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IP subnet calculator

Type an address with its prefix or mask to see the network, its usable range and masks. Split it into smaller subnets, or look up any prefix in the reference tables.

Network247.3.0.0/21
Usable hosts2,046
Subnet mask255.255.248.0
Addresses2,048
Network address
247.3.0.0
Broadcast address
247.3.7.255
First usable
247.3.0.1
Last usable
247.3.7.254
Usable hosts
2,046 (2,048 less the network and broadcast addresses)
Subnet mask
255.255.248.0
Wildcard mask
0.0.7.255 (Cisco ACLs, OSPF)
Prefix length
/21
Type
Reserved 240.0.0.0/4
Future use; not usable on most systems
Old class
E (reserved)
As numbers
Hex F7030000 · Integer 4144168960 to 4144171007
Reverse DNS zones
0.3.247.in-addr.arpa
1.3.247.in-addr.arpa
2.3.247.in-addr.arpa
3.3.247.in-addr.arpa
4.3.247.in-addr.arpa
5.3.247.in-addr.arpa
6.3.247.in-addr.arpa
7.3.247.in-addr.arpa
/21 is not on a 8-bit boundary, so it takes 8 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11110111.00000011.00000000.00000000247.3.0.0
Subnet mask11111111.11111111.11111000.00000000255.255.248.0
Network11110111.00000011.00000000.00000000247.3.0.0
Broadcast11110111.00000011.00000111.11111111247.3.7.255
Split into smaller subnets/30
/22 (2)/23 (4)/24 (8)/25 (16)/26 (32)/27 (64)/28 (128)/29 (256)/30 (512)/31 (1,024)/32 (2,048)

