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.

Network48.128.0.0/10
Usable hosts4,194,302
Subnet mask255.192.0.0
Addresses4,194,304
Network address
48.128.0.0
Broadcast address
48.191.255.255
First usable
48.128.0.1
Last usable
48.191.255.254
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 30800000 · Integer 813694976 to 817889279
Reverse DNS zones
128.48.in-addr.arpa
129.48.in-addr.arpa
130.48.in-addr.arpa
131.48.in-addr.arpa
132.48.in-addr.arpa
133.48.in-addr.arpa
134.48.in-addr.arpa
135.48.in-addr.arpa
136.48.in-addr.arpa
137.48.in-addr.arpa
138.48.in-addr.arpa
139.48.in-addr.arpa
140.48.in-addr.arpa
141.48.in-addr.arpa
142.48.in-addr.arpa
143.48.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
Address00110000.10000000.00000000.0000000048.128.0.0
Subnet mask11111111.11000000.00000000.00000000255.192.0.0
Network00110000.10000000.00000000.0000000048.128.0.0
Broadcast00110000.10111111.11111111.1111111148.191.255.255
Split into smaller subnets/17
/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)

48.128.0.0/10 makes 128 subnets of /17.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
148.128.0.0/1748.128.0.1 to 48.128.127.25448.128.127.25532,766
248.128.128.0/1748.128.128.1 to 48.128.255.25448.128.255.25532,766
348.129.0.0/1748.129.0.1 to 48.129.127.25448.129.127.25532,766
448.129.128.0/1748.129.128.1 to 48.129.255.25448.129.255.25532,766
548.130.0.0/1748.130.0.1 to 48.130.127.25448.130.127.25532,766
648.130.128.0/1748.130.128.1 to 48.130.255.25448.130.255.25532,766
748.131.0.0/1748.131.0.1 to 48.131.127.25448.131.127.25532,766
848.131.128.0/1748.131.128.1 to 48.131.255.25448.131.255.25532,766
948.132.0.0/1748.132.0.1 to 48.132.127.25448.132.127.25532,766
1048.132.128.0/1748.132.128.1 to 48.132.255.25448.132.255.25532,766
1148.133.0.0/1748.133.0.1 to 48.133.127.25448.133.127.25532,766
1248.133.128.0/1748.133.128.1 to 48.133.255.25448.133.255.25532,766
1348.134.0.0/1748.134.0.1 to 48.134.127.25448.134.127.25532,766
1448.134.128.0/1748.134.128.1 to 48.134.255.25448.134.255.25532,766
1548.135.0.0/1748.135.0.1 to 48.135.127.25448.135.127.25532,766
1648.135.128.0/1748.135.128.1 to 48.135.255.25448.135.255.25532,766
1748.136.0.0/1748.136.0.1 to 48.136.127.25448.136.127.25532,766
1848.136.128.0/1748.136.128.1 to 48.136.255.25448.136.255.25532,766
1948.137.0.0/1748.137.0.1 to 48.137.127.25448.137.127.25532,766
2048.137.128.0/1748.137.128.1 to 48.137.255.25448.137.255.25532,766
2148.138.0.0/1748.138.0.1 to 48.138.127.25448.138.127.25532,766
2248.138.128.0/1748.138.128.1 to 48.138.255.25448.138.255.25532,766
2348.139.0.0/1748.139.0.1 to 48.139.127.25448.139.127.25532,766
2448.139.128.0/1748.139.128.1 to 48.139.255.25448.139.255.25532,766
2548.140.0.0/1748.140.0.1 to 48.140.127.25448.140.127.25532,766
2648.140.128.0/1748.140.128.1 to 48.140.255.25448.140.255.25532,766
2748.141.0.0/1748.141.0.1 to 48.141.127.25448.141.127.25532,766
2848.141.128.0/1748.141.128.1 to 48.141.255.25448.141.255.25532,766
2948.142.0.0/1748.142.0.1 to 48.142.127.25448.142.127.25532,766
3048.142.128.0/1748.142.128.1 to 48.142.255.25448.142.255.25532,766
3148.143.0.0/1748.143.0.1 to 48.143.127.25448.143.127.25532,766
3248.143.128.0/1748.143.128.1 to 48.143.255.25448.143.255.25532,766
