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.

Network211.3.0.0/17
Usable hosts32,766
Subnet mask255.255.128.0
Addresses32,768
Network address
211.3.0.0
Broadcast address
211.3.127.255
First usable
211.3.0.1
Last usable
211.3.127.254
Usable hosts
32,766 (32,768 less the network and broadcast addresses)
Subnet mask
255.255.128.0
Wildcard mask
0.0.127.255 (Cisco ACLs, OSPF)
Prefix length
/17
Type
Public public
Old class
C (default /24)
As numbers
Hex D3030000 · Integer 3540189184 to 3540221951
Reverse DNS zones
0.3.211.in-addr.arpa
1.3.211.in-addr.arpa
2.3.211.in-addr.arpa
3.3.211.in-addr.arpa
4.3.211.in-addr.arpa
5.3.211.in-addr.arpa
6.3.211.in-addr.arpa
7.3.211.in-addr.arpa
8.3.211.in-addr.arpa
9.3.211.in-addr.arpa
10.3.211.in-addr.arpa
11.3.211.in-addr.arpa
12.3.211.in-addr.arpa
13.3.211.in-addr.arpa
14.3.211.in-addr.arpa
15.3.211.in-addr.arpa
and 112 more
/17 is not on a 8-bit boundary, so it takes 128 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11010011.00000011.00000000.00000000211.3.0.0
Subnet mask11111111.11111111.10000000.00000000255.255.128.0
Network11010011.00000011.00000000.00000000211.3.0.0
Broadcast11010011.00000011.01111111.11111111211.3.127.255
Split into smaller subnets/25
/18 (2)/19 (4)/20 (8)/21 (16)/22 (32)/23 (64)/24 (128)/25 (256)/26 (512)/27 (1,024)/28 (2,048)/29 (4,096)

211.3.0.0/17 makes 256 subnets of /25.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1211.3.0.0/25211.3.0.1 to 211.3.0.126211.3.0.127126
2211.3.0.128/25211.3.0.129 to 211.3.0.254211.3.0.255126
3211.3.1.0/25211.3.1.1 to 211.3.1.126211.3.1.127126
4211.3.1.128/25211.3.1.129 to 211.3.1.254211.3.1.255126
5211.3.2.0/25211.3.2.1 to 211.3.2.126211.3.2.127126
6211.3.2.128/25211.3.2.129 to 211.3.2.254211.3.2.255126
7211.3.3.0/25211.3.3.1 to 211.3.3.126211.3.3.127126
8211.3.3.128/25211.3.3.129 to 211.3.3.254211.3.3.255126
9211.3.4.0/25211.3.4.1 to 211.3.4.126211.3.4.127126
10211.3.4.128/25211.3.4.129 to 211.3.4.254211.3.4.255126
11211.3.5.0/25211.3.5.1 to 211.3.5.126211.3.5.127126
12211.3.5.128/25211.3.5.129 to 211.3.5.254211.3.5.255126
13211.3.6.0/25211.3.6.1 to 211.3.6.126211.3.6.127126
14211.3.6.128/25211.3.6.129 to 211.3.6.254211.3.6.255126
15211.3.7.0/25211.3.7.1 to 211.3.7.126211.3.7.127126
16211.3.7.128/25211.3.7.129 to 211.3.7.254211.3.7.255126
17211.3.8.0/25211.3.8.1 to 211.3.8.126211.3.8.127126
18211.3.8.128/25211.3.8.129 to 211.3.8.254211.3.8.255126
19211.3.9.0/25211.3.9.1 to 211.3.9.126211.3.9.127126
20211.3.9.128/25211.3.9.129 to 211.3.9.254211.3.9.255126
21211.3.10.0/25211.3.10.1 to 211.3.10.126211.3.10.127126
22211.3.10.128/25211.3.10.129 to 211.3.10.254211.3.10.255126
23211.3.11.0/25211.3.11.1 to 211.3.11.126211.3.11.127126
24211.3.11.128/25211.3.11.129 to 211.3.11.254211.3.11.255126
25211.3.12.0/25211.3.12.1 to 211.3.12.126211.3.12.127126
