Speed and call quality testMy IP addressIP subnet calculatorDNS reportWhoIs lookupRemote support

Internet and network

Speed and call quality testTest delay, jitter and speed, with a focus on phone calls.My IP addressYour public IPv4 and IPv6 addresses, provider and address range.WhoIs lookupWho owns a domain or IP address, when it expires, and its DNS.DNS reportEvery DNS record for a domain, with email setup checked.IP subnet calculatorWork out a network's range, mask and hosts, and split it into subnets.

Computers and devices

Update checkIs this computer, phone and browser up to date? With links to update.Camera and mic testCheck your webcam and microphone before a call.Test print pagePrint an A4 page to check a printer: edges, text, line art and colours.

Make and print

Clean textStrip hidden characters, smart quotes and odd spaces from pasted text.QR code makerMake a QR code for a link, contact or message. Nothing leaves your browser.Wi-Fi QR posterPrint an A4 poster that lets guests join your Wi-Fi by scanning.

Surftec support

Remote supportLet a Surftec engineer connect to your computer to help you.All workingA full-screen confirmation that everything is up and running.

Surftec

Surftec websiteServices, news and how to contact Surftec
Cloud Tools
Guest
GuestNot signed in

Surftec customers will be recognised automatically when they use these tools from their office network.

Customer sign-in is coming soon.

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.

Network99.2.16.0/20
Usable hosts4,094
Subnet mask255.255.240.0
Addresses4,096
Network address
99.2.16.0
Broadcast address
99.2.31.255
First usable
99.2.16.1
Last usable
99.2.31.254
Usable hosts
4,094 (4,096 less the network and broadcast addresses)
Subnet mask
255.255.240.0
Wildcard mask
0.0.15.255 (Cisco ACLs, OSPF)
Prefix length
/20
Type
Public public
Old class
A (default /8)
As numbers
Hex 63021000 · Integer 1661079552 to 1661083647
Reverse DNS zones
16.2.99.in-addr.arpa
17.2.99.in-addr.arpa
18.2.99.in-addr.arpa
19.2.99.in-addr.arpa
20.2.99.in-addr.arpa
21.2.99.in-addr.arpa
22.2.99.in-addr.arpa
23.2.99.in-addr.arpa
24.2.99.in-addr.arpa
25.2.99.in-addr.arpa
26.2.99.in-addr.arpa
27.2.99.in-addr.arpa
28.2.99.in-addr.arpa
29.2.99.in-addr.arpa
30.2.99.in-addr.arpa
31.2.99.in-addr.arpa
/20 is not on a 8-bit boundary, so it takes 16 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address01100011.00000010.00010000.0000000099.2.16.0
Subnet mask11111111.11111111.11110000.00000000255.255.240.0
Network01100011.00000010.00010000.0000000099.2.16.0
Broadcast01100011.00000010.00011111.1111111199.2.31.255
Split into smaller subnets/32
/21 (2)/22 (4)/23 (8)/24 (16)/25 (32)/26 (64)/27 (128)/28 (256)/29 (512)/30 (1,024)/31 (2,048)/32 (4,096)

