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.

Network43.0.0.0/9
Usable hosts8,388,606
Subnet mask255.128.0.0
Addresses8,388,608
Network address
43.0.0.0
Broadcast address
43.127.255.255
First usable
43.0.0.1
Last usable
43.127.255.254
Usable hosts
8,388,606 (8,388,608 less the network and broadcast addresses)
Subnet mask
255.128.0.0
Wildcard mask
0.127.255.255 (Cisco ACLs, OSPF)
Prefix length
/9
Type
Public public
Old class
A (default /8)
As numbers
Hex 2B000000 · Integer 721420288 to 729808895
Reverse DNS zones
0.43.in-addr.arpa
1.43.in-addr.arpa
2.43.in-addr.arpa
3.43.in-addr.arpa
4.43.in-addr.arpa
5.43.in-addr.arpa
6.43.in-addr.arpa
7.43.in-addr.arpa
8.43.in-addr.arpa
9.43.in-addr.arpa
10.43.in-addr.arpa
11.43.in-addr.arpa
12.43.in-addr.arpa
13.43.in-addr.arpa
14.43.in-addr.arpa
15.43.in-addr.arpa
and 112 more
/9 is not on a 8-bit boundary, so it takes 128 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00101011.00000000.00000000.0000000043.0.0.0
Subnet mask11111111.10000000.00000000.00000000255.128.0.0
Network00101011.00000000.00000000.0000000043.0.0.0
Broadcast00101011.01111111.11111111.1111111143.127.255.255
Split into smaller subnets/16
/10 (2)/11 (4)/12 (8)/13 (16)/14 (32)/15 (64)/16 (128)/17 (256)/18 (512)/19 (1,024)/20 (2,048)/21 (4,096)

43.0.0.0/9 makes 128 subnets of /16.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
143.0.0.0/1643.0.0.1 to 43.0.255.25443.0.255.25565,534
243.1.0.0/1643.1.0.1 to 43.1.255.25443.1.255.25565,534
343.2.0.0/1643.2.0.1 to 43.2.255.25443.2.255.25565,534
443.3.0.0/1643.3.0.1 to 43.3.255.25443.3.255.25565,534
543.4.0.0/1643.4.0.1 to 43.4.255.25443.4.255.25565,534
643.5.0.0/1643.5.0.1 to 43.5.255.25443.5.255.25565,534
743.6.0.0/1643.6.0.1 to 43.6.255.25443.6.255.25565,534
843.7.0.0/1643.7.0.1 to 43.7.255.25443.7.255.25565,534
943.8.0.0/1643.8.0.1 to 43.8.255.25443.8.255.25565,534
1043.9.0.0/1643.9.0.1 to 43.9.255.25443.9.255.25565,534
1143.10.0.0/1643.10.0.1 to 43.10.255.25443.10.255.25565,534
1243.11.0.0/1643.11.0.1 to 43.11.255.25443.11.255.25565,534
1343.12.0.0/1643.12.0.1 to 43.12.255.25443.12.255.25565,534
1443.13.0.0/1643.13.0.1 to 43.13.255.25443.13.255.25565,534
1543.14.0.0/1643.14.0.1 to 43.14.255.25443.14.255.25565,534
1643.15.0.0/1643.15.0.1 to 43.15.255.25443.15.255.25565,534
1743.16.0.0/1643.16.0.1 to 43.16.255.25443.16.255.25565,534
1843.17.0.0/1643.17.0.1 to 43.17.255.25443.17.255.25565,534
1943.18.0.0/1643.18.0.1 to 43.18.255.25443.18.255.25565,534
2043.19.0.0/1643.19.0.1 to 43.19.255.25443.19.255.25565,534
2143.20.0.0/1643.20.0.1 to 43.20.255.25443.20.255.25565,534
2243.21.0.0/1643.21.0.1 to 43.21.255.25443.21.255.25565,534
2343.22.0.0/1643.22.0.1 to 43.22.255.25443.22.255.25565,534
2443.23.0.0/1643.23.0.1 to 43.23.255.25443.23.255.25565,534
2543.24.0.0/1643.24.0.1 to 43.24.255.25443.24.255.25565,534
2643.25.0.0/1643.25.0.1 to 43.25.255.25443.25.255.25565,534
2743.26.0.0/1643.26.0.1 to 43.26.255.25443.26.255.25565,534
2843.27.0.0/1643.27.0.1 to 43.27.255.25443.27.255.25565,534
2943.28.0.0/1643.28.0.1 to 43.28.255.25443.28.255.25565,534
