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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
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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.

Prefix/9
Addresses2^119
/64 networks2^55
Network
ff00::/9
First address
ff00::
Last address
ff7f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
Addresses
664,613,997,892,457,936,451,903,530,140,172,288 (2^119)
/64 networks (LANs)
36,028,797,018,963,968 (2^55)
Full form
ff00:0000:0000:0000:0000:0000:0000:0000
Type
Multicast ff00::/8
One-to-many traffic; replaces broadcast
Reverse DNS zones
0.f.f.ip6.arpa
1.f.f.ip6.arpa
2.f.f.ip6.arpa
3.f.f.ip6.arpa
4.f.f.ip6.arpa
5.f.f.ip6.arpa
6.f.f.ip6.arpa
7.f.f.ip6.arpa
/9 is not on a 4-bit boundary, so it takes 8 /12 zones.
Split into smaller subnets/16
/10 (2)/11 (4)/12 (8)/13 (16)/16 (128)/20 (2,048)/24 (32,768)

ff00::/9 makes 128 subnets of /16.

Subnets
#SubnetLast address
1ff00::/16ff00:ffff:ffff:ffff:ffff:ffff:ffff:ffff
2ff01::/16ff01:ffff:ffff:ffff:ffff:ffff:ffff:ffff
3ff02::/16ff02:ffff:ffff:ffff:ffff:ffff:ffff:ffff
4ff03::/16ff03:ffff:ffff:ffff:ffff:ffff:ffff:ffff
5ff04::/16ff04:ffff:ffff:ffff:ffff:ffff:ffff:ffff
6ff05::/16ff05:ffff:ffff:ffff:ffff:ffff:ffff:ffff
7ff06::/16ff06:ffff:ffff:ffff:ffff:ffff:ffff:ffff
8ff07::/16ff07:ffff:ffff:ffff:ffff:ffff:ffff:ffff
9ff08::/16ff08:ffff:ffff:ffff:ffff:ffff:ffff:ffff
10ff09::/16ff09:ffff:ffff:ffff:ffff:ffff:ffff:ffff
11ff0a::/16ff0a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
12ff0b::/16ff0b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
13ff0c::/16ff0c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
14ff0d::/16ff0d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
15ff0e::/16ff0e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
16ff0f::/16ff0f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
17ff10::/16ff10:ffff:ffff:ffff:ffff:ffff:ffff:ffff
18ff11::/16ff11:ffff:ffff:ffff:ffff:ffff:ffff:ffff
19ff12::/16ff12:ffff:ffff:ffff:ffff:ffff:ffff:ffff
20ff13::/16ff13:ffff:ffff:ffff:ffff:ffff:ffff:ffff
21ff14::/16ff14:ffff:ffff:ffff:ffff:ffff:ffff:ffff
22ff15::/16ff15:ffff:ffff:ffff:ffff:ffff:ffff:ffff
23ff16::/16ff16:ffff:ffff:ffff:ffff:ffff:ffff:ffff
24ff17::/16ff17:ffff:ffff:ffff:ffff:ffff:ffff:ffff
25ff18::/16ff18:ffff:ffff:ffff:ffff:ffff:ffff:ffff
26ff19::/16ff19:ffff:ffff:ffff:ffff:ffff:ffff:ffff
27ff1a::/16ff1a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
28ff1b::/16ff1b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
29ff1c::/16ff1c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
30ff1d::/16ff1d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
31ff1e::/16ff1e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
32ff1f::/16ff1f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
33ff20::/16ff20:ffff:ffff:ffff:ffff:ffff:ffff:ffff
34ff21::/16ff21:ffff:ffff:ffff:ffff:ffff:ffff:ffff
35ff22::/16ff22:ffff:ffff:ffff:ffff:ffff:ffff:ffff
36ff23::/16ff23:ffff:ffff:ffff:ffff:ffff:ffff:ffff
37ff24::/16ff24:ffff:ffff:ffff:ffff:ffff:ffff:ffff
38ff25::/16ff25:ffff:ffff:ffff:ffff:ffff:ffff:ffff
39ff26::/16ff26:ffff:ffff:ffff:ffff:ffff:ffff:ffff
40ff27::/16ff27:ffff:ffff:ffff:ffff:ffff:ffff:ffff
41ff28::/16ff28:ffff:ffff:ffff:ffff:ffff:ffff:ffff
42ff29::/16ff29:ffff:ffff:ffff:ffff:ffff:ffff:ffff
43ff2a::/16ff2a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
44ff2b::/16ff2b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
45ff2c::/16ff2c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
46ff2d::/16ff2d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
47ff2e::/16ff2e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
48ff2f::/16ff2f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
49ff30::/16ff30:ffff:ffff:ffff:ffff:ffff:ffff:ffff
50ff31::/16ff31:ffff:ffff:ffff:ffff:ffff:ffff:ffff
51ff32::/16ff32:ffff:ffff:ffff:ffff:ffff:ffff:ffff
52ff33::/16ff33:ffff:ffff:ffff:ffff:ffff:ffff:ffff
53ff34::/16ff34:ffff:ffff:ffff:ffff:ffff:ffff:ffff
54ff35::/16ff35:ffff:ffff:ffff:ffff:ffff:ffff:ffff
55ff36::/16ff36:ffff:ffff:ffff:ffff:ffff:ffff:ffff
56ff37::/16ff37:ffff:ffff:ffff:ffff:ffff:ffff:ffff
57ff38::/16ff38:ffff:ffff:ffff:ffff:ffff:ffff:ffff
58ff39::/16ff39:ffff:ffff:ffff:ffff:ffff:ffff:ffff
