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.

Network191.0.0.0/8
Usable hosts16,777,214
Subnet mask255.0.0.0
Addresses16,777,216
Network address
191.0.0.0
Broadcast address
191.255.255.255
First usable
191.0.0.1
Last usable
191.255.255.254
Usable hosts
16,777,214 (16,777,216 less the network and broadcast addresses)
Subnet mask
255.0.0.0
Wildcard mask
0.255.255.255 (Cisco ACLs, OSPF)
Prefix length
/8
Type
Public public
Old class
B (default /16)
As numbers
Hex BF000000 · Integer 3204448256 to 3221225471
Reverse DNS zone
191.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address10111111..00000000.00000000.00000000191.0.0.0
Subnet mask11111111..00000000.00000000.00000000255.0.0.0
Network10111111..00000000.00000000.00000000191.0.0.0
Broadcast10111111..11111111.11111111.11111111191.255.255.255
Split into smaller subnets/19
/9 (2)/10 (4)/11 (8)/12 (16)/13 (32)/14 (64)/15 (128)/16 (256)/17 (512)/18 (1,024)/19 (2,048)/20 (4,096)

191.0.0.0/8 makes 2,048 subnets of /19; the first 256 are listed.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1191.0.0.0/19191.0.0.1 to 191.0.31.254191.0.31.2558,190
2191.0.32.0/19191.0.32.1 to 191.0.63.254191.0.63.2558,190
3191.0.64.0/19191.0.64.1 to 191.0.95.254191.0.95.2558,190
4191.0.96.0/19191.0.96.1 to 191.0.127.254191.0.127.2558,190
5191.0.128.0/19191.0.128.1 to 191.0.159.254191.0.159.2558,190
6191.0.160.0/19191.0.160.1 to 191.0.191.254191.0.191.2558,190
7191.0.192.0/19191.0.192.1 to 191.0.223.254191.0.223.2558,190
8191.0.224.0/19191.0.224.1 to 191.0.255.254191.0.255.2558,190
9191.1.0.0/19191.1.0.1 to 191.1.31.254191.1.31.2558,190
10191.1.32.0/19191.1.32.1 to 191.1.63.254191.1.63.2558,190
11191.1.64.0/19191.1.64.1 to 191.1.95.254191.1.95.2558,190
12191.1.96.0/19191.1.96.1 to 191.1.127.254191.1.127.2558,190
13191.1.128.0/19191.1.128.1 to 191.1.159.254191.1.159.2558,190
14191.1.160.0/19191.1.160.1 to 191.1.191.254191.1.191.2558,190
15191.1.192.0/19191.1.192.1 to 191.1.223.254191.1.223.2558,190
16191.1.224.0/19191.1.224.1 to 191.1.255.254191.1.255.2558,190
17191.2.0.0/19191.2.0.1 to 191.2.31.254191.2.31.2558,190
18191.2.32.0/19191.2.32.1 to 191.2.63.254191.2.63.2558,190
19191.2.64.0/19191.2.64.1 to 191.2.95.254191.2.95.2558,190
20191.2.96.0/19191.2.96.1 to 191.2.127.254191.2.127.2558,190
21191.2.128.0/19191.2.128.1 to 191.2.159.254191.2.159.2558,190
22191.2.160.0/19191.2.160.1 to 191.2.191.254191.2.191.2558,190
23191.2.192.0/19191.2.192.1 to 191.2.223.254191.2.223.2558,190
24191.2.224.0/19191.2.224.1 to 191.2.255.254191.2.255.2558,190
25191.3.0.0/19191.3.0.1 to 191.3.31.254191.3.31.2558,190
26191.3.32.0/19191.3.32.1 to 191.3.63.254191.3.63.2558,190
27191.3.64.0/19191.3.64.1 to 191.3.95.254191.3.95.2558,190
28191.3.96.0/19191.3.96.1 to 191.3.127.254191.3.127.2558,190
29191.3.128.0/19191.3.128.1 to 191.3.159.254191.3.159.2558,190
30191.3.160.0/19191.3.160.1 to 191.3.191.254191.3.191.2558,190
31191.3.192.0/19191.3.192.1 to 191.3.223.254191.3.223.2558,190
