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.

Network21.0.0.0/10
Usable hosts4,194,302
Subnet mask255.192.0.0
Addresses4,194,304
Network address
21.0.0.0
Broadcast address
21.63.255.255
First usable
21.0.0.1
Last usable
21.63.255.254
Usable hosts
4,194,302 (4,194,304 less the network and broadcast addresses)
Subnet mask
255.192.0.0
Wildcard mask
0.63.255.255 (Cisco ACLs, OSPF)
Prefix length
/10
Type
Public public
Old class
A (default /8)
As numbers
Hex 15000000 · Integer 352321536 to 356515839
Reverse DNS zones
0.21.in-addr.arpa
1.21.in-addr.arpa
2.21.in-addr.arpa
3.21.in-addr.arpa
4.21.in-addr.arpa
5.21.in-addr.arpa
6.21.in-addr.arpa
7.21.in-addr.arpa
8.21.in-addr.arpa
9.21.in-addr.arpa
10.21.in-addr.arpa
11.21.in-addr.arpa
12.21.in-addr.arpa
13.21.in-addr.arpa
14.21.in-addr.arpa
15.21.in-addr.arpa
and 48 more
/10 is not on a 8-bit boundary, so it takes 64 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00010101.00000000.00000000.0000000021.0.0.0
Subnet mask11111111.11000000.00000000.00000000255.192.0.0
Network00010101.00000000.00000000.0000000021.0.0.0
Broadcast00010101.00111111.11111111.1111111121.63.255.255
Split into smaller subnets/21
/11 (2)/12 (4)/13 (8)/14 (16)/15 (32)/16 (64)/17 (128)/18 (256)/19 (512)/20 (1,024)/21 (2,048)/22 (4,096)

21.0.0.0/10 makes 2,048 subnets of /21; the first 256 are listed.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
121.0.0.0/2121.0.0.1 to 21.0.7.25421.0.7.2552,046
221.0.8.0/2121.0.8.1 to 21.0.15.25421.0.15.2552,046
321.0.16.0/2121.0.16.1 to 21.0.23.25421.0.23.2552,046
421.0.24.0/2121.0.24.1 to 21.0.31.25421.0.31.2552,046
521.0.32.0/2121.0.32.1 to 21.0.39.25421.0.39.2552,046
621.0.40.0/2121.0.40.1 to 21.0.47.25421.0.47.2552,046
721.0.48.0/2121.0.48.1 to 21.0.55.25421.0.55.2552,046
821.0.56.0/2121.0.56.1 to 21.0.63.25421.0.63.2552,046
921.0.64.0/2121.0.64.1 to 21.0.71.25421.0.71.2552,046
1021.0.72.0/2121.0.72.1 to 21.0.79.25421.0.79.2552,046
1121.0.80.0/2121.0.80.1 to 21.0.87.25421.0.87.2552,046
1221.0.88.0/2121.0.88.1 to 21.0.95.25421.0.95.2552,046
1321.0.96.0/2121.0.96.1 to 21.0.103.25421.0.103.2552,046
1421.0.104.0/2121.0.104.1 to 21.0.111.25421.0.111.2552,046
1521.0.112.0/2121.0.112.1 to 21.0.119.25421.0.119.2552,046
1621.0.120.0/2121.0.120.1 to 21.0.127.25421.0.127.2552,046
1721.0.128.0/2121.0.128.1 to 21.0.135.25421.0.135.2552,046
1821.0.136.0/2121.0.136.1 to 21.0.143.25421.0.143.2552,046
1921.0.144.0/2121.0.144.1 to 21.0.151.25421.0.151.2552,046
2021.0.152.0/2121.0.152.1 to 21.0.159.25421.0.159.2552,046
2121.0.160.0/2121.0.160.1 to 21.0.167.25421.0.167.2552,046
2221.0.168.0/2121.0.168.1 to 21.0.175.25421.0.175.2552,046
2321.0.176.0/2121.0.176.1 to 21.0.183.25421.0.183.2552,046
