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.

Network172.0.0.0/7
Usable hosts33,554,430
Subnet mask254.0.0.0
Addresses33,554,432
Network address
172.0.0.0
Broadcast address
173.255.255.255
First usable
172.0.0.1
Last usable
173.255.255.254
Usable hosts
33,554,430 (33,554,432 less the network and broadcast addresses)
Subnet mask
254.0.0.0
Wildcard mask
1.255.255.255 (Cisco ACLs, OSPF)
Prefix length
/7
Type
Public public
Old class
B (default /16)
As numbers
Hex AC000000 · Integer 2885681152 to 2919235583
Reverse DNS zones
172.in-addr.arpa
173.in-addr.arpa
/7 is not on a 8-bit boundary, so it takes 2 /8 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address10101100.00000000.00000000.00000000172.0.0.0
Subnet mask11111110.00000000.00000000.00000000254.0.0.0
Network10101100.00000000.00000000.00000000172.0.0.0
Broadcast10101101.11111111.11111111.11111111173.255.255.255
Split into smaller subnets/19
/8 (2)/9 (4)/10 (8)/11 (16)/12 (32)/13 (64)/14 (128)/15 (256)/16 (512)/17 (1,024)/18 (2,048)/19 (4,096)

172.0.0.0/7 makes 4,096 subnets of /19; the first 256 are listed.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1172.0.0.0/19172.0.0.1 to 172.0.31.254172.0.31.2558,190
2172.0.32.0/19172.0.32.1 to 172.0.63.254172.0.63.2558,190
3172.0.64.0/19172.0.64.1 to 172.0.95.254172.0.95.2558,190
4172.0.96.0/19172.0.96.1 to 172.0.127.254172.0.127.2558,190
5172.0.128.0/19172.0.128.1 to 172.0.159.254172.0.159.2558,190
6172.0.160.0/19172.0.160.1 to 172.0.191.254172.0.191.2558,190
7172.0.192.0/19172.0.192.1 to 172.0.223.254172.0.223.2558,190
8172.0.224.0/19172.0.224.1 to 172.0.255.254172.0.255.2558,190
9172.1.0.0/19172.1.0.1 to 172.1.31.254172.1.31.2558,190
10172.1.32.0/19172.1.32.1 to 172.1.63.254172.1.63.2558,190
11172.1.64.0/19172.1.64.1 to 172.1.95.254172.1.95.2558,190
12172.1.96.0/19172.1.96.1 to 172.1.127.254172.1.127.2558,190
13172.1.128.0/19172.1.128.1 to 172.1.159.254172.1.159.2558,190
14172.1.160.0/19172.1.160.1 to 172.1.191.254172.1.191.2558,190
15172.1.192.0/19172.1.192.1 to 172.1.223.254172.1.223.2558,190
16172.1.224.0/19172.1.224.1 to 172.1.255.254172.1.255.2558,190
17172.2.0.0/19172.2.0.1 to 172.2.31.254172.2.31.2558,190
18172.2.32.0/19172.2.32.1 to 172.2.63.254172.2.63.2558,190
19172.2.64.0/19172.2.64.1 to 172.2.95.254172.2.95.2558,190
20172.2.96.0/19172.2.96.1 to 172.2.127.254172.2.127.2558,190
21172.2.128.0/19172.2.128.1 to 172.2.159.254172.2.159.2558,190
22172.2.160.0/19172.2.160.1 to 172.2.191.254172.2.191.2558,190
23172.2.192.0/19172.2.192.1 to 172.2.223.254172.2.223.2558,190
24172.2.224.0/19172.2.224.1 to 172.2.255.254172.2.255.2558,190
25172.3.0.0/19172.3.0.1 to 172.3.31.254172.3.31.2558,190
26172.3.32.0/19172.3.32.1 to 172.3.63.254172.3.63.2558,190
27172.3.64.0/19172.3.64.1 to 172.3.95.254172.3.95.2558,190
28172.3.96.0/19172.3.96.1 to 172.3.127.254172.3.127.2558,190
29172.3.128.0/19172.3.128.1 to 172.3.159.254172.3.159.2558,190
30172.3.160.0/19172.3.160.1 to 172.3.191.254172.3.191.2558,190
