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.

Network44.0.0.0/7
Usable hosts33,554,430
Subnet mask254.0.0.0
Addresses33,554,432
Network address
44.0.0.0
Broadcast address
45.255.255.255
First usable
44.0.0.1
Last usable
45.255.255.254
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 2C000000 · Integer 738197504 to 771751935
Reverse DNS zones
44.in-addr.arpa
45.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
Address00101100.00000000.00000000.0000000044.0.0.0
Subnet mask11111110.00000000.00000000.00000000254.0.0.0
Network00101100.00000000.00000000.0000000044.0.0.0
Broadcast00101101.11111111.11111111.1111111145.255.255.255
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)

44.0.0.0/7 makes 128 subnets of /14.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
144.0.0.0/1444.0.0.1 to 44.3.255.25444.3.255.255262,142
244.4.0.0/1444.4.0.1 to 44.7.255.25444.7.255.255262,142
344.8.0.0/1444.8.0.1 to 44.11.255.25444.11.255.255262,142
444.12.0.0/1444.12.0.1 to 44.15.255.25444.15.255.255262,142
544.16.0.0/1444.16.0.1 to 44.19.255.25444.19.255.255262,142
644.20.0.0/1444.20.0.1 to 44.23.255.25444.23.255.255262,142
744.24.0.0/1444.24.0.1 to 44.27.255.25444.27.255.255262,142
844.28.0.0/1444.28.0.1 to 44.31.255.25444.31.255.255262,142
944.32.0.0/1444.32.0.1 to 44.35.255.25444.35.255.255262,142
1044.36.0.0/1444.36.0.1 to 44.39.255.25444.39.255.255262,142
1144.40.0.0/1444.40.0.1 to 44.43.255.25444.43.255.255262,142
1244.44.0.0/1444.44.0.1 to 44.47.255.25444.47.255.255262,142
1344.48.0.0/1444.48.0.1 to 44.51.255.25444.51.255.255262,142
1444.52.0.0/1444.52.0.1 to 44.55.255.25444.55.255.255262,142
1544.56.0.0/1444.56.0.1 to 44.59.255.25444.59.255.255262,142
1644.60.0.0/1444.60.0.1 to 44.63.255.25444.63.255.255262,142
1744.64.0.0/1444.64.0.1 to 44.67.255.25444.67.255.255262,142
1844.68.0.0/1444.68.0.1 to 44.71.255.25444.71.255.255262,142
1944.72.0.0/1444.72.0.1 to 44.75.255.25444.75.255.255262,142
2044.76.0.0/1444.76.0.1 to 44.79.255.25444.79.255.255262,142
2144.80.0.0/1444.80.0.1 to 44.83.255.25444.83.255.255262,142
2244.84.0.0/1444.84.0.1 to 44.87.255.25444.87.255.255262,142
2344.88.0.0/1444.88.0.1 to 44.91.255.25444.91.255.255262,142
2444.92.0.0/1444.92.0.1 to 44.95.255.25444.95.255.255262,142
2544.96.0.0/1444.96.0.1 to 44.99.255.25444.99.255.255262,142
2644.100.0.0/1444.100.0.1 to 44.103.255.25444.103.255.255262,142
2744.104.0.0/1444.104.0.1 to 44.107.255.25444.107.255.255262,142
2844.108.0.0/1444.108.0.1 to 44.111.255.25444.111.255.255262,142
2944.112.0.0/1444.112.0.1 to 44.115.255.25444.115.255.255262,142
3044.116.0.0/1444.116.0.1 to 44.119.255.25444.119.255.255262,142
3144.120.0.0/1444.120.0.1 to 44.123.255.25444.123.255.255262,142
3244.124.0.0/1444.124.0.1 to 44.127.255.25444.127.255.255262,142
3344.128.0.0/1444.128.0.1 to 44.131.255.25444.131.255.255262,142
3444.132.0.0/1444.132.0.1 to 44.135.255.25444.135.255.255262,142
3544.136.0.0/1444.136.0.1 to 44.139.255.25444.139.255.255262,142
3644.140.0.0/1444.140.0.1 to 44.143.255.25444.143.255.255262,142
