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.

Network81.166.0.0/16
Usable hosts65,534
Subnet mask255.255.0.0
Addresses65,536
Network address
81.166.0.0
Broadcast address
81.166.255.255
First usable
81.166.0.1
Last usable
81.166.255.254
Usable hosts
65,534 (65,536 less the network and broadcast addresses)
Subnet mask
255.255.0.0
Wildcard mask
0.0.255.255 (Cisco ACLs, OSPF)
Prefix length
/16
Type
Public public
Old class
A (default /8)
As numbers
Hex 51A60000 · Integer 1369833472 to 1369899007
Reverse DNS zone
166.81.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address01010001.10100110..00000000.0000000081.166.0.0
Subnet mask11111111.11111111..00000000.00000000255.255.0.0
Network01010001.10100110..00000000.0000000081.166.0.0
Broadcast01010001.10100110..11111111.1111111181.166.255.255
Split into smaller subnets/24
/17 (2)/18 (4)/19 (8)/20 (16)/21 (32)/22 (64)/23 (128)/24 (256)/25 (512)/26 (1,024)/27 (2,048)/28 (4,096)

81.166.0.0/16 makes 256 subnets of /24.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
181.166.0.0/2481.166.0.1 to 81.166.0.25481.166.0.255254
281.166.1.0/2481.166.1.1 to 81.166.1.25481.166.1.255254
381.166.2.0/2481.166.2.1 to 81.166.2.25481.166.2.255254
481.166.3.0/2481.166.3.1 to 81.166.3.25481.166.3.255254
581.166.4.0/2481.166.4.1 to 81.166.4.25481.166.4.255254
681.166.5.0/2481.166.5.1 to 81.166.5.25481.166.5.255254
781.166.6.0/2481.166.6.1 to 81.166.6.25481.166.6.255254
881.166.7.0/2481.166.7.1 to 81.166.7.25481.166.7.255254
981.166.8.0/2481.166.8.1 to 81.166.8.25481.166.8.255254
1081.166.9.0/2481.166.9.1 to 81.166.9.25481.166.9.255254
1181.166.10.0/2481.166.10.1 to 81.166.10.25481.166.10.255254
1281.166.11.0/2481.166.11.1 to 81.166.11.25481.166.11.255254
1381.166.12.0/2481.166.12.1 to 81.166.12.25481.166.12.255254
1481.166.13.0/2481.166.13.1 to 81.166.13.25481.166.13.255254
1581.166.14.0/2481.166.14.1 to 81.166.14.25481.166.14.255254
1681.166.15.0/2481.166.15.1 to 81.166.15.25481.166.15.255254
1781.166.16.0/2481.166.16.1 to 81.166.16.25481.166.16.255254
1881.166.17.0/2481.166.17.1 to 81.166.17.25481.166.17.255254
1981.166.18.0/2481.166.18.1 to 81.166.18.25481.166.18.255254
2081.166.19.0/2481.166.19.1 to 81.166.19.25481.166.19.255254
2181.166.20.0/2481.166.20.1 to 81.166.20.25481.166.20.255254
2281.166.21.0/2481.166.21.1 to 81.166.21.25481.166.21.255254
2381.166.22.0/2481.166.22.1 to 81.166.22.25481.166.22.255254
2481.166.23.0/2481.166.23.1 to 81.166.23.25481.166.23.255254
2581.166.24.0/2481.166.24.1 to 81.166.24.25481.166.24.255254
2681.166.25.0/2481.166.25.1 to 81.166.25.25481.166.25.255254
2781.166.26.0/2481.166.26.1 to 81.166.26.25481.166.26.255254
2881.166.27.0/2481.166.27.1 to 81.166.27.25481.166.27.255254
2981.166.28.0/2481.166.28.1 to 81.166.28.25481.166.28.255254
3081.166.29.0/2481.166.29.1 to 81.166.29.25481.166.29.255254
3181.166.30.0/2481.166.30.1 to 81.166.30.25481.166.30.255254