3043.29.0.0/1643.29.0.1 to 43.29.255.25443.29.255.25565,534
3143.30.0.0/1643.30.0.1 to 43.30.255.25443.30.255.25565,534
3243.31.0.0/1643.31.0.1 to 43.31.255.25443.31.255.25565,534
3343.32.0.0/1643.32.0.1 to 43.32.255.25443.32.255.25565,534
3443.33.0.0/1643.33.0.1 to 43.33.255.25443.33.255.25565,534
3543.34.0.0/1643.34.0.1 to 43.34.255.25443.34.255.25565,534
3643.35.0.0/1643.35.0.1 to 43.35.255.25443.35.255.25565,534
3743.36.0.0/1643.36.0.1 to 43.36.255.25443.36.255.25565,534
3843.37.0.0/1643.37.0.1 to 43.37.255.25443.37.255.25565,534
3943.38.0.0/1643.38.0.1 to 43.38.255.25443.38.255.25565,534
4043.39.0.0/1643.39.0.1 to 43.39.255.25443.39.255.25565,534
4143.40.0.0/1643.40.0.1 to 43.40.255.25443.40.255.25565,534
4243.41.0.0/1643.41.0.1 to 43.41.255.25443.41.255.25565,534
4343.42.0.0/1643.42.0.1 to 43.42.255.25443.42.255.25565,534
4443.43.0.0/1643.43.0.1 to 43.43.255.25443.43.255.25565,534
4543.44.0.0/1643.44.0.1 to 43.44.255.25443.44.255.25565,534
4643.45.0.0/1643.45.0.1 to 43.45.255.25443.45.255.25565,534
4743.46.0.0/1643.46.0.1 to 43.46.255.25443.46.255.25565,534
4843.47.0.0/1643.47.0.1 to 43.47.255.25443.47.255.25565,534
4943.48.0.0/1643.48.0.1 to 43.48.255.25443.48.255.25565,534
5043.49.0.0/1643.49.0.1 to 43.49.255.25443.49.255.25565,534
5143.50.0.0/1643.50.0.1 to 43.50.255.25443.50.255.25565,534
5243.51.0.0/1643.51.0.1 to 43.51.255.25443.51.255.25565,534
5343.52.0.0/1643.52.0.1 to 43.52.255.25443.52.255.25565,534
5443.53.0.0/1643.53.0.1 to 43.53.255.25443.53.255.25565,534
5543.54.0.0/1643.54.0.1 to 43.54.255.25443.54.255.25565,534
5643.55.0.0/1643.55.0.1 to 43.55.255.25443.55.255.25565,534
5743.56.0.0/1643.56.0.1 to 43.56.255.25443.56.255.25565,534
5843.57.0.0/1643.57.0.1 to 43.57.255.25443.57.255.25565,534
5943.58.0.0/1643.58.0.1 to 43.58.255.25443.58.255.25565,534
6043.59.0.0/1643.59.0.1 to 43.59.255.25443.59.255.25565,534
6143.60.0.0/1643.60.0.1 to 43.60.255.25443.60.255.25565,534
6243.61.0.0/1643.61.0.1 to 43.61.255.25443.61.255.25565,534
6343.62.0.0/1643.62.0.1 to 43.62.255.25443.62.255.25565,534
6443.63.0.0/1643.63.0.1 to 43.63.255.25443.63.255.25565,534
6543.64.0.0/1643.64.0.1 to 43.64.255.25443.64.255.25565,534
6643.65.0.0/1643.65.0.1 to 43.65.255.25443.65.255.25565,534
6743.66.0.0/1643.66.0.1 to 43.66.255.25443.66.255.25565,534
6843.67.0.0/1643.67.0.1 to 43.67.255.25443.67.255.25565,534
6943.68.0.0/1643.68.0.1 to 43.68.255.25443.68.255.25565,534
7043.69.0.0/1643.69.0.1 to 43.69.255.25443.69.255.25565,534
7143.70.0.0/1643.70.0.1 to 43.70.255.25443.70.255.25565,534
7243.71.0.0/1643.71.0.1 to 43.71.255.25443.71.255.25565,534
7343.72.0.0/1643.72.0.1 to 43.72.255.25443.72.255.25565,534
7443.73.0.0/1643.73.0.1 to 43.73.255.25443.73.255.25565,534
7543.74.0.0/1643.74.0.1 to 43.74.255.25443.74.255.25565,534
7643.75.0.0/1643.75.0.1 to 43.75.255.25443.75.255.25565,534
7743.76.0.0/1643.76.0.1 to 43.76.255.25443.76.255.25565,534
7843.77.0.0/1643.77.0.1 to 43.77.255.25443.77.255.25565,534
7943.78.0.0/1643.78.0.1 to 43.78.255.25443.78.255.25565,534
8043.79.0.0/1643.79.0.1 to 43.79.255.25443.79.255.25565,534
