Usefull network scripts for linux

Hi all,
You can find a few usefull scripts about networking.

Which server is down (not network reachable) ?

while read serverip; do result="";
 result=`ping $serverip -c 1 -W 1|grep "100% packet loss"`; 
 test -n "$result" && echo $serverip;  
done < iplist.txt
# iplist.txt: contains server ip addresses.