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.

Network5.240.0.0/12
Usable hosts1,048,574
Subnet mask255.240.0.0
Addresses1,048,576
Network address
5.240.0.0
Broadcast address
5.255.255.255
First usable
5.240.0.1
Last usable
5.255.255.254
Usable hosts
1,048,574 (1,048,576 less the network and broadcast addresses)
Subnet mask
255.240.0.0
Wildcard mask
0.15.255.255 (Cisco ACLs, OSPF)
Prefix length
/12
Type
Public public
Old class
A (default /8)
As numbers
Hex 05F00000 · Integer 99614720 to 100663295
Reverse DNS zones
240.5.in-addr.arpa
241.5.in-addr.arpa
242.5.in-addr.arpa
243.5.in-addr.arpa
244.5.in-addr.arpa
245.5.in-addr.arpa
246.5.in-addr.arpa
247.5.in-addr.arpa
248.5.in-addr.arpa
249.5.in-addr.arpa
250.5.in-addr.arpa
251.5.in-addr.arpa
252.5.in-addr.arpa
253.5.in-addr.arpa
254.5.in-addr.arpa
255.5.in-addr.arpa
/12 is not on a 8-bit boundary, so it takes 16 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00000101.11110000.00000000.000000005.240.0.0
Subnet mask11111111.11110000.00000000.00000000255.240.0.0
Network00000101.11110000.00000000.000000005.240.0.0
Broadcast00000101.11111111.11111111.111111115.255.255.255
Split into smaller subnets/20
/13 (2)/14 (4)/15 (8)/16 (16)/17 (32)/18 (64)/19 (128)/20 (256)/21 (512)/22 (1,024)/23 (2,048)/24 (4,096)

5.240.0.0/12 makes 256 subnets of /20.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
15.240.0.0/205.240.0.1 to 5.240.15.2545.240.15.2554,094
25.240.16.0/205.240.16.1 to 5.240.31.2545.240.31.2554,094
35.240.32.0/205.240.32.1 to 5.240.47.2545.240.47.2554,094
45.240.48.0/205.240.48.1 to 5.240.63.2545.240.63.2554,094
55.240.64.0/205.240.64.1 to 5.240.79.2545.240.79.2554,094
65.240.80.0/205.240.80.1 to 5.240.95.2545.240.95.2554,094
75.240.96.0/205.240.96.1 to 5.240.111.2545.240.111.2554,094
85.240.112.0/205.240.112.1 to 5.240.127.2545.240.127.2554,094
95.240.128.0/205.240.128.1 to 5.240.143.2545.240.143.2554,094
105.240.144.0/205.240.144.1 to 5.240.159.2545.240.159.2554,094
115.240.160.0/205.240.160.1 to 5.240.175.2545.240.175.2554,094
125.240.176.0/205.240.176.1 to 5.240.191.2545.240.191.2554,094
135.240.192.0/205.240.192.1 to 5.240.207.2545.240.207.2554,094
145.240.208.0/205.240.208.1 to 5.240.223.2545.240.223.2554,094
155.240.224.0/205.240.224.1 to 5.240.239.2545.240.239.2554,094
165.240.240.0/205.240.240.1 to 5.240.255.2545.240.255.2554,094
175.241.0.0/205.241.0.1 to 5.241.15.2545.241.15.2554,094
185.241.16.0/205.241.16.1 to 5.241.31.2545.241.31.2554,094
195.241.32.0/205.241.32.1 to 5.241.47.2545.241.47.2554,094
205.241.48.0/205.241.48.1 to 5.241.63.2545.241.63.2554,094
215.241.64.0/205.241.64.1 to 5.241.79.2545.241.79.2554,094
225.241.80.0/205.241.80.1 to 5.241.95.2545.241.95.2554,094
235.241.96.0/205.241.96.1 to 5.241.111.2545.241.111.2554,094
245.241.112.0/205.241.112.1 to 5.241.127.2545.241.127.2554,094
255.241.128.0/205.241.128.1 to 5.241.143.2545.241.143.2554,094