99.2.16.0/20 makes 4,096 subnets of /32; the first 256 are listed.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
199.2.16.0/3299.2.16.0 to 99.2.16.0—1
299.2.16.1/3299.2.16.1 to 99.2.16.1—1
399.2.16.2/3299.2.16.2 to 99.2.16.2—1
499.2.16.3/3299.2.16.3 to 99.2.16.3—1
599.2.16.4/3299.2.16.4 to 99.2.16.4—1
699.2.16.5/3299.2.16.5 to 99.2.16.5—1
799.2.16.6/3299.2.16.6 to 99.2.16.6—1
899.2.16.7/3299.2.16.7 to 99.2.16.7—1
999.2.16.8/3299.2.16.8 to 99.2.16.8—1
1099.2.16.9/3299.2.16.9 to 99.2.16.9—1
1199.2.16.10/3299.2.16.10 to 99.2.16.10—1
1299.2.16.11/3299.2.16.11 to 99.2.16.11—1
1399.2.16.12/3299.2.16.12 to 99.2.16.12—1
1499.2.16.13/3299.2.16.13 to 99.2.16.13—1
1599.2.16.14/3299.2.16.14 to 99.2.16.14—1
1699.2.16.15/3299.2.16.15 to 99.2.16.15—1
1799.2.16.16/3299.2.16.16 to 99.2.16.16—1
1899.2.16.17/3299.2.16.17 to 99.2.16.17—1
1999.2.16.18/3299.2.16.18 to 99.2.16.18—1
2099.2.16.19/3299.2.16.19 to 99.2.16.19—1
2199.2.16.20/3299.2.16.20 to 99.2.16.20—1
2299.2.16.21/3299.2.16.21 to 99.2.16.21—1
2399.2.16.22/3299.2.16.22 to 99.2.16.22—1
2499.2.16.23/3299.2.16.23 to 99.2.16.23—1
2599.2.16.24/3299.2.16.24 to 99.2.16.24—1
2699.2.16.25/3299.2.16.25 to 99.2.16.25—1
2799.2.16.26/3299.2.16.26 to 99.2.16.26—1
2899.2.16.27/3299.2.16.27 to 99.2.16.27—1
2999.2.16.28/3299.2.16.28 to 99.2.16.28—1
3099.2.16.29/3299.2.16.29 to 99.2.16.29—1
3199.2.16.30/3299.2.16.30 to 99.2.16.30—1
3299.2.16.31/3299.2.16.31 to 99.2.16.31—1
3399.2.16.32/3299.2.16.32 to 99.2.16.32—1
3499.2.16.33/3299.2.16.33 to 99.2.16.33—1
3599.2.16.34/3299.2.16.34 to 99.2.16.34—1
3699.2.16.35/3299.2.16.35 to 99.2.16.35—1
3799.2.16.36/3299.2.16.36 to 99.2.16.36—1
3899.2.16.37/3299.2.16.37 to 99.2.16.37—1
3999.2.16.38/3299.2.16.38 to 99.2.16.38—1
4099.2.16.39/3299.2.16.39 to 99.2.16.39—1
4199.2.16.40/3299.2.16.40 to 99.2.16.40—1
4299.2.16.41/3299.2.16.41 to 99.2.16.41—1
4399.2.16.42/3299.2.16.42 to 99.2.16.42—1
4499.2.16.43/3299.2.16.43 to 99.2.16.43—1
4599.2.16.44/3299.2.16.44 to 99.2.16.44—1
4699.2.16.45/3299.2.16.45 to 99.2.16.45—1
4799.2.16.46/3299.2.16.46 to 99.2.16.46—1
4899.2.16.47/3299.2.16.47 to 99.2.16.47—1
4999.2.16.48/3299.2.16.48 to 99.2.16.48—1
5099.2.16.49/3299.2.16.49 to 99.2.16.49—1
5199.2.16.50/3299.2.16.50 to 99.2.16.50—1
5299.2.16.51/3299.2.16.51 to 99.2.16.51—1
5399.2.16.52/3299.2.16.52 to 99.2.16.52—1
5499.2.16.53/3299.2.16.53 to 99.2.16.53—1
5599.2.16.54/3299.2.16.54 to 99.2.16.54—1
5699.2.16.55/3299.2.16.55 to 99.2.16.55—1
5799.2.16.56/3299.2.16.56 to 99.2.16.56—1
5899.2.16.57/3299.2.16.57 to 99.2.16.57—1
5999.2.16.58/3299.2.16.58 to 99.2.16.58—1
6099.2.16.59/3299.2.16.59 to 99.2.16.59—1
6199.2.16.60/3299.2.16.60 to 99.2.16.60—1
6299.2.16.61/3299.2.16.61 to 99.2.16.61—1
6399.2.16.62/3299.2.16.62 to 99.2.16.62—1
6499.2.16.63/3299.2.16.63 to 99.2.16.63—1
6599.2.16.64/3299.2.16.64 to 99.2.16.64—1
6699.2.16.65/3299.2.16.65 to 99.2.16.65—1
6799.2.16.66/3299.2.16.66 to 99.2.16.66—1