32191.3.224.0/19191.3.224.1 to 191.3.255.254191.3.255.2558,190
33191.4.0.0/19191.4.0.1 to 191.4.31.254191.4.31.2558,190
34191.4.32.0/19191.4.32.1 to 191.4.63.254191.4.63.2558,190
35191.4.64.0/19191.4.64.1 to 191.4.95.254191.4.95.2558,190
36191.4.96.0/19191.4.96.1 to 191.4.127.254191.4.127.2558,190
37191.4.128.0/19191.4.128.1 to 191.4.159.254191.4.159.2558,190
38191.4.160.0/19191.4.160.1 to 191.4.191.254191.4.191.2558,190
39191.4.192.0/19191.4.192.1 to 191.4.223.254191.4.223.2558,190
40191.4.224.0/19191.4.224.1 to 191.4.255.254191.4.255.2558,190
41191.5.0.0/19191.5.0.1 to 191.5.31.254191.5.31.2558,190
42191.5.32.0/19191.5.32.1 to 191.5.63.254191.5.63.2558,190
43191.5.64.0/19191.5.64.1 to 191.5.95.254191.5.95.2558,190
44191.5.96.0/19191.5.96.1 to 191.5.127.254191.5.127.2558,190
45191.5.128.0/19191.5.128.1 to 191.5.159.254191.5.159.2558,190
46191.5.160.0/19191.5.160.1 to 191.5.191.254191.5.191.2558,190
47191.5.192.0/19191.5.192.1 to 191.5.223.254191.5.223.2558,190
48191.5.224.0/19191.5.224.1 to 191.5.255.254191.5.255.2558,190
49191.6.0.0/19191.6.0.1 to 191.6.31.254191.6.31.2558,190
50191.6.32.0/19191.6.32.1 to 191.6.63.254191.6.63.2558,190
51191.6.64.0/19191.6.64.1 to 191.6.95.254191.6.95.2558,190
52191.6.96.0/19191.6.96.1 to 191.6.127.254191.6.127.2558,190
53191.6.128.0/19191.6.128.1 to 191.6.159.254191.6.159.2558,190
54191.6.160.0/19191.6.160.1 to 191.6.191.254191.6.191.2558,190
55191.6.192.0/19191.6.192.1 to 191.6.223.254191.6.223.2558,190
56191.6.224.0/19191.6.224.1 to 191.6.255.254191.6.255.2558,190
57191.7.0.0/19191.7.0.1 to 191.7.31.254191.7.31.2558,190
58191.7.32.0/19191.7.32.1 to 191.7.63.254191.7.63.2558,190
59191.7.64.0/19191.7.64.1 to 191.7.95.254191.7.95.2558,190
60191.7.96.0/19191.7.96.1 to 191.7.127.254191.7.127.2558,190
61191.7.128.0/19191.7.128.1 to 191.7.159.254191.7.159.2558,190
62191.7.160.0/19191.7.160.1 to 191.7.191.254191.7.191.2558,190
63191.7.192.0/19191.7.192.1 to 191.7.223.254191.7.223.2558,190
64191.7.224.0/19191.7.224.1 to 191.7.255.254191.7.255.2558,190
65191.8.0.0/19191.8.0.1 to 191.8.31.254191.8.31.2558,190
66191.8.32.0/19191.8.32.1 to 191.8.63.254191.8.63.2558,190
67191.8.64.0/19191.8.64.1 to 191.8.95.254191.8.95.2558,190
68191.8.96.0/19191.8.96.1 to 191.8.127.254191.8.127.2558,190
69191.8.128.0/19191.8.128.1 to 191.8.159.254191.8.159.2558,190
70191.8.160.0/19191.8.160.1 to 191.8.191.254191.8.191.2558,190
71191.8.192.0/19191.8.192.1 to 191.8.223.254191.8.223.2558,190
72191.8.224.0/19191.8.224.1 to 191.8.255.254191.8.255.2558,190
73191.9.0.0/19191.9.0.1 to 191.9.31.254191.9.31.2558,190
74191.9.32.0/19191.9.32.1 to 191.9.63.254191.9.63.2558,190
75191.9.64.0/19191.9.64.1 to 191.9.95.254191.9.95.2558,190
76191.9.96.0/19191.9.96.1 to 191.9.127.254191.9.127.2558,190
77191.9.128.0/19191.9.128.1 to 191.9.159.254191.9.159.2558,190
78191.9.160.0/19191.9.160.1 to 191.9.191.254191.9.191.2558,190
79191.9.192.0/19191.9.192.1 to 191.9.223.254191.9.223.2558,190
