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.

Network11.0.0.0/8
Usable hosts16,777,214
Subnet mask255.0.0.0
Addresses16,777,216
Network address
11.0.0.0
Broadcast address
11.255.255.255
First usable
11.0.0.1
Last usable
11.255.255.254
Usable hosts
16,777,214 (16,777,216 less the network and broadcast addresses)
Subnet mask
255.0.0.0
Wildcard mask
0.255.255.255 (Cisco ACLs, OSPF)
Prefix length
/8
Type
Public public
Old class
A (default /8)
As numbers
Hex 0B000000 · Integer 184549376 to 201326591
Reverse DNS zone
11.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00001011..00000000.00000000.0000000011.0.0.0
Subnet mask11111111..00000000.00000000.00000000255.0.0.0
Network00001011..00000000.00000000.0000000011.0.0.0
Broadcast00001011..11111111.11111111.1111111111.255.255.255
Split into smaller subnets/15
/9 (2)/10 (4)/11 (8)/12 (16)/13 (32)/14 (64)/15 (128)/16 (256)/17 (512)/18 (1,024)/19 (2,048)/20 (4,096)

11.0.0.0/8 makes 128 subnets of /15.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
111.0.0.0/1511.0.0.1 to 11.1.255.25411.1.255.255131,070
211.2.0.0/1511.2.0.1 to 11.3.255.25411.3.255.255131,070
311.4.0.0/1511.4.0.1 to 11.5.255.25411.5.255.255131,070
411.6.0.0/1511.6.0.1 to 11.7.255.25411.7.255.255131,070
511.8.0.0/1511.8.0.1 to 11.9.255.25411.9.255.255131,070
611.10.0.0/1511.10.0.1 to 11.11.255.25411.11.255.255131,070
711.12.0.0/1511.12.0.1 to 11.13.255.25411.13.255.255131,070
811.14.0.0/1511.14.0.1 to 11.15.255.25411.15.255.255131,070
911.16.0.0/1511.16.0.1 to 11.17.255.25411.17.255.255131,070
1011.18.0.0/1511.18.0.1 to 11.19.255.25411.19.255.255131,070
1111.20.0.0/1511.20.0.1 to 11.21.255.25411.21.255.255131,070
1211.22.0.0/1511.22.0.1 to 11.23.255.25411.23.255.255131,070
1311.24.0.0/1511.24.0.1 to 11.25.255.25411.25.255.255131,070
1411.26.0.0/1511.26.0.1 to 11.27.255.25411.27.255.255131,070
1511.28.0.0/1511.28.0.1 to 11.29.255.25411.29.255.255131,070
1611.30.0.0/1511.30.0.1 to 11.31.255.25411.31.255.255131,070
1711.32.0.0/1511.32.0.1 to 11.33.255.25411.33.255.255131,070
1811.34.0.0/1511.34.0.1 to 11.35.255.25411.35.255.255131,070
1911.36.0.0/1511.36.0.1 to 11.37.255.25411.37.255.255131,070
2011.38.0.0/1511.38.0.1 to 11.39.255.25411.39.255.255131,070
2111.40.0.0/1511.40.0.1 to 11.41.255.25411.41.255.255131,070
2211.42.0.0/1511.42.0.1 to 11.43.255.25411.43.255.255131,070
2311.44.0.0/1511.44.0.1 to 11.45.255.25411.45.255.255131,070
2411.46.0.0/1511.46.0.1 to 11.47.255.25411.47.255.255131,070
2511.48.0.0/1511.48.0.1 to 11.49.255.25411.49.255.255131,070
2611.50.0.0/1511.50.0.1 to 11.51.255.25411.51.255.255131,070
2711.52.0.0/1511.52.0.1 to 11.53.255.25411.53.255.255131,070
2811.54.0.0/1511.54.0.1 to 11.55.255.25411.55.255.255131,070
2911.56.0.0/1511.56.0.1 to 11.57.255.25411.57.255.255131,070
3011.58.0.0/1511.58.0.1 to 11.59.255.25411.59.255.255131,070
3111.60.0.0/1511.60.0.1 to 11.61.255.25411.61.255.255131,070
3211.62.0.0/1511.62.0.1 to 11.63.255.25411.63.255.255131,070
3311.64.0.0/1511.64.0.1 to 11.65.255.25411.65.255.255131,070
3411.66.0.0/1511.66.0.1 to 11.67.255.25411.67.255.255131,070
