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.

Network205.40.0.0/13
Usable hosts524,286
Subnet mask255.248.0.0
Addresses524,288
Network address
205.40.0.0
Broadcast address
205.47.255.255
First usable
205.40.0.1
Last usable
205.47.255.254
Usable hosts
524,286 (524,288 less the network and broadcast addresses)
Subnet mask
255.248.0.0
Wildcard mask
0.7.255.255 (Cisco ACLs, OSPF)
Prefix length
/13
Type
Public public
Old class
C (default /24)
As numbers
Hex CD280000 · Integer 3441950720 to 3442475007
Reverse DNS zones
40.205.in-addr.arpa
41.205.in-addr.arpa
42.205.in-addr.arpa
43.205.in-addr.arpa
44.205.in-addr.arpa
45.205.in-addr.arpa
46.205.in-addr.arpa
47.205.in-addr.arpa
/13 is not on a 8-bit boundary, so it takes 8 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11001101.00101000.00000000.00000000205.40.0.0
Subnet mask11111111.11111000.00000000.00000000255.248.0.0
Network11001101.00101000.00000000.00000000205.40.0.0
Broadcast11001101.00101111.11111111.11111111205.47.255.255
Split into smaller subnets/21
/14 (2)/15 (4)/16 (8)/17 (16)/18 (32)/19 (64)/20 (128)/21 (256)/22 (512)/23 (1,024)/24 (2,048)/25 (4,096)

205.40.0.0/13 makes 256 subnets of /21.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1205.40.0.0/21205.40.0.1 to 205.40.7.254205.40.7.2552,046
2205.40.8.0/21205.40.8.1 to 205.40.15.254205.40.15.2552,046
3205.40.16.0/21205.40.16.1 to 205.40.23.254205.40.23.2552,046
4205.40.24.0/21205.40.24.1 to 205.40.31.254205.40.31.2552,046
5205.40.32.0/21205.40.32.1 to 205.40.39.254205.40.39.2552,046
6205.40.40.0/21205.40.40.1 to 205.40.47.254205.40.47.2552,046
7205.40.48.0/21205.40.48.1 to 205.40.55.254205.40.55.2552,046
8205.40.56.0/21205.40.56.1 to 205.40.63.254205.40.63.2552,046
9205.40.64.0/21205.40.64.1 to 205.40.71.254205.40.71.2552,046
10205.40.72.0/21205.40.72.1 to 205.40.79.254205.40.79.2552,046
11205.40.80.0/21205.40.80.1 to 205.40.87.254205.40.87.2552,046
12205.40.88.0/21205.40.88.1 to 205.40.95.254205.40.95.2552,046
13205.40.96.0/21205.40.96.1 to 205.40.103.254205.40.103.2552,046
14205.40.104.0/21205.40.104.1 to 205.40.111.254205.40.111.2552,046
15205.40.112.0/21205.40.112.1 to 205.40.119.254205.40.119.2552,046
16205.40.120.0/21205.40.120.1 to 205.40.127.254205.40.127.2552,046
17205.40.128.0/21205.40.128.1 to 205.40.135.254205.40.135.2552,046
18205.40.136.0/21205.40.136.1 to 205.40.143.254205.40.143.2552,046
19205.40.144.0/21205.40.144.1 to 205.40.151.254205.40.151.2552,046
20205.40.152.0/21205.40.152.1 to 205.40.159.254205.40.159.2552,046
21205.40.160.0/21205.40.160.1 to 205.40.167.254205.40.167.2552,046
22205.40.168.0/21205.40.168.1 to 205.40.175.254205.40.175.2552,046
23205.40.176.0/21205.40.176.1 to 205.40.183.254205.40.183.2552,046
24205.40.184.0/21205.40.184.1 to 205.40.191.254205.40.191.2552,046
25205.40.192.0/21205.40.192.1 to 205.40.199.254205.40.199.2552,046
26205.40.200.0/21205.40.200.1 to 205.40.207.254205.40.207.2552,046
27205.40.208.0/21205.40.208.1 to 205.40.215.254205.40.215.2552,046
28205.40.216.0/21205.40.216.1 to 205.40.223.254205.40.223.2552,046