247.3.0.0/21 makes 512 subnets of /30; the first 256 are listed.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1247.3.0.0/30247.3.0.1 to 247.3.0.2247.3.0.32
2247.3.0.4/30247.3.0.5 to 247.3.0.6247.3.0.72
3247.3.0.8/30247.3.0.9 to 247.3.0.10247.3.0.112
4247.3.0.12/30247.3.0.13 to 247.3.0.14247.3.0.152
5247.3.0.16/30247.3.0.17 to 247.3.0.18247.3.0.192
6247.3.0.20/30247.3.0.21 to 247.3.0.22247.3.0.232
7247.3.0.24/30247.3.0.25 to 247.3.0.26247.3.0.272
8247.3.0.28/30247.3.0.29 to 247.3.0.30247.3.0.312
9247.3.0.32/30247.3.0.33 to 247.3.0.34247.3.0.352
10247.3.0.36/30247.3.0.37 to 247.3.0.38247.3.0.392
11247.3.0.40/30247.3.0.41 to 247.3.0.42247.3.0.432
12247.3.0.44/30247.3.0.45 to 247.3.0.46247.3.0.472
13247.3.0.48/30247.3.0.49 to 247.3.0.50247.3.0.512
14247.3.0.52/30247.3.0.53 to 247.3.0.54247.3.0.552
15247.3.0.56/30247.3.0.57 to 247.3.0.58247.3.0.592
16247.3.0.60/30247.3.0.61 to 247.3.0.62247.3.0.632
17247.3.0.64/30247.3.0.65 to 247.3.0.66247.3.0.672
18247.3.0.68/30247.3.0.69 to 247.3.0.70247.3.0.712
19247.3.0.72/30247.3.0.73 to 247.3.0.74247.3.0.752
20247.3.0.76/30247.3.0.77 to 247.3.0.78247.3.0.792
21247.3.0.80/30247.3.0.81 to 247.3.0.82247.3.0.832
22247.3.0.84/30247.3.0.85 to 247.3.0.86247.3.0.872
23247.3.0.88/30247.3.0.89 to 247.3.0.90247.3.0.912
24247.3.0.92/30247.3.0.93 to 247.3.0.94247.3.0.952
25247.3.0.96/30247.3.0.97 to 247.3.0.98247.3.0.992
26247.3.0.100/30247.3.0.101 to 247.3.0.102247.3.0.1032
27247.3.0.104/30247.3.0.105 to 247.3.0.106247.3.0.1072
28247.3.0.108/30247.3.0.109 to 247.3.0.110247.3.0.1112
29247.3.0.112/30247.3.0.113 to 247.3.0.114247.3.0.1152
30247.3.0.116/30247.3.0.117 to 247.3.0.118247.3.0.1192
31247.3.0.120/30247.3.0.121 to 247.3.0.122247.3.0.1232
32247.3.0.124/30247.3.0.125 to 247.3.0.126247.3.0.1272
33247.3.0.128/30247.3.0.129 to 247.3.0.130247.3.0.1312
34247.3.0.132/30247.3.0.133 to 247.3.0.134247.3.0.1352
35247.3.0.136/30247.3.0.137 to 247.3.0.138247.3.0.1392
36247.3.0.140/30247.3.0.141 to 247.3.0.142247.3.0.1432
37247.3.0.144/30247.3.0.145 to 247.3.0.146247.3.0.1472
38247.3.0.148/30247.3.0.149 to 247.3.0.150247.3.0.1512
39247.3.0.152/30247.3.0.153 to 247.3.0.154247.3.0.1552
40247.3.0.156/30247.3.0.157 to 247.3.0.158247.3.0.1592
41247.3.0.160/30247.3.0.161 to 247.3.0.162247.3.0.1632
42247.3.0.164/30247.3.0.165 to 247.3.0.166247.3.0.1672
43247.3.0.168/30247.3.0.169 to 247.3.0.170247.3.0.1712
44247.3.0.172/30247.3.0.173 to 247.3.0.174247.3.0.1752
45247.3.0.176/30247.3.0.177 to 247.3.0.178247.3.0.1792
46247.3.0.180/30247.3.0.181 to 247.3.0.182247.3.0.1832
47247.3.0.184/30247.3.0.185 to 247.3.0.186247.3.0.1872
48247.3.0.188/30247.3.0.189 to 247.3.0.190247.3.0.1912
49247.3.0.192/30247.3.0.193 to 247.3.0.194247.3.0.1952
50247.3.0.196/30247.3.0.197 to 247.3.0.198247.3.0.1992
51247.3.0.200/30247.3.0.201 to 247.3.0.202247.3.0.2032
52247.3.0.204/30247.3.0.205 to 247.3.0.206247.3.0.2072
53247.3.0.208/30247.3.0.209 to 247.3.0.210247.3.0.2112
54247.3.0.212/30247.3.0.213 to 247.3.0.214247.3.0.2152
55247.3.0.216/30247.3.0.217 to 247.3.0.218247.3.0.2192
56247.3.0.220/30247.3.0.221 to 247.3.0.222247.3.0.2232
57247.3.0.224/30247.3.0.225 to 247.3.0.226247.3.0.2272
58247.3.0.228/30247.3.0.229 to 247.3.0.230247.3.0.2312
59247.3.0.232/30247.3.0.233 to 247.3.0.234247.3.0.2352
60247.3.0.236/30247.3.0.237 to 247.3.0.238247.3.0.2392
61247.3.0.240/30247.3.0.241 to 247.3.0.242247.3.0.2432
62247.3.0.244/30247.3.0.245 to 247.3.0.246247.3.0.2472
63247.3.0.248/30247.3.0.249 to 247.3.0.250247.3.0.2512
