Windows の nslookup を用いた２つの DNS のトラブルシューティング Tips

概要

Windows の nslookup を用いた２つの DNS のトラブルシューティング Tips を二つ紹介します。
1. 権限のある回答の調べ方
2. TTL の調べ方

内容

1. 権限のある回答の調べ方
例として、www.google.com の権限のある回答を調べる方法を紹介します。

権限のある回答を調べるために、まず -type=soa オプションをつけ SOA レコードを調べます。ここで出力された primary name server をメモしておきます。

調べた primary name server に対し、www.google.com の名前解決を実施します。
すると、権限のある回答を調べることができます。

2. TTL の調べ方
-debug オプションをつけることで TTL を調べることができます。

以下の例では A レコードの TTL が 1 分 20 秒であることがわかります。

C:\>nslookup -debug www.google.com
------------
Got answer:
     HEADER:
         opcode = QUERY, id = 1, rcode = NOERROR
         header flags: response, want recursion, recursion avail.
         questions = 1, answers = 1, authority records = 0, additional = 0

    QUESTIONS:
         2.0.0.10.in-addr.arpa, type = PTR, class = IN
     ANSWERS:
     -> 2.0.0.10.in-addr.arpa
         name = ip-10-0-0-2.ap-northeast-1.compute.internal
         ttl = 87 (1 min 27 secs)

------------
サーバー: ip-10-0-0-2.ap-northeast-1.compute.internal
Address: 10.0.0.2

------------
Got answer:
     HEADER:
         opcode = QUERY, id = 2, rcode = NXDOMAIN
         header flags: response, want recursion, recursion avail.
         questions = 1, answers = 0, authority records = 0, additional = 0

QUESTIONS:
www.google.com.ap-northeast-1.compute.internal, type = A, class = IN

------------
------------
Got answer:
     HEADER:
         opcode = QUERY, id = 3, rcode = NXDOMAIN
         header flags: response, want recursion, recursion avail.
         questions = 1, answers = 0, authority records = 0, additional = 0

QUESTIONS:
www.google.com.ap-northeast-1.compute.internal, type = AAAA, class = IN

------------
------------
Got answer:
     HEADER:
         opcode = QUERY, id = 4, rcode = NXDOMAIN
         header flags: response, want recursion, recursion avail.
         questions = 1, answers = 0, authority records = 0, additional = 0

QUESTIONS:
www.google.com.compute.internal, type = A, class = IN

------------
------------
Got answer:
     HEADER:
         opcode = QUERY, id = 5, rcode = NXDOMAIN
         header flags: response, want recursion, recursion avail.
         questions = 1, answers = 0, authority records = 0, additional = 0

QUESTIONS:
www.google.com.compute.internal, type = AAAA, class = IN

------------
------------
Got answer:
     HEADER:
         opcode = QUERY, id = 6, rcode = NOERROR
         header flags: response, want recursion, recursion avail.
         questions = 1, answers = 1, authority records = 0, additional = 0

    QUESTIONS:
         www.google.com, type = A, class = IN
     ANSWERS:
     -> www.google.com
         internet address = 172.217.175.100
         ttl = 80 (1 min 20 secs)

------------
権限のない回答:
------------
Got answer:
     HEADER:
         opcode = QUERY, id = 7, rcode = NOERROR
         header flags: response, want recursion, recursion avail.
         questions = 1, answers = 1, authority records = 0, additional = 0

    QUESTIONS:
         www.google.com, type = AAAA, class = IN
     ANSWERS:
     -> www.google.com
         AAAA IPv6 address = 2404:6800:4004:801::2004
         ttl = 24 (24 secs)

------------
名前: www.google.com
Addresses: 2404:6800:4004:801::2004
172.217.175.100