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.

Network22.0.0.0/7
Usable hosts33,554,430
Subnet mask254.0.0.0
Addresses33,554,432
Network address
22.0.0.0
Broadcast address
23.255.255.255
First usable
22.0.0.1
Last usable
23.255.255.254
Usable hosts
33,554,430 (33,554,432 less the network and broadcast addresses)
Subnet mask
254.0.0.0
Wildcard mask
1.255.255.255 (Cisco ACLs, OSPF)
Prefix length
/7
Type
Public public
Old class
A (default /8)
As numbers
Hex 16000000 · Integer 369098752 to 402653183
Reverse DNS zones
22.in-addr.arpa
23.in-addr.arpa
/7 is not on a 8-bit boundary, so it takes 2 /8 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00010110.00000000.00000000.0000000022.0.0.0
Subnet mask11111110.00000000.00000000.00000000254.0.0.0
Network00010110.00000000.00000000.0000000022.0.0.0
Broadcast00010111.11111111.11111111.1111111123.255.255.255
Split into smaller subnets/14
/8 (2)/9 (4)/10 (8)/11 (16)/12 (32)/13 (64)/14 (128)/15 (256)/16 (512)/17 (1,024)/18 (2,048)/19 (4,096)

22.0.0.0/7 makes 128 subnets of /14.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
122.0.0.0/1422.0.0.1 to 22.3.255.25422.3.255.255262,142
222.4.0.0/1422.4.0.1 to 22.7.255.25422.7.255.255262,142
322.8.0.0/1422.8.0.1 to 22.11.255.25422.11.255.255262,142
422.12.0.0/1422.12.0.1 to 22.15.255.25422.15.255.255262,142
522.16.0.0/1422.16.0.1 to 22.19.255.25422.19.255.255262,142
622.20.0.0/1422.20.0.1 to 22.23.255.25422.23.255.255262,142
722.24.0.0/1422.24.0.1 to 22.27.255.25422.27.255.255262,142
822.28.0.0/1422.28.0.1 to 22.31.255.25422.31.255.255262,142
922.32.0.0/1422.32.0.1 to 22.35.255.25422.35.255.255262,142
1022.36.0.0/1422.36.0.1 to 22.39.255.25422.39.255.255262,142
1122.40.0.0/1422.40.0.1 to 22.43.255.25422.43.255.255262,142
1222.44.0.0/1422.44.0.1 to 22.47.255.25422.47.255.255262,142
1322.48.0.0/1422.48.0.1 to 22.51.255.25422.51.255.255262,142
1422.52.0.0/1422.52.0.1 to 22.55.255.25422.55.255.255262,142
1522.56.0.0/1422.56.0.1 to 22.59.255.25422.59.255.255262,142
1622.60.0.0/1422.60.0.1 to 22.63.255.25422.63.255.255262,142
1722.64.0.0/1422.64.0.1 to 22.67.255.25422.67.255.255262,142
1822.68.0.0/1422.68.0.1 to 22.71.255.25422.71.255.255262,142
1922.72.0.0/1422.72.0.1 to 22.75.255.25422.75.255.255262,142
2022.76.0.0/1422.76.0.1 to 22.79.255.25422.79.255.255262,142
2122.80.0.0/1422.80.0.1 to 22.83.255.25422.83.255.255262,142
2222.84.0.0/1422.84.0.1 to 22.87.255.25422.87.255.255262,142
2322.88.0.0/1422.88.0.1 to 22.91.255.25422.91.255.255262,142
2422.92.0.0/1422.92.0.1 to 22.95.255.25422.95.255.255262,142
2522.96.0.0/1422.96.0.1 to 22.99.255.25422.99.255.255262,142
2622.100.0.0/1422.100.0.1 to 22.103.255.25422.103.255.255262,142
2722.104.0.0/1422.104.0.1 to 22.107.255.25422.107.255.255262,142
2822.108.0.0/1422.108.0.1 to 22.111.255.25422.111.255.255262,142
2922.112.0.0/1422.112.0.1 to 22.115.255.25422.115.255.255262,142
3022.116.0.0/1422.116.0.1 to 22.119.255.25422.119.255.255262,142
3122.120.0.0/1422.120.0.1 to 22.123.255.25422.123.255.255262,142
3222.124.0.0/1422.124.0.1 to 22.127.255.25422.127.255.255262,142
3322.128.0.0/1422.128.0.1 to 22.131.255.25422.131.255.255262,142
