IP Address Cheat Sheet
The Five IPv4 Classes:
Class Leading bits Start End Default Subnet Mask A (CIDR /8) 00000001 1.0.0.0 126.255.255.255 255.0.0.0 B (CIDR /16) 10000000 128.0.0.0 191.255.255.255 255.255.0.0 C (CIDR /24) 11000000 192.0.0.0 223.255.255.255 255.255.255.0 D 11100000 224.0.0.0 239.255.255.255 E 11110000 240.0.0.0 255.255.255.0
Possible subnets for a /8 suffix (traditional Class A):
CIDR Network Available Available Hosts Total notation Mask Networks per network usable hosts /8 256 255.0.0.0 1 16777214 16777214 00000000 /9 128 255.128.0.0 2 8388606 16777212 10000000 /10 64 255.192.0.0 4 4194302 16777208 11000000 /11 32 255.224.0.0 8 2097150 16777200 11100000 /12 16 255.240.0.0 16 1048574 16777184 11110000 /13 8 255.248.0.0 32 524286 16777152 11111000 /14 4 255.252.0.0 64 262142 16777088 11111100 /15 2 255.254.0.0 128 131070 16776960 11111110
Possible subnets for a /16 suffix (traditional Class B):
CIDR Network Available Available Hosts Total notation Mask Networks per network usable hosts /16 256 255.255.0.0 1 65534 65534 00000000 /17 128 255.255.128.0 2 32766 65532 10000000 /18 64 255.255.192.0 4 16382 65528 11000000 /19 32 255.255.224.0 8 8190 65520 11100000 /20 16 255.255.240.0 16 4094 65504 11110000 /21 8 255.255.248.0 32 2046 65472 11111000 /22 4 255.255.252.0 64 1022 65408 11111100 /23 2 255.255.254.0 128 510 65280 11111110
Possible subnets for a /24 suffix (traditional Class C):
CIDR Network Available Available Hosts Total notation Mask Networks per network usable hosts /24 256 255.255.255.0 1 254 254 00000000 /25 128 255.255.255.128 2 126 252 10000000 /26 64 255.255.255.192 4 62 248 11000000 /27 32 255.255.255.224 8 30 240 11100000 /28 16 255.255.255.240 16 14 224 11110000 /29 8 255.255.255.248 32 6 192 11111000 /30 4 255.255.255.252 64 2 128 11111100 /31 2 255.255.255.254 128 2 * 256 11111110 * only applicable on point-to-point links
The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private internets:
10.0.0.0 - 10.255.255.255 (10/8 prefix)
172.16.0.0 - 172.31.255.255 (172.16/12 prefix)
192.168.0.0 - 192.168.255.255 (192.168/16 prefix)
169.254.0.0 - 169.254.255.255 (Link-local/self assigned *)
We will refer to the first block as "24-bit block", the second as "20-bit block", and to the third as "16-bit" block. Note that (in pre-CIDR notation) the first block is nothing but a single class A network number, while the second block is a set of 16 contiguous class B network numbers, and third block is a set of 256 contiguous class C network numbers.
address from the reserved Link-local address range (169.254.0.0 - 169.254.255.255).
ping 127.0.0.1 is the diagnostic or loopback address.
Subnet Mask Blocks Hosts Subnets /22 .252 1024 1022 /23 .254 512 510 /24 .0 256 254 1 /25 .128 128 126 2 /26 .192 64 62 4 /27 .224 32 30 8 /28 .240 16 14 16 /29 .248 8 6 32 /30 .252 4 2 64 16 32 48 64 80 96 112 128 144 160 176 192 208 224 240 256