31172.3.192.0/19172.3.192.1 to 172.3.223.254172.3.223.2558,190
32172.3.224.0/19172.3.224.1 to 172.3.255.254172.3.255.2558,190
33172.4.0.0/19172.4.0.1 to 172.4.31.254172.4.31.2558,190
34172.4.32.0/19172.4.32.1 to 172.4.63.254172.4.63.2558,190
35172.4.64.0/19172.4.64.1 to 172.4.95.254172.4.95.2558,190
36172.4.96.0/19172.4.96.1 to 172.4.127.254172.4.127.2558,190
37172.4.128.0/19172.4.128.1 to 172.4.159.254172.4.159.2558,190
38172.4.160.0/19172.4.160.1 to 172.4.191.254172.4.191.2558,190
39172.4.192.0/19172.4.192.1 to 172.4.223.254172.4.223.2558,190
40172.4.224.0/19172.4.224.1 to 172.4.255.254172.4.255.2558,190
41172.5.0.0/19172.5.0.1 to 172.5.31.254172.5.31.2558,190
42172.5.32.0/19172.5.32.1 to 172.5.63.254172.5.63.2558,190
43172.5.64.0/19172.5.64.1 to 172.5.95.254172.5.95.2558,190
44172.5.96.0/19172.5.96.1 to 172.5.127.254172.5.127.2558,190
45172.5.128.0/19172.5.128.1 to 172.5.159.254172.5.159.2558,190
46172.5.160.0/19172.5.160.1 to 172.5.191.254172.5.191.2558,190
47172.5.192.0/19172.5.192.1 to 172.5.223.254172.5.223.2558,190
48172.5.224.0/19172.5.224.1 to 172.5.255.254172.5.255.2558,190
49172.6.0.0/19172.6.0.1 to 172.6.31.254172.6.31.2558,190
50172.6.32.0/19172.6.32.1 to 172.6.63.254172.6.63.2558,190
51172.6.64.0/19172.6.64.1 to 172.6.95.254172.6.95.2558,190
52172.6.96.0/19172.6.96.1 to 172.6.127.254172.6.127.2558,190
53172.6.128.0/19172.6.128.1 to 172.6.159.254172.6.159.2558,190
54172.6.160.0/19172.6.160.1 to 172.6.191.254172.6.191.2558,190
55172.6.192.0/19172.6.192.1 to 172.6.223.254172.6.223.2558,190
56172.6.224.0/19172.6.224.1 to 172.6.255.254172.6.255.2558,190
57172.7.0.0/19172.7.0.1 to 172.7.31.254172.7.31.2558,190
58172.7.32.0/19172.7.32.1 to 172.7.63.254172.7.63.2558,190
59172.7.64.0/19172.7.64.1 to 172.7.95.254172.7.95.2558,190
60172.7.96.0/19172.7.96.1 to 172.7.127.254172.7.127.2558,190
61172.7.128.0/19172.7.128.1 to 172.7.159.254172.7.159.2558,190
62172.7.160.0/19172.7.160.1 to 172.7.191.254172.7.191.2558,190
63172.7.192.0/19172.7.192.1 to 172.7.223.254172.7.223.2558,190
64172.7.224.0/19172.7.224.1 to 172.7.255.254172.7.255.2558,190
65172.8.0.0/19172.8.0.1 to 172.8.31.254172.8.31.2558,190
66172.8.32.0/19172.8.32.1 to 172.8.63.254172.8.63.2558,190
67172.8.64.0/19172.8.64.1 to 172.8.95.254172.8.95.2558,190
68172.8.96.0/19172.8.96.1 to 172.8.127.254172.8.127.2558,190
69172.8.128.0/19172.8.128.1 to 172.8.159.254172.8.159.2558,190
70172.8.160.0/19172.8.160.1 to 172.8.191.254172.8.191.2558,190
71172.8.192.0/19172.8.192.1 to 172.8.223.254172.8.223.2558,190
72172.8.224.0/19172.8.224.1 to 172.8.255.254172.8.255.2558,190
73172.9.0.0/19172.9.0.1 to 172.9.31.254172.9.31.2558,190
74172.9.32.0/19172.9.32.1 to 172.9.63.254172.9.63.2558,190
75172.9.64.0/19172.9.64.1 to 172.9.95.254172.9.95.2558,190
76172.9.96.0/19172.9.96.1 to 172.9.127.254172.9.127.2558,190
77172.9.128.0/19172.9.128.1 to 172.9.159.254172.9.159.2558,190
78172.9.160.0/19172.9.160.1 to 172.9.191.254172.9.191.2558,190
