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.

Network227.167.16.0/21
Usable hosts2,046
Subnet mask255.255.248.0
Addresses2,048
Network address
227.167.16.0
Broadcast address
227.167.23.255
First usable
227.167.16.1
Last usable
227.167.23.254
Usable hosts
2,046 (2,048 less the network and broadcast addresses)
Subnet mask
255.255.248.0
Wildcard mask
0.0.7.255 (Cisco ACLs, OSPF)
Prefix length
/21
Type
Multicast 224.0.0.0/4
One-to-many traffic, such as IPTV and routing protocols
Old class
D (multicast)
As numbers
Hex E3A71000 · Integer 3819376640 to 3819378687
Reverse DNS zones
16.167.227.in-addr.arpa
17.167.227.in-addr.arpa
18.167.227.in-addr.arpa
19.167.227.in-addr.arpa
20.167.227.in-addr.arpa
21.167.227.in-addr.arpa
22.167.227.in-addr.arpa
23.167.227.in-addr.arpa
/21 is not on a 8-bit boundary, so it takes 8 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11100011.10100111.00010000.00000000227.167.16.0
Subnet mask11111111.11111111.11111000.00000000255.255.248.0
Network11100011.10100111.00010000.00000000227.167.16.0
Broadcast11100011.10100111.00010111.11111111227.167.23.255
Split into smaller subnets/30
/22 (2)/23 (4)/24 (8)/25 (16)/26 (32)/27 (64)/28 (128)/29 (256)/30 (512)/31 (1,024)/32 (2,048)

227.167.16.0/21 makes 512 subnets of /30; the first 256 are listed.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1227.167.16.0/30227.167.16.1 to 227.167.16.2227.167.16.32
2227.167.16.4/30227.167.16.5 to 227.167.16.6227.167.16.72
3227.167.16.8/30227.167.16.9 to 227.167.16.10227.167.16.112
4227.167.16.12/30227.167.16.13 to 227.167.16.14227.167.16.152
5227.167.16.16/30227.167.16.17 to 227.167.16.18227.167.16.192
6227.167.16.20/30227.167.16.21 to 227.167.16.22227.167.16.232
7227.167.16.24/30227.167.16.25 to 227.167.16.26227.167.16.272
8227.167.16.28/30227.167.16.29 to 227.167.16.30227.167.16.312
9227.167.16.32/30227.167.16.33 to 227.167.16.34227.167.16.352
10227.167.16.36/30227.167.16.37 to 227.167.16.38227.167.16.392
11227.167.16.40/30227.167.16.41 to 227.167.16.42227.167.16.432
12227.167.16.44/30227.167.16.45 to 227.167.16.46227.167.16.472
13227.167.16.48/30227.167.16.49 to 227.167.16.50227.167.16.512
14227.167.16.52/30227.167.16.53 to 227.167.16.54227.167.16.552
15227.167.16.56/30227.167.16.57 to 227.167.16.58227.167.16.592
16227.167.16.60/30227.167.16.61 to 227.167.16.62227.167.16.632
17227.167.16.64/30227.167.16.65 to 227.167.16.66227.167.16.672
18227.167.16.68/30227.167.16.69 to 227.167.16.70227.167.16.712
19227.167.16.72/30227.167.16.73 to 227.167.16.74227.167.16.752
20227.167.16.76/30227.167.16.77 to 227.167.16.78227.167.16.792
21227.167.16.80/30227.167.16.81 to 227.167.16.82227.167.16.832
22227.167.16.84/30227.167.16.85 to 227.167.16.86227.167.16.872
23227.167.16.88/30227.167.16.89 to 227.167.16.90227.167.16.912
24227.167.16.92/30227.167.16.93 to 227.167.16.94227.167.16.952
25227.167.16.96/30227.167.16.97 to 227.167.16.98227.167.16.992
26227.167.16.100/30227.167.16.101 to 227.167.16.102227.167.16.1032
27227.167.16.104/30227.167.16.105 to 227.167.16.106227.167.16.1072