3281.166.31.0/2481.166.31.1 to 81.166.31.25481.166.31.255254
3381.166.32.0/2481.166.32.1 to 81.166.32.25481.166.32.255254
3481.166.33.0/2481.166.33.1 to 81.166.33.25481.166.33.255254
3581.166.34.0/2481.166.34.1 to 81.166.34.25481.166.34.255254
3681.166.35.0/2481.166.35.1 to 81.166.35.25481.166.35.255254
3781.166.36.0/2481.166.36.1 to 81.166.36.25481.166.36.255254
3881.166.37.0/2481.166.37.1 to 81.166.37.25481.166.37.255254
3981.166.38.0/2481.166.38.1 to 81.166.38.25481.166.38.255254
4081.166.39.0/2481.166.39.1 to 81.166.39.25481.166.39.255254
4181.166.40.0/2481.166.40.1 to 81.166.40.25481.166.40.255254
4281.166.41.0/2481.166.41.1 to 81.166.41.25481.166.41.255254
4381.166.42.0/2481.166.42.1 to 81.166.42.25481.166.42.255254
4481.166.43.0/2481.166.43.1 to 81.166.43.25481.166.43.255254
4581.166.44.0/2481.166.44.1 to 81.166.44.25481.166.44.255254
4681.166.45.0/2481.166.45.1 to 81.166.45.25481.166.45.255254
4781.166.46.0/2481.166.46.1 to 81.166.46.25481.166.46.255254
4881.166.47.0/2481.166.47.1 to 81.166.47.25481.166.47.255254
4981.166.48.0/2481.166.48.1 to 81.166.48.25481.166.48.255254
5081.166.49.0/2481.166.49.1 to 81.166.49.25481.166.49.255254
5181.166.50.0/2481.166.50.1 to 81.166.50.25481.166.50.255254
5281.166.51.0/2481.166.51.1 to 81.166.51.25481.166.51.255254
5381.166.52.0/2481.166.52.1 to 81.166.52.25481.166.52.255254
5481.166.53.0/2481.166.53.1 to 81.166.53.25481.166.53.255254
5581.166.54.0/2481.166.54.1 to 81.166.54.25481.166.54.255254
5681.166.55.0/2481.166.55.1 to 81.166.55.25481.166.55.255254
5781.166.56.0/2481.166.56.1 to 81.166.56.25481.166.56.255254
5881.166.57.0/2481.166.57.1 to 81.166.57.25481.166.57.255254
5981.166.58.0/2481.166.58.1 to 81.166.58.25481.166.58.255254
6081.166.59.0/2481.166.59.1 to 81.166.59.25481.166.59.255254
6181.166.60.0/2481.166.60.1 to 81.166.60.25481.166.60.255254
6281.166.61.0/2481.166.61.1 to 81.166.61.25481.166.61.255254
6381.166.62.0/2481.166.62.1 to 81.166.62.25481.166.62.255254
6481.166.63.0/2481.166.63.1 to 81.166.63.25481.166.63.255254
6581.166.64.0/2481.166.64.1 to 81.166.64.25481.166.64.255254
6681.166.65.0/2481.166.65.1 to 81.166.65.25481.166.65.255254
6781.166.66.0/2481.166.66.1 to 81.166.66.25481.166.66.255254
6881.166.67.0/2481.166.67.1 to 81.166.67.25481.166.67.255254
6981.166.68.0/2481.166.68.1 to 81.166.68.25481.166.68.255254
7081.166.69.0/2481.166.69.1 to 81.166.69.25481.166.69.255254
7181.166.70.0/2481.166.70.1 to 81.166.70.25481.166.70.255254
7281.166.71.0/2481.166.71.1 to 81.166.71.25481.166.71.255254
7381.166.72.0/2481.166.72.1 to 81.166.72.25481.166.72.255254
7481.166.73.0/2481.166.73.1 to 81.166.73.25481.166.73.255254
7581.166.74.0/2481.166.74.1 to 81.166.74.25481.166.74.255254
7681.166.75.0/2481.166.75.1 to 81.166.75.25481.166.75.255254
7781.166.76.0/2481.166.76.1 to 81.166.76.25481.166.76.255254
7881.166.77.0/2481.166.77.1 to 81.166.77.25481.166.77.255254
7981.166.78.0/2481.166.78.1 to 81.166.78.25481.166.78.255254