79172.9.192.0/19172.9.192.1 to 172.9.223.254172.9.223.2558,190
80172.9.224.0/19172.9.224.1 to 172.9.255.254172.9.255.2558,190
81172.10.0.0/19172.10.0.1 to 172.10.31.254172.10.31.2558,190
82172.10.32.0/19172.10.32.1 to 172.10.63.254172.10.63.2558,190
83172.10.64.0/19172.10.64.1 to 172.10.95.254172.10.95.2558,190
84172.10.96.0/19172.10.96.1 to 172.10.127.254172.10.127.2558,190
85172.10.128.0/19172.10.128.1 to 172.10.159.254172.10.159.2558,190
86172.10.160.0/19172.10.160.1 to 172.10.191.254172.10.191.2558,190
87172.10.192.0/19172.10.192.1 to 172.10.223.254172.10.223.2558,190
88172.10.224.0/19172.10.224.1 to 172.10.255.254172.10.255.2558,190
89172.11.0.0/19172.11.0.1 to 172.11.31.254172.11.31.2558,190
90172.11.32.0/19172.11.32.1 to 172.11.63.254172.11.63.2558,190
91172.11.64.0/19172.11.64.1 to 172.11.95.254172.11.95.2558,190
92172.11.96.0/19172.11.96.1 to 172.11.127.254172.11.127.2558,190
93172.11.128.0/19172.11.128.1 to 172.11.159.254172.11.159.2558,190
94172.11.160.0/19172.11.160.1 to 172.11.191.254172.11.191.2558,190
95172.11.192.0/19172.11.192.1 to 172.11.223.254172.11.223.2558,190
96172.11.224.0/19172.11.224.1 to 172.11.255.254172.11.255.2558,190
97172.12.0.0/19172.12.0.1 to 172.12.31.254172.12.31.2558,190
98172.12.32.0/19172.12.32.1 to 172.12.63.254172.12.63.2558,190
99172.12.64.0/19172.12.64.1 to 172.12.95.254172.12.95.2558,190
100172.12.96.0/19172.12.96.1 to 172.12.127.254172.12.127.2558,190
101172.12.128.0/19172.12.128.1 to 172.12.159.254172.12.159.2558,190
102172.12.160.0/19172.12.160.1 to 172.12.191.254172.12.191.2558,190
103172.12.192.0/19172.12.192.1 to 172.12.223.254172.12.223.2558,190
104172.12.224.0/19172.12.224.1 to 172.12.255.254172.12.255.2558,190
105172.13.0.0/19172.13.0.1 to 172.13.31.254172.13.31.2558,190
106172.13.32.0/19172.13.32.1 to 172.13.63.254172.13.63.2558,190
107172.13.64.0/19172.13.64.1 to 172.13.95.254172.13.95.2558,190
108172.13.96.0/19172.13.96.1 to 172.13.127.254172.13.127.2558,190
109172.13.128.0/19172.13.128.1 to 172.13.159.254172.13.159.2558,190
110172.13.160.0/19172.13.160.1 to 172.13.191.254172.13.191.2558,190
111172.13.192.0/19172.13.192.1 to 172.13.223.254172.13.223.2558,190
112172.13.224.0/19172.13.224.1 to 172.13.255.254172.13.255.2558,190
113172.14.0.0/19172.14.0.1 to 172.14.31.254172.14.31.2558,190
114172.14.32.0/19172.14.32.1 to 172.14.63.254172.14.63.2558,190
115172.14.64.0/19172.14.64.1 to 172.14.95.254172.14.95.2558,190
116172.14.96.0/19172.14.96.1 to 172.14.127.254172.14.127.2558,190
117172.14.128.0/19172.14.128.1 to 172.14.159.254172.14.159.2558,190
118172.14.160.0/19172.14.160.1 to 172.14.191.254172.14.191.2558,190
119172.14.192.0/19172.14.192.1 to 172.14.223.254172.14.223.2558,190
120172.14.224.0/19172.14.224.1 to 172.14.255.254172.14.255.2558,190
121172.15.0.0/19172.15.0.1 to 172.15.31.254172.15.31.2558,190
122172.15.32.0/19172.15.32.1 to 172.15.63.254172.15.63.2558,190
123172.15.64.0/19172.15.64.1 to 172.15.95.254172.15.95.2558,190