26211.3.12.128/25211.3.12.129 to 211.3.12.254211.3.12.255126
27211.3.13.0/25211.3.13.1 to 211.3.13.126211.3.13.127126
28211.3.13.128/25211.3.13.129 to 211.3.13.254211.3.13.255126
29211.3.14.0/25211.3.14.1 to 211.3.14.126211.3.14.127126
30211.3.14.128/25211.3.14.129 to 211.3.14.254211.3.14.255126
31211.3.15.0/25211.3.15.1 to 211.3.15.126211.3.15.127126
32211.3.15.128/25211.3.15.129 to 211.3.15.254211.3.15.255126
33211.3.16.0/25211.3.16.1 to 211.3.16.126211.3.16.127126
34211.3.16.128/25211.3.16.129 to 211.3.16.254211.3.16.255126
35211.3.17.0/25211.3.17.1 to 211.3.17.126211.3.17.127126
36211.3.17.128/25211.3.17.129 to 211.3.17.254211.3.17.255126
37211.3.18.0/25211.3.18.1 to 211.3.18.126211.3.18.127126
38211.3.18.128/25211.3.18.129 to 211.3.18.254211.3.18.255126
39211.3.19.0/25211.3.19.1 to 211.3.19.126211.3.19.127126
40211.3.19.128/25211.3.19.129 to 211.3.19.254211.3.19.255126
41211.3.20.0/25211.3.20.1 to 211.3.20.126211.3.20.127126
42211.3.20.128/25211.3.20.129 to 211.3.20.254211.3.20.255126
43211.3.21.0/25211.3.21.1 to 211.3.21.126211.3.21.127126
44211.3.21.128/25211.3.21.129 to 211.3.21.254211.3.21.255126
45211.3.22.0/25211.3.22.1 to 211.3.22.126211.3.22.127126
46211.3.22.128/25211.3.22.129 to 211.3.22.254211.3.22.255126
47211.3.23.0/25211.3.23.1 to 211.3.23.126211.3.23.127126
48211.3.23.128/25211.3.23.129 to 211.3.23.254211.3.23.255126
49211.3.24.0/25211.3.24.1 to 211.3.24.126211.3.24.127126
50211.3.24.128/25211.3.24.129 to 211.3.24.254211.3.24.255126
51211.3.25.0/25211.3.25.1 to 211.3.25.126211.3.25.127126
52211.3.25.128/25211.3.25.129 to 211.3.25.254211.3.25.255126
53211.3.26.0/25211.3.26.1 to 211.3.26.126211.3.26.127126
54211.3.26.128/25211.3.26.129 to 211.3.26.254211.3.26.255126
55211.3.27.0/25211.3.27.1 to 211.3.27.126211.3.27.127126
56211.3.27.128/25211.3.27.129 to 211.3.27.254211.3.27.255126
57211.3.28.0/25211.3.28.1 to 211.3.28.126211.3.28.127126
58211.3.28.128/25211.3.28.129 to 211.3.28.254211.3.28.255126
59211.3.29.0/25211.3.29.1 to 211.3.29.126211.3.29.127126
60211.3.29.128/25211.3.29.129 to 211.3.29.254211.3.29.255126
61211.3.30.0/25211.3.30.1 to 211.3.30.126211.3.30.127126
62211.3.30.128/25211.3.30.129 to 211.3.30.254211.3.30.255126
63211.3.31.0/25211.3.31.1 to 211.3.31.126211.3.31.127126
64211.3.31.128/25211.3.31.129 to 211.3.31.254211.3.31.255126
65211.3.32.0/25211.3.32.1 to 211.3.32.126211.3.32.127126
66211.3.32.128/25211.3.32.129 to 211.3.32.254211.3.32.255126
67211.3.33.0/25211.3.33.1 to 211.3.33.126211.3.33.127126
68211.3.33.128/25211.3.33.129 to 211.3.33.254211.3.33.255126
69211.3.34.0/25211.3.34.1 to 211.3.34.126211.3.34.127126
70211.3.34.128/25211.3.34.129 to 211.3.34.254211.3.34.255126
71211.3.35.0/25211.3.35.1 to 211.3.35.126211.3.35.127126
72211.3.35.128/25211.3.35.129 to 211.3.35.254211.3.35.255126
73211.3.36.0/25211.3.36.1 to 211.3.36.126211.3.36.127126
