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.

Network188.0.0.0/8
Usable hosts16,777,214
Subnet mask255.0.0.0
Addresses16,777,216
Network address
188.0.0.0
Broadcast address
188.255.255.255
First usable
188.0.0.1
Last usable
188.255.255.254
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
B (default /16)
As numbers
Hex BC000000 · Integer 3154116608 to 3170893823
Reverse DNS zone
188.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address10111100..00000000.00000000.00000000188.0.0.0
Subnet mask11111111..00000000.00000000.00000000255.0.0.0
Network10111100..00000000.00000000.00000000188.0.0.0
Broadcast10111100..11111111.11111111.11111111188.255.255.255
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)

188.0.0.0/8 makes 128 subnets of /15.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1188.0.0.0/15188.0.0.1 to 188.1.255.254188.1.255.255131,070
2188.2.0.0/15188.2.0.1 to 188.3.255.254188.3.255.255131,070
3188.4.0.0/15188.4.0.1 to 188.5.255.254188.5.255.255131,070
4188.6.0.0/15188.6.0.1 to 188.7.255.254188.7.255.255131,070
5188.8.0.0/15188.8.0.1 to 188.9.255.254188.9.255.255131,070
6188.10.0.0/15188.10.0.1 to 188.11.255.254188.11.255.255131,070
7188.12.0.0/15188.12.0.1 to 188.13.255.254188.13.255.255131,070
8188.14.0.0/15188.14.0.1 to 188.15.255.254188.15.255.255131,070
9188.16.0.0/15188.16.0.1 to 188.17.255.254188.17.255.255131,070
10188.18.0.0/15188.18.0.1 to 188.19.255.254188.19.255.255131,070
11188.20.0.0/15188.20.0.1 to 188.21.255.254188.21.255.255131,070
12188.22.0.0/15188.22.0.1 to 188.23.255.254188.23.255.255131,070
13188.24.0.0/15188.24.0.1 to 188.25.255.254188.25.255.255131,070
14188.26.0.0/15188.26.0.1 to 188.27.255.254188.27.255.255131,070
15188.28.0.0/15188.28.0.1 to 188.29.255.254188.29.255.255131,070
16188.30.0.0/15188.30.0.1 to 188.31.255.254188.31.255.255131,070
17188.32.0.0/15188.32.0.1 to 188.33.255.254188.33.255.255131,070
18188.34.0.0/15188.34.0.1 to 188.35.255.254188.35.255.255131,070
19188.36.0.0/15188.36.0.1 to 188.37.255.254188.37.255.255131,070
20188.38.0.0/15188.38.0.1 to 188.39.255.254188.39.255.255131,070
21188.40.0.0/15188.40.0.1 to 188.41.255.254188.41.255.255131,070
22188.42.0.0/15188.42.0.1 to 188.43.255.254188.43.255.255131,070
23188.44.0.0/15188.44.0.1 to 188.45.255.254188.45.255.255131,070
24188.46.0.0/15188.46.0.1 to 188.47.255.254188.47.255.255131,070
25188.48.0.0/15188.48.0.1 to 188.49.255.254188.49.255.255131,070
26188.50.0.0/15188.50.0.1 to 188.51.255.254188.51.255.255131,070
27188.52.0.0/15188.52.0.1 to 188.53.255.254188.53.255.255131,070
28188.54.0.0/15188.54.0.1 to 188.55.255.254188.55.255.255131,070
29188.56.0.0/15188.56.0.1 to 188.57.255.254188.57.255.255131,070
30188.58.0.0/15188.58.0.1 to 188.59.255.254188.59.255.255131,070
31188.60.0.0/15188.60.0.1 to 188.61.255.254188.61.255.255131,070
32188.62.0.0/15188.62.0.1 to 188.63.255.254188.63.255.255131,070
33188.64.0.0/15188.64.0.1 to 188.65.255.254188.65.255.255131,070
34188.66.0.0/15188.66.0.1 to 188.67.255.254188.67.255.255131,070
35188.68.0.0/15188.68.0.1 to 188.69.255.254188.69.255.255131,070
36188.70.0.0/15188.70.0.1 to 188.71.255.254188.71.255.255131,070
37188.72.0.0/15188.72.0.1 to 188.73.255.254188.73.255.255131,070