28227.167.16.108/30227.167.16.109 to 227.167.16.110227.167.16.1112
29227.167.16.112/30227.167.16.113 to 227.167.16.114227.167.16.1152
30227.167.16.116/30227.167.16.117 to 227.167.16.118227.167.16.1192
31227.167.16.120/30227.167.16.121 to 227.167.16.122227.167.16.1232
32227.167.16.124/30227.167.16.125 to 227.167.16.126227.167.16.1272
33227.167.16.128/30227.167.16.129 to 227.167.16.130227.167.16.1312
34227.167.16.132/30227.167.16.133 to 227.167.16.134227.167.16.1352
35227.167.16.136/30227.167.16.137 to 227.167.16.138227.167.16.1392
36227.167.16.140/30227.167.16.141 to 227.167.16.142227.167.16.1432
37227.167.16.144/30227.167.16.145 to 227.167.16.146227.167.16.1472
38227.167.16.148/30227.167.16.149 to 227.167.16.150227.167.16.1512
39227.167.16.152/30227.167.16.153 to 227.167.16.154227.167.16.1552
40227.167.16.156/30227.167.16.157 to 227.167.16.158227.167.16.1592
41227.167.16.160/30227.167.16.161 to 227.167.16.162227.167.16.1632
42227.167.16.164/30227.167.16.165 to 227.167.16.166227.167.16.1672
43227.167.16.168/30227.167.16.169 to 227.167.16.170227.167.16.1712
44227.167.16.172/30227.167.16.173 to 227.167.16.174227.167.16.1752
45227.167.16.176/30227.167.16.177 to 227.167.16.178227.167.16.1792
46227.167.16.180/30227.167.16.181 to 227.167.16.182227.167.16.1832
47227.167.16.184/30227.167.16.185 to 227.167.16.186227.167.16.1872
48227.167.16.188/30227.167.16.189 to 227.167.16.190227.167.16.1912
49227.167.16.192/30227.167.16.193 to 227.167.16.194227.167.16.1952
50227.167.16.196/30227.167.16.197 to 227.167.16.198227.167.16.1992
51227.167.16.200/30227.167.16.201 to 227.167.16.202227.167.16.2032
52227.167.16.204/30227.167.16.205 to 227.167.16.206227.167.16.2072
53227.167.16.208/30227.167.16.209 to 227.167.16.210227.167.16.2112
54227.167.16.212/30227.167.16.213 to 227.167.16.214227.167.16.2152
55227.167.16.216/30227.167.16.217 to 227.167.16.218227.167.16.2192
56227.167.16.220/30227.167.16.221 to 227.167.16.222227.167.16.2232
57227.167.16.224/30227.167.16.225 to 227.167.16.226227.167.16.2272
58227.167.16.228/30227.167.16.229 to 227.167.16.230227.167.16.2312
59227.167.16.232/30227.167.16.233 to 227.167.16.234227.167.16.2352
60227.167.16.236/30227.167.16.237 to 227.167.16.238227.167.16.2392
61227.167.16.240/30227.167.16.241 to 227.167.16.242227.167.16.2432
62227.167.16.244/30227.167.16.245 to 227.167.16.246227.167.16.2472
63227.167.16.248/30227.167.16.249 to 227.167.16.250227.167.16.2512
64227.167.16.252/30227.167.16.253 to 227.167.16.254227.167.16.2552
65227.167.17.0/30227.167.17.1 to 227.167.17.2227.167.17.32
66227.167.17.4/30227.167.17.5 to 227.167.17.6227.167.17.72
67227.167.17.8/30227.167.17.9 to 227.167.17.10227.167.17.112
68227.167.17.12/30227.167.17.13 to 227.167.17.14227.167.17.152
69227.167.17.16/30227.167.17.17 to 227.167.17.18227.167.17.192
70227.167.17.20/30227.167.17.21 to 227.167.17.22227.167.17.232
71227.167.17.24/30227.167.17.25 to 227.167.17.26227.167.17.272
72227.167.17.28/30227.167.17.29 to 227.167.17.30227.167.17.312
73227.167.17.32/30227.167.17.33 to 227.167.17.34227.167.17.352