74211.3.36.128/25211.3.36.129 to 211.3.36.254211.3.36.255126
75211.3.37.0/25211.3.37.1 to 211.3.37.126211.3.37.127126
76211.3.37.128/25211.3.37.129 to 211.3.37.254211.3.37.255126
77211.3.38.0/25211.3.38.1 to 211.3.38.126211.3.38.127126
78211.3.38.128/25211.3.38.129 to 211.3.38.254211.3.38.255126
79211.3.39.0/25211.3.39.1 to 211.3.39.126211.3.39.127126
80211.3.39.128/25211.3.39.129 to 211.3.39.254211.3.39.255126
81211.3.40.0/25211.3.40.1 to 211.3.40.126211.3.40.127126
82211.3.40.128/25211.3.40.129 to 211.3.40.254211.3.40.255126
83211.3.41.0/25211.3.41.1 to 211.3.41.126211.3.41.127126
84211.3.41.128/25211.3.41.129 to 211.3.41.254211.3.41.255126
85211.3.42.0/25211.3.42.1 to 211.3.42.126211.3.42.127126
86211.3.42.128/25211.3.42.129 to 211.3.42.254211.3.42.255126
87211.3.43.0/25211.3.43.1 to 211.3.43.126211.3.43.127126
88211.3.43.128/25211.3.43.129 to 211.3.43.254211.3.43.255126
89211.3.44.0/25211.3.44.1 to 211.3.44.126211.3.44.127126
90211.3.44.128/25211.3.44.129 to 211.3.44.254211.3.44.255126
91211.3.45.0/25211.3.45.1 to 211.3.45.126211.3.45.127126
92211.3.45.128/25211.3.45.129 to 211.3.45.254211.3.45.255126
93211.3.46.0/25211.3.46.1 to 211.3.46.126211.3.46.127126
94211.3.46.128/25211.3.46.129 to 211.3.46.254211.3.46.255126
95211.3.47.0/25211.3.47.1 to 211.3.47.126211.3.47.127126
96211.3.47.128/25211.3.47.129 to 211.3.47.254211.3.47.255126
97211.3.48.0/25211.3.48.1 to 211.3.48.126211.3.48.127126
98211.3.48.128/25211.3.48.129 to 211.3.48.254211.3.48.255126
99211.3.49.0/25211.3.49.1 to 211.3.49.126211.3.49.127126
100211.3.49.128/25211.3.49.129 to 211.3.49.254211.3.49.255126
101211.3.50.0/25211.3.50.1 to 211.3.50.126211.3.50.127126
102211.3.50.128/25211.3.50.129 to 211.3.50.254211.3.50.255126
103211.3.51.0/25211.3.51.1 to 211.3.51.126211.3.51.127126
104211.3.51.128/25211.3.51.129 to 211.3.51.254211.3.51.255126
105211.3.52.0/25211.3.52.1 to 211.3.52.126211.3.52.127126
106211.3.52.128/25211.3.52.129 to 211.3.52.254211.3.52.255126
107211.3.53.0/25211.3.53.1 to 211.3.53.126211.3.53.127126
108211.3.53.128/25211.3.53.129 to 211.3.53.254211.3.53.255126
109211.3.54.0/25211.3.54.1 to 211.3.54.126211.3.54.127126
110211.3.54.128/25211.3.54.129 to 211.3.54.254211.3.54.255126
111211.3.55.0/25211.3.55.1 to 211.3.55.126211.3.55.127126
112211.3.55.128/25211.3.55.129 to 211.3.55.254211.3.55.255126
113211.3.56.0/25211.3.56.1 to 211.3.56.126211.3.56.127126
114211.3.56.128/25211.3.56.129 to 211.3.56.254211.3.56.255126
115211.3.57.0/25211.3.57.1 to 211.3.57.126211.3.57.127126
116211.3.57.128/25211.3.57.129 to 211.3.57.254211.3.57.255126
117211.3.58.0/25211.3.58.1 to 211.3.58.126211.3.58.127126
118211.3.58.128/25211.3.58.129 to 211.3.58.254211.3.58.255126
119211.3.59.0/25211.3.59.1 to 211.3.59.126211.3.59.127126
120211.3.59.128/25211.3.59.129 to 211.3.59.254211.3.59.255126
