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.

Network30.0.0.0/8
Usable hosts16,777,214
Subnet mask255.0.0.0
Addresses16,777,216
Network address
30.0.0.0
Broadcast address
30.255.255.255
First usable
30.0.0.1
Last usable
30.255.255.254
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 1E000000 · Integer 503316480 to 520093695
Reverse DNS zone
30.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00011110..00000000.00000000.0000000030.0.0.0
Subnet mask11111111..00000000.00000000.00000000255.0.0.0
Network00011110..00000000.00000000.0000000030.0.0.0
Broadcast00011110..11111111.11111111.1111111130.255.255.255
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)

30.0.0.0/8 makes 128 subnets of /15.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
130.0.0.0/1530.0.0.1 to 30.1.255.25430.1.255.255131,070
230.2.0.0/1530.2.0.1 to 30.3.255.25430.3.255.255131,070
330.4.0.0/1530.4.0.1 to 30.5.255.25430.5.255.255131,070
430.6.0.0/1530.6.0.1 to 30.7.255.25430.7.255.255131,070
530.8.0.0/1530.8.0.1 to 30.9.255.25430.9.255.255131,070
630.10.0.0/1530.10.0.1 to 30.11.255.25430.11.255.255131,070
730.12.0.0/1530.12.0.1 to 30.13.255.25430.13.255.255131,070
830.14.0.0/1530.14.0.1 to 30.15.255.25430.15.255.255131,070
930.16.0.0/1530.16.0.1 to 30.17.255.25430.17.255.255131,070
1030.18.0.0/1530.18.0.1 to 30.19.255.25430.19.255.255131,070
1130.20.0.0/1530.20.0.1 to 30.21.255.25430.21.255.255131,070
1230.22.0.0/1530.22.0.1 to 30.23.255.25430.23.255.255131,070
1330.24.0.0/1530.24.0.1 to 30.25.255.25430.25.255.255131,070
1430.26.0.0/1530.26.0.1 to 30.27.255.25430.27.255.255131,070
1530.28.0.0/1530.28.0.1 to 30.29.255.25430.29.255.255131,070
1630.30.0.0/1530.30.0.1 to 30.31.255.25430.31.255.255131,070
1730.32.0.0/1530.32.0.1 to 30.33.255.25430.33.255.255131,070
1830.34.0.0/1530.34.0.1 to 30.35.255.25430.35.255.255131,070
1930.36.0.0/1530.36.0.1 to 30.37.255.25430.37.255.255131,070
2030.38.0.0/1530.38.0.1 to 30.39.255.25430.39.255.255131,070
2130.40.0.0/1530.40.0.1 to 30.41.255.25430.41.255.255131,070
2230.42.0.0/1530.42.0.1 to 30.43.255.25430.43.255.255131,070
2330.44.0.0/1530.44.0.1 to 30.45.255.25430.45.255.255131,070
2430.46.0.0/1530.46.0.1 to 30.47.255.25430.47.255.255131,070
2530.48.0.0/1530.48.0.1 to 30.49.255.25430.49.255.255131,070
2630.50.0.0/1530.50.0.1 to 30.51.255.25430.51.255.255131,070
2730.52.0.0/1530.52.0.1 to 30.53.255.25430.53.255.255131,070
2830.54.0.0/1530.54.0.1 to 30.55.255.25430.55.255.255131,070
2930.56.0.0/1530.56.0.1 to 30.57.255.25430.57.255.255131,070
3030.58.0.0/1530.58.0.1 to 30.59.255.25430.59.255.255131,070
3130.60.0.0/1530.60.0.1 to 30.61.255.25430.61.255.255131,070
3230.62.0.0/1530.62.0.1 to 30.63.255.25430.63.255.255131,070
3330.64.0.0/1530.64.0.1 to 30.65.255.25430.65.255.255131,070
3430.66.0.0/1530.66.0.1 to 30.67.255.25430.67.255.255131,070
3530.68.0.0/1530.68.0.1 to 30.69.255.25430.69.255.255131,070
3630.70.0.0/1530.70.0.1 to 30.71.255.25430.71.255.255131,070
3730.72.0.0/1530.72.0.1 to 30.73.255.25430.73.255.255131,070
