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.

Network48.2.0.0/16
Usable hosts65,534
Subnet mask255.255.0.0
Addresses65,536
Network address
48.2.0.0
Broadcast address
48.2.255.255
First usable
48.2.0.1
Last usable
48.2.255.254
Usable hosts
65,534 (65,536 less the network and broadcast addresses)
Subnet mask
255.255.0.0
Wildcard mask
0.0.255.255 (Cisco ACLs, OSPF)
Prefix length
/16
Type
Public public
Old class
A (default /8)
As numbers
Hex 30020000 · Integer 805437440 to 805502975
Reverse DNS zone
2.48.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00110000.00000010..00000000.0000000048.2.0.0
Subnet mask11111111.11111111..00000000.00000000255.255.0.0
Network00110000.00000010..00000000.0000000048.2.0.0
Broadcast00110000.00000010..11111111.1111111148.2.255.255
Split into smaller subnets/23
/17 (2)/18 (4)/19 (8)/20 (16)/21 (32)/22 (64)/23 (128)/24 (256)/25 (512)/26 (1,024)/27 (2,048)/28 (4,096)

48.2.0.0/16 makes 128 subnets of /23.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
148.2.0.0/2348.2.0.1 to 48.2.1.25448.2.1.255510
248.2.2.0/2348.2.2.1 to 48.2.3.25448.2.3.255510
348.2.4.0/2348.2.4.1 to 48.2.5.25448.2.5.255510
448.2.6.0/2348.2.6.1 to 48.2.7.25448.2.7.255510
548.2.8.0/2348.2.8.1 to 48.2.9.25448.2.9.255510
648.2.10.0/2348.2.10.1 to 48.2.11.25448.2.11.255510
748.2.12.0/2348.2.12.1 to 48.2.13.25448.2.13.255510
848.2.14.0/2348.2.14.1 to 48.2.15.25448.2.15.255510
948.2.16.0/2348.2.16.1 to 48.2.17.25448.2.17.255510
1048.2.18.0/2348.2.18.1 to 48.2.19.25448.2.19.255510
1148.2.20.0/2348.2.20.1 to 48.2.21.25448.2.21.255510
1248.2.22.0/2348.2.22.1 to 48.2.23.25448.2.23.255510
1348.2.24.0/2348.2.24.1 to 48.2.25.25448.2.25.255510
1448.2.26.0/2348.2.26.1 to 48.2.27.25448.2.27.255510
1548.2.28.0/2348.2.28.1 to 48.2.29.25448.2.29.255510
1648.2.30.0/2348.2.30.1 to 48.2.31.25448.2.31.255510
1748.2.32.0/2348.2.32.1 to 48.2.33.25448.2.33.255510
1848.2.34.0/2348.2.34.1 to 48.2.35.25448.2.35.255510
1948.2.36.0/2348.2.36.1 to 48.2.37.25448.2.37.255510
2048.2.38.0/2348.2.38.1 to 48.2.39.25448.2.39.255510
2148.2.40.0/2348.2.40.1 to 48.2.41.25448.2.41.255510
2248.2.42.0/2348.2.42.1 to 48.2.43.25448.2.43.255510
2348.2.44.0/2348.2.44.1 to 48.2.45.25448.2.45.255510
2448.2.46.0/2348.2.46.1 to 48.2.47.25448.2.47.255510
2548.2.48.0/2348.2.48.1 to 48.2.49.25448.2.49.255510
2648.2.50.0/2348.2.50.1 to 48.2.51.25448.2.51.255510
2748.2.52.0/2348.2.52.1 to 48.2.53.25448.2.53.255510
2848.2.54.0/2348.2.54.1 to 48.2.55.25448.2.55.255510
2948.2.56.0/2348.2.56.1 to 48.2.57.25448.2.57.255510
3048.2.58.0/2348.2.58.1 to 48.2.59.25448.2.59.255510
3148.2.60.0/2348.2.60.1 to 48.2.61.25448.2.61.255510
3248.2.62.0/2348.2.62.1 to 48.2.63.25448.2.63.255510
3348.2.64.0/2348.2.64.1 to 48.2.65.25448.2.65.255510
