$TTL    3600

@       IN      SOA     dns1.ipa.go.jp.    root.dns1.ipa.go.jp. (
        2002012101      ;Serial
        3600            ;Refresh
        900             ;Retry
        3600000         ;Expire
        3600 )          ;Minimum

        IN      NS      dns1.ipa.go.jp
        IN      MX      10      mail.ipa.go.jp.

YYY      IN      PTR     dns1.ipa.go.jp
XXX      IN      PTR     mail.ipa.go.jp
ZZZ      IN      PTR     www.ipa.go.jp