124172.15.96.0/19172.15.96.1 to 172.15.127.254172.15.127.2558,190
125172.15.128.0/19172.15.128.1 to 172.15.159.254172.15.159.2558,190
126172.15.160.0/19172.15.160.1 to 172.15.191.254172.15.191.2558,190
127172.15.192.0/19172.15.192.1 to 172.15.223.254172.15.223.2558,190
128172.15.224.0/19172.15.224.1 to 172.15.255.254172.15.255.2558,190
129172.16.0.0/19172.16.0.1 to 172.16.31.254172.16.31.2558,190
130172.16.32.0/19172.16.32.1 to 172.16.63.254172.16.63.2558,190
131172.16.64.0/19172.16.64.1 to 172.16.95.254172.16.95.2558,190
132172.16.96.0/19172.16.96.1 to 172.16.127.254172.16.127.2558,190
133172.16.128.0/19172.16.128.1 to 172.16.159.254172.16.159.2558,190
134172.16.160.0/19172.16.160.1 to 172.16.191.254172.16.191.2558,190
135172.16.192.0/19172.16.192.1 to 172.16.223.254172.16.223.2558,190
136172.16.224.0/19172.16.224.1 to 172.16.255.254172.16.255.2558,190
137172.17.0.0/19172.17.0.1 to 172.17.31.254172.17.31.2558,190
138172.17.32.0/19172.17.32.1 to 172.17.63.254172.17.63.2558,190
139172.17.64.0/19172.17.64.1 to 172.17.95.254172.17.95.2558,190
140172.17.96.0/19172.17.96.1 to 172.17.127.254172.17.127.2558,190
141172.17.128.0/19172.17.128.1 to 172.17.159.254172.17.159.2558,190
142172.17.160.0/19172.17.160.1 to 172.17.191.254172.17.191.2558,190
143172.17.192.0/19172.17.192.1 to 172.17.223.254172.17.223.2558,190
144172.17.224.0/19172.17.224.1 to 172.17.255.254172.17.255.2558,190
145172.18.0.0/19172.18.0.1 to 172.18.31.254172.18.31.2558,190
146172.18.32.0/19172.18.32.1 to 172.18.63.254172.18.63.2558,190
147172.18.64.0/19172.18.64.1 to 172.18.95.254172.18.95.2558,190
148172.18.96.0/19172.18.96.1 to 172.18.127.254172.18.127.2558,190
149172.18.128.0/19172.18.128.1 to 172.18.159.254172.18.159.2558,190
150172.18.160.0/19172.18.160.1 to 172.18.191.254172.18.191.2558,190
151172.18.192.0/19172.18.192.1 to 172.18.223.254172.18.223.2558,190
152172.18.224.0/19172.18.224.1 to 172.18.255.254172.18.255.2558,190
153172.19.0.0/19172.19.0.1 to 172.19.31.254172.19.31.2558,190
154172.19.32.0/19172.19.32.1 to 172.19.63.254172.19.63.2558,190
155172.19.64.0/19172.19.64.1 to 172.19.95.254172.19.95.2558,190
156172.19.96.0/19172.19.96.1 to 172.19.127.254172.19.127.2558,190
157172.19.128.0/19172.19.128.1 to 172.19.159.254172.19.159.2558,190
158172.19.160.0/19172.19.160.1 to 172.19.191.254172.19.191.2558,190
159172.19.192.0/19172.19.192.1 to 172.19.223.254172.19.223.2558,190
160172.19.224.0/19172.19.224.1 to 172.19.255.254172.19.255.2558,190
161172.20.0.0/19172.20.0.1 to 172.20.31.254172.20.31.2558,190
162172.20.32.0/19172.20.32.1 to 172.20.63.254172.20.63.2558,190
163172.20.64.0/19172.20.64.1 to 172.20.95.254172.20.95.2558,190
164172.20.96.0/19172.20.96.1 to 172.20.127.254172.20.127.2558,190
165172.20.128.0/19172.20.128.1 to 172.20.159.254172.20.159.2558,190
166172.20.160.0/19172.20.160.1 to 172.20.191.254172.20.191.2558,190
167172.20.192.0/19172.20.192.1 to 172.20.223.254172.20.223.2558,190
168172.20.224.0/19172.20.224.1 to 172.20.255.254172.20.255.2558,190
