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.

Network23.0.0.0/9
Usable hosts8,388,606
Subnet mask255.128.0.0
Addresses8,388,608
Network address
23.0.0.0
Broadcast address
23.127.255.255
First usable
23.0.0.1
Last usable
23.127.255.254
Usable hosts
8,388,606 (8,388,608 less the network and broadcast addresses)
Subnet mask
255.128.0.0
Wildcard mask
0.127.255.255 (Cisco ACLs, OSPF)
Prefix length
/9
Type
Public public
Old class
A (default /8)
As numbers
Hex 17000000 · Integer 385875968 to 394264575
Reverse DNS zones
0.23.in-addr.arpa
1.23.in-addr.arpa
2.23.in-addr.arpa
3.23.in-addr.arpa
4.23.in-addr.arpa
5.23.in-addr.arpa
6.23.in-addr.arpa
7.23.in-addr.arpa
8.23.in-addr.arpa
9.23.in-addr.arpa
10.23.in-addr.arpa
11.23.in-addr.arpa
12.23.in-addr.arpa
13.23.in-addr.arpa
14.23.in-addr.arpa
15.23.in-addr.arpa
and 112 more
/9 is not on a 8-bit boundary, so it takes 128 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00010111.00000000.00000000.0000000023.0.0.0
Subnet mask11111111.10000000.00000000.00000000255.128.0.0
Network00010111.00000000.00000000.0000000023.0.0.0
Broadcast00010111.01111111.11111111.1111111123.127.255.255
Split into smaller subnets/21
/10 (2)/11 (4)/12 (8)/13 (16)/14 (32)/15 (64)/16 (128)/17 (256)/18 (512)/19 (1,024)/20 (2,048)/21 (4,096)

23.0.0.0/9 makes 4,096 subnets of /21; the first 256 are listed.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
123.0.0.0/2123.0.0.1 to 23.0.7.25423.0.7.2552,046
223.0.8.0/2123.0.8.1 to 23.0.15.25423.0.15.2552,046
323.0.16.0/2123.0.16.1 to 23.0.23.25423.0.23.2552,046
423.0.24.0/2123.0.24.1 to 23.0.31.25423.0.31.2552,046
523.0.32.0/2123.0.32.1 to 23.0.39.25423.0.39.2552,046
623.0.40.0/2123.0.40.1 to 23.0.47.25423.0.47.2552,046
723.0.48.0/2123.0.48.1 to 23.0.55.25423.0.55.2552,046
823.0.56.0/2123.0.56.1 to 23.0.63.25423.0.63.2552,046
923.0.64.0/2123.0.64.1 to 23.0.71.25423.0.71.2552,046
1023.0.72.0/2123.0.72.1 to 23.0.79.25423.0.79.2552,046
1123.0.80.0/2123.0.80.1 to 23.0.87.25423.0.87.2552,046
1223.0.88.0/2123.0.88.1 to 23.0.95.25423.0.95.2552,046
1323.0.96.0/2123.0.96.1 to 23.0.103.25423.0.103.2552,046
1423.0.104.0/2123.0.104.1 to 23.0.111.25423.0.111.2552,046
1523.0.112.0/2123.0.112.1 to 23.0.119.25423.0.119.2552,046
1623.0.120.0/2123.0.120.1 to 23.0.127.25423.0.127.2552,046
1723.0.128.0/2123.0.128.1 to 23.0.135.25423.0.135.2552,046
1823.0.136.0/2123.0.136.1 to 23.0.143.25423.0.143.2552,046
1923.0.144.0/2123.0.144.1 to 23.0.151.25423.0.151.2552,046
2023.0.152.0/2123.0.152.1 to 23.0.159.25423.0.159.2552,046
2123.0.160.0/2123.0.160.1 to 23.0.167.25423.0.167.2552,046
2223.0.168.0/2123.0.168.1 to 23.0.175.25423.0.175.2552,046
2323.0.176.0/2123.0.176.1 to 23.0.183.25423.0.183.2552,046