8143.80.0.0/1643.80.0.1 to 43.80.255.25443.80.255.25565,534
8243.81.0.0/1643.81.0.1 to 43.81.255.25443.81.255.25565,534
8343.82.0.0/1643.82.0.1 to 43.82.255.25443.82.255.25565,534
8443.83.0.0/1643.83.0.1 to 43.83.255.25443.83.255.25565,534
8543.84.0.0/1643.84.0.1 to 43.84.255.25443.84.255.25565,534
8643.85.0.0/1643.85.0.1 to 43.85.255.25443.85.255.25565,534
8743.86.0.0/1643.86.0.1 to 43.86.255.25443.86.255.25565,534
8843.87.0.0/1643.87.0.1 to 43.87.255.25443.87.255.25565,534
8943.88.0.0/1643.88.0.1 to 43.88.255.25443.88.255.25565,534
9043.89.0.0/1643.89.0.1 to 43.89.255.25443.89.255.25565,534
9143.90.0.0/1643.90.0.1 to 43.90.255.25443.90.255.25565,534
9243.91.0.0/1643.91.0.1 to 43.91.255.25443.91.255.25565,534
9343.92.0.0/1643.92.0.1 to 43.92.255.25443.92.255.25565,534
9443.93.0.0/1643.93.0.1 to 43.93.255.25443.93.255.25565,534
9543.94.0.0/1643.94.0.1 to 43.94.255.25443.94.255.25565,534
9643.95.0.0/1643.95.0.1 to 43.95.255.25443.95.255.25565,534
9743.96.0.0/1643.96.0.1 to 43.96.255.25443.96.255.25565,534
9843.97.0.0/1643.97.0.1 to 43.97.255.25443.97.255.25565,534
9943.98.0.0/1643.98.0.1 to 43.98.255.25443.98.255.25565,534
10043.99.0.0/1643.99.0.1 to 43.99.255.25443.99.255.25565,534
10143.100.0.0/1643.100.0.1 to 43.100.255.25443.100.255.25565,534
10243.101.0.0/1643.101.0.1 to 43.101.255.25443.101.255.25565,534
10343.102.0.0/1643.102.0.1 to 43.102.255.25443.102.255.25565,534
10443.103.0.0/1643.103.0.1 to 43.103.255.25443.103.255.25565,534
10543.104.0.0/1643.104.0.1 to 43.104.255.25443.104.255.25565,534
10643.105.0.0/1643.105.0.1 to 43.105.255.25443.105.255.25565,534
10743.106.0.0/1643.106.0.1 to 43.106.255.25443.106.255.25565,534
10843.107.0.0/1643.107.0.1 to 43.107.255.25443.107.255.25565,534
10943.108.0.0/1643.108.0.1 to 43.108.255.25443.108.255.25565,534
11043.109.0.0/1643.109.0.1 to 43.109.255.25443.109.255.25565,534
11143.110.0.0/1643.110.0.1 to 43.110.255.25443.110.255.25565,534
11243.111.0.0/1643.111.0.1 to 43.111.255.25443.111.255.25565,534
11343.112.0.0/1643.112.0.1 to 43.112.255.25443.112.255.25565,534
11443.113.0.0/1643.113.0.1 to 43.113.255.25443.113.255.25565,534
11543.114.0.0/1643.114.0.1 to 43.114.255.25443.114.255.25565,534
11643.115.0.0/1643.115.0.1 to 43.115.255.25443.115.255.25565,534
11743.116.0.0/1643.116.0.1 to 43.116.255.25443.116.255.25565,534
11843.117.0.0/1643.117.0.1 to 43.117.255.25443.117.255.25565,534
11943.118.0.0/1643.118.0.1 to 43.118.255.25443.118.255.25565,534
12043.119.0.0/1643.119.0.1 to 43.119.255.25443.119.255.25565,534
12143.120.0.0/1643.120.0.1 to 43.120.255.25443.120.255.25565,534
12243.121.0.0/1643.121.0.1 to 43.121.255.25443.121.255.25565,534
12343.122.0.0/1643.122.0.1 to 43.122.255.25443.122.255.25565,534
12443.123.0.0/1643.123.0.1 to 43.123.255.25443.123.255.25565,534
12543.124.0.0/1643.124.0.1 to 43.124.255.25443.124.255.25565,534
12643.125.0.0/1643.125.0.1 to 43.125.255.25443.125.255.25565,534
12743.126.0.0/1643.126.0.1 to 43.126.255.25443.126.255.25565,534
12843.127.0.0/1643.127.0.1 to 43.127.255.25443.127.255.25565,534

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.