Name: youtube.com
Address: 173.194.38.69
1e100.netはGoogleが管理しているDomainでYouTubeもGoogleの傘下です。
# Googleは検索大手なのでDomainは幾つも持ってる。正引き/逆引きをしても良く分からない。
$nslookup -sil
> 173.194.38.69
Non-authoritative answer:
69.38.194.173.in-addr.arpa name = nrt19s17-in-f5.1e100.net.
Authoritative answers can be found from:
> nrt19s17-in-f5.1e100.net
Non-authoritative answer:
Name: nrt19s17-in-f5.1e100.net
Address: 173.194.38.69
> exit
最後のみが違うのでGoogle(YouTube)が管理しているDomainだと思います。
$ nslookup -sil
> youtube.com
Non-authoritative answer:
Name: youtube.com
Address: 173.194.38.108
Name: youtube.com
Address: 173.194.38.109
Name: youtube.com
Address: 173.194.38.110
Name: youtube.com
Address: 173.194.38.111
Name: youtube.com
Address: 173.194.38.96
Name: youtube.com
Address: 173.194.38.97
Name: youtube.com
Address: 173.194.38.98
Name: youtube.com
Address: 173.194.38.99
Name: youtube.com
Address: 173.194.38.100
Name: youtube.com
Address: 173.194.38.101
Name: youtube.com
Address: 173.194.38.102
Name: youtube.com
Address: 173.194.38.103
Name: youtube.com
Address: 173.194.38.104
Name: youtube.com
Address: 173.194.38.105
Name: youtube.com
Address: 173.194.38.106
Name: youtube.com
Address: 173.194.38.107
> exit
www.youtube.comなら正引き/逆引きでもヒットします。
# 最後の数字は違うかも
$ nslookup -sil
> www.youtube.com
Non-authoritative answer:
Name: www.youtube.com
Address: 74.125.235.76
> 74.125.235.76
Non-authoritative answer:
76.235.125.74.in-addr.arpa name = www.youtube.com.
Authoritative answers can be found from:
> exit