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.

Network210.0.0.0/8
Usable hosts16,777,214
Subnet mask255.0.0.0
Addresses16,777,216
Network address
210.0.0.0
Broadcast address
210.255.255.255
First usable
210.0.0.1
Last usable
210.255.255.254
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
C (default /24)
As numbers
Hex D2000000 · Integer 3523215360 to 3539992575
Reverse DNS zone
210.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11010010..00000000.00000000.00000000210.0.0.0
Subnet mask11111111..00000000.00000000.00000000255.0.0.0
Network11010010..00000000.00000000.00000000210.0.0.0
Broadcast11010010..11111111.11111111.11111111210.255.255.255
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)

210.0.0.0/8 makes 128 subnets of /15.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1210.0.0.0/15210.0.0.1 to 210.1.255.254210.1.255.255131,070
2210.2.0.0/15210.2.0.1 to 210.3.255.254210.3.255.255131,070
3210.4.0.0/15210.4.0.1 to 210.5.255.254210.5.255.255131,070
4210.6.0.0/15210.6.0.1 to 210.7.255.254210.7.255.255131,070
5210.8.0.0/15210.8.0.1 to 210.9.255.254210.9.255.255131,070
6210.10.0.0/15210.10.0.1 to 210.11.255.254210.11.255.255131,070
7210.12.0.0/15210.12.0.1 to 210.13.255.254210.13.255.255131,070
8210.14.0.0/15210.14.0.1 to 210.15.255.254210.15.255.255131,070
9210.16.0.0/15210.16.0.1 to 210.17.255.254210.17.255.255131,070
10210.18.0.0/15210.18.0.1 to 210.19.255.254210.19.255.255131,070
11210.20.0.0/15210.20.0.1 to 210.21.255.254210.21.255.255131,070
12210.22.0.0/15210.22.0.1 to 210.23.255.254210.23.255.255131,070
13210.24.0.0/15210.24.0.1 to 210.25.255.254210.25.255.255131,070
14210.26.0.0/15210.26.0.1 to 210.27.255.254210.27.255.255131,070
15210.28.0.0/15210.28.0.1 to 210.29.255.254210.29.255.255131,070
16210.30.0.0/15210.30.0.1 to 210.31.255.254210.31.255.255131,070
17210.32.0.0/15210.32.0.1 to 210.33.255.254210.33.255.255131,070
18210.34.0.0/15210.34.0.1 to 210.35.255.254210.35.255.255131,070
19210.36.0.0/15210.36.0.1 to 210.37.255.254210.37.255.255131,070
20210.38.0.0/15210.38.0.1 to 210.39.255.254210.39.255.255131,070
21210.40.0.0/15210.40.0.1 to 210.41.255.254210.41.255.255131,070
22210.42.0.0/15210.42.0.1 to 210.43.255.254210.43.255.255131,070
23210.44.0.0/15210.44.0.1 to 210.45.255.254210.45.255.255131,070
24210.46.0.0/15210.46.0.1 to 210.47.255.254210.47.255.255131,070
25210.48.0.0/15210.48.0.1 to 210.49.255.254210.49.255.255131,070
26210.50.0.0/15210.50.0.1 to 210.51.255.254210.51.255.255131,070
27210.52.0.0/15210.52.0.1 to 210.53.255.254210.53.255.255131,070
28210.54.0.0/15210.54.0.1 to 210.55.255.254210.55.255.255131,070
29210.56.0.0/15210.56.0.1 to 210.57.255.254210.57.255.255131,070
30210.58.0.0/15210.58.0.1 to 210.59.255.254210.59.255.255131,070
31210.60.0.0/15210.60.0.1 to 210.61.255.254210.61.255.255131,070
32210.62.0.0/15210.62.0.1 to 210.63.255.254210.63.255.255131,070
33210.64.0.0/15210.64.0.1 to 210.65.255.254210.65.255.255131,070
34210.66.0.0/15210.66.0.1 to 210.67.255.254210.67.255.255131,070
35210.68.0.0/15210.68.0.1 to 210.69.255.254210.69.255.255131,070
36210.70.0.0/15210.70.0.1 to 210.71.255.254210.71.255.255131,070
37210.72.0.0/15210.72.0.1 to 210.73.255.254210.73.255.255131,070
