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.

Network81.0.0.0/8
Usable hosts16,777,214
Subnet mask255.0.0.0
Addresses16,777,216
Network address
81.0.0.0
Broadcast address
81.255.255.255
First usable
81.0.0.1
Last usable
81.255.255.254
Usable hosts
16,777,214 (16,777,216 less the network and broadcast addresses)
Subnet mask
255.0.0.0
Wildcard mask
0.255.255.255 (Cisco ACLs, OSPF)
Prefix length
/8
Type
Public public
Old class
A (default /8)
As numbers
Hex 51000000 · Integer 1358954496 to 1375731711
Reverse DNS zone
81.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address01010001..00000000.00000000.0000000081.0.0.0
Subnet mask11111111..00000000.00000000.00000000255.0.0.0
Network01010001..00000000.00000000.0000000081.0.0.0
Broadcast01010001..11111111.11111111.1111111181.255.255.255
Split into smaller subnets/16
/9 (2)/10 (4)/11 (8)/12 (16)/13 (32)/14 (64)/15 (128)/16 (256)/17 (512)/18 (1,024)/19 (2,048)/20 (4,096)

81.0.0.0/8 makes 256 subnets of /16.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
181.0.0.0/1681.0.0.1 to 81.0.255.25481.0.255.25565,534
281.1.0.0/1681.1.0.1 to 81.1.255.25481.1.255.25565,534
381.2.0.0/1681.2.0.1 to 81.2.255.25481.2.255.25565,534
481.3.0.0/1681.3.0.1 to 81.3.255.25481.3.255.25565,534
581.4.0.0/1681.4.0.1 to 81.4.255.25481.4.255.25565,534
681.5.0.0/1681.5.0.1 to 81.5.255.25481.5.255.25565,534
781.6.0.0/1681.6.0.1 to 81.6.255.25481.6.255.25565,534
881.7.0.0/1681.7.0.1 to 81.7.255.25481.7.255.25565,534
981.8.0.0/1681.8.0.1 to 81.8.255.25481.8.255.25565,534
1081.9.0.0/1681.9.0.1 to 81.9.255.25481.9.255.25565,534
1181.10.0.0/1681.10.0.1 to 81.10.255.25481.10.255.25565,534
1281.11.0.0/1681.11.0.1 to 81.11.255.25481.11.255.25565,534
1381.12.0.0/1681.12.0.1 to 81.12.255.25481.12.255.25565,534
1481.13.0.0/1681.13.0.1 to 81.13.255.25481.13.255.25565,534
1581.14.0.0/1681.14.0.1 to 81.14.255.25481.14.255.25565,534
1681.15.0.0/1681.15.0.1 to 81.15.255.25481.15.255.25565,534
1781.16.0.0/1681.16.0.1 to 81.16.255.25481.16.255.25565,534
1881.17.0.0/1681.17.0.1 to 81.17.255.25481.17.255.25565,534
1981.18.0.0/1681.18.0.1 to 81.18.255.25481.18.255.25565,534
2081.19.0.0/1681.19.0.1 to 81.19.255.25481.19.255.25565,534
2181.20.0.0/1681.20.0.1 to 81.20.255.25481.20.255.25565,534
2281.21.0.0/1681.21.0.1 to 81.21.255.25481.21.255.25565,534
2381.22.0.0/1681.22.0.1 to 81.22.255.25481.22.255.25565,534
2481.23.0.0/1681.23.0.1 to 81.23.255.25481.23.255.25565,534
2581.24.0.0/1681.24.0.1 to 81.24.255.25481.24.255.25565,534
2681.25.0.0/1681.25.0.1 to 81.25.255.25481.25.255.25565,534
2781.26.0.0/1681.26.0.1 to 81.26.255.25481.26.255.25565,534
2881.27.0.0/1681.27.0.1 to 81.27.255.25481.27.255.25565,534
2981.28.0.0/1681.28.0.1 to 81.28.255.25481.28.255.25565,534
3081.29.0.0/1681.29.0.1 to 81.29.255.25481.29.255.25565,534
3181.30.0.0/1681.30.0.1 to 81.30.255.25481.30.255.25565,534