6899.2.16.67/3299.2.16.67 to 99.2.16.67—1
6999.2.16.68/3299.2.16.68 to 99.2.16.68—1
7099.2.16.69/3299.2.16.69 to 99.2.16.69—1
7199.2.16.70/3299.2.16.70 to 99.2.16.70—1
7299.2.16.71/3299.2.16.71 to 99.2.16.71—1
7399.2.16.72/3299.2.16.72 to 99.2.16.72—1
7499.2.16.73/3299.2.16.73 to 99.2.16.73—1
7599.2.16.74/3299.2.16.74 to 99.2.16.74—1
7699.2.16.75/3299.2.16.75 to 99.2.16.75—1
7799.2.16.76/3299.2.16.76 to 99.2.16.76—1
7899.2.16.77/3299.2.16.77 to 99.2.16.77—1
7999.2.16.78/3299.2.16.78 to 99.2.16.78—1
8099.2.16.79/3299.2.16.79 to 99.2.16.79—1
8199.2.16.80/3299.2.16.80 to 99.2.16.80—1
8299.2.16.81/3299.2.16.81 to 99.2.16.81—1
8399.2.16.82/3299.2.16.82 to 99.2.16.82—1
8499.2.16.83/3299.2.16.83 to 99.2.16.83—1
8599.2.16.84/3299.2.16.84 to 99.2.16.84—1
8699.2.16.85/3299.2.16.85 to 99.2.16.85—1
8799.2.16.86/3299.2.16.86 to 99.2.16.86—1
8899.2.16.87/3299.2.16.87 to 99.2.16.87—1
8999.2.16.88/3299.2.16.88 to 99.2.16.88—1
9099.2.16.89/3299.2.16.89 to 99.2.16.89—1
9199.2.16.90/3299.2.16.90 to 99.2.16.90—1
9299.2.16.91/3299.2.16.91 to 99.2.16.91—1
9399.2.16.92/3299.2.16.92 to 99.2.16.92—1
9499.2.16.93/3299.2.16.93 to 99.2.16.93—1
9599.2.16.94/3299.2.16.94 to 99.2.16.94—1
9699.2.16.95/3299.2.16.95 to 99.2.16.95—1
9799.2.16.96/3299.2.16.96 to 99.2.16.96—1
9899.2.16.97/3299.2.16.97 to 99.2.16.97—1
9999.2.16.98/3299.2.16.98 to 99.2.16.98—1
10099.2.16.99/3299.2.16.99 to 99.2.16.99—1
10199.2.16.100/3299.2.16.100 to 99.2.16.100—1
10299.2.16.101/3299.2.16.101 to 99.2.16.101—1
10399.2.16.102/3299.2.16.102 to 99.2.16.102—1
10499.2.16.103/3299.2.16.103 to 99.2.16.103—1
10599.2.16.104/3299.2.16.104 to 99.2.16.104—1
10699.2.16.105/3299.2.16.105 to 99.2.16.105—1
10799.2.16.106/3299.2.16.106 to 99.2.16.106—1
10899.2.16.107/3299.2.16.107 to 99.2.16.107—1
10999.2.16.108/3299.2.16.108 to 99.2.16.108—1
11099.2.16.109/3299.2.16.109 to 99.2.16.109—1
11199.2.16.110/3299.2.16.110 to 99.2.16.110—1
11299.2.16.111/3299.2.16.111 to 99.2.16.111—1
11399.2.16.112/3299.2.16.112 to 99.2.16.112—1
11499.2.16.113/3299.2.16.113 to 99.2.16.113—1
11599.2.16.114/3299.2.16.114 to 99.2.16.114—1
11699.2.16.115/3299.2.16.115 to 99.2.16.115—1
11799.2.16.116/3299.2.16.116 to 99.2.16.116—1
11899.2.16.117/3299.2.16.117 to 99.2.16.117—1
11999.2.16.118/3299.2.16.118 to 99.2.16.118—1
12099.2.16.119/3299.2.16.119 to 99.2.16.119—1
12199.2.16.120/3299.2.16.120 to 99.2.16.120—1
12299.2.16.121/3299.2.16.121 to 99.2.16.121—1
12399.2.16.122/3299.2.16.122 to 99.2.16.122—1
12499.2.16.123/3299.2.16.123 to 99.2.16.123—1
12599.2.16.124/3299.2.16.124 to 99.2.16.124—1
12699.2.16.125/3299.2.16.125 to 99.2.16.125—1
12799.2.16.126/3299.2.16.126 to 99.2.16.126—1
12899.2.16.127/3299.2.16.127 to 99.2.16.127—1
12999.2.16.128/3299.2.16.128 to 99.2.16.128—1
13099.2.16.129/3299.2.16.129 to 99.2.16.129—1
13199.2.16.130/3299.2.16.130 to 99.2.16.130—1
13299.2.16.131/3299.2.16.131 to 99.2.16.131—1
