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.

Network251.0.0.0/11
Usable hosts2,097,150
Subnet mask255.224.0.0
Addresses2,097,152
Network address
251.0.0.0
Broadcast address
251.31.255.255
First usable
251.0.0.1
Last usable
251.31.255.254
Usable hosts
2,097,150 (2,097,152 less the network and broadcast addresses)
Subnet mask
255.224.0.0
Wildcard mask
0.31.255.255 (Cisco ACLs, OSPF)
Prefix length
/11
Type
Reserved 240.0.0.0/4
Future use; not usable on most systems
Old class
E (reserved)
As numbers
Hex FB000000 · Integer 4211081216 to 4213178367
Reverse DNS zones
0.251.in-addr.arpa
1.251.in-addr.arpa
2.251.in-addr.arpa
3.251.in-addr.arpa
4.251.in-addr.arpa
5.251.in-addr.arpa
6.251.in-addr.arpa
7.251.in-addr.arpa
8.251.in-addr.arpa
9.251.in-addr.arpa
10.251.in-addr.arpa
11.251.in-addr.arpa
12.251.in-addr.arpa
13.251.in-addr.arpa
14.251.in-addr.arpa
15.251.in-addr.arpa
and 16 more
/11 is not on a 8-bit boundary, so it takes 32 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11111011.00000000.00000000.00000000251.0.0.0
Subnet mask11111111.11100000.00000000.00000000255.224.0.0
Network11111011.00000000.00000000.00000000251.0.0.0
Broadcast11111011.00011111.11111111.11111111251.31.255.255
Split into smaller subnets/23
/12 (2)/13 (4)/14 (8)/15 (16)/16 (32)/17 (64)/18 (128)/19 (256)/20 (512)/21 (1,024)/22 (2,048)/23 (4,096)

251.0.0.0/11 makes 4,096 subnets of /23; the first 256 are listed.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1251.0.0.0/23251.0.0.1 to 251.0.1.254251.0.1.255510
2251.0.2.0/23251.0.2.1 to 251.0.3.254251.0.3.255510
3251.0.4.0/23251.0.4.1 to 251.0.5.254251.0.5.255510
4251.0.6.0/23251.0.6.1 to 251.0.7.254251.0.7.255510
5251.0.8.0/23251.0.8.1 to 251.0.9.254251.0.9.255510
6251.0.10.0/23251.0.10.1 to 251.0.11.254251.0.11.255510
7251.0.12.0/23251.0.12.1 to 251.0.13.254251.0.13.255510
8251.0.14.0/23251.0.14.1 to 251.0.15.254251.0.15.255510
9251.0.16.0/23251.0.16.1 to 251.0.17.254251.0.17.255510
10251.0.18.0/23251.0.18.1 to 251.0.19.254251.0.19.255510
11251.0.20.0/23251.0.20.1 to 251.0.21.254251.0.21.255510
12251.0.22.0/23251.0.22.1 to 251.0.23.254251.0.23.255510
13251.0.24.0/23251.0.24.1 to 251.0.25.254251.0.25.255510
14251.0.26.0/23251.0.26.1 to 251.0.27.254251.0.27.255510
15251.0.28.0/23251.0.28.1 to 251.0.29.254251.0.29.255510
16251.0.30.0/23251.0.30.1 to 251.0.31.254251.0.31.255510
17251.0.32.0/23251.0.32.1 to 251.0.33.254251.0.33.255510
18251.0.34.0/23251.0.34.1 to 251.0.35.254251.0.35.255510
19251.0.36.0/23251.0.36.1 to 251.0.37.254251.0.37.255510
20251.0.38.0/23251.0.38.1 to 251.0.39.254251.0.39.255510
21251.0.40.0/23251.0.40.1 to 251.0.41.254251.0.41.255510
22251.0.42.0/23251.0.42.1 to 251.0.43.254251.0.43.255510
23251.0.44.0/23251.0.44.1 to 251.0.45.254251.0.45.255510
24251.0.46.0/23251.0.46.1 to 251.0.47.254251.0.47.255510
