Q:

Why does the "network" line need to be inside the interface file

In almost all the network configuration examples I can find, I always see this "network" line appear with an address ending in .0.   
auto eth0 iface eth0 inet static
    address 192.168.1.100
    netmask 255.255.255.0
 -> network 192.168.1.0
    broadcast 192.168.1.255
    gateway 192.168.1.1

According to this post, the value can be found by applying the mask to the IP using a logical AND.  If this is the case, why does the line even need to be in the file?  Can I remove it?

A:

It is the network address - see the man page here 
http://manpages.ubuntu.com/manpages/intrepid/man5/interfaces.5.html
If you know your IP and Netmask you can work out the Network address:
IP: 192.168.1.10
Netmask: 255.255.255.0
(Netmask means match first 3 chunks of your IP exactly and any for the last bit)
Network address: 192.168.1.0

Usually meaning that devices on your network will have an IP between 192.168.1.1 and 192.168.1.254
http://en.wikipedia.org/wiki/Subnetwork
Note: I have used interfaces files on several different Linux flavours and left out Network Address and its worked just fine. If it bothers you that much; backup, remove it and try!

