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.

Network181.0.0.0/8
Usable hosts16,777,214
Subnet mask255.0.0.0
Addresses16,777,216
Network address
181.0.0.0
Broadcast address
181.255.255.255
First usable
181.0.0.1
Last usable
181.255.255.254
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 B5000000 · Integer 3036676096 to 3053453311
Reverse DNS zone
181.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address10110101..00000000.00000000.00000000181.0.0.0
Subnet mask11111111..00000000.00000000.00000000255.0.0.0
Network10110101..00000000.00000000.00000000181.0.0.0
Broadcast10110101..11111111.11111111.11111111181.255.255.255
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)

181.0.0.0/8 makes 2,048 subnets of /19; the first 256 are listed.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1181.0.0.0/19181.0.0.1 to 181.0.31.254181.0.31.2558,190
2181.0.32.0/19181.0.32.1 to 181.0.63.254181.0.63.2558,190
3181.0.64.0/19181.0.64.1 to 181.0.95.254181.0.95.2558,190
4181.0.96.0/19181.0.96.1 to 181.0.127.254181.0.127.2558,190
5181.0.128.0/19181.0.128.1 to 181.0.159.254181.0.159.2558,190
6181.0.160.0/19181.0.160.1 to 181.0.191.254181.0.191.2558,190
7181.0.192.0/19181.0.192.1 to 181.0.223.254181.0.223.2558,190
8181.0.224.0/19181.0.224.1 to 181.0.255.254181.0.255.2558,190
9181.1.0.0/19181.1.0.1 to 181.1.31.254181.1.31.2558,190
10181.1.32.0/19181.1.32.1 to 181.1.63.254181.1.63.2558,190
11181.1.64.0/19181.1.64.1 to 181.1.95.254181.1.95.2558,190
12181.1.96.0/19181.1.96.1 to 181.1.127.254181.1.127.2558,190
13181.1.128.0/19181.1.128.1 to 181.1.159.254181.1.159.2558,190
14181.1.160.0/19181.1.160.1 to 181.1.191.254181.1.191.2558,190
15181.1.192.0/19181.1.192.1 to 181.1.223.254181.1.223.2558,190
16181.1.224.0/19181.1.224.1 to 181.1.255.254181.1.255.2558,190
17181.2.0.0/19181.2.0.1 to 181.2.31.254181.2.31.2558,190
18181.2.32.0/19181.2.32.1 to 181.2.63.254181.2.63.2558,190
19181.2.64.0/19181.2.64.1 to 181.2.95.254181.2.95.2558,190
20181.2.96.0/19181.2.96.1 to 181.2.127.254181.2.127.2558,190
21181.2.128.0/19181.2.128.1 to 181.2.159.254181.2.159.2558,190
22181.2.160.0/19181.2.160.1 to 181.2.191.254181.2.191.2558,190
23181.2.192.0/19181.2.192.1 to 181.2.223.254181.2.223.2558,190
24181.2.224.0/19181.2.224.1 to 181.2.255.254181.2.255.2558,190
25181.3.0.0/19181.3.0.1 to 181.3.31.254181.3.31.2558,190
26181.3.32.0/19181.3.32.1 to 181.3.63.254181.3.63.2558,190
27181.3.64.0/19181.3.64.1 to 181.3.95.254181.3.95.2558,190
28181.3.96.0/19181.3.96.1 to 181.3.127.254181.3.127.2558,190
29181.3.128.0/19181.3.128.1 to 181.3.159.254181.3.159.2558,190
30181.3.160.0/19181.3.160.1 to 181.3.191.254181.3.191.2558,190
31181.3.192.0/19181.3.192.1 to 181.3.223.254181.3.223.2558,190
32181.3.224.0/19181.3.224.1 to 181.3.255.254181.3.255.2558,190
33181.4.0.0/19181.4.0.1 to 181.4.31.254181.4.31.2558,190
34181.4.32.0/19181.4.32.1 to 181.4.63.254181.4.63.2558,190
