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.

Network44.0.40.0/22
Usable hosts1,022
Subnet mask255.255.252.0
Addresses1,024
Network address
44.0.40.0
Broadcast address
44.0.43.255
First usable
44.0.40.1
Last usable
44.0.43.254
Usable hosts
1,022 (1,024 less the network and broadcast addresses)
Subnet mask
255.255.252.0
Wildcard mask
0.0.3.255 (Cisco ACLs, OSPF)
Prefix length
/22
Type
Public public
Old class
A (default /8)
As numbers
Hex 2C002800 · Integer 738207744 to 738208767
Reverse DNS zones
40.0.44.in-addr.arpa
41.0.44.in-addr.arpa
42.0.44.in-addr.arpa
43.0.44.in-addr.arpa
/22 is not on a 8-bit boundary, so it takes 4 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00101100.00000000.00101000.0000000044.0.40.0
Subnet mask11111111.11111111.11111100.00000000255.255.252.0
Network00101100.00000000.00101000.0000000044.0.40.0
Broadcast00101100.00000000.00101011.1111111144.0.43.255
Split into smaller subnets/29
/23 (2)/24 (4)/25 (8)/26 (16)/27 (32)/28 (64)/29 (128)/30 (256)/31 (512)/32 (1,024)

44.0.40.0/22 makes 128 subnets of /29.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
144.0.40.0/2944.0.40.1 to 44.0.40.644.0.40.76
244.0.40.8/2944.0.40.9 to 44.0.40.1444.0.40.156
344.0.40.16/2944.0.40.17 to 44.0.40.2244.0.40.236
444.0.40.24/2944.0.40.25 to 44.0.40.3044.0.40.316
544.0.40.32/2944.0.40.33 to 44.0.40.3844.0.40.396
644.0.40.40/2944.0.40.41 to 44.0.40.4644.0.40.476
744.0.40.48/2944.0.40.49 to 44.0.40.5444.0.40.556
844.0.40.56/2944.0.40.57 to 44.0.40.6244.0.40.636
944.0.40.64/2944.0.40.65 to 44.0.40.7044.0.40.716
1044.0.40.72/2944.0.40.73 to 44.0.40.7844.0.40.796
1144.0.40.80/2944.0.40.81 to 44.0.40.8644.0.40.876
1244.0.40.88/2944.0.40.89 to 44.0.40.9444.0.40.956
1344.0.40.96/2944.0.40.97 to 44.0.40.10244.0.40.1036
1444.0.40.104/2944.0.40.105 to 44.0.40.11044.0.40.1116
1544.0.40.112/2944.0.40.113 to 44.0.40.11844.0.40.1196
1644.0.40.120/2944.0.40.121 to 44.0.40.12644.0.40.1276
1744.0.40.128/2944.0.40.129 to 44.0.40.13444.0.40.1356
1844.0.40.136/2944.0.40.137 to 44.0.40.14244.0.40.1436
1944.0.40.144/2944.0.40.145 to 44.0.40.15044.0.40.1516
2044.0.40.152/2944.0.40.153 to 44.0.40.15844.0.40.1596
2144.0.40.160/2944.0.40.161 to 44.0.40.16644.0.40.1676
2244.0.40.168/2944.0.40.169 to 44.0.40.17444.0.40.1756
2344.0.40.176/2944.0.40.177 to 44.0.40.18244.0.40.1836
2444.0.40.184/2944.0.40.185 to 44.0.40.19044.0.40.1916
2544.0.40.192/2944.0.40.193 to 44.0.40.19844.0.40.1996
2644.0.40.200/2944.0.40.201 to 44.0.40.20644.0.40.2076
2744.0.40.208/2944.0.40.209 to 44.0.40.21444.0.40.2156
2844.0.40.216/2944.0.40.217 to 44.0.40.22244.0.40.2236
2944.0.40.224/2944.0.40.225 to 44.0.40.23044.0.40.2316