64247.3.0.252/30247.3.0.253 to 247.3.0.254247.3.0.2552
65247.3.1.0/30247.3.1.1 to 247.3.1.2247.3.1.32
66247.3.1.4/30247.3.1.5 to 247.3.1.6247.3.1.72
67247.3.1.8/30247.3.1.9 to 247.3.1.10247.3.1.112
68247.3.1.12/30247.3.1.13 to 247.3.1.14247.3.1.152
69247.3.1.16/30247.3.1.17 to 247.3.1.18247.3.1.192
70247.3.1.20/30247.3.1.21 to 247.3.1.22247.3.1.232
71247.3.1.24/30247.3.1.25 to 247.3.1.26247.3.1.272
72247.3.1.28/30247.3.1.29 to 247.3.1.30247.3.1.312
73247.3.1.32/30247.3.1.33 to 247.3.1.34247.3.1.352
74247.3.1.36/30247.3.1.37 to 247.3.1.38247.3.1.392
75247.3.1.40/30247.3.1.41 to 247.3.1.42247.3.1.432
76247.3.1.44/30247.3.1.45 to 247.3.1.46247.3.1.472
77247.3.1.48/30247.3.1.49 to 247.3.1.50247.3.1.512
78247.3.1.52/30247.3.1.53 to 247.3.1.54247.3.1.552
79247.3.1.56/30247.3.1.57 to 247.3.1.58247.3.1.592
80247.3.1.60/30247.3.1.61 to 247.3.1.62247.3.1.632
81247.3.1.64/30247.3.1.65 to 247.3.1.66247.3.1.672
82247.3.1.68/30247.3.1.69 to 247.3.1.70247.3.1.712
83247.3.1.72/30247.3.1.73 to 247.3.1.74247.3.1.752
84247.3.1.76/30247.3.1.77 to 247.3.1.78247.3.1.792
85247.3.1.80/30247.3.1.81 to 247.3.1.82247.3.1.832
86247.3.1.84/30247.3.1.85 to 247.3.1.86247.3.1.872
87247.3.1.88/30247.3.1.89 to 247.3.1.90247.3.1.912
88247.3.1.92/30247.3.1.93 to 247.3.1.94247.3.1.952
89247.3.1.96/30247.3.1.97 to 247.3.1.98247.3.1.992
90247.3.1.100/30247.3.1.101 to 247.3.1.102247.3.1.1032
91247.3.1.104/30247.3.1.105 to 247.3.1.106247.3.1.1072
92247.3.1.108/30247.3.1.109 to 247.3.1.110247.3.1.1112
93247.3.1.112/30247.3.1.113 to 247.3.1.114247.3.1.1152
94247.3.1.116/30247.3.1.117 to 247.3.1.118247.3.1.1192
95247.3.1.120/30247.3.1.121 to 247.3.1.122247.3.1.1232
96247.3.1.124/30247.3.1.125 to 247.3.1.126247.3.1.1272
97247.3.1.128/30247.3.1.129 to 247.3.1.130247.3.1.1312
98247.3.1.132/30247.3.1.133 to 247.3.1.134247.3.1.1352
99247.3.1.136/30247.3.1.137 to 247.3.1.138247.3.1.1392
100247.3.1.140/30247.3.1.141 to 247.3.1.142247.3.1.1432
101247.3.1.144/30247.3.1.145 to 247.3.1.146247.3.1.1472
102247.3.1.148/30247.3.1.149 to 247.3.1.150247.3.1.1512
103247.3.1.152/30247.3.1.153 to 247.3.1.154247.3.1.1552
104247.3.1.156/30247.3.1.157 to 247.3.1.158247.3.1.1592
105247.3.1.160/30247.3.1.161 to 247.3.1.162247.3.1.1632
106247.3.1.164/30247.3.1.165 to 247.3.1.166247.3.1.1672
107247.3.1.168/30247.3.1.169 to 247.3.1.170247.3.1.1712
108247.3.1.172/30247.3.1.173 to 247.3.1.174247.3.1.1752
109247.3.1.176/30247.3.1.177 to 247.3.1.178247.3.1.1792
110247.3.1.180/30247.3.1.181 to 247.3.1.182247.3.1.1832
111247.3.1.184/30247.3.1.185 to 247.3.1.186247.3.1.1872
112247.3.1.188/30247.3.1.189 to 247.3.1.190247.3.1.1912
113247.3.1.192/30247.3.1.193 to 247.3.1.194247.3.1.1952
114247.3.1.196/30247.3.1.197 to 247.3.1.198247.3.1.1992
115247.3.1.200/30247.3.1.201 to 247.3.1.202247.3.1.2032
116247.3.1.204/30247.3.1.205 to 247.3.1.206247.3.1.2072
117247.3.1.208/30247.3.1.209 to 247.3.1.210247.3.1.2112
118247.3.1.212/30247.3.1.213 to 247.3.1.214247.3.1.2152
119247.3.1.216/30247.3.1.217 to 247.3.1.218247.3.1.2192
120247.3.1.220/30247.3.1.221 to 247.3.1.222247.3.1.2232
121247.3.1.224/30247.3.1.225 to 247.3.1.226247.3.1.2272
122247.3.1.228/30247.3.1.229 to 247.3.1.230247.3.1.2312
123247.3.1.232/30247.3.1.233 to 247.3.1.234247.3.1.2352
124247.3.1.236/30247.3.1.237 to 247.3.1.238247.3.1.2392
125247.3.1.240/30247.3.1.241 to 247.3.1.242247.3.1.2432
126247.3.1.244/30247.3.1.245 to 247.3.1.246247.3.1.2472
127247.3.1.248/30247.3.1.249 to 247.3.1.250247.3.1.2512
128247.3.1.252/30247.3.1.253 to 247.3.1.254247.3.1.2552