38188.74.0.0/15188.74.0.1 to 188.75.255.254188.75.255.255131,070
39188.76.0.0/15188.76.0.1 to 188.77.255.254188.77.255.255131,070
40188.78.0.0/15188.78.0.1 to 188.79.255.254188.79.255.255131,070
41188.80.0.0/15188.80.0.1 to 188.81.255.254188.81.255.255131,070
42188.82.0.0/15188.82.0.1 to 188.83.255.254188.83.255.255131,070
43188.84.0.0/15188.84.0.1 to 188.85.255.254188.85.255.255131,070
44188.86.0.0/15188.86.0.1 to 188.87.255.254188.87.255.255131,070
45188.88.0.0/15188.88.0.1 to 188.89.255.254188.89.255.255131,070
46188.90.0.0/15188.90.0.1 to 188.91.255.254188.91.255.255131,070
47188.92.0.0/15188.92.0.1 to 188.93.255.254188.93.255.255131,070
48188.94.0.0/15188.94.0.1 to 188.95.255.254188.95.255.255131,070
49188.96.0.0/15188.96.0.1 to 188.97.255.254188.97.255.255131,070
50188.98.0.0/15188.98.0.1 to 188.99.255.254188.99.255.255131,070
51188.100.0.0/15188.100.0.1 to 188.101.255.254188.101.255.255131,070
52188.102.0.0/15188.102.0.1 to 188.103.255.254188.103.255.255131,070
53188.104.0.0/15188.104.0.1 to 188.105.255.254188.105.255.255131,070
54188.106.0.0/15188.106.0.1 to 188.107.255.254188.107.255.255131,070
55188.108.0.0/15188.108.0.1 to 188.109.255.254188.109.255.255131,070
56188.110.0.0/15188.110.0.1 to 188.111.255.254188.111.255.255131,070
57188.112.0.0/15188.112.0.1 to 188.113.255.254188.113.255.255131,070
58188.114.0.0/15188.114.0.1 to 188.115.255.254188.115.255.255131,070
59188.116.0.0/15188.116.0.1 to 188.117.255.254188.117.255.255131,070
60188.118.0.0/15188.118.0.1 to 188.119.255.254188.119.255.255131,070
61188.120.0.0/15188.120.0.1 to 188.121.255.254188.121.255.255131,070
62188.122.0.0/15188.122.0.1 to 188.123.255.254188.123.255.255131,070
63188.124.0.0/15188.124.0.1 to 188.125.255.254188.125.255.255131,070
64188.126.0.0/15188.126.0.1 to 188.127.255.254188.127.255.255131,070
65188.128.0.0/15188.128.0.1 to 188.129.255.254188.129.255.255131,070
66188.130.0.0/15188.130.0.1 to 188.131.255.254188.131.255.255131,070
67188.132.0.0/15188.132.0.1 to 188.133.255.254188.133.255.255131,070
68188.134.0.0/15188.134.0.1 to 188.135.255.254188.135.255.255131,070
69188.136.0.0/15188.136.0.1 to 188.137.255.254188.137.255.255131,070
70188.138.0.0/15188.138.0.1 to 188.139.255.254188.139.255.255131,070
71188.140.0.0/15188.140.0.1 to 188.141.255.254188.141.255.255131,070
72188.142.0.0/15188.142.0.1 to 188.143.255.254188.143.255.255131,070
73188.144.0.0/15188.144.0.1 to 188.145.255.254188.145.255.255131,070
74188.146.0.0/15188.146.0.1 to 188.147.255.254188.147.255.255131,070
75188.148.0.0/15188.148.0.1 to 188.149.255.254188.149.255.255131,070
76188.150.0.0/15188.150.0.1 to 188.151.255.254188.151.255.255131,070
77188.152.0.0/15188.152.0.1 to 188.153.255.254188.153.255.255131,070
78188.154.0.0/15188.154.0.1 to 188.155.255.254188.155.255.255131,070
79188.156.0.0/15188.156.0.1 to 188.157.255.254188.157.255.255131,070
80188.158.0.0/15188.158.0.1 to 188.159.255.254188.159.255.255131,070
81188.160.0.0/15188.160.0.1 to 188.161.255.254188.161.255.255131,070
82188.162.0.0/15188.162.0.1 to 188.163.255.254188.163.255.255131,070
83188.164.0.0/15188.164.0.1 to 188.165.255.254188.165.255.255131,070