2423.0.184.0/2123.0.184.1 to 23.0.191.25423.0.191.2552,046
2523.0.192.0/2123.0.192.1 to 23.0.199.25423.0.199.2552,046
2623.0.200.0/2123.0.200.1 to 23.0.207.25423.0.207.2552,046
2723.0.208.0/2123.0.208.1 to 23.0.215.25423.0.215.2552,046
2823.0.216.0/2123.0.216.1 to 23.0.223.25423.0.223.2552,046
2923.0.224.0/2123.0.224.1 to 23.0.231.25423.0.231.2552,046
3023.0.232.0/2123.0.232.1 to 23.0.239.25423.0.239.2552,046
3123.0.240.0/2123.0.240.1 to 23.0.247.25423.0.247.2552,046
3223.0.248.0/2123.0.248.1 to 23.0.255.25423.0.255.2552,046
3323.1.0.0/2123.1.0.1 to 23.1.7.25423.1.7.2552,046
3423.1.8.0/2123.1.8.1 to 23.1.15.25423.1.15.2552,046
3523.1.16.0/2123.1.16.1 to 23.1.23.25423.1.23.2552,046
3623.1.24.0/2123.1.24.1 to 23.1.31.25423.1.31.2552,046
3723.1.32.0/2123.1.32.1 to 23.1.39.25423.1.39.2552,046
3823.1.40.0/2123.1.40.1 to 23.1.47.25423.1.47.2552,046
3923.1.48.0/2123.1.48.1 to 23.1.55.25423.1.55.2552,046
4023.1.56.0/2123.1.56.1 to 23.1.63.25423.1.63.2552,046
4123.1.64.0/2123.1.64.1 to 23.1.71.25423.1.71.2552,046
4223.1.72.0/2123.1.72.1 to 23.1.79.25423.1.79.2552,046
4323.1.80.0/2123.1.80.1 to 23.1.87.25423.1.87.2552,046
4423.1.88.0/2123.1.88.1 to 23.1.95.25423.1.95.2552,046
4523.1.96.0/2123.1.96.1 to 23.1.103.25423.1.103.2552,046
4623.1.104.0/2123.1.104.1 to 23.1.111.25423.1.111.2552,046
4723.1.112.0/2123.1.112.1 to 23.1.119.25423.1.119.2552,046
4823.1.120.0/2123.1.120.1 to 23.1.127.25423.1.127.2552,046
4923.1.128.0/2123.1.128.1 to 23.1.135.25423.1.135.2552,046
5023.1.136.0/2123.1.136.1 to 23.1.143.25423.1.143.2552,046
5123.1.144.0/2123.1.144.1 to 23.1.151.25423.1.151.2552,046
5223.1.152.0/2123.1.152.1 to 23.1.159.25423.1.159.2552,046
5323.1.160.0/2123.1.160.1 to 23.1.167.25423.1.167.2552,046
5423.1.168.0/2123.1.168.1 to 23.1.175.25423.1.175.2552,046
5523.1.176.0/2123.1.176.1 to 23.1.183.25423.1.183.2552,046
5623.1.184.0/2123.1.184.1 to 23.1.191.25423.1.191.2552,046
5723.1.192.0/2123.1.192.1 to 23.1.199.25423.1.199.2552,046
5823.1.200.0/2123.1.200.1 to 23.1.207.25423.1.207.2552,046
5923.1.208.0/2123.1.208.1 to 23.1.215.25423.1.215.2552,046
6023.1.216.0/2123.1.216.1 to 23.1.223.25423.1.223.2552,046
6123.1.224.0/2123.1.224.1 to 23.1.231.25423.1.231.2552,046
6223.1.232.0/2123.1.232.1 to 23.1.239.25423.1.239.2552,046
6323.1.240.0/2123.1.240.1 to 23.1.247.25423.1.247.2552,046
6423.1.248.0/2123.1.248.1 to 23.1.255.25423.1.255.2552,046
6523.2.0.0/2123.2.0.1 to 23.2.7.25423.2.7.2552,046
6623.2.8.0/2123.2.8.1 to 23.2.15.25423.2.15.2552,046
6723.2.16.0/2123.2.16.1 to 23.2.23.25423.2.23.2552,046
6823.2.24.0/2123.2.24.1 to 23.2.31.25423.2.31.2552,046
6923.2.32.0/2123.2.32.1 to 23.2.39.25423.2.39.2552,046
7023.2.40.0/2123.2.40.1 to 23.2.47.25423.2.47.2552,046
7123.2.48.0/2123.2.48.1 to 23.2.55.25423.2.55.2552,046