3044.0.40.232/2944.0.40.233 to 44.0.40.23844.0.40.2396
3144.0.40.240/2944.0.40.241 to 44.0.40.24644.0.40.2476
3244.0.40.248/2944.0.40.249 to 44.0.40.25444.0.40.2556
3344.0.41.0/2944.0.41.1 to 44.0.41.644.0.41.76
3444.0.41.8/2944.0.41.9 to 44.0.41.1444.0.41.156
3544.0.41.16/2944.0.41.17 to 44.0.41.2244.0.41.236
3644.0.41.24/2944.0.41.25 to 44.0.41.3044.0.41.316
3744.0.41.32/2944.0.41.33 to 44.0.41.3844.0.41.396
3844.0.41.40/2944.0.41.41 to 44.0.41.4644.0.41.476
3944.0.41.48/2944.0.41.49 to 44.0.41.5444.0.41.556
4044.0.41.56/2944.0.41.57 to 44.0.41.6244.0.41.636
4144.0.41.64/2944.0.41.65 to 44.0.41.7044.0.41.716
4244.0.41.72/2944.0.41.73 to 44.0.41.7844.0.41.796
4344.0.41.80/2944.0.41.81 to 44.0.41.8644.0.41.876
4444.0.41.88/2944.0.41.89 to 44.0.41.9444.0.41.956
4544.0.41.96/2944.0.41.97 to 44.0.41.10244.0.41.1036
4644.0.41.104/2944.0.41.105 to 44.0.41.11044.0.41.1116
4744.0.41.112/2944.0.41.113 to 44.0.41.11844.0.41.1196
4844.0.41.120/2944.0.41.121 to 44.0.41.12644.0.41.1276
4944.0.41.128/2944.0.41.129 to 44.0.41.13444.0.41.1356
5044.0.41.136/2944.0.41.137 to 44.0.41.14244.0.41.1436
5144.0.41.144/2944.0.41.145 to 44.0.41.15044.0.41.1516
5244.0.41.152/2944.0.41.153 to 44.0.41.15844.0.41.1596
5344.0.41.160/2944.0.41.161 to 44.0.41.16644.0.41.1676
5444.0.41.168/2944.0.41.169 to 44.0.41.17444.0.41.1756
5544.0.41.176/2944.0.41.177 to 44.0.41.18244.0.41.1836
5644.0.41.184/2944.0.41.185 to 44.0.41.19044.0.41.1916
5744.0.41.192/2944.0.41.193 to 44.0.41.19844.0.41.1996
5844.0.41.200/2944.0.41.201 to 44.0.41.20644.0.41.2076
5944.0.41.208/2944.0.41.209 to 44.0.41.21444.0.41.2156
6044.0.41.216/2944.0.41.217 to 44.0.41.22244.0.41.2236
6144.0.41.224/2944.0.41.225 to 44.0.41.23044.0.41.2316
6244.0.41.232/2944.0.41.233 to 44.0.41.23844.0.41.2396
6344.0.41.240/2944.0.41.241 to 44.0.41.24644.0.41.2476
6444.0.41.248/2944.0.41.249 to 44.0.41.25444.0.41.2556
6544.0.42.0/2944.0.42.1 to 44.0.42.644.0.42.76
6644.0.42.8/2944.0.42.9 to 44.0.42.1444.0.42.156
6744.0.42.16/2944.0.42.17 to 44.0.42.2244.0.42.236
6844.0.42.24/2944.0.42.25 to 44.0.42.3044.0.42.316
6944.0.42.32/2944.0.42.33 to 44.0.42.3844.0.42.396
7044.0.42.40/2944.0.42.41 to 44.0.42.4644.0.42.476
7144.0.42.48/2944.0.42.49 to 44.0.42.5444.0.42.556
7244.0.42.56/2944.0.42.57 to 44.0.42.6244.0.42.636
7344.0.42.64/2944.0.42.65 to 44.0.42.7044.0.42.716
7444.0.42.72/2944.0.42.73 to 44.0.42.7844.0.42.796
7544.0.42.80/2944.0.42.81 to 44.0.42.8644.0.42.876
7644.0.42.88/2944.0.42.89 to 44.0.42.9444.0.42.956
7744.0.42.96/2944.0.42.97 to 44.0.42.10244.0.42.1036
7844.0.42.104/2944.0.42.105 to 44.0.42.11044.0.42.1116
7944.0.42.112/2944.0.42.113 to 44.0.42.11844.0.42.1196
8044.0.42.120/2944.0.42.121 to 44.0.42.12644.0.42.1276