3830.74.0.0/1530.74.0.1 to 30.75.255.25430.75.255.255131,070
3930.76.0.0/1530.76.0.1 to 30.77.255.25430.77.255.255131,070
4030.78.0.0/1530.78.0.1 to 30.79.255.25430.79.255.255131,070
4130.80.0.0/1530.80.0.1 to 30.81.255.25430.81.255.255131,070
4230.82.0.0/1530.82.0.1 to 30.83.255.25430.83.255.255131,070
4330.84.0.0/1530.84.0.1 to 30.85.255.25430.85.255.255131,070
4430.86.0.0/1530.86.0.1 to 30.87.255.25430.87.255.255131,070
4530.88.0.0/1530.88.0.1 to 30.89.255.25430.89.255.255131,070
4630.90.0.0/1530.90.0.1 to 30.91.255.25430.91.255.255131,070
4730.92.0.0/1530.92.0.1 to 30.93.255.25430.93.255.255131,070
4830.94.0.0/1530.94.0.1 to 30.95.255.25430.95.255.255131,070
4930.96.0.0/1530.96.0.1 to 30.97.255.25430.97.255.255131,070
5030.98.0.0/1530.98.0.1 to 30.99.255.25430.99.255.255131,070
5130.100.0.0/1530.100.0.1 to 30.101.255.25430.101.255.255131,070
5230.102.0.0/1530.102.0.1 to 30.103.255.25430.103.255.255131,070
5330.104.0.0/1530.104.0.1 to 30.105.255.25430.105.255.255131,070
5430.106.0.0/1530.106.0.1 to 30.107.255.25430.107.255.255131,070
5530.108.0.0/1530.108.0.1 to 30.109.255.25430.109.255.255131,070
5630.110.0.0/1530.110.0.1 to 30.111.255.25430.111.255.255131,070
5730.112.0.0/1530.112.0.1 to 30.113.255.25430.113.255.255131,070
5830.114.0.0/1530.114.0.1 to 30.115.255.25430.115.255.255131,070
5930.116.0.0/1530.116.0.1 to 30.117.255.25430.117.255.255131,070
6030.118.0.0/1530.118.0.1 to 30.119.255.25430.119.255.255131,070
6130.120.0.0/1530.120.0.1 to 30.121.255.25430.121.255.255131,070
6230.122.0.0/1530.122.0.1 to 30.123.255.25430.123.255.255131,070
6330.124.0.0/1530.124.0.1 to 30.125.255.25430.125.255.255131,070
6430.126.0.0/1530.126.0.1 to 30.127.255.25430.127.255.255131,070
6530.128.0.0/1530.128.0.1 to 30.129.255.25430.129.255.255131,070
6630.130.0.0/1530.130.0.1 to 30.131.255.25430.131.255.255131,070
6730.132.0.0/1530.132.0.1 to 30.133.255.25430.133.255.255131,070
6830.134.0.0/1530.134.0.1 to 30.135.255.25430.135.255.255131,070
6930.136.0.0/1530.136.0.1 to 30.137.255.25430.137.255.255131,070
7030.138.0.0/1530.138.0.1 to 30.139.255.25430.139.255.255131,070
7130.140.0.0/1530.140.0.1 to 30.141.255.25430.141.255.255131,070
7230.142.0.0/1530.142.0.1 to 30.143.255.25430.143.255.255131,070
7330.144.0.0/1530.144.0.1 to 30.145.255.25430.145.255.255131,070
7430.146.0.0/1530.146.0.1 to 30.147.255.25430.147.255.255131,070
7530.148.0.0/1530.148.0.1 to 30.149.255.25430.149.255.255131,070
7630.150.0.0/1530.150.0.1 to 30.151.255.25430.151.255.255131,070
7730.152.0.0/1530.152.0.1 to 30.153.255.25430.153.255.255131,070
7830.154.0.0/1530.154.0.1 to 30.155.255.25430.155.255.255131,070
7930.156.0.0/1530.156.0.1 to 30.157.255.25430.157.255.255131,070
8030.158.0.0/1530.158.0.1 to 30.159.255.25430.159.255.255131,070
8130.160.0.0/1530.160.0.1 to 30.161.255.25430.161.255.255131,070
8230.162.0.0/1530.162.0.1 to 30.163.255.25430.163.255.255131,070
8330.164.0.0/1530.164.0.1 to 30.165.255.25430.165.255.255131,070
