All possible netmasks expanded. Netmask Netmask (binary) CIDR Notes 255.255.255.255 11111111.11111111.11111111.11111111 /32 Host (single address) 255.255.255.254 11111111.11111111.11111111.11111110 /31 Unuseable 255.255.255.252 11111111.11111111.11111111.11111100 /30 2 useable 255.255.255.248 11111111.11111111.11111111.11111000 /29 6 useable 255.255.255.240 11111111.11111111.11111111.11110000 /28 14 useable 255.255.255.224 11111111.11111111.11111111.11100000 /27 30 useable 255.255.255.192 11111111.11111111.11111111.11000000 /26 62 useable 255.255.255.128 11111111.11111111.11111111.10000000 /25 126 useable 255.255.255.0 11111111.11111111.11111111.00000000 /24 "Class C" 254 useable Netmask 255.255.255.0 /24 (11111111.11111111.11111111.00000000) 1 subnet LOW IP HI IP x.x.x.0 x.x.x.255 Netmask 255.255.255.128 /25 (11111111.11111111.11111111.10000000) 2 subnets LOW IP HI IP x.x.x.0 x.x.x.127 x.x.x.128 x.x.x.255 Netmask 255.255.255.192 /26 (11111111.11111111.11111111.11000000) 4 subnets x.x.x.0 x.x.x.63 x.x.x.64 x.x.x.127 x.x.x.128 x.x.x.191 x.x.x.192 x.x.x.255 Netmask 255.255.255.224 /27 (11111111.11111111.11111111.11100000) 8 subnets x.x.x.0 x.x.x.31 x.x.x.32 x.x.x.63 x.x.x.64 x.x.x.95 x.x.x.96 x.x.x.127 x.x.x.128 x.x.x.159 x.x.x.160 x.x.x.191 x.x.x.192 x.x.x.223 x.x.x.224 x.x.x.255 Netmask 255.255.255.240 /28 (11111111.11111111.11111111.11110000) 16 subnets x.x.x.0 x.x.x.15 x.x.x.16 x.x.x.31 x.x.x.32 x.x.x.47 x.x.x.48 x.x.x.63 x.x.x.64 x.x.x.79 x.x.x.80 x.x.x.95 x.x.x.96 x.x.x.111 x.x.x.112 x.x.x.127 x.x.x.128 x.x.x.143 x.x.x.144 x.x.x.159 x.x.x.160 x.x.x.175 x.x.x.176 x.x.x.191 x.x.x.192 x.x.x.207 x.x.x.208 x.x.x.223 x.x.x.224 x.x.x.239 x.x.x.240 x.x.x.255 Netmask 255.255.255.248 /29 (11111111.11111111.11111111.11111000) 32 subnets x.x.x.0 x.x.x.7 x.x.x.8 x.x.x.15 x.x.x.16 x.x.x.23 x.x.x.24 x.x.x.31 x.x.x.32 x.x.x.39 x.x.x.40 x.x.x.47 x.x.x.48 x.x.x.55 x.x.x.56 x.x.x.63 x.x.x.64 x.x.x.71 x.x.x.72 x.x.x.79 x.x.x.80 x.x.x.87 x.x.x.88 x.x.x.95 x.x.x.96 x.x.x.103 x.x.x.104 x.x.x.111 x.x.x.112 x.x.x.119 x.x.x.120 x.x.x.127 x.x.x.128 x.x.x.135 x.x.x.136 x.x.x.143 x.x.x.144 x.x.x.151 x.x.x.152 x.x.x.159 x.x.x.160 x.x.x.167 x.x.x.168 x.x.x.175 x.x.x.176 x.x.x.183 x.x.x.184 x.x.x.191 x.x.x.192 x.x.x.199 x.x.x.200 x.x.x.207 x.x.x.208 x.x.x.215 x.x.x.216 x.x.x.223 x.x.x.224 x.x.x.231 x.x.x.232 x.x.x.239 x.x.x.240 x.x.x.247 x.x.x.248 x.x.x.255 Netmask 255.255.255.252 /30 (11111111.11111111.11111111.11111100) 64 subnets LOW IP HI IP x.x.x.0 x.x.x.3 x.x.x.4 x.x.x.7 x.x.x.8 x.x.x.11 x.x.x.12 x.x.x.15 x.x.x.16 x.x.x.19 x.x.x.20 x.x.x.23 x.x.x.24 x.x.x.27 x.x.x.28 x.x.x.31 x.x.x.32 x.x.x.35 x.x.x.36 x.x.x.39 x.x.x.40 x.x.x.43 