29205.40.224.0/21205.40.224.1 to 205.40.231.254205.40.231.2552,046
30205.40.232.0/21205.40.232.1 to 205.40.239.254205.40.239.2552,046
31205.40.240.0/21205.40.240.1 to 205.40.247.254205.40.247.2552,046
32205.40.248.0/21205.40.248.1 to 205.40.255.254205.40.255.2552,046
33205.41.0.0/21205.41.0.1 to 205.41.7.254205.41.7.2552,046
34205.41.8.0/21205.41.8.1 to 205.41.15.254205.41.15.2552,046
35205.41.16.0/21205.41.16.1 to 205.41.23.254205.41.23.2552,046
36205.41.24.0/21205.41.24.1 to 205.41.31.254205.41.31.2552,046
37205.41.32.0/21205.41.32.1 to 205.41.39.254205.41.39.2552,046
38205.41.40.0/21205.41.40.1 to 205.41.47.254205.41.47.2552,046
39205.41.48.0/21205.41.48.1 to 205.41.55.254205.41.55.2552,046
40205.41.56.0/21205.41.56.1 to 205.41.63.254205.41.63.2552,046
41205.41.64.0/21205.41.64.1 to 205.41.71.254205.41.71.2552,046
42205.41.72.0/21205.41.72.1 to 205.41.79.254205.41.79.2552,046
43205.41.80.0/21205.41.80.1 to 205.41.87.254205.41.87.2552,046
44205.41.88.0/21205.41.88.1 to 205.41.95.254205.41.95.2552,046
45205.41.96.0/21205.41.96.1 to 205.41.103.254205.41.103.2552,046
46205.41.104.0/21205.41.104.1 to 205.41.111.254205.41.111.2552,046
47205.41.112.0/21205.41.112.1 to 205.41.119.254205.41.119.2552,046
48205.41.120.0/21205.41.120.1 to 205.41.127.254205.41.127.2552,046
49205.41.128.0/21205.41.128.1 to 205.41.135.254205.41.135.2552,046
50205.41.136.0/21205.41.136.1 to 205.41.143.254205.41.143.2552,046
51205.41.144.0/21205.41.144.1 to 205.41.151.254205.41.151.2552,046
52205.41.152.0/21205.41.152.1 to 205.41.159.254205.41.159.2552,046
53205.41.160.0/21205.41.160.1 to 205.41.167.254205.41.167.2552,046
54205.41.168.0/21205.41.168.1 to 205.41.175.254205.41.175.2552,046
55205.41.176.0/21205.41.176.1 to 205.41.183.254205.41.183.2552,046
56205.41.184.0/21205.41.184.1 to 205.41.191.254205.41.191.2552,046
57205.41.192.0/21205.41.192.1 to 205.41.199.254205.41.199.2552,046
58205.41.200.0/21205.41.200.1 to 205.41.207.254205.41.207.2552,046
59205.41.208.0/21205.41.208.1 to 205.41.215.254205.41.215.2552,046
60205.41.216.0/21205.41.216.1 to 205.41.223.254205.41.223.2552,046
61205.41.224.0/21205.41.224.1 to 205.41.231.254205.41.231.2552,046
62205.41.232.0/21205.41.232.1 to 205.41.239.254205.41.239.2552,046
63205.41.240.0/21205.41.240.1 to 205.41.247.254205.41.247.2552,046
64205.41.248.0/21205.41.248.1 to 205.41.255.254205.41.255.2552,046
65205.42.0.0/21205.42.0.1 to 205.42.7.254205.42.7.2552,046
66205.42.8.0/21205.42.8.1 to 205.42.15.254205.42.15.2552,046
67205.42.16.0/21205.42.16.1 to 205.42.23.254205.42.23.2552,046
68205.42.24.0/21205.42.24.1 to 205.42.31.254205.42.31.2552,046
69205.42.32.0/21205.42.32.1 to 205.42.39.254205.42.39.2552,046
70205.42.40.0/21205.42.40.1 to 205.42.47.254205.42.47.2552,046
71205.42.48.0/21205.42.48.1 to 205.42.55.254205.42.55.2552,046
72205.42.56.0/21205.42.56.1 to 205.42.63.254205.42.63.2552,046
73205.42.64.0/21205.42.64.1 to 205.42.71.254205.42.71.2552,046
74205.42.72.0/21205.42.72.1 to 205.42.79.254205.42.79.2552,046
