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.

Network68.0.0.0/20
Usable hosts4,094
Subnet mask255.255.240.0
Addresses4,096
Network address
68.0.0.0
Broadcast address
68.0.15.255
First usable
68.0.0.1
Last usable
68.0.15.254
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 44000000 · Integer 1140850688 to 1140854783
Reverse DNS zones
0.0.68.in-addr.arpa
1.0.68.in-addr.arpa
2.0.68.in-addr.arpa
3.0.68.in-addr.arpa
4.0.68.in-addr.arpa
5.0.68.in-addr.arpa
6.0.68.in-addr.arpa
7.0.68.in-addr.arpa
8.0.68.in-addr.arpa
9.0.68.in-addr.arpa
10.0.68.in-addr.arpa
11.0.68.in-addr.arpa
12.0.68.in-addr.arpa
13.0.68.in-addr.arpa
14.0.68.in-addr.arpa
15.0.68.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
Address01000100.00000000.00000000.0000000068.0.0.0
Subnet mask11111111.11111111.11110000.00000000255.255.240.0
Network01000100.00000000.00000000.0000000068.0.0.0
Broadcast01000100.00000000.00001111.1111111168.0.15.255
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)

68.0.0.0/20 makes 4,096 subnets of /32; the first 256 are listed.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
168.0.0.0/3268.0.0.0 to 68.0.0.0—1
268.0.0.1/3268.0.0.1 to 68.0.0.1—1
368.0.0.2/3268.0.0.2 to 68.0.0.2—1
468.0.0.3/3268.0.0.3 to 68.0.0.3—1
568.0.0.4/3268.0.0.4 to 68.0.0.4—1
668.0.0.5/3268.0.0.5 to 68.0.0.5—1
768.0.0.6/3268.0.0.6 to 68.0.0.6—1
868.0.0.7/3268.0.0.7 to 68.0.0.7—1
968.0.0.8/3268.0.0.8 to 68.0.0.8—1
1068.0.0.9/3268.0.0.9 to 68.0.0.9—1
1168.0.0.10/3268.0.0.10 to 68.0.0.10—1
1268.0.0.11/3268.0.0.11 to 68.0.0.11—1
1368.0.0.12/3268.0.0.12 to 68.0.0.12—1
1468.0.0.13/3268.0.0.13 to 68.0.0.13—1
1568.0.0.14/3268.0.0.14 to 68.0.0.14—1
1668.0.0.15/3268.0.0.15 to 68.0.0.15—1
1768.0.0.16/3268.0.0.16 to 68.0.0.16—1
1868.0.0.17/3268.0.0.17 to 68.0.0.17—1
1968.0.0.18/3268.0.0.18 to 68.0.0.18—1
2068.0.0.19/3268.0.0.19 to 68.0.0.19—1
2168.0.0.20/3268.0.0.20 to 68.0.0.20—1
2268.0.0.21/3268.0.0.21 to 68.0.0.21—1
2368.0.0.22/3268.0.0.22 to 68.0.0.22—1
2468.0.0.23/3268.0.0.23 to 68.0.0.23—1
2568.0.0.24/3268.0.0.24 to 68.0.0.24—1
2668.0.0.25/3268.0.0.25 to 68.0.0.25—1
2768.0.0.26/3268.0.0.26 to 68.0.0.26—1
2868.0.0.27/3268.0.0.27 to 68.0.0.27—1
2968.0.0.28/3268.0.0.28 to 68.0.0.28—1
3068.0.0.29/3268.0.0.29 to 68.0.0.29—1
3168.0.0.30/3268.0.0.30 to 68.0.0.30—1
3268.0.0.31/3268.0.0.31 to 68.0.0.31—1
3368.0.0.32/3268.0.0.32 to 68.0.0.32—1