80191.9.224.0/19191.9.224.1 to 191.9.255.254191.9.255.2558,190
81191.10.0.0/19191.10.0.1 to 191.10.31.254191.10.31.2558,190
82191.10.32.0/19191.10.32.1 to 191.10.63.254191.10.63.2558,190
83191.10.64.0/19191.10.64.1 to 191.10.95.254191.10.95.2558,190
84191.10.96.0/19191.10.96.1 to 191.10.127.254191.10.127.2558,190
85191.10.128.0/19191.10.128.1 to 191.10.159.254191.10.159.2558,190
86191.10.160.0/19191.10.160.1 to 191.10.191.254191.10.191.2558,190
87191.10.192.0/19191.10.192.1 to 191.10.223.254191.10.223.2558,190
88191.10.224.0/19191.10.224.1 to 191.10.255.254191.10.255.2558,190
89191.11.0.0/19191.11.0.1 to 191.11.31.254191.11.31.2558,190
90191.11.32.0/19191.11.32.1 to 191.11.63.254191.11.63.2558,190
91191.11.64.0/19191.11.64.1 to 191.11.95.254191.11.95.2558,190
92191.11.96.0/19191.11.96.1 to 191.11.127.254191.11.127.2558,190
93191.11.128.0/19191.11.128.1 to 191.11.159.254191.11.159.2558,190
94191.11.160.0/19191.11.160.1 to 191.11.191.254191.11.191.2558,190
95191.11.192.0/19191.11.192.1 to 191.11.223.254191.11.223.2558,190
96191.11.224.0/19191.11.224.1 to 191.11.255.254191.11.255.2558,190
97191.12.0.0/19191.12.0.1 to 191.12.31.254191.12.31.2558,190
98191.12.32.0/19191.12.32.1 to 191.12.63.254191.12.63.2558,190
99191.12.64.0/19191.12.64.1 to 191.12.95.254191.12.95.2558,190
100191.12.96.0/19191.12.96.1 to 191.12.127.254191.12.127.2558,190
101191.12.128.0/19191.12.128.1 to 191.12.159.254191.12.159.2558,190
102191.12.160.0/19191.12.160.1 to 191.12.191.254191.12.191.2558,190
103191.12.192.0/19191.12.192.1 to 191.12.223.254191.12.223.2558,190
104191.12.224.0/19191.12.224.1 to 191.12.255.254191.12.255.2558,190
105191.13.0.0/19191.13.0.1 to 191.13.31.254191.13.31.2558,190
106191.13.32.0/19191.13.32.1 to 191.13.63.254191.13.63.2558,190
107191.13.64.0/19191.13.64.1 to 191.13.95.254191.13.95.2558,190
108191.13.96.0/19191.13.96.1 to 191.13.127.254191.13.127.2558,190
109191.13.128.0/19191.13.128.1 to 191.13.159.254191.13.159.2558,190
110191.13.160.0/19191.13.160.1 to 191.13.191.254191.13.191.2558,190
111191.13.192.0/19191.13.192.1 to 191.13.223.254191.13.223.2558,190
112191.13.224.0/19191.13.224.1 to 191.13.255.254191.13.255.2558,190
113191.14.0.0/19191.14.0.1 to 191.14.31.254191.14.31.2558,190
114191.14.32.0/19191.14.32.1 to 191.14.63.254191.14.63.2558,190
115191.14.64.0/19191.14.64.1 to 191.14.95.254191.14.95.2558,190
116191.14.96.0/19191.14.96.1 to 191.14.127.254191.14.127.2558,190
117191.14.128.0/19191.14.128.1 to 191.14.159.254191.14.159.2558,190
118191.14.160.0/19191.14.160.1 to 191.14.191.254191.14.191.2558,190
119191.14.192.0/19191.14.192.1 to 191.14.223.254191.14.223.2558,190
120191.14.224.0/19191.14.224.1 to 191.14.255.254191.14.255.2558,190
121191.15.0.0/19191.15.0.1 to 191.15.31.254191.15.31.2558,190
122191.15.32.0/19191.15.32.1 to 191.15.63.254191.15.63.2558,190
123191.15.64.0/19191.15.64.1 to 191.15.95.254191.15.95.2558,190
124191.15.96.0/19191.15.96.1 to 191.15.127.254191.15.127.2558,190
