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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.

Network10.167.68.0/22
Usable hosts1,022
Subnet mask255.255.252.0
Addresses1,024
Network address
10.167.68.0
Broadcast address
10.167.71.255
First usable
10.167.68.1
Last usable
10.167.71.254
Usable hosts
1,022 (1,024 less the network and broadcast addresses)
Subnet mask
255.255.252.0
Wildcard mask
0.0.3.255 (Cisco ACLs, OSPF)
Prefix length
/22
Type
Private (RFC 1918) 10.0.0.0/8
Office and home networks; not routed on the internet
Old class
A (default /8)
As numbers
Hex 0AA74400 · Integer 178734080 to 178735103
Reverse DNS zones
68.167.10.in-addr.arpa
69.167.10.in-addr.arpa
70.167.10.in-addr.arpa
71.167.10.in-addr.arpa
/22 is not on a 8-bit boundary, so it takes 4 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00001010.10100111.01000100.0000000010.167.68.0
Subnet mask11111111.11111111.11111100.00000000255.255.252.0
Network00001010.10100111.01000100.0000000010.167.68.0
Broadcast00001010.10100111.01000111.1111111110.167.71.255
Split into smaller subnets/32
/23 (2)/24 (4)/25 (8)/26 (16)/27 (32)/28 (64)/29 (128)/30 (256)/31 (512)/32 (1,024)

10.167.68.0/22 makes 1,024 subnets of /32; the first 256 are listed.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
110.167.68.0/3210.167.68.0 to 10.167.68.0—1
210.167.68.1/3210.167.68.1 to 10.167.68.1—1
310.167.68.2/3210.167.68.2 to 10.167.68.2—1
410.167.68.3/3210.167.68.3 to 10.167.68.3—1
510.167.68.4/3210.167.68.4 to 10.167.68.4—1
610.167.68.5/3210.167.68.5 to 10.167.68.5—1
710.167.68.6/3210.167.68.6 to 10.167.68.6—1
810.167.68.7/3210.167.68.7 to 10.167.68.7—1
910.167.68.8/3210.167.68.8 to 10.167.68.8—1
1010.167.68.9/3210.167.68.9 to 10.167.68.9—1
1110.167.68.10/3210.167.68.10 to 10.167.68.10—1
1210.167.68.11/3210.167.68.11 to 10.167.68.11—1
1310.167.68.12/3210.167.68.12 to 10.167.68.12—1
1410.167.68.13/3210.167.68.13 to 10.167.68.13—1
1510.167.68.14/3210.167.68.14 to 10.167.68.14—1
1610.167.68.15/3210.167.68.15 to 10.167.68.15—1
1710.167.68.16/3210.167.68.16 to 10.167.68.16—1
1810.167.68.17/3210.167.68.17 to 10.167.68.17—1
1910.167.68.18/3210.167.68.18 to 10.167.68.18—1
2010.167.68.19/3210.167.68.19 to 10.167.68.19—1
2110.167.68.20/3210.167.68.20 to 10.167.68.20—1
2210.167.68.21/3210.167.68.21 to 10.167.68.21—1
2310.167.68.22/3210.167.68.22 to 10.167.68.22—1
2410.167.68.23/3210.167.68.23 to 10.167.68.23—1
2510.167.68.24/3210.167.68.24 to 10.167.68.24—1
2610.167.68.25/3210.167.68.25 to 10.167.68.25—1
2710.167.68.26/3210.167.68.26 to 10.167.68.26—1
2810.167.68.27/3210.167.68.27 to 10.167.68.27—1
2910.167.68.28/3210.167.68.28 to 10.167.68.28—1
3010.167.68.29/3210.167.68.29 to 10.167.68.29—1
3110.167.68.30/3210.167.68.30 to 10.167.68.30—1
3210.167.68.31/3210.167.68.31 to 10.167.68.31—1
3310.167.68.32/3210.167.68.32 to 10.167.68.32—1
3410.167.68.33/3210.167.68.33 to 10.167.68.33—1
3510.167.68.34/3210.167.68.34 to 10.167.68.34—1
3610.167.68.35/3210.167.68.35 to 10.167.68.35—1
3710.167.68.36/3210.167.68.36 to 10.167.68.36—1