129247.3.2.0/30247.3.2.1 to 247.3.2.2247.3.2.32
130247.3.2.4/30247.3.2.5 to 247.3.2.6247.3.2.72
131247.3.2.8/30247.3.2.9 to 247.3.2.10247.3.2.112
132247.3.2.12/30247.3.2.13 to 247.3.2.14247.3.2.152
133247.3.2.16/30247.3.2.17 to 247.3.2.18247.3.2.192
134247.3.2.20/30247.3.2.21 to 247.3.2.22247.3.2.232
135247.3.2.24/30247.3.2.25 to 247.3.2.26247.3.2.272
136247.3.2.28/30247.3.2.29 to 247.3.2.30247.3.2.312
137247.3.2.32/30247.3.2.33 to 247.3.2.34247.3.2.352
138247.3.2.36/30247.3.2.37 to 247.3.2.38247.3.2.392
139247.3.2.40/30247.3.2.41 to 247.3.2.42247.3.2.432
140247.3.2.44/30247.3.2.45 to 247.3.2.46247.3.2.472
141247.3.2.48/30247.3.2.49 to 247.3.2.50247.3.2.512
142247.3.2.52/30247.3.2.53 to 247.3.2.54247.3.2.552
143247.3.2.56/30247.3.2.57 to 247.3.2.58247.3.2.592
144247.3.2.60/30247.3.2.61 to 247.3.2.62247.3.2.632
145247.3.2.64/30247.3.2.65 to 247.3.2.66247.3.2.672
146247.3.2.68/30247.3.2.69 to 247.3.2.70247.3.2.712
147247.3.2.72/30247.3.2.73 to 247.3.2.74247.3.2.752
148247.3.2.76/30247.3.2.77 to 247.3.2.78247.3.2.792
149247.3.2.80/30247.3.2.81 to 247.3.2.82247.3.2.832
150247.3.2.84/30247.3.2.85 to 247.3.2.86247.3.2.872
151247.3.2.88/30247.3.2.89 to 247.3.2.90247.3.2.912
152247.3.2.92/30247.3.2.93 to 247.3.2.94247.3.2.952
153247.3.2.96/30247.3.2.97 to 247.3.2.98247.3.2.992
154247.3.2.100/30247.3.2.101 to 247.3.2.102247.3.2.1032
155247.3.2.104/30247.3.2.105 to 247.3.2.106247.3.2.1072
156247.3.2.108/30247.3.2.109 to 247.3.2.110247.3.2.1112
157247.3.2.112/30247.3.2.113 to 247.3.2.114247.3.2.1152
158247.3.2.116/30247.3.2.117 to 247.3.2.118247.3.2.1192
159247.3.2.120/30247.3.2.121 to 247.3.2.122247.3.2.1232
160247.3.2.124/30247.3.2.125 to 247.3.2.126247.3.2.1272
161247.3.2.128/30247.3.2.129 to 247.3.2.130247.3.2.1312
162247.3.2.132/30247.3.2.133 to 247.3.2.134247.3.2.1352
163247.3.2.136/30247.3.2.137 to 247.3.2.138247.3.2.1392
164247.3.2.140/30247.3.2.141 to 247.3.2.142247.3.2.1432
165247.3.2.144/30247.3.2.145 to 247.3.2.146247.3.2.1472
166247.3.2.148/30247.3.2.149 to 247.3.2.150247.3.2.1512
167247.3.2.152/30247.3.2.153 to 247.3.2.154247.3.2.1552
168247.3.2.156/30247.3.2.157 to 247.3.2.158247.3.2.1592
169247.3.2.160/30247.3.2.161 to 247.3.2.162247.3.2.1632
170247.3.2.164/30247.3.2.165 to 247.3.2.166247.3.2.1672
171247.3.2.168/30247.3.2.169 to 247.3.2.170247.3.2.1712
172247.3.2.172/30247.3.2.173 to 247.3.2.174247.3.2.1752
173247.3.2.176/30247.3.2.177 to 247.3.2.178247.3.2.1792
174247.3.2.180/30247.3.2.181 to 247.3.2.182247.3.2.1832
175247.3.2.184/30247.3.2.185 to 247.3.2.186247.3.2.1872
176247.3.2.188/30247.3.2.189 to 247.3.2.190247.3.2.1912
177247.3.2.192/30247.3.2.193 to 247.3.2.194247.3.2.1952
178247.3.2.196/30247.3.2.197 to 247.3.2.198247.3.2.1992
179247.3.2.200/30247.3.2.201 to 247.3.2.202247.3.2.2032
180247.3.2.204/30247.3.2.205 to 247.3.2.206247.3.2.2072
181247.3.2.208/30247.3.2.209 to 247.3.2.210247.3.2.2112
182247.3.2.212/30247.3.2.213 to 247.3.2.214247.3.2.2152
183247.3.2.216/30247.3.2.217 to 247.3.2.218247.3.2.2192
184247.3.2.220/30247.3.2.221 to 247.3.2.222247.3.2.2232
185247.3.2.224/30247.3.2.225 to 247.3.2.226247.3.2.2272
186247.3.2.228/30247.3.2.229 to 247.3.2.230247.3.2.2312
187247.3.2.232/30247.3.2.233 to 247.3.2.234247.3.2.2352
188247.3.2.236/30247.3.2.237 to 247.3.2.238247.3.2.2392
189247.3.2.240/30247.3.2.241 to 247.3.2.242247.3.2.2432
190247.3.2.244/30247.3.2.245 to 247.3.2.246247.3.2.2472
191247.3.2.248/30247.3.2.249 to 247.3.2.250247.3.2.2512
192247.3.2.252/30247.3.2.253 to 247.3.2.254247.3.2.2552