125191.15.128.0/19191.15.128.1 to 191.15.159.254191.15.159.2558,190
126191.15.160.0/19191.15.160.1 to 191.15.191.254191.15.191.2558,190
127191.15.192.0/19191.15.192.1 to 191.15.223.254191.15.223.2558,190
128191.15.224.0/19191.15.224.1 to 191.15.255.254191.15.255.2558,190
129191.16.0.0/19191.16.0.1 to 191.16.31.254191.16.31.2558,190
130191.16.32.0/19191.16.32.1 to 191.16.63.254191.16.63.2558,190
131191.16.64.0/19191.16.64.1 to 191.16.95.254191.16.95.2558,190
132191.16.96.0/19191.16.96.1 to 191.16.127.254191.16.127.2558,190
133191.16.128.0/19191.16.128.1 to 191.16.159.254191.16.159.2558,190
134191.16.160.0/19191.16.160.1 to 191.16.191.254191.16.191.2558,190
135191.16.192.0/19191.16.192.1 to 191.16.223.254191.16.223.2558,190
136191.16.224.0/19191.16.224.1 to 191.16.255.254191.16.255.2558,190
137191.17.0.0/19191.17.0.1 to 191.17.31.254191.17.31.2558,190
138191.17.32.0/19191.17.32.1 to 191.17.63.254191.17.63.2558,190
139191.17.64.0/19191.17.64.1 to 191.17.95.254191.17.95.2558,190
140191.17.96.0/19191.17.96.1 to 191.17.127.254191.17.127.2558,190
141191.17.128.0/19191.17.128.1 to 191.17.159.254191.17.159.2558,190
142191.17.160.0/19191.17.160.1 to 191.17.191.254191.17.191.2558,190
143191.17.192.0/19191.17.192.1 to 191.17.223.254191.17.223.2558,190
144191.17.224.0/19191.17.224.1 to 191.17.255.254191.17.255.2558,190
145191.18.0.0/19191.18.0.1 to 191.18.31.254191.18.31.2558,190
146191.18.32.0/19191.18.32.1 to 191.18.63.254191.18.63.2558,190
147191.18.64.0/19191.18.64.1 to 191.18.95.254191.18.95.2558,190
148191.18.96.0/19191.18.96.1 to 191.18.127.254191.18.127.2558,190
149191.18.128.0/19191.18.128.1 to 191.18.159.254191.18.159.2558,190
150191.18.160.0/19191.18.160.1 to 191.18.191.254191.18.191.2558,190
151191.18.192.0/19191.18.192.1 to 191.18.223.254191.18.223.2558,190
152191.18.224.0/19191.18.224.1 to 191.18.255.254191.18.255.2558,190
153191.19.0.0/19191.19.0.1 to 191.19.31.254191.19.31.2558,190
154191.19.32.0/19191.19.32.1 to 191.19.63.254191.19.63.2558,190
155191.19.64.0/19191.19.64.1 to 191.19.95.254191.19.95.2558,190
156191.19.96.0/19191.19.96.1 to 191.19.127.254191.19.127.2558,190
157191.19.128.0/19191.19.128.1 to 191.19.159.254191.19.159.2558,190
158191.19.160.0/19191.19.160.1 to 191.19.191.254191.19.191.2558,190
159191.19.192.0/19191.19.192.1 to 191.19.223.254191.19.223.2558,190
160191.19.224.0/19191.19.224.1 to 191.19.255.254191.19.255.2558,190
161191.20.0.0/19191.20.0.1 to 191.20.31.254191.20.31.2558,190
162191.20.32.0/19191.20.32.1 to 191.20.63.254191.20.63.2558,190
163191.20.64.0/19191.20.64.1 to 191.20.95.254191.20.95.2558,190
164191.20.96.0/19191.20.96.1 to 191.20.127.254191.20.127.2558,190
165191.20.128.0/19191.20.128.1 to 191.20.159.254191.20.159.2558,190
166191.20.160.0/19191.20.160.1 to 191.20.191.254191.20.191.2558,190
167191.20.192.0/19191.20.192.1 to 191.20.223.254191.20.223.2558,190
168191.20.224.0/19191.20.224.1 to 191.20.255.254191.20.255.2558,190
