8000 256 512 1024 2048 4096 beyond
	8 9  10   11   12   13
32-13=19   /19=2^13

ip zero-subnet  ==> .1.0 (subnet) can be used 
.1.0/26 ==> .1.0 ~ .1.63 ==> total 64 ip
.1.0 (iP), .1.63 (ip) cannot be used
.1.1 ~.1.62 (62 ip)

/16    172.16.0.0
/18    172.16.64.0 ~ 172.16.127.255
/19    172.16.128.0~172.16.159.255

cost = 100 M / bandwidth
100Mbps = 1
10Mbps  = 10
56Kbps = 1785