35181.4.64.0/19181.4.64.1 to 181.4.95.254181.4.95.2558,190
36181.4.96.0/19181.4.96.1 to 181.4.127.254181.4.127.2558,190
37181.4.128.0/19181.4.128.1 to 181.4.159.254181.4.159.2558,190
38181.4.160.0/19181.4.160.1 to 181.4.191.254181.4.191.2558,190
39181.4.192.0/19181.4.192.1 to 181.4.223.254181.4.223.2558,190
40181.4.224.0/19181.4.224.1 to 181.4.255.254181.4.255.2558,190
41181.5.0.0/19181.5.0.1 to 181.5.31.254181.5.31.2558,190
42181.5.32.0/19181.5.32.1 to 181.5.63.254181.5.63.2558,190
43181.5.64.0/19181.5.64.1 to 181.5.95.254181.5.95.2558,190
44181.5.96.0/19181.5.96.1 to 181.5.127.254181.5.127.2558,190
45181.5.128.0/19181.5.128.1 to 181.5.159.254181.5.159.2558,190
46181.5.160.0/19181.5.160.1 to 181.5.191.254181.5.191.2558,190
47181.5.192.0/19181.5.192.1 to 181.5.223.254181.5.223.2558,190
48181.5.224.0/19181.5.224.1 to 181.5.255.254181.5.255.2558,190
49181.6.0.0/19181.6.0.1 to 181.6.31.254181.6.31.2558,190
50181.6.32.0/19181.6.32.1 to 181.6.63.254181.6.63.2558,190
51181.6.64.0/19181.6.64.1 to 181.6.95.254181.6.95.2558,190
52181.6.96.0/19181.6.96.1 to 181.6.127.254181.6.127.2558,190
53181.6.128.0/19181.6.128.1 to 181.6.159.254181.6.159.2558,190
54181.6.160.0/19181.6.160.1 to 181.6.191.254181.6.191.2558,190
55181.6.192.0/19181.6.192.1 to 181.6.223.254181.6.223.2558,190
56181.6.224.0/19181.6.224.1 to 181.6.255.254181.6.255.2558,190
57181.7.0.0/19181.7.0.1 to 181.7.31.254181.7.31.2558,190
58181.7.32.0/19181.7.32.1 to 181.7.63.254181.7.63.2558,190
59181.7.64.0/19181.7.64.1 to 181.7.95.254181.7.95.2558,190
60181.7.96.0/19181.7.96.1 to 181.7.127.254181.7.127.2558,190
61181.7.128.0/19181.7.128.1 to 181.7.159.254181.7.159.2558,190
62181.7.160.0/19181.7.160.1 to 181.7.191.254181.7.191.2558,190
63181.7.192.0/19181.7.192.1 to 181.7.223.254181.7.223.2558,190
64181.7.224.0/19181.7.224.1 to 181.7.255.254181.7.255.2558,190
65181.8.0.0/19181.8.0.1 to 181.8.31.254181.8.31.2558,190
66181.8.32.0/19181.8.32.1 to 181.8.63.254181.8.63.2558,190
67181.8.64.0/19181.8.64.1 to 181.8.95.254181.8.95.2558,190
68181.8.96.0/19181.8.96.1 to 181.8.127.254181.8.127.2558,190
69181.8.128.0/19181.8.128.1 to 181.8.159.254181.8.159.2558,190
70181.8.160.0/19181.8.160.1 to 181.8.191.254181.8.191.2558,190
71181.8.192.0/19181.8.192.1 to 181.8.223.254181.8.223.2558,190
72181.8.224.0/19181.8.224.1 to 181.8.255.254181.8.255.2558,190
73181.9.0.0/19181.9.0.1 to 181.9.31.254181.9.31.2558,190
74181.9.32.0/19181.9.32.1 to 181.9.63.254181.9.63.2558,190
75181.9.64.0/19181.9.64.1 to 181.9.95.254181.9.95.2558,190
76181.9.96.0/19181.9.96.1 to 181.9.127.254181.9.127.2558,190
77181.9.128.0/19181.9.128.1 to 181.9.159.254181.9.159.2558,190
78181.9.160.0/19181.9.160.1 to 181.9.191.254181.9.191.2558,190
79181.9.192.0/19181.9.192.1 to 181.9.223.254181.9.223.2558,190
80181.9.224.0/19181.9.224.1 to 181.9.255.254181.9.255.2558,190
81181.10.0.0/19181.10.0.1 to 181.10.31.254181.10.31.2558,190