7223.2.56.0/2123.2.56.1 to 23.2.63.25423.2.63.2552,046
7323.2.64.0/2123.2.64.1 to 23.2.71.25423.2.71.2552,046
7423.2.72.0/2123.2.72.1 to 23.2.79.25423.2.79.2552,046
7523.2.80.0/2123.2.80.1 to 23.2.87.25423.2.87.2552,046
7623.2.88.0/2123.2.88.1 to 23.2.95.25423.2.95.2552,046
7723.2.96.0/2123.2.96.1 to 23.2.103.25423.2.103.2552,046
7823.2.104.0/2123.2.104.1 to 23.2.111.25423.2.111.2552,046
7923.2.112.0/2123.2.112.1 to 23.2.119.25423.2.119.2552,046
8023.2.120.0/2123.2.120.1 to 23.2.127.25423.2.127.2552,046
8123.2.128.0/2123.2.128.1 to 23.2.135.25423.2.135.2552,046
8223.2.136.0/2123.2.136.1 to 23.2.143.25423.2.143.2552,046
8323.2.144.0/2123.2.144.1 to 23.2.151.25423.2.151.2552,046
8423.2.152.0/2123.2.152.1 to 23.2.159.25423.2.159.2552,046
8523.2.160.0/2123.2.160.1 to 23.2.167.25423.2.167.2552,046
8623.2.168.0/2123.2.168.1 to 23.2.175.25423.2.175.2552,046
8723.2.176.0/2123.2.176.1 to 23.2.183.25423.2.183.2552,046
8823.2.184.0/2123.2.184.1 to 23.2.191.25423.2.191.2552,046
8923.2.192.0/2123.2.192.1 to 23.2.199.25423.2.199.2552,046
9023.2.200.0/2123.2.200.1 to 23.2.207.25423.2.207.2552,046
9123.2.208.0/2123.2.208.1 to 23.2.215.25423.2.215.2552,046
9223.2.216.0/2123.2.216.1 to 23.2.223.25423.2.223.2552,046
9323.2.224.0/2123.2.224.1 to 23.2.231.25423.2.231.2552,046
9423.2.232.0/2123.2.232.1 to 23.2.239.25423.2.239.2552,046
9523.2.240.0/2123.2.240.1 to 23.2.247.25423.2.247.2552,046
9623.2.248.0/2123.2.248.1 to 23.2.255.25423.2.255.2552,046
9723.3.0.0/2123.3.0.1 to 23.3.7.25423.3.7.2552,046
9823.3.8.0/2123.3.8.1 to 23.3.15.25423.3.15.2552,046
9923.3.16.0/2123.3.16.1 to 23.3.23.25423.3.23.2552,046
10023.3.24.0/2123.3.24.1 to 23.3.31.25423.3.31.2552,046
10123.3.32.0/2123.3.32.1 to 23.3.39.25423.3.39.2552,046
10223.3.40.0/2123.3.40.1 to 23.3.47.25423.3.47.2552,046
10323.3.48.0/2123.3.48.1 to 23.3.55.25423.3.55.2552,046
10423.3.56.0/2123.3.56.1 to 23.3.63.25423.3.63.2552,046
10523.3.64.0/2123.3.64.1 to 23.3.71.25423.3.71.2552,046
10623.3.72.0/2123.3.72.1 to 23.3.79.25423.3.79.2552,046
10723.3.80.0/2123.3.80.1 to 23.3.87.25423.3.87.2552,046
10823.3.88.0/2123.3.88.1 to 23.3.95.25423.3.95.2552,046
10923.3.96.0/2123.3.96.1 to 23.3.103.25423.3.103.2552,046
11023.3.104.0/2123.3.104.1 to 23.3.111.25423.3.111.2552,046
11123.3.112.0/2123.3.112.1 to 23.3.119.25423.3.119.2552,046
11223.3.120.0/2123.3.120.1 to 23.3.127.25423.3.127.2552,046
11323.3.128.0/2123.3.128.1 to 23.3.135.25423.3.135.2552,046
11423.3.136.0/2123.3.136.1 to 23.3.143.25423.3.143.2552,046
11523.3.144.0/2123.3.144.1 to 23.3.151.25423.3.151.2552,046
11623.3.152.0/2123.3.152.1 to 23.3.159.25423.3.159.2552,046
11723.3.160.0/2123.3.160.1 to 23.3.167.25423.3.167.2552,046
11823.3.168.0/2123.3.168.1 to 23.3.175.25423.3.175.2552,046
