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.

Network187.3.16.0/20
Usable hosts4,094
Subnet mask255.255.240.0
Addresses4,096
Network address
187.3.16.0
Broadcast address
187.3.31.255
First usable
187.3.16.1
Last usable
187.3.31.254
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
B (default /16)
As numbers
Hex BB031000 · Integer 3137540096 to 3137544191
Reverse DNS zones
16.3.187.in-addr.arpa
17.3.187.in-addr.arpa
18.3.187.in-addr.arpa
19.3.187.in-addr.arpa
20.3.187.in-addr.arpa
21.3.187.in-addr.arpa
22.3.187.in-addr.arpa
23.3.187.in-addr.arpa
24.3.187.in-addr.arpa
25.3.187.in-addr.arpa
26.3.187.in-addr.arpa
27.3.187.in-addr.arpa
28.3.187.in-addr.arpa
29.3.187.in-addr.arpa
30.3.187.in-addr.arpa
31.3.187.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
Address10111011.00000011.00010000.00000000187.3.16.0
Subnet mask11111111.11111111.11110000.00000000255.255.240.0
Network10111011.00000011.00010000.00000000187.3.16.0
Broadcast10111011.00000011.00011111.11111111187.3.31.255
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)

187.3.16.0/20 makes 4,096 subnets of /32; the first 256 are listed.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1187.3.16.0/32187.3.16.0 to 187.3.16.0—1
2187.3.16.1/32187.3.16.1 to 187.3.16.1—1
3187.3.16.2/32187.3.16.2 to 187.3.16.2—1
4187.3.16.3/32187.3.16.3 to 187.3.16.3—1
5187.3.16.4/32187.3.16.4 to 187.3.16.4—1
6187.3.16.5/32187.3.16.5 to 187.3.16.5—1
7187.3.16.6/32187.3.16.6 to 187.3.16.6—1
8187.3.16.7/32187.3.16.7 to 187.3.16.7—1
9187.3.16.8/32187.3.16.8 to 187.3.16.8—1
10187.3.16.9/32187.3.16.9 to 187.3.16.9—1
11187.3.16.10/32187.3.16.10 to 187.3.16.10—1
12187.3.16.11/32187.3.16.11 to 187.3.16.11—1
13187.3.16.12/32187.3.16.12 to 187.3.16.12—1
14187.3.16.13/32187.3.16.13 to 187.3.16.13—1
15187.3.16.14/32187.3.16.14 to 187.3.16.14—1
16187.3.16.15/32187.3.16.15 to 187.3.16.15—1
17187.3.16.16/32187.3.16.16 to 187.3.16.16—1
18187.3.16.17/32187.3.16.17 to 187.3.16.17—1
19187.3.16.18/32187.3.16.18 to 187.3.16.18—1
20187.3.16.19/32187.3.16.19 to 187.3.16.19—1
21187.3.16.20/32187.3.16.20 to 187.3.16.20—1
22187.3.16.21/32187.3.16.21 to 187.3.16.21—1
23187.3.16.22/32187.3.16.22 to 187.3.16.22—1
24187.3.16.23/32187.3.16.23 to 187.3.16.23—1
25187.3.16.24/32187.3.16.24 to 187.3.16.24—1
26187.3.16.25/32187.3.16.25 to 187.3.16.25—1
27187.3.16.26/32187.3.16.26 to 187.3.16.26—1
28187.3.16.27/32187.3.16.27 to 187.3.16.27—1
29187.3.16.28/32187.3.16.28 to 187.3.16.28—1
30187.3.16.29/32187.3.16.29 to 187.3.16.29—1
31187.3.16.30/32187.3.16.30 to 187.3.16.30—1
32187.3.16.31/32187.3.16.31 to 187.3.16.31—1
33187.3.16.32/32187.3.16.32 to 187.3.16.32—1
34187.3.16.33/32187.3.16.33 to 187.3.16.33—1
