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.

Network19.64.0.0/11
Usable hosts2,097,150
Subnet mask255.224.0.0
Addresses2,097,152
Network address
19.64.0.0
Broadcast address
19.95.255.255
First usable
19.64.0.1
Last usable
19.95.255.254
Usable hosts
2,097,150 (2,097,152 less the network and broadcast addresses)
Subnet mask
255.224.0.0
Wildcard mask
0.31.255.255 (Cisco ACLs, OSPF)
Prefix length
/11
Type
Public public
Old class
A (default /8)
As numbers
Hex 13400000 · Integer 322961408 to 325058559
Reverse DNS zones
64.19.in-addr.arpa
65.19.in-addr.arpa
66.19.in-addr.arpa
67.19.in-addr.arpa
68.19.in-addr.arpa
69.19.in-addr.arpa
70.19.in-addr.arpa
71.19.in-addr.arpa
72.19.in-addr.arpa
73.19.in-addr.arpa
74.19.in-addr.arpa
75.19.in-addr.arpa
76.19.in-addr.arpa
77.19.in-addr.arpa
78.19.in-addr.arpa
79.19.in-addr.arpa
and 16 more
/11 is not on a 8-bit boundary, so it takes 32 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00010011.01000000.00000000.0000000019.64.0.0
Subnet mask11111111.11100000.00000000.00000000255.224.0.0
Network00010011.01000000.00000000.0000000019.64.0.0
Broadcast00010011.01011111.11111111.1111111119.95.255.255
Split into smaller subnets/18
/12 (2)/13 (4)/14 (8)/15 (16)/16 (32)/17 (64)/18 (128)/19 (256)/20 (512)/21 (1,024)/22 (2,048)/23 (4,096)

19.64.0.0/11 makes 128 subnets of /18.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
119.64.0.0/1819.64.0.1 to 19.64.63.25419.64.63.25516,382
219.64.64.0/1819.64.64.1 to 19.64.127.25419.64.127.25516,382
319.64.128.0/1819.64.128.1 to 19.64.191.25419.64.191.25516,382
419.64.192.0/1819.64.192.1 to 19.64.255.25419.64.255.25516,382
519.65.0.0/1819.65.0.1 to 19.65.63.25419.65.63.25516,382
619.65.64.0/1819.65.64.1 to 19.65.127.25419.65.127.25516,382
719.65.128.0/1819.65.128.1 to 19.65.191.25419.65.191.25516,382
819.65.192.0/1819.65.192.1 to 19.65.255.25419.65.255.25516,382
919.66.0.0/1819.66.0.1 to 19.66.63.25419.66.63.25516,382
1019.66.64.0/1819.66.64.1 to 19.66.127.25419.66.127.25516,382
1119.66.128.0/1819.66.128.1 to 19.66.191.25419.66.191.25516,382
1219.66.192.0/1819.66.192.1 to 19.66.255.25419.66.255.25516,382
1319.67.0.0/1819.67.0.1 to 19.67.63.25419.67.63.25516,382
1419.67.64.0/1819.67.64.1 to 19.67.127.25419.67.127.25516,382
1519.67.128.0/1819.67.128.1 to 19.67.191.25419.67.191.25516,382
1619.67.192.0/1819.67.192.1 to 19.67.255.25419.67.255.25516,382
1719.68.0.0/1819.68.0.1 to 19.68.63.25419.68.63.25516,382
1819.68.64.0/1819.68.64.1 to 19.68.127.25419.68.127.25516,382
1919.68.128.0/1819.68.128.1 to 19.68.191.25419.68.191.25516,382
2019.68.192.0/1819.68.192.1 to 19.68.255.25419.68.255.25516,382
2119.69.0.0/1819.69.0.1 to 19.69.63.25419.69.63.25516,382
2219.69.64.0/1819.69.64.1 to 19.69.127.25419.69.127.25516,382
2319.69.128.0/1819.69.128.1 to 19.69.191.25419.69.191.25516,382
2419.69.192.0/1819.69.192.1 to 19.69.255.25419.69.255.25516,382
2519.70.0.0/1819.70.0.1 to 19.70.63.25419.70.63.25516,382
2619.70.64.0/1819.70.64.1 to 19.70.127.25419.70.127.25516,382
2719.70.128.0/1819.70.128.1 to 19.70.191.25419.70.191.25516,382
2819.70.192.0/1819.70.192.1 to 19.70.255.25419.70.255.25516,382