11923.3.176.0/2123.3.176.1 to 23.3.183.25423.3.183.2552,046
12023.3.184.0/2123.3.184.1 to 23.3.191.25423.3.191.2552,046
12123.3.192.0/2123.3.192.1 to 23.3.199.25423.3.199.2552,046
12223.3.200.0/2123.3.200.1 to 23.3.207.25423.3.207.2552,046
12323.3.208.0/2123.3.208.1 to 23.3.215.25423.3.215.2552,046
12423.3.216.0/2123.3.216.1 to 23.3.223.25423.3.223.2552,046
12523.3.224.0/2123.3.224.1 to 23.3.231.25423.3.231.2552,046
12623.3.232.0/2123.3.232.1 to 23.3.239.25423.3.239.2552,046
12723.3.240.0/2123.3.240.1 to 23.3.247.25423.3.247.2552,046
12823.3.248.0/2123.3.248.1 to 23.3.255.25423.3.255.2552,046
12923.4.0.0/2123.4.0.1 to 23.4.7.25423.4.7.2552,046
13023.4.8.0/2123.4.8.1 to 23.4.15.25423.4.15.2552,046
13123.4.16.0/2123.4.16.1 to 23.4.23.25423.4.23.2552,046
13223.4.24.0/2123.4.24.1 to 23.4.31.25423.4.31.2552,046
13323.4.32.0/2123.4.32.1 to 23.4.39.25423.4.39.2552,046
13423.4.40.0/2123.4.40.1 to 23.4.47.25423.4.47.2552,046
13523.4.48.0/2123.4.48.1 to 23.4.55.25423.4.55.2552,046
13623.4.56.0/2123.4.56.1 to 23.4.63.25423.4.63.2552,046
13723.4.64.0/2123.4.64.1 to 23.4.71.25423.4.71.2552,046
13823.4.72.0/2123.4.72.1 to 23.4.79.25423.4.79.2552,046
13923.4.80.0/2123.4.80.1 to 23.4.87.25423.4.87.2552,046
14023.4.88.0/2123.4.88.1 to 23.4.95.25423.4.95.2552,046
14123.4.96.0/2123.4.96.1 to 23.4.103.25423.4.103.2552,046
14223.4.104.0/2123.4.104.1 to 23.4.111.25423.4.111.2552,046
14323.4.112.0/2123.4.112.1 to 23.4.119.25423.4.119.2552,046
14423.4.120.0/2123.4.120.1 to 23.4.127.25423.4.127.2552,046
14523.4.128.0/2123.4.128.1 to 23.4.135.25423.4.135.2552,046
14623.4.136.0/2123.4.136.1 to 23.4.143.25423.4.143.2552,046
14723.4.144.0/2123.4.144.1 to 23.4.151.25423.4.151.2552,046
14823.4.152.0/2123.4.152.1 to 23.4.159.25423.4.159.2552,046
14923.4.160.0/2123.4.160.1 to 23.4.167.25423.4.167.2552,046
15023.4.168.0/2123.4.168.1 to 23.4.175.25423.4.175.2552,046
15123.4.176.0/2123.4.176.1 to 23.4.183.25423.4.183.2552,046
15223.4.184.0/2123.4.184.1 to 23.4.191.25423.4.191.2552,046
15323.4.192.0/2123.4.192.1 to 23.4.199.25423.4.199.2552,046
15423.4.200.0/2123.4.200.1 to 23.4.207.25423.4.207.2552,046
15523.4.208.0/2123.4.208.1 to 23.4.215.25423.4.215.2552,046
15623.4.216.0/2123.4.216.1 to 23.4.223.25423.4.223.2552,046
15723.4.224.0/2123.4.224.1 to 23.4.231.25423.4.231.2552,046
15823.4.232.0/2123.4.232.1 to 23.4.239.25423.4.239.2552,046
15923.4.240.0/2123.4.240.1 to 23.4.247.25423.4.247.2552,046
16023.4.248.0/2123.4.248.1 to 23.4.255.25423.4.255.2552,046
16123.5.0.0/2123.5.0.1 to 23.5.7.25423.5.7.2552,046
16223.5.8.0/2123.5.8.1 to 23.5.15.25423.5.15.2552,046
16323.5.16.0/2123.5.16.1 to 23.5.23.25423.5.23.2552,046
16423.5.24.0/2123.5.24.1 to 23.5.31.25423.5.31.2552,046