3281.31.0.0/1681.31.0.1 to 81.31.255.25481.31.255.25565,534
3381.32.0.0/1681.32.0.1 to 81.32.255.25481.32.255.25565,534
3481.33.0.0/1681.33.0.1 to 81.33.255.25481.33.255.25565,534
3581.34.0.0/1681.34.0.1 to 81.34.255.25481.34.255.25565,534
3681.35.0.0/1681.35.0.1 to 81.35.255.25481.35.255.25565,534
3781.36.0.0/1681.36.0.1 to 81.36.255.25481.36.255.25565,534
3881.37.0.0/1681.37.0.1 to 81.37.255.25481.37.255.25565,534
3981.38.0.0/1681.38.0.1 to 81.38.255.25481.38.255.25565,534
4081.39.0.0/1681.39.0.1 to 81.39.255.25481.39.255.25565,534
4181.40.0.0/1681.40.0.1 to 81.40.255.25481.40.255.25565,534
4281.41.0.0/1681.41.0.1 to 81.41.255.25481.41.255.25565,534
4381.42.0.0/1681.42.0.1 to 81.42.255.25481.42.255.25565,534
4481.43.0.0/1681.43.0.1 to 81.43.255.25481.43.255.25565,534
4581.44.0.0/1681.44.0.1 to 81.44.255.25481.44.255.25565,534
4681.45.0.0/1681.45.0.1 to 81.45.255.25481.45.255.25565,534
4781.46.0.0/1681.46.0.1 to 81.46.255.25481.46.255.25565,534
4881.47.0.0/1681.47.0.1 to 81.47.255.25481.47.255.25565,534
4981.48.0.0/1681.48.0.1 to 81.48.255.25481.48.255.25565,534
5081.49.0.0/1681.49.0.1 to 81.49.255.25481.49.255.25565,534
5181.50.0.0/1681.50.0.1 to 81.50.255.25481.50.255.25565,534
5281.51.0.0/1681.51.0.1 to 81.51.255.25481.51.255.25565,534
5381.52.0.0/1681.52.0.1 to 81.52.255.25481.52.255.25565,534
5481.53.0.0/1681.53.0.1 to 81.53.255.25481.53.255.25565,534
5581.54.0.0/1681.54.0.1 to 81.54.255.25481.54.255.25565,534
5681.55.0.0/1681.55.0.1 to 81.55.255.25481.55.255.25565,534
5781.56.0.0/1681.56.0.1 to 81.56.255.25481.56.255.25565,534
5881.57.0.0/1681.57.0.1 to 81.57.255.25481.57.255.25565,534
5981.58.0.0/1681.58.0.1 to 81.58.255.25481.58.255.25565,534
6081.59.0.0/1681.59.0.1 to 81.59.255.25481.59.255.25565,534
6181.60.0.0/1681.60.0.1 to 81.60.255.25481.60.255.25565,534
6281.61.0.0/1681.61.0.1 to 81.61.255.25481.61.255.25565,534
6381.62.0.0/1681.62.0.1 to 81.62.255.25481.62.255.25565,534
6481.63.0.0/1681.63.0.1 to 81.63.255.25481.63.255.25565,534
6581.64.0.0/1681.64.0.1 to 81.64.255.25481.64.255.25565,534
6681.65.0.0/1681.65.0.1 to 81.65.255.25481.65.255.25565,534
6781.66.0.0/1681.66.0.1 to 81.66.255.25481.66.255.25565,534
6881.67.0.0/1681.67.0.1 to 81.67.255.25481.67.255.25565,534
6981.68.0.0/1681.68.0.1 to 81.68.255.25481.68.255.25565,534
7081.69.0.0/1681.69.0.1 to 81.69.255.25481.69.255.25565,534
7181.70.0.0/1681.70.0.1 to 81.70.255.25481.70.255.25565,534
7281.71.0.0/1681.71.0.1 to 81.71.255.25481.71.255.25565,534
7381.72.0.0/1681.72.0.1 to 81.72.255.25481.72.255.25565,534
7481.73.0.0/1681.73.0.1 to 81.73.255.25481.73.255.25565,534
7581.74.0.0/1681.74.0.1 to 81.74.255.25481.74.255.25565,534
7681.75.0.0/1681.75.0.1 to 81.75.255.25481.75.255.25565,534
7781.76.0.0/1681.76.0.1 to 81.76.255.25481.76.255.25565,534
7881.77.0.0/1681.77.0.1 to 81.77.255.25481.77.255.25565,534
7981.78.0.0/1681.78.0.1 to 81.78.255.25481.78.255.25565,534
