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.

Network220.0.0.0/6
Usable hosts67,108,862
Subnet mask252.0.0.0
Addresses67,108,864
Network address
220.0.0.0
Broadcast address
223.255.255.255
First usable
220.0.0.1
Last usable
223.255.255.254
Usable hosts
67,108,862 (67,108,864 less the network and broadcast addresses)
Subnet mask
252.0.0.0
Wildcard mask
3.255.255.255 (Cisco ACLs, OSPF)
Prefix length
/6
Type
Public public
Old class
C (default /24)
As numbers
Hex DC000000 · Integer 3690987520 to 3758096383
Reverse DNS zones
220.in-addr.arpa
221.in-addr.arpa
222.in-addr.arpa
223.in-addr.arpa
/6 is not on a 8-bit boundary, so it takes 4 /8 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11011100.00000000.00000000.00000000220.0.0.0
Subnet mask11111100.00000000.00000000.00000000252.0.0.0
Network11011100.00000000.00000000.00000000220.0.0.0
Broadcast11011111.11111111.11111111.11111111223.255.255.255
Split into smaller subnets/13
/7 (2)/8 (4)/9 (8)/10 (16)/11 (32)/12 (64)/13 (128)/14 (256)/15 (512)/16 (1,024)/17 (2,048)/18 (4,096)

220.0.0.0/6 makes 128 subnets of /13.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1220.0.0.0/13220.0.0.1 to 220.7.255.254220.7.255.255524,286
2220.8.0.0/13220.8.0.1 to 220.15.255.254220.15.255.255524,286
3220.16.0.0/13220.16.0.1 to 220.23.255.254220.23.255.255524,286
4220.24.0.0/13220.24.0.1 to 220.31.255.254220.31.255.255524,286
5220.32.0.0/13220.32.0.1 to 220.39.255.254220.39.255.255524,286
6220.40.0.0/13220.40.0.1 to 220.47.255.254220.47.255.255524,286
7220.48.0.0/13220.48.0.1 to 220.55.255.254220.55.255.255524,286
8220.56.0.0/13220.56.0.1 to 220.63.255.254220.63.255.255524,286
9220.64.0.0/13220.64.0.1 to 220.71.255.254220.71.255.255524,286
10220.72.0.0/13220.72.0.1 to 220.79.255.254220.79.255.255524,286
11220.80.0.0/13220.80.0.1 to 220.87.255.254220.87.255.255524,286
12220.88.0.0/13220.88.0.1 to 220.95.255.254220.95.255.255524,286
13220.96.0.0/13220.96.0.1 to 220.103.255.254220.103.255.255524,286
14220.104.0.0/13220.104.0.1 to 220.111.255.254220.111.255.255524,286
15220.112.0.0/13220.112.0.1 to 220.119.255.254220.119.255.255524,286
16220.120.0.0/13220.120.0.1 to 220.127.255.254220.127.255.255524,286
17220.128.0.0/13220.128.0.1 to 220.135.255.254220.135.255.255524,286
18220.136.0.0/13220.136.0.1 to 220.143.255.254220.143.255.255524,286
19220.144.0.0/13220.144.0.1 to 220.151.255.254220.151.255.255524,286
20220.152.0.0/13220.152.0.1 to 220.159.255.254220.159.255.255524,286
21220.160.0.0/13220.160.0.1 to 220.167.255.254220.167.255.255524,286
22220.168.0.0/13220.168.0.1 to 220.175.255.254220.175.255.255524,286
23220.176.0.0/13220.176.0.1 to 220.183.255.254220.183.255.255524,286
24220.184.0.0/13220.184.0.1 to 220.191.255.254220.191.255.255524,286
25220.192.0.0/13220.192.0.1 to 220.199.255.254220.199.255.255524,286
26220.200.0.0/13220.200.0.1 to 220.207.255.254220.207.255.255524,286
27220.208.0.0/13220.208.0.1 to 220.215.255.254220.215.255.255524,286
28220.216.0.0/13220.216.0.1 to 220.223.255.254220.223.255.255524,286
29220.224.0.0/13220.224.0.1 to 220.231.255.254220.231.255.255524,286
30220.232.0.0/13220.232.0.1 to 220.239.255.254220.239.255.255524,286
31220.240.0.0/13220.240.0.1 to 220.247.255.254220.247.255.255524,286
32220.248.0.0/13220.248.0.1 to 220.255.255.254220.255.255.255524,286