3468.0.0.33/3268.0.0.33 to 68.0.0.33—1
3568.0.0.34/3268.0.0.34 to 68.0.0.34—1
3668.0.0.35/3268.0.0.35 to 68.0.0.35—1
3768.0.0.36/3268.0.0.36 to 68.0.0.36—1
3868.0.0.37/3268.0.0.37 to 68.0.0.37—1
3968.0.0.38/3268.0.0.38 to 68.0.0.38—1
4068.0.0.39/3268.0.0.39 to 68.0.0.39—1
4168.0.0.40/3268.0.0.40 to 68.0.0.40—1
4268.0.0.41/3268.0.0.41 to 68.0.0.41—1
4368.0.0.42/3268.0.0.42 to 68.0.0.42—1
4468.0.0.43/3268.0.0.43 to 68.0.0.43—1
4568.0.0.44/3268.0.0.44 to 68.0.0.44—1
4668.0.0.45/3268.0.0.45 to 68.0.0.45—1
4768.0.0.46/3268.0.0.46 to 68.0.0.46—1
4868.0.0.47/3268.0.0.47 to 68.0.0.47—1
4968.0.0.48/3268.0.0.48 to 68.0.0.48—1
5068.0.0.49/3268.0.0.49 to 68.0.0.49—1
5168.0.0.50/3268.0.0.50 to 68.0.0.50—1
5268.0.0.51/3268.0.0.51 to 68.0.0.51—1
5368.0.0.52/3268.0.0.52 to 68.0.0.52—1
5468.0.0.53/3268.0.0.53 to 68.0.0.53—1
5568.0.0.54/3268.0.0.54 to 68.0.0.54—1
5668.0.0.55/3268.0.0.55 to 68.0.0.55—1
5768.0.0.56/3268.0.0.56 to 68.0.0.56—1
5868.0.0.57/3268.0.0.57 to 68.0.0.57—1
5968.0.0.58/3268.0.0.58 to 68.0.0.58—1
6068.0.0.59/3268.0.0.59 to 68.0.0.59—1
6168.0.0.60/3268.0.0.60 to 68.0.0.60—1
6268.0.0.61/3268.0.0.61 to 68.0.0.61—1
6368.0.0.62/3268.0.0.62 to 68.0.0.62—1
6468.0.0.63/3268.0.0.63 to 68.0.0.63—1
6568.0.0.64/3268.0.0.64 to 68.0.0.64—1
6668.0.0.65/3268.0.0.65 to 68.0.0.65—1
6768.0.0.66/3268.0.0.66 to 68.0.0.66—1
6868.0.0.67/3268.0.0.67 to 68.0.0.67—1
6968.0.0.68/3268.0.0.68 to 68.0.0.68—1
7068.0.0.69/3268.0.0.69 to 68.0.0.69—1
7168.0.0.70/3268.0.0.70 to 68.0.0.70—1
7268.0.0.71/3268.0.0.71 to 68.0.0.71—1
7368.0.0.72/3268.0.0.72 to 68.0.0.72—1
7468.0.0.73/3268.0.0.73 to 68.0.0.73—1
7568.0.0.74/3268.0.0.74 to 68.0.0.74—1
7668.0.0.75/3268.0.0.75 to 68.0.0.75—1
7768.0.0.76/3268.0.0.76 to 68.0.0.76—1
7868.0.0.77/3268.0.0.77 to 68.0.0.77—1
7968.0.0.78/3268.0.0.78 to 68.0.0.78—1
8068.0.0.79/3268.0.0.79 to 68.0.0.79—1
8168.0.0.80/3268.0.0.80 to 68.0.0.80—1
8268.0.0.81/3268.0.0.81 to 68.0.0.81—1
8368.0.0.82/3268.0.0.82 to 68.0.0.82—1
8468.0.0.83/3268.0.0.83 to 68.0.0.83—1
8568.0.0.84/3268.0.0.84 to 68.0.0.84—1
8668.0.0.85/3268.0.0.85 to 68.0.0.85—1
8768.0.0.86/3268.0.0.86 to 68.0.0.86—1
8868.0.0.87/3268.0.0.87 to 68.0.0.87—1
8968.0.0.88/3268.0.0.88 to 68.0.0.88—1
9068.0.0.89/3268.0.0.89 to 68.0.0.89—1
9168.0.0.90/3268.0.0.90 to 68.0.0.90—1
9268.0.0.91/3268.0.0.91 to 68.0.0.91—1
9368.0.0.92/3268.0.0.92 to 68.0.0.92—1
