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.

Network224.0.0.0/4
Usable hosts268,435,454
Subnet mask240.0.0.0
Addresses268,435,456
Network address
224.0.0.0
Broadcast address
239.255.255.255
First usable
224.0.0.1
Last usable
239.255.255.254
Usable hosts
268,435,454 (268,435,456 less the network and broadcast addresses)
Subnet mask
240.0.0.0
Wildcard mask
15.255.255.255 (Cisco ACLs, OSPF)
Prefix length
/4
Type
Multicast 224.0.0.0/4
One-to-many traffic, such as IPTV and routing protocols
Old class
D (multicast)
As numbers
Hex E0000000 · Integer 3758096384 to 4026531839
Reverse DNS zones
224.in-addr.arpa
225.in-addr.arpa
226.in-addr.arpa
227.in-addr.arpa
228.in-addr.arpa
229.in-addr.arpa
230.in-addr.arpa
231.in-addr.arpa
232.in-addr.arpa
233.in-addr.arpa
234.in-addr.arpa
235.in-addr.arpa
236.in-addr.arpa
237.in-addr.arpa
238.in-addr.arpa
239.in-addr.arpa
/4 is not on a 8-bit boundary, so it takes 16 /8 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11100000.00000000.00000000.00000000224.0.0.0
Subnet mask11110000.00000000.00000000.00000000240.0.0.0
Network11100000.00000000.00000000.00000000224.0.0.0
Broadcast11101111.11111111.11111111.11111111239.255.255.255
Split into smaller subnets/11
/5 (2)/6 (4)/7 (8)/8 (16)/9 (32)/10 (64)/11 (128)/12 (256)/13 (512)/14 (1,024)/15 (2,048)/16 (4,096)

224.0.0.0/4 makes 128 subnets of /11.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1224.0.0.0/11224.0.0.1 to 224.31.255.254224.31.255.2552,097,150
2224.32.0.0/11224.32.0.1 to 224.63.255.254224.63.255.2552,097,150
3224.64.0.0/11224.64.0.1 to 224.95.255.254224.95.255.2552,097,150
4224.96.0.0/11224.96.0.1 to 224.127.255.254224.127.255.2552,097,150
5224.128.0.0/11224.128.0.1 to 224.159.255.254224.159.255.2552,097,150
6224.160.0.0/11224.160.0.1 to 224.191.255.254224.191.255.2552,097,150
7224.192.0.0/11224.192.0.1 to 224.223.255.254224.223.255.2552,097,150
8224.224.0.0/11224.224.0.1 to 224.255.255.254224.255.255.2552,097,150
9225.0.0.0/11225.0.0.1 to 225.31.255.254225.31.255.2552,097,150
10225.32.0.0/11225.32.0.1 to 225.63.255.254225.63.255.2552,097,150
11225.64.0.0/11225.64.0.1 to 225.95.255.254225.95.255.2552,097,150
12225.96.0.0/11225.96.0.1 to 225.127.255.254225.127.255.2552,097,150
13225.128.0.0/11225.128.0.1 to 225.159.255.254225.159.255.2552,097,150
14225.160.0.0/11225.160.0.1 to 225.191.255.254225.191.255.2552,097,150
15225.192.0.0/11225.192.0.1 to 225.223.255.254225.223.255.2552,097,150
16225.224.0.0/11225.224.0.1 to 225.255.255.254225.255.255.2552,097,150
17226.0.0.0/11226.0.0.1 to 226.31.255.254226.31.255.2552,097,150
18226.32.0.0/11226.32.0.1 to 226.63.255.254226.63.255.2552,097,150
19226.64.0.0/11226.64.0.1 to 226.95.255.254226.95.255.2552,097,150
20226.96.0.0/11226.96.0.1 to 226.127.255.254226.127.255.2552,097,150
21226.128.0.0/11226.128.0.1 to 226.159.255.254226.159.255.2552,097,150
22226.160.0.0/11226.160.0.1 to 226.191.255.254226.191.255.2552,097,150
23226.192.0.0/11226.192.0.1 to 226.223.255.254226.223.255.2552,097,150
24226.224.0.0/11226.224.0.1 to 226.255.255.254226.255.255.2552,097,150
25227.0.0.0/11227.0.0.1 to 227.31.255.254227.31.255.2552,097,150
26227.32.0.0/11227.32.0.1 to 227.63.255.254227.63.255.2552,097,150
27227.64.0.0/11227.64.0.1 to 227.95.255.254227.95.255.2552,097,150
28227.96.0.0/11227.96.0.1 to 227.127.255.254227.127.255.2552,097,150
29227.128.0.0/11227.128.0.1 to 227.159.255.254227.159.255.2552,097,150
30227.160.0.0/11227.160.0.1 to 227.191.255.254227.191.255.2552,097,150
