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.

Network12.0.0.0/7
Usable hosts33,554,430
Subnet mask254.0.0.0
Addresses33,554,432
Network address
12.0.0.0
Broadcast address
13.255.255.255
First usable
12.0.0.1
Last usable
13.255.255.254
Usable hosts
33,554,430 (33,554,432 less the network and broadcast addresses)
Subnet mask
254.0.0.0
Wildcard mask
1.255.255.255 (Cisco ACLs, OSPF)
Prefix length
/7
Type
Public public
Old class
A (default /8)
As numbers
Hex 0C000000 · Integer 201326592 to 234881023
Reverse DNS zones
12.in-addr.arpa
13.in-addr.arpa
/7 is not on a 8-bit boundary, so it takes 2 /8 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00001100.00000000.00000000.0000000012.0.0.0
Subnet mask11111110.00000000.00000000.00000000254.0.0.0
Network00001100.00000000.00000000.0000000012.0.0.0
Broadcast00001101.11111111.11111111.1111111113.255.255.255
Split into smaller subnets/15
/8 (2)/9 (4)/10 (8)/11 (16)/12 (32)/13 (64)/14 (128)/15 (256)/16 (512)/17 (1,024)/18 (2,048)/19 (4,096)

12.0.0.0/7 makes 256 subnets of /15.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
112.0.0.0/1512.0.0.1 to 12.1.255.25412.1.255.255131,070
212.2.0.0/1512.2.0.1 to 12.3.255.25412.3.255.255131,070
312.4.0.0/1512.4.0.1 to 12.5.255.25412.5.255.255131,070
412.6.0.0/1512.6.0.1 to 12.7.255.25412.7.255.255131,070
512.8.0.0/1512.8.0.1 to 12.9.255.25412.9.255.255131,070
612.10.0.0/1512.10.0.1 to 12.11.255.25412.11.255.255131,070
712.12.0.0/1512.12.0.1 to 12.13.255.25412.13.255.255131,070
812.14.0.0/1512.14.0.1 to 12.15.255.25412.15.255.255131,070
912.16.0.0/1512.16.0.1 to 12.17.255.25412.17.255.255131,070
1012.18.0.0/1512.18.0.1 to 12.19.255.25412.19.255.255131,070
1112.20.0.0/1512.20.0.1 to 12.21.255.25412.21.255.255131,070
1212.22.0.0/1512.22.0.1 to 12.23.255.25412.23.255.255131,070
1312.24.0.0/1512.24.0.1 to 12.25.255.25412.25.255.255131,070
1412.26.0.0/1512.26.0.1 to 12.27.255.25412.27.255.255131,070
1512.28.0.0/1512.28.0.1 to 12.29.255.25412.29.255.255131,070
1612.30.0.0/1512.30.0.1 to 12.31.255.25412.31.255.255131,070
1712.32.0.0/1512.32.0.1 to 12.33.255.25412.33.255.255131,070
1812.34.0.0/1512.34.0.1 to 12.35.255.25412.35.255.255131,070
1912.36.0.0/1512.36.0.1 to 12.37.255.25412.37.255.255131,070
2012.38.0.0/1512.38.0.1 to 12.39.255.25412.39.255.255131,070
2112.40.0.0/1512.40.0.1 to 12.41.255.25412.41.255.255131,070
2212.42.0.0/1512.42.0.1 to 12.43.255.25412.43.255.255131,070
2312.44.0.0/1512.44.0.1 to 12.45.255.25412.45.255.255131,070
2412.46.0.0/1512.46.0.1 to 12.47.255.25412.47.255.255131,070
2512.48.0.0/1512.48.0.1 to 12.49.255.25412.49.255.255131,070
2612.50.0.0/1512.50.0.1 to 12.51.255.25412.51.255.255131,070
2712.52.0.0/1512.52.0.1 to 12.53.255.25412.53.255.255131,070
2812.54.0.0/1512.54.0.1 to 12.55.255.25412.55.255.255131,070
2912.56.0.0/1512.56.0.1 to 12.57.255.25412.57.255.255131,070
3012.58.0.0/1512.58.0.1 to 12.59.255.25412.59.255.255131,070