25251.0.48.0/23251.0.48.1 to 251.0.49.254251.0.49.255510
26251.0.50.0/23251.0.50.1 to 251.0.51.254251.0.51.255510
27251.0.52.0/23251.0.52.1 to 251.0.53.254251.0.53.255510
28251.0.54.0/23251.0.54.1 to 251.0.55.254251.0.55.255510
29251.0.56.0/23251.0.56.1 to 251.0.57.254251.0.57.255510
30251.0.58.0/23251.0.58.1 to 251.0.59.254251.0.59.255510
31251.0.60.0/23251.0.60.1 to 251.0.61.254251.0.61.255510
32251.0.62.0/23251.0.62.1 to 251.0.63.254251.0.63.255510
33251.0.64.0/23251.0.64.1 to 251.0.65.254251.0.65.255510
34251.0.66.0/23251.0.66.1 to 251.0.67.254251.0.67.255510
35251.0.68.0/23251.0.68.1 to 251.0.69.254251.0.69.255510
36251.0.70.0/23251.0.70.1 to 251.0.71.254251.0.71.255510
37251.0.72.0/23251.0.72.1 to 251.0.73.254251.0.73.255510
38251.0.74.0/23251.0.74.1 to 251.0.75.254251.0.75.255510
39251.0.76.0/23251.0.76.1 to 251.0.77.254251.0.77.255510
40251.0.78.0/23251.0.78.1 to 251.0.79.254251.0.79.255510
41251.0.80.0/23251.0.80.1 to 251.0.81.254251.0.81.255510
42251.0.82.0/23251.0.82.1 to 251.0.83.254251.0.83.255510
43251.0.84.0/23251.0.84.1 to 251.0.85.254251.0.85.255510
44251.0.86.0/23251.0.86.1 to 251.0.87.254251.0.87.255510
45251.0.88.0/23251.0.88.1 to 251.0.89.254251.0.89.255510
46251.0.90.0/23251.0.90.1 to 251.0.91.254251.0.91.255510
47251.0.92.0/23251.0.92.1 to 251.0.93.254251.0.93.255510
48251.0.94.0/23251.0.94.1 to 251.0.95.254251.0.95.255510
49251.0.96.0/23251.0.96.1 to 251.0.97.254251.0.97.255510
50251.0.98.0/23251.0.98.1 to 251.0.99.254251.0.99.255510
51251.0.100.0/23251.0.100.1 to 251.0.101.254251.0.101.255510
52251.0.102.0/23251.0.102.1 to 251.0.103.254251.0.103.255510
53251.0.104.0/23251.0.104.1 to 251.0.105.254251.0.105.255510
54251.0.106.0/23251.0.106.1 to 251.0.107.254251.0.107.255510
55251.0.108.0/23251.0.108.1 to 251.0.109.254251.0.109.255510
56251.0.110.0/23251.0.110.1 to 251.0.111.254251.0.111.255510
57251.0.112.0/23251.0.112.1 to 251.0.113.254251.0.113.255510
58251.0.114.0/23251.0.114.1 to 251.0.115.254251.0.115.255510
59251.0.116.0/23251.0.116.1 to 251.0.117.254251.0.117.255510
60251.0.118.0/23251.0.118.1 to 251.0.119.254251.0.119.255510
61251.0.120.0/23251.0.120.1 to 251.0.121.254251.0.121.255510
62251.0.122.0/23251.0.122.1 to 251.0.123.254251.0.123.255510
63251.0.124.0/23251.0.124.1 to 251.0.125.254251.0.125.255510
64251.0.126.0/23251.0.126.1 to 251.0.127.254251.0.127.255510
65251.0.128.0/23251.0.128.1 to 251.0.129.254251.0.129.255510
66251.0.130.0/23251.0.130.1 to 251.0.131.254251.0.131.255510
67251.0.132.0/23251.0.132.1 to 251.0.133.254251.0.133.255510
68251.0.134.0/23251.0.134.1 to 251.0.135.254251.0.135.255510
69251.0.136.0/23251.0.136.1 to 251.0.137.254251.0.137.255510
70251.0.138.0/23251.0.138.1 to 251.0.139.254251.0.139.255510
71251.0.140.0/23251.0.140.1 to 251.0.141.254251.0.141.255510
72251.0.142.0/23251.0.142.1 to 251.0.143.254251.0.143.255510
