It would help if you post your /etc/sysconfig/network file in it's entirety! Not knowing the other lines makes it very difficult to figure out what it means!
Also, whenever your ask a question about system related things you should always say which distro you are using. I am assuming it is one of the Fedora's but for a question like this one knowing what distro you are running is very important!
As for your second question :
2 )Nsswitch :
I know nsswitch means "Name Service Swich" but i can't understand what is it's activity .
A little more info would help! Is this a file name?, a line in a file?, if so which one?, a command?, an app? I don't know what it means straight off the top of my head, but if I know where you saw it I will be able to find out for you.