265.241.144.0/205.241.144.1 to 5.241.159.2545.241.159.2554,094
275.241.160.0/205.241.160.1 to 5.241.175.2545.241.175.2554,094
285.241.176.0/205.241.176.1 to 5.241.191.2545.241.191.2554,094
295.241.192.0/205.241.192.1 to 5.241.207.2545.241.207.2554,094
305.241.208.0/205.241.208.1 to 5.241.223.2545.241.223.2554,094
315.241.224.0/205.241.224.1 to 5.241.239.2545.241.239.2554,094
325.241.240.0/205.241.240.1 to 5.241.255.2545.241.255.2554,094
335.242.0.0/205.242.0.1 to 5.242.15.2545.242.15.2554,094
345.242.16.0/205.242.16.1 to 5.242.31.2545.242.31.2554,094
355.242.32.0/205.242.32.1 to 5.242.47.2545.242.47.2554,094
365.242.48.0/205.242.48.1 to 5.242.63.2545.242.63.2554,094
375.242.64.0/205.242.64.1 to 5.242.79.2545.242.79.2554,094
385.242.80.0/205.242.80.1 to 5.242.95.2545.242.95.2554,094
395.242.96.0/205.242.96.1 to 5.242.111.2545.242.111.2554,094
405.242.112.0/205.242.112.1 to 5.242.127.2545.242.127.2554,094
415.242.128.0/205.242.128.1 to 5.242.143.2545.242.143.2554,094
425.242.144.0/205.242.144.1 to 5.242.159.2545.242.159.2554,094
435.242.160.0/205.242.160.1 to 5.242.175.2545.242.175.2554,094
445.242.176.0/205.242.176.1 to 5.242.191.2545.242.191.2554,094
455.242.192.0/205.242.192.1 to 5.242.207.2545.242.207.2554,094
465.242.208.0/205.242.208.1 to 5.242.223.2545.242.223.2554,094
475.242.224.0/205.242.224.1 to 5.242.239.2545.242.239.2554,094
485.242.240.0/205.242.240.1 to 5.242.255.2545.242.255.2554,094
495.243.0.0/205.243.0.1 to 5.243.15.2545.243.15.2554,094
505.243.16.0/205.243.16.1 to 5.243.31.2545.243.31.2554,094
515.243.32.0/205.243.32.1 to 5.243.47.2545.243.47.2554,094
525.243.48.0/205.243.48.1 to 5.243.63.2545.243.63.2554,094
535.243.64.0/205.243.64.1 to 5.243.79.2545.243.79.2554,094
545.243.80.0/205.243.80.1 to 5.243.95.2545.243.95.2554,094
555.243.96.0/205.243.96.1 to 5.243.111.2545.243.111.2554,094
565.243.112.0/205.243.112.1 to 5.243.127.2545.243.127.2554,094
575.243.128.0/205.243.128.1 to 5.243.143.2545.243.143.2554,094
585.243.144.0/205.243.144.1 to 5.243.159.2545.243.159.2554,094
595.243.160.0/205.243.160.1 to 5.243.175.2545.243.175.2554,094
605.243.176.0/205.243.176.1 to 5.243.191.2545.243.191.2554,094
615.243.192.0/205.243.192.1 to 5.243.207.2545.243.207.2554,094
625.243.208.0/205.243.208.1 to 5.243.223.2545.243.223.2554,094
635.243.224.0/205.243.224.1 to 5.243.239.2545.243.239.2554,094
645.243.240.0/205.243.240.1 to 5.243.255.2545.243.255.2554,094
655.244.0.0/205.244.0.1 to 5.244.15.2545.244.15.2554,094
665.244.16.0/205.244.16.1 to 5.244.31.2545.244.31.2554,094
675.244.32.0/205.244.32.1 to 5.244.47.2545.244.47.2554,094
685.244.48.0/205.244.48.1 to 5.244.63.2545.244.63.2554,094
695.244.64.0/205.244.64.1 to 5.244.79.2545.244.79.2554,094
705.244.80.0/205.244.80.1 to 5.244.95.2545.244.95.2554,094
715.244.96.0/205.244.96.1 to 5.244.111.2545.244.111.2554,094
725.244.112.0/205.244.112.1 to 5.244.127.2545.244.127.2554,094