35187.3.16.34/32187.3.16.34 to 187.3.16.34—1
36187.3.16.35/32187.3.16.35 to 187.3.16.35—1
37187.3.16.36/32187.3.16.36 to 187.3.16.36—1
38187.3.16.37/32187.3.16.37 to 187.3.16.37—1
39187.3.16.38/32187.3.16.38 to 187.3.16.38—1
40187.3.16.39/32187.3.16.39 to 187.3.16.39—1
41187.3.16.40/32187.3.16.40 to 187.3.16.40—1
42187.3.16.41/32187.3.16.41 to 187.3.16.41—1
43187.3.16.42/32187.3.16.42 to 187.3.16.42—1
44187.3.16.43/32187.3.16.43 to 187.3.16.43—1
45187.3.16.44/32187.3.16.44 to 187.3.16.44—1
46187.3.16.45/32187.3.16.45 to 187.3.16.45—1
47187.3.16.46/32187.3.16.46 to 187.3.16.46—1
48187.3.16.47/32187.3.16.47 to 187.3.16.47—1
49187.3.16.48/32187.3.16.48 to 187.3.16.48—1
50187.3.16.49/32187.3.16.49 to 187.3.16.49—1
51187.3.16.50/32187.3.16.50 to 187.3.16.50—1
52187.3.16.51/32187.3.16.51 to 187.3.16.51—1
53187.3.16.52/32187.3.16.52 to 187.3.16.52—1
54187.3.16.53/32187.3.16.53 to 187.3.16.53—1
55187.3.16.54/32187.3.16.54 to 187.3.16.54—1
56187.3.16.55/32187.3.16.55 to 187.3.16.55—1
57187.3.16.56/32187.3.16.56 to 187.3.16.56—1
58187.3.16.57/32187.3.16.57 to 187.3.16.57—1
59187.3.16.58/32187.3.16.58 to 187.3.16.58—1
60187.3.16.59/32187.3.16.59 to 187.3.16.59—1
61187.3.16.60/32187.3.16.60 to 187.3.16.60—1
62187.3.16.61/32187.3.16.61 to 187.3.16.61—1
63187.3.16.62/32187.3.16.62 to 187.3.16.62—1
64187.3.16.63/32187.3.16.63 to 187.3.16.63—1
65187.3.16.64/32187.3.16.64 to 187.3.16.64—1
66187.3.16.65/32187.3.16.65 to 187.3.16.65—1
67187.3.16.66/32187.3.16.66 to 187.3.16.66—1
68187.3.16.67/32187.3.16.67 to 187.3.16.67—1
69187.3.16.68/32187.3.16.68 to 187.3.16.68—1
70187.3.16.69/32187.3.16.69 to 187.3.16.69—1
71187.3.16.70/32187.3.16.70 to 187.3.16.70—1
72187.3.16.71/32187.3.16.71 to 187.3.16.71—1
73187.3.16.72/32187.3.16.72 to 187.3.16.72—1
74187.3.16.73/32187.3.16.73 to 187.3.16.73—1
75187.3.16.74/32187.3.16.74 to 187.3.16.74—1
76187.3.16.75/32187.3.16.75 to 187.3.16.75—1
77187.3.16.76/32187.3.16.76 to 187.3.16.76—1
78187.3.16.77/32187.3.16.77 to 187.3.16.77—1
79187.3.16.78/32187.3.16.78 to 187.3.16.78—1
80187.3.16.79/32187.3.16.79 to 187.3.16.79—1
81187.3.16.80/32187.3.16.80 to 187.3.16.80—1
82187.3.16.81/32187.3.16.81 to 187.3.16.81—1
83187.3.16.82/32187.3.16.82 to 187.3.16.82—1
84187.3.16.83/32187.3.16.83 to 187.3.16.83—1
85187.3.16.84/32187.3.16.84 to 187.3.16.84—1
86187.3.16.85/32187.3.16.85 to 187.3.16.85—1
87187.3.16.86/32187.3.16.86 to 187.3.16.86—1
88187.3.16.87/32187.3.16.87 to 187.3.16.87—1
89187.3.16.88/32187.3.16.88 to 187.3.16.88—1
90187.3.16.89/32187.3.16.89 to 187.3.16.89—1
91187.3.16.90/32187.3.16.90 to 187.3.16.90—1
92187.3.16.91/32187.3.16.91 to 187.3.16.91—1
93187.3.16.92/32187.3.16.92 to 187.3.16.92—1