13399.2.16.132/3299.2.16.132 to 99.2.16.132—1
13499.2.16.133/3299.2.16.133 to 99.2.16.133—1
13599.2.16.134/3299.2.16.134 to 99.2.16.134—1
13699.2.16.135/3299.2.16.135 to 99.2.16.135—1
13799.2.16.136/3299.2.16.136 to 99.2.16.136—1
13899.2.16.137/3299.2.16.137 to 99.2.16.137—1
13999.2.16.138/3299.2.16.138 to 99.2.16.138—1
14099.2.16.139/3299.2.16.139 to 99.2.16.139—1
14199.2.16.140/3299.2.16.140 to 99.2.16.140—1
14299.2.16.141/3299.2.16.141 to 99.2.16.141—1
14399.2.16.142/3299.2.16.142 to 99.2.16.142—1
14499.2.16.143/3299.2.16.143 to 99.2.16.143—1
14599.2.16.144/3299.2.16.144 to 99.2.16.144—1
14699.2.16.145/3299.2.16.145 to 99.2.16.145—1
14799.2.16.146/3299.2.16.146 to 99.2.16.146—1
14899.2.16.147/3299.2.16.147 to 99.2.16.147—1
14999.2.16.148/3299.2.16.148 to 99.2.16.148—1
15099.2.16.149/3299.2.16.149 to 99.2.16.149—1
15199.2.16.150/3299.2.16.150 to 99.2.16.150—1
15299.2.16.151/3299.2.16.151 to 99.2.16.151—1
15399.2.16.152/3299.2.16.152 to 99.2.16.152—1
15499.2.16.153/3299.2.16.153 to 99.2.16.153—1
15599.2.16.154/3299.2.16.154 to 99.2.16.154—1
15699.2.16.155/3299.2.16.155 to 99.2.16.155—1
15799.2.16.156/3299.2.16.156 to 99.2.16.156—1
15899.2.16.157/3299.2.16.157 to 99.2.16.157—1
15999.2.16.158/3299.2.16.158 to 99.2.16.158—1
16099.2.16.159/3299.2.16.159 to 99.2.16.159—1
16199.2.16.160/3299.2.16.160 to 99.2.16.160—1
16299.2.16.161/3299.2.16.161 to 99.2.16.161—1
16399.2.16.162/3299.2.16.162 to 99.2.16.162—1
16499.2.16.163/3299.2.16.163 to 99.2.16.163—1
16599.2.16.164/3299.2.16.164 to 99.2.16.164—1
16699.2.16.165/3299.2.16.165 to 99.2.16.165—1
16799.2.16.166/3299.2.16.166 to 99.2.16.166—1
16899.2.16.167/3299.2.16.167 to 99.2.16.167—1
16999.2.16.168/3299.2.16.168 to 99.2.16.168—1
17099.2.16.169/3299.2.16.169 to 99.2.16.169—1
17199.2.16.170/3299.2.16.170 to 99.2.16.170—1
17299.2.16.171/3299.2.16.171 to 99.2.16.171—1
17399.2.16.172/3299.2.16.172 to 99.2.16.172—1
17499.2.16.173/3299.2.16.173 to 99.2.16.173—1
17599.2.16.174/3299.2.16.174 to 99.2.16.174—1
17699.2.16.175/3299.2.16.175 to 99.2.16.175—1
17799.2.16.176/3299.2.16.176 to 99.2.16.176—1
17899.2.16.177/3299.2.16.177 to 99.2.16.177—1
17999.2.16.178/3299.2.16.178 to 99.2.16.178—1
18099.2.16.179/3299.2.16.179 to 99.2.16.179—1
18199.2.16.180/3299.2.16.180 to 99.2.16.180—1
18299.2.16.181/3299.2.16.181 to 99.2.16.181—1
18399.2.16.182/3299.2.16.182 to 99.2.16.182—1
18499.2.16.183/3299.2.16.183 to 99.2.16.183—1
18599.2.16.184/3299.2.16.184 to 99.2.16.184—1
18699.2.16.185/3299.2.16.185 to 99.2.16.185—1
18799.2.16.186/3299.2.16.186 to 99.2.16.186—1
18899.2.16.187/3299.2.16.187 to 99.2.16.187—1
18999.2.16.188/3299.2.16.188 to 99.2.16.188—1
19099.2.16.189/3299.2.16.189 to 99.2.16.189—1
19199.2.16.190/3299.2.16.190 to 99.2.16.190—1
19299.2.16.191/3299.2.16.191 to 99.2.16.191—1
19399.2.16.192/3299.2.16.192 to 99.2.16.192—1
19499.2.16.193/3299.2.16.193 to 99.2.16.193—1
19599.2.16.194/3299.2.16.194 to 99.2.16.194—1