3112.60.0.0/1512.60.0.1 to 12.61.255.25412.61.255.255131,070
3212.62.0.0/1512.62.0.1 to 12.63.255.25412.63.255.255131,070
3312.64.0.0/1512.64.0.1 to 12.65.255.25412.65.255.255131,070
3412.66.0.0/1512.66.0.1 to 12.67.255.25412.67.255.255131,070
3512.68.0.0/1512.68.0.1 to 12.69.255.25412.69.255.255131,070
3612.70.0.0/1512.70.0.1 to 12.71.255.25412.71.255.255131,070
3712.72.0.0/1512.72.0.1 to 12.73.255.25412.73.255.255131,070
3812.74.0.0/1512.74.0.1 to 12.75.255.25412.75.255.255131,070
3912.76.0.0/1512.76.0.1 to 12.77.255.25412.77.255.255131,070
4012.78.0.0/1512.78.0.1 to 12.79.255.25412.79.255.255131,070
4112.80.0.0/1512.80.0.1 to 12.81.255.25412.81.255.255131,070
4212.82.0.0/1512.82.0.1 to 12.83.255.25412.83.255.255131,070
4312.84.0.0/1512.84.0.1 to 12.85.255.25412.85.255.255131,070
4412.86.0.0/1512.86.0.1 to 12.87.255.25412.87.255.255131,070
4512.88.0.0/1512.88.0.1 to 12.89.255.25412.89.255.255131,070
4612.90.0.0/1512.90.0.1 to 12.91.255.25412.91.255.255131,070
4712.92.0.0/1512.92.0.1 to 12.93.255.25412.93.255.255131,070
4812.94.0.0/1512.94.0.1 to 12.95.255.25412.95.255.255131,070
4912.96.0.0/1512.96.0.1 to 12.97.255.25412.97.255.255131,070
5012.98.0.0/1512.98.0.1 to 12.99.255.25412.99.255.255131,070
5112.100.0.0/1512.100.0.1 to 12.101.255.25412.101.255.255131,070
5212.102.0.0/1512.102.0.1 to 12.103.255.25412.103.255.255131,070
5312.104.0.0/1512.104.0.1 to 12.105.255.25412.105.255.255131,070
5412.106.0.0/1512.106.0.1 to 12.107.255.25412.107.255.255131,070
5512.108.0.0/1512.108.0.1 to 12.109.255.25412.109.255.255131,070
5612.110.0.0/1512.110.0.1 to 12.111.255.25412.111.255.255131,070
5712.112.0.0/1512.112.0.1 to 12.113.255.25412.113.255.255131,070
5812.114.0.0/1512.114.0.1 to 12.115.255.25412.115.255.255131,070
5912.116.0.0/1512.116.0.1 to 12.117.255.25412.117.255.255131,070
6012.118.0.0/1512.118.0.1 to 12.119.255.25412.119.255.255131,070
6112.120.0.0/1512.120.0.1 to 12.121.255.25412.121.255.255131,070
6212.122.0.0/1512.122.0.1 to 12.123.255.25412.123.255.255131,070
6312.124.0.0/1512.124.0.1 to 12.125.255.25412.125.255.255131,070
6412.126.0.0/1512.126.0.1 to 12.127.255.25412.127.255.255131,070
6512.128.0.0/1512.128.0.1 to 12.129.255.25412.129.255.255131,070
6612.130.0.0/1512.130.0.1 to 12.131.255.25412.131.255.255131,070
6712.132.0.0/1512.132.0.1 to 12.133.255.25412.133.255.255131,070
6812.134.0.0/1512.134.0.1 to 12.135.255.25412.135.255.255131,070
6912.136.0.0/1512.136.0.1 to 12.137.255.25412.137.255.255131,070
7012.138.0.0/1512.138.0.1 to 12.139.255.25412.139.255.255131,070
7112.140.0.0/1512.140.0.1 to 12.141.255.25412.141.255.255131,070
7212.142.0.0/1512.142.0.1 to 12.143.255.25412.143.255.255131,070
7312.144.0.0/1512.144.0.1 to 12.145.255.25412.145.255.255131,070
7412.146.0.0/1512.146.0.1 to 12.147.255.25412.147.255.255131,070
7512.148.0.0/1512.148.0.1 to 12.149.255.25412.149.255.255131,070
7612.150.0.0/1512.150.0.1 to 12.151.255.25412.151.255.255131,070