3810.167.68.37/3210.167.68.37 to 10.167.68.37—1
3910.167.68.38/3210.167.68.38 to 10.167.68.38—1
4010.167.68.39/3210.167.68.39 to 10.167.68.39—1
4110.167.68.40/3210.167.68.40 to 10.167.68.40—1
4210.167.68.41/3210.167.68.41 to 10.167.68.41—1
4310.167.68.42/3210.167.68.42 to 10.167.68.42—1
4410.167.68.43/3210.167.68.43 to 10.167.68.43—1
4510.167.68.44/3210.167.68.44 to 10.167.68.44—1
4610.167.68.45/3210.167.68.45 to 10.167.68.45—1
4710.167.68.46/3210.167.68.46 to 10.167.68.46—1
4810.167.68.47/3210.167.68.47 to 10.167.68.47—1
4910.167.68.48/3210.167.68.48 to 10.167.68.48—1
5010.167.68.49/3210.167.68.49 to 10.167.68.49—1
5110.167.68.50/3210.167.68.50 to 10.167.68.50—1
5210.167.68.51/3210.167.68.51 to 10.167.68.51—1
5310.167.68.52/3210.167.68.52 to 10.167.68.52—1
5410.167.68.53/3210.167.68.53 to 10.167.68.53—1
5510.167.68.54/3210.167.68.54 to 10.167.68.54—1
5610.167.68.55/3210.167.68.55 to 10.167.68.55—1
5710.167.68.56/3210.167.68.56 to 10.167.68.56—1
5810.167.68.57/3210.167.68.57 to 10.167.68.57—1
5910.167.68.58/3210.167.68.58 to 10.167.68.58—1
6010.167.68.59/3210.167.68.59 to 10.167.68.59—1
6110.167.68.60/3210.167.68.60 to 10.167.68.60—1
6210.167.68.61/3210.167.68.61 to 10.167.68.61—1
6310.167.68.62/3210.167.68.62 to 10.167.68.62—1
6410.167.68.63/3210.167.68.63 to 10.167.68.63—1
6510.167.68.64/3210.167.68.64 to 10.167.68.64—1
6610.167.68.65/3210.167.68.65 to 10.167.68.65—1
6710.167.68.66/3210.167.68.66 to 10.167.68.66—1
6810.167.68.67/3210.167.68.67 to 10.167.68.67—1
6910.167.68.68/3210.167.68.68 to 10.167.68.68—1
7010.167.68.69/3210.167.68.69 to 10.167.68.69—1
7110.167.68.70/3210.167.68.70 to 10.167.68.70—1
7210.167.68.71/3210.167.68.71 to 10.167.68.71—1
7310.167.68.72/3210.167.68.72 to 10.167.68.72—1
7410.167.68.73/3210.167.68.73 to 10.167.68.73—1
7510.167.68.74/3210.167.68.74 to 10.167.68.74—1
7610.167.68.75/3210.167.68.75 to 10.167.68.75—1
7710.167.68.76/3210.167.68.76 to 10.167.68.76—1
7810.167.68.77/3210.167.68.77 to 10.167.68.77—1
7910.167.68.78/3210.167.68.78 to 10.167.68.78—1
8010.167.68.79/3210.167.68.79 to 10.167.68.79—1
8110.167.68.80/3210.167.68.80 to 10.167.68.80—1
8210.167.68.81/3210.167.68.81 to 10.167.68.81—1
8310.167.68.82/3210.167.68.82 to 10.167.68.82—1
8410.167.68.83/3210.167.68.83 to 10.167.68.83—1
8510.167.68.84/3210.167.68.84 to 10.167.68.84—1
8610.167.68.85/3210.167.68.85 to 10.167.68.85—1
8710.167.68.86/3210.167.68.86 to 10.167.68.86—1
8810.167.68.87/3210.167.68.87 to 10.167.68.87—1
8910.167.68.88/3210.167.68.88 to 10.167.68.88—1
9010.167.68.89/3210.167.68.89 to 10.167.68.89—1
9110.167.68.90/3210.167.68.90 to 10.167.68.90—1
9210.167.68.91/3210.167.68.91 to 10.167.68.91—1
9310.167.68.92/3210.167.68.92 to 10.167.68.92—1
9410.167.68.93/3210.167.68.93 to 10.167.68.93—1
9510.167.68.94/3210.167.68.94 to 10.167.68.94—1
9610.167.68.95/3210.167.68.95 to 10.167.68.95—1
9710.167.68.96/3210.167.68.96 to 10.167.68.96—1
9810.167.68.97/3210.167.68.97 to 10.167.68.97—1
9910.167.68.98/3210.167.68.98 to 10.167.68.98—1
10010.167.68.99/3210.167.68.99 to 10.167.68.99—1
