name error. The query name is either the name given in the query sec-
   tion or the last connonical name when there are CNAMEs in the answer
   section.
   
   Negative responses without SOA records SHOULD NOT be cached as there is
   no way to reliably purge them from the cache.
   
   When caching a negative response a server MUST store the contents of the
   received SOA in the authority section such that it can be restored in
   the answer's additional section. The TTL of this stored record decre-
   ments with time.
   
   
    - Changes from RFC 1034
   
   Non-authoritative negative answers MAY be cached.
   
   The SOA record from the authority section MUST be cached so that it is
   retrievable by reference to the <query name, QTYPE, QCLASS> tuple.  Name
   error indications need only match <query name, QCLASS>.
   
   A cached SOA record MAY be added to the response. This was explicitly
   NOT allowed.
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
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   References
   
   [RFC1034]P. Mockapetris, ``DOMAIN NAMES - CONCEPTS AND FACILITIES,'' RFC
           1034, ISI, November 1987.
   
   
   Authors' Addresses
   
           Mark Andrews
              CSIRO - Mathematical and Information Sciences
              Locked Bag 17
              North Ryde NSW 2113
              AUSTRALIA
              +61 2 9325 3148
              <Mark.Andrews@cmis.csiro.au>
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
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