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.

Network16.192.0.0/10
Usable hosts4,194,302
Subnet mask255.192.0.0
Addresses4,194,304
Network address
16.192.0.0
Broadcast address
16.255.255.255
First usable
16.192.0.1
Last usable
16.255.255.254
Usable hosts
4,194,302 (4,194,304 less the network and broadcast addresses)
Subnet mask
255.192.0.0
Wildcard mask
0.63.255.255 (Cisco ACLs, OSPF)
Prefix length
/10
Type
Public public
Old class
A (default /8)
As numbers
Hex 10C00000 · Integer 281018368 to 285212671
Reverse DNS zones
192.16.in-addr.arpa
193.16.in-addr.arpa
194.16.in-addr.arpa
195.16.in-addr.arpa
196.16.in-addr.arpa
197.16.in-addr.arpa
198.16.in-addr.arpa
199.16.in-addr.arpa
200.16.in-addr.arpa
201.16.in-addr.arpa
202.16.in-addr.arpa
203.16.in-addr.arpa
204.16.in-addr.arpa
205.16.in-addr.arpa
206.16.in-addr.arpa
207.16.in-addr.arpa
and 48 more
/10 is not on a 8-bit boundary, so it takes 64 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00010000.11000000.00000000.0000000016.192.0.0
Subnet mask11111111.11000000.00000000.00000000255.192.0.0
Network00010000.11000000.00000000.0000000016.192.0.0
Broadcast00010000.11111111.11111111.1111111116.255.255.255
Split into smaller subnets/16
/11 (2)/12 (4)/13 (8)/14 (16)/15 (32)/16 (64)/17 (128)/18 (256)/19 (512)/20 (1,024)/21 (2,048)/22 (4,096)

