おそらく、その特定のホストのDNSサーバーがダウンしています。ドメインのレコードをチェックwhois
して、どのDNSサーバーが信頼できるかを検出し、次にそれらの各サーバーを順番にチェックしhost
て、すべてが解決されることを確認します。
例whois stackoverflow.com
:
Name Servers:
ns1.serverfault.com
ns2.serverfault.com
ns3.serverfault.com
それで:
$ host www.stackoverflow.com ns1.serverfault.com
Using domain server:
Name: ns1.serverfault.com
Address: 64.34.119.33#53
Aliases:
www.stackoverflow.com is an alias for stackoverflow.com.
stackoverflow.com has address 64.34.119.12
stackoverflow.com mail is handled by 10 STACKOVERFLOW.COM.S9A1.PSMTP.com.
stackoverflow.com mail is handled by 20 STACKOVERFLOW.COM.S9A2.PSMTP.com.
stackoverflow.com mail is handled by 30 STACKOVERFLOW.COM.S9B1.PSMTP.com.
stackoverflow.com mail is handled by 40 STACKOVERFLOW.COM.S9B2.PSMTP.com.
$ host www.stackoverflow.com ns2.serverfault.com
Using domain server:
Name: ns2.serverfault.com
Address: 64.34.119.34#53
Aliases:
www.stackoverflow.com is an alias for stackoverflow.com.
stackoverflow.com has address 64.34.119.12
stackoverflow.com mail is handled by 30 STACKOVERFLOW.COM.S9B1.PSMTP.com.
stackoverflow.com mail is handled by 40 STACKOVERFLOW.COM.S9B2.PSMTP.com.
stackoverflow.com mail is handled by 10 STACKOVERFLOW.COM.S9A1.PSMTP.com.
stackoverflow.com mail is handled by 20 STACKOVERFLOW.COM.S9A2.PSMTP.com.
$ host www.stackoverflow.com ns3.serverfault.com
Using domain server:
Name: ns3.serverfault.com
Address: 69.59.196.217#53
Aliases:
www.stackoverflow.com is an alias for stackoverflow.com.
stackoverflow.com has address 64.34.119.12
stackoverflow.com mail is handled by 30 STACKOVERFLOW.COM.S9B1.PSMTP.com.
stackoverflow.com mail is handled by 40 STACKOVERFLOW.COM.S9B2.PSMTP.com.
stackoverflow.com mail is handled by 10 STACKOVERFLOW.COM.S9A1.PSMTP.com.
stackoverflow.com mail is handled by 20 STACKOVERFLOW.COM.S9A2.PSMTP.com.
$
3台のサーバーすべてがの要求に応答したためwww.stackoverflow.com
、3台のサーバーすべてが機能しています。