3348.144.0.0/1748.144.0.1 to 48.144.127.25448.144.127.25532,766
3448.144.128.0/1748.144.128.1 to 48.144.255.25448.144.255.25532,766
3548.145.0.0/1748.145.0.1 to 48.145.127.25448.145.127.25532,766
3648.145.128.0/1748.145.128.1 to 48.145.255.25448.145.255.25532,766
3748.146.0.0/1748.146.0.1 to 48.146.127.25448.146.127.25532,766
3848.146.128.0/1748.146.128.1 to 48.146.255.25448.146.255.25532,766
3948.147.0.0/1748.147.0.1 to 48.147.127.25448.147.127.25532,766
4048.147.128.0/1748.147.128.1 to 48.147.255.25448.147.255.25532,766
4148.148.0.0/1748.148.0.1 to 48.148.127.25448.148.127.25532,766
4248.148.128.0/1748.148.128.1 to 48.148.255.25448.148.255.25532,766
4348.149.0.0/1748.149.0.1 to 48.149.127.25448.149.127.25532,766
4448.149.128.0/1748.149.128.1 to 48.149.255.25448.149.255.25532,766
4548.150.0.0/1748.150.0.1 to 48.150.127.25448.150.127.25532,766
4648.150.128.0/1748.150.128.1 to 48.150.255.25448.150.255.25532,766
4748.151.0.0/1748.151.0.1 to 48.151.127.25448.151.127.25532,766
4848.151.128.0/1748.151.128.1 to 48.151.255.25448.151.255.25532,766
4948.152.0.0/1748.152.0.1 to 48.152.127.25448.152.127.25532,766
5048.152.128.0/1748.152.128.1 to 48.152.255.25448.152.255.25532,766
5148.153.0.0/1748.153.0.1 to 48.153.127.25448.153.127.25532,766
5248.153.128.0/1748.153.128.1 to 48.153.255.25448.153.255.25532,766
5348.154.0.0/1748.154.0.1 to 48.154.127.25448.154.127.25532,766
5448.154.128.0/1748.154.128.1 to 48.154.255.25448.154.255.25532,766
5548.155.0.0/1748.155.0.1 to 48.155.127.25448.155.127.25532,766
5648.155.128.0/1748.155.128.1 to 48.155.255.25448.155.255.25532,766
5748.156.0.0/1748.156.0.1 to 48.156.127.25448.156.127.25532,766
5848.156.128.0/1748.156.128.1 to 48.156.255.25448.156.255.25532,766
5948.157.0.0/1748.157.0.1 to 48.157.127.25448.157.127.25532,766
6048.157.128.0/1748.157.128.1 to 48.157.255.25448.157.255.25532,766
6148.158.0.0/1748.158.0.1 to 48.158.127.25448.158.127.25532,766
6248.158.128.0/1748.158.128.1 to 48.158.255.25448.158.255.25532,766
6348.159.0.0/1748.159.0.1 to 48.159.127.25448.159.127.25532,766
6448.159.128.0/1748.159.128.1 to 48.159.255.25448.159.255.25532,766
6548.160.0.0/1748.160.0.1 to 48.160.127.25448.160.127.25532,766
6648.160.128.0/1748.160.128.1 to 48.160.255.25448.160.255.25532,766
6748.161.0.0/1748.161.0.1 to 48.161.127.25448.161.127.25532,766
6848.161.128.0/1748.161.128.1 to 48.161.255.25448.161.255.25532,766
6948.162.0.0/1748.162.0.1 to 48.162.127.25448.162.127.25532,766
7048.162.128.0/1748.162.128.1 to 48.162.255.25448.162.255.25532,766
7148.163.0.0/1748.163.0.1 to 48.163.127.25448.163.127.25532,766
7248.163.128.0/1748.163.128.1 to 48.163.255.25448.163.255.25532,766
7348.164.0.0/1748.164.0.1 to 48.164.127.25448.164.127.25532,766
7448.164.128.0/1748.164.128.1 to 48.164.255.25448.164.255.25532,766
7548.165.0.0/1748.165.0.1 to 48.165.127.25448.165.127.25532,766
7648.165.128.0/1748.165.128.1 to 48.165.255.25448.165.255.25532,766
7748.166.0.0/1748.166.0.1 to 48.166.127.25448.166.127.25532,766
7848.166.128.0/1748.166.128.1 to 48.166.255.25448.166.255.25532,766
7948.167.0.0/1748.167.0.1 to 48.167.127.25448.167.127.25532,766
8048.167.128.0/1748.167.128.1 to 48.167.255.25448.167.255.25532,766
8148.168.0.0/1748.168.0.1 to 48.168.127.25448.168.127.25532,766