2919.71.0.0/1819.71.0.1 to 19.71.63.25419.71.63.25516,382
3019.71.64.0/1819.71.64.1 to 19.71.127.25419.71.127.25516,382
3119.71.128.0/1819.71.128.1 to 19.71.191.25419.71.191.25516,382
3219.71.192.0/1819.71.192.1 to 19.71.255.25419.71.255.25516,382
3319.72.0.0/1819.72.0.1 to 19.72.63.25419.72.63.25516,382
3419.72.64.0/1819.72.64.1 to 19.72.127.25419.72.127.25516,382
3519.72.128.0/1819.72.128.1 to 19.72.191.25419.72.191.25516,382
3619.72.192.0/1819.72.192.1 to 19.72.255.25419.72.255.25516,382
3719.73.0.0/1819.73.0.1 to 19.73.63.25419.73.63.25516,382
3819.73.64.0/1819.73.64.1 to 19.73.127.25419.73.127.25516,382
3919.73.128.0/1819.73.128.1 to 19.73.191.25419.73.191.25516,382
4019.73.192.0/1819.73.192.1 to 19.73.255.25419.73.255.25516,382
4119.74.0.0/1819.74.0.1 to 19.74.63.25419.74.63.25516,382
4219.74.64.0/1819.74.64.1 to 19.74.127.25419.74.127.25516,382
4319.74.128.0/1819.74.128.1 to 19.74.191.25419.74.191.25516,382
4419.74.192.0/1819.74.192.1 to 19.74.255.25419.74.255.25516,382
4519.75.0.0/1819.75.0.1 to 19.75.63.25419.75.63.25516,382
4619.75.64.0/1819.75.64.1 to 19.75.127.25419.75.127.25516,382
4719.75.128.0/1819.75.128.1 to 19.75.191.25419.75.191.25516,382
4819.75.192.0/1819.75.192.1 to 19.75.255.25419.75.255.25516,382
4919.76.0.0/1819.76.0.1 to 19.76.63.25419.76.63.25516,382
5019.76.64.0/1819.76.64.1 to 19.76.127.25419.76.127.25516,382
5119.76.128.0/1819.76.128.1 to 19.76.191.25419.76.191.25516,382
5219.76.192.0/1819.76.192.1 to 19.76.255.25419.76.255.25516,382
5319.77.0.0/1819.77.0.1 to 19.77.63.25419.77.63.25516,382
5419.77.64.0/1819.77.64.1 to 19.77.127.25419.77.127.25516,382
5519.77.128.0/1819.77.128.1 to 19.77.191.25419.77.191.25516,382
5619.77.192.0/1819.77.192.1 to 19.77.255.25419.77.255.25516,382
5719.78.0.0/1819.78.0.1 to 19.78.63.25419.78.63.25516,382
5819.78.64.0/1819.78.64.1 to 19.78.127.25419.78.127.25516,382
5919.78.128.0/1819.78.128.1 to 19.78.191.25419.78.191.25516,382
6019.78.192.0/1819.78.192.1 to 19.78.255.25419.78.255.25516,382
6119.79.0.0/1819.79.0.1 to 19.79.63.25419.79.63.25516,382
6219.79.64.0/1819.79.64.1 to 19.79.127.25419.79.127.25516,382
6319.79.128.0/1819.79.128.1 to 19.79.191.25419.79.191.25516,382
6419.79.192.0/1819.79.192.1 to 19.79.255.25419.79.255.25516,382
6519.80.0.0/1819.80.0.1 to 19.80.63.25419.80.63.25516,382
6619.80.64.0/1819.80.64.1 to 19.80.127.25419.80.127.25516,382
6719.80.128.0/1819.80.128.1 to 19.80.191.25419.80.191.25516,382
6819.80.192.0/1819.80.192.1 to 19.80.255.25419.80.255.25516,382
6919.81.0.0/1819.81.0.1 to 19.81.63.25419.81.63.25516,382
7019.81.64.0/1819.81.64.1 to 19.81.127.25419.81.127.25516,382
7119.81.128.0/1819.81.128.1 to 19.81.191.25419.81.191.25516,382
7219.81.192.0/1819.81.192.1 to 19.81.255.25419.81.255.25516,382
7319.82.0.0/1819.82.0.1 to 19.82.63.25419.82.63.25516,382
7419.82.64.0/1819.82.64.1 to 19.82.127.25419.82.127.25516,382
7519.82.128.0/1819.82.128.1 to 19.82.191.25419.82.191.25516,382
7619.82.192.0/1819.82.192.1 to 19.82.255.25419.82.255.25516,382
7719.83.0.0/1819.83.0.1 to 19.83.63.25419.83.63.25516,382
7819.83.64.0/1819.83.64.1 to 19.83.127.25419.83.127.25516,382
7919.83.128.0/1819.83.128.1 to 19.83.191.25419.83.191.25516,382