8144.0.42.128/2944.0.42.129 to 44.0.42.13444.0.42.1356
8244.0.42.136/2944.0.42.137 to 44.0.42.14244.0.42.1436
8344.0.42.144/2944.0.42.145 to 44.0.42.15044.0.42.1516
8444.0.42.152/2944.0.42.153 to 44.0.42.15844.0.42.1596
8544.0.42.160/2944.0.42.161 to 44.0.42.16644.0.42.1676
8644.0.42.168/2944.0.42.169 to 44.0.42.17444.0.42.1756
8744.0.42.176/2944.0.42.177 to 44.0.42.18244.0.42.1836
8844.0.42.184/2944.0.42.185 to 44.0.42.19044.0.42.1916
8944.0.42.192/2944.0.42.193 to 44.0.42.19844.0.42.1996
9044.0.42.200/2944.0.42.201 to 44.0.42.20644.0.42.2076
9144.0.42.208/2944.0.42.209 to 44.0.42.21444.0.42.2156
9244.0.42.216/2944.0.42.217 to 44.0.42.22244.0.42.2236
9344.0.42.224/2944.0.42.225 to 44.0.42.23044.0.42.2316
9444.0.42.232/2944.0.42.233 to 44.0.42.23844.0.42.2396
9544.0.42.240/2944.0.42.241 to 44.0.42.24644.0.42.2476
9644.0.42.248/2944.0.42.249 to 44.0.42.25444.0.42.2556
9744.0.43.0/2944.0.43.1 to 44.0.43.644.0.43.76
9844.0.43.8/2944.0.43.9 to 44.0.43.1444.0.43.156
9944.0.43.16/2944.0.43.17 to 44.0.43.2244.0.43.236
10044.0.43.24/2944.0.43.25 to 44.0.43.3044.0.43.316
10144.0.43.32/2944.0.43.33 to 44.0.43.3844.0.43.396
10244.0.43.40/2944.0.43.41 to 44.0.43.4644.0.43.476
10344.0.43.48/2944.0.43.49 to 44.0.43.5444.0.43.556
10444.0.43.56/2944.0.43.57 to 44.0.43.6244.0.43.636
10544.0.43.64/2944.0.43.65 to 44.0.43.7044.0.43.716
10644.0.43.72/2944.0.43.73 to 44.0.43.7844.0.43.796
10744.0.43.80/2944.0.43.81 to 44.0.43.8644.0.43.876
10844.0.43.88/2944.0.43.89 to 44.0.43.9444.0.43.956
10944.0.43.96/2944.0.43.97 to 44.0.43.10244.0.43.1036
11044.0.43.104/2944.0.43.105 to 44.0.43.11044.0.43.1116
11144.0.43.112/2944.0.43.113 to 44.0.43.11844.0.43.1196
11244.0.43.120/2944.0.43.121 to 44.0.43.12644.0.43.1276
11344.0.43.128/2944.0.43.129 to 44.0.43.13444.0.43.1356
11444.0.43.136/2944.0.43.137 to 44.0.43.14244.0.43.1436
11544.0.43.144/2944.0.43.145 to 44.0.43.15044.0.43.1516
11644.0.43.152/2944.0.43.153 to 44.0.43.15844.0.43.1596
11744.0.43.160/2944.0.43.161 to 44.0.43.16644.0.43.1676
11844.0.43.168/2944.0.43.169 to 44.0.43.17444.0.43.1756
11944.0.43.176/2944.0.43.177 to 44.0.43.18244.0.43.1836
12044.0.43.184/2944.0.43.185 to 44.0.43.19044.0.43.1916
12144.0.43.192/2944.0.43.193 to 44.0.43.19844.0.43.1996
12244.0.43.200/2944.0.43.201 to 44.0.43.20644.0.43.2076
12344.0.43.208/2944.0.43.209 to 44.0.43.21444.0.43.2156
12444.0.43.216/2944.0.43.217 to 44.0.43.22244.0.43.2236
12544.0.43.224/2944.0.43.225 to 44.0.43.23044.0.43.2316
12644.0.43.232/2944.0.43.233 to 44.0.43.23844.0.43.2396
12744.0.43.240/2944.0.43.241 to 44.0.43.24644.0.43.2476
12844.0.43.248/2944.0.43.249 to 44.0.43.25444.0.43.2556

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.