19699.2.16.195/3299.2.16.195 to 99.2.16.195—1
19799.2.16.196/3299.2.16.196 to 99.2.16.196—1
19899.2.16.197/3299.2.16.197 to 99.2.16.197—1
19999.2.16.198/3299.2.16.198 to 99.2.16.198—1
20099.2.16.199/3299.2.16.199 to 99.2.16.199—1
20199.2.16.200/3299.2.16.200 to 99.2.16.200—1
20299.2.16.201/3299.2.16.201 to 99.2.16.201—1
20399.2.16.202/3299.2.16.202 to 99.2.16.202—1
20499.2.16.203/3299.2.16.203 to 99.2.16.203—1
20599.2.16.204/3299.2.16.204 to 99.2.16.204—1
20699.2.16.205/3299.2.16.205 to 99.2.16.205—1
20799.2.16.206/3299.2.16.206 to 99.2.16.206—1
20899.2.16.207/3299.2.16.207 to 99.2.16.207—1
20999.2.16.208/3299.2.16.208 to 99.2.16.208—1
21099.2.16.209/3299.2.16.209 to 99.2.16.209—1
21199.2.16.210/3299.2.16.210 to 99.2.16.210—1
21299.2.16.211/3299.2.16.211 to 99.2.16.211—1
21399.2.16.212/3299.2.16.212 to 99.2.16.212—1
21499.2.16.213/3299.2.16.213 to 99.2.16.213—1
21599.2.16.214/3299.2.16.214 to 99.2.16.214—1
21699.2.16.215/3299.2.16.215 to 99.2.16.215—1
21799.2.16.216/3299.2.16.216 to 99.2.16.216—1
21899.2.16.217/3299.2.16.217 to 99.2.16.217—1
21999.2.16.218/3299.2.16.218 to 99.2.16.218—1
22099.2.16.219/3299.2.16.219 to 99.2.16.219—1
22199.2.16.220/3299.2.16.220 to 99.2.16.220—1
22299.2.16.221/3299.2.16.221 to 99.2.16.221—1
22399.2.16.222/3299.2.16.222 to 99.2.16.222—1
22499.2.16.223/3299.2.16.223 to 99.2.16.223—1
22599.2.16.224/3299.2.16.224 to 99.2.16.224—1
22699.2.16.225/3299.2.16.225 to 99.2.16.225—1
22799.2.16.226/3299.2.16.226 to 99.2.16.226—1
22899.2.16.227/3299.2.16.227 to 99.2.16.227—1
22999.2.16.228/3299.2.16.228 to 99.2.16.228—1
23099.2.16.229/3299.2.16.229 to 99.2.16.229—1
23199.2.16.230/3299.2.16.230 to 99.2.16.230—1
23299.2.16.231/3299.2.16.231 to 99.2.16.231—1
23399.2.16.232/3299.2.16.232 to 99.2.16.232—1
23499.2.16.233/3299.2.16.233 to 99.2.16.233—1
23599.2.16.234/3299.2.16.234 to 99.2.16.234—1
23699.2.16.235/3299.2.16.235 to 99.2.16.235—1
23799.2.16.236/3299.2.16.236 to 99.2.16.236—1
23899.2.16.237/3299.2.16.237 to 99.2.16.237—1
23999.2.16.238/3299.2.16.238 to 99.2.16.238—1
24099.2.16.239/3299.2.16.239 to 99.2.16.239—1
24199.2.16.240/3299.2.16.240 to 99.2.16.240—1
24299.2.16.241/3299.2.16.241 to 99.2.16.241—1
24399.2.16.242/3299.2.16.242 to 99.2.16.242—1
24499.2.16.243/3299.2.16.243 to 99.2.16.243—1
24599.2.16.244/3299.2.16.244 to 99.2.16.244—1
24699.2.16.245/3299.2.16.245 to 99.2.16.245—1
24799.2.16.246/3299.2.16.246 to 99.2.16.246—1
24899.2.16.247/3299.2.16.247 to 99.2.16.247—1
24999.2.16.248/3299.2.16.248 to 99.2.16.248—1
25099.2.16.249/3299.2.16.249 to 99.2.16.249—1
25199.2.16.250/3299.2.16.250 to 99.2.16.250—1
25299.2.16.251/3299.2.16.251 to 99.2.16.251—1
25399.2.16.252/3299.2.16.252 to 99.2.16.252—1
25499.2.16.253/3299.2.16.253 to 99.2.16.253—1
25599.2.16.254/3299.2.16.254 to 99.2.16.254—1
25699.2.16.255/3299.2.16.255 to 99.2.16.255—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.