2421.0.184.0/2121.0.184.1 to 21.0.191.25421.0.191.2552,046
2521.0.192.0/2121.0.192.1 to 21.0.199.25421.0.199.2552,046
2621.0.200.0/2121.0.200.1 to 21.0.207.25421.0.207.2552,046
2721.0.208.0/2121.0.208.1 to 21.0.215.25421.0.215.2552,046
2821.0.216.0/2121.0.216.1 to 21.0.223.25421.0.223.2552,046
2921.0.224.0/2121.0.224.1 to 21.0.231.25421.0.231.2552,046
3021.0.232.0/2121.0.232.1 to 21.0.239.25421.0.239.2552,046
3121.0.240.0/2121.0.240.1 to 21.0.247.25421.0.247.2552,046
3221.0.248.0/2121.0.248.1 to 21.0.255.25421.0.255.2552,046
3321.1.0.0/2121.1.0.1 to 21.1.7.25421.1.7.2552,046
3421.1.8.0/2121.1.8.1 to 21.1.15.25421.1.15.2552,046
3521.1.16.0/2121.1.16.1 to 21.1.23.25421.1.23.2552,046
3621.1.24.0/2121.1.24.1 to 21.1.31.25421.1.31.2552,046
3721.1.32.0/2121.1.32.1 to 21.1.39.25421.1.39.2552,046
3821.1.40.0/2121.1.40.1 to 21.1.47.25421.1.47.2552,046
3921.1.48.0/2121.1.48.1 to 21.1.55.25421.1.55.2552,046
4021.1.56.0/2121.1.56.1 to 21.1.63.25421.1.63.2552,046
4121.1.64.0/2121.1.64.1 to 21.1.71.25421.1.71.2552,046
4221.1.72.0/2121.1.72.1 to 21.1.79.25421.1.79.2552,046
4321.1.80.0/2121.1.80.1 to 21.1.87.25421.1.87.2552,046
4421.1.88.0/2121.1.88.1 to 21.1.95.25421.1.95.2552,046
4521.1.96.0/2121.1.96.1 to 21.1.103.25421.1.103.2552,046
4621.1.104.0/2121.1.104.1 to 21.1.111.25421.1.111.2552,046
4721.1.112.0/2121.1.112.1 to 21.1.119.25421.1.119.2552,046
4821.1.120.0/2121.1.120.1 to 21.1.127.25421.1.127.2552,046
4921.1.128.0/2121.1.128.1 to 21.1.135.25421.1.135.2552,046
5021.1.136.0/2121.1.136.1 to 21.1.143.25421.1.143.2552,046
5121.1.144.0/2121.1.144.1 to 21.1.151.25421.1.151.2552,046
5221.1.152.0/2121.1.152.1 to 21.1.159.25421.1.159.2552,046
5321.1.160.0/2121.1.160.1 to 21.1.167.25421.1.167.2552,046
5421.1.168.0/2121.1.168.1 to 21.1.175.25421.1.175.2552,046
5521.1.176.0/2121.1.176.1 to 21.1.183.25421.1.183.2552,046
5621.1.184.0/2121.1.184.1 to 21.1.191.25421.1.191.2552,046
5721.1.192.0/2121.1.192.1 to 21.1.199.25421.1.199.2552,046
5821.1.200.0/2121.1.200.1 to 21.1.207.25421.1.207.2552,046
5921.1.208.0/2121.1.208.1 to 21.1.215.25421.1.215.2552,046
6021.1.216.0/2121.1.216.1 to 21.1.223.25421.1.223.2552,046
6121.1.224.0/2121.1.224.1 to 21.1.231.25421.1.231.2552,046
6221.1.232.0/2121.1.232.1 to 21.1.239.25421.1.239.2552,046
6321.1.240.0/2121.1.240.1 to 21.1.247.25421.1.247.2552,046
6421.1.248.0/2121.1.248.1 to 21.1.255.25421.1.255.2552,046
6521.2.0.0/2121.2.0.1 to 21.2.7.25421.2.7.2552,046
6621.2.8.0/2121.2.8.1 to 21.2.15.25421.2.15.2552,046
6721.2.16.0/2121.2.16.1 to 21.2.23.25421.2.23.2552,046
6821.2.24.0/2121.2.24.1 to 21.2.31.25421.2.31.2552,046
6921.2.32.0/2121.2.32.1 to 21.2.39.25421.2.39.2552,046
7021.2.40.0/2121.2.40.1 to 21.2.47.25421.2.47.2552,046
7121.2.48.0/2121.2.48.1 to 21.2.55.25421.2.55.2552,046