74227.167.17.36/30227.167.17.37 to 227.167.17.38227.167.17.392
75227.167.17.40/30227.167.17.41 to 227.167.17.42227.167.17.432
76227.167.17.44/30227.167.17.45 to 227.167.17.46227.167.17.472
77227.167.17.48/30227.167.17.49 to 227.167.17.50227.167.17.512
78227.167.17.52/30227.167.17.53 to 227.167.17.54227.167.17.552
79227.167.17.56/30227.167.17.57 to 227.167.17.58227.167.17.592
80227.167.17.60/30227.167.17.61 to 227.167.17.62227.167.17.632
81227.167.17.64/30227.167.17.65 to 227.167.17.66227.167.17.672
82227.167.17.68/30227.167.17.69 to 227.167.17.70227.167.17.712
83227.167.17.72/30227.167.17.73 to 227.167.17.74227.167.17.752
84227.167.17.76/30227.167.17.77 to 227.167.17.78227.167.17.792
85227.167.17.80/30227.167.17.81 to 227.167.17.82227.167.17.832
86227.167.17.84/30227.167.17.85 to 227.167.17.86227.167.17.872
87227.167.17.88/30227.167.17.89 to 227.167.17.90227.167.17.912
88227.167.17.92/30227.167.17.93 to 227.167.17.94227.167.17.952
89227.167.17.96/30227.167.17.97 to 227.167.17.98227.167.17.992
90227.167.17.100/30227.167.17.101 to 227.167.17.102227.167.17.1032
91227.167.17.104/30227.167.17.105 to 227.167.17.106227.167.17.1072
92227.167.17.108/30227.167.17.109 to 227.167.17.110227.167.17.1112
93227.167.17.112/30227.167.17.113 to 227.167.17.114227.167.17.1152
94227.167.17.116/30227.167.17.117 to 227.167.17.118227.167.17.1192
95227.167.17.120/30227.167.17.121 to 227.167.17.122227.167.17.1232
96227.167.17.124/30227.167.17.125 to 227.167.17.126227.167.17.1272
97227.167.17.128/30227.167.17.129 to 227.167.17.130227.167.17.1312
98227.167.17.132/30227.167.17.133 to 227.167.17.134227.167.17.1352
99227.167.17.136/30227.167.17.137 to 227.167.17.138227.167.17.1392
100227.167.17.140/30227.167.17.141 to 227.167.17.142227.167.17.1432
101227.167.17.144/30227.167.17.145 to 227.167.17.146227.167.17.1472
102227.167.17.148/30227.167.17.149 to 227.167.17.150227.167.17.1512
103227.167.17.152/30227.167.17.153 to 227.167.17.154227.167.17.1552
104227.167.17.156/30227.167.17.157 to 227.167.17.158227.167.17.1592
105227.167.17.160/30227.167.17.161 to 227.167.17.162227.167.17.1632
106227.167.17.164/30227.167.17.165 to 227.167.17.166227.167.17.1672
107227.167.17.168/30227.167.17.169 to 227.167.17.170227.167.17.1712
108227.167.17.172/30227.167.17.173 to 227.167.17.174227.167.17.1752
109227.167.17.176/30227.167.17.177 to 227.167.17.178227.167.17.1792
110227.167.17.180/30227.167.17.181 to 227.167.17.182227.167.17.1832
111227.167.17.184/30227.167.17.185 to 227.167.17.186227.167.17.1872
112227.167.17.188/30227.167.17.189 to 227.167.17.190227.167.17.1912
113227.167.17.192/30227.167.17.193 to 227.167.17.194227.167.17.1952
114227.167.17.196/30227.167.17.197 to 227.167.17.198227.167.17.1992
115227.167.17.200/30227.167.17.201 to 227.167.17.202227.167.17.2032
116227.167.17.204/30227.167.17.205 to 227.167.17.206227.167.17.2072
117227.167.17.208/30227.167.17.209 to 227.167.17.210227.167.17.2112
118227.167.17.212/30227.167.17.213 to 227.167.17.214227.167.17.2152
119227.167.17.216/30227.167.17.217 to 227.167.17.218227.167.17.2192