75205.42.80.0/21205.42.80.1 to 205.42.87.254205.42.87.2552,046
76205.42.88.0/21205.42.88.1 to 205.42.95.254205.42.95.2552,046
77205.42.96.0/21205.42.96.1 to 205.42.103.254205.42.103.2552,046
78205.42.104.0/21205.42.104.1 to 205.42.111.254205.42.111.2552,046
79205.42.112.0/21205.42.112.1 to 205.42.119.254205.42.119.2552,046
80205.42.120.0/21205.42.120.1 to 205.42.127.254205.42.127.2552,046
81205.42.128.0/21205.42.128.1 to 205.42.135.254205.42.135.2552,046
82205.42.136.0/21205.42.136.1 to 205.42.143.254205.42.143.2552,046
83205.42.144.0/21205.42.144.1 to 205.42.151.254205.42.151.2552,046
84205.42.152.0/21205.42.152.1 to 205.42.159.254205.42.159.2552,046
85205.42.160.0/21205.42.160.1 to 205.42.167.254205.42.167.2552,046
86205.42.168.0/21205.42.168.1 to 205.42.175.254205.42.175.2552,046
87205.42.176.0/21205.42.176.1 to 205.42.183.254205.42.183.2552,046
88205.42.184.0/21205.42.184.1 to 205.42.191.254205.42.191.2552,046
89205.42.192.0/21205.42.192.1 to 205.42.199.254205.42.199.2552,046
90205.42.200.0/21205.42.200.1 to 205.42.207.254205.42.207.2552,046
91205.42.208.0/21205.42.208.1 to 205.42.215.254205.42.215.2552,046
92205.42.216.0/21205.42.216.1 to 205.42.223.254205.42.223.2552,046
93205.42.224.0/21205.42.224.1 to 205.42.231.254205.42.231.2552,046
94205.42.232.0/21205.42.232.1 to 205.42.239.254205.42.239.2552,046
95205.42.240.0/21205.42.240.1 to 205.42.247.254205.42.247.2552,046
96205.42.248.0/21205.42.248.1 to 205.42.255.254205.42.255.2552,046
97205.43.0.0/21205.43.0.1 to 205.43.7.254205.43.7.2552,046
98205.43.8.0/21205.43.8.1 to 205.43.15.254205.43.15.2552,046
99205.43.16.0/21205.43.16.1 to 205.43.23.254205.43.23.2552,046
100205.43.24.0/21205.43.24.1 to 205.43.31.254205.43.31.2552,046
101205.43.32.0/21205.43.32.1 to 205.43.39.254205.43.39.2552,046
102205.43.40.0/21205.43.40.1 to 205.43.47.254205.43.47.2552,046
103205.43.48.0/21205.43.48.1 to 205.43.55.254205.43.55.2552,046
104205.43.56.0/21205.43.56.1 to 205.43.63.254205.43.63.2552,046
105205.43.64.0/21205.43.64.1 to 205.43.71.254205.43.71.2552,046
106205.43.72.0/21205.43.72.1 to 205.43.79.254205.43.79.2552,046
107205.43.80.0/21205.43.80.1 to 205.43.87.254205.43.87.2552,046
108205.43.88.0/21205.43.88.1 to 205.43.95.254205.43.95.2552,046
109205.43.96.0/21205.43.96.1 to 205.43.103.254205.43.103.2552,046
110205.43.104.0/21205.43.104.1 to 205.43.111.254205.43.111.2552,046
111205.43.112.0/21205.43.112.1 to 205.43.119.254205.43.119.2552,046
112205.43.120.0/21205.43.120.1 to 205.43.127.254205.43.127.2552,046
113205.43.128.0/21205.43.128.1 to 205.43.135.254205.43.135.2552,046
114205.43.136.0/21205.43.136.1 to 205.43.143.254205.43.143.2552,046
115205.43.144.0/21205.43.144.1 to 205.43.151.254205.43.151.2552,046
116205.43.152.0/21205.43.152.1 to 205.43.159.254205.43.159.2552,046
117205.43.160.0/21205.43.160.1 to 205.43.167.254205.43.167.2552,046
118205.43.168.0/21205.43.168.1 to 205.43.175.254205.43.175.2552,046
119205.43.176.0/21205.43.176.1 to 205.43.183.254205.43.183.2552,046
120205.43.184.0/21205.43.184.1 to 205.43.191.254205.43.191.2552,046