82181.10.32.0/19181.10.32.1 to 181.10.63.254181.10.63.2558,190
83181.10.64.0/19181.10.64.1 to 181.10.95.254181.10.95.2558,190
84181.10.96.0/19181.10.96.1 to 181.10.127.254181.10.127.2558,190
85181.10.128.0/19181.10.128.1 to 181.10.159.254181.10.159.2558,190
86181.10.160.0/19181.10.160.1 to 181.10.191.254181.10.191.2558,190
87181.10.192.0/19181.10.192.1 to 181.10.223.254181.10.223.2558,190
88181.10.224.0/19181.10.224.1 to 181.10.255.254181.10.255.2558,190
89181.11.0.0/19181.11.0.1 to 181.11.31.254181.11.31.2558,190
90181.11.32.0/19181.11.32.1 to 181.11.63.254181.11.63.2558,190
91181.11.64.0/19181.11.64.1 to 181.11.95.254181.11.95.2558,190
92181.11.96.0/19181.11.96.1 to 181.11.127.254181.11.127.2558,190
93181.11.128.0/19181.11.128.1 to 181.11.159.254181.11.159.2558,190
94181.11.160.0/19181.11.160.1 to 181.11.191.254181.11.191.2558,190
95181.11.192.0/19181.11.192.1 to 181.11.223.254181.11.223.2558,190
96181.11.224.0/19181.11.224.1 to 181.11.255.254181.11.255.2558,190
97181.12.0.0/19181.12.0.1 to 181.12.31.254181.12.31.2558,190
98181.12.32.0/19181.12.32.1 to 181.12.63.254181.12.63.2558,190
99181.12.64.0/19181.12.64.1 to 181.12.95.254181.12.95.2558,190
100181.12.96.0/19181.12.96.1 to 181.12.127.254181.12.127.2558,190
101181.12.128.0/19181.12.128.1 to 181.12.159.254181.12.159.2558,190
102181.12.160.0/19181.12.160.1 to 181.12.191.254181.12.191.2558,190
103181.12.192.0/19181.12.192.1 to 181.12.223.254181.12.223.2558,190
104181.12.224.0/19181.12.224.1 to 181.12.255.254181.12.255.2558,190
105181.13.0.0/19181.13.0.1 to 181.13.31.254181.13.31.2558,190
106181.13.32.0/19181.13.32.1 to 181.13.63.254181.13.63.2558,190
107181.13.64.0/19181.13.64.1 to 181.13.95.254181.13.95.2558,190
108181.13.96.0/19181.13.96.1 to 181.13.127.254181.13.127.2558,190
109181.13.128.0/19181.13.128.1 to 181.13.159.254181.13.159.2558,190
110181.13.160.0/19181.13.160.1 to 181.13.191.254181.13.191.2558,190
111181.13.192.0/19181.13.192.1 to 181.13.223.254181.13.223.2558,190
112181.13.224.0/19181.13.224.1 to 181.13.255.254181.13.255.2558,190
113181.14.0.0/19181.14.0.1 to 181.14.31.254181.14.31.2558,190
114181.14.32.0/19181.14.32.1 to 181.14.63.254181.14.63.2558,190
115181.14.64.0/19181.14.64.1 to 181.14.95.254181.14.95.2558,190
116181.14.96.0/19181.14.96.1 to 181.14.127.254181.14.127.2558,190
117181.14.128.0/19181.14.128.1 to 181.14.159.254181.14.159.2558,190
118181.14.160.0/19181.14.160.1 to 181.14.191.254181.14.191.2558,190
119181.14.192.0/19181.14.192.1 to 181.14.223.254181.14.223.2558,190
120181.14.224.0/19181.14.224.1 to 181.14.255.254181.14.255.2558,190
121181.15.0.0/19181.15.0.1 to 181.15.31.254181.15.31.2558,190
122181.15.32.0/19181.15.32.1 to 181.15.63.254181.15.63.2558,190
123181.15.64.0/19181.15.64.1 to 181.15.95.254181.15.95.2558,190
124181.15.96.0/19181.15.96.1 to 181.15.127.254181.15.127.2558,190
125181.15.128.0/19181.15.128.1 to 181.15.159.254181.15.159.2558,190
126181.15.160.0/19181.15.160.1 to 181.15.191.254181.15.191.2558,190
