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.

Network68.4.0.0/15
Usable hosts131,070
Subnet mask255.254.0.0
Addresses131,072
Network address
68.4.0.0
Broadcast address
68.5.255.255
First usable
68.4.0.1
Last usable
68.5.255.254
Usable hosts
131,070 (131,072 less the network and broadcast addresses)
Subnet mask
255.254.0.0
Wildcard mask
0.1.255.255 (Cisco ACLs, OSPF)
Prefix length
/15
Type
Public public
Old class
A (default /8)
As numbers
Hex 44040000 · Integer 1141112832 to 1141243903
Reverse DNS zones
4.68.in-addr.arpa
5.68.in-addr.arpa
/15 is not on a 8-bit boundary, so it takes 2 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address01000100.00000100.00000000.0000000068.4.0.0
Subnet mask11111111.11111110.00000000.00000000255.254.0.0
Network01000100.00000100.00000000.0000000068.4.0.0
Broadcast01000100.00000101.11111111.1111111168.5.255.255
Split into smaller subnets/22
/16 (2)/17 (4)/18 (8)/19 (16)/20 (32)/21 (64)/22 (128)/23 (256)/24 (512)/25 (1,024)/26 (2,048)/27 (4,096)

68.4.0.0/15 makes 128 subnets of /22.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
168.4.0.0/2268.4.0.1 to 68.4.3.25468.4.3.2551,022
268.4.4.0/2268.4.4.1 to 68.4.7.25468.4.7.2551,022
368.4.8.0/2268.4.8.1 to 68.4.11.25468.4.11.2551,022
468.4.12.0/2268.4.12.1 to 68.4.15.25468.4.15.2551,022
568.4.16.0/2268.4.16.1 to 68.4.19.25468.4.19.2551,022
668.4.20.0/2268.4.20.1 to 68.4.23.25468.4.23.2551,022
768.4.24.0/2268.4.24.1 to 68.4.27.25468.4.27.2551,022
868.4.28.0/2268.4.28.1 to 68.4.31.25468.4.31.2551,022
968.4.32.0/2268.4.32.1 to 68.4.35.25468.4.35.2551,022
1068.4.36.0/2268.4.36.1 to 68.4.39.25468.4.39.2551,022
1168.4.40.0/2268.4.40.1 to 68.4.43.25468.4.43.2551,022
1268.4.44.0/2268.4.44.1 to 68.4.47.25468.4.47.2551,022
1368.4.48.0/2268.4.48.1 to 68.4.51.25468.4.51.2551,022
1468.4.52.0/2268.4.52.1 to 68.4.55.25468.4.55.2551,022
1568.4.56.0/2268.4.56.1 to 68.4.59.25468.4.59.2551,022
1668.4.60.0/2268.4.60.1 to 68.4.63.25468.4.63.2551,022
1768.4.64.0/2268.4.64.1 to 68.4.67.25468.4.67.2551,022
1868.4.68.0/2268.4.68.1 to 68.4.71.25468.4.71.2551,022
1968.4.72.0/2268.4.72.1 to 68.4.75.25468.4.75.2551,022
2068.4.76.0/2268.4.76.1 to 68.4.79.25468.4.79.2551,022
2168.4.80.0/2268.4.80.1 to 68.4.83.25468.4.83.2551,022
2268.4.84.0/2268.4.84.1 to 68.4.87.25468.4.87.2551,022
2368.4.88.0/2268.4.88.1 to 68.4.91.25468.4.91.2551,022
2468.4.92.0/2268.4.92.1 to 68.4.95.25468.4.95.2551,022
2568.4.96.0/2268.4.96.1 to 68.4.99.25468.4.99.2551,022
2668.4.100.0/2268.4.100.1 to 68.4.103.25468.4.103.2551,022
2768.4.104.0/2268.4.104.1 to 68.4.107.25468.4.107.2551,022
2868.4.108.0/2268.4.108.1 to 68.4.111.25468.4.111.2551,022
2968.4.112.0/2268.4.112.1 to 68.4.115.25468.4.115.2551,022
3068.4.116.0/2268.4.116.1 to 68.4.119.25468.4.119.2551,022
3168.4.120.0/2268.4.120.1 to 68.4.123.25468.4.123.2551,022