16523.5.32.0/2123.5.32.1 to 23.5.39.25423.5.39.2552,046
16623.5.40.0/2123.5.40.1 to 23.5.47.25423.5.47.2552,046
16723.5.48.0/2123.5.48.1 to 23.5.55.25423.5.55.2552,046
16823.5.56.0/2123.5.56.1 to 23.5.63.25423.5.63.2552,046
16923.5.64.0/2123.5.64.1 to 23.5.71.25423.5.71.2552,046
17023.5.72.0/2123.5.72.1 to 23.5.79.25423.5.79.2552,046
17123.5.80.0/2123.5.80.1 to 23.5.87.25423.5.87.2552,046
17223.5.88.0/2123.5.88.1 to 23.5.95.25423.5.95.2552,046
17323.5.96.0/2123.5.96.1 to 23.5.103.25423.5.103.2552,046
17423.5.104.0/2123.5.104.1 to 23.5.111.25423.5.111.2552,046
17523.5.112.0/2123.5.112.1 to 23.5.119.25423.5.119.2552,046
17623.5.120.0/2123.5.120.1 to 23.5.127.25423.5.127.2552,046
17723.5.128.0/2123.5.128.1 to 23.5.135.25423.5.135.2552,046
17823.5.136.0/2123.5.136.1 to 23.5.143.25423.5.143.2552,046
17923.5.144.0/2123.5.144.1 to 23.5.151.25423.5.151.2552,046
18023.5.152.0/2123.5.152.1 to 23.5.159.25423.5.159.2552,046
18123.5.160.0/2123.5.160.1 to 23.5.167.25423.5.167.2552,046
18223.5.168.0/2123.5.168.1 to 23.5.175.25423.5.175.2552,046
18323.5.176.0/2123.5.176.1 to 23.5.183.25423.5.183.2552,046
18423.5.184.0/2123.5.184.1 to 23.5.191.25423.5.191.2552,046
18523.5.192.0/2123.5.192.1 to 23.5.199.25423.5.199.2552,046
18623.5.200.0/2123.5.200.1 to 23.5.207.25423.5.207.2552,046
18723.5.208.0/2123.5.208.1 to 23.5.215.25423.5.215.2552,046
18823.5.216.0/2123.5.216.1 to 23.5.223.25423.5.223.2552,046
18923.5.224.0/2123.5.224.1 to 23.5.231.25423.5.231.2552,046
19023.5.232.0/2123.5.232.1 to 23.5.239.25423.5.239.2552,046
19123.5.240.0/2123.5.240.1 to 23.5.247.25423.5.247.2552,046
19223.5.248.0/2123.5.248.1 to 23.5.255.25423.5.255.2552,046
19323.6.0.0/2123.6.0.1 to 23.6.7.25423.6.7.2552,046
19423.6.8.0/2123.6.8.1 to 23.6.15.25423.6.15.2552,046
19523.6.16.0/2123.6.16.1 to 23.6.23.25423.6.23.2552,046
19623.6.24.0/2123.6.24.1 to 23.6.31.25423.6.31.2552,046
19723.6.32.0/2123.6.32.1 to 23.6.39.25423.6.39.2552,046
19823.6.40.0/2123.6.40.1 to 23.6.47.25423.6.47.2552,046
19923.6.48.0/2123.6.48.1 to 23.6.55.25423.6.55.2552,046
20023.6.56.0/2123.6.56.1 to 23.6.63.25423.6.63.2552,046
20123.6.64.0/2123.6.64.1 to 23.6.71.25423.6.71.2552,046
20223.6.72.0/2123.6.72.1 to 23.6.79.25423.6.79.2552,046
20323.6.80.0/2123.6.80.1 to 23.6.87.25423.6.87.2552,046
20423.6.88.0/2123.6.88.1 to 23.6.95.25423.6.95.2552,046
20523.6.96.0/2123.6.96.1 to 23.6.103.25423.6.103.2552,046
20623.6.104.0/2123.6.104.1 to 23.6.111.25423.6.111.2552,046
20723.6.112.0/2123.6.112.1 to 23.6.119.25423.6.119.2552,046
20823.6.120.0/2123.6.120.1 to 23.6.127.25423.6.127.2552,046
20923.6.128.0/2123.6.128.1 to 23.6.135.25423.6.135.2552,046
21023.6.136.0/2123.6.136.1 to 23.6.143.25423.6.143.2552,046
21123.6.144.0/2123.6.144.1 to 23.6.151.25423.6.151.2552,046