7221.2.56.0/2121.2.56.1 to 21.2.63.25421.2.63.2552,046
7321.2.64.0/2121.2.64.1 to 21.2.71.25421.2.71.2552,046
7421.2.72.0/2121.2.72.1 to 21.2.79.25421.2.79.2552,046
7521.2.80.0/2121.2.80.1 to 21.2.87.25421.2.87.2552,046
7621.2.88.0/2121.2.88.1 to 21.2.95.25421.2.95.2552,046
7721.2.96.0/2121.2.96.1 to 21.2.103.25421.2.103.2552,046
7821.2.104.0/2121.2.104.1 to 21.2.111.25421.2.111.2552,046
7921.2.112.0/2121.2.112.1 to 21.2.119.25421.2.119.2552,046
8021.2.120.0/2121.2.120.1 to 21.2.127.25421.2.127.2552,046
8121.2.128.0/2121.2.128.1 to 21.2.135.25421.2.135.2552,046
8221.2.136.0/2121.2.136.1 to 21.2.143.25421.2.143.2552,046
8321.2.144.0/2121.2.144.1 to 21.2.151.25421.2.151.2552,046
8421.2.152.0/2121.2.152.1 to 21.2.159.25421.2.159.2552,046
8521.2.160.0/2121.2.160.1 to 21.2.167.25421.2.167.2552,046
8621.2.168.0/2121.2.168.1 to 21.2.175.25421.2.175.2552,046
8721.2.176.0/2121.2.176.1 to 21.2.183.25421.2.183.2552,046
8821.2.184.0/2121.2.184.1 to 21.2.191.25421.2.191.2552,046
8921.2.192.0/2121.2.192.1 to 21.2.199.25421.2.199.2552,046
9021.2.200.0/2121.2.200.1 to 21.2.207.25421.2.207.2552,046
9121.2.208.0/2121.2.208.1 to 21.2.215.25421.2.215.2552,046
9221.2.216.0/2121.2.216.1 to 21.2.223.25421.2.223.2552,046
9321.2.224.0/2121.2.224.1 to 21.2.231.25421.2.231.2552,046
9421.2.232.0/2121.2.232.1 to 21.2.239.25421.2.239.2552,046
9521.2.240.0/2121.2.240.1 to 21.2.247.25421.2.247.2552,046
9621.2.248.0/2121.2.248.1 to 21.2.255.25421.2.255.2552,046
9721.3.0.0/2121.3.0.1 to 21.3.7.25421.3.7.2552,046
9821.3.8.0/2121.3.8.1 to 21.3.15.25421.3.15.2552,046
9921.3.16.0/2121.3.16.1 to 21.3.23.25421.3.23.2552,046
10021.3.24.0/2121.3.24.1 to 21.3.31.25421.3.31.2552,046
10121.3.32.0/2121.3.32.1 to 21.3.39.25421.3.39.2552,046
10221.3.40.0/2121.3.40.1 to 21.3.47.25421.3.47.2552,046
10321.3.48.0/2121.3.48.1 to 21.3.55.25421.3.55.2552,046
10421.3.56.0/2121.3.56.1 to 21.3.63.25421.3.63.2552,046
10521.3.64.0/2121.3.64.1 to 21.3.71.25421.3.71.2552,046
10621.3.72.0/2121.3.72.1 to 21.3.79.25421.3.79.2552,046
10721.3.80.0/2121.3.80.1 to 21.3.87.25421.3.87.2552,046
10821.3.88.0/2121.3.88.1 to 21.3.95.25421.3.95.2552,046
10921.3.96.0/2121.3.96.1 to 21.3.103.25421.3.103.2552,046
11021.3.104.0/2121.3.104.1 to 21.3.111.25421.3.111.2552,046
11121.3.112.0/2121.3.112.1 to 21.3.119.25421.3.119.2552,046
11221.3.120.0/2121.3.120.1 to 21.3.127.25421.3.127.2552,046
11321.3.128.0/2121.3.128.1 to 21.3.135.25421.3.135.2552,046
11421.3.136.0/2121.3.136.1 to 21.3.143.25421.3.143.2552,046
11521.3.144.0/2121.3.144.1 to 21.3.151.25421.3.151.2552,046
11621.3.152.0/2121.3.152.1 to 21.3.159.25421.3.159.2552,046
11721.3.160.0/2121.3.160.1 to 21.3.167.25421.3.167.2552,046
11821.3.168.0/2121.3.168.1 to 21.3.175.25421.3.175.2552,046