169191.21.0.0/19191.21.0.1 to 191.21.31.254191.21.31.2558,190
170191.21.32.0/19191.21.32.1 to 191.21.63.254191.21.63.2558,190
171191.21.64.0/19191.21.64.1 to 191.21.95.254191.21.95.2558,190
172191.21.96.0/19191.21.96.1 to 191.21.127.254191.21.127.2558,190
173191.21.128.0/19191.21.128.1 to 191.21.159.254191.21.159.2558,190
174191.21.160.0/19191.21.160.1 to 191.21.191.254191.21.191.2558,190
175191.21.192.0/19191.21.192.1 to 191.21.223.254191.21.223.2558,190
176191.21.224.0/19191.21.224.1 to 191.21.255.254191.21.255.2558,190
177191.22.0.0/19191.22.0.1 to 191.22.31.254191.22.31.2558,190
178191.22.32.0/19191.22.32.1 to 191.22.63.254191.22.63.2558,190
179191.22.64.0/19191.22.64.1 to 191.22.95.254191.22.95.2558,190
180191.22.96.0/19191.22.96.1 to 191.22.127.254191.22.127.2558,190
181191.22.128.0/19191.22.128.1 to 191.22.159.254191.22.159.2558,190
182191.22.160.0/19191.22.160.1 to 191.22.191.254191.22.191.2558,190
183191.22.192.0/19191.22.192.1 to 191.22.223.254191.22.223.2558,190
184191.22.224.0/19191.22.224.1 to 191.22.255.254191.22.255.2558,190
185191.23.0.0/19191.23.0.1 to 191.23.31.254191.23.31.2558,190
186191.23.32.0/19191.23.32.1 to 191.23.63.254191.23.63.2558,190
187191.23.64.0/19191.23.64.1 to 191.23.95.254191.23.95.2558,190
188191.23.96.0/19191.23.96.1 to 191.23.127.254191.23.127.2558,190
189191.23.128.0/19191.23.128.1 to 191.23.159.254191.23.159.2558,190
190191.23.160.0/19191.23.160.1 to 191.23.191.254191.23.191.2558,190
191191.23.192.0/19191.23.192.1 to 191.23.223.254191.23.223.2558,190
192191.23.224.0/19191.23.224.1 to 191.23.255.254191.23.255.2558,190
193191.24.0.0/19191.24.0.1 to 191.24.31.254191.24.31.2558,190
194191.24.32.0/19191.24.32.1 to 191.24.63.254191.24.63.2558,190
195191.24.64.0/19191.24.64.1 to 191.24.95.254191.24.95.2558,190
196191.24.96.0/19191.24.96.1 to 191.24.127.254191.24.127.2558,190
197191.24.128.0/19191.24.128.1 to 191.24.159.254191.24.159.2558,190
198191.24.160.0/19191.24.160.1 to 191.24.191.254191.24.191.2558,190
199191.24.192.0/19191.24.192.1 to 191.24.223.254191.24.223.2558,190
200191.24.224.0/19191.24.224.1 to 191.24.255.254191.24.255.2558,190
201191.25.0.0/19191.25.0.1 to 191.25.31.254191.25.31.2558,190
202191.25.32.0/19191.25.32.1 to 191.25.63.254191.25.63.2558,190
203191.25.64.0/19191.25.64.1 to 191.25.95.254191.25.95.2558,190
204191.25.96.0/19191.25.96.1 to 191.25.127.254191.25.127.2558,190
205191.25.128.0/19191.25.128.1 to 191.25.159.254191.25.159.2558,190
206191.25.160.0/19191.25.160.1 to 191.25.191.254191.25.191.2558,190
207191.25.192.0/19191.25.192.1 to 191.25.223.254191.25.223.2558,190
208191.25.224.0/19191.25.224.1 to 191.25.255.254191.25.255.2558,190
209191.26.0.0/19191.26.0.1 to 191.26.31.254191.26.31.2558,190
210191.26.32.0/19191.26.32.1 to 191.26.63.254191.26.63.2558,190
211191.26.64.0/19191.26.64.1 to 191.26.95.254191.26.95.2558,190
212191.26.96.0/19191.26.96.1 to 191.26.127.254191.26.127.2558,190
213191.26.128.0/19191.26.128.1 to 191.26.159.254191.26.159.2558,190