94187.3.16.93/32187.3.16.93 to 187.3.16.93—1
95187.3.16.94/32187.3.16.94 to 187.3.16.94—1
96187.3.16.95/32187.3.16.95 to 187.3.16.95—1
97187.3.16.96/32187.3.16.96 to 187.3.16.96—1
98187.3.16.97/32187.3.16.97 to 187.3.16.97—1
99187.3.16.98/32187.3.16.98 to 187.3.16.98—1
100187.3.16.99/32187.3.16.99 to 187.3.16.99—1
101187.3.16.100/32187.3.16.100 to 187.3.16.100—1
102187.3.16.101/32187.3.16.101 to 187.3.16.101—1
103187.3.16.102/32187.3.16.102 to 187.3.16.102—1
104187.3.16.103/32187.3.16.103 to 187.3.16.103—1
105187.3.16.104/32187.3.16.104 to 187.3.16.104—1
106187.3.16.105/32187.3.16.105 to 187.3.16.105—1
107187.3.16.106/32187.3.16.106 to 187.3.16.106—1
108187.3.16.107/32187.3.16.107 to 187.3.16.107—1
109187.3.16.108/32187.3.16.108 to 187.3.16.108—1
110187.3.16.109/32187.3.16.109 to 187.3.16.109—1
111187.3.16.110/32187.3.16.110 to 187.3.16.110—1
112187.3.16.111/32187.3.16.111 to 187.3.16.111—1
113187.3.16.112/32187.3.16.112 to 187.3.16.112—1
114187.3.16.113/32187.3.16.113 to 187.3.16.113—1
115187.3.16.114/32187.3.16.114 to 187.3.16.114—1
116187.3.16.115/32187.3.16.115 to 187.3.16.115—1
117187.3.16.116/32187.3.16.116 to 187.3.16.116—1
118187.3.16.117/32187.3.16.117 to 187.3.16.117—1
119187.3.16.118/32187.3.16.118 to 187.3.16.118—1
120187.3.16.119/32187.3.16.119 to 187.3.16.119—1
121187.3.16.120/32187.3.16.120 to 187.3.16.120—1
122187.3.16.121/32187.3.16.121 to 187.3.16.121—1
123187.3.16.122/32187.3.16.122 to 187.3.16.122—1
124187.3.16.123/32187.3.16.123 to 187.3.16.123—1
125187.3.16.124/32187.3.16.124 to 187.3.16.124—1
126187.3.16.125/32187.3.16.125 to 187.3.16.125—1
127187.3.16.126/32187.3.16.126 to 187.3.16.126—1
128187.3.16.127/32187.3.16.127 to 187.3.16.127—1
129187.3.16.128/32187.3.16.128 to 187.3.16.128—1
130187.3.16.129/32187.3.16.129 to 187.3.16.129—1
131187.3.16.130/32187.3.16.130 to 187.3.16.130—1
132187.3.16.131/32187.3.16.131 to 187.3.16.131—1
133187.3.16.132/32187.3.16.132 to 187.3.16.132—1
134187.3.16.133/32187.3.16.133 to 187.3.16.133—1
135187.3.16.134/32187.3.16.134 to 187.3.16.134—1
136187.3.16.135/32187.3.16.135 to 187.3.16.135—1
137187.3.16.136/32187.3.16.136 to 187.3.16.136—1
138187.3.16.137/32187.3.16.137 to 187.3.16.137—1
139187.3.16.138/32187.3.16.138 to 187.3.16.138—1
140187.3.16.139/32187.3.16.139 to 187.3.16.139—1
141187.3.16.140/32187.3.16.140 to 187.3.16.140—1
142187.3.16.141/32187.3.16.141 to 187.3.16.141—1
143187.3.16.142/32187.3.16.142 to 187.3.16.142—1
144187.3.16.143/32187.3.16.143 to 187.3.16.143—1
145187.3.16.144/32187.3.16.144 to 187.3.16.144—1
146187.3.16.145/32187.3.16.145 to 187.3.16.145—1
147187.3.16.146/32187.3.16.146 to 187.3.16.146—1
148187.3.16.147/32187.3.16.147 to 187.3.16.147—1