3448.2.66.0/2348.2.66.1 to 48.2.67.25448.2.67.255510
3548.2.68.0/2348.2.68.1 to 48.2.69.25448.2.69.255510
3648.2.70.0/2348.2.70.1 to 48.2.71.25448.2.71.255510
3748.2.72.0/2348.2.72.1 to 48.2.73.25448.2.73.255510
3848.2.74.0/2348.2.74.1 to 48.2.75.25448.2.75.255510
3948.2.76.0/2348.2.76.1 to 48.2.77.25448.2.77.255510
4048.2.78.0/2348.2.78.1 to 48.2.79.25448.2.79.255510
4148.2.80.0/2348.2.80.1 to 48.2.81.25448.2.81.255510
4248.2.82.0/2348.2.82.1 to 48.2.83.25448.2.83.255510
4348.2.84.0/2348.2.84.1 to 48.2.85.25448.2.85.255510
4448.2.86.0/2348.2.86.1 to 48.2.87.25448.2.87.255510
4548.2.88.0/2348.2.88.1 to 48.2.89.25448.2.89.255510
4648.2.90.0/2348.2.90.1 to 48.2.91.25448.2.91.255510
4748.2.92.0/2348.2.92.1 to 48.2.93.25448.2.93.255510
4848.2.94.0/2348.2.94.1 to 48.2.95.25448.2.95.255510
4948.2.96.0/2348.2.96.1 to 48.2.97.25448.2.97.255510
5048.2.98.0/2348.2.98.1 to 48.2.99.25448.2.99.255510
5148.2.100.0/2348.2.100.1 to 48.2.101.25448.2.101.255510
5248.2.102.0/2348.2.102.1 to 48.2.103.25448.2.103.255510
5348.2.104.0/2348.2.104.1 to 48.2.105.25448.2.105.255510
5448.2.106.0/2348.2.106.1 to 48.2.107.25448.2.107.255510
5548.2.108.0/2348.2.108.1 to 48.2.109.25448.2.109.255510
5648.2.110.0/2348.2.110.1 to 48.2.111.25448.2.111.255510
5748.2.112.0/2348.2.112.1 to 48.2.113.25448.2.113.255510
5848.2.114.0/2348.2.114.1 to 48.2.115.25448.2.115.255510
5948.2.116.0/2348.2.116.1 to 48.2.117.25448.2.117.255510
6048.2.118.0/2348.2.118.1 to 48.2.119.25448.2.119.255510
6148.2.120.0/2348.2.120.1 to 48.2.121.25448.2.121.255510
6248.2.122.0/2348.2.122.1 to 48.2.123.25448.2.123.255510
6348.2.124.0/2348.2.124.1 to 48.2.125.25448.2.125.255510
6448.2.126.0/2348.2.126.1 to 48.2.127.25448.2.127.255510
6548.2.128.0/2348.2.128.1 to 48.2.129.25448.2.129.255510
6648.2.130.0/2348.2.130.1 to 48.2.131.25448.2.131.255510
6748.2.132.0/2348.2.132.1 to 48.2.133.25448.2.133.255510
6848.2.134.0/2348.2.134.1 to 48.2.135.25448.2.135.255510
6948.2.136.0/2348.2.136.1 to 48.2.137.25448.2.137.255510
7048.2.138.0/2348.2.138.1 to 48.2.139.25448.2.139.255510
7148.2.140.0/2348.2.140.1 to 48.2.141.25448.2.141.255510
7248.2.142.0/2348.2.142.1 to 48.2.143.25448.2.143.255510
7348.2.144.0/2348.2.144.1 to 48.2.145.25448.2.145.255510
7448.2.146.0/2348.2.146.1 to 48.2.147.25448.2.147.255510
7548.2.148.0/2348.2.148.1 to 48.2.149.25448.2.149.255510
7648.2.150.0/2348.2.150.1 to 48.2.151.25448.2.151.255510
7748.2.152.0/2348.2.152.1 to 48.2.153.25448.2.153.255510
7848.2.154.0/2348.2.154.1 to 48.2.155.25448.2.155.255510
7948.2.156.0/2348.2.156.1 to 48.2.157.25448.2.157.255510
8048.2.158.0/2348.2.158.1 to 48.2.159.25448.2.159.255510
8148.2.160.0/2348.2.160.1 to 48.2.161.25448.2.161.255510
8248.2.162.0/2348.2.162.1 to 48.2.163.25448.2.163.255510
