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.

Network196.0.0.0/7
Usable hosts33,554,430
Subnet mask254.0.0.0
Addresses33,554,432
Network address
196.0.0.0
Broadcast address
197.255.255.255
First usable
196.0.0.1
Last usable
197.255.255.254
Usable hosts
33,554,430 (33,554,432 less the network and broadcast addresses)
Subnet mask
254.0.0.0
Wildcard mask
1.255.255.255 (Cisco ACLs, OSPF)
Prefix length
/7
Type
Public public
Old class
C (default /24)
As numbers
Hex C4000000 · Integer 3288334336 to 3321888767
Reverse DNS zones
196.in-addr.arpa
197.in-addr.arpa
/7 is not on a 8-bit boundary, so it takes 2 /8 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11000100.00000000.00000000.00000000196.0.0.0
Subnet mask11111110.00000000.00000000.00000000254.0.0.0
Network11000100.00000000.00000000.00000000196.0.0.0
Broadcast11000101.11111111.11111111.11111111197.255.255.255
Split into smaller subnets/13
/8 (2)/9 (4)/10 (8)/11 (16)/12 (32)/13 (64)/14 (128)/15 (256)/16 (512)/17 (1,024)/18 (2,048)/19 (4,096)

196.0.0.0/7 makes 64 subnets of /13.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1196.0.0.0/13196.0.0.1 to 196.7.255.254196.7.255.255524,286
2196.8.0.0/13196.8.0.1 to 196.15.255.254196.15.255.255524,286
3196.16.0.0/13196.16.0.1 to 196.23.255.254196.23.255.255524,286
4196.24.0.0/13196.24.0.1 to 196.31.255.254196.31.255.255524,286
5196.32.0.0/13196.32.0.1 to 196.39.255.254196.39.255.255524,286
6196.40.0.0/13196.40.0.1 to 196.47.255.254196.47.255.255524,286
7196.48.0.0/13196.48.0.1 to 196.55.255.254196.55.255.255524,286
8196.56.0.0/13196.56.0.1 to 196.63.255.254196.63.255.255524,286
9196.64.0.0/13196.64.0.1 to 196.71.255.254196.71.255.255524,286
10196.72.0.0/13196.72.0.1 to 196.79.255.254196.79.255.255524,286
11196.80.0.0/13196.80.0.1 to 196.87.255.254196.87.255.255524,286
12196.88.0.0/13196.88.0.1 to 196.95.255.254196.95.255.255524,286
13196.96.0.0/13196.96.0.1 to 196.103.255.254196.103.255.255524,286
14196.104.0.0/13196.104.0.1 to 196.111.255.254196.111.255.255524,286
15196.112.0.0/13196.112.0.1 to 196.119.255.254196.119.255.255524,286
16196.120.0.0/13196.120.0.1 to 196.127.255.254196.127.255.255524,286
17196.128.0.0/13196.128.0.1 to 196.135.255.254196.135.255.255524,286
18196.136.0.0/13196.136.0.1 to 196.143.255.254196.143.255.255524,286
19196.144.0.0/13196.144.0.1 to 196.151.255.254196.151.255.255524,286
20196.152.0.0/13196.152.0.1 to 196.159.255.254196.159.255.255524,286
21196.160.0.0/13196.160.0.1 to 196.167.255.254196.167.255.255524,286
22196.168.0.0/13196.168.0.1 to 196.175.255.254196.175.255.255524,286
23196.176.0.0/13196.176.0.1 to 196.183.255.254196.183.255.255524,286
24196.184.0.0/13196.184.0.1 to 196.191.255.254196.191.255.255524,286
25196.192.0.0/13196.192.0.1 to 196.199.255.254196.199.255.255524,286
26196.200.0.0/13196.200.0.1 to 196.207.255.254196.207.255.255524,286
27196.208.0.0/13196.208.0.1 to 196.215.255.254196.215.255.255524,286
28196.216.0.0/13196.216.0.1 to 196.223.255.254196.223.255.255524,286
29196.224.0.0/13196.224.0.1 to 196.231.255.254196.231.255.255524,286
30196.232.0.0/13196.232.0.1 to 196.239.255.254196.239.255.255524,286
31196.240.0.0/13196.240.0.1 to 196.247.255.254196.247.255.255524,286
32196.248.0.0/13196.248.0.1 to 196.255.255.254196.255.255.255524,286
33197.0.0.0/13197.0.0.1 to 197.7.255.254197.7.255.255524,286
34197.8.0.0/13197.8.0.1 to 197.15.255.254197.15.255.255524,286
35197.16.0.0/13197.16.0.1 to 197.23.255.254197.23.255.255524,286
36197.24.0.0/13197.24.0.1 to 197.31.255.254197.31.255.255524,286
37197.32.0.0/13197.32.0.1 to 197.39.255.254197.39.255.255524,286
38197.40.0.0/13197.40.0.1 to 197.47.255.254197.47.255.255524,286
39197.48.0.0/13197.48.0.1 to 197.55.255.254197.55.255.255524,286
40197.56.0.0/13197.56.0.1 to 197.63.255.254197.63.255.255524,286
41197.64.0.0/13197.64.0.1 to 197.71.255.254197.71.255.255524,286
42197.72.0.0/13197.72.0.1 to 197.79.255.254197.79.255.255524,286
43197.80.0.0/13197.80.0.1 to 197.87.255.254197.87.255.255524,286
44197.88.0.0/13197.88.0.1 to 197.95.255.254197.95.255.255524,286
45197.96.0.0/13197.96.0.1 to 197.103.255.254197.103.255.255524,286
46197.104.0.0/13197.104.0.1 to 197.111.255.254197.111.255.255524,286
47197.112.0.0/13197.112.0.1 to 197.119.255.254197.119.255.255524,286
48197.120.0.0/13197.120.0.1 to 197.127.255.254197.127.255.255524,286
49197.128.0.0/13197.128.0.1 to 197.135.255.254197.135.255.255524,286
50197.136.0.0/13197.136.0.1 to 197.143.255.254197.143.255.255524,286
51197.144.0.0/13197.144.0.1 to 197.151.255.254197.151.255.255524,286
52197.152.0.0/13197.152.0.1 to 197.159.255.254197.159.255.255524,286
53197.160.0.0/13197.160.0.1 to 197.167.255.254197.167.255.255524,286
54197.168.0.0/13197.168.0.1 to 197.175.255.254197.175.255.255524,286
55197.176.0.0/13197.176.0.1 to 197.183.255.254197.183.255.255524,286
56197.184.0.0/13197.184.0.1 to 197.191.255.254197.191.255.255524,286
57197.192.0.0/13197.192.0.1 to 197.199.255.254197.199.255.255524,286
58197.200.0.0/13197.200.0.1 to 197.207.255.254197.207.255.255524,286
59197.208.0.0/13197.208.0.1 to 197.215.255.254197.215.255.255524,286
60197.216.0.0/13197.216.0.1 to 197.223.255.254197.223.255.255524,286
61197.224.0.0/13197.224.0.1 to 197.231.255.254197.231.255.255524,286
62197.232.0.0/13197.232.0.1 to 197.239.255.254197.239.255.255524,286
63197.240.0.0/13197.240.0.1 to 197.247.255.254197.247.255.255524,286
64197.248.0.0/13197.248.0.1 to 197.255.255.254197.255.255.255524,286

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.