735.244.128.0/205.244.128.1 to 5.244.143.2545.244.143.2554,094
745.244.144.0/205.244.144.1 to 5.244.159.2545.244.159.2554,094
755.244.160.0/205.244.160.1 to 5.244.175.2545.244.175.2554,094
765.244.176.0/205.244.176.1 to 5.244.191.2545.244.191.2554,094
775.244.192.0/205.244.192.1 to 5.244.207.2545.244.207.2554,094
785.244.208.0/205.244.208.1 to 5.244.223.2545.244.223.2554,094
795.244.224.0/205.244.224.1 to 5.244.239.2545.244.239.2554,094
805.244.240.0/205.244.240.1 to 5.244.255.2545.244.255.2554,094
815.245.0.0/205.245.0.1 to 5.245.15.2545.245.15.2554,094
825.245.16.0/205.245.16.1 to 5.245.31.2545.245.31.2554,094
835.245.32.0/205.245.32.1 to 5.245.47.2545.245.47.2554,094
845.245.48.0/205.245.48.1 to 5.245.63.2545.245.63.2554,094
855.245.64.0/205.245.64.1 to 5.245.79.2545.245.79.2554,094
865.245.80.0/205.245.80.1 to 5.245.95.2545.245.95.2554,094
875.245.96.0/205.245.96.1 to 5.245.111.2545.245.111.2554,094
885.245.112.0/205.245.112.1 to 5.245.127.2545.245.127.2554,094
895.245.128.0/205.245.128.1 to 5.245.143.2545.245.143.2554,094
905.245.144.0/205.245.144.1 to 5.245.159.2545.245.159.2554,094
915.245.160.0/205.245.160.1 to 5.245.175.2545.245.175.2554,094
925.245.176.0/205.245.176.1 to 5.245.191.2545.245.191.2554,094
935.245.192.0/205.245.192.1 to 5.245.207.2545.245.207.2554,094
945.245.208.0/205.245.208.1 to 5.245.223.2545.245.223.2554,094
955.245.224.0/205.245.224.1 to 5.245.239.2545.245.239.2554,094
965.245.240.0/205.245.240.1 to 5.245.255.2545.245.255.2554,094
975.246.0.0/205.246.0.1 to 5.246.15.2545.246.15.2554,094
985.246.16.0/205.246.16.1 to 5.246.31.2545.246.31.2554,094
995.246.32.0/205.246.32.1 to 5.246.47.2545.246.47.2554,094
1005.246.48.0/205.246.48.1 to 5.246.63.2545.246.63.2554,094
1015.246.64.0/205.246.64.1 to 5.246.79.2545.246.79.2554,094
1025.246.80.0/205.246.80.1 to 5.246.95.2545.246.95.2554,094
1035.246.96.0/205.246.96.1 to 5.246.111.2545.246.111.2554,094
1045.246.112.0/205.246.112.1 to 5.246.127.2545.246.127.2554,094
1055.246.128.0/205.246.128.1 to 5.246.143.2545.246.143.2554,094
1065.246.144.0/205.246.144.1 to 5.246.159.2545.246.159.2554,094
1075.246.160.0/205.246.160.1 to 5.246.175.2545.246.175.2554,094
1085.246.176.0/205.246.176.1 to 5.246.191.2545.246.191.2554,094
1095.246.192.0/205.246.192.1 to 5.246.207.2545.246.207.2554,094
1105.246.208.0/205.246.208.1 to 5.246.223.2545.246.223.2554,094
1115.246.224.0/205.246.224.1 to 5.246.239.2545.246.239.2554,094
1125.246.240.0/205.246.240.1 to 5.246.255.2545.246.255.2554,094
1135.247.0.0/205.247.0.1 to 5.247.15.2545.247.15.2554,094
1145.247.16.0/205.247.16.1 to 5.247.31.2545.247.31.2554,094
1155.247.32.0/205.247.32.1 to 5.247.47.2545.247.47.2554,094
1165.247.48.0/205.247.48.1 to 5.247.63.2545.247.63.2554,094
1175.247.64.0/205.247.64.1 to 5.247.79.2545.247.79.2554,094
1185.247.80.0/205.247.80.1 to 5.247.95.2545.247.95.2554,094
1195.247.96.0/205.247.96.1 to 5.247.111.2545.247.111.2554,094