8348.2.164.0/2348.2.164.1 to 48.2.165.25448.2.165.255510
8448.2.166.0/2348.2.166.1 to 48.2.167.25448.2.167.255510
8548.2.168.0/2348.2.168.1 to 48.2.169.25448.2.169.255510
8648.2.170.0/2348.2.170.1 to 48.2.171.25448.2.171.255510
8748.2.172.0/2348.2.172.1 to 48.2.173.25448.2.173.255510
8848.2.174.0/2348.2.174.1 to 48.2.175.25448.2.175.255510
8948.2.176.0/2348.2.176.1 to 48.2.177.25448.2.177.255510
9048.2.178.0/2348.2.178.1 to 48.2.179.25448.2.179.255510
9148.2.180.0/2348.2.180.1 to 48.2.181.25448.2.181.255510
9248.2.182.0/2348.2.182.1 to 48.2.183.25448.2.183.255510
9348.2.184.0/2348.2.184.1 to 48.2.185.25448.2.185.255510
9448.2.186.0/2348.2.186.1 to 48.2.187.25448.2.187.255510
9548.2.188.0/2348.2.188.1 to 48.2.189.25448.2.189.255510
9648.2.190.0/2348.2.190.1 to 48.2.191.25448.2.191.255510
9748.2.192.0/2348.2.192.1 to 48.2.193.25448.2.193.255510
9848.2.194.0/2348.2.194.1 to 48.2.195.25448.2.195.255510
9948.2.196.0/2348.2.196.1 to 48.2.197.25448.2.197.255510
10048.2.198.0/2348.2.198.1 to 48.2.199.25448.2.199.255510
10148.2.200.0/2348.2.200.1 to 48.2.201.25448.2.201.255510
10248.2.202.0/2348.2.202.1 to 48.2.203.25448.2.203.255510
10348.2.204.0/2348.2.204.1 to 48.2.205.25448.2.205.255510
10448.2.206.0/2348.2.206.1 to 48.2.207.25448.2.207.255510
10548.2.208.0/2348.2.208.1 to 48.2.209.25448.2.209.255510
10648.2.210.0/2348.2.210.1 to 48.2.211.25448.2.211.255510
10748.2.212.0/2348.2.212.1 to 48.2.213.25448.2.213.255510
10848.2.214.0/2348.2.214.1 to 48.2.215.25448.2.215.255510
10948.2.216.0/2348.2.216.1 to 48.2.217.25448.2.217.255510
11048.2.218.0/2348.2.218.1 to 48.2.219.25448.2.219.255510
11148.2.220.0/2348.2.220.1 to 48.2.221.25448.2.221.255510
11248.2.222.0/2348.2.222.1 to 48.2.223.25448.2.223.255510
11348.2.224.0/2348.2.224.1 to 48.2.225.25448.2.225.255510
11448.2.226.0/2348.2.226.1 to 48.2.227.25448.2.227.255510
11548.2.228.0/2348.2.228.1 to 48.2.229.25448.2.229.255510
11648.2.230.0/2348.2.230.1 to 48.2.231.25448.2.231.255510
11748.2.232.0/2348.2.232.1 to 48.2.233.25448.2.233.255510
11848.2.234.0/2348.2.234.1 to 48.2.235.25448.2.235.255510
11948.2.236.0/2348.2.236.1 to 48.2.237.25448.2.237.255510
12048.2.238.0/2348.2.238.1 to 48.2.239.25448.2.239.255510
12148.2.240.0/2348.2.240.1 to 48.2.241.25448.2.241.255510
12248.2.242.0/2348.2.242.1 to 48.2.243.25448.2.243.255510
12348.2.244.0/2348.2.244.1 to 48.2.245.25448.2.245.255510
12448.2.246.0/2348.2.246.1 to 48.2.247.25448.2.247.255510
12548.2.248.0/2348.2.248.1 to 48.2.249.25448.2.249.255510
12648.2.250.0/2348.2.250.1 to 48.2.251.25448.2.251.255510
12748.2.252.0/2348.2.252.1 to 48.2.253.25448.2.253.255510
12848.2.254.0/2348.2.254.1 to 48.2.255.25448.2.255.255510

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.