31227.192.0.0/11227.192.0.1 to 227.223.255.254227.223.255.2552,097,150
32227.224.0.0/11227.224.0.1 to 227.255.255.254227.255.255.2552,097,150
33228.0.0.0/11228.0.0.1 to 228.31.255.254228.31.255.2552,097,150
34228.32.0.0/11228.32.0.1 to 228.63.255.254228.63.255.2552,097,150
35228.64.0.0/11228.64.0.1 to 228.95.255.254228.95.255.2552,097,150
36228.96.0.0/11228.96.0.1 to 228.127.255.254228.127.255.2552,097,150
37228.128.0.0/11228.128.0.1 to 228.159.255.254228.159.255.2552,097,150
38228.160.0.0/11228.160.0.1 to 228.191.255.254228.191.255.2552,097,150
39228.192.0.0/11228.192.0.1 to 228.223.255.254228.223.255.2552,097,150
40228.224.0.0/11228.224.0.1 to 228.255.255.254228.255.255.2552,097,150
41229.0.0.0/11229.0.0.1 to 229.31.255.254229.31.255.2552,097,150
42229.32.0.0/11229.32.0.1 to 229.63.255.254229.63.255.2552,097,150
43229.64.0.0/11229.64.0.1 to 229.95.255.254229.95.255.2552,097,150
44229.96.0.0/11229.96.0.1 to 229.127.255.254229.127.255.2552,097,150
45229.128.0.0/11229.128.0.1 to 229.159.255.254229.159.255.2552,097,150
46229.160.0.0/11229.160.0.1 to 229.191.255.254229.191.255.2552,097,150
47229.192.0.0/11229.192.0.1 to 229.223.255.254229.223.255.2552,097,150
48229.224.0.0/11229.224.0.1 to 229.255.255.254229.255.255.2552,097,150
49230.0.0.0/11230.0.0.1 to 230.31.255.254230.31.255.2552,097,150
50230.32.0.0/11230.32.0.1 to 230.63.255.254230.63.255.2552,097,150
51230.64.0.0/11230.64.0.1 to 230.95.255.254230.95.255.2552,097,150
52230.96.0.0/11230.96.0.1 to 230.127.255.254230.127.255.2552,097,150
53230.128.0.0/11230.128.0.1 to 230.159.255.254230.159.255.2552,097,150
54230.160.0.0/11230.160.0.1 to 230.191.255.254230.191.255.2552,097,150
55230.192.0.0/11230.192.0.1 to 230.223.255.254230.223.255.2552,097,150
56230.224.0.0/11230.224.0.1 to 230.255.255.254230.255.255.2552,097,150
57231.0.0.0/11231.0.0.1 to 231.31.255.254231.31.255.2552,097,150
58231.32.0.0/11231.32.0.1 to 231.63.255.254231.63.255.2552,097,150
59231.64.0.0/11231.64.0.1 to 231.95.255.254231.95.255.2552,097,150
60231.96.0.0/11231.96.0.1 to 231.127.255.254231.127.255.2552,097,150
61231.128.0.0/11231.128.0.1 to 231.159.255.254231.159.255.2552,097,150
62231.160.0.0/11231.160.0.1 to 231.191.255.254231.191.255.2552,097,150
63231.192.0.0/11231.192.0.1 to 231.223.255.254231.223.255.2552,097,150
64231.224.0.0/11231.224.0.1 to 231.255.255.254231.255.255.2552,097,150
65232.0.0.0/11232.0.0.1 to 232.31.255.254232.31.255.2552,097,150
66232.32.0.0/11232.32.0.1 to 232.63.255.254232.63.255.2552,097,150
67232.64.0.0/11232.64.0.1 to 232.95.255.254232.95.255.2552,097,150
68232.96.0.0/11232.96.0.1 to 232.127.255.254232.127.255.2552,097,150
69232.128.0.0/11232.128.0.1 to 232.159.255.254232.159.255.2552,097,150
70232.160.0.0/11232.160.0.1 to 232.191.255.254232.191.255.2552,097,150
71232.192.0.0/11232.192.0.1 to 232.223.255.254232.223.255.2552,097,150
72232.224.0.0/11232.224.0.1 to 232.255.255.254232.255.255.2552,097,150
73233.0.0.0/11233.0.0.1 to 233.31.255.254233.31.255.2552,097,150
74233.32.0.0/11233.32.0.1 to 233.63.255.254233.63.255.2552,097,150
75233.64.0.0/11233.64.0.1 to 233.95.255.254233.95.255.2552,097,150
76233.96.0.0/11233.96.0.1 to 233.127.255.254233.127.255.2552,097,150
77233.128.0.0/11233.128.0.1 to 233.159.255.254233.159.255.2552,097,150
78233.160.0.0/11233.160.0.1 to 233.191.255.254233.191.255.2552,097,150
79233.192.0.0/11233.192.0.1 to 233.223.255.254233.223.255.2552,097,150