8248.168.128.0/1748.168.128.1 to 48.168.255.25448.168.255.25532,766
8348.169.0.0/1748.169.0.1 to 48.169.127.25448.169.127.25532,766
8448.169.128.0/1748.169.128.1 to 48.169.255.25448.169.255.25532,766
8548.170.0.0/1748.170.0.1 to 48.170.127.25448.170.127.25532,766
8648.170.128.0/1748.170.128.1 to 48.170.255.25448.170.255.25532,766
8748.171.0.0/1748.171.0.1 to 48.171.127.25448.171.127.25532,766
8848.171.128.0/1748.171.128.1 to 48.171.255.25448.171.255.25532,766
8948.172.0.0/1748.172.0.1 to 48.172.127.25448.172.127.25532,766
9048.172.128.0/1748.172.128.1 to 48.172.255.25448.172.255.25532,766
9148.173.0.0/1748.173.0.1 to 48.173.127.25448.173.127.25532,766
9248.173.128.0/1748.173.128.1 to 48.173.255.25448.173.255.25532,766
9348.174.0.0/1748.174.0.1 to 48.174.127.25448.174.127.25532,766
9448.174.128.0/1748.174.128.1 to 48.174.255.25448.174.255.25532,766
9548.175.0.0/1748.175.0.1 to 48.175.127.25448.175.127.25532,766
9648.175.128.0/1748.175.128.1 to 48.175.255.25448.175.255.25532,766
9748.176.0.0/1748.176.0.1 to 48.176.127.25448.176.127.25532,766
9848.176.128.0/1748.176.128.1 to 48.176.255.25448.176.255.25532,766
9948.177.0.0/1748.177.0.1 to 48.177.127.25448.177.127.25532,766
10048.177.128.0/1748.177.128.1 to 48.177.255.25448.177.255.25532,766
10148.178.0.0/1748.178.0.1 to 48.178.127.25448.178.127.25532,766
10248.178.128.0/1748.178.128.1 to 48.178.255.25448.178.255.25532,766
10348.179.0.0/1748.179.0.1 to 48.179.127.25448.179.127.25532,766
10448.179.128.0/1748.179.128.1 to 48.179.255.25448.179.255.25532,766
10548.180.0.0/1748.180.0.1 to 48.180.127.25448.180.127.25532,766
10648.180.128.0/1748.180.128.1 to 48.180.255.25448.180.255.25532,766
10748.181.0.0/1748.181.0.1 to 48.181.127.25448.181.127.25532,766
10848.181.128.0/1748.181.128.1 to 48.181.255.25448.181.255.25532,766
10948.182.0.0/1748.182.0.1 to 48.182.127.25448.182.127.25532,766
11048.182.128.0/1748.182.128.1 to 48.182.255.25448.182.255.25532,766
11148.183.0.0/1748.183.0.1 to 48.183.127.25448.183.127.25532,766
11248.183.128.0/1748.183.128.1 to 48.183.255.25448.183.255.25532,766
11348.184.0.0/1748.184.0.1 to 48.184.127.25448.184.127.25532,766
11448.184.128.0/1748.184.128.1 to 48.184.255.25448.184.255.25532,766
11548.185.0.0/1748.185.0.1 to 48.185.127.25448.185.127.25532,766
11648.185.128.0/1748.185.128.1 to 48.185.255.25448.185.255.25532,766
11748.186.0.0/1748.186.0.1 to 48.186.127.25448.186.127.25532,766
11848.186.128.0/1748.186.128.1 to 48.186.255.25448.186.255.25532,766
11948.187.0.0/1748.187.0.1 to 48.187.127.25448.187.127.25532,766
12048.187.128.0/1748.187.128.1 to 48.187.255.25448.187.255.25532,766
12148.188.0.0/1748.188.0.1 to 48.188.127.25448.188.127.25532,766
12248.188.128.0/1748.188.128.1 to 48.188.255.25448.188.255.25532,766
12348.189.0.0/1748.189.0.1 to 48.189.127.25448.189.127.25532,766
12448.189.128.0/1748.189.128.1 to 48.189.255.25448.189.255.25532,766
12548.190.0.0/1748.190.0.1 to 48.190.127.25448.190.127.25532,766
12648.190.128.0/1748.190.128.1 to 48.190.255.25448.190.255.25532,766
12748.191.0.0/1748.191.0.1 to 48.191.127.25448.191.127.25532,766
12848.191.128.0/1748.191.128.1 to 48.191.255.25448.191.255.25532,766

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.