3268.4.124.0/2268.4.124.1 to 68.4.127.25468.4.127.2551,022
3368.4.128.0/2268.4.128.1 to 68.4.131.25468.4.131.2551,022
3468.4.132.0/2268.4.132.1 to 68.4.135.25468.4.135.2551,022
3568.4.136.0/2268.4.136.1 to 68.4.139.25468.4.139.2551,022
3668.4.140.0/2268.4.140.1 to 68.4.143.25468.4.143.2551,022
3768.4.144.0/2268.4.144.1 to 68.4.147.25468.4.147.2551,022
3868.4.148.0/2268.4.148.1 to 68.4.151.25468.4.151.2551,022
3968.4.152.0/2268.4.152.1 to 68.4.155.25468.4.155.2551,022
4068.4.156.0/2268.4.156.1 to 68.4.159.25468.4.159.2551,022
4168.4.160.0/2268.4.160.1 to 68.4.163.25468.4.163.2551,022
4268.4.164.0/2268.4.164.1 to 68.4.167.25468.4.167.2551,022
4368.4.168.0/2268.4.168.1 to 68.4.171.25468.4.171.2551,022
4468.4.172.0/2268.4.172.1 to 68.4.175.25468.4.175.2551,022
4568.4.176.0/2268.4.176.1 to 68.4.179.25468.4.179.2551,022
4668.4.180.0/2268.4.180.1 to 68.4.183.25468.4.183.2551,022
4768.4.184.0/2268.4.184.1 to 68.4.187.25468.4.187.2551,022
4868.4.188.0/2268.4.188.1 to 68.4.191.25468.4.191.2551,022
4968.4.192.0/2268.4.192.1 to 68.4.195.25468.4.195.2551,022
5068.4.196.0/2268.4.196.1 to 68.4.199.25468.4.199.2551,022
5168.4.200.0/2268.4.200.1 to 68.4.203.25468.4.203.2551,022
5268.4.204.0/2268.4.204.1 to 68.4.207.25468.4.207.2551,022
5368.4.208.0/2268.4.208.1 to 68.4.211.25468.4.211.2551,022
5468.4.212.0/2268.4.212.1 to 68.4.215.25468.4.215.2551,022
5568.4.216.0/2268.4.216.1 to 68.4.219.25468.4.219.2551,022
5668.4.220.0/2268.4.220.1 to 68.4.223.25468.4.223.2551,022
5768.4.224.0/2268.4.224.1 to 68.4.227.25468.4.227.2551,022
5868.4.228.0/2268.4.228.1 to 68.4.231.25468.4.231.2551,022
5968.4.232.0/2268.4.232.1 to 68.4.235.25468.4.235.2551,022
6068.4.236.0/2268.4.236.1 to 68.4.239.25468.4.239.2551,022
6168.4.240.0/2268.4.240.1 to 68.4.243.25468.4.243.2551,022
6268.4.244.0/2268.4.244.1 to 68.4.247.25468.4.247.2551,022
6368.4.248.0/2268.4.248.1 to 68.4.251.25468.4.251.2551,022
6468.4.252.0/2268.4.252.1 to 68.4.255.25468.4.255.2551,022
6568.5.0.0/2268.5.0.1 to 68.5.3.25468.5.3.2551,022
6668.5.4.0/2268.5.4.1 to 68.5.7.25468.5.7.2551,022
6768.5.8.0/2268.5.8.1 to 68.5.11.25468.5.11.2551,022
6868.5.12.0/2268.5.12.1 to 68.5.15.25468.5.15.2551,022
6968.5.16.0/2268.5.16.1 to 68.5.19.25468.5.19.2551,022
7068.5.20.0/2268.5.20.1 to 68.5.23.25468.5.23.2551,022
7168.5.24.0/2268.5.24.1 to 68.5.27.25468.5.27.2551,022
7268.5.28.0/2268.5.28.1 to 68.5.31.25468.5.31.2551,022
7368.5.32.0/2268.5.32.1 to 68.5.35.25468.5.35.2551,022
7468.5.36.0/2268.5.36.1 to 68.5.39.25468.5.39.2551,022
7568.5.40.0/2268.5.40.1 to 68.5.43.25468.5.43.2551,022
7668.5.44.0/2268.5.44.1 to 68.5.47.25468.5.47.2551,022
7768.5.48.0/2268.5.48.1 to 68.5.51.25468.5.51.2551,022
7868.5.52.0/2268.5.52.1 to 68.5.55.25468.5.55.2551,022
7968.5.56.0/2268.5.56.1 to 68.5.59.25468.5.59.2551,022
8068.5.60.0/2268.5.60.1 to 68.5.63.25468.5.63.2551,022
8168.5.64.0/2268.5.64.1 to 68.5.67.25468.5.67.2551,022