73251.0.144.0/23251.0.144.1 to 251.0.145.254251.0.145.255510
74251.0.146.0/23251.0.146.1 to 251.0.147.254251.0.147.255510
75251.0.148.0/23251.0.148.1 to 251.0.149.254251.0.149.255510
76251.0.150.0/23251.0.150.1 to 251.0.151.254251.0.151.255510
77251.0.152.0/23251.0.152.1 to 251.0.153.254251.0.153.255510
78251.0.154.0/23251.0.154.1 to 251.0.155.254251.0.155.255510
79251.0.156.0/23251.0.156.1 to 251.0.157.254251.0.157.255510
80251.0.158.0/23251.0.158.1 to 251.0.159.254251.0.159.255510
81251.0.160.0/23251.0.160.1 to 251.0.161.254251.0.161.255510
82251.0.162.0/23251.0.162.1 to 251.0.163.254251.0.163.255510
83251.0.164.0/23251.0.164.1 to 251.0.165.254251.0.165.255510
84251.0.166.0/23251.0.166.1 to 251.0.167.254251.0.167.255510
85251.0.168.0/23251.0.168.1 to 251.0.169.254251.0.169.255510
86251.0.170.0/23251.0.170.1 to 251.0.171.254251.0.171.255510
87251.0.172.0/23251.0.172.1 to 251.0.173.254251.0.173.255510
88251.0.174.0/23251.0.174.1 to 251.0.175.254251.0.175.255510
89251.0.176.0/23251.0.176.1 to 251.0.177.254251.0.177.255510
90251.0.178.0/23251.0.178.1 to 251.0.179.254251.0.179.255510
91251.0.180.0/23251.0.180.1 to 251.0.181.254251.0.181.255510
92251.0.182.0/23251.0.182.1 to 251.0.183.254251.0.183.255510
93251.0.184.0/23251.0.184.1 to 251.0.185.254251.0.185.255510
94251.0.186.0/23251.0.186.1 to 251.0.187.254251.0.187.255510
95251.0.188.0/23251.0.188.1 to 251.0.189.254251.0.189.255510
96251.0.190.0/23251.0.190.1 to 251.0.191.254251.0.191.255510
97251.0.192.0/23251.0.192.1 to 251.0.193.254251.0.193.255510
98251.0.194.0/23251.0.194.1 to 251.0.195.254251.0.195.255510
99251.0.196.0/23251.0.196.1 to 251.0.197.254251.0.197.255510
100251.0.198.0/23251.0.198.1 to 251.0.199.254251.0.199.255510
101251.0.200.0/23251.0.200.1 to 251.0.201.254251.0.201.255510
102251.0.202.0/23251.0.202.1 to 251.0.203.254251.0.203.255510
103251.0.204.0/23251.0.204.1 to 251.0.205.254251.0.205.255510
104251.0.206.0/23251.0.206.1 to 251.0.207.254251.0.207.255510
105251.0.208.0/23251.0.208.1 to 251.0.209.254251.0.209.255510
106251.0.210.0/23251.0.210.1 to 251.0.211.254251.0.211.255510
107251.0.212.0/23251.0.212.1 to 251.0.213.254251.0.213.255510
108251.0.214.0/23251.0.214.1 to 251.0.215.254251.0.215.255510
109251.0.216.0/23251.0.216.1 to 251.0.217.254251.0.217.255510
110251.0.218.0/23251.0.218.1 to 251.0.219.254251.0.219.255510
111251.0.220.0/23251.0.220.1 to 251.0.221.254251.0.221.255510
112251.0.222.0/23251.0.222.1 to 251.0.223.254251.0.223.255510
113251.0.224.0/23251.0.224.1 to 251.0.225.254251.0.225.255510
114251.0.226.0/23251.0.226.1 to 251.0.227.254251.0.227.255510
115251.0.228.0/23251.0.228.1 to 251.0.229.254251.0.229.255510
116251.0.230.0/23251.0.230.1 to 251.0.231.254251.0.231.255510
117251.0.232.0/23251.0.232.1 to 251.0.233.254251.0.233.255510