121205.43.192.0/21205.43.192.1 to 205.43.199.254205.43.199.2552,046
122205.43.200.0/21205.43.200.1 to 205.43.207.254205.43.207.2552,046
123205.43.208.0/21205.43.208.1 to 205.43.215.254205.43.215.2552,046
124205.43.216.0/21205.43.216.1 to 205.43.223.254205.43.223.2552,046
125205.43.224.0/21205.43.224.1 to 205.43.231.254205.43.231.2552,046
126205.43.232.0/21205.43.232.1 to 205.43.239.254205.43.239.2552,046
127205.43.240.0/21205.43.240.1 to 205.43.247.254205.43.247.2552,046
128205.43.248.0/21205.43.248.1 to 205.43.255.254205.43.255.2552,046
129205.44.0.0/21205.44.0.1 to 205.44.7.254205.44.7.2552,046
130205.44.8.0/21205.44.8.1 to 205.44.15.254205.44.15.2552,046
131205.44.16.0/21205.44.16.1 to 205.44.23.254205.44.23.2552,046
132205.44.24.0/21205.44.24.1 to 205.44.31.254205.44.31.2552,046
133205.44.32.0/21205.44.32.1 to 205.44.39.254205.44.39.2552,046
134205.44.40.0/21205.44.40.1 to 205.44.47.254205.44.47.2552,046
135205.44.48.0/21205.44.48.1 to 205.44.55.254205.44.55.2552,046
136205.44.56.0/21205.44.56.1 to 205.44.63.254205.44.63.2552,046
137205.44.64.0/21205.44.64.1 to 205.44.71.254205.44.71.2552,046
138205.44.72.0/21205.44.72.1 to 205.44.79.254205.44.79.2552,046
139205.44.80.0/21205.44.80.1 to 205.44.87.254205.44.87.2552,046
140205.44.88.0/21205.44.88.1 to 205.44.95.254205.44.95.2552,046
141205.44.96.0/21205.44.96.1 to 205.44.103.254205.44.103.2552,046
142205.44.104.0/21205.44.104.1 to 205.44.111.254205.44.111.2552,046
143205.44.112.0/21205.44.112.1 to 205.44.119.254205.44.119.2552,046
144205.44.120.0/21205.44.120.1 to 205.44.127.254205.44.127.2552,046
145205.44.128.0/21205.44.128.1 to 205.44.135.254205.44.135.2552,046
146205.44.136.0/21205.44.136.1 to 205.44.143.254205.44.143.2552,046
147205.44.144.0/21205.44.144.1 to 205.44.151.254205.44.151.2552,046
148205.44.152.0/21205.44.152.1 to 205.44.159.254205.44.159.2552,046
149205.44.160.0/21205.44.160.1 to 205.44.167.254205.44.167.2552,046
150205.44.168.0/21205.44.168.1 to 205.44.175.254205.44.175.2552,046
151205.44.176.0/21205.44.176.1 to 205.44.183.254205.44.183.2552,046
152205.44.184.0/21205.44.184.1 to 205.44.191.254205.44.191.2552,046
153205.44.192.0/21205.44.192.1 to 205.44.199.254205.44.199.2552,046
154205.44.200.0/21205.44.200.1 to 205.44.207.254205.44.207.2552,046
155205.44.208.0/21205.44.208.1 to 205.44.215.254205.44.215.2552,046
156205.44.216.0/21205.44.216.1 to 205.44.223.254205.44.223.2552,046
157205.44.224.0/21205.44.224.1 to 205.44.231.254205.44.231.2552,046
158205.44.232.0/21205.44.232.1 to 205.44.239.254205.44.239.2552,046
159205.44.240.0/21205.44.240.1 to 205.44.247.254205.44.247.2552,046
160205.44.248.0/21205.44.248.1 to 205.44.255.254205.44.255.2552,046
161205.45.0.0/21205.45.0.1 to 205.45.7.254205.45.7.2552,046
162205.45.8.0/21205.45.8.1 to 205.45.15.254205.45.15.2552,046
163205.45.16.0/21205.45.16.1 to 205.45.23.254205.45.23.2552,046
164205.45.24.0/21205.45.24.1 to 205.45.31.254205.45.31.2552,046
165205.45.32.0/21205.45.32.1 to 205.45.39.254205.45.39.2552,046
166205.45.40.0/21205.45.40.1 to 205.45.47.254205.45.47.2552,046