11921.3.176.0/2121.3.176.1 to 21.3.183.25421.3.183.2552,046
12021.3.184.0/2121.3.184.1 to 21.3.191.25421.3.191.2552,046
12121.3.192.0/2121.3.192.1 to 21.3.199.25421.3.199.2552,046
12221.3.200.0/2121.3.200.1 to 21.3.207.25421.3.207.2552,046
12321.3.208.0/2121.3.208.1 to 21.3.215.25421.3.215.2552,046
12421.3.216.0/2121.3.216.1 to 21.3.223.25421.3.223.2552,046
12521.3.224.0/2121.3.224.1 to 21.3.231.25421.3.231.2552,046
12621.3.232.0/2121.3.232.1 to 21.3.239.25421.3.239.2552,046
12721.3.240.0/2121.3.240.1 to 21.3.247.25421.3.247.2552,046
12821.3.248.0/2121.3.248.1 to 21.3.255.25421.3.255.2552,046
12921.4.0.0/2121.4.0.1 to 21.4.7.25421.4.7.2552,046
13021.4.8.0/2121.4.8.1 to 21.4.15.25421.4.15.2552,046
13121.4.16.0/2121.4.16.1 to 21.4.23.25421.4.23.2552,046
13221.4.24.0/2121.4.24.1 to 21.4.31.25421.4.31.2552,046
13321.4.32.0/2121.4.32.1 to 21.4.39.25421.4.39.2552,046
13421.4.40.0/2121.4.40.1 to 21.4.47.25421.4.47.2552,046
13521.4.48.0/2121.4.48.1 to 21.4.55.25421.4.55.2552,046
13621.4.56.0/2121.4.56.1 to 21.4.63.25421.4.63.2552,046
13721.4.64.0/2121.4.64.1 to 21.4.71.25421.4.71.2552,046
13821.4.72.0/2121.4.72.1 to 21.4.79.25421.4.79.2552,046
13921.4.80.0/2121.4.80.1 to 21.4.87.25421.4.87.2552,046
14021.4.88.0/2121.4.88.1 to 21.4.95.25421.4.95.2552,046
14121.4.96.0/2121.4.96.1 to 21.4.103.25421.4.103.2552,046
14221.4.104.0/2121.4.104.1 to 21.4.111.25421.4.111.2552,046
14321.4.112.0/2121.4.112.1 to 21.4.119.25421.4.119.2552,046
14421.4.120.0/2121.4.120.1 to 21.4.127.25421.4.127.2552,046
14521.4.128.0/2121.4.128.1 to 21.4.135.25421.4.135.2552,046
14621.4.136.0/2121.4.136.1 to 21.4.143.25421.4.143.2552,046
14721.4.144.0/2121.4.144.1 to 21.4.151.25421.4.151.2552,046
14821.4.152.0/2121.4.152.1 to 21.4.159.25421.4.159.2552,046
14921.4.160.0/2121.4.160.1 to 21.4.167.25421.4.167.2552,046
15021.4.168.0/2121.4.168.1 to 21.4.175.25421.4.175.2552,046
15121.4.176.0/2121.4.176.1 to 21.4.183.25421.4.183.2552,046
15221.4.184.0/2121.4.184.1 to 21.4.191.25421.4.191.2552,046
15321.4.192.0/2121.4.192.1 to 21.4.199.25421.4.199.2552,046
15421.4.200.0/2121.4.200.1 to 21.4.207.25421.4.207.2552,046
15521.4.208.0/2121.4.208.1 to 21.4.215.25421.4.215.2552,046
15621.4.216.0/2121.4.216.1 to 21.4.223.25421.4.223.2552,046
15721.4.224.0/2121.4.224.1 to 21.4.231.25421.4.231.2552,046
15821.4.232.0/2121.4.232.1 to 21.4.239.25421.4.239.2552,046
15921.4.240.0/2121.4.240.1 to 21.4.247.25421.4.247.2552,046
16021.4.248.0/2121.4.248.1 to 21.4.255.25421.4.255.2552,046
16121.5.0.0/2121.5.0.1 to 21.5.7.25421.5.7.2552,046
16221.5.8.0/2121.5.8.1 to 21.5.15.25421.5.15.2552,046
16321.5.16.0/2121.5.16.1 to 21.5.23.25421.5.23.2552,046
16421.5.24.0/2121.5.24.1 to 21.5.31.25421.5.31.2552,046