118251.0.234.0/23251.0.234.1 to 251.0.235.254251.0.235.255510
119251.0.236.0/23251.0.236.1 to 251.0.237.254251.0.237.255510
120251.0.238.0/23251.0.238.1 to 251.0.239.254251.0.239.255510
121251.0.240.0/23251.0.240.1 to 251.0.241.254251.0.241.255510
122251.0.242.0/23251.0.242.1 to 251.0.243.254251.0.243.255510
123251.0.244.0/23251.0.244.1 to 251.0.245.254251.0.245.255510
124251.0.246.0/23251.0.246.1 to 251.0.247.254251.0.247.255510
125251.0.248.0/23251.0.248.1 to 251.0.249.254251.0.249.255510
126251.0.250.0/23251.0.250.1 to 251.0.251.254251.0.251.255510
127251.0.252.0/23251.0.252.1 to 251.0.253.254251.0.253.255510
128251.0.254.0/23251.0.254.1 to 251.0.255.254251.0.255.255510
129251.1.0.0/23251.1.0.1 to 251.1.1.254251.1.1.255510
130251.1.2.0/23251.1.2.1 to 251.1.3.254251.1.3.255510
131251.1.4.0/23251.1.4.1 to 251.1.5.254251.1.5.255510
132251.1.6.0/23251.1.6.1 to 251.1.7.254251.1.7.255510
133251.1.8.0/23251.1.8.1 to 251.1.9.254251.1.9.255510
134251.1.10.0/23251.1.10.1 to 251.1.11.254251.1.11.255510
135251.1.12.0/23251.1.12.1 to 251.1.13.254251.1.13.255510
136251.1.14.0/23251.1.14.1 to 251.1.15.254251.1.15.255510
137251.1.16.0/23251.1.16.1 to 251.1.17.254251.1.17.255510
138251.1.18.0/23251.1.18.1 to 251.1.19.254251.1.19.255510
139251.1.20.0/23251.1.20.1 to 251.1.21.254251.1.21.255510
140251.1.22.0/23251.1.22.1 to 251.1.23.254251.1.23.255510
141251.1.24.0/23251.1.24.1 to 251.1.25.254251.1.25.255510
142251.1.26.0/23251.1.26.1 to 251.1.27.254251.1.27.255510
143251.1.28.0/23251.1.28.1 to 251.1.29.254251.1.29.255510
144251.1.30.0/23251.1.30.1 to 251.1.31.254251.1.31.255510
145251.1.32.0/23251.1.32.1 to 251.1.33.254251.1.33.255510
146251.1.34.0/23251.1.34.1 to 251.1.35.254251.1.35.255510
147251.1.36.0/23251.1.36.1 to 251.1.37.254251.1.37.255510
148251.1.38.0/23251.1.38.1 to 251.1.39.254251.1.39.255510
149251.1.40.0/23251.1.40.1 to 251.1.41.254251.1.41.255510
150251.1.42.0/23251.1.42.1 to 251.1.43.254251.1.43.255510
151251.1.44.0/23251.1.44.1 to 251.1.45.254251.1.45.255510
152251.1.46.0/23251.1.46.1 to 251.1.47.254251.1.47.255510
153251.1.48.0/23251.1.48.1 to 251.1.49.254251.1.49.255510
154251.1.50.0/23251.1.50.1 to 251.1.51.254251.1.51.255510
155251.1.52.0/23251.1.52.1 to 251.1.53.254251.1.53.255510
156251.1.54.0/23251.1.54.1 to 251.1.55.254251.1.55.255510
157251.1.56.0/23251.1.56.1 to 251.1.57.254251.1.57.255510
158251.1.58.0/23251.1.58.1 to 251.1.59.254251.1.59.255510
159251.1.60.0/23251.1.60.1 to 251.1.61.254251.1.61.255510
160251.1.62.0/23251.1.62.1 to 251.1.63.254251.1.63.255510
161251.1.64.0/23251.1.64.1 to 251.1.65.254251.1.65.255510
162251.1.66.0/23251.1.66.1 to 251.1.67.254251.1.67.255510
163251.1.68.0/23251.1.68.1 to 251.1.69.254251.1.69.255510
164251.1.70.0/23251.1.70.1 to 251.1.71.254251.1.71.255510
165251.1.72.0/23251.1.72.1 to 251.1.73.254251.1.73.255510