10110.167.68.100/3210.167.68.100 to 10.167.68.100—1
10210.167.68.101/3210.167.68.101 to 10.167.68.101—1
10310.167.68.102/3210.167.68.102 to 10.167.68.102—1
10410.167.68.103/3210.167.68.103 to 10.167.68.103—1
10510.167.68.104/3210.167.68.104 to 10.167.68.104—1
10610.167.68.105/3210.167.68.105 to 10.167.68.105—1
10710.167.68.106/3210.167.68.106 to 10.167.68.106—1
10810.167.68.107/3210.167.68.107 to 10.167.68.107—1
10910.167.68.108/3210.167.68.108 to 10.167.68.108—1
11010.167.68.109/3210.167.68.109 to 10.167.68.109—1
11110.167.68.110/3210.167.68.110 to 10.167.68.110—1
11210.167.68.111/3210.167.68.111 to 10.167.68.111—1
11310.167.68.112/3210.167.68.112 to 10.167.68.112—1
11410.167.68.113/3210.167.68.113 to 10.167.68.113—1
11510.167.68.114/3210.167.68.114 to 10.167.68.114—1
11610.167.68.115/3210.167.68.115 to 10.167.68.115—1
11710.167.68.116/3210.167.68.116 to 10.167.68.116—1
11810.167.68.117/3210.167.68.117 to 10.167.68.117—1
11910.167.68.118/3210.167.68.118 to 10.167.68.118—1
12010.167.68.119/3210.167.68.119 to 10.167.68.119—1
12110.167.68.120/3210.167.68.120 to 10.167.68.120—1
12210.167.68.121/3210.167.68.121 to 10.167.68.121—1
12310.167.68.122/3210.167.68.122 to 10.167.68.122—1
12410.167.68.123/3210.167.68.123 to 10.167.68.123—1
12510.167.68.124/3210.167.68.124 to 10.167.68.124—1
12610.167.68.125/3210.167.68.125 to 10.167.68.125—1
12710.167.68.126/3210.167.68.126 to 10.167.68.126—1
12810.167.68.127/3210.167.68.127 to 10.167.68.127—1
12910.167.68.128/3210.167.68.128 to 10.167.68.128—1
13010.167.68.129/3210.167.68.129 to 10.167.68.129—1
13110.167.68.130/3210.167.68.130 to 10.167.68.130—1
13210.167.68.131/3210.167.68.131 to 10.167.68.131—1
13310.167.68.132/3210.167.68.132 to 10.167.68.132—1
13410.167.68.133/3210.167.68.133 to 10.167.68.133—1
13510.167.68.134/3210.167.68.134 to 10.167.68.134—1
13610.167.68.135/3210.167.68.135 to 10.167.68.135—1
13710.167.68.136/3210.167.68.136 to 10.167.68.136—1
13810.167.68.137/3210.167.68.137 to 10.167.68.137—1
13910.167.68.138/3210.167.68.138 to 10.167.68.138—1
14010.167.68.139/3210.167.68.139 to 10.167.68.139—1
14110.167.68.140/3210.167.68.140 to 10.167.68.140—1
14210.167.68.141/3210.167.68.141 to 10.167.68.141—1
14310.167.68.142/3210.167.68.142 to 10.167.68.142—1
14410.167.68.143/3210.167.68.143 to 10.167.68.143—1
14510.167.68.144/3210.167.68.144 to 10.167.68.144—1
14610.167.68.145/3210.167.68.145 to 10.167.68.145—1
14710.167.68.146/3210.167.68.146 to 10.167.68.146—1
14810.167.68.147/3210.167.68.147 to 10.167.68.147—1
14910.167.68.148/3210.167.68.148 to 10.167.68.148—1
15010.167.68.149/3210.167.68.149 to 10.167.68.149—1
15110.167.68.150/3210.167.68.150 to 10.167.68.150—1
15210.167.68.151/3210.167.68.151 to 10.167.68.151—1
15310.167.68.152/3210.167.68.152 to 10.167.68.152—1
15410.167.68.153/3210.167.68.153 to 10.167.68.153—1
15510.167.68.154/3210.167.68.154 to 10.167.68.154—1
15610.167.68.155/3210.167.68.155 to 10.167.68.155—1
15710.167.68.156/3210.167.68.156 to 10.167.68.156—1
15810.167.68.157/3210.167.68.157 to 10.167.68.157—1
15910.167.68.158/3210.167.68.158 to 10.167.68.158—1
