## page was renamed from DNS/基礎知識/資源レコード/DNAME
## page was renamed from DNS/資源レコード/DNAME
## page was renamed from DNS/DNAME
DNS/DNAMEについて、ここに記述してください。

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The DNAME RR has mnemonic DNAME and type code 39 (decimal).  It is CLASS-insensitive.

[[/Acceptance]]　[[/tinydns]] [[/解説]]

[[watchNS/jaist.jp]]

DNAMEが作られたゾーンのNSレコードにどういう意味があるのだろう。
 glueと同様の意味しかない。まともなレコードは作れないのだから。
　　サブドメインはすべてリダイレクトされるし。(ワイルドカードを含めて)
-- ToshinoriMaeno <<DateTime(2019-09-04T11:24:01+0900)>>
 
== 探索の手順の変更 ==
QNAMEにマッチする名前がない場合に、先頭のラベルを削って再度ゾーンを探索する。(ダメ)
　DNAMEレコードが見つかったら、...

qname minimisationとの整合性はあるのか。-- ToshinoriMaeno <<DateTime(2019-09-06T13:05:17+0900)>>

いや、それよりもDNAMEがなかったときの探索との整合性は?

https://tools.ietf.org/html/rfc6672
 DNAME Redirection in the DNS
   https://www.nic.ad.jp/ja/translation/rfc/2672.html (旧版の日本語)
Abstract
{{{
   The DNAME record provides redirection for a subtree of the domain
   name tree in the DNS.  That is, all names that end with a particular
   suffix are redirected to another part of the DNS.  This document
   obsoletes the original specification in RFC 2672 as well as updates
   the document on representing IPv6 addresses in DNS (RFC 3363).

  That is, all names that end with a particular suffix are redirected to another part of the DNS.
}}}
This document obsoletes the original specification in RFC 2672 as well as updates
the document on representing IPv6 addresses in DNS (RFC 3363).

{{{
2.2.  The DNAME Substitution

   When following step 3 of the algorithm in RFC 1034 [RFC1034], Section
   4.3.2, "start matching down, label by label, in the zone" and a node
   is found to own a DNAME resource record, a DNAME substitution occurs.
}}}

こういう手順で探索しているのですかね。
　DJBのlookupはそうではない。


{{{
   The name being sought may be the original query name or a name that
   is the result of a CNAME resource record being followed or a
   previously encountered DNAME.  As in the case when finding a CNAME
   resource record or NS resource record set, the processing of a DNAME
   will happen prior to finding the desired domain name.
}}}

{{{
   A DNAME substitution is performed by replacing the suffix labels of
   the name being sought matching the owner name of the DNAME resource
   record with the string of labels in the RDATA field.  The matching
   labels end with the root label in all cases.  Only whole labels are
   replaced.  See the table of examples for common cases and corner cases.

   In the table below, the QNAME refers to the query name.  The owner is
   the DNAME owner domain name, and the target refers to the target of
   the DNAME record.  The result is the resulting name after performing
   the DNAME substitution on the query name. "no match" means that the

   query did not match the DNAME, and thus no substitution is performed
   and a possible error message is returned (if no other result is
   possible).  Thus, every line contains one example substitution.  In
   the examples below, 'cyc' and 'shortloop' contain loops.

    QNAME            owner  DNAME   target         result
    ---------------- -------------- -------------- -----------------
    com.             example.com.   example.net.   <no match>
    example.com.     example.com.   example.net.   [0]
    a.example.com.   example.com.   example.net.   a.example.net.
    a.b.example.com. example.com.   example.net.   a.b.example.net.
    ab.example.com.  b.example.com. example.net.   <no match>
    foo.example.com. example.com.   example.net.   foo.example.net.
    a.x.example.com. x.example.com. example.net.   a.example.net.
    a.example.com.   example.com.   y.example.net. a.y.example.net.
    cyc.example.com. example.com.   example.com.   cyc.example.com.
    cyc.example.com. example.com.   c.example.com. cyc.c.example.com.
    shortloop.x.x.   x.             .              shortloop.x.
    shortloop.x.     x.             .              shortloop.

   [0] The result depends on the QTYPE.  If the QTYPE = DNAME, then
       the result is "example.com.", else "<no match>".

                   Table 1. DNAME Substitution Examples
}}}
<no match> は置換えを行わないということ。-- ToshinoriMaeno <<DateTime(2019-09-06T19:26:20+0900)>>


5.1.  Canonical Hostnames Cannot Be below DNAME Owners

{{{
The names listed as target names of MX, NS, PTR, and SRV [RFC2782]
   records must be canonical hostnames.  This means no CNAME or DNAME
   redirection may be present during DNS lookup of the address records
   for the host. 
}}}

5.3.  DNSSEC and DNAME   どうなるのか。(署名)

6.  Examples of DNAME Use in a Zone

8.  Security Considerations

If a validating resolver accepts wildcarded DNAMEs, this creates
   security issues.  Since the processing of a wildcarded DNAME is non-
   deterministic and the CNAME that was substituted by the server has no
   signature, the resolver may choose a different result than what the
   server meant, and consequently end up at the wrong destination.  Use
   of wildcarded DNAMEs is discouraged in any case [RFC4592].