149187.3.16.148/32187.3.16.148 to 187.3.16.148—1
150187.3.16.149/32187.3.16.149 to 187.3.16.149—1
151187.3.16.150/32187.3.16.150 to 187.3.16.150—1
152187.3.16.151/32187.3.16.151 to 187.3.16.151—1
153187.3.16.152/32187.3.16.152 to 187.3.16.152—1
154187.3.16.153/32187.3.16.153 to 187.3.16.153—1
155187.3.16.154/32187.3.16.154 to 187.3.16.154—1
156187.3.16.155/32187.3.16.155 to 187.3.16.155—1
157187.3.16.156/32187.3.16.156 to 187.3.16.156—1
158187.3.16.157/32187.3.16.157 to 187.3.16.157—1
159187.3.16.158/32187.3.16.158 to 187.3.16.158—1
160187.3.16.159/32187.3.16.159 to 187.3.16.159—1
161187.3.16.160/32187.3.16.160 to 187.3.16.160—1
162187.3.16.161/32187.3.16.161 to 187.3.16.161—1
163187.3.16.162/32187.3.16.162 to 187.3.16.162—1
164187.3.16.163/32187.3.16.163 to 187.3.16.163—1
165187.3.16.164/32187.3.16.164 to 187.3.16.164—1
166187.3.16.165/32187.3.16.165 to 187.3.16.165—1
167187.3.16.166/32187.3.16.166 to 187.3.16.166—1
168187.3.16.167/32187.3.16.167 to 187.3.16.167—1
169187.3.16.168/32187.3.16.168 to 187.3.16.168—1
170187.3.16.169/32187.3.16.169 to 187.3.16.169—1
171187.3.16.170/32187.3.16.170 to 187.3.16.170—1
172187.3.16.171/32187.3.16.171 to 187.3.16.171—1
173187.3.16.172/32187.3.16.172 to 187.3.16.172—1
174187.3.16.173/32187.3.16.173 to 187.3.16.173—1
175187.3.16.174/32187.3.16.174 to 187.3.16.174—1
176187.3.16.175/32187.3.16.175 to 187.3.16.175—1
177187.3.16.176/32187.3.16.176 to 187.3.16.176—1
178187.3.16.177/32187.3.16.177 to 187.3.16.177—1
179187.3.16.178/32187.3.16.178 to 187.3.16.178—1
180187.3.16.179/32187.3.16.179 to 187.3.16.179—1
181187.3.16.180/32187.3.16.180 to 187.3.16.180—1
182187.3.16.181/32187.3.16.181 to 187.3.16.181—1
183187.3.16.182/32187.3.16.182 to 187.3.16.182—1
184187.3.16.183/32187.3.16.183 to 187.3.16.183—1
185187.3.16.184/32187.3.16.184 to 187.3.16.184—1
186187.3.16.185/32187.3.16.185 to 187.3.16.185—1
187187.3.16.186/32187.3.16.186 to 187.3.16.186—1
188187.3.16.187/32187.3.16.187 to 187.3.16.187—1
189187.3.16.188/32187.3.16.188 to 187.3.16.188—1
190187.3.16.189/32187.3.16.189 to 187.3.16.189—1
191187.3.16.190/32187.3.16.190 to 187.3.16.190—1
192187.3.16.191/32187.3.16.191 to 187.3.16.191—1
193187.3.16.192/32187.3.16.192 to 187.3.16.192—1
194187.3.16.193/32187.3.16.193 to 187.3.16.193—1
195187.3.16.194/32187.3.16.194 to 187.3.16.194—1
196187.3.16.195/32187.3.16.195 to 187.3.16.195—1
197187.3.16.196/32187.3.16.196 to 187.3.16.196—1
198187.3.16.197/32187.3.16.197 to 187.3.16.197—1
199187.3.16.198/32187.3.16.198 to 187.3.16.198—1
200187.3.16.199/32187.3.16.199 to 187.3.16.199—1
201187.3.16.200/32187.3.16.200 to 187.3.16.200—1
202187.3.16.201/32187.3.16.201 to 187.3.16.201—1
203187.3.16.202/32187.3.16.202 to 187.3.16.202—1
