127.255.255.255 won't ping why?
do u mean ping fails? or other error ? is it in cisco routers?
this is a loopback broadcast. Interesting, but the 127 falls under the class A IP addresses. Without specification of subnetmask you wouldn't be able to ping the broadcast. Also, are you sure you created a loopback interface in the first place? you should either see a U.U.U etc for destination is Unreachable, or the pings will fail. Does this help what you are looking for?
if you ping 127.255.255.255, you should be able to get replay back from any other host in your range that's 127.x.x.x. This range is reserved for loopback.