167205.45.48.0/21205.45.48.1 to 205.45.55.254205.45.55.2552,046
168205.45.56.0/21205.45.56.1 to 205.45.63.254205.45.63.2552,046
169205.45.64.0/21205.45.64.1 to 205.45.71.254205.45.71.2552,046
170205.45.72.0/21205.45.72.1 to 205.45.79.254205.45.79.2552,046
171205.45.80.0/21205.45.80.1 to 205.45.87.254205.45.87.2552,046
172205.45.88.0/21205.45.88.1 to 205.45.95.254205.45.95.2552,046
173205.45.96.0/21205.45.96.1 to 205.45.103.254205.45.103.2552,046
174205.45.104.0/21205.45.104.1 to 205.45.111.254205.45.111.2552,046
175205.45.112.0/21205.45.112.1 to 205.45.119.254205.45.119.2552,046
176205.45.120.0/21205.45.120.1 to 205.45.127.254205.45.127.2552,046
177205.45.128.0/21205.45.128.1 to 205.45.135.254205.45.135.2552,046
178205.45.136.0/21205.45.136.1 to 205.45.143.254205.45.143.2552,046
179205.45.144.0/21205.45.144.1 to 205.45.151.254205.45.151.2552,046
180205.45.152.0/21205.45.152.1 to 205.45.159.254205.45.159.2552,046
181205.45.160.0/21205.45.160.1 to 205.45.167.254205.45.167.2552,046
182205.45.168.0/21205.45.168.1 to 205.45.175.254205.45.175.2552,046
183205.45.176.0/21205.45.176.1 to 205.45.183.254205.45.183.2552,046
184205.45.184.0/21205.45.184.1 to 205.45.191.254205.45.191.2552,046
185205.45.192.0/21205.45.192.1 to 205.45.199.254205.45.199.2552,046
186205.45.200.0/21205.45.200.1 to 205.45.207.254205.45.207.2552,046
187205.45.208.0/21205.45.208.1 to 205.45.215.254205.45.215.2552,046
188205.45.216.0/21205.45.216.1 to 205.45.223.254205.45.223.2552,046
189205.45.224.0/21205.45.224.1 to 205.45.231.254205.45.231.2552,046
190205.45.232.0/21205.45.232.1 to 205.45.239.254205.45.239.2552,046
191205.45.240.0/21205.45.240.1 to 205.45.247.254205.45.247.2552,046
192205.45.248.0/21205.45.248.1 to 205.45.255.254205.45.255.2552,046
193205.46.0.0/21205.46.0.1 to 205.46.7.254205.46.7.2552,046
194205.46.8.0/21205.46.8.1 to 205.46.15.254205.46.15.2552,046
195205.46.16.0/21205.46.16.1 to 205.46.23.254205.46.23.2552,046
196205.46.24.0/21205.46.24.1 to 205.46.31.254205.46.31.2552,046
197205.46.32.0/21205.46.32.1 to 205.46.39.254205.46.39.2552,046
198205.46.40.0/21205.46.40.1 to 205.46.47.254205.46.47.2552,046
199205.46.48.0/21205.46.48.1 to 205.46.55.254205.46.55.2552,046
200205.46.56.0/21205.46.56.1 to 205.46.63.254205.46.63.2552,046
201205.46.64.0/21205.46.64.1 to 205.46.71.254205.46.71.2552,046
202205.46.72.0/21205.46.72.1 to 205.46.79.254205.46.79.2552,046
203205.46.80.0/21205.46.80.1 to 205.46.87.254205.46.87.2552,046
204205.46.88.0/21205.46.88.1 to 205.46.95.254205.46.95.2552,046
205205.46.96.0/21205.46.96.1 to 205.46.103.254205.46.103.2552,046
206205.46.104.0/21205.46.104.1 to 205.46.111.254205.46.111.2552,046
207205.46.112.0/21205.46.112.1 to 205.46.119.254205.46.119.2552,046
208205.46.120.0/21205.46.120.1 to 205.46.127.254205.46.127.2552,046
209205.46.128.0/21205.46.128.1 to 205.46.135.254205.46.135.2552,046
210205.46.136.0/21205.46.136.1 to 205.46.143.254205.46.143.2552,046
211205.46.144.0/21205.46.144.1 to 205.46.151.254205.46.151.2552,046
212205.46.152.0/21205.46.152.1 to 205.46.159.254205.46.159.2552,046