8268.5.68.0/2268.5.68.1 to 68.5.71.25468.5.71.2551,022
8368.5.72.0/2268.5.72.1 to 68.5.75.25468.5.75.2551,022
8468.5.76.0/2268.5.76.1 to 68.5.79.25468.5.79.2551,022
8568.5.80.0/2268.5.80.1 to 68.5.83.25468.5.83.2551,022
8668.5.84.0/2268.5.84.1 to 68.5.87.25468.5.87.2551,022
8768.5.88.0/2268.5.88.1 to 68.5.91.25468.5.91.2551,022
8868.5.92.0/2268.5.92.1 to 68.5.95.25468.5.95.2551,022
8968.5.96.0/2268.5.96.1 to 68.5.99.25468.5.99.2551,022
9068.5.100.0/2268.5.100.1 to 68.5.103.25468.5.103.2551,022
9168.5.104.0/2268.5.104.1 to 68.5.107.25468.5.107.2551,022
9268.5.108.0/2268.5.108.1 to 68.5.111.25468.5.111.2551,022
9368.5.112.0/2268.5.112.1 to 68.5.115.25468.5.115.2551,022
9468.5.116.0/2268.5.116.1 to 68.5.119.25468.5.119.2551,022
9568.5.120.0/2268.5.120.1 to 68.5.123.25468.5.123.2551,022
9668.5.124.0/2268.5.124.1 to 68.5.127.25468.5.127.2551,022
9768.5.128.0/2268.5.128.1 to 68.5.131.25468.5.131.2551,022
9868.5.132.0/2268.5.132.1 to 68.5.135.25468.5.135.2551,022
9968.5.136.0/2268.5.136.1 to 68.5.139.25468.5.139.2551,022
10068.5.140.0/2268.5.140.1 to 68.5.143.25468.5.143.2551,022
10168.5.144.0/2268.5.144.1 to 68.5.147.25468.5.147.2551,022
10268.5.148.0/2268.5.148.1 to 68.5.151.25468.5.151.2551,022
10368.5.152.0/2268.5.152.1 to 68.5.155.25468.5.155.2551,022
10468.5.156.0/2268.5.156.1 to 68.5.159.25468.5.159.2551,022
10568.5.160.0/2268.5.160.1 to 68.5.163.25468.5.163.2551,022
10668.5.164.0/2268.5.164.1 to 68.5.167.25468.5.167.2551,022
10768.5.168.0/2268.5.168.1 to 68.5.171.25468.5.171.2551,022
10868.5.172.0/2268.5.172.1 to 68.5.175.25468.5.175.2551,022
10968.5.176.0/2268.5.176.1 to 68.5.179.25468.5.179.2551,022
11068.5.180.0/2268.5.180.1 to 68.5.183.25468.5.183.2551,022
11168.5.184.0/2268.5.184.1 to 68.5.187.25468.5.187.2551,022
11268.5.188.0/2268.5.188.1 to 68.5.191.25468.5.191.2551,022
11368.5.192.0/2268.5.192.1 to 68.5.195.25468.5.195.2551,022
11468.5.196.0/2268.5.196.1 to 68.5.199.25468.5.199.2551,022
11568.5.200.0/2268.5.200.1 to 68.5.203.25468.5.203.2551,022
11668.5.204.0/2268.5.204.1 to 68.5.207.25468.5.207.2551,022
11768.5.208.0/2268.5.208.1 to 68.5.211.25468.5.211.2551,022
11868.5.212.0/2268.5.212.1 to 68.5.215.25468.5.215.2551,022
11968.5.216.0/2268.5.216.1 to 68.5.219.25468.5.219.2551,022
12068.5.220.0/2268.5.220.1 to 68.5.223.25468.5.223.2551,022
12168.5.224.0/2268.5.224.1 to 68.5.227.25468.5.227.2551,022
12268.5.228.0/2268.5.228.1 to 68.5.231.25468.5.231.2551,022
12368.5.232.0/2268.5.232.1 to 68.5.235.25468.5.235.2551,022
12468.5.236.0/2268.5.236.1 to 68.5.239.25468.5.239.2551,022
12568.5.240.0/2268.5.240.1 to 68.5.243.25468.5.243.2551,022
12668.5.244.0/2268.5.244.1 to 68.5.247.25468.5.247.2551,022
12768.5.248.0/2268.5.248.1 to 68.5.251.25468.5.251.2551,022
12868.5.252.0/2268.5.252.1 to 68.5.255.25468.5.255.2551,022

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.