8081.166.79.0/2481.166.79.1 to 81.166.79.25481.166.79.255254
8181.166.80.0/2481.166.80.1 to 81.166.80.25481.166.80.255254
8281.166.81.0/2481.166.81.1 to 81.166.81.25481.166.81.255254
8381.166.82.0/2481.166.82.1 to 81.166.82.25481.166.82.255254
8481.166.83.0/2481.166.83.1 to 81.166.83.25481.166.83.255254
8581.166.84.0/2481.166.84.1 to 81.166.84.25481.166.84.255254
8681.166.85.0/2481.166.85.1 to 81.166.85.25481.166.85.255254
8781.166.86.0/2481.166.86.1 to 81.166.86.25481.166.86.255254
8881.166.87.0/2481.166.87.1 to 81.166.87.25481.166.87.255254
8981.166.88.0/2481.166.88.1 to 81.166.88.25481.166.88.255254
9081.166.89.0/2481.166.89.1 to 81.166.89.25481.166.89.255254
9181.166.90.0/2481.166.90.1 to 81.166.90.25481.166.90.255254
9281.166.91.0/2481.166.91.1 to 81.166.91.25481.166.91.255254
9381.166.92.0/2481.166.92.1 to 81.166.92.25481.166.92.255254
9481.166.93.0/2481.166.93.1 to 81.166.93.25481.166.93.255254
9581.166.94.0/2481.166.94.1 to 81.166.94.25481.166.94.255254
9681.166.95.0/2481.166.95.1 to 81.166.95.25481.166.95.255254
9781.166.96.0/2481.166.96.1 to 81.166.96.25481.166.96.255254
9881.166.97.0/2481.166.97.1 to 81.166.97.25481.166.97.255254
9981.166.98.0/2481.166.98.1 to 81.166.98.25481.166.98.255254
10081.166.99.0/2481.166.99.1 to 81.166.99.25481.166.99.255254
10181.166.100.0/2481.166.100.1 to 81.166.100.25481.166.100.255254
10281.166.101.0/2481.166.101.1 to 81.166.101.25481.166.101.255254
10381.166.102.0/2481.166.102.1 to 81.166.102.25481.166.102.255254
10481.166.103.0/2481.166.103.1 to 81.166.103.25481.166.103.255254
10581.166.104.0/2481.166.104.1 to 81.166.104.25481.166.104.255254
10681.166.105.0/2481.166.105.1 to 81.166.105.25481.166.105.255254
10781.166.106.0/2481.166.106.1 to 81.166.106.25481.166.106.255254
10881.166.107.0/2481.166.107.1 to 81.166.107.25481.166.107.255254
10981.166.108.0/2481.166.108.1 to 81.166.108.25481.166.108.255254
11081.166.109.0/2481.166.109.1 to 81.166.109.25481.166.109.255254
11181.166.110.0/2481.166.110.1 to 81.166.110.25481.166.110.255254
11281.166.111.0/2481.166.111.1 to 81.166.111.25481.166.111.255254
11381.166.112.0/2481.166.112.1 to 81.166.112.25481.166.112.255254
11481.166.113.0/2481.166.113.1 to 81.166.113.25481.166.113.255254
11581.166.114.0/2481.166.114.1 to 81.166.114.25481.166.114.255254
11681.166.115.0/2481.166.115.1 to 81.166.115.25481.166.115.255254
11781.166.116.0/2481.166.116.1 to 81.166.116.25481.166.116.255254
11881.166.117.0/2481.166.117.1 to 81.166.117.25481.166.117.255254
11981.166.118.0/2481.166.118.1 to 81.166.118.25481.166.118.255254
12081.166.119.0/2481.166.119.1 to 81.166.119.25481.166.119.255254
12181.166.120.0/2481.166.120.1 to 81.166.120.25481.166.120.255254
12281.166.121.0/2481.166.121.1 to 81.166.121.25481.166.121.255254
12381.166.122.0/2481.166.122.1 to 81.166.122.25481.166.122.255254
12481.166.123.0/2481.166.123.1 to 81.166.123.25481.166.123.255254
12581.166.124.0/2481.166.124.1 to 81.166.124.25481.166.124.255254