121211.3.60.0/25211.3.60.1 to 211.3.60.126211.3.60.127126
122211.3.60.128/25211.3.60.129 to 211.3.60.254211.3.60.255126
123211.3.61.0/25211.3.61.1 to 211.3.61.126211.3.61.127126
124211.3.61.128/25211.3.61.129 to 211.3.61.254211.3.61.255126
125211.3.62.0/25211.3.62.1 to 211.3.62.126211.3.62.127126
126211.3.62.128/25211.3.62.129 to 211.3.62.254211.3.62.255126
127211.3.63.0/25211.3.63.1 to 211.3.63.126211.3.63.127126
128211.3.63.128/25211.3.63.129 to 211.3.63.254211.3.63.255126
129211.3.64.0/25211.3.64.1 to 211.3.64.126211.3.64.127126
130211.3.64.128/25211.3.64.129 to 211.3.64.254211.3.64.255126
131211.3.65.0/25211.3.65.1 to 211.3.65.126211.3.65.127126
132211.3.65.128/25211.3.65.129 to 211.3.65.254211.3.65.255126
133211.3.66.0/25211.3.66.1 to 211.3.66.126211.3.66.127126
134211.3.66.128/25211.3.66.129 to 211.3.66.254211.3.66.255126
135211.3.67.0/25211.3.67.1 to 211.3.67.126211.3.67.127126
136211.3.67.128/25211.3.67.129 to 211.3.67.254211.3.67.255126
137211.3.68.0/25211.3.68.1 to 211.3.68.126211.3.68.127126
138211.3.68.128/25211.3.68.129 to 211.3.68.254211.3.68.255126
139211.3.69.0/25211.3.69.1 to 211.3.69.126211.3.69.127126
140211.3.69.128/25211.3.69.129 to 211.3.69.254211.3.69.255126
141211.3.70.0/25211.3.70.1 to 211.3.70.126211.3.70.127126
142211.3.70.128/25211.3.70.129 to 211.3.70.254211.3.70.255126
143211.3.71.0/25211.3.71.1 to 211.3.71.126211.3.71.127126
144211.3.71.128/25211.3.71.129 to 211.3.71.254211.3.71.255126
145211.3.72.0/25211.3.72.1 to 211.3.72.126211.3.72.127126
146211.3.72.128/25211.3.72.129 to 211.3.72.254211.3.72.255126
147211.3.73.0/25211.3.73.1 to 211.3.73.126211.3.73.127126
148211.3.73.128/25211.3.73.129 to 211.3.73.254211.3.73.255126
149211.3.74.0/25211.3.74.1 to 211.3.74.126211.3.74.127126
150211.3.74.128/25211.3.74.129 to 211.3.74.254211.3.74.255126
151211.3.75.0/25211.3.75.1 to 211.3.75.126211.3.75.127126
152211.3.75.128/25211.3.75.129 to 211.3.75.254211.3.75.255126
153211.3.76.0/25211.3.76.1 to 211.3.76.126211.3.76.127126
154211.3.76.128/25211.3.76.129 to 211.3.76.254211.3.76.255126
155211.3.77.0/25211.3.77.1 to 211.3.77.126211.3.77.127126
156211.3.77.128/25211.3.77.129 to 211.3.77.254211.3.77.255126
157211.3.78.0/25211.3.78.1 to 211.3.78.126211.3.78.127126
158211.3.78.128/25211.3.78.129 to 211.3.78.254211.3.78.255126
159211.3.79.0/25211.3.79.1 to 211.3.79.126211.3.79.127126
160211.3.79.128/25211.3.79.129 to 211.3.79.254211.3.79.255126
161211.3.80.0/25211.3.80.1 to 211.3.80.126211.3.80.127126
162211.3.80.128/25211.3.80.129 to 211.3.80.254211.3.80.255126
163211.3.81.0/25211.3.81.1 to 211.3.81.126211.3.81.127126
164211.3.81.128/25211.3.81.129 to 211.3.81.254211.3.81.255126
165211.3.82.0/25211.3.82.1 to 211.3.82.126211.3.82.127126
166211.3.82.128/25211.3.82.129 to 211.3.82.254211.3.82.255126
167211.3.83.0/25211.3.83.1 to 211.3.83.126211.3.83.127126