9468.0.0.93/3268.0.0.93 to 68.0.0.93—1
9568.0.0.94/3268.0.0.94 to 68.0.0.94—1
9668.0.0.95/3268.0.0.95 to 68.0.0.95—1
9768.0.0.96/3268.0.0.96 to 68.0.0.96—1
9868.0.0.97/3268.0.0.97 to 68.0.0.97—1
9968.0.0.98/3268.0.0.98 to 68.0.0.98—1
10068.0.0.99/3268.0.0.99 to 68.0.0.99—1
10168.0.0.100/3268.0.0.100 to 68.0.0.100—1
10268.0.0.101/3268.0.0.101 to 68.0.0.101—1
10368.0.0.102/3268.0.0.102 to 68.0.0.102—1
10468.0.0.103/3268.0.0.103 to 68.0.0.103—1
10568.0.0.104/3268.0.0.104 to 68.0.0.104—1
10668.0.0.105/3268.0.0.105 to 68.0.0.105—1
10768.0.0.106/3268.0.0.106 to 68.0.0.106—1
10868.0.0.107/3268.0.0.107 to 68.0.0.107—1
10968.0.0.108/3268.0.0.108 to 68.0.0.108—1
11068.0.0.109/3268.0.0.109 to 68.0.0.109—1
11168.0.0.110/3268.0.0.110 to 68.0.0.110—1
11268.0.0.111/3268.0.0.111 to 68.0.0.111—1
11368.0.0.112/3268.0.0.112 to 68.0.0.112—1
11468.0.0.113/3268.0.0.113 to 68.0.0.113—1
11568.0.0.114/3268.0.0.114 to 68.0.0.114—1
11668.0.0.115/3268.0.0.115 to 68.0.0.115—1
11768.0.0.116/3268.0.0.116 to 68.0.0.116—1
11868.0.0.117/3268.0.0.117 to 68.0.0.117—1
11968.0.0.118/3268.0.0.118 to 68.0.0.118—1
12068.0.0.119/3268.0.0.119 to 68.0.0.119—1
12168.0.0.120/3268.0.0.120 to 68.0.0.120—1
12268.0.0.121/3268.0.0.121 to 68.0.0.121—1
12368.0.0.122/3268.0.0.122 to 68.0.0.122—1
12468.0.0.123/3268.0.0.123 to 68.0.0.123—1
12568.0.0.124/3268.0.0.124 to 68.0.0.124—1
12668.0.0.125/3268.0.0.125 to 68.0.0.125—1
12768.0.0.126/3268.0.0.126 to 68.0.0.126—1
12868.0.0.127/3268.0.0.127 to 68.0.0.127—1
12968.0.0.128/3268.0.0.128 to 68.0.0.128—1
13068.0.0.129/3268.0.0.129 to 68.0.0.129—1
13168.0.0.130/3268.0.0.130 to 68.0.0.130—1
13268.0.0.131/3268.0.0.131 to 68.0.0.131—1
13368.0.0.132/3268.0.0.132 to 68.0.0.132—1
13468.0.0.133/3268.0.0.133 to 68.0.0.133—1
13568.0.0.134/3268.0.0.134 to 68.0.0.134—1
13668.0.0.135/3268.0.0.135 to 68.0.0.135—1
13768.0.0.136/3268.0.0.136 to 68.0.0.136—1
13868.0.0.137/3268.0.0.137 to 68.0.0.137—1
13968.0.0.138/3268.0.0.138 to 68.0.0.138—1
14068.0.0.139/3268.0.0.139 to 68.0.0.139—1
14168.0.0.140/3268.0.0.140 to 68.0.0.140—1
14268.0.0.141/3268.0.0.141 to 68.0.0.141—1
14368.0.0.142/3268.0.0.142 to 68.0.0.142—1
14468.0.0.143/3268.0.0.143 to 68.0.0.143—1
14568.0.0.144/3268.0.0.144 to 68.0.0.144—1
14668.0.0.145/3268.0.0.145 to 68.0.0.145—1
14768.0.0.146/3268.0.0.146 to 68.0.0.146—1
14868.0.0.147/3268.0.0.147 to 68.0.0.147—1