8081.79.0.0/1681.79.0.1 to 81.79.255.25481.79.255.25565,534
8181.80.0.0/1681.80.0.1 to 81.80.255.25481.80.255.25565,534
8281.81.0.0/1681.81.0.1 to 81.81.255.25481.81.255.25565,534
8381.82.0.0/1681.82.0.1 to 81.82.255.25481.82.255.25565,534
8481.83.0.0/1681.83.0.1 to 81.83.255.25481.83.255.25565,534
8581.84.0.0/1681.84.0.1 to 81.84.255.25481.84.255.25565,534
8681.85.0.0/1681.85.0.1 to 81.85.255.25481.85.255.25565,534
8781.86.0.0/1681.86.0.1 to 81.86.255.25481.86.255.25565,534
8881.87.0.0/1681.87.0.1 to 81.87.255.25481.87.255.25565,534
8981.88.0.0/1681.88.0.1 to 81.88.255.25481.88.255.25565,534
9081.89.0.0/1681.89.0.1 to 81.89.255.25481.89.255.25565,534
9181.90.0.0/1681.90.0.1 to 81.90.255.25481.90.255.25565,534
9281.91.0.0/1681.91.0.1 to 81.91.255.25481.91.255.25565,534
9381.92.0.0/1681.92.0.1 to 81.92.255.25481.92.255.25565,534
9481.93.0.0/1681.93.0.1 to 81.93.255.25481.93.255.25565,534
9581.94.0.0/1681.94.0.1 to 81.94.255.25481.94.255.25565,534
9681.95.0.0/1681.95.0.1 to 81.95.255.25481.95.255.25565,534
9781.96.0.0/1681.96.0.1 to 81.96.255.25481.96.255.25565,534
9881.97.0.0/1681.97.0.1 to 81.97.255.25481.97.255.25565,534
9981.98.0.0/1681.98.0.1 to 81.98.255.25481.98.255.25565,534
10081.99.0.0/1681.99.0.1 to 81.99.255.25481.99.255.25565,534
10181.100.0.0/1681.100.0.1 to 81.100.255.25481.100.255.25565,534
10281.101.0.0/1681.101.0.1 to 81.101.255.25481.101.255.25565,534
10381.102.0.0/1681.102.0.1 to 81.102.255.25481.102.255.25565,534
10481.103.0.0/1681.103.0.1 to 81.103.255.25481.103.255.25565,534
10581.104.0.0/1681.104.0.1 to 81.104.255.25481.104.255.25565,534
10681.105.0.0/1681.105.0.1 to 81.105.255.25481.105.255.25565,534
10781.106.0.0/1681.106.0.1 to 81.106.255.25481.106.255.25565,534
10881.107.0.0/1681.107.0.1 to 81.107.255.25481.107.255.25565,534
10981.108.0.0/1681.108.0.1 to 81.108.255.25481.108.255.25565,534
11081.109.0.0/1681.109.0.1 to 81.109.255.25481.109.255.25565,534
11181.110.0.0/1681.110.0.1 to 81.110.255.25481.110.255.25565,534
11281.111.0.0/1681.111.0.1 to 81.111.255.25481.111.255.25565,534
11381.112.0.0/1681.112.0.1 to 81.112.255.25481.112.255.25565,534
11481.113.0.0/1681.113.0.1 to 81.113.255.25481.113.255.25565,534
11581.114.0.0/1681.114.0.1 to 81.114.255.25481.114.255.25565,534
11681.115.0.0/1681.115.0.1 to 81.115.255.25481.115.255.25565,534
11781.116.0.0/1681.116.0.1 to 81.116.255.25481.116.255.25565,534
11881.117.0.0/1681.117.0.1 to 81.117.255.25481.117.255.25565,534
11981.118.0.0/1681.118.0.1 to 81.118.255.25481.118.255.25565,534
12081.119.0.0/1681.119.0.1 to 81.119.255.25481.119.255.25565,534
12181.120.0.0/1681.120.0.1 to 81.120.255.25481.120.255.25565,534
12281.121.0.0/1681.121.0.1 to 81.121.255.25481.121.255.25565,534
12381.122.0.0/1681.122.0.1 to 81.122.255.25481.122.255.25565,534
12481.123.0.0/1681.123.0.1 to 81.123.255.25481.123.255.25565,534
12581.124.0.0/1681.124.0.1 to 81.124.255.25481.124.255.25565,534