1205.247.112.0/205.247.112.1 to 5.247.127.2545.247.127.2554,094
1215.247.128.0/205.247.128.1 to 5.247.143.2545.247.143.2554,094
1225.247.144.0/205.247.144.1 to 5.247.159.2545.247.159.2554,094
1235.247.160.0/205.247.160.1 to 5.247.175.2545.247.175.2554,094
1245.247.176.0/205.247.176.1 to 5.247.191.2545.247.191.2554,094
1255.247.192.0/205.247.192.1 to 5.247.207.2545.247.207.2554,094
1265.247.208.0/205.247.208.1 to 5.247.223.2545.247.223.2554,094
1275.247.224.0/205.247.224.1 to 5.247.239.2545.247.239.2554,094
1285.247.240.0/205.247.240.1 to 5.247.255.2545.247.255.2554,094
1295.248.0.0/205.248.0.1 to 5.248.15.2545.248.15.2554,094
1305.248.16.0/205.248.16.1 to 5.248.31.2545.248.31.2554,094
1315.248.32.0/205.248.32.1 to 5.248.47.2545.248.47.2554,094
1325.248.48.0/205.248.48.1 to 5.248.63.2545.248.63.2554,094
1335.248.64.0/205.248.64.1 to 5.248.79.2545.248.79.2554,094
1345.248.80.0/205.248.80.1 to 5.248.95.2545.248.95.2554,094
1355.248.96.0/205.248.96.1 to 5.248.111.2545.248.111.2554,094
1365.248.112.0/205.248.112.1 to 5.248.127.2545.248.127.2554,094
1375.248.128.0/205.248.128.1 to 5.248.143.2545.248.143.2554,094
1385.248.144.0/205.248.144.1 to 5.248.159.2545.248.159.2554,094
1395.248.160.0/205.248.160.1 to 5.248.175.2545.248.175.2554,094
1405.248.176.0/205.248.176.1 to 5.248.191.2545.248.191.2554,094
1415.248.192.0/205.248.192.1 to 5.248.207.2545.248.207.2554,094
1425.248.208.0/205.248.208.1 to 5.248.223.2545.248.223.2554,094
1435.248.224.0/205.248.224.1 to 5.248.239.2545.248.239.2554,094
1445.248.240.0/205.248.240.1 to 5.248.255.2545.248.255.2554,094
1455.249.0.0/205.249.0.1 to 5.249.15.2545.249.15.2554,094
1465.249.16.0/205.249.16.1 to 5.249.31.2545.249.31.2554,094
1475.249.32.0/205.249.32.1 to 5.249.47.2545.249.47.2554,094
1485.249.48.0/205.249.48.1 to 5.249.63.2545.249.63.2554,094
1495.249.64.0/205.249.64.1 to 5.249.79.2545.249.79.2554,094
1505.249.80.0/205.249.80.1 to 5.249.95.2545.249.95.2554,094
1515.249.96.0/205.249.96.1 to 5.249.111.2545.249.111.2554,094
1525.249.112.0/205.249.112.1 to 5.249.127.2545.249.127.2554,094
1535.249.128.0/205.249.128.1 to 5.249.143.2545.249.143.2554,094
1545.249.144.0/205.249.144.1 to 5.249.159.2545.249.159.2554,094
1555.249.160.0/205.249.160.1 to 5.249.175.2545.249.175.2554,094
1565.249.176.0/205.249.176.1 to 5.249.191.2545.249.191.2554,094
1575.249.192.0/205.249.192.1 to 5.249.207.2545.249.207.2554,094
1585.249.208.0/205.249.208.1 to 5.249.223.2545.249.223.2554,094
1595.249.224.0/205.249.224.1 to 5.249.239.2545.249.239.2554,094
1605.249.240.0/205.249.240.1 to 5.249.255.2545.249.255.2554,094
1615.250.0.0/205.250.0.1 to 5.250.15.2545.250.15.2554,094
1625.250.16.0/205.250.16.1 to 5.250.31.2545.250.31.2554,094
1635.250.32.0/205.250.32.1 to 5.250.47.2545.250.47.2554,094
1645.250.48.0/205.250.48.1 to 5.250.63.2545.250.63.2554,094
1655.250.64.0/205.250.64.1 to 5.250.79.2545.250.79.2554,094