33221.0.0.0/13221.0.0.1 to 221.7.255.254221.7.255.255524,286
34221.8.0.0/13221.8.0.1 to 221.15.255.254221.15.255.255524,286
35221.16.0.0/13221.16.0.1 to 221.23.255.254221.23.255.255524,286
36221.24.0.0/13221.24.0.1 to 221.31.255.254221.31.255.255524,286
37221.32.0.0/13221.32.0.1 to 221.39.255.254221.39.255.255524,286
38221.40.0.0/13221.40.0.1 to 221.47.255.254221.47.255.255524,286
39221.48.0.0/13221.48.0.1 to 221.55.255.254221.55.255.255524,286
40221.56.0.0/13221.56.0.1 to 221.63.255.254221.63.255.255524,286
41221.64.0.0/13221.64.0.1 to 221.71.255.254221.71.255.255524,286
42221.72.0.0/13221.72.0.1 to 221.79.255.254221.79.255.255524,286
43221.80.0.0/13221.80.0.1 to 221.87.255.254221.87.255.255524,286
44221.88.0.0/13221.88.0.1 to 221.95.255.254221.95.255.255524,286
45221.96.0.0/13221.96.0.1 to 221.103.255.254221.103.255.255524,286
46221.104.0.0/13221.104.0.1 to 221.111.255.254221.111.255.255524,286
47221.112.0.0/13221.112.0.1 to 221.119.255.254221.119.255.255524,286
48221.120.0.0/13221.120.0.1 to 221.127.255.254221.127.255.255524,286
49221.128.0.0/13221.128.0.1 to 221.135.255.254221.135.255.255524,286
50221.136.0.0/13221.136.0.1 to 221.143.255.254221.143.255.255524,286
51221.144.0.0/13221.144.0.1 to 221.151.255.254221.151.255.255524,286
52221.152.0.0/13221.152.0.1 to 221.159.255.254221.159.255.255524,286
53221.160.0.0/13221.160.0.1 to 221.167.255.254221.167.255.255524,286
54221.168.0.0/13221.168.0.1 to 221.175.255.254221.175.255.255524,286
55221.176.0.0/13221.176.0.1 to 221.183.255.254221.183.255.255524,286
56221.184.0.0/13221.184.0.1 to 221.191.255.254221.191.255.255524,286
57221.192.0.0/13221.192.0.1 to 221.199.255.254221.199.255.255524,286
58221.200.0.0/13221.200.0.1 to 221.207.255.254221.207.255.255524,286
59221.208.0.0/13221.208.0.1 to 221.215.255.254221.215.255.255524,286
60221.216.0.0/13221.216.0.1 to 221.223.255.254221.223.255.255524,286
61221.224.0.0/13221.224.0.1 to 221.231.255.254221.231.255.255524,286
62221.232.0.0/13221.232.0.1 to 221.239.255.254221.239.255.255524,286
63221.240.0.0/13221.240.0.1 to 221.247.255.254221.247.255.255524,286
64221.248.0.0/13221.248.0.1 to 221.255.255.254221.255.255.255524,286
65222.0.0.0/13222.0.0.1 to 222.7.255.254222.7.255.255524,286
66222.8.0.0/13222.8.0.1 to 222.15.255.254222.15.255.255524,286
67222.16.0.0/13222.16.0.1 to 222.23.255.254222.23.255.255524,286
68222.24.0.0/13222.24.0.1 to 222.31.255.254222.31.255.255524,286
69222.32.0.0/13222.32.0.1 to 222.39.255.254222.39.255.255524,286
70222.40.0.0/13222.40.0.1 to 222.47.255.254222.47.255.255524,286
71222.48.0.0/13222.48.0.1 to 222.55.255.254222.55.255.255524,286
72222.56.0.0/13222.56.0.1 to 222.63.255.254222.63.255.255524,286
73222.64.0.0/13222.64.0.1 to 222.71.255.254222.71.255.255524,286
74222.72.0.0/13222.72.0.1 to 222.79.255.254222.79.255.255524,286
75222.80.0.0/13222.80.0.1 to 222.87.255.254222.87.255.255524,286
76222.88.0.0/13222.88.0.1 to 222.95.255.254222.95.255.255524,286
77222.96.0.0/13222.96.0.1 to 222.103.255.254222.103.255.255524,286
78222.104.0.0/13222.104.0.1 to 222.111.255.254222.111.255.255524,286
79222.112.0.0/13222.112.0.1 to 222.119.255.254222.119.255.255524,286
80222.120.0.0/13222.120.0.1 to 222.127.255.254222.127.255.255524,286
81222.128.0.0/13222.128.0.1 to 222.135.255.254222.135.255.255524,286
