ubuntu package - bind9-host

host主要拿來作DNS的lookup，和nslookup一樣，可以作正解(lookup/由domain name找到IP)，也可以作反解(reverse lookup/由IP找到domain name)，大多數的User比較常接觸到的是正解。

brook@ubuntu:~$ host dns.hinet.net
dns.hinet.net has address 168.95.1.1
brook@ubuntu:~$ 
brook@ubuntu:~$ host 168.95.1.1
1.1.95.168.in-addr.arpa domain name pointer dns.hinet.net.
brook@ubuntu:~$ 
brook@ubuntu:~$ host www.google.com
www.google.com is an alias for www.l.google.com.
www.l.google.com has address 72.14.203.99
www.l.google.com has address 72.14.203.147
www.l.google.com has address 72.14.203.104
www.l.google.com has address 72.14.203.103
www.l.google.com has address 72.14.203.105
www.l.google.com has address 72.14.203.106
brook@ubuntu:~$ 
brook@ubuntu:~$ host 72.14.203.99
99.203.14.72.in-addr.arpa domain name pointer tx-in-f99.1e100.net.

建議參考資料︰
　　http://linux.vbird.org/linux_server/0350dns.php
　　http://plog.longwin.com.tw/news_security/2005/11/06/dns_error_top_3