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.

Network205.0.0.0/8
Usable hosts16,777,214
Subnet mask255.0.0.0
Addresses16,777,216
Network address
205.0.0.0
Broadcast address
205.255.255.255
First usable
205.0.0.1
Last usable
205.255.255.254
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
C (default /24)
As numbers
Hex CD000000 · Integer 3439329280 to 3456106495
Reverse DNS zone
205.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11001101..00000000.00000000.00000000205.0.0.0
Subnet mask11111111..00000000.00000000.00000000255.0.0.0
Network11001101..00000000.00000000.00000000205.0.0.0
Broadcast11001101..11111111.11111111.11111111205.255.255.255
Split into smaller subnets/16
/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)

205.0.0.0/8 makes 256 subnets of /16.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1205.0.0.0/16205.0.0.1 to 205.0.255.254205.0.255.25565,534
2205.1.0.0/16205.1.0.1 to 205.1.255.254205.1.255.25565,534
3205.2.0.0/16205.2.0.1 to 205.2.255.254205.2.255.25565,534
4205.3.0.0/16205.3.0.1 to 205.3.255.254205.3.255.25565,534
5205.4.0.0/16205.4.0.1 to 205.4.255.254205.4.255.25565,534
6205.5.0.0/16205.5.0.1 to 205.5.255.254205.5.255.25565,534
7205.6.0.0/16205.6.0.1 to 205.6.255.254205.6.255.25565,534
8205.7.0.0/16205.7.0.1 to 205.7.255.254205.7.255.25565,534
9205.8.0.0/16205.8.0.1 to 205.8.255.254205.8.255.25565,534
10205.9.0.0/16205.9.0.1 to 205.9.255.254205.9.255.25565,534
11205.10.0.0/16205.10.0.1 to 205.10.255.254205.10.255.25565,534
12205.11.0.0/16205.11.0.1 to 205.11.255.254205.11.255.25565,534
13205.12.0.0/16205.12.0.1 to 205.12.255.254205.12.255.25565,534
14205.13.0.0/16205.13.0.1 to 205.13.255.254205.13.255.25565,534
15205.14.0.0/16205.14.0.1 to 205.14.255.254205.14.255.25565,534
16205.15.0.0/16205.15.0.1 to 205.15.255.254205.15.255.25565,534
17205.16.0.0/16205.16.0.1 to 205.16.255.254205.16.255.25565,534
18205.17.0.0/16205.17.0.1 to 205.17.255.254205.17.255.25565,534
19205.18.0.0/16205.18.0.1 to 205.18.255.254205.18.255.25565,534
20205.19.0.0/16205.19.0.1 to 205.19.255.254205.19.255.25565,534
21205.20.0.0/16205.20.0.1 to 205.20.255.254205.20.255.25565,534
22205.21.0.0/16205.21.0.1 to 205.21.255.254205.21.255.25565,534
23205.22.0.0/16205.22.0.1 to 205.22.255.254205.22.255.25565,534
24205.23.0.0/16205.23.0.1 to 205.23.255.254205.23.255.25565,534
25205.24.0.0/16205.24.0.1 to 205.24.255.254205.24.255.25565,534
26205.25.0.0/16205.25.0.1 to 205.25.255.254205.25.255.25565,534
27205.26.0.0/16205.26.0.1 to 205.26.255.254205.26.255.25565,534
28205.27.0.0/16205.27.0.1 to 205.27.255.254205.27.255.25565,534
29205.28.0.0/16205.28.0.1 to 205.28.255.254205.28.255.25565,534
30205.29.0.0/16205.29.0.1 to 205.29.255.254205.29.255.25565,534
31205.30.0.0/16205.30.0.1 to 205.30.255.254205.30.255.25565,534
32205.31.0.0/16205.31.0.1 to 205.31.255.254205.31.255.25565,534
33205.32.0.0/16205.32.0.1 to 205.32.255.254205.32.255.25565,534
34205.33.0.0/16205.33.0.1 to 205.33.255.254205.33.255.25565,534