127181.15.192.0/19181.15.192.1 to 181.15.223.254181.15.223.2558,190
128181.15.224.0/19181.15.224.1 to 181.15.255.254181.15.255.2558,190
129181.16.0.0/19181.16.0.1 to 181.16.31.254181.16.31.2558,190
130181.16.32.0/19181.16.32.1 to 181.16.63.254181.16.63.2558,190
131181.16.64.0/19181.16.64.1 to 181.16.95.254181.16.95.2558,190
132181.16.96.0/19181.16.96.1 to 181.16.127.254181.16.127.2558,190
133181.16.128.0/19181.16.128.1 to 181.16.159.254181.16.159.2558,190
134181.16.160.0/19181.16.160.1 to 181.16.191.254181.16.191.2558,190
135181.16.192.0/19181.16.192.1 to 181.16.223.254181.16.223.2558,190
136181.16.224.0/19181.16.224.1 to 181.16.255.254181.16.255.2558,190
137181.17.0.0/19181.17.0.1 to 181.17.31.254181.17.31.2558,190
138181.17.32.0/19181.17.32.1 to 181.17.63.254181.17.63.2558,190
139181.17.64.0/19181.17.64.1 to 181.17.95.254181.17.95.2558,190
140181.17.96.0/19181.17.96.1 to 181.17.127.254181.17.127.2558,190
141181.17.128.0/19181.17.128.1 to 181.17.159.254181.17.159.2558,190
142181.17.160.0/19181.17.160.1 to 181.17.191.254181.17.191.2558,190
143181.17.192.0/19181.17.192.1 to 181.17.223.254181.17.223.2558,190
144181.17.224.0/19181.17.224.1 to 181.17.255.254181.17.255.2558,190
145181.18.0.0/19181.18.0.1 to 181.18.31.254181.18.31.2558,190
146181.18.32.0/19181.18.32.1 to 181.18.63.254181.18.63.2558,190
147181.18.64.0/19181.18.64.1 to 181.18.95.254181.18.95.2558,190
148181.18.96.0/19181.18.96.1 to 181.18.127.254181.18.127.2558,190
149181.18.128.0/19181.18.128.1 to 181.18.159.254181.18.159.2558,190
150181.18.160.0/19181.18.160.1 to 181.18.191.254181.18.191.2558,190
151181.18.192.0/19181.18.192.1 to 181.18.223.254181.18.223.2558,190
152181.18.224.0/19181.18.224.1 to 181.18.255.254181.18.255.2558,190
153181.19.0.0/19181.19.0.1 to 181.19.31.254181.19.31.2558,190
154181.19.32.0/19181.19.32.1 to 181.19.63.254181.19.63.2558,190
155181.19.64.0/19181.19.64.1 to 181.19.95.254181.19.95.2558,190
156181.19.96.0/19181.19.96.1 to 181.19.127.254181.19.127.2558,190
157181.19.128.0/19181.19.128.1 to 181.19.159.254181.19.159.2558,190
158181.19.160.0/19181.19.160.1 to 181.19.191.254181.19.191.2558,190
159181.19.192.0/19181.19.192.1 to 181.19.223.254181.19.223.2558,190
160181.19.224.0/19181.19.224.1 to 181.19.255.254181.19.255.2558,190
161181.20.0.0/19181.20.0.1 to 181.20.31.254181.20.31.2558,190
162181.20.32.0/19181.20.32.1 to 181.20.63.254181.20.63.2558,190
163181.20.64.0/19181.20.64.1 to 181.20.95.254181.20.95.2558,190
164181.20.96.0/19181.20.96.1 to 181.20.127.254181.20.127.2558,190
165181.20.128.0/19181.20.128.1 to 181.20.159.254181.20.159.2558,190
166181.20.160.0/19181.20.160.1 to 181.20.191.254181.20.191.2558,190
167181.20.192.0/19181.20.192.1 to 181.20.223.254181.20.223.2558,190
168181.20.224.0/19181.20.224.1 to 181.20.255.254181.20.255.2558,190
169181.21.0.0/19181.21.0.1 to 181.21.31.254181.21.31.2558,190