1665.250.80.0/205.250.80.1 to 5.250.95.2545.250.95.2554,094
1675.250.96.0/205.250.96.1 to 5.250.111.2545.250.111.2554,094
1685.250.112.0/205.250.112.1 to 5.250.127.2545.250.127.2554,094
1695.250.128.0/205.250.128.1 to 5.250.143.2545.250.143.2554,094
1705.250.144.0/205.250.144.1 to 5.250.159.2545.250.159.2554,094
1715.250.160.0/205.250.160.1 to 5.250.175.2545.250.175.2554,094
1725.250.176.0/205.250.176.1 to 5.250.191.2545.250.191.2554,094
1735.250.192.0/205.250.192.1 to 5.250.207.2545.250.207.2554,094
1745.250.208.0/205.250.208.1 to 5.250.223.2545.250.223.2554,094
1755.250.224.0/205.250.224.1 to 5.250.239.2545.250.239.2554,094
1765.250.240.0/205.250.240.1 to 5.250.255.2545.250.255.2554,094
1775.251.0.0/205.251.0.1 to 5.251.15.2545.251.15.2554,094
1785.251.16.0/205.251.16.1 to 5.251.31.2545.251.31.2554,094
1795.251.32.0/205.251.32.1 to 5.251.47.2545.251.47.2554,094
1805.251.48.0/205.251.48.1 to 5.251.63.2545.251.63.2554,094
1815.251.64.0/205.251.64.1 to 5.251.79.2545.251.79.2554,094
1825.251.80.0/205.251.80.1 to 5.251.95.2545.251.95.2554,094
1835.251.96.0/205.251.96.1 to 5.251.111.2545.251.111.2554,094
1845.251.112.0/205.251.112.1 to 5.251.127.2545.251.127.2554,094
1855.251.128.0/205.251.128.1 to 5.251.143.2545.251.143.2554,094
1865.251.144.0/205.251.144.1 to 5.251.159.2545.251.159.2554,094
1875.251.160.0/205.251.160.1 to 5.251.175.2545.251.175.2554,094
1885.251.176.0/205.251.176.1 to 5.251.191.2545.251.191.2554,094
1895.251.192.0/205.251.192.1 to 5.251.207.2545.251.207.2554,094
1905.251.208.0/205.251.208.1 to 5.251.223.2545.251.223.2554,094
1915.251.224.0/205.251.224.1 to 5.251.239.2545.251.239.2554,094
1925.251.240.0/205.251.240.1 to 5.251.255.2545.251.255.2554,094
1935.252.0.0/205.252.0.1 to 5.252.15.2545.252.15.2554,094
1945.252.16.0/205.252.16.1 to 5.252.31.2545.252.31.2554,094
1955.252.32.0/205.252.32.1 to 5.252.47.2545.252.47.2554,094
1965.252.48.0/205.252.48.1 to 5.252.63.2545.252.63.2554,094
1975.252.64.0/205.252.64.1 to 5.252.79.2545.252.79.2554,094
1985.252.80.0/205.252.80.1 to 5.252.95.2545.252.95.2554,094
1995.252.96.0/205.252.96.1 to 5.252.111.2545.252.111.2554,094
2005.252.112.0/205.252.112.1 to 5.252.127.2545.252.127.2554,094
2015.252.128.0/205.252.128.1 to 5.252.143.2545.252.143.2554,094
2025.252.144.0/205.252.144.1 to 5.252.159.2545.252.159.2554,094
2035.252.160.0/205.252.160.1 to 5.252.175.2545.252.175.2554,094
2045.252.176.0/205.252.176.1 to 5.252.191.2545.252.191.2554,094
2055.252.192.0/205.252.192.1 to 5.252.207.2545.252.207.2554,094
2065.252.208.0/205.252.208.1 to 5.252.223.2545.252.223.2554,094
2075.252.224.0/205.252.224.1 to 5.252.239.2545.252.239.2554,094
2085.252.240.0/205.252.240.1 to 5.252.255.2545.252.255.2554,094
2095.253.0.0/205.253.0.1 to 5.253.15.2545.253.15.2554,094
2105.253.16.0/205.253.16.1 to 5.253.31.2545.253.31.2554,094
2115.253.32.0/205.253.32.1 to 5.253.47.2545.253.47.2554,094