35205.34.0.0/16205.34.0.1 to 205.34.255.254205.34.255.25565,534
36205.35.0.0/16205.35.0.1 to 205.35.255.254205.35.255.25565,534
37205.36.0.0/16205.36.0.1 to 205.36.255.254205.36.255.25565,534
38205.37.0.0/16205.37.0.1 to 205.37.255.254205.37.255.25565,534
39205.38.0.0/16205.38.0.1 to 205.38.255.254205.38.255.25565,534
40205.39.0.0/16205.39.0.1 to 205.39.255.254205.39.255.25565,534
41205.40.0.0/16205.40.0.1 to 205.40.255.254205.40.255.25565,534
42205.41.0.0/16205.41.0.1 to 205.41.255.254205.41.255.25565,534
43205.42.0.0/16205.42.0.1 to 205.42.255.254205.42.255.25565,534
44205.43.0.0/16205.43.0.1 to 205.43.255.254205.43.255.25565,534
45205.44.0.0/16205.44.0.1 to 205.44.255.254205.44.255.25565,534
46205.45.0.0/16205.45.0.1 to 205.45.255.254205.45.255.25565,534
47205.46.0.0/16205.46.0.1 to 205.46.255.254205.46.255.25565,534
48205.47.0.0/16205.47.0.1 to 205.47.255.254205.47.255.25565,534
49205.48.0.0/16205.48.0.1 to 205.48.255.254205.48.255.25565,534
50205.49.0.0/16205.49.0.1 to 205.49.255.254205.49.255.25565,534
51205.50.0.0/16205.50.0.1 to 205.50.255.254205.50.255.25565,534
52205.51.0.0/16205.51.0.1 to 205.51.255.254205.51.255.25565,534
53205.52.0.0/16205.52.0.1 to 205.52.255.254205.52.255.25565,534
54205.53.0.0/16205.53.0.1 to 205.53.255.254205.53.255.25565,534
55205.54.0.0/16205.54.0.1 to 205.54.255.254205.54.255.25565,534
56205.55.0.0/16205.55.0.1 to 205.55.255.254205.55.255.25565,534
57205.56.0.0/16205.56.0.1 to 205.56.255.254205.56.255.25565,534
58205.57.0.0/16205.57.0.1 to 205.57.255.254205.57.255.25565,534
59205.58.0.0/16205.58.0.1 to 205.58.255.254205.58.255.25565,534
60205.59.0.0/16205.59.0.1 to 205.59.255.254205.59.255.25565,534
61205.60.0.0/16205.60.0.1 to 205.60.255.254205.60.255.25565,534
62205.61.0.0/16205.61.0.1 to 205.61.255.254205.61.255.25565,534
63205.62.0.0/16205.62.0.1 to 205.62.255.254205.62.255.25565,534
64205.63.0.0/16205.63.0.1 to 205.63.255.254205.63.255.25565,534
65205.64.0.0/16205.64.0.1 to 205.64.255.254205.64.255.25565,534
66205.65.0.0/16205.65.0.1 to 205.65.255.254205.65.255.25565,534
67205.66.0.0/16205.66.0.1 to 205.66.255.254205.66.255.25565,534
68205.67.0.0/16205.67.0.1 to 205.67.255.254205.67.255.25565,534
69205.68.0.0/16205.68.0.1 to 205.68.255.254205.68.255.25565,534
70205.69.0.0/16205.69.0.1 to 205.69.255.254205.69.255.25565,534
71205.70.0.0/16205.70.0.1 to 205.70.255.254205.70.255.25565,534
72205.71.0.0/16205.71.0.1 to 205.71.255.254205.71.255.25565,534
73205.72.0.0/16205.72.0.1 to 205.72.255.254205.72.255.25565,534
74205.73.0.0/16205.73.0.1 to 205.73.255.254205.73.255.25565,534
75205.74.0.0/16205.74.0.1 to 205.74.255.254205.74.255.25565,534
76205.75.0.0/16205.75.0.1 to 205.75.255.254205.75.255.25565,534
77205.76.0.0/16205.76.0.1 to 205.76.255.254205.76.255.25565,534
78205.77.0.0/16205.77.0.1 to 205.77.255.254205.77.255.25565,534
79205.78.0.0/16205.78.0.1 to 205.78.255.254205.78.255.25565,534
80205.79.0.0/16205.79.0.1 to 205.79.255.254205.79.255.25565,534
81205.80.0.0/16205.80.0.1 to 205.80.255.254205.80.255.25565,534