80233.224.0.0/11233.224.0.1 to 233.255.255.254233.255.255.2552,097,150
81234.0.0.0/11234.0.0.1 to 234.31.255.254234.31.255.2552,097,150
82234.32.0.0/11234.32.0.1 to 234.63.255.254234.63.255.2552,097,150
83234.64.0.0/11234.64.0.1 to 234.95.255.254234.95.255.2552,097,150
84234.96.0.0/11234.96.0.1 to 234.127.255.254234.127.255.2552,097,150
85234.128.0.0/11234.128.0.1 to 234.159.255.254234.159.255.2552,097,150
86234.160.0.0/11234.160.0.1 to 234.191.255.254234.191.255.2552,097,150
87234.192.0.0/11234.192.0.1 to 234.223.255.254234.223.255.2552,097,150
88234.224.0.0/11234.224.0.1 to 234.255.255.254234.255.255.2552,097,150
89235.0.0.0/11235.0.0.1 to 235.31.255.254235.31.255.2552,097,150
90235.32.0.0/11235.32.0.1 to 235.63.255.254235.63.255.2552,097,150
91235.64.0.0/11235.64.0.1 to 235.95.255.254235.95.255.2552,097,150
92235.96.0.0/11235.96.0.1 to 235.127.255.254235.127.255.2552,097,150
93235.128.0.0/11235.128.0.1 to 235.159.255.254235.159.255.2552,097,150
94235.160.0.0/11235.160.0.1 to 235.191.255.254235.191.255.2552,097,150
95235.192.0.0/11235.192.0.1 to 235.223.255.254235.223.255.2552,097,150
96235.224.0.0/11235.224.0.1 to 235.255.255.254235.255.255.2552,097,150
97236.0.0.0/11236.0.0.1 to 236.31.255.254236.31.255.2552,097,150
98236.32.0.0/11236.32.0.1 to 236.63.255.254236.63.255.2552,097,150
99236.64.0.0/11236.64.0.1 to 236.95.255.254236.95.255.2552,097,150
100236.96.0.0/11236.96.0.1 to 236.127.255.254236.127.255.2552,097,150
101236.128.0.0/11236.128.0.1 to 236.159.255.254236.159.255.2552,097,150
102236.160.0.0/11236.160.0.1 to 236.191.255.254236.191.255.2552,097,150
103236.192.0.0/11236.192.0.1 to 236.223.255.254236.223.255.2552,097,150
104236.224.0.0/11236.224.0.1 to 236.255.255.254236.255.255.2552,097,150
105237.0.0.0/11237.0.0.1 to 237.31.255.254237.31.255.2552,097,150
106237.32.0.0/11237.32.0.1 to 237.63.255.254237.63.255.2552,097,150
107237.64.0.0/11237.64.0.1 to 237.95.255.254237.95.255.2552,097,150
108237.96.0.0/11237.96.0.1 to 237.127.255.254237.127.255.2552,097,150
109237.128.0.0/11237.128.0.1 to 237.159.255.254237.159.255.2552,097,150
110237.160.0.0/11237.160.0.1 to 237.191.255.254237.191.255.2552,097,150
111237.192.0.0/11237.192.0.1 to 237.223.255.254237.223.255.2552,097,150
112237.224.0.0/11237.224.0.1 to 237.255.255.254237.255.255.2552,097,150
113238.0.0.0/11238.0.0.1 to 238.31.255.254238.31.255.2552,097,150
114238.32.0.0/11238.32.0.1 to 238.63.255.254238.63.255.2552,097,150
115238.64.0.0/11238.64.0.1 to 238.95.255.254238.95.255.2552,097,150
116238.96.0.0/11238.96.0.1 to 238.127.255.254238.127.255.2552,097,150
117238.128.0.0/11238.128.0.1 to 238.159.255.254238.159.255.2552,097,150
118238.160.0.0/11238.160.0.1 to 238.191.255.254238.191.255.2552,097,150
119238.192.0.0/11238.192.0.1 to 238.223.255.254238.223.255.2552,097,150
120238.224.0.0/11238.224.0.1 to 238.255.255.254238.255.255.2552,097,150
121239.0.0.0/11239.0.0.1 to 239.31.255.254239.31.255.2552,097,150
122239.32.0.0/11239.32.0.1 to 239.63.255.254239.63.255.2552,097,150
123239.64.0.0/11239.64.0.1 to 239.95.255.254239.95.255.2552,097,150
124239.96.0.0/11239.96.0.1 to 239.127.255.254239.127.255.2552,097,150
125239.128.0.0/11239.128.0.1 to 239.159.255.254239.159.255.2552,097,150
126239.160.0.0/11239.160.0.1 to 239.191.255.254239.191.255.2552,097,150
127239.192.0.0/11239.192.0.1 to 239.223.255.254239.223.255.2552,097,150
128239.224.0.0/11239.224.0.1 to 239.255.255.254239.255.255.2552,097,150

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.