3422.132.0.0/1422.132.0.1 to 22.135.255.25422.135.255.255262,142
3522.136.0.0/1422.136.0.1 to 22.139.255.25422.139.255.255262,142
3622.140.0.0/1422.140.0.1 to 22.143.255.25422.143.255.255262,142
3722.144.0.0/1422.144.0.1 to 22.147.255.25422.147.255.255262,142
3822.148.0.0/1422.148.0.1 to 22.151.255.25422.151.255.255262,142
3922.152.0.0/1422.152.0.1 to 22.155.255.25422.155.255.255262,142
4022.156.0.0/1422.156.0.1 to 22.159.255.25422.159.255.255262,142
4122.160.0.0/1422.160.0.1 to 22.163.255.25422.163.255.255262,142
4222.164.0.0/1422.164.0.1 to 22.167.255.25422.167.255.255262,142
4322.168.0.0/1422.168.0.1 to 22.171.255.25422.171.255.255262,142
4422.172.0.0/1422.172.0.1 to 22.175.255.25422.175.255.255262,142
4522.176.0.0/1422.176.0.1 to 22.179.255.25422.179.255.255262,142
4622.180.0.0/1422.180.0.1 to 22.183.255.25422.183.255.255262,142
4722.184.0.0/1422.184.0.1 to 22.187.255.25422.187.255.255262,142
4822.188.0.0/1422.188.0.1 to 22.191.255.25422.191.255.255262,142
4922.192.0.0/1422.192.0.1 to 22.195.255.25422.195.255.255262,142
5022.196.0.0/1422.196.0.1 to 22.199.255.25422.199.255.255262,142
5122.200.0.0/1422.200.0.1 to 22.203.255.25422.203.255.255262,142
5222.204.0.0/1422.204.0.1 to 22.207.255.25422.207.255.255262,142
5322.208.0.0/1422.208.0.1 to 22.211.255.25422.211.255.255262,142
5422.212.0.0/1422.212.0.1 to 22.215.255.25422.215.255.255262,142
5522.216.0.0/1422.216.0.1 to 22.219.255.25422.219.255.255262,142
5622.220.0.0/1422.220.0.1 to 22.223.255.25422.223.255.255262,142
5722.224.0.0/1422.224.0.1 to 22.227.255.25422.227.255.255262,142
5822.228.0.0/1422.228.0.1 to 22.231.255.25422.231.255.255262,142
5922.232.0.0/1422.232.0.1 to 22.235.255.25422.235.255.255262,142
6022.236.0.0/1422.236.0.1 to 22.239.255.25422.239.255.255262,142
6122.240.0.0/1422.240.0.1 to 22.243.255.25422.243.255.255262,142
6222.244.0.0/1422.244.0.1 to 22.247.255.25422.247.255.255262,142
6322.248.0.0/1422.248.0.1 to 22.251.255.25422.251.255.255262,142
6422.252.0.0/1422.252.0.1 to 22.255.255.25422.255.255.255262,142
6523.0.0.0/1423.0.0.1 to 23.3.255.25423.3.255.255262,142
6623.4.0.0/1423.4.0.1 to 23.7.255.25423.7.255.255262,142
6723.8.0.0/1423.8.0.1 to 23.11.255.25423.11.255.255262,142
6823.12.0.0/1423.12.0.1 to 23.15.255.25423.15.255.255262,142
6923.16.0.0/1423.16.0.1 to 23.19.255.25423.19.255.255262,142
7023.20.0.0/1423.20.0.1 to 23.23.255.25423.23.255.255262,142
7123.24.0.0/1423.24.0.1 to 23.27.255.25423.27.255.255262,142
7223.28.0.0/1423.28.0.1 to 23.31.255.25423.31.255.255262,142
7323.32.0.0/1423.32.0.1 to 23.35.255.25423.35.255.255262,142
7423.36.0.0/1423.36.0.1 to 23.39.255.25423.39.255.255262,142
7523.40.0.0/1423.40.0.1 to 23.43.255.25423.43.255.255262,142
7623.44.0.0/1423.44.0.1 to 23.47.255.25423.47.255.255262,142
7723.48.0.0/1423.48.0.1 to 23.51.255.25423.51.255.255262,142
7823.52.0.0/1423.52.0.1 to 23.55.255.25423.55.255.255262,142
7923.56.0.0/1423.56.0.1 to 23.59.255.25423.59.255.255262,142
8023.60.0.0/1423.60.0.1 to 23.63.255.25423.63.255.255262,142
8123.64.0.0/1423.64.0.1 to 23.67.255.25423.67.255.255262,142