82205.81.0.0/16205.81.0.1 to 205.81.255.254205.81.255.25565,534
83205.82.0.0/16205.82.0.1 to 205.82.255.254205.82.255.25565,534
84205.83.0.0/16205.83.0.1 to 205.83.255.254205.83.255.25565,534
85205.84.0.0/16205.84.0.1 to 205.84.255.254205.84.255.25565,534
86205.85.0.0/16205.85.0.1 to 205.85.255.254205.85.255.25565,534
87205.86.0.0/16205.86.0.1 to 205.86.255.254205.86.255.25565,534
88205.87.0.0/16205.87.0.1 to 205.87.255.254205.87.255.25565,534
89205.88.0.0/16205.88.0.1 to 205.88.255.254205.88.255.25565,534
90205.89.0.0/16205.89.0.1 to 205.89.255.254205.89.255.25565,534
91205.90.0.0/16205.90.0.1 to 205.90.255.254205.90.255.25565,534
92205.91.0.0/16205.91.0.1 to 205.91.255.254205.91.255.25565,534
93205.92.0.0/16205.92.0.1 to 205.92.255.254205.92.255.25565,534
94205.93.0.0/16205.93.0.1 to 205.93.255.254205.93.255.25565,534
95205.94.0.0/16205.94.0.1 to 205.94.255.254205.94.255.25565,534
96205.95.0.0/16205.95.0.1 to 205.95.255.254205.95.255.25565,534
97205.96.0.0/16205.96.0.1 to 205.96.255.254205.96.255.25565,534
98205.97.0.0/16205.97.0.1 to 205.97.255.254205.97.255.25565,534
99205.98.0.0/16205.98.0.1 to 205.98.255.254205.98.255.25565,534
100205.99.0.0/16205.99.0.1 to 205.99.255.254205.99.255.25565,534
101205.100.0.0/16205.100.0.1 to 205.100.255.254205.100.255.25565,534
102205.101.0.0/16205.101.0.1 to 205.101.255.254205.101.255.25565,534
103205.102.0.0/16205.102.0.1 to 205.102.255.254205.102.255.25565,534
104205.103.0.0/16205.103.0.1 to 205.103.255.254205.103.255.25565,534
105205.104.0.0/16205.104.0.1 to 205.104.255.254205.104.255.25565,534
106205.105.0.0/16205.105.0.1 to 205.105.255.254205.105.255.25565,534
107205.106.0.0/16205.106.0.1 to 205.106.255.254205.106.255.25565,534
108205.107.0.0/16205.107.0.1 to 205.107.255.254205.107.255.25565,534
109205.108.0.0/16205.108.0.1 to 205.108.255.254205.108.255.25565,534
110205.109.0.0/16205.109.0.1 to 205.109.255.254205.109.255.25565,534
111205.110.0.0/16205.110.0.1 to 205.110.255.254205.110.255.25565,534
112205.111.0.0/16205.111.0.1 to 205.111.255.254205.111.255.25565,534
113205.112.0.0/16205.112.0.1 to 205.112.255.254205.112.255.25565,534
114205.113.0.0/16205.113.0.1 to 205.113.255.254205.113.255.25565,534
115205.114.0.0/16205.114.0.1 to 205.114.255.254205.114.255.25565,534
116205.115.0.0/16205.115.0.1 to 205.115.255.254205.115.255.25565,534
117205.116.0.0/16205.116.0.1 to 205.116.255.254205.116.255.25565,534
118205.117.0.0/16205.117.0.1 to 205.117.255.254205.117.255.25565,534
119205.118.0.0/16205.118.0.1 to 205.118.255.254205.118.255.25565,534
120205.119.0.0/16205.119.0.1 to 205.119.255.254205.119.255.25565,534
121205.120.0.0/16205.120.0.1 to 205.120.255.254205.120.255.25565,534
122205.121.0.0/16205.121.0.1 to 205.121.255.254205.121.255.25565,534
123205.122.0.0/16205.122.0.1 to 205.122.255.254205.122.255.25565,534
124205.123.0.0/16205.123.0.1 to 205.123.255.254205.123.255.25565,534
125205.124.0.0/16205.124.0.1 to 205.124.255.254205.124.255.25565,534
126205.125.0.0/16205.125.0.1 to 205.125.255.254205.125.255.25565,534
