link redireciona para o link que tem um IP diferente Endereço do que facebook.com. Há também o ssl.facebook.com, mas não tenho certeza do que é usado:
$ host facebook.com
facebook.com has address 69.171.229.11
facebook.com has address 69.171.224.37
facebook.com has address 66.220.158.11
facebook.com has address 66.220.149.11
facebook.com has address 69.171.242.11
facebook.com has IPv6 address 2a03:2880:10:1f02:face:b00c:0:25
facebook.com has IPv6 address 2a03:2880:2110:3f01:face:b00c::
facebook.com has IPv6 address 2a03:2880:10:8f01:face:b00c:0:25
facebook.com mail is handled by 10 smtpin.mx.facebook.com.
$ host www.facebook.com
www.facebook.com has address 69.171.237.16
www.facebook.com has IPv6 address 2a03:2880:10:1f03:face:b00c:0:25
$ host ssl.facebook.com
ssl.facebook.com is an alias for star.facebook.com.
star.facebook.com has address 69.171.234.39
star.facebook.com has IPv6 address 2a03:2880:10:cf02:face:b00c:0:4
Para o java.com, por outro lado, as entradas são as mesmas para ambos os sites: www.java.com e java.com:
$ host java.com
java.com has address 137.254.16.66
java.com mail is handled by 10 mx5.sun.com.
java.com mail is handled by 10 mx6.sun.com.
java.com mail is handled by 10 mx8.sun.com.
java.com mail is handled by 10 mx9.sun.com.
$ host www.java.com
www.java.com is an alias for java.com.
java.com has address 137.254.16.66
java.com mail is handled by 10 mx5.sun.com.
java.com mail is handled by 10 mx6.sun.com.
java.com mail is handled by 10 mx8.sun.com.
java.com mail is handled by 10 mx9.sun.com.