170181.21.32.0/19181.21.32.1 to 181.21.63.254181.21.63.2558,190
171181.21.64.0/19181.21.64.1 to 181.21.95.254181.21.95.2558,190
172181.21.96.0/19181.21.96.1 to 181.21.127.254181.21.127.2558,190
173181.21.128.0/19181.21.128.1 to 181.21.159.254181.21.159.2558,190
174181.21.160.0/19181.21.160.1 to 181.21.191.254181.21.191.2558,190
175181.21.192.0/19181.21.192.1 to 181.21.223.254181.21.223.2558,190
176181.21.224.0/19181.21.224.1 to 181.21.255.254181.21.255.2558,190
177181.22.0.0/19181.22.0.1 to 181.22.31.254181.22.31.2558,190
178181.22.32.0/19181.22.32.1 to 181.22.63.254181.22.63.2558,190
179181.22.64.0/19181.22.64.1 to 181.22.95.254181.22.95.2558,190
180181.22.96.0/19181.22.96.1 to 181.22.127.254181.22.127.2558,190
181181.22.128.0/19181.22.128.1 to 181.22.159.254181.22.159.2558,190
182181.22.160.0/19181.22.160.1 to 181.22.191.254181.22.191.2558,190
183181.22.192.0/19181.22.192.1 to 181.22.223.254181.22.223.2558,190
184181.22.224.0/19181.22.224.1 to 181.22.255.254181.22.255.2558,190
185181.23.0.0/19181.23.0.1 to 181.23.31.254181.23.31.2558,190
186181.23.32.0/19181.23.32.1 to 181.23.63.254181.23.63.2558,190
187181.23.64.0/19181.23.64.1 to 181.23.95.254181.23.95.2558,190
188181.23.96.0/19181.23.96.1 to 181.23.127.254181.23.127.2558,190
189181.23.128.0/19181.23.128.1 to 181.23.159.254181.23.159.2558,190
190181.23.160.0/19181.23.160.1 to 181.23.191.254181.23.191.2558,190
191181.23.192.0/19181.23.192.1 to 181.23.223.254181.23.223.2558,190
192181.23.224.0/19181.23.224.1 to 181.23.255.254181.23.255.2558,190
193181.24.0.0/19181.24.0.1 to 181.24.31.254181.24.31.2558,190
194181.24.32.0/19181.24.32.1 to 181.24.63.254181.24.63.2558,190
195181.24.64.0/19181.24.64.1 to 181.24.95.254181.24.95.2558,190
196181.24.96.0/19181.24.96.1 to 181.24.127.254181.24.127.2558,190
197181.24.128.0/19181.24.128.1 to 181.24.159.254181.24.159.2558,190
198181.24.160.0/19181.24.160.1 to 181.24.191.254181.24.191.2558,190
199181.24.192.0/19181.24.192.1 to 181.24.223.254181.24.223.2558,190
200181.24.224.0/19181.24.224.1 to 181.24.255.254181.24.255.2558,190
201181.25.0.0/19181.25.0.1 to 181.25.31.254181.25.31.2558,190
202181.25.32.0/19181.25.32.1 to 181.25.63.254181.25.63.2558,190
203181.25.64.0/19181.25.64.1 to 181.25.95.254181.25.95.2558,190
204181.25.96.0/19181.25.96.1 to 181.25.127.254181.25.127.2558,190
205181.25.128.0/19181.25.128.1 to 181.25.159.254181.25.159.2558,190
206181.25.160.0/19181.25.160.1 to 181.25.191.254181.25.191.2558,190
207181.25.192.0/19181.25.192.1 to 181.25.223.254181.25.223.2558,190
208181.25.224.0/19181.25.224.1 to 181.25.255.254181.25.255.2558,190
209181.26.0.0/19181.26.0.1 to 181.26.31.254181.26.31.2558,190
210181.26.32.0/19181.26.32.1 to 181.26.63.254181.26.63.2558,190
211181.26.64.0/19181.26.64.1 to 181.26.95.254181.26.95.2558,190
212181.26.96.0/19181.26.96.1 to 181.26.127.254181.26.127.2558,190
213181.26.128.0/19181.26.128.1 to 181.26.159.254181.26.159.2558,190