193247.3.3.0/30247.3.3.1 to 247.3.3.2247.3.3.32
194247.3.3.4/30247.3.3.5 to 247.3.3.6247.3.3.72
195247.3.3.8/30247.3.3.9 to 247.3.3.10247.3.3.112
196247.3.3.12/30247.3.3.13 to 247.3.3.14247.3.3.152
197247.3.3.16/30247.3.3.17 to 247.3.3.18247.3.3.192
198247.3.3.20/30247.3.3.21 to 247.3.3.22247.3.3.232
199247.3.3.24/30247.3.3.25 to 247.3.3.26247.3.3.272
200247.3.3.28/30247.3.3.29 to 247.3.3.30247.3.3.312
201247.3.3.32/30247.3.3.33 to 247.3.3.34247.3.3.352
202247.3.3.36/30247.3.3.37 to 247.3.3.38247.3.3.392
203247.3.3.40/30247.3.3.41 to 247.3.3.42247.3.3.432
204247.3.3.44/30247.3.3.45 to 247.3.3.46247.3.3.472
205247.3.3.48/30247.3.3.49 to 247.3.3.50247.3.3.512
206247.3.3.52/30247.3.3.53 to 247.3.3.54247.3.3.552
207247.3.3.56/30247.3.3.57 to 247.3.3.58247.3.3.592
208247.3.3.60/30247.3.3.61 to 247.3.3.62247.3.3.632
209247.3.3.64/30247.3.3.65 to 247.3.3.66247.3.3.672
210247.3.3.68/30247.3.3.69 to 247.3.3.70247.3.3.712
211247.3.3.72/30247.3.3.73 to 247.3.3.74247.3.3.752
212247.3.3.76/30247.3.3.77 to 247.3.3.78247.3.3.792
213247.3.3.80/30247.3.3.81 to 247.3.3.82247.3.3.832
214247.3.3.84/30247.3.3.85 to 247.3.3.86247.3.3.872
215247.3.3.88/30247.3.3.89 to 247.3.3.90247.3.3.912
216247.3.3.92/30247.3.3.93 to 247.3.3.94247.3.3.952
217247.3.3.96/30247.3.3.97 to 247.3.3.98247.3.3.992
218247.3.3.100/30247.3.3.101 to 247.3.3.102247.3.3.1032
219247.3.3.104/30247.3.3.105 to 247.3.3.106247.3.3.1072
220247.3.3.108/30247.3.3.109 to 247.3.3.110247.3.3.1112
221247.3.3.112/30247.3.3.113 to 247.3.3.114247.3.3.1152
222247.3.3.116/30247.3.3.117 to 247.3.3.118247.3.3.1192
223247.3.3.120/30247.3.3.121 to 247.3.3.122247.3.3.1232
224247.3.3.124/30247.3.3.125 to 247.3.3.126247.3.3.1272
225247.3.3.128/30247.3.3.129 to 247.3.3.130247.3.3.1312
226247.3.3.132/30247.3.3.133 to 247.3.3.134247.3.3.1352
227247.3.3.136/30247.3.3.137 to 247.3.3.138247.3.3.1392
228247.3.3.140/30247.3.3.141 to 247.3.3.142247.3.3.1432
229247.3.3.144/30247.3.3.145 to 247.3.3.146247.3.3.1472
230247.3.3.148/30247.3.3.149 to 247.3.3.150247.3.3.1512
231247.3.3.152/30247.3.3.153 to 247.3.3.154247.3.3.1552
232247.3.3.156/30247.3.3.157 to 247.3.3.158247.3.3.1592
233247.3.3.160/30247.3.3.161 to 247.3.3.162247.3.3.1632
234247.3.3.164/30247.3.3.165 to 247.3.3.166247.3.3.1672
235247.3.3.168/30247.3.3.169 to 247.3.3.170247.3.3.1712
236247.3.3.172/30247.3.3.173 to 247.3.3.174247.3.3.1752
237247.3.3.176/30247.3.3.177 to 247.3.3.178247.3.3.1792
238247.3.3.180/30247.3.3.181 to 247.3.3.182247.3.3.1832
239247.3.3.184/30247.3.3.185 to 247.3.3.186247.3.3.1872
240247.3.3.188/30247.3.3.189 to 247.3.3.190247.3.3.1912
241247.3.3.192/30247.3.3.193 to 247.3.3.194247.3.3.1952
242247.3.3.196/30247.3.3.197 to 247.3.3.198247.3.3.1992
243247.3.3.200/30247.3.3.201 to 247.3.3.202247.3.3.2032
244247.3.3.204/30247.3.3.205 to 247.3.3.206247.3.3.2072
245247.3.3.208/30247.3.3.209 to 247.3.3.210247.3.3.2112
246247.3.3.212/30247.3.3.213 to 247.3.3.214247.3.3.2152
247247.3.3.216/30247.3.3.217 to 247.3.3.218247.3.3.2192
248247.3.3.220/30247.3.3.221 to 247.3.3.222247.3.3.2232
249247.3.3.224/30247.3.3.225 to 247.3.3.226247.3.3.2272
250247.3.3.228/30247.3.3.229 to 247.3.3.230247.3.3.2312
251247.3.3.232/30247.3.3.233 to 247.3.3.234247.3.3.2352
252247.3.3.236/30247.3.3.237 to 247.3.3.238247.3.3.2392
253247.3.3.240/30247.3.3.241 to 247.3.3.242247.3.3.2432
254247.3.3.244/30247.3.3.245 to 247.3.3.246247.3.3.2472
255247.3.3.248/30247.3.3.249 to 247.3.3.250247.3.3.2512
256247.3.3.252/30247.3.3.253 to 247.3.3.254247.3.3.2552