12681.125.0.0/1681.125.0.1 to 81.125.255.25481.125.255.25565,534
12781.126.0.0/1681.126.0.1 to 81.126.255.25481.126.255.25565,534
12881.127.0.0/1681.127.0.1 to 81.127.255.25481.127.255.25565,534
12981.128.0.0/1681.128.0.1 to 81.128.255.25481.128.255.25565,534
13081.129.0.0/1681.129.0.1 to 81.129.255.25481.129.255.25565,534
13181.130.0.0/1681.130.0.1 to 81.130.255.25481.130.255.25565,534
13281.131.0.0/1681.131.0.1 to 81.131.255.25481.131.255.25565,534
13381.132.0.0/1681.132.0.1 to 81.132.255.25481.132.255.25565,534
13481.133.0.0/1681.133.0.1 to 81.133.255.25481.133.255.25565,534
13581.134.0.0/1681.134.0.1 to 81.134.255.25481.134.255.25565,534
13681.135.0.0/1681.135.0.1 to 81.135.255.25481.135.255.25565,534
13781.136.0.0/1681.136.0.1 to 81.136.255.25481.136.255.25565,534
13881.137.0.0/1681.137.0.1 to 81.137.255.25481.137.255.25565,534
13981.138.0.0/1681.138.0.1 to 81.138.255.25481.138.255.25565,534
14081.139.0.0/1681.139.0.1 to 81.139.255.25481.139.255.25565,534
14181.140.0.0/1681.140.0.1 to 81.140.255.25481.140.255.25565,534
14281.141.0.0/1681.141.0.1 to 81.141.255.25481.141.255.25565,534
14381.142.0.0/1681.142.0.1 to 81.142.255.25481.142.255.25565,534
14481.143.0.0/1681.143.0.1 to 81.143.255.25481.143.255.25565,534
14581.144.0.0/1681.144.0.1 to 81.144.255.25481.144.255.25565,534
14681.145.0.0/1681.145.0.1 to 81.145.255.25481.145.255.25565,534
14781.146.0.0/1681.146.0.1 to 81.146.255.25481.146.255.25565,534
14881.147.0.0/1681.147.0.1 to 81.147.255.25481.147.255.25565,534
14981.148.0.0/1681.148.0.1 to 81.148.255.25481.148.255.25565,534
15081.149.0.0/1681.149.0.1 to 81.149.255.25481.149.255.25565,534
15181.150.0.0/1681.150.0.1 to 81.150.255.25481.150.255.25565,534
15281.151.0.0/1681.151.0.1 to 81.151.255.25481.151.255.25565,534
15381.152.0.0/1681.152.0.1 to 81.152.255.25481.152.255.25565,534
15481.153.0.0/1681.153.0.1 to 81.153.255.25481.153.255.25565,534
15581.154.0.0/1681.154.0.1 to 81.154.255.25481.154.255.25565,534
15681.155.0.0/1681.155.0.1 to 81.155.255.25481.155.255.25565,534
15781.156.0.0/1681.156.0.1 to 81.156.255.25481.156.255.25565,534
15881.157.0.0/1681.157.0.1 to 81.157.255.25481.157.255.25565,534
15981.158.0.0/1681.158.0.1 to 81.158.255.25481.158.255.25565,534
16081.159.0.0/1681.159.0.1 to 81.159.255.25481.159.255.25565,534
16181.160.0.0/1681.160.0.1 to 81.160.255.25481.160.255.25565,534
16281.161.0.0/1681.161.0.1 to 81.161.255.25481.161.255.25565,534
16381.162.0.0/1681.162.0.1 to 81.162.255.25481.162.255.25565,534
16481.163.0.0/1681.163.0.1 to 81.163.255.25481.163.255.25565,534
16581.164.0.0/1681.164.0.1 to 81.164.255.25481.164.255.25565,534
16681.165.0.0/1681.165.0.1 to 81.165.255.25481.165.255.25565,534
16781.166.0.0/1681.166.0.1 to 81.166.255.25481.166.255.25565,534
16881.167.0.0/1681.167.0.1 to 81.167.255.25481.167.255.25565,534
16981.168.0.0/1681.168.0.1 to 81.168.255.25481.168.255.25565,534