3511.68.0.0/1511.68.0.1 to 11.69.255.25411.69.255.255131,070
3611.70.0.0/1511.70.0.1 to 11.71.255.25411.71.255.255131,070
3711.72.0.0/1511.72.0.1 to 11.73.255.25411.73.255.255131,070
3811.74.0.0/1511.74.0.1 to 11.75.255.25411.75.255.255131,070
3911.76.0.0/1511.76.0.1 to 11.77.255.25411.77.255.255131,070
4011.78.0.0/1511.78.0.1 to 11.79.255.25411.79.255.255131,070
4111.80.0.0/1511.80.0.1 to 11.81.255.25411.81.255.255131,070
4211.82.0.0/1511.82.0.1 to 11.83.255.25411.83.255.255131,070
4311.84.0.0/1511.84.0.1 to 11.85.255.25411.85.255.255131,070
4411.86.0.0/1511.86.0.1 to 11.87.255.25411.87.255.255131,070
4511.88.0.0/1511.88.0.1 to 11.89.255.25411.89.255.255131,070
4611.90.0.0/1511.90.0.1 to 11.91.255.25411.91.255.255131,070
4711.92.0.0/1511.92.0.1 to 11.93.255.25411.93.255.255131,070
4811.94.0.0/1511.94.0.1 to 11.95.255.25411.95.255.255131,070
4911.96.0.0/1511.96.0.1 to 11.97.255.25411.97.255.255131,070
5011.98.0.0/1511.98.0.1 to 11.99.255.25411.99.255.255131,070
5111.100.0.0/1511.100.0.1 to 11.101.255.25411.101.255.255131,070
5211.102.0.0/1511.102.0.1 to 11.103.255.25411.103.255.255131,070
5311.104.0.0/1511.104.0.1 to 11.105.255.25411.105.255.255131,070
5411.106.0.0/1511.106.0.1 to 11.107.255.25411.107.255.255131,070
5511.108.0.0/1511.108.0.1 to 11.109.255.25411.109.255.255131,070
5611.110.0.0/1511.110.0.1 to 11.111.255.25411.111.255.255131,070
5711.112.0.0/1511.112.0.1 to 11.113.255.25411.113.255.255131,070
5811.114.0.0/1511.114.0.1 to 11.115.255.25411.115.255.255131,070
5911.116.0.0/1511.116.0.1 to 11.117.255.25411.117.255.255131,070
6011.118.0.0/1511.118.0.1 to 11.119.255.25411.119.255.255131,070
6111.120.0.0/1511.120.0.1 to 11.121.255.25411.121.255.255131,070
6211.122.0.0/1511.122.0.1 to 11.123.255.25411.123.255.255131,070
6311.124.0.0/1511.124.0.1 to 11.125.255.25411.125.255.255131,070
6411.126.0.0/1511.126.0.1 to 11.127.255.25411.127.255.255131,070
6511.128.0.0/1511.128.0.1 to 11.129.255.25411.129.255.255131,070
6611.130.0.0/1511.130.0.1 to 11.131.255.25411.131.255.255131,070
6711.132.0.0/1511.132.0.1 to 11.133.255.25411.133.255.255131,070
6811.134.0.0/1511.134.0.1 to 11.135.255.25411.135.255.255131,070
6911.136.0.0/1511.136.0.1 to 11.137.255.25411.137.255.255131,070
7011.138.0.0/1511.138.0.1 to 11.139.255.25411.139.255.255131,070
7111.140.0.0/1511.140.0.1 to 11.141.255.25411.141.255.255131,070
7211.142.0.0/1511.142.0.1 to 11.143.255.25411.143.255.255131,070
7311.144.0.0/1511.144.0.1 to 11.145.255.25411.145.255.255131,070
7411.146.0.0/1511.146.0.1 to 11.147.255.25411.147.255.255131,070
7511.148.0.0/1511.148.0.1 to 11.149.255.25411.149.255.255131,070
7611.150.0.0/1511.150.0.1 to 11.151.255.25411.151.255.255131,070
7711.152.0.0/1511.152.0.1 to 11.153.255.25411.153.255.255131,070
7811.154.0.0/1511.154.0.1 to 11.155.255.25411.155.255.255131,070
7911.156.0.0/1511.156.0.1 to 11.157.255.25411.157.255.255131,070
8011.158.0.0/1511.158.0.1 to 11.159.255.25411.159.255.255131,070
8111.160.0.0/1511.160.0.1 to 11.161.255.25411.161.255.255131,070
8211.162.0.0/1511.162.0.1 to 11.163.255.25411.163.255.255131,070