IPv4 CIDR reference (/0 to /32)

IPv4 prefix lengths
PrefixSubnet maskWildcardAddressesUsable hostsSizeTypical use
/00.0.0.0255.255.255.2554,294,967,2964,294,967,29416,777,216 × /24
/1128.0.0.0127.255.255.2552,147,483,6482,147,483,6468,388,608 × /24
/2192.0.0.063.255.255.2551,073,741,8241,073,741,8224,194,304 × /24
/3224.0.0.031.255.255.255536,870,912536,870,9102,097,152 × /24
/4240.0.0.015.255.255.255268,435,456268,435,4541,048,576 × /24
/5248.0.0.07.255.255.255134,217,728134,217,726524,288 × /24
/6252.0.0.03.255.255.25567,108,86467,108,862262,144 × /24
/7254.0.0.01.255.255.25533,554,43233,554,430131,072 × /24
/8255.0.0.00.255.255.25516,777,21616,777,21465,536 × /24Old class A; 10.0.0.0/8
/9255.128.0.00.127.255.2558,388,6088,388,60632,768 × /24
/10255.192.0.00.63.255.2554,194,3044,194,30216,384 × /24
/11255.224.0.00.31.255.2552,097,1522,097,1508,192 × /24
/12255.240.0.00.15.255.2551,048,5761,048,5744,096 × /24172.16.0.0/12
/13255.248.0.00.7.255.255524,288524,2862,048 × /24
/14255.252.0.00.3.255.255262,144262,1421,024 × /24
/15255.254.0.00.1.255.255131,072131,070512 × /24
/16255.255.0.00.0.255.25565,53665,534256 × /24Old class B; 192.168.0.0/16
/17255.255.128.00.0.127.25532,76832,766128 × /24
/18255.255.192.00.0.63.25516,38416,38264 × /24
/19255.255.224.00.0.31.2558,1928,19032 × /24
/20255.255.240.00.0.15.2554,0964,09416 × /24
/21255.255.248.00.0.7.2552,0482,0468 × /24
/22255.255.252.00.0.3.2551,0241,0224 × /24Large office or guest Wi-Fi (1,022 hosts)
/23255.255.254.00.0.1.2555125102 × /24Larger office LAN (510 hosts)
/24255.255.255.00.0.0.2552562541 × /24Typical office LAN (old class C)
/25255.255.255.1280.0.0.1271281261/2 of a /24Smaller LAN or VLAN
/26255.255.255.1920.0.0.6364621/4 of a /24Smaller LAN or VLAN
/27255.255.255.2240.0.0.3132301/8 of a /24Small VLAN, phones, cameras
/28255.255.255.2400.0.0.1516141/16 of a /24Small VLAN, phones, cameras
/29255.255.255.2480.0.0.7861/32 of a /24Small fixed public block (5 usable)
/30255.255.255.2520.0.0.3421/64 of a /24Point-to-point (old style)
/31255.255.255.2540.0.0.1221/128 of a /24Point-to-point link (RFC 3021)
/32255.255.255.2550.0.0.0111/256 of a /24One host