17081.169.0.0/1681.169.0.1 to 81.169.255.25481.169.255.25565,534
17181.170.0.0/1681.170.0.1 to 81.170.255.25481.170.255.25565,534
17281.171.0.0/1681.171.0.1 to 81.171.255.25481.171.255.25565,534
17381.172.0.0/1681.172.0.1 to 81.172.255.25481.172.255.25565,534
17481.173.0.0/1681.173.0.1 to 81.173.255.25481.173.255.25565,534
17581.174.0.0/1681.174.0.1 to 81.174.255.25481.174.255.25565,534
17681.175.0.0/1681.175.0.1 to 81.175.255.25481.175.255.25565,534
17781.176.0.0/1681.176.0.1 to 81.176.255.25481.176.255.25565,534
17881.177.0.0/1681.177.0.1 to 81.177.255.25481.177.255.25565,534
17981.178.0.0/1681.178.0.1 to 81.178.255.25481.178.255.25565,534
18081.179.0.0/1681.179.0.1 to 81.179.255.25481.179.255.25565,534
18181.180.0.0/1681.180.0.1 to 81.180.255.25481.180.255.25565,534
18281.181.0.0/1681.181.0.1 to 81.181.255.25481.181.255.25565,534
18381.182.0.0/1681.182.0.1 to 81.182.255.25481.182.255.25565,534
18481.183.0.0/1681.183.0.1 to 81.183.255.25481.183.255.25565,534
18581.184.0.0/1681.184.0.1 to 81.184.255.25481.184.255.25565,534
18681.185.0.0/1681.185.0.1 to 81.185.255.25481.185.255.25565,534
18781.186.0.0/1681.186.0.1 to 81.186.255.25481.186.255.25565,534
18881.187.0.0/1681.187.0.1 to 81.187.255.25481.187.255.25565,534
18981.188.0.0/1681.188.0.1 to 81.188.255.25481.188.255.25565,534
19081.189.0.0/1681.189.0.1 to 81.189.255.25481.189.255.25565,534
19181.190.0.0/1681.190.0.1 to 81.190.255.25481.190.255.25565,534
19281.191.0.0/1681.191.0.1 to 81.191.255.25481.191.255.25565,534
19381.192.0.0/1681.192.0.1 to 81.192.255.25481.192.255.25565,534
19481.193.0.0/1681.193.0.1 to 81.193.255.25481.193.255.25565,534
19581.194.0.0/1681.194.0.1 to 81.194.255.25481.194.255.25565,534
19681.195.0.0/1681.195.0.1 to 81.195.255.25481.195.255.25565,534
19781.196.0.0/1681.196.0.1 to 81.196.255.25481.196.255.25565,534
19881.197.0.0/1681.197.0.1 to 81.197.255.25481.197.255.25565,534
19981.198.0.0/1681.198.0.1 to 81.198.255.25481.198.255.25565,534
20081.199.0.0/1681.199.0.1 to 81.199.255.25481.199.255.25565,534
20181.200.0.0/1681.200.0.1 to 81.200.255.25481.200.255.25565,534
20281.201.0.0/1681.201.0.1 to 81.201.255.25481.201.255.25565,534
20381.202.0.0/1681.202.0.1 to 81.202.255.25481.202.255.25565,534
20481.203.0.0/1681.203.0.1 to 81.203.255.25481.203.255.25565,534
20581.204.0.0/1681.204.0.1 to 81.204.255.25481.204.255.25565,534
20681.205.0.0/1681.205.0.1 to 81.205.255.25481.205.255.25565,534
20781.206.0.0/1681.206.0.1 to 81.206.255.25481.206.255.25565,534
20881.207.0.0/1681.207.0.1 to 81.207.255.25481.207.255.25565,534
20981.208.0.0/1681.208.0.1 to 81.208.255.25481.208.255.25565,534
21081.209.0.0/1681.209.0.1 to 81.209.255.25481.209.255.25565,534
21181.210.0.0/1681.210.0.1 to 81.210.255.25481.210.255.25565,534
21281.211.0.0/1681.211.0.1 to 81.211.255.25481.211.255.25565,534
21381.212.0.0/1681.212.0.1 to 81.212.255.25481.212.255.25565,534