12681.166.125.0/2481.166.125.1 to 81.166.125.25481.166.125.255254
12781.166.126.0/2481.166.126.1 to 81.166.126.25481.166.126.255254
12881.166.127.0/2481.166.127.1 to 81.166.127.25481.166.127.255254
12981.166.128.0/2481.166.128.1 to 81.166.128.25481.166.128.255254
13081.166.129.0/2481.166.129.1 to 81.166.129.25481.166.129.255254
13181.166.130.0/2481.166.130.1 to 81.166.130.25481.166.130.255254
13281.166.131.0/2481.166.131.1 to 81.166.131.25481.166.131.255254
13381.166.132.0/2481.166.132.1 to 81.166.132.25481.166.132.255254
13481.166.133.0/2481.166.133.1 to 81.166.133.25481.166.133.255254
13581.166.134.0/2481.166.134.1 to 81.166.134.25481.166.134.255254
13681.166.135.0/2481.166.135.1 to 81.166.135.25481.166.135.255254
13781.166.136.0/2481.166.136.1 to 81.166.136.25481.166.136.255254
13881.166.137.0/2481.166.137.1 to 81.166.137.25481.166.137.255254
13981.166.138.0/2481.166.138.1 to 81.166.138.25481.166.138.255254
14081.166.139.0/2481.166.139.1 to 81.166.139.25481.166.139.255254
14181.166.140.0/2481.166.140.1 to 81.166.140.25481.166.140.255254
14281.166.141.0/2481.166.141.1 to 81.166.141.25481.166.141.255254
14381.166.142.0/2481.166.142.1 to 81.166.142.25481.166.142.255254
14481.166.143.0/2481.166.143.1 to 81.166.143.25481.166.143.255254
14581.166.144.0/2481.166.144.1 to 81.166.144.25481.166.144.255254
14681.166.145.0/2481.166.145.1 to 81.166.145.25481.166.145.255254
14781.166.146.0/2481.166.146.1 to 81.166.146.25481.166.146.255254
14881.166.147.0/2481.166.147.1 to 81.166.147.25481.166.147.255254
14981.166.148.0/2481.166.148.1 to 81.166.148.25481.166.148.255254
15081.166.149.0/2481.166.149.1 to 81.166.149.25481.166.149.255254
15181.166.150.0/2481.166.150.1 to 81.166.150.25481.166.150.255254
15281.166.151.0/2481.166.151.1 to 81.166.151.25481.166.151.255254
15381.166.152.0/2481.166.152.1 to 81.166.152.25481.166.152.255254
15481.166.153.0/2481.166.153.1 to 81.166.153.25481.166.153.255254
15581.166.154.0/2481.166.154.1 to 81.166.154.25481.166.154.255254
15681.166.155.0/2481.166.155.1 to 81.166.155.25481.166.155.255254
15781.166.156.0/2481.166.156.1 to 81.166.156.25481.166.156.255254
15881.166.157.0/2481.166.157.1 to 81.166.157.25481.166.157.255254
15981.166.158.0/2481.166.158.1 to 81.166.158.25481.166.158.255254
16081.166.159.0/2481.166.159.1 to 81.166.159.25481.166.159.255254
16181.166.160.0/2481.166.160.1 to 81.166.160.25481.166.160.255254
16281.166.161.0/2481.166.161.1 to 81.166.161.25481.166.161.255254
16381.166.162.0/2481.166.162.1 to 81.166.162.25481.166.162.255254
16481.166.163.0/2481.166.163.1 to 81.166.163.25481.166.163.255254
16581.166.164.0/2481.166.164.1 to 81.166.164.25481.166.164.255254
16681.166.165.0/2481.166.165.1 to 81.166.165.25481.166.165.255254
16781.166.166.0/2481.166.166.1 to 81.166.166.25481.166.166.255254
16881.166.167.0/2481.166.167.1 to 81.166.167.25481.166.167.255254
16981.166.168.0/2481.166.168.1 to 81.166.168.25481.166.168.255254