16521.5.32.0/2121.5.32.1 to 21.5.39.25421.5.39.2552,046
16621.5.40.0/2121.5.40.1 to 21.5.47.25421.5.47.2552,046
16721.5.48.0/2121.5.48.1 to 21.5.55.25421.5.55.2552,046
16821.5.56.0/2121.5.56.1 to 21.5.63.25421.5.63.2552,046
16921.5.64.0/2121.5.64.1 to 21.5.71.25421.5.71.2552,046
17021.5.72.0/2121.5.72.1 to 21.5.79.25421.5.79.2552,046
17121.5.80.0/2121.5.80.1 to 21.5.87.25421.5.87.2552,046
17221.5.88.0/2121.5.88.1 to 21.5.95.25421.5.95.2552,046
17321.5.96.0/2121.5.96.1 to 21.5.103.25421.5.103.2552,046
17421.5.104.0/2121.5.104.1 to 21.5.111.25421.5.111.2552,046
17521.5.112.0/2121.5.112.1 to 21.5.119.25421.5.119.2552,046
17621.5.120.0/2121.5.120.1 to 21.5.127.25421.5.127.2552,046
17721.5.128.0/2121.5.128.1 to 21.5.135.25421.5.135.2552,046
17821.5.136.0/2121.5.136.1 to 21.5.143.25421.5.143.2552,046
17921.5.144.0/2121.5.144.1 to 21.5.151.25421.5.151.2552,046
18021.5.152.0/2121.5.152.1 to 21.5.159.25421.5.159.2552,046
18121.5.160.0/2121.5.160.1 to 21.5.167.25421.5.167.2552,046
18221.5.168.0/2121.5.168.1 to 21.5.175.25421.5.175.2552,046
18321.5.176.0/2121.5.176.1 to 21.5.183.25421.5.183.2552,046
18421.5.184.0/2121.5.184.1 to 21.5.191.25421.5.191.2552,046
18521.5.192.0/2121.5.192.1 to 21.5.199.25421.5.199.2552,046
18621.5.200.0/2121.5.200.1 to 21.5.207.25421.5.207.2552,046
18721.5.208.0/2121.5.208.1 to 21.5.215.25421.5.215.2552,046
18821.5.216.0/2121.5.216.1 to 21.5.223.25421.5.223.2552,046
18921.5.224.0/2121.5.224.1 to 21.5.231.25421.5.231.2552,046
19021.5.232.0/2121.5.232.1 to 21.5.239.25421.5.239.2552,046
19121.5.240.0/2121.5.240.1 to 21.5.247.25421.5.247.2552,046
19221.5.248.0/2121.5.248.1 to 21.5.255.25421.5.255.2552,046
19321.6.0.0/2121.6.0.1 to 21.6.7.25421.6.7.2552,046
19421.6.8.0/2121.6.8.1 to 21.6.15.25421.6.15.2552,046
19521.6.16.0/2121.6.16.1 to 21.6.23.25421.6.23.2552,046
19621.6.24.0/2121.6.24.1 to 21.6.31.25421.6.31.2552,046
19721.6.32.0/2121.6.32.1 to 21.6.39.25421.6.39.2552,046
19821.6.40.0/2121.6.40.1 to 21.6.47.25421.6.47.2552,046
19921.6.48.0/2121.6.48.1 to 21.6.55.25421.6.55.2552,046
20021.6.56.0/2121.6.56.1 to 21.6.63.25421.6.63.2552,046
20121.6.64.0/2121.6.64.1 to 21.6.71.25421.6.71.2552,046
20221.6.72.0/2121.6.72.1 to 21.6.79.25421.6.79.2552,046
20321.6.80.0/2121.6.80.1 to 21.6.87.25421.6.87.2552,046
20421.6.88.0/2121.6.88.1 to 21.6.95.25421.6.95.2552,046
20521.6.96.0/2121.6.96.1 to 21.6.103.25421.6.103.2552,046
20621.6.104.0/2121.6.104.1 to 21.6.111.25421.6.111.2552,046
20721.6.112.0/2121.6.112.1 to 21.6.119.25421.6.119.2552,046
20821.6.120.0/2121.6.120.1 to 21.6.127.25421.6.127.2552,046
20921.6.128.0/2121.6.128.1 to 21.6.135.25421.6.135.2552,046
21021.6.136.0/2121.6.136.1 to 21.6.143.25421.6.143.2552,046
21121.6.144.0/2121.6.144.1 to 21.6.151.25421.6.151.2552,046