21481.213.0.0/1681.213.0.1 to 81.213.255.25481.213.255.25565,534
21581.214.0.0/1681.214.0.1 to 81.214.255.25481.214.255.25565,534
21681.215.0.0/1681.215.0.1 to 81.215.255.25481.215.255.25565,534
21781.216.0.0/1681.216.0.1 to 81.216.255.25481.216.255.25565,534
21881.217.0.0/1681.217.0.1 to 81.217.255.25481.217.255.25565,534
21981.218.0.0/1681.218.0.1 to 81.218.255.25481.218.255.25565,534
22081.219.0.0/1681.219.0.1 to 81.219.255.25481.219.255.25565,534
22181.220.0.0/1681.220.0.1 to 81.220.255.25481.220.255.25565,534
22281.221.0.0/1681.221.0.1 to 81.221.255.25481.221.255.25565,534
22381.222.0.0/1681.222.0.1 to 81.222.255.25481.222.255.25565,534
22481.223.0.0/1681.223.0.1 to 81.223.255.25481.223.255.25565,534
22581.224.0.0/1681.224.0.1 to 81.224.255.25481.224.255.25565,534
22681.225.0.0/1681.225.0.1 to 81.225.255.25481.225.255.25565,534
22781.226.0.0/1681.226.0.1 to 81.226.255.25481.226.255.25565,534
22881.227.0.0/1681.227.0.1 to 81.227.255.25481.227.255.25565,534
22981.228.0.0/1681.228.0.1 to 81.228.255.25481.228.255.25565,534
23081.229.0.0/1681.229.0.1 to 81.229.255.25481.229.255.25565,534
23181.230.0.0/1681.230.0.1 to 81.230.255.25481.230.255.25565,534
23281.231.0.0/1681.231.0.1 to 81.231.255.25481.231.255.25565,534
23381.232.0.0/1681.232.0.1 to 81.232.255.25481.232.255.25565,534
23481.233.0.0/1681.233.0.1 to 81.233.255.25481.233.255.25565,534
23581.234.0.0/1681.234.0.1 to 81.234.255.25481.234.255.25565,534
23681.235.0.0/1681.235.0.1 to 81.235.255.25481.235.255.25565,534
23781.236.0.0/1681.236.0.1 to 81.236.255.25481.236.255.25565,534
23881.237.0.0/1681.237.0.1 to 81.237.255.25481.237.255.25565,534
23981.238.0.0/1681.238.0.1 to 81.238.255.25481.238.255.25565,534
24081.239.0.0/1681.239.0.1 to 81.239.255.25481.239.255.25565,534
24181.240.0.0/1681.240.0.1 to 81.240.255.25481.240.255.25565,534
24281.241.0.0/1681.241.0.1 to 81.241.255.25481.241.255.25565,534
24381.242.0.0/1681.242.0.1 to 81.242.255.25481.242.255.25565,534
24481.243.0.0/1681.243.0.1 to 81.243.255.25481.243.255.25565,534
24581.244.0.0/1681.244.0.1 to 81.244.255.25481.244.255.25565,534
24681.245.0.0/1681.245.0.1 to 81.245.255.25481.245.255.25565,534
24781.246.0.0/1681.246.0.1 to 81.246.255.25481.246.255.25565,534
24881.247.0.0/1681.247.0.1 to 81.247.255.25481.247.255.25565,534
24981.248.0.0/1681.248.0.1 to 81.248.255.25481.248.255.25565,534
25081.249.0.0/1681.249.0.1 to 81.249.255.25481.249.255.25565,534
25181.250.0.0/1681.250.0.1 to 81.250.255.25481.250.255.25565,534
25281.251.0.0/1681.251.0.1 to 81.251.255.25481.251.255.25565,534
25381.252.0.0/1681.252.0.1 to 81.252.255.25481.252.255.25565,534
25481.253.0.0/1681.253.0.1 to 81.253.255.25481.253.255.25565,534
25581.254.0.0/1681.254.0.1 to 81.254.255.25481.254.255.25565,534
25681.255.0.0/1681.255.0.1 to 81.255.255.25481.255.255.25565,534

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.