by 1 /32 255.255.255.255 0xffffffff
2 /31 255.255.255.254 0xfffffffe
4 /30 255.255.255.252 0xfffffffc
8 /29 255.255.255.248 0xfffffff8
16 /28 255.255.255.240 0xfffffff0
32 /27 255.255.255.224 0xffffffe0
64 /26 255.255.255.192 0xffffffc0
128 /25 255.255.255.128 0xffffff80
256 /24 255.255.255.0 0xffffff00