120227.167.17.220/30227.167.17.221 to 227.167.17.222227.167.17.2232
121227.167.17.224/30227.167.17.225 to 227.167.17.226227.167.17.2272
122227.167.17.228/30227.167.17.229 to 227.167.17.230227.167.17.2312
123227.167.17.232/30227.167.17.233 to 227.167.17.234227.167.17.2352
124227.167.17.236/30227.167.17.237 to 227.167.17.238227.167.17.2392
125227.167.17.240/30227.167.17.241 to 227.167.17.242227.167.17.2432
126227.167.17.244/30227.167.17.245 to 227.167.17.246227.167.17.2472
127227.167.17.248/30227.167.17.249 to 227.167.17.250227.167.17.2512
128227.167.17.252/30227.167.17.253 to 227.167.17.254227.167.17.2552
129227.167.18.0/30227.167.18.1 to 227.167.18.2227.167.18.32
130227.167.18.4/30227.167.18.5 to 227.167.18.6227.167.18.72
131227.167.18.8/30227.167.18.9 to 227.167.18.10227.167.18.112
132227.167.18.12/30227.167.18.13 to 227.167.18.14227.167.18.152
133227.167.18.16/30227.167.18.17 to 227.167.18.18227.167.18.192
134227.167.18.20/30227.167.18.21 to 227.167.18.22227.167.18.232
135227.167.18.24/30227.167.18.25 to 227.167.18.26227.167.18.272
136227.167.18.28/30227.167.18.29 to 227.167.18.30227.167.18.312
137227.167.18.32/30227.167.18.33 to 227.167.18.34227.167.18.352
138227.167.18.36/30227.167.18.37 to 227.167.18.38227.167.18.392
139227.167.18.40/30227.167.18.41 to 227.167.18.42227.167.18.432
140227.167.18.44/30227.167.18.45 to 227.167.18.46227.167.18.472
141227.167.18.48/30227.167.18.49 to 227.167.18.50227.167.18.512
142227.167.18.52/30227.167.18.53 to 227.167.18.54227.167.18.552
143227.167.18.56/30227.167.18.57 to 227.167.18.58227.167.18.592
144227.167.18.60/30227.167.18.61 to 227.167.18.62227.167.18.632
145227.167.18.64/30227.167.18.65 to 227.167.18.66227.167.18.672
146227.167.18.68/30227.167.18.69 to 227.167.18.70227.167.18.712
147227.167.18.72/30227.167.18.73 to 227.167.18.74227.167.18.752
148227.167.18.76/30227.167.18.77 to 227.167.18.78227.167.18.792
149227.167.18.80/30227.167.18.81 to 227.167.18.82227.167.18.832
150227.167.18.84/30227.167.18.85 to 227.167.18.86227.167.18.872
151227.167.18.88/30227.167.18.89 to 227.167.18.90227.167.18.912
152227.167.18.92/30227.167.18.93 to 227.167.18.94227.167.18.952
153227.167.18.96/30227.167.18.97 to 227.167.18.98227.167.18.992
154227.167.18.100/30227.167.18.101 to 227.167.18.102227.167.18.1032
155227.167.18.104/30227.167.18.105 to 227.167.18.106227.167.18.1072
156227.167.18.108/30227.167.18.109 to 227.167.18.110227.167.18.1112
157227.167.18.112/30227.167.18.113 to 227.167.18.114227.167.18.1152
158227.167.18.116/30227.167.18.117 to 227.167.18.118227.167.18.1192
159227.167.18.120/30227.167.18.121 to 227.167.18.122227.167.18.1232
160227.167.18.124/30227.167.18.125 to 227.167.18.126227.167.18.1272
161227.167.18.128/30227.167.18.129 to 227.167.18.130227.167.18.1312
162227.167.18.132/30227.167.18.133 to 227.167.18.134227.167.18.1352
163227.167.18.136/30227.167.18.137 to 227.167.18.138227.167.18.1392
164227.167.18.140/30227.167.18.141 to 227.167.18.142227.167.18.1432
165227.167.18.144/30227.167.18.145 to 227.167.18.146227.167.18.1472
166227.167.18.148/30227.167.18.149 to 227.167.18.150227.167.18.1512
