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.

Network79.167.2.0/24
Usable hosts254
Subnet mask255.255.255.0
Addresses256
Network address
79.167.2.0
Broadcast address
79.167.2.255
First usable
79.167.2.1
Last usable
79.167.2.254
Usable hosts
254 (256 less the network and broadcast addresses)
Subnet mask
255.255.255.0
Wildcard mask
0.0.0.255 (Cisco ACLs, OSPF)
Prefix length
/24
Type
Public public
Old class
A (default /8)
As numbers
Hex 4FA70200 · Integer 1336345088 to 1336345343
Reverse DNS zone
2.167.79.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address01001111.10100111.00000010..0000000079.167.2.0
Subnet mask11111111.11111111.11111111..00000000255.255.255.0
Network01001111.10100111.00000010..0000000079.167.2.0
Broadcast01001111.10100111.00000010..1111111179.167.2.255
Split into smaller subnets/30
/25 (2)/26 (4)/27 (8)/28 (16)/29 (32)/30 (64)/31 (128)/32 (256)

79.167.2.0/24 makes 64 subnets of /30.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
179.167.2.0/3079.167.2.1 to 79.167.2.279.167.2.32
279.167.2.4/3079.167.2.5 to 79.167.2.679.167.2.72
379.167.2.8/3079.167.2.9 to 79.167.2.1079.167.2.112
479.167.2.12/3079.167.2.13 to 79.167.2.1479.167.2.152
579.167.2.16/3079.167.2.17 to 79.167.2.1879.167.2.192
679.167.2.20/3079.167.2.21 to 79.167.2.2279.167.2.232
779.167.2.24/3079.167.2.25 to 79.167.2.2679.167.2.272
879.167.2.28/3079.167.2.29 to 79.167.2.3079.167.2.312
979.167.2.32/3079.167.2.33 to 79.167.2.3479.167.2.352
1079.167.2.36/3079.167.2.37 to 79.167.2.3879.167.2.392
1179.167.2.40/3079.167.2.41 to 79.167.2.4279.167.2.432
1279.167.2.44/3079.167.2.45 to 79.167.2.4679.167.2.472
1379.167.2.48/3079.167.2.49 to 79.167.2.5079.167.2.512
1479.167.2.52/3079.167.2.53 to 79.167.2.5479.167.2.552
1579.167.2.56/3079.167.2.57 to 79.167.2.5879.167.2.592
1679.167.2.60/3079.167.2.61 to 79.167.2.6279.167.2.632
1779.167.2.64/3079.167.2.65 to 79.167.2.6679.167.2.672
1879.167.2.68/3079.167.2.69 to 79.167.2.7079.167.2.712
1979.167.2.72/3079.167.2.73 to 79.167.2.7479.167.2.752
2079.167.2.76/3079.167.2.77 to 79.167.2.7879.167.2.792
2179.167.2.80/3079.167.2.81 to 79.167.2.8279.167.2.832
2279.167.2.84/3079.167.2.85 to 79.167.2.8679.167.2.872
2379.167.2.88/3079.167.2.89 to 79.167.2.9079.167.2.912
2479.167.2.92/3079.167.2.93 to 79.167.2.9479.167.2.952
2579.167.2.96/3079.167.2.97 to 79.167.2.9879.167.2.992
2679.167.2.100/3079.167.2.101 to 79.167.2.10279.167.2.1032
2779.167.2.104/3079.167.2.105 to 79.167.2.10679.167.2.1072
2879.167.2.108/3079.167.2.109 to 79.167.2.11079.167.2.1112
2979.167.2.112/3079.167.2.113 to 79.167.2.11479.167.2.1152
3079.167.2.116/3079.167.2.117 to 79.167.2.11879.167.2.1192
3179.167.2.120/3079.167.2.121 to 79.167.2.12279.167.2.1232
3279.167.2.124/3079.167.2.125 to 79.167.2.12679.167.2.1272
3379.167.2.128/3079.167.2.129 to 79.167.2.13079.167.2.1312
3479.167.2.132/3079.167.2.133 to 79.167.2.13479.167.2.1352
3579.167.2.136/3079.167.2.137 to 79.167.2.13879.167.2.1392
3679.167.2.140/3079.167.2.141 to 79.167.2.14279.167.2.1432
3779.167.2.144/3079.167.2.145 to 79.167.2.14679.167.2.1472
3879.167.2.148/3079.167.2.149 to 79.167.2.15079.167.2.1512
3979.167.2.152/3079.167.2.153 to 79.167.2.15479.167.2.1552
4079.167.2.156/3079.167.2.157 to 79.167.2.15879.167.2.1592
4179.167.2.160/3079.167.2.161 to 79.167.2.16279.167.2.1632
4279.167.2.164/3079.167.2.165 to 79.167.2.16679.167.2.1672
4379.167.2.168/3079.167.2.169 to 79.167.2.17079.167.2.1712
4479.167.2.172/3079.167.2.173 to 79.167.2.17479.167.2.1752
4579.167.2.176/3079.167.2.177 to 79.167.2.17879.167.2.1792
4679.167.2.180/3079.167.2.181 to 79.167.2.18279.167.2.1832
4779.167.2.184/3079.167.2.185 to 79.167.2.18679.167.2.1872
4879.167.2.188/3079.167.2.189 to 79.167.2.19079.167.2.1912
4979.167.2.192/3079.167.2.193 to 79.167.2.19479.167.2.1952
5079.167.2.196/3079.167.2.197 to 79.167.2.19879.167.2.1992
5179.167.2.200/3079.167.2.201 to 79.167.2.20279.167.2.2032
5279.167.2.204/3079.167.2.205 to 79.167.2.20679.167.2.2072
5379.167.2.208/3079.167.2.209 to 79.167.2.21079.167.2.2112
5479.167.2.212/3079.167.2.213 to 79.167.2.21479.167.2.2152
5579.167.2.216/3079.167.2.217 to 79.167.2.21879.167.2.2192
5679.167.2.220/3079.167.2.221 to 79.167.2.22279.167.2.2232
5779.167.2.224/3079.167.2.225 to 79.167.2.22679.167.2.2272
5879.167.2.228/3079.167.2.229 to 79.167.2.23079.167.2.2312
5979.167.2.232/3079.167.2.233 to 79.167.2.23479.167.2.2352
6079.167.2.236/3079.167.2.237 to 79.167.2.23879.167.2.2392
6179.167.2.240/3079.167.2.241 to 79.167.2.24279.167.2.2432
6279.167.2.244/3079.167.2.245 to 79.167.2.24679.167.2.2472
6379.167.2.248/3079.167.2.249 to 79.167.2.25079.167.2.2512
6479.167.2.252/3079.167.2.253 to 79.167.2.25479.167.2.2552

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.