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Subnetting

IPv4 Classes

ClassLeading BitsStartEndSubnet Mask
A (CIDR /8) 0 0.0.0.0127.255.255.255255.0.0.0
B (CIDR /16)10 128.0.0.0191.255.255.255255.255.0.0
C (CIDR /24)110 192.0.0.0223.255.255.255255.255.255.0
D 1110224.0.0.0239.255.255.255Multicasting
E 1111240.0.0.0255.255.255.255Reserved

IANA-Reserved IPv4 Network Ranges

 StartEndNo. of Addresses
24-bit Block (/8 Prefix, 1 x A) 10.0.0.0 10.255.255.255 16,777,216
20-bit Block (/12 Prefix, 16 x B) 172.16.0.0 172.31.255.255 1,048,576
16-bit Block (/16 Prefix, 256 x C)192.168.0.0192.168.255.25565,536

Class C Host/Subnet Table

Class C BitsSubnet MaskEffective SubnetsEffective HostsNumber of Subnet
Mask Bits
Binary Suffix
0255.255.255.0 1 256/2400000000
1255.255.255.1282 126/2510000000
2255.255.255.1924 62/2611000000
3255.255.255.2248 30/2711100000
4255.255.255.24016 14/2811110000
5255.255.255.24832 6/2911111000
6255.255.255.25264 2/3011111100
Table from cisco.com and technically a /24 isn't strictly to the subnetting standard.

Class C Blocks

/25 -- 2 Subnets -- 126 Hosts/Subnet

Network #IP RangeBroadcast
.0 .1-.126 .127
.128.129-.254.255

/26 -- 4 Subnets -- 62 Hosts/Subnet

Network #IP RangeBroadcast
.0.1-.62 .63
.64.65-.126.127
.128.129-.190.191
.192.193-.254.255

/27 -- 8 Subnets -- 30 Hosts/Subnet

Network #IP RangeBroadcast
.0.1-.30 .31
.32.33-.62 .63
.64.65-.94 .95
.96.97-.126.127
.128.129-.158.159
.160.161-.190.191
.192.193-.222.223
.224.225-.254.255

/28 -- 16 Subnets -- 14 Hosts/Subnet

Network #IP RangeBroadcast
.0.1-.14.15
.16.17-.30.31
.32.33-.46.47
.48.49-.62.63
.64.65-.78.79
.80.81-.94.95
.96.97-.110.111
.112.113-.126.127
.128.129-.142.143
.144.145-.158.159
.160.161-.174.175
.176.177-.190.191
.192.193-.206.207
.208.209-.222.223
.224.225-.238.239
.240.241-.254.255

/29 -- 32 Subnets -- 6 Hosts/Subnet

Network #IP RangeBroadcast
.01-.6.7
.89-.14.15
.1617-.22.23
.2425-.30.31
.3233-.38.39
.4041-.46.47
.4849-.54.55
.5657-.62.63
.6465-.70.71
.7273-.78.79
.8081-.86.87
.8889-.94.95
.9697-.102.103
.104105-.110.111
.112113-.118.119
.120121-.126.127
.128129-.134.135
.136137-.142.143
.144.145-.150.151
.152.153-.158.159
.160.161-.166.167
.168.169-.174.175
.176.177-.182.183
.184.185-.190.191
.192.193-.198.199
.200.201-.206.207
.208.209-.214.215
.216.217-.222.223
.224.225-.230.231
.232.233-.238.239
.240.241-.246.247
.248.249-.254.255

/30 -- 64 Subnets -- 2 Hosts/Subnet

Network #IP RangeBroadcast
.0.1-.2.3
.4.5-.6.7
.8.9-.10.11
.12.13-.14.15
.16.17-.18.19
.20.21-.22.23
.24.25-.26.27
.28.29-.30.31
.32.33-.34.35
.36.37-.38.39
.40.41-.42.43
.44.45-.46.47
.48.49-.50.51
.52.53-.54.55
.56.57-.58.59
.60.61-.62.63
.64.65-.66.67
.68.69-.70.71
.72.73-.74.75
.76.77-.78.79
.80.81-.82.83
.84.85-.86.87
.88.89-.90.91
.92.93-.94.95
.96.97-.98.99
.100.101-.102.103
.104.105-.106.107
.108.109-.110.111
.112.113-.114.115
.116.117-.118.119
.120.121-.122.123
.124.125-.126.127
.128.129-.130.131
.132.133-.134.135
.136.137-.138.139
.140.141-.142.143
.144.145-.146.147
.148.149-.150.151
.152.153-.154.155
.156.157-.158.159
.160.161-.162.163
.164.165-.166.167
.168.169-.170.171
.172.173-.174.175
.176.177-.178.179
.180.181-.182.183
.184.185-.186.187
.188.189-.190.191
.192.193-.194.195
.196.197-.198.199
.200.201-.202.203
.204.205-.206.207
.208.209-.210.211
.212.213-.214.215
.216.217-.218.219
.220.221-.222.223
.224.225-.226.227
.228.229-.230.231
.232.233-.234.235
.236.237-.238.239
.240.241-.242.243
.244.245-.246.247
.248.249-.250.251
.252.253-.254.255
Class C Blocks tables from krow.net