168211.3.83.128/25211.3.83.129 to 211.3.83.254211.3.83.255126
169211.3.84.0/25211.3.84.1 to 211.3.84.126211.3.84.127126
170211.3.84.128/25211.3.84.129 to 211.3.84.254211.3.84.255126
171211.3.85.0/25211.3.85.1 to 211.3.85.126211.3.85.127126
172211.3.85.128/25211.3.85.129 to 211.3.85.254211.3.85.255126
173211.3.86.0/25211.3.86.1 to 211.3.86.126211.3.86.127126
174211.3.86.128/25211.3.86.129 to 211.3.86.254211.3.86.255126
175211.3.87.0/25211.3.87.1 to 211.3.87.126211.3.87.127126
176211.3.87.128/25211.3.87.129 to 211.3.87.254211.3.87.255126
177211.3.88.0/25211.3.88.1 to 211.3.88.126211.3.88.127126
178211.3.88.128/25211.3.88.129 to 211.3.88.254211.3.88.255126
179211.3.89.0/25211.3.89.1 to 211.3.89.126211.3.89.127126
180211.3.89.128/25211.3.89.129 to 211.3.89.254211.3.89.255126
181211.3.90.0/25211.3.90.1 to 211.3.90.126211.3.90.127126
182211.3.90.128/25211.3.90.129 to 211.3.90.254211.3.90.255126
183211.3.91.0/25211.3.91.1 to 211.3.91.126211.3.91.127126
184211.3.91.128/25211.3.91.129 to 211.3.91.254211.3.91.255126
185211.3.92.0/25211.3.92.1 to 211.3.92.126211.3.92.127126
186211.3.92.128/25211.3.92.129 to 211.3.92.254211.3.92.255126
187211.3.93.0/25211.3.93.1 to 211.3.93.126211.3.93.127126
188211.3.93.128/25211.3.93.129 to 211.3.93.254211.3.93.255126
189211.3.94.0/25211.3.94.1 to 211.3.94.126211.3.94.127126
190211.3.94.128/25211.3.94.129 to 211.3.94.254211.3.94.255126
191211.3.95.0/25211.3.95.1 to 211.3.95.126211.3.95.127126
192211.3.95.128/25211.3.95.129 to 211.3.95.254211.3.95.255126
193211.3.96.0/25211.3.96.1 to 211.3.96.126211.3.96.127126
194211.3.96.128/25211.3.96.129 to 211.3.96.254211.3.96.255126
195211.3.97.0/25211.3.97.1 to 211.3.97.126211.3.97.127126
196211.3.97.128/25211.3.97.129 to 211.3.97.254211.3.97.255126
197211.3.98.0/25211.3.98.1 to 211.3.98.126211.3.98.127126
198211.3.98.128/25211.3.98.129 to 211.3.98.254211.3.98.255126
199211.3.99.0/25211.3.99.1 to 211.3.99.126211.3.99.127126
200211.3.99.128/25211.3.99.129 to 211.3.99.254211.3.99.255126
201211.3.100.0/25211.3.100.1 to 211.3.100.126211.3.100.127126
202211.3.100.128/25211.3.100.129 to 211.3.100.254211.3.100.255126
203211.3.101.0/25211.3.101.1 to 211.3.101.126211.3.101.127126
204211.3.101.128/25211.3.101.129 to 211.3.101.254211.3.101.255126
205211.3.102.0/25211.3.102.1 to 211.3.102.126211.3.102.127126
206211.3.102.128/25211.3.102.129 to 211.3.102.254211.3.102.255126
207211.3.103.0/25211.3.103.1 to 211.3.103.126211.3.103.127126
208211.3.103.128/25211.3.103.129 to 211.3.103.254211.3.103.255126
209211.3.104.0/25211.3.104.1 to 211.3.104.126211.3.104.127126
210211.3.104.128/25211.3.104.129 to 211.3.104.254211.3.104.255126
211211.3.105.0/25211.3.105.1 to 211.3.105.126211.3.105.127126
212211.3.105.128/25211.3.105.129 to 211.3.105.254211.3.105.255126
213211.3.106.0/25211.3.106.1 to 211.3.106.126211.3.106.127126