x.x.x.44 x.x.x.47 x.x.x.48 x.x.x.51 x.x.x.52 x.x.x.55 x.x.x.56 x.x.x.59 x.x.x.60 x.x.x.63 x.x.x.64 x.x.x.67 x.x.x.68 x.x.x.71 x.x.x.72 x.x.x.75 x.x.x.76 x.x.x.79 x.x.x.80 x.x.x.83 x.x.x.84 x.x.x.87 x.x.x.88 x.x.x.91 x.x.x.92 x.x.x.95 x.x.x.96 x.x.x.99 x.x.x.100 x.x.x.103 x.x.x.104 x.x.x.107 x.x.x.108 x.x.x.111 x.x.x.112 x.x.x.115 x.x.x.116 x.x.x.119 x.x.x.120 x.x.x.123 x.x.x.124 x.x.x.127 x.x.x.128 x.x.x.131 x.x.x.132 x.x.x.135 x.x.x.136 x.x.x.139 x.x.x.140 x.x.x.143 x.x.x.144 x.x.x.147 x.x.x.148 x.x.x.151 x.x.x.152 x.x.x.155 x.x.x.156 x.x.x.159 x.x.x.160 x.x.x.163 x.x.x.164 x.x.x.167 x.x.x.168 x.x.x.171 x.x.x.172 x.x.x.175 x.x.x.176 x.x.x.179 x.x.x.180 x.x.x.183 x.x.x.184 x.x.x.187 x.x.x.188 x.x.x.191 x.x.x.192 x.x.x.195 x.x.x.196 x.x.x.199 x.x.x.200 x.x.x.203 x.x.x.204 x.x.x.207 x.x.x.208 x.x.x.211 x.x.x.212 x.x.x.215 x.x.x.216 x.x.x.219 x.x.x.220 x.x.x.223 x.x.x.224 x.x.x.227 x.x.x.228 x.x.x.231 x.x.x.232 x.x.x.235 x.x.x.236 x.x.x.239 x.x.x.240 x.x.x.243 x.x.x.244 x.x.x.247 x.x.x.248 x.x.x.251 x.x.x.252 x.x.x.255 net mask: 1111 11 00 == 252 Pozar's two-bit(tm) addressing 4-bit m m m m 2-bit m m (.1) 0 0 0 0 0 0 0 1 (.2) 0 0 0 0 0 0 1 0 (.17) 0 0 0 1 0 0 0 1 (.18) 0 0 0 1 0 0 1 0 (.33) 0 0 1 0 0 0 0 1 (.34) 0 0 1 0 0 0 1 0 (.49) 0 0 1 1 0 0 0 1 (.50) 0 0 1 1 0 0 1 0 (.65) 0 1 0 0 0 0 0 1 (.66) 0 1 0 0 0 0 1 0 (.129) 1 0 0 0 0 0 0 1 (.130) 1 0 0 0 0 0 1 0 (.193) 1 1 0 0 0 0 0 1 (.194) 1 1 0 0 0 0 1 0 (.225) 1 1 1 0 0 0 0 1 (.226) 1 1 1 0 0 0 1 0 CIDR: Classless Inter-Domain Routing -- Standard Boundaries (inverse mask) Netmask bits # IPs # C's source-wildcard 255.255.255.255 /32 1 < 0.0.0.0 255.255.255.254 /31 2 < 0.0.0.1 255.255.255.252 /30 4 < 0.0.0.3 255.255.255.248 /29 8 < 0.0.0.7 255.255.255.240 /28 16 < 0.0.0.15 255.255.255.224 /27 32 < 0.0.0.31 255.255.255.192 /26 64 < 0.0.0.63 255.255.255.128 /25 128 < 0.0.0.127 255.255.255.0 /24 256 1 0.0.0.255 255.255.254.0 /23 512 2 0.0.1.255 255.255.252.0 /22 1024 4 0.0.3.255 255.255.248.0 /21 2048 8 0.0.7.255 255.255.240.0 /20 4096 16 0.0.15.255 255.255.224.0 /19 8192 32 0.0.31.255 255.255.192.0 /18 16384 64 0.0.63.255 255.255.128.0 /17 32768 128 0.0.127.255 255.255.0.0 /16 65536 256 0.0.255.255 255.254.0.0 /15 131072 512 0.1.255.255 255.252.0.0 /14 262144 1024 0.3.255.255 255.248.0.0 /13 524288 2048 0.7.255.255 255.240.0.0 /12 1048576 4096 0.15.255.255 255.224.0.0 /11 2097152 8192 0.31.255.255 255.192.0.0 /10 4194304 16384 0.63.255.255 255.128.0.0 /9 8388608 32768 0.127.255.255 255.0.0.0 /8 16777216 65536 0.255.255.255 254.0.0.0 /7 33554432 131072 1.255.255.255 252.0.0.0 /6 67108864 262144 3.255.255.255 248.0.0.0 /5 134217.72K 524288 7.255.255.255 240.0.0.0 /4 268435.44K 1048576 15.255.255.255 224.0.0.0 /3 536870.88K 2097152 31.255.255.255 192.0.0.0 /2 1073741.7K 4194304 63.255.255.255 128.0.0.0 /1 2147483.4K 8388608 127.255.255.255 0.0.0.0 /0 4294966.8K 16777216 255.255.255.255 ---------- Here's some general rules about how this allocation works. Keep in mind that all of these "masks" are really based on binary AND/OR masking, thus a decimal "255" is binary 11111111 and a decimal "0" is binary "00000000". Here's a little table in binary which may be of help: 255.255.255.255 /32 11111111.11111111.11111111.11111111 255.255.255.254 /31 11111111.11111111.11111111.11111110 255.255.255.252 /30 11111111.11111111.11111111.11111100 255.255.255.248 /29 11111111.11111111.11111111.11111000 255.255.255.240 /28 11111111.11111111.11111111.11110000 255.255.255.224 /27 11111111.11111111.11111111.11100000 255.255.255.192 /26 11111111.11111111.11111111.11000000 255.255.255.128 /25 11111111.11111111.11111111.10000000 255.255.255.0 /24 11111111.11111111.11111111.00000000 255.255.254.0 /23 11111111.11111111.11111110.00000000 255.255.252.0 /22 11111111.11111111.11111100.00000000 255.255.248.0 /21 11111111.11111111.11111000.00000000 255.255.240.0 /20 11111111.11111111.11110000.00000000 255.255.224.0 /19 11111111.11111111.11100000.00000000 255.255.192.0 /18 11111111.11111111.11000000.00000000 255.255.128.0 /17 11111111.11111111.10000000.00000000 255.255.0.0 /16 11111111.11111111.00000000.00000000 ... etc ... A /32 is an allocation of 1 IP, and there is 256 /32's in a /24. A /31 is an allocation of 2 IP's, and there is 128 /31's in a /24. A /30 is an allocation of 4 IP's, and there is 64 /30's in a /24. A /29 is an allocation of 8 IP's, and there is 32 /29's in a /24. A /28 is an allocation of 16 IP's, and there is 16 /28's in a /24. A /27 is an allocation of 32 IP's, and there is 8 /27's in a /24. A /26 is an allocation of 64 IP's, and there is 4 /26's in a /24. A /25 is an allocation of 128 IP's, and there is 2 /25's in a /24. A /24 is an allocation of 256 IP's, and there is 1 /24 in a /24. ---------- Starting "Network" IP address of Subnetted /24's (last octet value): NOTE: *0 - Zero subnet may not functional on ALL CPE types /32: Any IP is an individual /32. /31: IP evenly divisible by 2. (e.g. *0,2,4,6,8,10,12,14,16,18 ... 252,254) /30: IP evenly divisible by 4. (e.g. *0,4,8,12,16,20,24,28,32, ... 248,252) /29: IP evenly divisible by 8. (e.g. *0,8,16,24,32,40,48,56,64, ... 240,248) /28: IP evenly divisible by 16. (e.g. *0,16,32,48,64,80,96,112, ... 224,240) /27: IP evenly divisible by 32. (e.g. *0,32,64,96,128,160,192,224) /26: IP evenly divisible by 64. (e.g. *0,64,128,192) --