14968.0.0.148/3268.0.0.148 to 68.0.0.148—1
15068.0.0.149/3268.0.0.149 to 68.0.0.149—1
15168.0.0.150/3268.0.0.150 to 68.0.0.150—1
15268.0.0.151/3268.0.0.151 to 68.0.0.151—1
15368.0.0.152/3268.0.0.152 to 68.0.0.152—1
15468.0.0.153/3268.0.0.153 to 68.0.0.153—1
15568.0.0.154/3268.0.0.154 to 68.0.0.154—1
15668.0.0.155/3268.0.0.155 to 68.0.0.155—1
15768.0.0.156/3268.0.0.156 to 68.0.0.156—1
15868.0.0.157/3268.0.0.157 to 68.0.0.157—1
15968.0.0.158/3268.0.0.158 to 68.0.0.158—1
16068.0.0.159/3268.0.0.159 to 68.0.0.159—1
16168.0.0.160/3268.0.0.160 to 68.0.0.160—1
16268.0.0.161/3268.0.0.161 to 68.0.0.161—1
16368.0.0.162/3268.0.0.162 to 68.0.0.162—1
16468.0.0.163/3268.0.0.163 to 68.0.0.163—1
16568.0.0.164/3268.0.0.164 to 68.0.0.164—1
16668.0.0.165/3268.0.0.165 to 68.0.0.165—1
16768.0.0.166/3268.0.0.166 to 68.0.0.166—1
16868.0.0.167/3268.0.0.167 to 68.0.0.167—1
16968.0.0.168/3268.0.0.168 to 68.0.0.168—1
17068.0.0.169/3268.0.0.169 to 68.0.0.169—1
17168.0.0.170/3268.0.0.170 to 68.0.0.170—1
17268.0.0.171/3268.0.0.171 to 68.0.0.171—1
17368.0.0.172/3268.0.0.172 to 68.0.0.172—1
17468.0.0.173/3268.0.0.173 to 68.0.0.173—1
17568.0.0.174/3268.0.0.174 to 68.0.0.174—1
17668.0.0.175/3268.0.0.175 to 68.0.0.175—1
17768.0.0.176/3268.0.0.176 to 68.0.0.176—1
17868.0.0.177/3268.0.0.177 to 68.0.0.177—1
17968.0.0.178/3268.0.0.178 to 68.0.0.178—1
18068.0.0.179/3268.0.0.179 to 68.0.0.179—1
18168.0.0.180/3268.0.0.180 to 68.0.0.180—1
18268.0.0.181/3268.0.0.181 to 68.0.0.181—1
18368.0.0.182/3268.0.0.182 to 68.0.0.182—1
18468.0.0.183/3268.0.0.183 to 68.0.0.183—1
18568.0.0.184/3268.0.0.184 to 68.0.0.184—1
18668.0.0.185/3268.0.0.185 to 68.0.0.185—1
18768.0.0.186/3268.0.0.186 to 68.0.0.186—1
18868.0.0.187/3268.0.0.187 to 68.0.0.187—1
18968.0.0.188/3268.0.0.188 to 68.0.0.188—1
19068.0.0.189/3268.0.0.189 to 68.0.0.189—1
19168.0.0.190/3268.0.0.190 to 68.0.0.190—1
19268.0.0.191/3268.0.0.191 to 68.0.0.191—1
19368.0.0.192/3268.0.0.192 to 68.0.0.192—1
19468.0.0.193/3268.0.0.193 to 68.0.0.193—1
19568.0.0.194/3268.0.0.194 to 68.0.0.194—1
19668.0.0.195/3268.0.0.195 to 68.0.0.195—1
19768.0.0.196/3268.0.0.196 to 68.0.0.196—1
19868.0.0.197/3268.0.0.197 to 68.0.0.197—1
19968.0.0.198/3268.0.0.198 to 68.0.0.198—1
20068.0.0.199/3268.0.0.199 to 68.0.0.199—1
20168.0.0.200/3268.0.0.200 to 68.0.0.200—1
20268.0.0.201/3268.0.0.201 to 68.0.0.201—1
20368.0.0.202/3268.0.0.202 to 68.0.0.202—1