59ff3a::/16ff3a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
60ff3b::/16ff3b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
61ff3c::/16ff3c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
62ff3d::/16ff3d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
63ff3e::/16ff3e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
64ff3f::/16ff3f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
65ff40::/16ff40:ffff:ffff:ffff:ffff:ffff:ffff:ffff
66ff41::/16ff41:ffff:ffff:ffff:ffff:ffff:ffff:ffff
67ff42::/16ff42:ffff:ffff:ffff:ffff:ffff:ffff:ffff
68ff43::/16ff43:ffff:ffff:ffff:ffff:ffff:ffff:ffff
69ff44::/16ff44:ffff:ffff:ffff:ffff:ffff:ffff:ffff
70ff45::/16ff45:ffff:ffff:ffff:ffff:ffff:ffff:ffff
71ff46::/16ff46:ffff:ffff:ffff:ffff:ffff:ffff:ffff
72ff47::/16ff47:ffff:ffff:ffff:ffff:ffff:ffff:ffff
73ff48::/16ff48:ffff:ffff:ffff:ffff:ffff:ffff:ffff
74ff49::/16ff49:ffff:ffff:ffff:ffff:ffff:ffff:ffff
75ff4a::/16ff4a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
76ff4b::/16ff4b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
77ff4c::/16ff4c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
78ff4d::/16ff4d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
79ff4e::/16ff4e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
80ff4f::/16ff4f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
81ff50::/16ff50:ffff:ffff:ffff:ffff:ffff:ffff:ffff
82ff51::/16ff51:ffff:ffff:ffff:ffff:ffff:ffff:ffff
83ff52::/16ff52:ffff:ffff:ffff:ffff:ffff:ffff:ffff
84ff53::/16ff53:ffff:ffff:ffff:ffff:ffff:ffff:ffff
85ff54::/16ff54:ffff:ffff:ffff:ffff:ffff:ffff:ffff
86ff55::/16ff55:ffff:ffff:ffff:ffff:ffff:ffff:ffff
87ff56::/16ff56:ffff:ffff:ffff:ffff:ffff:ffff:ffff
88ff57::/16ff57:ffff:ffff:ffff:ffff:ffff:ffff:ffff
89ff58::/16ff58:ffff:ffff:ffff:ffff:ffff:ffff:ffff
90ff59::/16ff59:ffff:ffff:ffff:ffff:ffff:ffff:ffff
91ff5a::/16ff5a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
92ff5b::/16ff5b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
93ff5c::/16ff5c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
94ff5d::/16ff5d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
95ff5e::/16ff5e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
96ff5f::/16ff5f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
97ff60::/16ff60:ffff:ffff:ffff:ffff:ffff:ffff:ffff
98ff61::/16ff61:ffff:ffff:ffff:ffff:ffff:ffff:ffff
99ff62::/16ff62:ffff:ffff:ffff:ffff:ffff:ffff:ffff
100ff63::/16ff63:ffff:ffff:ffff:ffff:ffff:ffff:ffff
101ff64::/16ff64:ffff:ffff:ffff:ffff:ffff:ffff:ffff
102ff65::/16ff65:ffff:ffff:ffff:ffff:ffff:ffff:ffff
103ff66::/16ff66:ffff:ffff:ffff:ffff:ffff:ffff:ffff
104ff67::/16ff67:ffff:ffff:ffff:ffff:ffff:ffff:ffff
105ff68::/16ff68:ffff:ffff:ffff:ffff:ffff:ffff:ffff
106ff69::/16ff69:ffff:ffff:ffff:ffff:ffff:ffff:ffff
107ff6a::/16ff6a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
108ff6b::/16ff6b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
109ff6c::/16ff6c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
110ff6d::/16ff6d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
111ff6e::/16ff6e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
112ff6f::/16ff6f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
113ff70::/16ff70:ffff:ffff:ffff:ffff:ffff:ffff:ffff
114ff71::/16ff71:ffff:ffff:ffff:ffff:ffff:ffff:ffff
115ff72::/16ff72:ffff:ffff:ffff:ffff:ffff:ffff:ffff
116ff73::/16ff73:ffff:ffff:ffff:ffff:ffff:ffff:ffff
117ff74::/16ff74:ffff:ffff:ffff:ffff:ffff:ffff:ffff
118ff75::/16ff75:ffff:ffff:ffff:ffff:ffff:ffff:ffff
119ff76::/16ff76:ffff:ffff:ffff:ffff:ffff:ffff:ffff
120ff77::/16ff77:ffff:ffff:ffff:ffff:ffff:ffff:ffff
121ff78::/16ff78:ffff:ffff:ffff:ffff:ffff:ffff:ffff
122ff79::/16ff79:ffff:ffff:ffff:ffff:ffff:ffff:ffff
123ff7a::/16ff7a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
124ff7b::/16ff7b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
125ff7c::/16ff7c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
126ff7d::/16ff7d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
127ff7e::/16ff7e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
128ff7f::/16ff7f:ffff:ffff:ffff:ffff:ffff:ffff:ffff

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.