38210.74.0.0/15210.74.0.1 to 210.75.255.254210.75.255.255131,070
39210.76.0.0/15210.76.0.1 to 210.77.255.254210.77.255.255131,070
40210.78.0.0/15210.78.0.1 to 210.79.255.254210.79.255.255131,070
41210.80.0.0/15210.80.0.1 to 210.81.255.254210.81.255.255131,070
42210.82.0.0/15210.82.0.1 to 210.83.255.254210.83.255.255131,070
43210.84.0.0/15210.84.0.1 to 210.85.255.254210.85.255.255131,070
44210.86.0.0/15210.86.0.1 to 210.87.255.254210.87.255.255131,070
45210.88.0.0/15210.88.0.1 to 210.89.255.254210.89.255.255131,070
46210.90.0.0/15210.90.0.1 to 210.91.255.254210.91.255.255131,070
47210.92.0.0/15210.92.0.1 to 210.93.255.254210.93.255.255131,070
48210.94.0.0/15210.94.0.1 to 210.95.255.254210.95.255.255131,070
49210.96.0.0/15210.96.0.1 to 210.97.255.254210.97.255.255131,070
50210.98.0.0/15210.98.0.1 to 210.99.255.254210.99.255.255131,070
51210.100.0.0/15210.100.0.1 to 210.101.255.254210.101.255.255131,070
52210.102.0.0/15210.102.0.1 to 210.103.255.254210.103.255.255131,070
53210.104.0.0/15210.104.0.1 to 210.105.255.254210.105.255.255131,070
54210.106.0.0/15210.106.0.1 to 210.107.255.254210.107.255.255131,070
55210.108.0.0/15210.108.0.1 to 210.109.255.254210.109.255.255131,070
56210.110.0.0/15210.110.0.1 to 210.111.255.254210.111.255.255131,070
57210.112.0.0/15210.112.0.1 to 210.113.255.254210.113.255.255131,070
58210.114.0.0/15210.114.0.1 to 210.115.255.254210.115.255.255131,070
59210.116.0.0/15210.116.0.1 to 210.117.255.254210.117.255.255131,070
60210.118.0.0/15210.118.0.1 to 210.119.255.254210.119.255.255131,070
61210.120.0.0/15210.120.0.1 to 210.121.255.254210.121.255.255131,070
62210.122.0.0/15210.122.0.1 to 210.123.255.254210.123.255.255131,070
63210.124.0.0/15210.124.0.1 to 210.125.255.254210.125.255.255131,070
64210.126.0.0/15210.126.0.1 to 210.127.255.254210.127.255.255131,070
65210.128.0.0/15210.128.0.1 to 210.129.255.254210.129.255.255131,070
66210.130.0.0/15210.130.0.1 to 210.131.255.254210.131.255.255131,070
67210.132.0.0/15210.132.0.1 to 210.133.255.254210.133.255.255131,070
68210.134.0.0/15210.134.0.1 to 210.135.255.254210.135.255.255131,070
69210.136.0.0/15210.136.0.1 to 210.137.255.254210.137.255.255131,070
70210.138.0.0/15210.138.0.1 to 210.139.255.254210.139.255.255131,070
71210.140.0.0/15210.140.0.1 to 210.141.255.254210.141.255.255131,070
72210.142.0.0/15210.142.0.1 to 210.143.255.254210.143.255.255131,070
73210.144.0.0/15210.144.0.1 to 210.145.255.254210.145.255.255131,070
74210.146.0.0/15210.146.0.1 to 210.147.255.254210.147.255.255131,070
75210.148.0.0/15210.148.0.1 to 210.149.255.254210.149.255.255131,070
76210.150.0.0/15210.150.0.1 to 210.151.255.254210.151.255.255131,070
77210.152.0.0/15210.152.0.1 to 210.153.255.254210.153.255.255131,070
78210.154.0.0/15210.154.0.1 to 210.155.255.254210.155.255.255131,070
79210.156.0.0/15210.156.0.1 to 210.157.255.254210.157.255.255131,070
80210.158.0.0/15210.158.0.1 to 210.159.255.254210.159.255.255131,070
81210.160.0.0/15210.160.0.1 to 210.161.255.254210.161.255.255131,070
82210.162.0.0/15210.162.0.1 to 210.163.255.254210.163.255.255131,070
83210.164.0.0/15210.164.0.1 to 210.165.255.254210.165.255.255131,070