21223.6.152.0/2123.6.152.1 to 23.6.159.25423.6.159.2552,046
21323.6.160.0/2123.6.160.1 to 23.6.167.25423.6.167.2552,046
21423.6.168.0/2123.6.168.1 to 23.6.175.25423.6.175.2552,046
21523.6.176.0/2123.6.176.1 to 23.6.183.25423.6.183.2552,046
21623.6.184.0/2123.6.184.1 to 23.6.191.25423.6.191.2552,046
21723.6.192.0/2123.6.192.1 to 23.6.199.25423.6.199.2552,046
21823.6.200.0/2123.6.200.1 to 23.6.207.25423.6.207.2552,046
21923.6.208.0/2123.6.208.1 to 23.6.215.25423.6.215.2552,046
22023.6.216.0/2123.6.216.1 to 23.6.223.25423.6.223.2552,046
22123.6.224.0/2123.6.224.1 to 23.6.231.25423.6.231.2552,046
22223.6.232.0/2123.6.232.1 to 23.6.239.25423.6.239.2552,046
22323.6.240.0/2123.6.240.1 to 23.6.247.25423.6.247.2552,046
22423.6.248.0/2123.6.248.1 to 23.6.255.25423.6.255.2552,046
22523.7.0.0/2123.7.0.1 to 23.7.7.25423.7.7.2552,046
22623.7.8.0/2123.7.8.1 to 23.7.15.25423.7.15.2552,046
22723.7.16.0/2123.7.16.1 to 23.7.23.25423.7.23.2552,046
22823.7.24.0/2123.7.24.1 to 23.7.31.25423.7.31.2552,046
22923.7.32.0/2123.7.32.1 to 23.7.39.25423.7.39.2552,046
23023.7.40.0/2123.7.40.1 to 23.7.47.25423.7.47.2552,046
23123.7.48.0/2123.7.48.1 to 23.7.55.25423.7.55.2552,046
23223.7.56.0/2123.7.56.1 to 23.7.63.25423.7.63.2552,046
23323.7.64.0/2123.7.64.1 to 23.7.71.25423.7.71.2552,046
23423.7.72.0/2123.7.72.1 to 23.7.79.25423.7.79.2552,046
23523.7.80.0/2123.7.80.1 to 23.7.87.25423.7.87.2552,046
23623.7.88.0/2123.7.88.1 to 23.7.95.25423.7.95.2552,046
23723.7.96.0/2123.7.96.1 to 23.7.103.25423.7.103.2552,046
23823.7.104.0/2123.7.104.1 to 23.7.111.25423.7.111.2552,046
23923.7.112.0/2123.7.112.1 to 23.7.119.25423.7.119.2552,046
24023.7.120.0/2123.7.120.1 to 23.7.127.25423.7.127.2552,046
24123.7.128.0/2123.7.128.1 to 23.7.135.25423.7.135.2552,046
24223.7.136.0/2123.7.136.1 to 23.7.143.25423.7.143.2552,046
24323.7.144.0/2123.7.144.1 to 23.7.151.25423.7.151.2552,046
24423.7.152.0/2123.7.152.1 to 23.7.159.25423.7.159.2552,046
24523.7.160.0/2123.7.160.1 to 23.7.167.25423.7.167.2552,046
24623.7.168.0/2123.7.168.1 to 23.7.175.25423.7.175.2552,046
24723.7.176.0/2123.7.176.1 to 23.7.183.25423.7.183.2552,046
24823.7.184.0/2123.7.184.1 to 23.7.191.25423.7.191.2552,046
24923.7.192.0/2123.7.192.1 to 23.7.199.25423.7.199.2552,046
25023.7.200.0/2123.7.200.1 to 23.7.207.25423.7.207.2552,046
25123.7.208.0/2123.7.208.1 to 23.7.215.25423.7.215.2552,046
25223.7.216.0/2123.7.216.1 to 23.7.223.25423.7.223.2552,046
25323.7.224.0/2123.7.224.1 to 23.7.231.25423.7.231.2552,046
25423.7.232.0/2123.7.232.1 to 23.7.239.25423.7.239.2552,046
25523.7.240.0/2123.7.240.1 to 23.7.247.25423.7.247.2552,046
25623.7.248.0/2123.7.248.1 to 23.7.255.25423.7.255.2552,046

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.