7712.152.0.0/1512.152.0.1 to 12.153.255.25412.153.255.255131,070
7812.154.0.0/1512.154.0.1 to 12.155.255.25412.155.255.255131,070
7912.156.0.0/1512.156.0.1 to 12.157.255.25412.157.255.255131,070
8012.158.0.0/1512.158.0.1 to 12.159.255.25412.159.255.255131,070
8112.160.0.0/1512.160.0.1 to 12.161.255.25412.161.255.255131,070
8212.162.0.0/1512.162.0.1 to 12.163.255.25412.163.255.255131,070
8312.164.0.0/1512.164.0.1 to 12.165.255.25412.165.255.255131,070
8412.166.0.0/1512.166.0.1 to 12.167.255.25412.167.255.255131,070
8512.168.0.0/1512.168.0.1 to 12.169.255.25412.169.255.255131,070
8612.170.0.0/1512.170.0.1 to 12.171.255.25412.171.255.255131,070
8712.172.0.0/1512.172.0.1 to 12.173.255.25412.173.255.255131,070
8812.174.0.0/1512.174.0.1 to 12.175.255.25412.175.255.255131,070
8912.176.0.0/1512.176.0.1 to 12.177.255.25412.177.255.255131,070
9012.178.0.0/1512.178.0.1 to 12.179.255.25412.179.255.255131,070
9112.180.0.0/1512.180.0.1 to 12.181.255.25412.181.255.255131,070
9212.182.0.0/1512.182.0.1 to 12.183.255.25412.183.255.255131,070
9312.184.0.0/1512.184.0.1 to 12.185.255.25412.185.255.255131,070
9412.186.0.0/1512.186.0.1 to 12.187.255.25412.187.255.255131,070
9512.188.0.0/1512.188.0.1 to 12.189.255.25412.189.255.255131,070
9612.190.0.0/1512.190.0.1 to 12.191.255.25412.191.255.255131,070
9712.192.0.0/1512.192.0.1 to 12.193.255.25412.193.255.255131,070
9812.194.0.0/1512.194.0.1 to 12.195.255.25412.195.255.255131,070
9912.196.0.0/1512.196.0.1 to 12.197.255.25412.197.255.255131,070
10012.198.0.0/1512.198.0.1 to 12.199.255.25412.199.255.255131,070
10112.200.0.0/1512.200.0.1 to 12.201.255.25412.201.255.255131,070
10212.202.0.0/1512.202.0.1 to 12.203.255.25412.203.255.255131,070
10312.204.0.0/1512.204.0.1 to 12.205.255.25412.205.255.255131,070
10412.206.0.0/1512.206.0.1 to 12.207.255.25412.207.255.255131,070
10512.208.0.0/1512.208.0.1 to 12.209.255.25412.209.255.255131,070
10612.210.0.0/1512.210.0.1 to 12.211.255.25412.211.255.255131,070
10712.212.0.0/1512.212.0.1 to 12.213.255.25412.213.255.255131,070
10812.214.0.0/1512.214.0.1 to 12.215.255.25412.215.255.255131,070
10912.216.0.0/1512.216.0.1 to 12.217.255.25412.217.255.255131,070
11012.218.0.0/1512.218.0.1 to 12.219.255.25412.219.255.255131,070
11112.220.0.0/1512.220.0.1 to 12.221.255.25412.221.255.255131,070
11212.222.0.0/1512.222.0.1 to 12.223.255.25412.223.255.255131,070
11312.224.0.0/1512.224.0.1 to 12.225.255.25412.225.255.255131,070
11412.226.0.0/1512.226.0.1 to 12.227.255.25412.227.255.255131,070
11512.228.0.0/1512.228.0.1 to 12.229.255.25412.229.255.255131,070
11612.230.0.0/1512.230.0.1 to 12.231.255.25412.231.255.255131,070
11712.232.0.0/1512.232.0.1 to 12.233.255.25412.233.255.255131,070
11812.234.0.0/1512.234.0.1 to 12.235.255.25412.235.255.255131,070
11912.236.0.0/1512.236.0.1 to 12.237.255.25412.237.255.255131,070
12012.238.0.0/1512.238.0.1 to 12.239.255.25412.239.255.255131,070
12112.240.0.0/1512.240.0.1 to 12.241.255.25412.241.255.255131,070