213205.46.160.0/21205.46.160.1 to 205.46.167.254205.46.167.2552,046
214205.46.168.0/21205.46.168.1 to 205.46.175.254205.46.175.2552,046
215205.46.176.0/21205.46.176.1 to 205.46.183.254205.46.183.2552,046
216205.46.184.0/21205.46.184.1 to 205.46.191.254205.46.191.2552,046
217205.46.192.0/21205.46.192.1 to 205.46.199.254205.46.199.2552,046
218205.46.200.0/21205.46.200.1 to 205.46.207.254205.46.207.2552,046
219205.46.208.0/21205.46.208.1 to 205.46.215.254205.46.215.2552,046
220205.46.216.0/21205.46.216.1 to 205.46.223.254205.46.223.2552,046
221205.46.224.0/21205.46.224.1 to 205.46.231.254205.46.231.2552,046
222205.46.232.0/21205.46.232.1 to 205.46.239.254205.46.239.2552,046
223205.46.240.0/21205.46.240.1 to 205.46.247.254205.46.247.2552,046
224205.46.248.0/21205.46.248.1 to 205.46.255.254205.46.255.2552,046
225205.47.0.0/21205.47.0.1 to 205.47.7.254205.47.7.2552,046
226205.47.8.0/21205.47.8.1 to 205.47.15.254205.47.15.2552,046
227205.47.16.0/21205.47.16.1 to 205.47.23.254205.47.23.2552,046
228205.47.24.0/21205.47.24.1 to 205.47.31.254205.47.31.2552,046
229205.47.32.0/21205.47.32.1 to 205.47.39.254205.47.39.2552,046
230205.47.40.0/21205.47.40.1 to 205.47.47.254205.47.47.2552,046
231205.47.48.0/21205.47.48.1 to 205.47.55.254205.47.55.2552,046
232205.47.56.0/21205.47.56.1 to 205.47.63.254205.47.63.2552,046
233205.47.64.0/21205.47.64.1 to 205.47.71.254205.47.71.2552,046
234205.47.72.0/21205.47.72.1 to 205.47.79.254205.47.79.2552,046
235205.47.80.0/21205.47.80.1 to 205.47.87.254205.47.87.2552,046
236205.47.88.0/21205.47.88.1 to 205.47.95.254205.47.95.2552,046
237205.47.96.0/21205.47.96.1 to 205.47.103.254205.47.103.2552,046
238205.47.104.0/21205.47.104.1 to 205.47.111.254205.47.111.2552,046
239205.47.112.0/21205.47.112.1 to 205.47.119.254205.47.119.2552,046
240205.47.120.0/21205.47.120.1 to 205.47.127.254205.47.127.2552,046
241205.47.128.0/21205.47.128.1 to 205.47.135.254205.47.135.2552,046
242205.47.136.0/21205.47.136.1 to 205.47.143.254205.47.143.2552,046
243205.47.144.0/21205.47.144.1 to 205.47.151.254205.47.151.2552,046
244205.47.152.0/21205.47.152.1 to 205.47.159.254205.47.159.2552,046
245205.47.160.0/21205.47.160.1 to 205.47.167.254205.47.167.2552,046
246205.47.168.0/21205.47.168.1 to 205.47.175.254205.47.175.2552,046
247205.47.176.0/21205.47.176.1 to 205.47.183.254205.47.183.2552,046
248205.47.184.0/21205.47.184.1 to 205.47.191.254205.47.191.2552,046
249205.47.192.0/21205.47.192.1 to 205.47.199.254205.47.199.2552,046
250205.47.200.0/21205.47.200.1 to 205.47.207.254205.47.207.2552,046
251205.47.208.0/21205.47.208.1 to 205.47.215.254205.47.215.2552,046
252205.47.216.0/21205.47.216.1 to 205.47.223.254205.47.223.2552,046
253205.47.224.0/21205.47.224.1 to 205.47.231.254205.47.231.2552,046
254205.47.232.0/21205.47.232.1 to 205.47.239.254205.47.239.2552,046
255205.47.240.0/21205.47.240.1 to 205.47.247.254205.47.247.2552,046
256205.47.248.0/21205.47.248.1 to 205.47.255.254205.47.255.2552,046

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.