16010.167.68.159/3210.167.68.159 to 10.167.68.159—1
16110.167.68.160/3210.167.68.160 to 10.167.68.160—1
16210.167.68.161/3210.167.68.161 to 10.167.68.161—1
16310.167.68.162/3210.167.68.162 to 10.167.68.162—1
16410.167.68.163/3210.167.68.163 to 10.167.68.163—1
16510.167.68.164/3210.167.68.164 to 10.167.68.164—1
16610.167.68.165/3210.167.68.165 to 10.167.68.165—1
16710.167.68.166/3210.167.68.166 to 10.167.68.166—1
16810.167.68.167/3210.167.68.167 to 10.167.68.167—1
16910.167.68.168/3210.167.68.168 to 10.167.68.168—1
17010.167.68.169/3210.167.68.169 to 10.167.68.169—1
17110.167.68.170/3210.167.68.170 to 10.167.68.170—1
17210.167.68.171/3210.167.68.171 to 10.167.68.171—1
17310.167.68.172/3210.167.68.172 to 10.167.68.172—1
17410.167.68.173/3210.167.68.173 to 10.167.68.173—1
17510.167.68.174/3210.167.68.174 to 10.167.68.174—1
17610.167.68.175/3210.167.68.175 to 10.167.68.175—1
17710.167.68.176/3210.167.68.176 to 10.167.68.176—1
17810.167.68.177/3210.167.68.177 to 10.167.68.177—1
17910.167.68.178/3210.167.68.178 to 10.167.68.178—1
18010.167.68.179/3210.167.68.179 to 10.167.68.179—1
18110.167.68.180/3210.167.68.180 to 10.167.68.180—1
18210.167.68.181/3210.167.68.181 to 10.167.68.181—1
18310.167.68.182/3210.167.68.182 to 10.167.68.182—1
18410.167.68.183/3210.167.68.183 to 10.167.68.183—1
18510.167.68.184/3210.167.68.184 to 10.167.68.184—1
18610.167.68.185/3210.167.68.185 to 10.167.68.185—1
18710.167.68.186/3210.167.68.186 to 10.167.68.186—1
18810.167.68.187/3210.167.68.187 to 10.167.68.187—1
18910.167.68.188/3210.167.68.188 to 10.167.68.188—1
19010.167.68.189/3210.167.68.189 to 10.167.68.189—1
19110.167.68.190/3210.167.68.190 to 10.167.68.190—1
19210.167.68.191/3210.167.68.191 to 10.167.68.191—1
19310.167.68.192/3210.167.68.192 to 10.167.68.192—1
19410.167.68.193/3210.167.68.193 to 10.167.68.193—1
19510.167.68.194/3210.167.68.194 to 10.167.68.194—1
19610.167.68.195/3210.167.68.195 to 10.167.68.195—1
19710.167.68.196/3210.167.68.196 to 10.167.68.196—1
19810.167.68.197/3210.167.68.197 to 10.167.68.197—1
19910.167.68.198/3210.167.68.198 to 10.167.68.198—1
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20210.167.68.201/3210.167.68.201 to 10.167.68.201—1
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20710.167.68.206/3210.167.68.206 to 10.167.68.206—1
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21610.167.68.215/3210.167.68.215 to 10.167.68.215—1
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22010.167.68.219/3210.167.68.219 to 10.167.68.219—1
22110.167.68.220/3210.167.68.220 to 10.167.68.220—1
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25010.167.68.249/3210.167.68.249 to 10.167.68.249—1
25110.167.68.250/3210.167.68.250 to 10.167.68.250—1
25210.167.68.251/3210.167.68.251 to 10.167.68.251—1
25310.167.68.252/3210.167.68.252 to 10.167.68.252—1
25410.167.68.253/3210.167.68.253 to 10.167.68.253—1
25510.167.68.254/3210.167.68.254 to 10.167.68.254—1
25610.167.68.255/3210.167.68.255 to 10.167.68.255—1

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.