16.192.0.0/10 makes 64 subnets of /16.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
116.192.0.0/1616.192.0.1 to 16.192.255.25416.192.255.25565,534
216.193.0.0/1616.193.0.1 to 16.193.255.25416.193.255.25565,534
316.194.0.0/1616.194.0.1 to 16.194.255.25416.194.255.25565,534
416.195.0.0/1616.195.0.1 to 16.195.255.25416.195.255.25565,534
516.196.0.0/1616.196.0.1 to 16.196.255.25416.196.255.25565,534
616.197.0.0/1616.197.0.1 to 16.197.255.25416.197.255.25565,534
716.198.0.0/1616.198.0.1 to 16.198.255.25416.198.255.25565,534
816.199.0.0/1616.199.0.1 to 16.199.255.25416.199.255.25565,534
916.200.0.0/1616.200.0.1 to 16.200.255.25416.200.255.25565,534
1016.201.0.0/1616.201.0.1 to 16.201.255.25416.201.255.25565,534
1116.202.0.0/1616.202.0.1 to 16.202.255.25416.202.255.25565,534
1216.203.0.0/1616.203.0.1 to 16.203.255.25416.203.255.25565,534
1316.204.0.0/1616.204.0.1 to 16.204.255.25416.204.255.25565,534
1416.205.0.0/1616.205.0.1 to 16.205.255.25416.205.255.25565,534
1516.206.0.0/1616.206.0.1 to 16.206.255.25416.206.255.25565,534
1616.207.0.0/1616.207.0.1 to 16.207.255.25416.207.255.25565,534
1716.208.0.0/1616.208.0.1 to 16.208.255.25416.208.255.25565,534
1816.209.0.0/1616.209.0.1 to 16.209.255.25416.209.255.25565,534
1916.210.0.0/1616.210.0.1 to 16.210.255.25416.210.255.25565,534
2016.211.0.0/1616.211.0.1 to 16.211.255.25416.211.255.25565,534
2116.212.0.0/1616.212.0.1 to 16.212.255.25416.212.255.25565,534
2216.213.0.0/1616.213.0.1 to 16.213.255.25416.213.255.25565,534
2316.214.0.0/1616.214.0.1 to 16.214.255.25416.214.255.25565,534
2416.215.0.0/1616.215.0.1 to 16.215.255.25416.215.255.25565,534
2516.216.0.0/1616.216.0.1 to 16.216.255.25416.216.255.25565,534
2616.217.0.0/1616.217.0.1 to 16.217.255.25416.217.255.25565,534
2716.218.0.0/1616.218.0.1 to 16.218.255.25416.218.255.25565,534
2816.219.0.0/1616.219.0.1 to 16.219.255.25416.219.255.25565,534
2916.220.0.0/1616.220.0.1 to 16.220.255.25416.220.255.25565,534
3016.221.0.0/1616.221.0.1 to 16.221.255.25416.221.255.25565,534
3116.222.0.0/1616.222.0.1 to 16.222.255.25416.222.255.25565,534
3216.223.0.0/1616.223.0.1 to 16.223.255.25416.223.255.25565,534
3316.224.0.0/1616.224.0.1 to 16.224.255.25416.224.255.25565,534
3416.225.0.0/1616.225.0.1 to 16.225.255.25416.225.255.25565,534
3516.226.0.0/1616.226.0.1 to 16.226.255.25416.226.255.25565,534
3616.227.0.0/1616.227.0.1 to 16.227.255.25416.227.255.25565,534
3716.228.0.0/1616.228.0.1 to 16.228.255.25416.228.255.25565,534
3816.229.0.0/1616.229.0.1 to 16.229.255.25416.229.255.25565,534
3916.230.0.0/1616.230.0.1 to 16.230.255.25416.230.255.25565,534
4016.231.0.0/1616.231.0.1 to 16.231.255.25416.231.255.25565,534
4116.232.0.0/1616.232.0.1 to 16.232.255.25416.232.255.25565,534
4216.233.0.0/1616.233.0.1 to 16.233.255.25416.233.255.25565,534
4316.234.0.0/1616.234.0.1 to 16.234.255.25416.234.255.25565,534
4416.235.0.0/1616.235.0.1 to 16.235.255.25416.235.255.25565,534
4516.236.0.0/1616.236.0.1 to 16.236.255.25416.236.255.25565,534
4616.237.0.0/1616.237.0.1 to 16.237.255.25416.237.255.25565,534
4716.238.0.0/1616.238.0.1 to 16.238.255.25416.238.255.25565,534
4816.239.0.0/1616.239.0.1 to 16.239.255.25416.239.255.25565,534
4916.240.0.0/1616.240.0.1 to 16.240.255.25416.240.255.25565,534
5016.241.0.0/1616.241.0.1 to 16.241.255.25416.241.255.25565,534
5116.242.0.0/1616.242.0.1 to 16.242.255.25416.242.255.25565,534
5216.243.0.0/1616.243.0.1 to 16.243.255.25416.243.255.25565,534
5316.244.0.0/1616.244.0.1 to 16.244.255.25416.244.255.25565,534
5416.245.0.0/1616.245.0.1 to 16.245.255.25416.245.255.25565,534
5516.246.0.0/1616.246.0.1 to 16.246.255.25416.246.255.25565,534
5616.247.0.0/1616.247.0.1 to 16.247.255.25416.247.255.25565,534
5716.248.0.0/1616.248.0.1 to 16.248.255.25416.248.255.25565,534
5816.249.0.0/1616.249.0.1 to 16.249.255.25416.249.255.25565,534
5916.250.0.0/1616.250.0.1 to 16.250.255.25416.250.255.25565,534
6016.251.0.0/1616.251.0.1 to 16.251.255.25416.251.255.25565,534
6116.252.0.0/1616.252.0.1 to 16.252.255.25416.252.255.25565,534
6216.253.0.0/1616.253.0.1 to 16.253.255.25416.253.255.25565,534
6316.254.0.0/1616.254.0.1 to 16.254.255.25416.254.255.25565,534
6416.255.0.0/1616.255.0.1 to 16.255.255.25416.255.255.25565,534

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.