84210.166.0.0/15210.166.0.1 to 210.167.255.254210.167.255.255131,070
85210.168.0.0/15210.168.0.1 to 210.169.255.254210.169.255.255131,070
86210.170.0.0/15210.170.0.1 to 210.171.255.254210.171.255.255131,070
87210.172.0.0/15210.172.0.1 to 210.173.255.254210.173.255.255131,070
88210.174.0.0/15210.174.0.1 to 210.175.255.254210.175.255.255131,070
89210.176.0.0/15210.176.0.1 to 210.177.255.254210.177.255.255131,070
90210.178.0.0/15210.178.0.1 to 210.179.255.254210.179.255.255131,070
91210.180.0.0/15210.180.0.1 to 210.181.255.254210.181.255.255131,070
92210.182.0.0/15210.182.0.1 to 210.183.255.254210.183.255.255131,070
93210.184.0.0/15210.184.0.1 to 210.185.255.254210.185.255.255131,070
94210.186.0.0/15210.186.0.1 to 210.187.255.254210.187.255.255131,070
95210.188.0.0/15210.188.0.1 to 210.189.255.254210.189.255.255131,070
96210.190.0.0/15210.190.0.1 to 210.191.255.254210.191.255.255131,070
97210.192.0.0/15210.192.0.1 to 210.193.255.254210.193.255.255131,070
98210.194.0.0/15210.194.0.1 to 210.195.255.254210.195.255.255131,070
99210.196.0.0/15210.196.0.1 to 210.197.255.254210.197.255.255131,070
100210.198.0.0/15210.198.0.1 to 210.199.255.254210.199.255.255131,070
101210.200.0.0/15210.200.0.1 to 210.201.255.254210.201.255.255131,070
102210.202.0.0/15210.202.0.1 to 210.203.255.254210.203.255.255131,070
103210.204.0.0/15210.204.0.1 to 210.205.255.254210.205.255.255131,070
104210.206.0.0/15210.206.0.1 to 210.207.255.254210.207.255.255131,070
105210.208.0.0/15210.208.0.1 to 210.209.255.254210.209.255.255131,070
106210.210.0.0/15210.210.0.1 to 210.211.255.254210.211.255.255131,070
107210.212.0.0/15210.212.0.1 to 210.213.255.254210.213.255.255131,070
108210.214.0.0/15210.214.0.1 to 210.215.255.254210.215.255.255131,070
109210.216.0.0/15210.216.0.1 to 210.217.255.254210.217.255.255131,070
110210.218.0.0/15210.218.0.1 to 210.219.255.254210.219.255.255131,070
111210.220.0.0/15210.220.0.1 to 210.221.255.254210.221.255.255131,070
112210.222.0.0/15210.222.0.1 to 210.223.255.254210.223.255.255131,070
113210.224.0.0/15210.224.0.1 to 210.225.255.254210.225.255.255131,070
114210.226.0.0/15210.226.0.1 to 210.227.255.254210.227.255.255131,070
115210.228.0.0/15210.228.0.1 to 210.229.255.254210.229.255.255131,070
116210.230.0.0/15210.230.0.1 to 210.231.255.254210.231.255.255131,070
117210.232.0.0/15210.232.0.1 to 210.233.255.254210.233.255.255131,070
118210.234.0.0/15210.234.0.1 to 210.235.255.254210.235.255.255131,070
119210.236.0.0/15210.236.0.1 to 210.237.255.254210.237.255.255131,070
120210.238.0.0/15210.238.0.1 to 210.239.255.254210.239.255.255131,070
121210.240.0.0/15210.240.0.1 to 210.241.255.254210.241.255.255131,070
122210.242.0.0/15210.242.0.1 to 210.243.255.254210.243.255.255131,070
123210.244.0.0/15210.244.0.1 to 210.245.255.254210.245.255.255131,070
124210.246.0.0/15210.246.0.1 to 210.247.255.254210.247.255.255131,070
125210.248.0.0/15210.248.0.1 to 210.249.255.254210.249.255.255131,070
126210.250.0.0/15210.250.0.1 to 210.251.255.254210.251.255.255131,070
127210.252.0.0/15210.252.0.1 to 210.253.255.254210.253.255.255131,070
128210.254.0.0/15210.254.0.1 to 210.255.255.254210.255.255.255131,070

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.