204187.3.16.203/32187.3.16.203 to 187.3.16.203—1
205187.3.16.204/32187.3.16.204 to 187.3.16.204—1
206187.3.16.205/32187.3.16.205 to 187.3.16.205—1
207187.3.16.206/32187.3.16.206 to 187.3.16.206—1
208187.3.16.207/32187.3.16.207 to 187.3.16.207—1
209187.3.16.208/32187.3.16.208 to 187.3.16.208—1
210187.3.16.209/32187.3.16.209 to 187.3.16.209—1
211187.3.16.210/32187.3.16.210 to 187.3.16.210—1
212187.3.16.211/32187.3.16.211 to 187.3.16.211—1
213187.3.16.212/32187.3.16.212 to 187.3.16.212—1
214187.3.16.213/32187.3.16.213 to 187.3.16.213—1
215187.3.16.214/32187.3.16.214 to 187.3.16.214—1
216187.3.16.215/32187.3.16.215 to 187.3.16.215—1
217187.3.16.216/32187.3.16.216 to 187.3.16.216—1
218187.3.16.217/32187.3.16.217 to 187.3.16.217—1
219187.3.16.218/32187.3.16.218 to 187.3.16.218—1
220187.3.16.219/32187.3.16.219 to 187.3.16.219—1
221187.3.16.220/32187.3.16.220 to 187.3.16.220—1
222187.3.16.221/32187.3.16.221 to 187.3.16.221—1
223187.3.16.222/32187.3.16.222 to 187.3.16.222—1
224187.3.16.223/32187.3.16.223 to 187.3.16.223—1
225187.3.16.224/32187.3.16.224 to 187.3.16.224—1
226187.3.16.225/32187.3.16.225 to 187.3.16.225—1
227187.3.16.226/32187.3.16.226 to 187.3.16.226—1
228187.3.16.227/32187.3.16.227 to 187.3.16.227—1
229187.3.16.228/32187.3.16.228 to 187.3.16.228—1
230187.3.16.229/32187.3.16.229 to 187.3.16.229—1
231187.3.16.230/32187.3.16.230 to 187.3.16.230—1
232187.3.16.231/32187.3.16.231 to 187.3.16.231—1
233187.3.16.232/32187.3.16.232 to 187.3.16.232—1
234187.3.16.233/32187.3.16.233 to 187.3.16.233—1
235187.3.16.234/32187.3.16.234 to 187.3.16.234—1
236187.3.16.235/32187.3.16.235 to 187.3.16.235—1
237187.3.16.236/32187.3.16.236 to 187.3.16.236—1
238187.3.16.237/32187.3.16.237 to 187.3.16.237—1
239187.3.16.238/32187.3.16.238 to 187.3.16.238—1
240187.3.16.239/32187.3.16.239 to 187.3.16.239—1
241187.3.16.240/32187.3.16.240 to 187.3.16.240—1
242187.3.16.241/32187.3.16.241 to 187.3.16.241—1
243187.3.16.242/32187.3.16.242 to 187.3.16.242—1
244187.3.16.243/32187.3.16.243 to 187.3.16.243—1
245187.3.16.244/32187.3.16.244 to 187.3.16.244—1
246187.3.16.245/32187.3.16.245 to 187.3.16.245—1
247187.3.16.246/32187.3.16.246 to 187.3.16.246—1
248187.3.16.247/32187.3.16.247 to 187.3.16.247—1
249187.3.16.248/32187.3.16.248 to 187.3.16.248—1
250187.3.16.249/32187.3.16.249 to 187.3.16.249—1
251187.3.16.250/32187.3.16.250 to 187.3.16.250—1
252187.3.16.251/32187.3.16.251 to 187.3.16.251—1
253187.3.16.252/32187.3.16.252 to 187.3.16.252—1
254187.3.16.253/32187.3.16.253 to 187.3.16.253—1
255187.3.16.254/32187.3.16.254 to 187.3.16.254—1
256187.3.16.255/32187.3.16.255 to 187.3.16.255—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.