3744.144.0.0/1444.144.0.1 to 44.147.255.25444.147.255.255262,142
3844.148.0.0/1444.148.0.1 to 44.151.255.25444.151.255.255262,142
3944.152.0.0/1444.152.0.1 to 44.155.255.25444.155.255.255262,142
4044.156.0.0/1444.156.0.1 to 44.159.255.25444.159.255.255262,142
4144.160.0.0/1444.160.0.1 to 44.163.255.25444.163.255.255262,142
4244.164.0.0/1444.164.0.1 to 44.167.255.25444.167.255.255262,142
4344.168.0.0/1444.168.0.1 to 44.171.255.25444.171.255.255262,142
4444.172.0.0/1444.172.0.1 to 44.175.255.25444.175.255.255262,142
4544.176.0.0/1444.176.0.1 to 44.179.255.25444.179.255.255262,142
4644.180.0.0/1444.180.0.1 to 44.183.255.25444.183.255.255262,142
4744.184.0.0/1444.184.0.1 to 44.187.255.25444.187.255.255262,142
4844.188.0.0/1444.188.0.1 to 44.191.255.25444.191.255.255262,142
4944.192.0.0/1444.192.0.1 to 44.195.255.25444.195.255.255262,142
5044.196.0.0/1444.196.0.1 to 44.199.255.25444.199.255.255262,142
5144.200.0.0/1444.200.0.1 to 44.203.255.25444.203.255.255262,142
5244.204.0.0/1444.204.0.1 to 44.207.255.25444.207.255.255262,142
5344.208.0.0/1444.208.0.1 to 44.211.255.25444.211.255.255262,142
5444.212.0.0/1444.212.0.1 to 44.215.255.25444.215.255.255262,142
5544.216.0.0/1444.216.0.1 to 44.219.255.25444.219.255.255262,142
5644.220.0.0/1444.220.0.1 to 44.223.255.25444.223.255.255262,142
5744.224.0.0/1444.224.0.1 to 44.227.255.25444.227.255.255262,142
5844.228.0.0/1444.228.0.1 to 44.231.255.25444.231.255.255262,142
5944.232.0.0/1444.232.0.1 to 44.235.255.25444.235.255.255262,142
6044.236.0.0/1444.236.0.1 to 44.239.255.25444.239.255.255262,142
6144.240.0.0/1444.240.0.1 to 44.243.255.25444.243.255.255262,142
6244.244.0.0/1444.244.0.1 to 44.247.255.25444.247.255.255262,142
6344.248.0.0/1444.248.0.1 to 44.251.255.25444.251.255.255262,142
6444.252.0.0/1444.252.0.1 to 44.255.255.25444.255.255.255262,142
6545.0.0.0/1445.0.0.1 to 45.3.255.25445.3.255.255262,142
6645.4.0.0/1445.4.0.1 to 45.7.255.25445.7.255.255262,142
6745.8.0.0/1445.8.0.1 to 45.11.255.25445.11.255.255262,142
6845.12.0.0/1445.12.0.1 to 45.15.255.25445.15.255.255262,142
6945.16.0.0/1445.16.0.1 to 45.19.255.25445.19.255.255262,142
7045.20.0.0/1445.20.0.1 to 45.23.255.25445.23.255.255262,142
7145.24.0.0/1445.24.0.1 to 45.27.255.25445.27.255.255262,142
7245.28.0.0/1445.28.0.1 to 45.31.255.25445.31.255.255262,142
7345.32.0.0/1445.32.0.1 to 45.35.255.25445.35.255.255262,142
7445.36.0.0/1445.36.0.1 to 45.39.255.25445.39.255.255262,142
7545.40.0.0/1445.40.0.1 to 45.43.255.25445.43.255.255262,142
7645.44.0.0/1445.44.0.1 to 45.47.255.25445.47.255.255262,142
7745.48.0.0/1445.48.0.1 to 45.51.255.25445.51.255.255262,142
7845.52.0.0/1445.52.0.1 to 45.55.255.25445.55.255.255262,142
7945.56.0.0/1445.56.0.1 to 45.59.255.25445.59.255.255262,142
8045.60.0.0/1445.60.0.1 to 45.63.255.25445.63.255.255262,142
8145.64.0.0/1445.64.0.1 to 45.67.255.25445.67.255.255262,142
8245.68.0.0/1445.68.0.1 to 45.71.255.25445.71.255.255262,142
8345.72.0.0/1445.72.0.1 to 45.75.255.25445.75.255.255262,142
