CIDR Conversion Table

cidr notation accomplishes the same task as network subnet masking cidr defines which ip addresses, and how many host ip addresses are allowed on the network the following table details how many networks and ip addresses are allowed with each cidr length and equivalent subnet masks what does cidr mean? cidr stands for classless inter domain routing it enables network administrators to group blocks of ip addresses into single routing networks cidr accomplishes the same task as traditional subnet masking to understand what cidr notation means, take the ip address 192 168 0 15 and the /24 cidr, for example 192 168 0 15 defines the address prefix, and /24 defines the number of bits reserved for the netmask this means that the first 24 bits of the ip address are reserved for network routing thus, writing 192 168 0 15/24 means the same thing as using the 255 255 255 0 subnet mask for the 192 168 0 15 ip address this means that the last 8 bits of the ip address are reserved for host ip addresses, thus ip addresses 192 168 0 15 through 192 168 0 255 are allowed as host ip addresses on the network cidr conversion table cidr length mask number of networks number of hosts /1 128 0 0 0 128 a 2,147,483,392 /2 192 0 0 0 64 a 1,073,741,696 /3 224 0 0 0 32 a 536,870,848 /4 240 0 0 0 16 a 268,435,424 /5 248 0 0 0 8 a 134,217,712 /6 252 0 0 0 4 a 67,108,856 /7 254 0 0 0 2 a 33,554,428 /8 255 0 0 0 1 a 16,777,214 /9 255 128 0 0 128 b 8,388,352 /10 255 192 0 0 64 b 4,194,176 /11 255 224 0 0 32 b 2,097,088 /12 255 240 0 0 16 b 1,048,544 /13 255 248 0 0 8 b 524,272 /14 255 252 0 0 4 b 262,136 /15 255 254 0 0 2 b 131,068 /16 255 255 0 0 1 b 65,025 /17 255 255 128 0 128 c 32,512 /18 255 255 192 0 64 c 16,256 /19 255 255 224 0 32 c 8,128 /20 255 255 240 0 16 c 4,064 /21 255 255 248 0 8 c 2,032 /22 255 255 252 0 4 c 1,016 /23 255 255 254 0 2 c 508 /24 255 255 255 0 1 c 254 /25 255 255 255 128 2 subnets 124 /26 255 255 255 192 4 subnets 62 /27 255 255 255 224 8 subnets 30 /28 255 255 255 240 16 subnets 14 /29 255 255 255 248 32 subnets 6 /30 255 255 255 252 64 subnets 2 /31 255 255 255 254 none none /32 255 255 255 255 none 1 class a, b, and c networks the above table uses class a, b, and c to define network types network classes define how many addresses are allowed on the network, with class a being the largest and class c being the smallest specific size details are defined in the following class definitions class a allows 16777216 host addresses on the network the starting host address is 0 0 0 0 and the ending address is 127 0 0 0 these networks use the 255 0 0 0 subnet mask, or /8 cidr notation class b allows 65536 host addresses on the network the starting host address is 128 0 0 0 and the ending address is 191 255 0 0 these networks use the 255 255 0 0 subnet mask, or /16 cidr notation class c allows 256 host addresses on the network the starting host address is 192 0 0 0 and the ending address is 223 255 255 0 these networks use the 255 255 255 0 subnet mask, or /24 cidr notation