メモ：DNS応答メッセージのSOAレコード

DNS

RFC 1035に書いてあった．http://www.ietf.org/rfc/rfc1035.txt

3.3.13. SOA RDATA format

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    /                     MNAME                     /
    /                                               /
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    /                     RNAME                     /
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                    SERIAL                     |
    |                                               |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                    REFRESH                    |
    |                                               |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                     RETRY                     |
    |                                               |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                    EXPIRE                     |
    |                                               |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                    MINIMUM                    |
    |                                               |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

where:

MNAME           The  of the name server that was the
                original or primary source of data for this zone.

RNAME           A  which specifies the mailbox of the
                person responsible for this zone.

SERIAL          The unsigned 32 bit version number of the original copy
                of the zone.  Zone transfers preserve this value.  This
                value wraps and should be compared using sequence space
                arithmetic.

REFRESH         A 32 bit time interval before the zone should be
                refreshed.

RETRY           A 32 bit time interval that should elapse before a
                failed refresh should be retried.

EXPIRE          A 32 bit time value that specifies the upper limit on
                the time interval that can elapse before the zone is no
                longer authoritative.

MINIMUM         The unsigned 32 bit minimum TTL field that should be
                exported with any RR from this zone.

SOA records cause no additional section processing.

All times are in units of seconds.


digでSOAレコードを調べるには，-t soaと指定すれば良い．

$ dig -t soa hatena.ne.jp

; <<>> DiG 9.7.6-P1 <<>> -t soa hatena.ne.jp
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 20277
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;hatena.ne.jp.			IN	SOA

;; ANSWER SECTION:
hatena.ne.jp.		3600	IN	SOA	ns0.future-s.com. dnsadmin.future-s.com. 2013021406 7200 3600 604800 3600

;; Query time: 109 msec
;; SERVER: 192.168.0.254#53(192.168.0.254)
;; WHEN: Fri Apr  5 20:11:08 2013
;; MSG SIZE  rcvd: 91

hatena.ne.jpのドメインはfuture-s.com，フューチャースピリッツという会社が管理しているのがわかる．フューチャースピリッツは京都に本社がある会社らしい（http://www.future-s.com/company/profile.html）．はてなと関係あるのか？知らない．


livedoor.jpを調べてみると，

$ dig -t soa livedoor.jp
;; QUESTION SECTION:
;livedoor.jp.			IN	SOA

;; ANSWER SECTION:
livedoor.jp.		1907	IN	SOA	zns05.data-hotel.net. hostmaster.data-hotel.net. 2013011802 10800 3600 604800 3600

てな感じでデータホテルになっているのが分かる．少し前，ライブドアの一部がNHN Japanになって，その後ライブドアがデータホテルに名前を変更した．


ちなみに，java.comはというと，

$ dig -t soa java.com
;; QUESTION SECTION:
;java.com.			IN	SOA

;; ANSWER SECTION:
java.com.		10800	IN	SOA	ns1.oracle.com. hostmaster.oracle.com. 2013021204 21600 3600 604800 900

oracle.comでした（笑）