12212.242.0.0/1512.242.0.1 to 12.243.255.25412.243.255.255131,070
12312.244.0.0/1512.244.0.1 to 12.245.255.25412.245.255.255131,070
12412.246.0.0/1512.246.0.1 to 12.247.255.25412.247.255.255131,070
12512.248.0.0/1512.248.0.1 to 12.249.255.25412.249.255.255131,070
12612.250.0.0/1512.250.0.1 to 12.251.255.25412.251.255.255131,070
12712.252.0.0/1512.252.0.1 to 12.253.255.25412.253.255.255131,070
12812.254.0.0/1512.254.0.1 to 12.255.255.25412.255.255.255131,070
12913.0.0.0/1513.0.0.1 to 13.1.255.25413.1.255.255131,070
13013.2.0.0/1513.2.0.1 to 13.3.255.25413.3.255.255131,070
13113.4.0.0/1513.4.0.1 to 13.5.255.25413.5.255.255131,070
13213.6.0.0/1513.6.0.1 to 13.7.255.25413.7.255.255131,070
13313.8.0.0/1513.8.0.1 to 13.9.255.25413.9.255.255131,070
13413.10.0.0/1513.10.0.1 to 13.11.255.25413.11.255.255131,070
13513.12.0.0/1513.12.0.1 to 13.13.255.25413.13.255.255131,070
13613.14.0.0/1513.14.0.1 to 13.15.255.25413.15.255.255131,070
13713.16.0.0/1513.16.0.1 to 13.17.255.25413.17.255.255131,070
13813.18.0.0/1513.18.0.1 to 13.19.255.25413.19.255.255131,070
13913.20.0.0/1513.20.0.1 to 13.21.255.25413.21.255.255131,070
14013.22.0.0/1513.22.0.1 to 13.23.255.25413.23.255.255131,070
14113.24.0.0/1513.24.0.1 to 13.25.255.25413.25.255.255131,070
14213.26.0.0/1513.26.0.1 to 13.27.255.25413.27.255.255131,070
14313.28.0.0/1513.28.0.1 to 13.29.255.25413.29.255.255131,070
14413.30.0.0/1513.30.0.1 to 13.31.255.25413.31.255.255131,070
14513.32.0.0/1513.32.0.1 to 13.33.255.25413.33.255.255131,070
14613.34.0.0/1513.34.0.1 to 13.35.255.25413.35.255.255131,070
14713.36.0.0/1513.36.0.1 to 13.37.255.25413.37.255.255131,070
14813.38.0.0/1513.38.0.1 to 13.39.255.25413.39.255.255131,070
14913.40.0.0/1513.40.0.1 to 13.41.255.25413.41.255.255131,070
15013.42.0.0/1513.42.0.1 to 13.43.255.25413.43.255.255131,070
15113.44.0.0/1513.44.0.1 to 13.45.255.25413.45.255.255131,070
15213.46.0.0/1513.46.0.1 to 13.47.255.25413.47.255.255131,070
15313.48.0.0/1513.48.0.1 to 13.49.255.25413.49.255.255131,070
15413.50.0.0/1513.50.0.1 to 13.51.255.25413.51.255.255131,070
15513.52.0.0/1513.52.0.1 to 13.53.255.25413.53.255.255131,070
15613.54.0.0/1513.54.0.1 to 13.55.255.25413.55.255.255131,070
15713.56.0.0/1513.56.0.1 to 13.57.255.25413.57.255.255131,070
15813.58.0.0/1513.58.0.1 to 13.59.255.25413.59.255.255131,070
15913.60.0.0/1513.60.0.1 to 13.61.255.25413.61.255.255131,070
16013.62.0.0/1513.62.0.1 to 13.63.255.25413.63.255.255131,070
16113.64.0.0/1513.64.0.1 to 13.65.255.25413.65.255.255131,070
16213.66.0.0/1513.66.0.1 to 13.67.255.25413.67.255.255131,070
16313.68.0.0/1513.68.0.1 to 13.69.255.25413.69.255.255131,070
16413.70.0.0/1513.70.0.1 to 13.71.255.25413.71.255.255131,070
16513.72.0.0/1513.72.0.1 to 13.73.255.25413.73.255.255131,070
16613.74.0.0/1513.74.0.1 to 13.75.255.25413.75.255.255131,070
16713.76.0.0/1513.76.0.1 to 13.77.255.25413.77.255.255131,070
16813.78.0.0/1513.78.0.1 to 13.79.255.25413.79.255.255131,070