2125.253.48.0/205.253.48.1 to 5.253.63.2545.253.63.2554,094
2135.253.64.0/205.253.64.1 to 5.253.79.2545.253.79.2554,094
2145.253.80.0/205.253.80.1 to 5.253.95.2545.253.95.2554,094
2155.253.96.0/205.253.96.1 to 5.253.111.2545.253.111.2554,094
2165.253.112.0/205.253.112.1 to 5.253.127.2545.253.127.2554,094
2175.253.128.0/205.253.128.1 to 5.253.143.2545.253.143.2554,094
2185.253.144.0/205.253.144.1 to 5.253.159.2545.253.159.2554,094
2195.253.160.0/205.253.160.1 to 5.253.175.2545.253.175.2554,094
2205.253.176.0/205.253.176.1 to 5.253.191.2545.253.191.2554,094
2215.253.192.0/205.253.192.1 to 5.253.207.2545.253.207.2554,094
2225.253.208.0/205.253.208.1 to 5.253.223.2545.253.223.2554,094
2235.253.224.0/205.253.224.1 to 5.253.239.2545.253.239.2554,094
2245.253.240.0/205.253.240.1 to 5.253.255.2545.253.255.2554,094
2255.254.0.0/205.254.0.1 to 5.254.15.2545.254.15.2554,094
2265.254.16.0/205.254.16.1 to 5.254.31.2545.254.31.2554,094
2275.254.32.0/205.254.32.1 to 5.254.47.2545.254.47.2554,094
2285.254.48.0/205.254.48.1 to 5.254.63.2545.254.63.2554,094
2295.254.64.0/205.254.64.1 to 5.254.79.2545.254.79.2554,094
2305.254.80.0/205.254.80.1 to 5.254.95.2545.254.95.2554,094
2315.254.96.0/205.254.96.1 to 5.254.111.2545.254.111.2554,094
2325.254.112.0/205.254.112.1 to 5.254.127.2545.254.127.2554,094
2335.254.128.0/205.254.128.1 to 5.254.143.2545.254.143.2554,094
2345.254.144.0/205.254.144.1 to 5.254.159.2545.254.159.2554,094
2355.254.160.0/205.254.160.1 to 5.254.175.2545.254.175.2554,094
2365.254.176.0/205.254.176.1 to 5.254.191.2545.254.191.2554,094
2375.254.192.0/205.254.192.1 to 5.254.207.2545.254.207.2554,094
2385.254.208.0/205.254.208.1 to 5.254.223.2545.254.223.2554,094
2395.254.224.0/205.254.224.1 to 5.254.239.2545.254.239.2554,094
2405.254.240.0/205.254.240.1 to 5.254.255.2545.254.255.2554,094
2415.255.0.0/205.255.0.1 to 5.255.15.2545.255.15.2554,094
2425.255.16.0/205.255.16.1 to 5.255.31.2545.255.31.2554,094
2435.255.32.0/205.255.32.1 to 5.255.47.2545.255.47.2554,094
2445.255.48.0/205.255.48.1 to 5.255.63.2545.255.63.2554,094
2455.255.64.0/205.255.64.1 to 5.255.79.2545.255.79.2554,094
2465.255.80.0/205.255.80.1 to 5.255.95.2545.255.95.2554,094
2475.255.96.0/205.255.96.1 to 5.255.111.2545.255.111.2554,094
2485.255.112.0/205.255.112.1 to 5.255.127.2545.255.127.2554,094
2495.255.128.0/205.255.128.1 to 5.255.143.2545.255.143.2554,094
2505.255.144.0/205.255.144.1 to 5.255.159.2545.255.159.2554,094
2515.255.160.0/205.255.160.1 to 5.255.175.2545.255.175.2554,094
2525.255.176.0/205.255.176.1 to 5.255.191.2545.255.191.2554,094
2535.255.192.0/205.255.192.1 to 5.255.207.2545.255.207.2554,094
2545.255.208.0/205.255.208.1 to 5.255.223.2545.255.223.2554,094
2555.255.224.0/205.255.224.1 to 5.255.239.2545.255.239.2554,094
2565.255.240.0/205.255.240.1 to 5.255.255.2545.255.255.2554,094

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.