214191.26.160.0/19191.26.160.1 to 191.26.191.254191.26.191.2558,190
215191.26.192.0/19191.26.192.1 to 191.26.223.254191.26.223.2558,190
216191.26.224.0/19191.26.224.1 to 191.26.255.254191.26.255.2558,190
217191.27.0.0/19191.27.0.1 to 191.27.31.254191.27.31.2558,190
218191.27.32.0/19191.27.32.1 to 191.27.63.254191.27.63.2558,190
219191.27.64.0/19191.27.64.1 to 191.27.95.254191.27.95.2558,190
220191.27.96.0/19191.27.96.1 to 191.27.127.254191.27.127.2558,190
221191.27.128.0/19191.27.128.1 to 191.27.159.254191.27.159.2558,190
222191.27.160.0/19191.27.160.1 to 191.27.191.254191.27.191.2558,190
223191.27.192.0/19191.27.192.1 to 191.27.223.254191.27.223.2558,190
224191.27.224.0/19191.27.224.1 to 191.27.255.254191.27.255.2558,190
225191.28.0.0/19191.28.0.1 to 191.28.31.254191.28.31.2558,190
226191.28.32.0/19191.28.32.1 to 191.28.63.254191.28.63.2558,190
227191.28.64.0/19191.28.64.1 to 191.28.95.254191.28.95.2558,190
228191.28.96.0/19191.28.96.1 to 191.28.127.254191.28.127.2558,190
229191.28.128.0/19191.28.128.1 to 191.28.159.254191.28.159.2558,190
230191.28.160.0/19191.28.160.1 to 191.28.191.254191.28.191.2558,190
231191.28.192.0/19191.28.192.1 to 191.28.223.254191.28.223.2558,190
232191.28.224.0/19191.28.224.1 to 191.28.255.254191.28.255.2558,190
233191.29.0.0/19191.29.0.1 to 191.29.31.254191.29.31.2558,190
234191.29.32.0/19191.29.32.1 to 191.29.63.254191.29.63.2558,190
235191.29.64.0/19191.29.64.1 to 191.29.95.254191.29.95.2558,190
236191.29.96.0/19191.29.96.1 to 191.29.127.254191.29.127.2558,190
237191.29.128.0/19191.29.128.1 to 191.29.159.254191.29.159.2558,190
238191.29.160.0/19191.29.160.1 to 191.29.191.254191.29.191.2558,190
239191.29.192.0/19191.29.192.1 to 191.29.223.254191.29.223.2558,190
240191.29.224.0/19191.29.224.1 to 191.29.255.254191.29.255.2558,190
241191.30.0.0/19191.30.0.1 to 191.30.31.254191.30.31.2558,190
242191.30.32.0/19191.30.32.1 to 191.30.63.254191.30.63.2558,190
243191.30.64.0/19191.30.64.1 to 191.30.95.254191.30.95.2558,190
244191.30.96.0/19191.30.96.1 to 191.30.127.254191.30.127.2558,190
245191.30.128.0/19191.30.128.1 to 191.30.159.254191.30.159.2558,190
246191.30.160.0/19191.30.160.1 to 191.30.191.254191.30.191.2558,190
247191.30.192.0/19191.30.192.1 to 191.30.223.254191.30.223.2558,190
248191.30.224.0/19191.30.224.1 to 191.30.255.254191.30.255.2558,190
249191.31.0.0/19191.31.0.1 to 191.31.31.254191.31.31.2558,190
250191.31.32.0/19191.31.32.1 to 191.31.63.254191.31.63.2558,190
251191.31.64.0/19191.31.64.1 to 191.31.95.254191.31.95.2558,190
252191.31.96.0/19191.31.96.1 to 191.31.127.254191.31.127.2558,190
253191.31.128.0/19191.31.128.1 to 191.31.159.254191.31.159.2558,190
254191.31.160.0/19191.31.160.1 to 191.31.191.254191.31.191.2558,190
255191.31.192.0/19191.31.192.1 to 191.31.223.254191.31.223.2558,190
256191.31.224.0/19191.31.224.1 to 191.31.255.254191.31.255.2558,190

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.