8430.166.0.0/1530.166.0.1 to 30.167.255.25430.167.255.255131,070
8530.168.0.0/1530.168.0.1 to 30.169.255.25430.169.255.255131,070
8630.170.0.0/1530.170.0.1 to 30.171.255.25430.171.255.255131,070
8730.172.0.0/1530.172.0.1 to 30.173.255.25430.173.255.255131,070
8830.174.0.0/1530.174.0.1 to 30.175.255.25430.175.255.255131,070
8930.176.0.0/1530.176.0.1 to 30.177.255.25430.177.255.255131,070
9030.178.0.0/1530.178.0.1 to 30.179.255.25430.179.255.255131,070
9130.180.0.0/1530.180.0.1 to 30.181.255.25430.181.255.255131,070
9230.182.0.0/1530.182.0.1 to 30.183.255.25430.183.255.255131,070
9330.184.0.0/1530.184.0.1 to 30.185.255.25430.185.255.255131,070
9430.186.0.0/1530.186.0.1 to 30.187.255.25430.187.255.255131,070
9530.188.0.0/1530.188.0.1 to 30.189.255.25430.189.255.255131,070
9630.190.0.0/1530.190.0.1 to 30.191.255.25430.191.255.255131,070
9730.192.0.0/1530.192.0.1 to 30.193.255.25430.193.255.255131,070
9830.194.0.0/1530.194.0.1 to 30.195.255.25430.195.255.255131,070
9930.196.0.0/1530.196.0.1 to 30.197.255.25430.197.255.255131,070
10030.198.0.0/1530.198.0.1 to 30.199.255.25430.199.255.255131,070
10130.200.0.0/1530.200.0.1 to 30.201.255.25430.201.255.255131,070
10230.202.0.0/1530.202.0.1 to 30.203.255.25430.203.255.255131,070
10330.204.0.0/1530.204.0.1 to 30.205.255.25430.205.255.255131,070
10430.206.0.0/1530.206.0.1 to 30.207.255.25430.207.255.255131,070
10530.208.0.0/1530.208.0.1 to 30.209.255.25430.209.255.255131,070
10630.210.0.0/1530.210.0.1 to 30.211.255.25430.211.255.255131,070
10730.212.0.0/1530.212.0.1 to 30.213.255.25430.213.255.255131,070
10830.214.0.0/1530.214.0.1 to 30.215.255.25430.215.255.255131,070
10930.216.0.0/1530.216.0.1 to 30.217.255.25430.217.255.255131,070
11030.218.0.0/1530.218.0.1 to 30.219.255.25430.219.255.255131,070
11130.220.0.0/1530.220.0.1 to 30.221.255.25430.221.255.255131,070
11230.222.0.0/1530.222.0.1 to 30.223.255.25430.223.255.255131,070
11330.224.0.0/1530.224.0.1 to 30.225.255.25430.225.255.255131,070
11430.226.0.0/1530.226.0.1 to 30.227.255.25430.227.255.255131,070
11530.228.0.0/1530.228.0.1 to 30.229.255.25430.229.255.255131,070
11630.230.0.0/1530.230.0.1 to 30.231.255.25430.231.255.255131,070
11730.232.0.0/1530.232.0.1 to 30.233.255.25430.233.255.255131,070
11830.234.0.0/1530.234.0.1 to 30.235.255.25430.235.255.255131,070
11930.236.0.0/1530.236.0.1 to 30.237.255.25430.237.255.255131,070
12030.238.0.0/1530.238.0.1 to 30.239.255.25430.239.255.255131,070
12130.240.0.0/1530.240.0.1 to 30.241.255.25430.241.255.255131,070
12230.242.0.0/1530.242.0.1 to 30.243.255.25430.243.255.255131,070
12330.244.0.0/1530.244.0.1 to 30.245.255.25430.245.255.255131,070
12430.246.0.0/1530.246.0.1 to 30.247.255.25430.247.255.255131,070
12530.248.0.0/1530.248.0.1 to 30.249.255.25430.249.255.255131,070
12630.250.0.0/1530.250.0.1 to 30.251.255.25430.251.255.255131,070
12730.252.0.0/1530.252.0.1 to 30.253.255.25430.253.255.255131,070
12830.254.0.0/1530.254.0.1 to 30.255.255.25430.255.255.255131,070

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.