127205.126.0.0/16205.126.0.1 to 205.126.255.254205.126.255.25565,534
128205.127.0.0/16205.127.0.1 to 205.127.255.254205.127.255.25565,534
129205.128.0.0/16205.128.0.1 to 205.128.255.254205.128.255.25565,534
130205.129.0.0/16205.129.0.1 to 205.129.255.254205.129.255.25565,534
131205.130.0.0/16205.130.0.1 to 205.130.255.254205.130.255.25565,534
132205.131.0.0/16205.131.0.1 to 205.131.255.254205.131.255.25565,534
133205.132.0.0/16205.132.0.1 to 205.132.255.254205.132.255.25565,534
134205.133.0.0/16205.133.0.1 to 205.133.255.254205.133.255.25565,534
135205.134.0.0/16205.134.0.1 to 205.134.255.254205.134.255.25565,534
136205.135.0.0/16205.135.0.1 to 205.135.255.254205.135.255.25565,534
137205.136.0.0/16205.136.0.1 to 205.136.255.254205.136.255.25565,534
138205.137.0.0/16205.137.0.1 to 205.137.255.254205.137.255.25565,534
139205.138.0.0/16205.138.0.1 to 205.138.255.254205.138.255.25565,534
140205.139.0.0/16205.139.0.1 to 205.139.255.254205.139.255.25565,534
141205.140.0.0/16205.140.0.1 to 205.140.255.254205.140.255.25565,534
142205.141.0.0/16205.141.0.1 to 205.141.255.254205.141.255.25565,534
143205.142.0.0/16205.142.0.1 to 205.142.255.254205.142.255.25565,534
144205.143.0.0/16205.143.0.1 to 205.143.255.254205.143.255.25565,534
145205.144.0.0/16205.144.0.1 to 205.144.255.254205.144.255.25565,534
146205.145.0.0/16205.145.0.1 to 205.145.255.254205.145.255.25565,534
147205.146.0.0/16205.146.0.1 to 205.146.255.254205.146.255.25565,534
148205.147.0.0/16205.147.0.1 to 205.147.255.254205.147.255.25565,534
149205.148.0.0/16205.148.0.1 to 205.148.255.254205.148.255.25565,534
150205.149.0.0/16205.149.0.1 to 205.149.255.254205.149.255.25565,534
151205.150.0.0/16205.150.0.1 to 205.150.255.254205.150.255.25565,534
152205.151.0.0/16205.151.0.1 to 205.151.255.254205.151.255.25565,534
153205.152.0.0/16205.152.0.1 to 205.152.255.254205.152.255.25565,534
154205.153.0.0/16205.153.0.1 to 205.153.255.254205.153.255.25565,534
155205.154.0.0/16205.154.0.1 to 205.154.255.254205.154.255.25565,534
156205.155.0.0/16205.155.0.1 to 205.155.255.254205.155.255.25565,534
157205.156.0.0/16205.156.0.1 to 205.156.255.254205.156.255.25565,534
158205.157.0.0/16205.157.0.1 to 205.157.255.254205.157.255.25565,534
159205.158.0.0/16205.158.0.1 to 205.158.255.254205.158.255.25565,534
160205.159.0.0/16205.159.0.1 to 205.159.255.254205.159.255.25565,534
161205.160.0.0/16205.160.0.1 to 205.160.255.254205.160.255.25565,534
162205.161.0.0/16205.161.0.1 to 205.161.255.254205.161.255.25565,534
163205.162.0.0/16205.162.0.1 to 205.162.255.254205.162.255.25565,534
164205.163.0.0/16205.163.0.1 to 205.163.255.254205.163.255.25565,534
165205.164.0.0/16205.164.0.1 to 205.164.255.254205.164.255.25565,534
166205.165.0.0/16205.165.0.1 to 205.165.255.254205.165.255.25565,534
167205.166.0.0/16205.166.0.1 to 205.166.255.254205.166.255.25565,534
168205.167.0.0/16205.167.0.1 to 205.167.255.254205.167.255.25565,534
169205.168.0.0/16205.168.0.1 to 205.168.255.254205.168.255.25565,534
170205.169.0.0/16205.169.0.1 to 205.169.255.254205.169.255.25565,534