17081.166.169.0/2481.166.169.1 to 81.166.169.25481.166.169.255254
17181.166.170.0/2481.166.170.1 to 81.166.170.25481.166.170.255254
17281.166.171.0/2481.166.171.1 to 81.166.171.25481.166.171.255254
17381.166.172.0/2481.166.172.1 to 81.166.172.25481.166.172.255254
17481.166.173.0/2481.166.173.1 to 81.166.173.25481.166.173.255254
17581.166.174.0/2481.166.174.1 to 81.166.174.25481.166.174.255254
17681.166.175.0/2481.166.175.1 to 81.166.175.25481.166.175.255254
17781.166.176.0/2481.166.176.1 to 81.166.176.25481.166.176.255254
17881.166.177.0/2481.166.177.1 to 81.166.177.25481.166.177.255254
17981.166.178.0/2481.166.178.1 to 81.166.178.25481.166.178.255254
18081.166.179.0/2481.166.179.1 to 81.166.179.25481.166.179.255254
18181.166.180.0/2481.166.180.1 to 81.166.180.25481.166.180.255254
18281.166.181.0/2481.166.181.1 to 81.166.181.25481.166.181.255254
18381.166.182.0/2481.166.182.1 to 81.166.182.25481.166.182.255254
18481.166.183.0/2481.166.183.1 to 81.166.183.25481.166.183.255254
18581.166.184.0/2481.166.184.1 to 81.166.184.25481.166.184.255254
18681.166.185.0/2481.166.185.1 to 81.166.185.25481.166.185.255254
18781.166.186.0/2481.166.186.1 to 81.166.186.25481.166.186.255254
18881.166.187.0/2481.166.187.1 to 81.166.187.25481.166.187.255254
18981.166.188.0/2481.166.188.1 to 81.166.188.25481.166.188.255254
19081.166.189.0/2481.166.189.1 to 81.166.189.25481.166.189.255254
19181.166.190.0/2481.166.190.1 to 81.166.190.25481.166.190.255254
19281.166.191.0/2481.166.191.1 to 81.166.191.25481.166.191.255254
19381.166.192.0/2481.166.192.1 to 81.166.192.25481.166.192.255254
19481.166.193.0/2481.166.193.1 to 81.166.193.25481.166.193.255254
19581.166.194.0/2481.166.194.1 to 81.166.194.25481.166.194.255254
19681.166.195.0/2481.166.195.1 to 81.166.195.25481.166.195.255254
19781.166.196.0/2481.166.196.1 to 81.166.196.25481.166.196.255254
19881.166.197.0/2481.166.197.1 to 81.166.197.25481.166.197.255254
19981.166.198.0/2481.166.198.1 to 81.166.198.25481.166.198.255254
20081.166.199.0/2481.166.199.1 to 81.166.199.25481.166.199.255254
20181.166.200.0/2481.166.200.1 to 81.166.200.25481.166.200.255254
20281.166.201.0/2481.166.201.1 to 81.166.201.25481.166.201.255254
20381.166.202.0/2481.166.202.1 to 81.166.202.25481.166.202.255254
20481.166.203.0/2481.166.203.1 to 81.166.203.25481.166.203.255254
20581.166.204.0/2481.166.204.1 to 81.166.204.25481.166.204.255254
20681.166.205.0/2481.166.205.1 to 81.166.205.25481.166.205.255254
20781.166.206.0/2481.166.206.1 to 81.166.206.25481.166.206.255254
20881.166.207.0/2481.166.207.1 to 81.166.207.25481.166.207.255254
20981.166.208.0/2481.166.208.1 to 81.166.208.25481.166.208.255254
21081.166.209.0/2481.166.209.1 to 81.166.209.25481.166.209.255254
21181.166.210.0/2481.166.210.1 to 81.166.210.25481.166.210.255254
21281.166.211.0/2481.166.211.1 to 81.166.211.25481.166.211.255254
21381.166.212.0/2481.166.212.1 to 81.166.212.25481.166.212.255254