82222.136.0.0/13222.136.0.1 to 222.143.255.254222.143.255.255524,286
83222.144.0.0/13222.144.0.1 to 222.151.255.254222.151.255.255524,286
84222.152.0.0/13222.152.0.1 to 222.159.255.254222.159.255.255524,286
85222.160.0.0/13222.160.0.1 to 222.167.255.254222.167.255.255524,286
86222.168.0.0/13222.168.0.1 to 222.175.255.254222.175.255.255524,286
87222.176.0.0/13222.176.0.1 to 222.183.255.254222.183.255.255524,286
88222.184.0.0/13222.184.0.1 to 222.191.255.254222.191.255.255524,286
89222.192.0.0/13222.192.0.1 to 222.199.255.254222.199.255.255524,286
90222.200.0.0/13222.200.0.1 to 222.207.255.254222.207.255.255524,286
91222.208.0.0/13222.208.0.1 to 222.215.255.254222.215.255.255524,286
92222.216.0.0/13222.216.0.1 to 222.223.255.254222.223.255.255524,286
93222.224.0.0/13222.224.0.1 to 222.231.255.254222.231.255.255524,286
94222.232.0.0/13222.232.0.1 to 222.239.255.254222.239.255.255524,286
95222.240.0.0/13222.240.0.1 to 222.247.255.254222.247.255.255524,286
96222.248.0.0/13222.248.0.1 to 222.255.255.254222.255.255.255524,286
97223.0.0.0/13223.0.0.1 to 223.7.255.254223.7.255.255524,286
98223.8.0.0/13223.8.0.1 to 223.15.255.254223.15.255.255524,286
99223.16.0.0/13223.16.0.1 to 223.23.255.254223.23.255.255524,286
100223.24.0.0/13223.24.0.1 to 223.31.255.254223.31.255.255524,286
101223.32.0.0/13223.32.0.1 to 223.39.255.254223.39.255.255524,286
102223.40.0.0/13223.40.0.1 to 223.47.255.254223.47.255.255524,286
103223.48.0.0/13223.48.0.1 to 223.55.255.254223.55.255.255524,286
104223.56.0.0/13223.56.0.1 to 223.63.255.254223.63.255.255524,286
105223.64.0.0/13223.64.0.1 to 223.71.255.254223.71.255.255524,286
106223.72.0.0/13223.72.0.1 to 223.79.255.254223.79.255.255524,286
107223.80.0.0/13223.80.0.1 to 223.87.255.254223.87.255.255524,286
108223.88.0.0/13223.88.0.1 to 223.95.255.254223.95.255.255524,286
109223.96.0.0/13223.96.0.1 to 223.103.255.254223.103.255.255524,286
110223.104.0.0/13223.104.0.1 to 223.111.255.254223.111.255.255524,286
111223.112.0.0/13223.112.0.1 to 223.119.255.254223.119.255.255524,286
112223.120.0.0/13223.120.0.1 to 223.127.255.254223.127.255.255524,286
113223.128.0.0/13223.128.0.1 to 223.135.255.254223.135.255.255524,286
114223.136.0.0/13223.136.0.1 to 223.143.255.254223.143.255.255524,286
115223.144.0.0/13223.144.0.1 to 223.151.255.254223.151.255.255524,286
116223.152.0.0/13223.152.0.1 to 223.159.255.254223.159.255.255524,286
117223.160.0.0/13223.160.0.1 to 223.167.255.254223.167.255.255524,286
118223.168.0.0/13223.168.0.1 to 223.175.255.254223.175.255.255524,286
119223.176.0.0/13223.176.0.1 to 223.183.255.254223.183.255.255524,286
120223.184.0.0/13223.184.0.1 to 223.191.255.254223.191.255.255524,286
121223.192.0.0/13223.192.0.1 to 223.199.255.254223.199.255.255524,286
122223.200.0.0/13223.200.0.1 to 223.207.255.254223.207.255.255524,286
123223.208.0.0/13223.208.0.1 to 223.215.255.254223.215.255.255524,286
124223.216.0.0/13223.216.0.1 to 223.223.255.254223.223.255.255524,286
125223.224.0.0/13223.224.0.1 to 223.231.255.254223.231.255.255524,286
126223.232.0.0/13223.232.0.1 to 223.239.255.254223.239.255.255524,286
127223.240.0.0/13223.240.0.1 to 223.247.255.254223.247.255.255524,286
128223.248.0.0/13223.248.0.1 to 223.255.255.254223.255.255.255524,286

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.