16913.80.0.0/1513.80.0.1 to 13.81.255.25413.81.255.255131,070
17013.82.0.0/1513.82.0.1 to 13.83.255.25413.83.255.255131,070
17113.84.0.0/1513.84.0.1 to 13.85.255.25413.85.255.255131,070
17213.86.0.0/1513.86.0.1 to 13.87.255.25413.87.255.255131,070
17313.88.0.0/1513.88.0.1 to 13.89.255.25413.89.255.255131,070
17413.90.0.0/1513.90.0.1 to 13.91.255.25413.91.255.255131,070
17513.92.0.0/1513.92.0.1 to 13.93.255.25413.93.255.255131,070
17613.94.0.0/1513.94.0.1 to 13.95.255.25413.95.255.255131,070
17713.96.0.0/1513.96.0.1 to 13.97.255.25413.97.255.255131,070
17813.98.0.0/1513.98.0.1 to 13.99.255.25413.99.255.255131,070
17913.100.0.0/1513.100.0.1 to 13.101.255.25413.101.255.255131,070
18013.102.0.0/1513.102.0.1 to 13.103.255.25413.103.255.255131,070
18113.104.0.0/1513.104.0.1 to 13.105.255.25413.105.255.255131,070
18213.106.0.0/1513.106.0.1 to 13.107.255.25413.107.255.255131,070
18313.108.0.0/1513.108.0.1 to 13.109.255.25413.109.255.255131,070
18413.110.0.0/1513.110.0.1 to 13.111.255.25413.111.255.255131,070
18513.112.0.0/1513.112.0.1 to 13.113.255.25413.113.255.255131,070
18613.114.0.0/1513.114.0.1 to 13.115.255.25413.115.255.255131,070
18713.116.0.0/1513.116.0.1 to 13.117.255.25413.117.255.255131,070
18813.118.0.0/1513.118.0.1 to 13.119.255.25413.119.255.255131,070
18913.120.0.0/1513.120.0.1 to 13.121.255.25413.121.255.255131,070
19013.122.0.0/1513.122.0.1 to 13.123.255.25413.123.255.255131,070
19113.124.0.0/1513.124.0.1 to 13.125.255.25413.125.255.255131,070
19213.126.0.0/1513.126.0.1 to 13.127.255.25413.127.255.255131,070
19313.128.0.0/1513.128.0.1 to 13.129.255.25413.129.255.255131,070
19413.130.0.0/1513.130.0.1 to 13.131.255.25413.131.255.255131,070
19513.132.0.0/1513.132.0.1 to 13.133.255.25413.133.255.255131,070
19613.134.0.0/1513.134.0.1 to 13.135.255.25413.135.255.255131,070
19713.136.0.0/1513.136.0.1 to 13.137.255.25413.137.255.255131,070
19813.138.0.0/1513.138.0.1 to 13.139.255.25413.139.255.255131,070
19913.140.0.0/1513.140.0.1 to 13.141.255.25413.141.255.255131,070
20013.142.0.0/1513.142.0.1 to 13.143.255.25413.143.255.255131,070
20113.144.0.0/1513.144.0.1 to 13.145.255.25413.145.255.255131,070
20213.146.0.0/1513.146.0.1 to 13.147.255.25413.147.255.255131,070
20313.148.0.0/1513.148.0.1 to 13.149.255.25413.149.255.255131,070
20413.150.0.0/1513.150.0.1 to 13.151.255.25413.151.255.255131,070
20513.152.0.0/1513.152.0.1 to 13.153.255.25413.153.255.255131,070
20613.154.0.0/1513.154.0.1 to 13.155.255.25413.155.255.255131,070
20713.156.0.0/1513.156.0.1 to 13.157.255.25413.157.255.255131,070
20813.158.0.0/1513.158.0.1 to 13.159.255.25413.159.255.255131,070
20913.160.0.0/1513.160.0.1 to 13.161.255.25413.161.255.255131,070
21013.162.0.0/1513.162.0.1 to 13.163.255.25413.163.255.255131,070
21113.164.0.0/1513.164.0.1 to 13.165.255.25413.165.255.255131,070
21213.166.0.0/1513.166.0.1 to 13.167.255.25413.167.255.255131,070
21313.168.0.0/1513.168.0.1 to 13.169.255.25413.169.255.255131,070