8223.68.0.0/1423.68.0.1 to 23.71.255.25423.71.255.255262,142
8323.72.0.0/1423.72.0.1 to 23.75.255.25423.75.255.255262,142
8423.76.0.0/1423.76.0.1 to 23.79.255.25423.79.255.255262,142
8523.80.0.0/1423.80.0.1 to 23.83.255.25423.83.255.255262,142
8623.84.0.0/1423.84.0.1 to 23.87.255.25423.87.255.255262,142
8723.88.0.0/1423.88.0.1 to 23.91.255.25423.91.255.255262,142
8823.92.0.0/1423.92.0.1 to 23.95.255.25423.95.255.255262,142
8923.96.0.0/1423.96.0.1 to 23.99.255.25423.99.255.255262,142
9023.100.0.0/1423.100.0.1 to 23.103.255.25423.103.255.255262,142
9123.104.0.0/1423.104.0.1 to 23.107.255.25423.107.255.255262,142
9223.108.0.0/1423.108.0.1 to 23.111.255.25423.111.255.255262,142
9323.112.0.0/1423.112.0.1 to 23.115.255.25423.115.255.255262,142
9423.116.0.0/1423.116.0.1 to 23.119.255.25423.119.255.255262,142
9523.120.0.0/1423.120.0.1 to 23.123.255.25423.123.255.255262,142
9623.124.0.0/1423.124.0.1 to 23.127.255.25423.127.255.255262,142
9723.128.0.0/1423.128.0.1 to 23.131.255.25423.131.255.255262,142
9823.132.0.0/1423.132.0.1 to 23.135.255.25423.135.255.255262,142
9923.136.0.0/1423.136.0.1 to 23.139.255.25423.139.255.255262,142
10023.140.0.0/1423.140.0.1 to 23.143.255.25423.143.255.255262,142
10123.144.0.0/1423.144.0.1 to 23.147.255.25423.147.255.255262,142
10223.148.0.0/1423.148.0.1 to 23.151.255.25423.151.255.255262,142
10323.152.0.0/1423.152.0.1 to 23.155.255.25423.155.255.255262,142
10423.156.0.0/1423.156.0.1 to 23.159.255.25423.159.255.255262,142
10523.160.0.0/1423.160.0.1 to 23.163.255.25423.163.255.255262,142
10623.164.0.0/1423.164.0.1 to 23.167.255.25423.167.255.255262,142
10723.168.0.0/1423.168.0.1 to 23.171.255.25423.171.255.255262,142
10823.172.0.0/1423.172.0.1 to 23.175.255.25423.175.255.255262,142
10923.176.0.0/1423.176.0.1 to 23.179.255.25423.179.255.255262,142
11023.180.0.0/1423.180.0.1 to 23.183.255.25423.183.255.255262,142
11123.184.0.0/1423.184.0.1 to 23.187.255.25423.187.255.255262,142
11223.188.0.0/1423.188.0.1 to 23.191.255.25423.191.255.255262,142
11323.192.0.0/1423.192.0.1 to 23.195.255.25423.195.255.255262,142
11423.196.0.0/1423.196.0.1 to 23.199.255.25423.199.255.255262,142
11523.200.0.0/1423.200.0.1 to 23.203.255.25423.203.255.255262,142
11623.204.0.0/1423.204.0.1 to 23.207.255.25423.207.255.255262,142
11723.208.0.0/1423.208.0.1 to 23.211.255.25423.211.255.255262,142
11823.212.0.0/1423.212.0.1 to 23.215.255.25423.215.255.255262,142
11923.216.0.0/1423.216.0.1 to 23.219.255.25423.219.255.255262,142
12023.220.0.0/1423.220.0.1 to 23.223.255.25423.223.255.255262,142
12123.224.0.0/1423.224.0.1 to 23.227.255.25423.227.255.255262,142
12223.228.0.0/1423.228.0.1 to 23.231.255.25423.231.255.255262,142
12323.232.0.0/1423.232.0.1 to 23.235.255.25423.235.255.255262,142
12423.236.0.0/1423.236.0.1 to 23.239.255.25423.239.255.255262,142
12523.240.0.0/1423.240.0.1 to 23.243.255.25423.243.255.255262,142
12623.244.0.0/1423.244.0.1 to 23.247.255.25423.247.255.255262,142
12723.248.0.0/1423.248.0.1 to 23.251.255.25423.251.255.255262,142
12823.252.0.0/1423.252.0.1 to 23.255.255.25423.255.255.255262,142

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.