169172.21.0.0/19172.21.0.1 to 172.21.31.254172.21.31.2558,190
170172.21.32.0/19172.21.32.1 to 172.21.63.254172.21.63.2558,190
171172.21.64.0/19172.21.64.1 to 172.21.95.254172.21.95.2558,190
172172.21.96.0/19172.21.96.1 to 172.21.127.254172.21.127.2558,190
173172.21.128.0/19172.21.128.1 to 172.21.159.254172.21.159.2558,190
174172.21.160.0/19172.21.160.1 to 172.21.191.254172.21.191.2558,190
175172.21.192.0/19172.21.192.1 to 172.21.223.254172.21.223.2558,190
176172.21.224.0/19172.21.224.1 to 172.21.255.254172.21.255.2558,190
177172.22.0.0/19172.22.0.1 to 172.22.31.254172.22.31.2558,190
178172.22.32.0/19172.22.32.1 to 172.22.63.254172.22.63.2558,190
179172.22.64.0/19172.22.64.1 to 172.22.95.254172.22.95.2558,190
180172.22.96.0/19172.22.96.1 to 172.22.127.254172.22.127.2558,190
181172.22.128.0/19172.22.128.1 to 172.22.159.254172.22.159.2558,190
182172.22.160.0/19172.22.160.1 to 172.22.191.254172.22.191.2558,190
183172.22.192.0/19172.22.192.1 to 172.22.223.254172.22.223.2558,190
184172.22.224.0/19172.22.224.1 to 172.22.255.254172.22.255.2558,190
185172.23.0.0/19172.23.0.1 to 172.23.31.254172.23.31.2558,190
186172.23.32.0/19172.23.32.1 to 172.23.63.254172.23.63.2558,190
187172.23.64.0/19172.23.64.1 to 172.23.95.254172.23.95.2558,190
188172.23.96.0/19172.23.96.1 to 172.23.127.254172.23.127.2558,190
189172.23.128.0/19172.23.128.1 to 172.23.159.254172.23.159.2558,190
190172.23.160.0/19172.23.160.1 to 172.23.191.254172.23.191.2558,190
191172.23.192.0/19172.23.192.1 to 172.23.223.254172.23.223.2558,190
192172.23.224.0/19172.23.224.1 to 172.23.255.254172.23.255.2558,190
193172.24.0.0/19172.24.0.1 to 172.24.31.254172.24.31.2558,190
194172.24.32.0/19172.24.32.1 to 172.24.63.254172.24.63.2558,190
195172.24.64.0/19172.24.64.1 to 172.24.95.254172.24.95.2558,190
196172.24.96.0/19172.24.96.1 to 172.24.127.254172.24.127.2558,190
197172.24.128.0/19172.24.128.1 to 172.24.159.254172.24.159.2558,190
198172.24.160.0/19172.24.160.1 to 172.24.191.254172.24.191.2558,190
199172.24.192.0/19172.24.192.1 to 172.24.223.254172.24.223.2558,190
200172.24.224.0/19172.24.224.1 to 172.24.255.254172.24.255.2558,190
201172.25.0.0/19172.25.0.1 to 172.25.31.254172.25.31.2558,190
202172.25.32.0/19172.25.32.1 to 172.25.63.254172.25.63.2558,190
203172.25.64.0/19172.25.64.1 to 172.25.95.254172.25.95.2558,190
204172.25.96.0/19172.25.96.1 to 172.25.127.254172.25.127.2558,190
205172.25.128.0/19172.25.128.1 to 172.25.159.254172.25.159.2558,190
206172.25.160.0/19172.25.160.1 to 172.25.191.254172.25.191.2558,190
207172.25.192.0/19172.25.192.1 to 172.25.223.254172.25.223.2558,190
208172.25.224.0/19172.25.224.1 to 172.25.255.254172.25.255.2558,190
209172.26.0.0/19172.26.0.1 to 172.26.31.254172.26.31.2558,190
210172.26.32.0/19172.26.32.1 to 172.26.63.254172.26.63.2558,190
211172.26.64.0/19172.26.64.1 to 172.26.95.254172.26.95.2558,190
212172.26.96.0/19172.26.96.1 to 172.26.127.254172.26.127.2558,190