21413.170.0.0/1513.170.0.1 to 13.171.255.25413.171.255.255131,070
21513.172.0.0/1513.172.0.1 to 13.173.255.25413.173.255.255131,070
21613.174.0.0/1513.174.0.1 to 13.175.255.25413.175.255.255131,070
21713.176.0.0/1513.176.0.1 to 13.177.255.25413.177.255.255131,070
21813.178.0.0/1513.178.0.1 to 13.179.255.25413.179.255.255131,070
21913.180.0.0/1513.180.0.1 to 13.181.255.25413.181.255.255131,070
22013.182.0.0/1513.182.0.1 to 13.183.255.25413.183.255.255131,070
22113.184.0.0/1513.184.0.1 to 13.185.255.25413.185.255.255131,070
22213.186.0.0/1513.186.0.1 to 13.187.255.25413.187.255.255131,070
22313.188.0.0/1513.188.0.1 to 13.189.255.25413.189.255.255131,070
22413.190.0.0/1513.190.0.1 to 13.191.255.25413.191.255.255131,070
22513.192.0.0/1513.192.0.1 to 13.193.255.25413.193.255.255131,070
22613.194.0.0/1513.194.0.1 to 13.195.255.25413.195.255.255131,070
22713.196.0.0/1513.196.0.1 to 13.197.255.25413.197.255.255131,070
22813.198.0.0/1513.198.0.1 to 13.199.255.25413.199.255.255131,070
22913.200.0.0/1513.200.0.1 to 13.201.255.25413.201.255.255131,070
23013.202.0.0/1513.202.0.1 to 13.203.255.25413.203.255.255131,070
23113.204.0.0/1513.204.0.1 to 13.205.255.25413.205.255.255131,070
23213.206.0.0/1513.206.0.1 to 13.207.255.25413.207.255.255131,070
23313.208.0.0/1513.208.0.1 to 13.209.255.25413.209.255.255131,070
23413.210.0.0/1513.210.0.1 to 13.211.255.25413.211.255.255131,070
23513.212.0.0/1513.212.0.1 to 13.213.255.25413.213.255.255131,070
23613.214.0.0/1513.214.0.1 to 13.215.255.25413.215.255.255131,070
23713.216.0.0/1513.216.0.1 to 13.217.255.25413.217.255.255131,070
23813.218.0.0/1513.218.0.1 to 13.219.255.25413.219.255.255131,070
23913.220.0.0/1513.220.0.1 to 13.221.255.25413.221.255.255131,070
24013.222.0.0/1513.222.0.1 to 13.223.255.25413.223.255.255131,070
24113.224.0.0/1513.224.0.1 to 13.225.255.25413.225.255.255131,070
24213.226.0.0/1513.226.0.1 to 13.227.255.25413.227.255.255131,070
24313.228.0.0/1513.228.0.1 to 13.229.255.25413.229.255.255131,070
24413.230.0.0/1513.230.0.1 to 13.231.255.25413.231.255.255131,070
24513.232.0.0/1513.232.0.1 to 13.233.255.25413.233.255.255131,070
24613.234.0.0/1513.234.0.1 to 13.235.255.25413.235.255.255131,070
24713.236.0.0/1513.236.0.1 to 13.237.255.25413.237.255.255131,070
24813.238.0.0/1513.238.0.1 to 13.239.255.25413.239.255.255131,070
24913.240.0.0/1513.240.0.1 to 13.241.255.25413.241.255.255131,070
25013.242.0.0/1513.242.0.1 to 13.243.255.25413.243.255.255131,070
25113.244.0.0/1513.244.0.1 to 13.245.255.25413.245.255.255131,070
25213.246.0.0/1513.246.0.1 to 13.247.255.25413.247.255.255131,070
25313.248.0.0/1513.248.0.1 to 13.249.255.25413.249.255.255131,070
25413.250.0.0/1513.250.0.1 to 13.251.255.25413.251.255.255131,070
25513.252.0.0/1513.252.0.1 to 13.253.255.25413.253.255.255131,070
25613.254.0.0/1513.254.0.1 to 13.255.255.25413.255.255.255131,070

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.