171205.170.0.0/16205.170.0.1 to 205.170.255.254205.170.255.25565,534
172205.171.0.0/16205.171.0.1 to 205.171.255.254205.171.255.25565,534
173205.172.0.0/16205.172.0.1 to 205.172.255.254205.172.255.25565,534
174205.173.0.0/16205.173.0.1 to 205.173.255.254205.173.255.25565,534
175205.174.0.0/16205.174.0.1 to 205.174.255.254205.174.255.25565,534
176205.175.0.0/16205.175.0.1 to 205.175.255.254205.175.255.25565,534
177205.176.0.0/16205.176.0.1 to 205.176.255.254205.176.255.25565,534
178205.177.0.0/16205.177.0.1 to 205.177.255.254205.177.255.25565,534
179205.178.0.0/16205.178.0.1 to 205.178.255.254205.178.255.25565,534
180205.179.0.0/16205.179.0.1 to 205.179.255.254205.179.255.25565,534
181205.180.0.0/16205.180.0.1 to 205.180.255.254205.180.255.25565,534
182205.181.0.0/16205.181.0.1 to 205.181.255.254205.181.255.25565,534
183205.182.0.0/16205.182.0.1 to 205.182.255.254205.182.255.25565,534
184205.183.0.0/16205.183.0.1 to 205.183.255.254205.183.255.25565,534
185205.184.0.0/16205.184.0.1 to 205.184.255.254205.184.255.25565,534
186205.185.0.0/16205.185.0.1 to 205.185.255.254205.185.255.25565,534
187205.186.0.0/16205.186.0.1 to 205.186.255.254205.186.255.25565,534
188205.187.0.0/16205.187.0.1 to 205.187.255.254205.187.255.25565,534
189205.188.0.0/16205.188.0.1 to 205.188.255.254205.188.255.25565,534
190205.189.0.0/16205.189.0.1 to 205.189.255.254205.189.255.25565,534
191205.190.0.0/16205.190.0.1 to 205.190.255.254205.190.255.25565,534
192205.191.0.0/16205.191.0.1 to 205.191.255.254205.191.255.25565,534
193205.192.0.0/16205.192.0.1 to 205.192.255.254205.192.255.25565,534
194205.193.0.0/16205.193.0.1 to 205.193.255.254205.193.255.25565,534
195205.194.0.0/16205.194.0.1 to 205.194.255.254205.194.255.25565,534
196205.195.0.0/16205.195.0.1 to 205.195.255.254205.195.255.25565,534
197205.196.0.0/16205.196.0.1 to 205.196.255.254205.196.255.25565,534
198205.197.0.0/16205.197.0.1 to 205.197.255.254205.197.255.25565,534
199205.198.0.0/16205.198.0.1 to 205.198.255.254205.198.255.25565,534
200205.199.0.0/16205.199.0.1 to 205.199.255.254205.199.255.25565,534
201205.200.0.0/16205.200.0.1 to 205.200.255.254205.200.255.25565,534
202205.201.0.0/16205.201.0.1 to 205.201.255.254205.201.255.25565,534
203205.202.0.0/16205.202.0.1 to 205.202.255.254205.202.255.25565,534
204205.203.0.0/16205.203.0.1 to 205.203.255.254205.203.255.25565,534
205205.204.0.0/16205.204.0.1 to 205.204.255.254205.204.255.25565,534
206205.205.0.0/16205.205.0.1 to 205.205.255.254205.205.255.25565,534
207205.206.0.0/16205.206.0.1 to 205.206.255.254205.206.255.25565,534
208205.207.0.0/16205.207.0.1 to 205.207.255.254205.207.255.25565,534
209205.208.0.0/16205.208.0.1 to 205.208.255.254205.208.255.25565,534
210205.209.0.0/16205.209.0.1 to 205.209.255.254205.209.255.25565,534
211205.210.0.0/16205.210.0.1 to 205.210.255.254205.210.255.25565,534
212205.211.0.0/16205.211.0.1 to 205.211.255.254205.211.255.25565,534
213205.212.0.0/16205.212.0.1 to 205.212.255.254205.212.255.25565,534