213172.26.128.0/19172.26.128.1 to 172.26.159.254172.26.159.2558,190
214172.26.160.0/19172.26.160.1 to 172.26.191.254172.26.191.2558,190
215172.26.192.0/19172.26.192.1 to 172.26.223.254172.26.223.2558,190
216172.26.224.0/19172.26.224.1 to 172.26.255.254172.26.255.2558,190
217172.27.0.0/19172.27.0.1 to 172.27.31.254172.27.31.2558,190
218172.27.32.0/19172.27.32.1 to 172.27.63.254172.27.63.2558,190
219172.27.64.0/19172.27.64.1 to 172.27.95.254172.27.95.2558,190
220172.27.96.0/19172.27.96.1 to 172.27.127.254172.27.127.2558,190
221172.27.128.0/19172.27.128.1 to 172.27.159.254172.27.159.2558,190
222172.27.160.0/19172.27.160.1 to 172.27.191.254172.27.191.2558,190
223172.27.192.0/19172.27.192.1 to 172.27.223.254172.27.223.2558,190
224172.27.224.0/19172.27.224.1 to 172.27.255.254172.27.255.2558,190
225172.28.0.0/19172.28.0.1 to 172.28.31.254172.28.31.2558,190
226172.28.32.0/19172.28.32.1 to 172.28.63.254172.28.63.2558,190
227172.28.64.0/19172.28.64.1 to 172.28.95.254172.28.95.2558,190
228172.28.96.0/19172.28.96.1 to 172.28.127.254172.28.127.2558,190
229172.28.128.0/19172.28.128.1 to 172.28.159.254172.28.159.2558,190
230172.28.160.0/19172.28.160.1 to 172.28.191.254172.28.191.2558,190
231172.28.192.0/19172.28.192.1 to 172.28.223.254172.28.223.2558,190
232172.28.224.0/19172.28.224.1 to 172.28.255.254172.28.255.2558,190
233172.29.0.0/19172.29.0.1 to 172.29.31.254172.29.31.2558,190
234172.29.32.0/19172.29.32.1 to 172.29.63.254172.29.63.2558,190
235172.29.64.0/19172.29.64.1 to 172.29.95.254172.29.95.2558,190
236172.29.96.0/19172.29.96.1 to 172.29.127.254172.29.127.2558,190
237172.29.128.0/19172.29.128.1 to 172.29.159.254172.29.159.2558,190
238172.29.160.0/19172.29.160.1 to 172.29.191.254172.29.191.2558,190
239172.29.192.0/19172.29.192.1 to 172.29.223.254172.29.223.2558,190
240172.29.224.0/19172.29.224.1 to 172.29.255.254172.29.255.2558,190
241172.30.0.0/19172.30.0.1 to 172.30.31.254172.30.31.2558,190
242172.30.32.0/19172.30.32.1 to 172.30.63.254172.30.63.2558,190
243172.30.64.0/19172.30.64.1 to 172.30.95.254172.30.95.2558,190
244172.30.96.0/19172.30.96.1 to 172.30.127.254172.30.127.2558,190
245172.30.128.0/19172.30.128.1 to 172.30.159.254172.30.159.2558,190
246172.30.160.0/19172.30.160.1 to 172.30.191.254172.30.191.2558,190
247172.30.192.0/19172.30.192.1 to 172.30.223.254172.30.223.2558,190
248172.30.224.0/19172.30.224.1 to 172.30.255.254172.30.255.2558,190
249172.31.0.0/19172.31.0.1 to 172.31.31.254172.31.31.2558,190
250172.31.32.0/19172.31.32.1 to 172.31.63.254172.31.63.2558,190
251172.31.64.0/19172.31.64.1 to 172.31.95.254172.31.95.2558,190
252172.31.96.0/19172.31.96.1 to 172.31.127.254172.31.127.2558,190
253172.31.128.0/19172.31.128.1 to 172.31.159.254172.31.159.2558,190
254172.31.160.0/19172.31.160.1 to 172.31.191.254172.31.191.2558,190
255172.31.192.0/19172.31.192.1 to 172.31.223.254172.31.223.2558,190
256172.31.224.0/19172.31.224.1 to 172.31.255.254172.31.255.2558,190

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.