IPv6 prefix reference

IPv6 prefix lengths
PrefixAddresses/64 LANs/48 sitesNibbleTypical use
/342,535,295,865,117,307,932,921,825,928,971,026,432 (2^125)2,305,843,009,213,693,95235,184,372,088,832NoAll global unicast (2000::/3)
/165,192,296,858,534,827,628,530,496,329,220,096 (2^112)281,474,976,710,6564,294,967,296Yes
/20324,518,553,658,426,726,783,156,020,576,256 (2^108)17,592,186,044,416268,435,456YesLarge provider allocation (RIPE minimum for some)
/29633,825,300,114,114,700,748,351,602,688 (2^99)34,359,738,368524,288NoRIPE allocation to a provider (often)
/3279,228,162,514,264,337,593,543,950,336 (2^96)4,294,967,29665,536YesProvider allocation (RIPE default)
/364,951,760,157,141,521,099,596,496,896 (2^92)268,435,4564,096Yes
/40309,485,009,821,345,068,724,781,056 (2^88)16,777,216256Yes
/4419,342,813,113,834,066,795,298,816 (2^84)1,048,57616Yes
/481,208,925,819,614,629,174,706,176 (2^80)65,5361YesOne site or organisation (RIPE PI / assignment)
/5275,557,863,725,914,323,419,136 (2^76)4,096Yes
/564,722,366,482,869,645,213,696 (2^72)256YesSmall site or home (common provider assignment)
/60295,147,905,179,352,825,856 (2^68)16YesSome home broadband (16 LANs)
/6418,446,744,073,709,551,616 (2^64)1YesOne LAN or VLAN (needed for SLAAC)
/7272,057,594,037,927,936 (2^56)1/256 of a /64Yes
/80281,474,976,710,656 (2^48)1/65,536 of a /64Yes
/964,294,967,2961/4,294,967,296 of a /64YesEmbeds an IPv4 address (NAT64)
/11265,5361/281,474,976,710,656 of a /64Yes
/1202561/72,057,594,037,927,936 of a /64Yes
/124161/1,152,921,504,606,846,976 of a /64Yes
/12641/4,611,686,018,427,387,904 of a /64No
/12721/9,223,372,036,854,775,808 of a /64NoPoint-to-point link (RFC 6164)
/12811/18,446,744,073,709,551,616 of a /64YesOne host or loopback