84188.166.0.0/15188.166.0.1 to 188.167.255.254188.167.255.255131,070
85188.168.0.0/15188.168.0.1 to 188.169.255.254188.169.255.255131,070
86188.170.0.0/15188.170.0.1 to 188.171.255.254188.171.255.255131,070
87188.172.0.0/15188.172.0.1 to 188.173.255.254188.173.255.255131,070
88188.174.0.0/15188.174.0.1 to 188.175.255.254188.175.255.255131,070
89188.176.0.0/15188.176.0.1 to 188.177.255.254188.177.255.255131,070
90188.178.0.0/15188.178.0.1 to 188.179.255.254188.179.255.255131,070
91188.180.0.0/15188.180.0.1 to 188.181.255.254188.181.255.255131,070
92188.182.0.0/15188.182.0.1 to 188.183.255.254188.183.255.255131,070
93188.184.0.0/15188.184.0.1 to 188.185.255.254188.185.255.255131,070
94188.186.0.0/15188.186.0.1 to 188.187.255.254188.187.255.255131,070
95188.188.0.0/15188.188.0.1 to 188.189.255.254188.189.255.255131,070
96188.190.0.0/15188.190.0.1 to 188.191.255.254188.191.255.255131,070
97188.192.0.0/15188.192.0.1 to 188.193.255.254188.193.255.255131,070
98188.194.0.0/15188.194.0.1 to 188.195.255.254188.195.255.255131,070
99188.196.0.0/15188.196.0.1 to 188.197.255.254188.197.255.255131,070
100188.198.0.0/15188.198.0.1 to 188.199.255.254188.199.255.255131,070
101188.200.0.0/15188.200.0.1 to 188.201.255.254188.201.255.255131,070
102188.202.0.0/15188.202.0.1 to 188.203.255.254188.203.255.255131,070
103188.204.0.0/15188.204.0.1 to 188.205.255.254188.205.255.255131,070
104188.206.0.0/15188.206.0.1 to 188.207.255.254188.207.255.255131,070
105188.208.0.0/15188.208.0.1 to 188.209.255.254188.209.255.255131,070
106188.210.0.0/15188.210.0.1 to 188.211.255.254188.211.255.255131,070
107188.212.0.0/15188.212.0.1 to 188.213.255.254188.213.255.255131,070
108188.214.0.0/15188.214.0.1 to 188.215.255.254188.215.255.255131,070
109188.216.0.0/15188.216.0.1 to 188.217.255.254188.217.255.255131,070
110188.218.0.0/15188.218.0.1 to 188.219.255.254188.219.255.255131,070
111188.220.0.0/15188.220.0.1 to 188.221.255.254188.221.255.255131,070
112188.222.0.0/15188.222.0.1 to 188.223.255.254188.223.255.255131,070
113188.224.0.0/15188.224.0.1 to 188.225.255.254188.225.255.255131,070
114188.226.0.0/15188.226.0.1 to 188.227.255.254188.227.255.255131,070
115188.228.0.0/15188.228.0.1 to 188.229.255.254188.229.255.255131,070
116188.230.0.0/15188.230.0.1 to 188.231.255.254188.231.255.255131,070
117188.232.0.0/15188.232.0.1 to 188.233.255.254188.233.255.255131,070
118188.234.0.0/15188.234.0.1 to 188.235.255.254188.235.255.255131,070
119188.236.0.0/15188.236.0.1 to 188.237.255.254188.237.255.255131,070
120188.238.0.0/15188.238.0.1 to 188.239.255.254188.239.255.255131,070
121188.240.0.0/15188.240.0.1 to 188.241.255.254188.241.255.255131,070
122188.242.0.0/15188.242.0.1 to 188.243.255.254188.243.255.255131,070
123188.244.0.0/15188.244.0.1 to 188.245.255.254188.245.255.255131,070
124188.246.0.0/15188.246.0.1 to 188.247.255.254188.247.255.255131,070
125188.248.0.0/15188.248.0.1 to 188.249.255.254188.249.255.255131,070
126188.250.0.0/15188.250.0.1 to 188.251.255.254188.251.255.255131,070
127188.252.0.0/15188.252.0.1 to 188.253.255.254188.253.255.255131,070
128188.254.0.0/15188.254.0.1 to 188.255.255.254188.255.255.255131,070

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.