8019.83.192.0/1819.83.192.1 to 19.83.255.25419.83.255.25516,382
8119.84.0.0/1819.84.0.1 to 19.84.63.25419.84.63.25516,382
8219.84.64.0/1819.84.64.1 to 19.84.127.25419.84.127.25516,382
8319.84.128.0/1819.84.128.1 to 19.84.191.25419.84.191.25516,382
8419.84.192.0/1819.84.192.1 to 19.84.255.25419.84.255.25516,382
8519.85.0.0/1819.85.0.1 to 19.85.63.25419.85.63.25516,382
8619.85.64.0/1819.85.64.1 to 19.85.127.25419.85.127.25516,382
8719.85.128.0/1819.85.128.1 to 19.85.191.25419.85.191.25516,382
8819.85.192.0/1819.85.192.1 to 19.85.255.25419.85.255.25516,382
8919.86.0.0/1819.86.0.1 to 19.86.63.25419.86.63.25516,382
9019.86.64.0/1819.86.64.1 to 19.86.127.25419.86.127.25516,382
9119.86.128.0/1819.86.128.1 to 19.86.191.25419.86.191.25516,382
9219.86.192.0/1819.86.192.1 to 19.86.255.25419.86.255.25516,382
9319.87.0.0/1819.87.0.1 to 19.87.63.25419.87.63.25516,382
9419.87.64.0/1819.87.64.1 to 19.87.127.25419.87.127.25516,382
9519.87.128.0/1819.87.128.1 to 19.87.191.25419.87.191.25516,382
9619.87.192.0/1819.87.192.1 to 19.87.255.25419.87.255.25516,382
9719.88.0.0/1819.88.0.1 to 19.88.63.25419.88.63.25516,382
9819.88.64.0/1819.88.64.1 to 19.88.127.25419.88.127.25516,382
9919.88.128.0/1819.88.128.1 to 19.88.191.25419.88.191.25516,382
10019.88.192.0/1819.88.192.1 to 19.88.255.25419.88.255.25516,382
10119.89.0.0/1819.89.0.1 to 19.89.63.25419.89.63.25516,382
10219.89.64.0/1819.89.64.1 to 19.89.127.25419.89.127.25516,382
10319.89.128.0/1819.89.128.1 to 19.89.191.25419.89.191.25516,382
10419.89.192.0/1819.89.192.1 to 19.89.255.25419.89.255.25516,382
10519.90.0.0/1819.90.0.1 to 19.90.63.25419.90.63.25516,382
10619.90.64.0/1819.90.64.1 to 19.90.127.25419.90.127.25516,382
10719.90.128.0/1819.90.128.1 to 19.90.191.25419.90.191.25516,382
10819.90.192.0/1819.90.192.1 to 19.90.255.25419.90.255.25516,382
10919.91.0.0/1819.91.0.1 to 19.91.63.25419.91.63.25516,382
11019.91.64.0/1819.91.64.1 to 19.91.127.25419.91.127.25516,382
11119.91.128.0/1819.91.128.1 to 19.91.191.25419.91.191.25516,382
11219.91.192.0/1819.91.192.1 to 19.91.255.25419.91.255.25516,382
11319.92.0.0/1819.92.0.1 to 19.92.63.25419.92.63.25516,382
11419.92.64.0/1819.92.64.1 to 19.92.127.25419.92.127.25516,382
11519.92.128.0/1819.92.128.1 to 19.92.191.25419.92.191.25516,382
11619.92.192.0/1819.92.192.1 to 19.92.255.25419.92.255.25516,382
11719.93.0.0/1819.93.0.1 to 19.93.63.25419.93.63.25516,382
11819.93.64.0/1819.93.64.1 to 19.93.127.25419.93.127.25516,382
11919.93.128.0/1819.93.128.1 to 19.93.191.25419.93.191.25516,382
12019.93.192.0/1819.93.192.1 to 19.93.255.25419.93.255.25516,382
12119.94.0.0/1819.94.0.1 to 19.94.63.25419.94.63.25516,382
12219.94.64.0/1819.94.64.1 to 19.94.127.25419.94.127.25516,382
12319.94.128.0/1819.94.128.1 to 19.94.191.25419.94.191.25516,382
12419.94.192.0/1819.94.192.1 to 19.94.255.25419.94.255.25516,382
12519.95.0.0/1819.95.0.1 to 19.95.63.25419.95.63.25516,382
12619.95.64.0/1819.95.64.1 to 19.95.127.25419.95.127.25516,382
12719.95.128.0/1819.95.128.1 to 19.95.191.25419.95.191.25516,382
12819.95.192.0/1819.95.192.1 to 19.95.255.25419.95.255.25516,382

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.