21221.6.152.0/2121.6.152.1 to 21.6.159.25421.6.159.2552,046
21321.6.160.0/2121.6.160.1 to 21.6.167.25421.6.167.2552,046
21421.6.168.0/2121.6.168.1 to 21.6.175.25421.6.175.2552,046
21521.6.176.0/2121.6.176.1 to 21.6.183.25421.6.183.2552,046
21621.6.184.0/2121.6.184.1 to 21.6.191.25421.6.191.2552,046
21721.6.192.0/2121.6.192.1 to 21.6.199.25421.6.199.2552,046
21821.6.200.0/2121.6.200.1 to 21.6.207.25421.6.207.2552,046
21921.6.208.0/2121.6.208.1 to 21.6.215.25421.6.215.2552,046
22021.6.216.0/2121.6.216.1 to 21.6.223.25421.6.223.2552,046
22121.6.224.0/2121.6.224.1 to 21.6.231.25421.6.231.2552,046
22221.6.232.0/2121.6.232.1 to 21.6.239.25421.6.239.2552,046
22321.6.240.0/2121.6.240.1 to 21.6.247.25421.6.247.2552,046
22421.6.248.0/2121.6.248.1 to 21.6.255.25421.6.255.2552,046
22521.7.0.0/2121.7.0.1 to 21.7.7.25421.7.7.2552,046
22621.7.8.0/2121.7.8.1 to 21.7.15.25421.7.15.2552,046
22721.7.16.0/2121.7.16.1 to 21.7.23.25421.7.23.2552,046
22821.7.24.0/2121.7.24.1 to 21.7.31.25421.7.31.2552,046
22921.7.32.0/2121.7.32.1 to 21.7.39.25421.7.39.2552,046
23021.7.40.0/2121.7.40.1 to 21.7.47.25421.7.47.2552,046
23121.7.48.0/2121.7.48.1 to 21.7.55.25421.7.55.2552,046
23221.7.56.0/2121.7.56.1 to 21.7.63.25421.7.63.2552,046
23321.7.64.0/2121.7.64.1 to 21.7.71.25421.7.71.2552,046
23421.7.72.0/2121.7.72.1 to 21.7.79.25421.7.79.2552,046
23521.7.80.0/2121.7.80.1 to 21.7.87.25421.7.87.2552,046
23621.7.88.0/2121.7.88.1 to 21.7.95.25421.7.95.2552,046
23721.7.96.0/2121.7.96.1 to 21.7.103.25421.7.103.2552,046
23821.7.104.0/2121.7.104.1 to 21.7.111.25421.7.111.2552,046
23921.7.112.0/2121.7.112.1 to 21.7.119.25421.7.119.2552,046
24021.7.120.0/2121.7.120.1 to 21.7.127.25421.7.127.2552,046
24121.7.128.0/2121.7.128.1 to 21.7.135.25421.7.135.2552,046
24221.7.136.0/2121.7.136.1 to 21.7.143.25421.7.143.2552,046
24321.7.144.0/2121.7.144.1 to 21.7.151.25421.7.151.2552,046
24421.7.152.0/2121.7.152.1 to 21.7.159.25421.7.159.2552,046
24521.7.160.0/2121.7.160.1 to 21.7.167.25421.7.167.2552,046
24621.7.168.0/2121.7.168.1 to 21.7.175.25421.7.175.2552,046
24721.7.176.0/2121.7.176.1 to 21.7.183.25421.7.183.2552,046
24821.7.184.0/2121.7.184.1 to 21.7.191.25421.7.191.2552,046
24921.7.192.0/2121.7.192.1 to 21.7.199.25421.7.199.2552,046
25021.7.200.0/2121.7.200.1 to 21.7.207.25421.7.207.2552,046
25121.7.208.0/2121.7.208.1 to 21.7.215.25421.7.215.2552,046
25221.7.216.0/2121.7.216.1 to 21.7.223.25421.7.223.2552,046
25321.7.224.0/2121.7.224.1 to 21.7.231.25421.7.231.2552,046
25421.7.232.0/2121.7.232.1 to 21.7.239.25421.7.239.2552,046
25521.7.240.0/2121.7.240.1 to 21.7.247.25421.7.247.2552,046
25621.7.248.0/2121.7.248.1 to 21.7.255.25421.7.255.2552,046

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.