167227.167.18.152/30227.167.18.153 to 227.167.18.154227.167.18.1552
168227.167.18.156/30227.167.18.157 to 227.167.18.158227.167.18.1592
169227.167.18.160/30227.167.18.161 to 227.167.18.162227.167.18.1632
170227.167.18.164/30227.167.18.165 to 227.167.18.166227.167.18.1672
171227.167.18.168/30227.167.18.169 to 227.167.18.170227.167.18.1712
172227.167.18.172/30227.167.18.173 to 227.167.18.174227.167.18.1752
173227.167.18.176/30227.167.18.177 to 227.167.18.178227.167.18.1792
174227.167.18.180/30227.167.18.181 to 227.167.18.182227.167.18.1832
175227.167.18.184/30227.167.18.185 to 227.167.18.186227.167.18.1872
176227.167.18.188/30227.167.18.189 to 227.167.18.190227.167.18.1912
177227.167.18.192/30227.167.18.193 to 227.167.18.194227.167.18.1952
178227.167.18.196/30227.167.18.197 to 227.167.18.198227.167.18.1992
179227.167.18.200/30227.167.18.201 to 227.167.18.202227.167.18.2032
180227.167.18.204/30227.167.18.205 to 227.167.18.206227.167.18.2072
181227.167.18.208/30227.167.18.209 to 227.167.18.210227.167.18.2112
182227.167.18.212/30227.167.18.213 to 227.167.18.214227.167.18.2152
183227.167.18.216/30227.167.18.217 to 227.167.18.218227.167.18.2192
184227.167.18.220/30227.167.18.221 to 227.167.18.222227.167.18.2232
185227.167.18.224/30227.167.18.225 to 227.167.18.226227.167.18.2272
186227.167.18.228/30227.167.18.229 to 227.167.18.230227.167.18.2312
187227.167.18.232/30227.167.18.233 to 227.167.18.234227.167.18.2352
188227.167.18.236/30227.167.18.237 to 227.167.18.238227.167.18.2392
189227.167.18.240/30227.167.18.241 to 227.167.18.242227.167.18.2432
190227.167.18.244/30227.167.18.245 to 227.167.18.246227.167.18.2472
191227.167.18.248/30227.167.18.249 to 227.167.18.250227.167.18.2512
192227.167.18.252/30227.167.18.253 to 227.167.18.254227.167.18.2552
193227.167.19.0/30227.167.19.1 to 227.167.19.2227.167.19.32
194227.167.19.4/30227.167.19.5 to 227.167.19.6227.167.19.72
195227.167.19.8/30227.167.19.9 to 227.167.19.10227.167.19.112
196227.167.19.12/30227.167.19.13 to 227.167.19.14227.167.19.152
197227.167.19.16/30227.167.19.17 to 227.167.19.18227.167.19.192
198227.167.19.20/30227.167.19.21 to 227.167.19.22227.167.19.232
199227.167.19.24/30227.167.19.25 to 227.167.19.26227.167.19.272
200227.167.19.28/30227.167.19.29 to 227.167.19.30227.167.19.312
201227.167.19.32/30227.167.19.33 to 227.167.19.34227.167.19.352
202227.167.19.36/30227.167.19.37 to 227.167.19.38227.167.19.392
203227.167.19.40/30227.167.19.41 to 227.167.19.42227.167.19.432
204227.167.19.44/30227.167.19.45 to 227.167.19.46227.167.19.472
205227.167.19.48/30227.167.19.49 to 227.167.19.50227.167.19.512
206227.167.19.52/30227.167.19.53 to 227.167.19.54227.167.19.552
207227.167.19.56/30227.167.19.57 to 227.167.19.58227.167.19.592
208227.167.19.60/30227.167.19.61 to 227.167.19.62227.167.19.632
209227.167.19.64/30227.167.19.65 to 227.167.19.66227.167.19.672
210227.167.19.68/30227.167.19.69 to 227.167.19.70227.167.19.712
211227.167.19.72/30227.167.19.73 to 227.167.19.74227.167.19.752
212227.167.19.76/30227.167.19.77 to 227.167.19.78227.167.19.792