8311.164.0.0/1511.164.0.1 to 11.165.255.25411.165.255.255131,070
8411.166.0.0/1511.166.0.1 to 11.167.255.25411.167.255.255131,070
8511.168.0.0/1511.168.0.1 to 11.169.255.25411.169.255.255131,070
8611.170.0.0/1511.170.0.1 to 11.171.255.25411.171.255.255131,070
8711.172.0.0/1511.172.0.1 to 11.173.255.25411.173.255.255131,070
8811.174.0.0/1511.174.0.1 to 11.175.255.25411.175.255.255131,070
8911.176.0.0/1511.176.0.1 to 11.177.255.25411.177.255.255131,070
9011.178.0.0/1511.178.0.1 to 11.179.255.25411.179.255.255131,070
9111.180.0.0/1511.180.0.1 to 11.181.255.25411.181.255.255131,070
9211.182.0.0/1511.182.0.1 to 11.183.255.25411.183.255.255131,070
9311.184.0.0/1511.184.0.1 to 11.185.255.25411.185.255.255131,070
9411.186.0.0/1511.186.0.1 to 11.187.255.25411.187.255.255131,070
9511.188.0.0/1511.188.0.1 to 11.189.255.25411.189.255.255131,070
9611.190.0.0/1511.190.0.1 to 11.191.255.25411.191.255.255131,070
9711.192.0.0/1511.192.0.1 to 11.193.255.25411.193.255.255131,070
9811.194.0.0/1511.194.0.1 to 11.195.255.25411.195.255.255131,070
9911.196.0.0/1511.196.0.1 to 11.197.255.25411.197.255.255131,070
10011.198.0.0/1511.198.0.1 to 11.199.255.25411.199.255.255131,070
10111.200.0.0/1511.200.0.1 to 11.201.255.25411.201.255.255131,070
10211.202.0.0/1511.202.0.1 to 11.203.255.25411.203.255.255131,070
10311.204.0.0/1511.204.0.1 to 11.205.255.25411.205.255.255131,070
10411.206.0.0/1511.206.0.1 to 11.207.255.25411.207.255.255131,070
10511.208.0.0/1511.208.0.1 to 11.209.255.25411.209.255.255131,070
10611.210.0.0/1511.210.0.1 to 11.211.255.25411.211.255.255131,070
10711.212.0.0/1511.212.0.1 to 11.213.255.25411.213.255.255131,070
10811.214.0.0/1511.214.0.1 to 11.215.255.25411.215.255.255131,070
10911.216.0.0/1511.216.0.1 to 11.217.255.25411.217.255.255131,070
11011.218.0.0/1511.218.0.1 to 11.219.255.25411.219.255.255131,070
11111.220.0.0/1511.220.0.1 to 11.221.255.25411.221.255.255131,070
11211.222.0.0/1511.222.0.1 to 11.223.255.25411.223.255.255131,070
11311.224.0.0/1511.224.0.1 to 11.225.255.25411.225.255.255131,070
11411.226.0.0/1511.226.0.1 to 11.227.255.25411.227.255.255131,070
11511.228.0.0/1511.228.0.1 to 11.229.255.25411.229.255.255131,070
11611.230.0.0/1511.230.0.1 to 11.231.255.25411.231.255.255131,070
11711.232.0.0/1511.232.0.1 to 11.233.255.25411.233.255.255131,070
11811.234.0.0/1511.234.0.1 to 11.235.255.25411.235.255.255131,070
11911.236.0.0/1511.236.0.1 to 11.237.255.25411.237.255.255131,070
12011.238.0.0/1511.238.0.1 to 11.239.255.25411.239.255.255131,070
12111.240.0.0/1511.240.0.1 to 11.241.255.25411.241.255.255131,070
12211.242.0.0/1511.242.0.1 to 11.243.255.25411.243.255.255131,070
12311.244.0.0/1511.244.0.1 to 11.245.255.25411.245.255.255131,070
12411.246.0.0/1511.246.0.1 to 11.247.255.25411.247.255.255131,070
12511.248.0.0/1511.248.0.1 to 11.249.255.25411.249.255.255131,070
12611.250.0.0/1511.250.0.1 to 11.251.255.25411.251.255.255131,070
12711.252.0.0/1511.252.0.1 to 11.253.255.25411.253.255.255131,070
12811.254.0.0/1511.254.0.1 to 11.255.255.25411.255.255.255131,070

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.