214211.3.106.128/25211.3.106.129 to 211.3.106.254211.3.106.255126
215211.3.107.0/25211.3.107.1 to 211.3.107.126211.3.107.127126
216211.3.107.128/25211.3.107.129 to 211.3.107.254211.3.107.255126
217211.3.108.0/25211.3.108.1 to 211.3.108.126211.3.108.127126
218211.3.108.128/25211.3.108.129 to 211.3.108.254211.3.108.255126
219211.3.109.0/25211.3.109.1 to 211.3.109.126211.3.109.127126
220211.3.109.128/25211.3.109.129 to 211.3.109.254211.3.109.255126
221211.3.110.0/25211.3.110.1 to 211.3.110.126211.3.110.127126
222211.3.110.128/25211.3.110.129 to 211.3.110.254211.3.110.255126
223211.3.111.0/25211.3.111.1 to 211.3.111.126211.3.111.127126
224211.3.111.128/25211.3.111.129 to 211.3.111.254211.3.111.255126
225211.3.112.0/25211.3.112.1 to 211.3.112.126211.3.112.127126
226211.3.112.128/25211.3.112.129 to 211.3.112.254211.3.112.255126
227211.3.113.0/25211.3.113.1 to 211.3.113.126211.3.113.127126
228211.3.113.128/25211.3.113.129 to 211.3.113.254211.3.113.255126
229211.3.114.0/25211.3.114.1 to 211.3.114.126211.3.114.127126
230211.3.114.128/25211.3.114.129 to 211.3.114.254211.3.114.255126
231211.3.115.0/25211.3.115.1 to 211.3.115.126211.3.115.127126
232211.3.115.128/25211.3.115.129 to 211.3.115.254211.3.115.255126
233211.3.116.0/25211.3.116.1 to 211.3.116.126211.3.116.127126
234211.3.116.128/25211.3.116.129 to 211.3.116.254211.3.116.255126
235211.3.117.0/25211.3.117.1 to 211.3.117.126211.3.117.127126
236211.3.117.128/25211.3.117.129 to 211.3.117.254211.3.117.255126
237211.3.118.0/25211.3.118.1 to 211.3.118.126211.3.118.127126
238211.3.118.128/25211.3.118.129 to 211.3.118.254211.3.118.255126
239211.3.119.0/25211.3.119.1 to 211.3.119.126211.3.119.127126
240211.3.119.128/25211.3.119.129 to 211.3.119.254211.3.119.255126
241211.3.120.0/25211.3.120.1 to 211.3.120.126211.3.120.127126
242211.3.120.128/25211.3.120.129 to 211.3.120.254211.3.120.255126
243211.3.121.0/25211.3.121.1 to 211.3.121.126211.3.121.127126
244211.3.121.128/25211.3.121.129 to 211.3.121.254211.3.121.255126
245211.3.122.0/25211.3.122.1 to 211.3.122.126211.3.122.127126
246211.3.122.128/25211.3.122.129 to 211.3.122.254211.3.122.255126
247211.3.123.0/25211.3.123.1 to 211.3.123.126211.3.123.127126
248211.3.123.128/25211.3.123.129 to 211.3.123.254211.3.123.255126
249211.3.124.0/25211.3.124.1 to 211.3.124.126211.3.124.127126
250211.3.124.128/25211.3.124.129 to 211.3.124.254211.3.124.255126
251211.3.125.0/25211.3.125.1 to 211.3.125.126211.3.125.127126
252211.3.125.128/25211.3.125.129 to 211.3.125.254211.3.125.255126
253211.3.126.0/25211.3.126.1 to 211.3.126.126211.3.126.127126
254211.3.126.128/25211.3.126.129 to 211.3.126.254211.3.126.255126
255211.3.127.0/25211.3.127.1 to 211.3.127.126211.3.127.127126
256211.3.127.128/25211.3.127.129 to 211.3.127.254211.3.127.255126

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.