8445.76.0.0/1445.76.0.1 to 45.79.255.25445.79.255.255262,142
8545.80.0.0/1445.80.0.1 to 45.83.255.25445.83.255.255262,142
8645.84.0.0/1445.84.0.1 to 45.87.255.25445.87.255.255262,142
8745.88.0.0/1445.88.0.1 to 45.91.255.25445.91.255.255262,142
8845.92.0.0/1445.92.0.1 to 45.95.255.25445.95.255.255262,142
8945.96.0.0/1445.96.0.1 to 45.99.255.25445.99.255.255262,142
9045.100.0.0/1445.100.0.1 to 45.103.255.25445.103.255.255262,142
9145.104.0.0/1445.104.0.1 to 45.107.255.25445.107.255.255262,142
9245.108.0.0/1445.108.0.1 to 45.111.255.25445.111.255.255262,142
9345.112.0.0/1445.112.0.1 to 45.115.255.25445.115.255.255262,142
9445.116.0.0/1445.116.0.1 to 45.119.255.25445.119.255.255262,142
9545.120.0.0/1445.120.0.1 to 45.123.255.25445.123.255.255262,142
9645.124.0.0/1445.124.0.1 to 45.127.255.25445.127.255.255262,142
9745.128.0.0/1445.128.0.1 to 45.131.255.25445.131.255.255262,142
9845.132.0.0/1445.132.0.1 to 45.135.255.25445.135.255.255262,142
9945.136.0.0/1445.136.0.1 to 45.139.255.25445.139.255.255262,142
10045.140.0.0/1445.140.0.1 to 45.143.255.25445.143.255.255262,142
10145.144.0.0/1445.144.0.1 to 45.147.255.25445.147.255.255262,142
10245.148.0.0/1445.148.0.1 to 45.151.255.25445.151.255.255262,142
10345.152.0.0/1445.152.0.1 to 45.155.255.25445.155.255.255262,142
10445.156.0.0/1445.156.0.1 to 45.159.255.25445.159.255.255262,142
10545.160.0.0/1445.160.0.1 to 45.163.255.25445.163.255.255262,142
10645.164.0.0/1445.164.0.1 to 45.167.255.25445.167.255.255262,142
10745.168.0.0/1445.168.0.1 to 45.171.255.25445.171.255.255262,142
10845.172.0.0/1445.172.0.1 to 45.175.255.25445.175.255.255262,142
10945.176.0.0/1445.176.0.1 to 45.179.255.25445.179.255.255262,142
11045.180.0.0/1445.180.0.1 to 45.183.255.25445.183.255.255262,142
11145.184.0.0/1445.184.0.1 to 45.187.255.25445.187.255.255262,142
11245.188.0.0/1445.188.0.1 to 45.191.255.25445.191.255.255262,142
11345.192.0.0/1445.192.0.1 to 45.195.255.25445.195.255.255262,142
11445.196.0.0/1445.196.0.1 to 45.199.255.25445.199.255.255262,142
11545.200.0.0/1445.200.0.1 to 45.203.255.25445.203.255.255262,142
11645.204.0.0/1445.204.0.1 to 45.207.255.25445.207.255.255262,142
11745.208.0.0/1445.208.0.1 to 45.211.255.25445.211.255.255262,142
11845.212.0.0/1445.212.0.1 to 45.215.255.25445.215.255.255262,142
11945.216.0.0/1445.216.0.1 to 45.219.255.25445.219.255.255262,142
12045.220.0.0/1445.220.0.1 to 45.223.255.25445.223.255.255262,142
12145.224.0.0/1445.224.0.1 to 45.227.255.25445.227.255.255262,142
12245.228.0.0/1445.228.0.1 to 45.231.255.25445.231.255.255262,142
12345.232.0.0/1445.232.0.1 to 45.235.255.25445.235.255.255262,142
12445.236.0.0/1445.236.0.1 to 45.239.255.25445.239.255.255262,142
12545.240.0.0/1445.240.0.1 to 45.243.255.25445.243.255.255262,142
12645.244.0.0/1445.244.0.1 to 45.247.255.25445.247.255.255262,142
12745.248.0.0/1445.248.0.1 to 45.251.255.25445.251.255.255262,142
12845.252.0.0/1445.252.0.1 to 45.255.255.25445.255.255.255262,142

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.