213227.167.19.80/30227.167.19.81 to 227.167.19.82227.167.19.832
214227.167.19.84/30227.167.19.85 to 227.167.19.86227.167.19.872
215227.167.19.88/30227.167.19.89 to 227.167.19.90227.167.19.912
216227.167.19.92/30227.167.19.93 to 227.167.19.94227.167.19.952
217227.167.19.96/30227.167.19.97 to 227.167.19.98227.167.19.992
218227.167.19.100/30227.167.19.101 to 227.167.19.102227.167.19.1032
219227.167.19.104/30227.167.19.105 to 227.167.19.106227.167.19.1072
220227.167.19.108/30227.167.19.109 to 227.167.19.110227.167.19.1112
221227.167.19.112/30227.167.19.113 to 227.167.19.114227.167.19.1152
222227.167.19.116/30227.167.19.117 to 227.167.19.118227.167.19.1192
223227.167.19.120/30227.167.19.121 to 227.167.19.122227.167.19.1232
224227.167.19.124/30227.167.19.125 to 227.167.19.126227.167.19.1272
225227.167.19.128/30227.167.19.129 to 227.167.19.130227.167.19.1312
226227.167.19.132/30227.167.19.133 to 227.167.19.134227.167.19.1352
227227.167.19.136/30227.167.19.137 to 227.167.19.138227.167.19.1392
228227.167.19.140/30227.167.19.141 to 227.167.19.142227.167.19.1432
229227.167.19.144/30227.167.19.145 to 227.167.19.146227.167.19.1472
230227.167.19.148/30227.167.19.149 to 227.167.19.150227.167.19.1512
231227.167.19.152/30227.167.19.153 to 227.167.19.154227.167.19.1552
232227.167.19.156/30227.167.19.157 to 227.167.19.158227.167.19.1592
233227.167.19.160/30227.167.19.161 to 227.167.19.162227.167.19.1632
234227.167.19.164/30227.167.19.165 to 227.167.19.166227.167.19.1672
235227.167.19.168/30227.167.19.169 to 227.167.19.170227.167.19.1712
236227.167.19.172/30227.167.19.173 to 227.167.19.174227.167.19.1752
237227.167.19.176/30227.167.19.177 to 227.167.19.178227.167.19.1792
238227.167.19.180/30227.167.19.181 to 227.167.19.182227.167.19.1832
239227.167.19.184/30227.167.19.185 to 227.167.19.186227.167.19.1872
240227.167.19.188/30227.167.19.189 to 227.167.19.190227.167.19.1912
241227.167.19.192/30227.167.19.193 to 227.167.19.194227.167.19.1952
242227.167.19.196/30227.167.19.197 to 227.167.19.198227.167.19.1992
243227.167.19.200/30227.167.19.201 to 227.167.19.202227.167.19.2032
244227.167.19.204/30227.167.19.205 to 227.167.19.206227.167.19.2072
245227.167.19.208/30227.167.19.209 to 227.167.19.210227.167.19.2112
246227.167.19.212/30227.167.19.213 to 227.167.19.214227.167.19.2152
247227.167.19.216/30227.167.19.217 to 227.167.19.218227.167.19.2192
248227.167.19.220/30227.167.19.221 to 227.167.19.222227.167.19.2232
249227.167.19.224/30227.167.19.225 to 227.167.19.226227.167.19.2272
250227.167.19.228/30227.167.19.229 to 227.167.19.230227.167.19.2312
251227.167.19.232/30227.167.19.233 to 227.167.19.234227.167.19.2352
252227.167.19.236/30227.167.19.237 to 227.167.19.238227.167.19.2392
253227.167.19.240/30227.167.19.241 to 227.167.19.242227.167.19.2432
254227.167.19.244/30227.167.19.245 to 227.167.19.246227.167.19.2472
255227.167.19.248/30227.167.19.249 to 227.167.19.250227.167.19.2512
256227.167.19.252/30227.167.19.253 to 227.167.19.254227.167.19.2552

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.