166251.1.74.0/23251.1.74.1 to 251.1.75.254251.1.75.255510
167251.1.76.0/23251.1.76.1 to 251.1.77.254251.1.77.255510
168251.1.78.0/23251.1.78.1 to 251.1.79.254251.1.79.255510
169251.1.80.0/23251.1.80.1 to 251.1.81.254251.1.81.255510
170251.1.82.0/23251.1.82.1 to 251.1.83.254251.1.83.255510
171251.1.84.0/23251.1.84.1 to 251.1.85.254251.1.85.255510
172251.1.86.0/23251.1.86.1 to 251.1.87.254251.1.87.255510
173251.1.88.0/23251.1.88.1 to 251.1.89.254251.1.89.255510
174251.1.90.0/23251.1.90.1 to 251.1.91.254251.1.91.255510
175251.1.92.0/23251.1.92.1 to 251.1.93.254251.1.93.255510
176251.1.94.0/23251.1.94.1 to 251.1.95.254251.1.95.255510
177251.1.96.0/23251.1.96.1 to 251.1.97.254251.1.97.255510
178251.1.98.0/23251.1.98.1 to 251.1.99.254251.1.99.255510
179251.1.100.0/23251.1.100.1 to 251.1.101.254251.1.101.255510
180251.1.102.0/23251.1.102.1 to 251.1.103.254251.1.103.255510
181251.1.104.0/23251.1.104.1 to 251.1.105.254251.1.105.255510
182251.1.106.0/23251.1.106.1 to 251.1.107.254251.1.107.255510
183251.1.108.0/23251.1.108.1 to 251.1.109.254251.1.109.255510
184251.1.110.0/23251.1.110.1 to 251.1.111.254251.1.111.255510
185251.1.112.0/23251.1.112.1 to 251.1.113.254251.1.113.255510
186251.1.114.0/23251.1.114.1 to 251.1.115.254251.1.115.255510
187251.1.116.0/23251.1.116.1 to 251.1.117.254251.1.117.255510
188251.1.118.0/23251.1.118.1 to 251.1.119.254251.1.119.255510
189251.1.120.0/23251.1.120.1 to 251.1.121.254251.1.121.255510
190251.1.122.0/23251.1.122.1 to 251.1.123.254251.1.123.255510
191251.1.124.0/23251.1.124.1 to 251.1.125.254251.1.125.255510
192251.1.126.0/23251.1.126.1 to 251.1.127.254251.1.127.255510
193251.1.128.0/23251.1.128.1 to 251.1.129.254251.1.129.255510
194251.1.130.0/23251.1.130.1 to 251.1.131.254251.1.131.255510
195251.1.132.0/23251.1.132.1 to 251.1.133.254251.1.133.255510
196251.1.134.0/23251.1.134.1 to 251.1.135.254251.1.135.255510
197251.1.136.0/23251.1.136.1 to 251.1.137.254251.1.137.255510
198251.1.138.0/23251.1.138.1 to 251.1.139.254251.1.139.255510
199251.1.140.0/23251.1.140.1 to 251.1.141.254251.1.141.255510
200251.1.142.0/23251.1.142.1 to 251.1.143.254251.1.143.255510
201251.1.144.0/23251.1.144.1 to 251.1.145.254251.1.145.255510
202251.1.146.0/23251.1.146.1 to 251.1.147.254251.1.147.255510
203251.1.148.0/23251.1.148.1 to 251.1.149.254251.1.149.255510
204251.1.150.0/23251.1.150.1 to 251.1.151.254251.1.151.255510
205251.1.152.0/23251.1.152.1 to 251.1.153.254251.1.153.255510
206251.1.154.0/23251.1.154.1 to 251.1.155.254251.1.155.255510
207251.1.156.0/23251.1.156.1 to 251.1.157.254251.1.157.255510
208251.1.158.0/23251.1.158.1 to 251.1.159.254251.1.159.255510
209251.1.160.0/23251.1.160.1 to 251.1.161.254251.1.161.255510
210251.1.162.0/23251.1.162.1 to 251.1.163.254251.1.163.255510
211251.1.164.0/23251.1.164.1 to 251.1.165.254251.1.165.255510
212251.1.166.0/23251.1.166.1 to 251.1.167.254251.1.167.255510