Private and special ranges

IPv4

Special-purpose ranges
RangeNameWhat it is
255.255.255.255/32Limited broadcastEvery host on the local network
0.0.0.0/8This networkNot routed; 0.0.0.0 means "any address" in settings
10.0.0.0/8Private (RFC 1918)Office and home networks; not routed on the internet
100.64.0.0/10Shared address space (CGNAT)Used by providers behind carrier-grade NAT (RFC 6598)
127.0.0.0/8LoopbackThis computer
169.254.0.0/16Link-local (APIPA)Self-assigned when no DHCP server answers
172.16.0.0/12Private (RFC 1918)Office and home networks; not routed on the internet
192.0.0.0/24IETF protocol assignmentsSpecial uses such as DS-Lite
192.0.2.0/24Documentation (TEST-NET-1)For examples; never used on a network
192.88.99.0/246to4 relay (deprecated)Formerly anycast for 6to4
192.168.0.0/16Private (RFC 1918)Office and home networks; not routed on the internet
198.18.0.0/15BenchmarkingNetwork equipment testing (RFC 2544)
198.51.100.0/24Documentation (TEST-NET-2)For examples; never used on a network
203.0.113.0/24Documentation (TEST-NET-3)For examples; never used on a network
224.0.0.0/4MulticastOne-to-many traffic, such as IPTV and routing protocols
240.0.0.0/4ReservedFuture use; not usable on most systems

IPv6

Special-purpose ranges
RangeNameWhat it is
::/128UnspecifiedNo address; :: means "any address" in settings
::1/128LoopbackThis computer
::ffff:0:0/96IPv4-mappedAn IPv4 address written as IPv6
64:ff9b::/96NAT64IPv4 addresses reached through a NAT64 gateway
100::/64Discard onlyTraffic sent here is dropped (RFC 6666)
2001:db8::/32DocumentationFor examples; never used on a network
2001::/32TeredoIPv6 tunnelled over IPv4 UDP
2002::/166to4IPv6 tunnelled over IPv4 (largely retired)
3fff::/20DocumentationFor examples (RFC 9637)
fc00::/7Unique local (ULA)Private IPv6, like RFC 1918; usually fd00::/8
fe80::/10Link-localEvery IPv6 interface has one; not routed
ff00::/8MulticastOne-to-many traffic; replaces broadcast
2000::/3Global unicastPublic internet addresses

About this tool

A network is written as an address and a prefix length, such as 192.168.1.0/24: the first 24 bits name the network and the rest number the devices on it. The calculator works out where the network starts and ends, how many devices it holds, its subnet and wildcard masks, and the reverse DNS zone to ask your provider for.

It also splits a network into equal smaller ones (one per VLAN or site), turns a range of addresses into the fewest CIDR blocks for a firewall rule, and lists every IPv4 prefix length and the common IPv6 ones in reference tables.

Common questions

Why are two addresses lost in every IPv4 subnet?

The first address names the network and the last is the broadcast address, so a /24 has 256 addresses but 254 for devices. A /31 (a link between two routers) and a /32 (one host) are the exceptions.

What size of IPv6 network should a LAN use?

Always /64. Devices pick their own address within it (SLAAC), which needs the full 64 bits. A site usually gets a /48 or /56 from its provider, which holds 65,536 or 256 LANs.

What is a wildcard mask?

The subnet mask turned inside out: 255.255.255.0 becomes 0.0.0.255. Cisco access lists and OSPF use it to say which bits must match.

Which ranges can I use inside an office?

IPv4: 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. IPv6: unique local addresses from fd00::/8, though most networks use the public prefix from their provider.