21481.166.213.0/2481.166.213.1 to 81.166.213.25481.166.213.255254
21581.166.214.0/2481.166.214.1 to 81.166.214.25481.166.214.255254
21681.166.215.0/2481.166.215.1 to 81.166.215.25481.166.215.255254
21781.166.216.0/2481.166.216.1 to 81.166.216.25481.166.216.255254
21881.166.217.0/2481.166.217.1 to 81.166.217.25481.166.217.255254
21981.166.218.0/2481.166.218.1 to 81.166.218.25481.166.218.255254
22081.166.219.0/2481.166.219.1 to 81.166.219.25481.166.219.255254
22181.166.220.0/2481.166.220.1 to 81.166.220.25481.166.220.255254
22281.166.221.0/2481.166.221.1 to 81.166.221.25481.166.221.255254
22381.166.222.0/2481.166.222.1 to 81.166.222.25481.166.222.255254
22481.166.223.0/2481.166.223.1 to 81.166.223.25481.166.223.255254
22581.166.224.0/2481.166.224.1 to 81.166.224.25481.166.224.255254
22681.166.225.0/2481.166.225.1 to 81.166.225.25481.166.225.255254
22781.166.226.0/2481.166.226.1 to 81.166.226.25481.166.226.255254
22881.166.227.0/2481.166.227.1 to 81.166.227.25481.166.227.255254
22981.166.228.0/2481.166.228.1 to 81.166.228.25481.166.228.255254
23081.166.229.0/2481.166.229.1 to 81.166.229.25481.166.229.255254
23181.166.230.0/2481.166.230.1 to 81.166.230.25481.166.230.255254
23281.166.231.0/2481.166.231.1 to 81.166.231.25481.166.231.255254
23381.166.232.0/2481.166.232.1 to 81.166.232.25481.166.232.255254
23481.166.233.0/2481.166.233.1 to 81.166.233.25481.166.233.255254
23581.166.234.0/2481.166.234.1 to 81.166.234.25481.166.234.255254
23681.166.235.0/2481.166.235.1 to 81.166.235.25481.166.235.255254
23781.166.236.0/2481.166.236.1 to 81.166.236.25481.166.236.255254
23881.166.237.0/2481.166.237.1 to 81.166.237.25481.166.237.255254
23981.166.238.0/2481.166.238.1 to 81.166.238.25481.166.238.255254
24081.166.239.0/2481.166.239.1 to 81.166.239.25481.166.239.255254
24181.166.240.0/2481.166.240.1 to 81.166.240.25481.166.240.255254
24281.166.241.0/2481.166.241.1 to 81.166.241.25481.166.241.255254
24381.166.242.0/2481.166.242.1 to 81.166.242.25481.166.242.255254
24481.166.243.0/2481.166.243.1 to 81.166.243.25481.166.243.255254
24581.166.244.0/2481.166.244.1 to 81.166.244.25481.166.244.255254
24681.166.245.0/2481.166.245.1 to 81.166.245.25481.166.245.255254
24781.166.246.0/2481.166.246.1 to 81.166.246.25481.166.246.255254
24881.166.247.0/2481.166.247.1 to 81.166.247.25481.166.247.255254
24981.166.248.0/2481.166.248.1 to 81.166.248.25481.166.248.255254
25081.166.249.0/2481.166.249.1 to 81.166.249.25481.166.249.255254
25181.166.250.0/2481.166.250.1 to 81.166.250.25481.166.250.255254
25281.166.251.0/2481.166.251.1 to 81.166.251.25481.166.251.255254
25381.166.252.0/2481.166.252.1 to 81.166.252.25481.166.252.255254
25481.166.253.0/2481.166.253.1 to 81.166.253.25481.166.253.255254
25581.166.254.0/2481.166.254.1 to 81.166.254.25481.166.254.255254
25681.166.255.0/2481.166.255.1 to 81.166.255.25481.166.255.255254

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.