213251.1.168.0/23251.1.168.1 to 251.1.169.254251.1.169.255510
214251.1.170.0/23251.1.170.1 to 251.1.171.254251.1.171.255510
215251.1.172.0/23251.1.172.1 to 251.1.173.254251.1.173.255510
216251.1.174.0/23251.1.174.1 to 251.1.175.254251.1.175.255510
217251.1.176.0/23251.1.176.1 to 251.1.177.254251.1.177.255510
218251.1.178.0/23251.1.178.1 to 251.1.179.254251.1.179.255510
219251.1.180.0/23251.1.180.1 to 251.1.181.254251.1.181.255510
220251.1.182.0/23251.1.182.1 to 251.1.183.254251.1.183.255510
221251.1.184.0/23251.1.184.1 to 251.1.185.254251.1.185.255510
222251.1.186.0/23251.1.186.1 to 251.1.187.254251.1.187.255510
223251.1.188.0/23251.1.188.1 to 251.1.189.254251.1.189.255510
224251.1.190.0/23251.1.190.1 to 251.1.191.254251.1.191.255510
225251.1.192.0/23251.1.192.1 to 251.1.193.254251.1.193.255510
226251.1.194.0/23251.1.194.1 to 251.1.195.254251.1.195.255510
227251.1.196.0/23251.1.196.1 to 251.1.197.254251.1.197.255510
228251.1.198.0/23251.1.198.1 to 251.1.199.254251.1.199.255510
229251.1.200.0/23251.1.200.1 to 251.1.201.254251.1.201.255510
230251.1.202.0/23251.1.202.1 to 251.1.203.254251.1.203.255510
231251.1.204.0/23251.1.204.1 to 251.1.205.254251.1.205.255510
232251.1.206.0/23251.1.206.1 to 251.1.207.254251.1.207.255510
233251.1.208.0/23251.1.208.1 to 251.1.209.254251.1.209.255510
234251.1.210.0/23251.1.210.1 to 251.1.211.254251.1.211.255510
235251.1.212.0/23251.1.212.1 to 251.1.213.254251.1.213.255510
236251.1.214.0/23251.1.214.1 to 251.1.215.254251.1.215.255510
237251.1.216.0/23251.1.216.1 to 251.1.217.254251.1.217.255510
238251.1.218.0/23251.1.218.1 to 251.1.219.254251.1.219.255510
239251.1.220.0/23251.1.220.1 to 251.1.221.254251.1.221.255510
240251.1.222.0/23251.1.222.1 to 251.1.223.254251.1.223.255510
241251.1.224.0/23251.1.224.1 to 251.1.225.254251.1.225.255510
242251.1.226.0/23251.1.226.1 to 251.1.227.254251.1.227.255510
243251.1.228.0/23251.1.228.1 to 251.1.229.254251.1.229.255510
244251.1.230.0/23251.1.230.1 to 251.1.231.254251.1.231.255510
245251.1.232.0/23251.1.232.1 to 251.1.233.254251.1.233.255510
246251.1.234.0/23251.1.234.1 to 251.1.235.254251.1.235.255510
247251.1.236.0/23251.1.236.1 to 251.1.237.254251.1.237.255510
248251.1.238.0/23251.1.238.1 to 251.1.239.254251.1.239.255510
249251.1.240.0/23251.1.240.1 to 251.1.241.254251.1.241.255510
250251.1.242.0/23251.1.242.1 to 251.1.243.254251.1.243.255510
251251.1.244.0/23251.1.244.1 to 251.1.245.254251.1.245.255510
252251.1.246.0/23251.1.246.1 to 251.1.247.254251.1.247.255510
253251.1.248.0/23251.1.248.1 to 251.1.249.254251.1.249.255510
254251.1.250.0/23251.1.250.1 to 251.1.251.254251.1.251.255510
255251.1.252.0/23251.1.252.1 to 251.1.253.254251.1.253.255510
256251.1.254.0/23251.1.254.1 to 251.1.255.254251.1.255.255510

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.