214205.213.0.0/16205.213.0.1 to 205.213.255.254205.213.255.25565,534
215205.214.0.0/16205.214.0.1 to 205.214.255.254205.214.255.25565,534
216205.215.0.0/16205.215.0.1 to 205.215.255.254205.215.255.25565,534
217205.216.0.0/16205.216.0.1 to 205.216.255.254205.216.255.25565,534
218205.217.0.0/16205.217.0.1 to 205.217.255.254205.217.255.25565,534
219205.218.0.0/16205.218.0.1 to 205.218.255.254205.218.255.25565,534
220205.219.0.0/16205.219.0.1 to 205.219.255.254205.219.255.25565,534
221205.220.0.0/16205.220.0.1 to 205.220.255.254205.220.255.25565,534
222205.221.0.0/16205.221.0.1 to 205.221.255.254205.221.255.25565,534
223205.222.0.0/16205.222.0.1 to 205.222.255.254205.222.255.25565,534
224205.223.0.0/16205.223.0.1 to 205.223.255.254205.223.255.25565,534
225205.224.0.0/16205.224.0.1 to 205.224.255.254205.224.255.25565,534
226205.225.0.0/16205.225.0.1 to 205.225.255.254205.225.255.25565,534
227205.226.0.0/16205.226.0.1 to 205.226.255.254205.226.255.25565,534
228205.227.0.0/16205.227.0.1 to 205.227.255.254205.227.255.25565,534
229205.228.0.0/16205.228.0.1 to 205.228.255.254205.228.255.25565,534
230205.229.0.0/16205.229.0.1 to 205.229.255.254205.229.255.25565,534
231205.230.0.0/16205.230.0.1 to 205.230.255.254205.230.255.25565,534
232205.231.0.0/16205.231.0.1 to 205.231.255.254205.231.255.25565,534
233205.232.0.0/16205.232.0.1 to 205.232.255.254205.232.255.25565,534
234205.233.0.0/16205.233.0.1 to 205.233.255.254205.233.255.25565,534
235205.234.0.0/16205.234.0.1 to 205.234.255.254205.234.255.25565,534
236205.235.0.0/16205.235.0.1 to 205.235.255.254205.235.255.25565,534
237205.236.0.0/16205.236.0.1 to 205.236.255.254205.236.255.25565,534
238205.237.0.0/16205.237.0.1 to 205.237.255.254205.237.255.25565,534
239205.238.0.0/16205.238.0.1 to 205.238.255.254205.238.255.25565,534
240205.239.0.0/16205.239.0.1 to 205.239.255.254205.239.255.25565,534
241205.240.0.0/16205.240.0.1 to 205.240.255.254205.240.255.25565,534
242205.241.0.0/16205.241.0.1 to 205.241.255.254205.241.255.25565,534
243205.242.0.0/16205.242.0.1 to 205.242.255.254205.242.255.25565,534
244205.243.0.0/16205.243.0.1 to 205.243.255.254205.243.255.25565,534
245205.244.0.0/16205.244.0.1 to 205.244.255.254205.244.255.25565,534
246205.245.0.0/16205.245.0.1 to 205.245.255.254205.245.255.25565,534
247205.246.0.0/16205.246.0.1 to 205.246.255.254205.246.255.25565,534
248205.247.0.0/16205.247.0.1 to 205.247.255.254205.247.255.25565,534
249205.248.0.0/16205.248.0.1 to 205.248.255.254205.248.255.25565,534
250205.249.0.0/16205.249.0.1 to 205.249.255.254205.249.255.25565,534
251205.250.0.0/16205.250.0.1 to 205.250.255.254205.250.255.25565,534
252205.251.0.0/16205.251.0.1 to 205.251.255.254205.251.255.25565,534
253205.252.0.0/16205.252.0.1 to 205.252.255.254205.252.255.25565,534
254205.253.0.0/16205.253.0.1 to 205.253.255.254205.253.255.25565,534
255205.254.0.0/16205.254.0.1 to 205.254.255.254205.254.255.25565,534
256205.255.0.0/16205.255.0.1 to 205.255.255.254205.255.255.25565,534

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.