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.

Network65.167.78.0/24
Usable hosts254
Subnet mask255.255.255.0
Addresses256
Network address
65.167.78.0
Broadcast address
65.167.78.255
First usable
65.167.78.1
Last usable
65.167.78.254
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 41A74E00 · Integer 1101483520 to 1101483775
Reverse DNS zone
78.167.65.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address01000001.10100111.01001110..0000000065.167.78.0
Subnet mask11111111.11111111.11111111..00000000255.255.255.0
Network01000001.10100111.01001110..0000000065.167.78.0
Broadcast01000001.10100111.01001110..1111111165.167.78.255
Split into smaller subnets/30
/25 (2)/26 (4)/27 (8)/28 (16)/29 (32)/30 (64)/31 (128)/32 (256)

65.167.78.0/24 makes 64 subnets of /30.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
165.167.78.0/3065.167.78.1 to 65.167.78.265.167.78.32
265.167.78.4/3065.167.78.5 to 65.167.78.665.167.78.72
365.167.78.8/3065.167.78.9 to 65.167.78.1065.167.78.112
465.167.78.12/3065.167.78.13 to 65.167.78.1465.167.78.152
565.167.78.16/3065.167.78.17 to 65.167.78.1865.167.78.192
665.167.78.20/3065.167.78.21 to 65.167.78.2265.167.78.232
765.167.78.24/3065.167.78.25 to 65.167.78.2665.167.78.272
865.167.78.28/3065.167.78.29 to 65.167.78.3065.167.78.312
965.167.78.32/3065.167.78.33 to 65.167.78.3465.167.78.352
1065.167.78.36/3065.167.78.37 to 65.167.78.3865.167.78.392
1165.167.78.40/3065.167.78.41 to 65.167.78.4265.167.78.432
1265.167.78.44/3065.167.78.45 to 65.167.78.4665.167.78.472
1365.167.78.48/3065.167.78.49 to 65.167.78.5065.167.78.512
1465.167.78.52/3065.167.78.53 to 65.167.78.5465.167.78.552
1565.167.78.56/3065.167.78.57 to 65.167.78.5865.167.78.592
1665.167.78.60/3065.167.78.61 to 65.167.78.6265.167.78.632
1765.167.78.64/3065.167.78.65 to 65.167.78.6665.167.78.672
1865.167.78.68/3065.167.78.69 to 65.167.78.7065.167.78.712
1965.167.78.72/3065.167.78.73 to 65.167.78.7465.167.78.752
2065.167.78.76/3065.167.78.77 to 65.167.78.7865.167.78.792
2165.167.78.80/3065.167.78.81 to 65.167.78.8265.167.78.832
2265.167.78.84/3065.167.78.85 to 65.167.78.8665.167.78.872
2365.167.78.88/3065.167.78.89 to 65.167.78.9065.167.78.912
2465.167.78.92/3065.167.78.93 to 65.167.78.9465.167.78.952
2565.167.78.96/3065.167.78.97 to 65.167.78.9865.167.78.992
2665.167.78.100/3065.167.78.101 to 65.167.78.10265.167.78.1032
2765.167.78.104/3065.167.78.105 to 65.167.78.10665.167.78.1072
2865.167.78.108/3065.167.78.109 to 65.167.78.11065.167.78.1112
2965.167.78.112/3065.167.78.113 to 65.167.78.11465.167.78.1152
3065.167.78.116/3065.167.78.117 to 65.167.78.11865.167.78.1192
3165.167.78.120/3065.167.78.121 to 65.167.78.12265.167.78.1232
3265.167.78.124/3065.167.78.125 to 65.167.78.12665.167.78.1272
3365.167.78.128/3065.167.78.129 to 65.167.78.13065.167.78.1312
3465.167.78.132/3065.167.78.133 to 65.167.78.13465.167.78.1352
3565.167.78.136/3065.167.78.137 to 65.167.78.13865.167.78.1392
3665.167.78.140/3065.167.78.141 to 65.167.78.14265.167.78.1432
3765.167.78.144/3065.167.78.145 to 65.167.78.14665.167.78.1472
3865.167.78.148/3065.167.78.149 to 65.167.78.15065.167.78.1512
3965.167.78.152/3065.167.78.153 to 65.167.78.15465.167.78.1552
4065.167.78.156/3065.167.78.157 to 65.167.78.15865.167.78.1592
4165.167.78.160/3065.167.78.161 to 65.167.78.16265.167.78.1632
4265.167.78.164/3065.167.78.165 to 65.167.78.16665.167.78.1672
4365.167.78.168/3065.167.78.169 to 65.167.78.17065.167.78.1712
4465.167.78.172/3065.167.78.173 to 65.167.78.17465.167.78.1752
4565.167.78.176/3065.167.78.177 to 65.167.78.17865.167.78.1792
4665.167.78.180/3065.167.78.181 to 65.167.78.18265.167.78.1832
4765.167.78.184/3065.167.78.185 to 65.167.78.18665.167.78.1872
4865.167.78.188/3065.167.78.189 to 65.167.78.19065.167.78.1912
4965.167.78.192/3065.167.78.193 to 65.167.78.19465.167.78.1952
5065.167.78.196/3065.167.78.197 to 65.167.78.19865.167.78.1992
5165.167.78.200/3065.167.78.201 to 65.167.78.20265.167.78.2032
5265.167.78.204/3065.167.78.205 to 65.167.78.20665.167.78.2072
5365.167.78.208/3065.167.78.209 to 65.167.78.21065.167.78.2112
5465.167.78.212/3065.167.78.213 to 65.167.78.21465.167.78.2152
5565.167.78.216/3065.167.78.217 to 65.167.78.21865.167.78.2192
5665.167.78.220/3065.167.78.221 to 65.167.78.22265.167.78.2232
5765.167.78.224/3065.167.78.225 to 65.167.78.22665.167.78.2272
5865.167.78.228/3065.167.78.229 to 65.167.78.23065.167.78.2312
5965.167.78.232/3065.167.78.233 to 65.167.78.23465.167.78.2352
6065.167.78.236/3065.167.78.237 to 65.167.78.23865.167.78.2392
6165.167.78.240/3065.167.78.241 to 65.167.78.24265.167.78.2432
6265.167.78.244/3065.167.78.245 to 65.167.78.24665.167.78.2472
6365.167.78.248/3065.167.78.249 to 65.167.78.25065.167.78.2512
6465.167.78.252/3065.167.78.253 to 65.167.78.25465.167.78.2552

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.