20468.0.0.203/3268.0.0.203 to 68.0.0.203—1
20568.0.0.204/3268.0.0.204 to 68.0.0.204—1
20668.0.0.205/3268.0.0.205 to 68.0.0.205—1
20768.0.0.206/3268.0.0.206 to 68.0.0.206—1
20868.0.0.207/3268.0.0.207 to 68.0.0.207—1
20968.0.0.208/3268.0.0.208 to 68.0.0.208—1
21068.0.0.209/3268.0.0.209 to 68.0.0.209—1
21168.0.0.210/3268.0.0.210 to 68.0.0.210—1
21268.0.0.211/3268.0.0.211 to 68.0.0.211—1
21368.0.0.212/3268.0.0.212 to 68.0.0.212—1
21468.0.0.213/3268.0.0.213 to 68.0.0.213—1
21568.0.0.214/3268.0.0.214 to 68.0.0.214—1
21668.0.0.215/3268.0.0.215 to 68.0.0.215—1
21768.0.0.216/3268.0.0.216 to 68.0.0.216—1
21868.0.0.217/3268.0.0.217 to 68.0.0.217—1
21968.0.0.218/3268.0.0.218 to 68.0.0.218—1
22068.0.0.219/3268.0.0.219 to 68.0.0.219—1
22168.0.0.220/3268.0.0.220 to 68.0.0.220—1
22268.0.0.221/3268.0.0.221 to 68.0.0.221—1
22368.0.0.222/3268.0.0.222 to 68.0.0.222—1
22468.0.0.223/3268.0.0.223 to 68.0.0.223—1
22568.0.0.224/3268.0.0.224 to 68.0.0.224—1
22668.0.0.225/3268.0.0.225 to 68.0.0.225—1
22768.0.0.226/3268.0.0.226 to 68.0.0.226—1
22868.0.0.227/3268.0.0.227 to 68.0.0.227—1
22968.0.0.228/3268.0.0.228 to 68.0.0.228—1
23068.0.0.229/3268.0.0.229 to 68.0.0.229—1
23168.0.0.230/3268.0.0.230 to 68.0.0.230—1
23268.0.0.231/3268.0.0.231 to 68.0.0.231—1
23368.0.0.232/3268.0.0.232 to 68.0.0.232—1
23468.0.0.233/3268.0.0.233 to 68.0.0.233—1
23568.0.0.234/3268.0.0.234 to 68.0.0.234—1
23668.0.0.235/3268.0.0.235 to 68.0.0.235—1
23768.0.0.236/3268.0.0.236 to 68.0.0.236—1
23868.0.0.237/3268.0.0.237 to 68.0.0.237—1
23968.0.0.238/3268.0.0.238 to 68.0.0.238—1
24068.0.0.239/3268.0.0.239 to 68.0.0.239—1
24168.0.0.240/3268.0.0.240 to 68.0.0.240—1
24268.0.0.241/3268.0.0.241 to 68.0.0.241—1
24368.0.0.242/3268.0.0.242 to 68.0.0.242—1
24468.0.0.243/3268.0.0.243 to 68.0.0.243—1
24568.0.0.244/3268.0.0.244 to 68.0.0.244—1
24668.0.0.245/3268.0.0.245 to 68.0.0.245—1
24768.0.0.246/3268.0.0.246 to 68.0.0.246—1
24868.0.0.247/3268.0.0.247 to 68.0.0.247—1
24968.0.0.248/3268.0.0.248 to 68.0.0.248—1
25068.0.0.249/3268.0.0.249 to 68.0.0.249—1
25168.0.0.250/3268.0.0.250 to 68.0.0.250—1
25268.0.0.251/3268.0.0.251 to 68.0.0.251—1
25368.0.0.252/3268.0.0.252 to 68.0.0.252—1
25468.0.0.253/3268.0.0.253 to 68.0.0.253—1
25568.0.0.254/3268.0.0.254 to 68.0.0.254—1
25668.0.0.255/3268.0.0.255 to 68.0.0.255—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.