214181.26.160.0/19181.26.160.1 to 181.26.191.254181.26.191.2558,190
215181.26.192.0/19181.26.192.1 to 181.26.223.254181.26.223.2558,190
216181.26.224.0/19181.26.224.1 to 181.26.255.254181.26.255.2558,190
217181.27.0.0/19181.27.0.1 to 181.27.31.254181.27.31.2558,190
218181.27.32.0/19181.27.32.1 to 181.27.63.254181.27.63.2558,190
219181.27.64.0/19181.27.64.1 to 181.27.95.254181.27.95.2558,190
220181.27.96.0/19181.27.96.1 to 181.27.127.254181.27.127.2558,190
221181.27.128.0/19181.27.128.1 to 181.27.159.254181.27.159.2558,190
222181.27.160.0/19181.27.160.1 to 181.27.191.254181.27.191.2558,190
223181.27.192.0/19181.27.192.1 to 181.27.223.254181.27.223.2558,190
224181.27.224.0/19181.27.224.1 to 181.27.255.254181.27.255.2558,190
225181.28.0.0/19181.28.0.1 to 181.28.31.254181.28.31.2558,190
226181.28.32.0/19181.28.32.1 to 181.28.63.254181.28.63.2558,190
227181.28.64.0/19181.28.64.1 to 181.28.95.254181.28.95.2558,190
228181.28.96.0/19181.28.96.1 to 181.28.127.254181.28.127.2558,190
229181.28.128.0/19181.28.128.1 to 181.28.159.254181.28.159.2558,190
230181.28.160.0/19181.28.160.1 to 181.28.191.254181.28.191.2558,190
231181.28.192.0/19181.28.192.1 to 181.28.223.254181.28.223.2558,190
232181.28.224.0/19181.28.224.1 to 181.28.255.254181.28.255.2558,190
233181.29.0.0/19181.29.0.1 to 181.29.31.254181.29.31.2558,190
234181.29.32.0/19181.29.32.1 to 181.29.63.254181.29.63.2558,190
235181.29.64.0/19181.29.64.1 to 181.29.95.254181.29.95.2558,190
236181.29.96.0/19181.29.96.1 to 181.29.127.254181.29.127.2558,190
237181.29.128.0/19181.29.128.1 to 181.29.159.254181.29.159.2558,190
238181.29.160.0/19181.29.160.1 to 181.29.191.254181.29.191.2558,190
239181.29.192.0/19181.29.192.1 to 181.29.223.254181.29.223.2558,190
240181.29.224.0/19181.29.224.1 to 181.29.255.254181.29.255.2558,190
241181.30.0.0/19181.30.0.1 to 181.30.31.254181.30.31.2558,190
242181.30.32.0/19181.30.32.1 to 181.30.63.254181.30.63.2558,190
243181.30.64.0/19181.30.64.1 to 181.30.95.254181.30.95.2558,190
244181.30.96.0/19181.30.96.1 to 181.30.127.254181.30.127.2558,190
245181.30.128.0/19181.30.128.1 to 181.30.159.254181.30.159.2558,190
246181.30.160.0/19181.30.160.1 to 181.30.191.254181.30.191.2558,190
247181.30.192.0/19181.30.192.1 to 181.30.223.254181.30.223.2558,190
248181.30.224.0/19181.30.224.1 to 181.30.255.254181.30.255.2558,190
249181.31.0.0/19181.31.0.1 to 181.31.31.254181.31.31.2558,190
250181.31.32.0/19181.31.32.1 to 181.31.63.254181.31.63.2558,190
251181.31.64.0/19181.31.64.1 to 181.31.95.254181.31.95.2558,190
252181.31.96.0/19181.31.96.1 to 181.31.127.254181.31.127.2558,190
253181.31.128.0/19181.31.128.1 to 181.31.159.254181.31.159.2558,190
254181.31.160.0/19181.31.160.1 to 181.31.191.254181.31.191.2558,190
255181.31.192.0/19181.31.192.1 to 181.31.223.254181.31.223.2558,190
256181.31.224.0/19181.31.224.1 to 181.31.255.254181.31.255.2558,190

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.