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.

Network16.32.0.0/11
Usable hosts2,097,150
Subnet mask255.224.0.0
Addresses2,097,152
Network address
16.32.0.0
Broadcast address
16.63.255.255
First usable
16.32.0.1
Last usable
16.63.255.254
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 10200000 · Integer 270532608 to 272629759
Reverse DNS zones
32.16.in-addr.arpa
33.16.in-addr.arpa
34.16.in-addr.arpa
35.16.in-addr.arpa
36.16.in-addr.arpa
37.16.in-addr.arpa
38.16.in-addr.arpa
39.16.in-addr.arpa
40.16.in-addr.arpa
41.16.in-addr.arpa
42.16.in-addr.arpa
43.16.in-addr.arpa
44.16.in-addr.arpa
45.16.in-addr.arpa
46.16.in-addr.arpa
47.16.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
Address00010000.00100000.00000000.0000000016.32.0.0
Subnet mask11111111.11100000.00000000.00000000255.224.0.0
Network00010000.00100000.00000000.0000000016.32.0.0
Broadcast00010000.00111111.11111111.1111111116.63.255.255
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)

16.32.0.0/11 makes 128 subnets of /18.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
116.32.0.0/1816.32.0.1 to 16.32.63.25416.32.63.25516,382
216.32.64.0/1816.32.64.1 to 16.32.127.25416.32.127.25516,382
316.32.128.0/1816.32.128.1 to 16.32.191.25416.32.191.25516,382
416.32.192.0/1816.32.192.1 to 16.32.255.25416.32.255.25516,382
516.33.0.0/1816.33.0.1 to 16.33.63.25416.33.63.25516,382
616.33.64.0/1816.33.64.1 to 16.33.127.25416.33.127.25516,382
716.33.128.0/1816.33.128.1 to 16.33.191.25416.33.191.25516,382
816.33.192.0/1816.33.192.1 to 16.33.255.25416.33.255.25516,382
916.34.0.0/1816.34.0.1 to 16.34.63.25416.34.63.25516,382
1016.34.64.0/1816.34.64.1 to 16.34.127.25416.34.127.25516,382
1116.34.128.0/1816.34.128.1 to 16.34.191.25416.34.191.25516,382
1216.34.192.0/1816.34.192.1 to 16.34.255.25416.34.255.25516,382
1316.35.0.0/1816.35.0.1 to 16.35.63.25416.35.63.25516,382
1416.35.64.0/1816.35.64.1 to 16.35.127.25416.35.127.25516,382
1516.35.128.0/1816.35.128.1 to 16.35.191.25416.35.191.25516,382
1616.35.192.0/1816.35.192.1 to 16.35.255.25416.35.255.25516,382
1716.36.0.0/1816.36.0.1 to 16.36.63.25416.36.63.25516,382
1816.36.64.0/1816.36.64.1 to 16.36.127.25416.36.127.25516,382
1916.36.128.0/1816.36.128.1 to 16.36.191.25416.36.191.25516,382
2016.36.192.0/1816.36.192.1 to 16.36.255.25416.36.255.25516,382
2116.37.0.0/1816.37.0.1 to 16.37.63.25416.37.63.25516,382
2216.37.64.0/1816.37.64.1 to 16.37.127.25416.37.127.25516,382
2316.37.128.0/1816.37.128.1 to 16.37.191.25416.37.191.25516,382
2416.37.192.0/1816.37.192.1 to 16.37.255.25416.37.255.25516,382
2516.38.0.0/1816.38.0.1 to 16.38.63.25416.38.63.25516,382
2616.38.64.0/1816.38.64.1 to 16.38.127.25416.38.127.25516,382
2716.38.128.0/1816.38.128.1 to 16.38.191.25416.38.191.25516,382
2816.38.192.0/1816.38.192.1 to 16.38.255.25416.38.255.25516,382
2916.39.0.0/1816.39.0.1 to 16.39.63.25416.39.63.25516,382
3016.39.64.0/1816.39.64.1 to 16.39.127.25416.39.127.25516,382
3116.39.128.0/1816.39.128.1 to 16.39.191.25416.39.191.25516,382
3216.39.192.0/1816.39.192.1 to 16.39.255.25416.39.255.25516,382
3316.40.0.0/1816.40.0.1 to 16.40.63.25416.40.63.25516,382
3416.40.64.0/1816.40.64.1 to 16.40.127.25416.40.127.25516,382
3516.40.128.0/1816.40.128.1 to 16.40.191.25416.40.191.25516,382
3616.40.192.0/1816.40.192.1 to 16.40.255.25416.40.255.25516,382
3716.41.0.0/1816.41.0.1 to 16.41.63.25416.41.63.25516,382
3816.41.64.0/1816.41.64.1 to 16.41.127.25416.41.127.25516,382
3916.41.128.0/1816.41.128.1 to 16.41.191.25416.41.191.25516,382
4016.41.192.0/1816.41.192.1 to 16.41.255.25416.41.255.25516,382
4116.42.0.0/1816.42.0.1 to 16.42.63.25416.42.63.25516,382
4216.42.64.0/1816.42.64.1 to 16.42.127.25416.42.127.25516,382
4316.42.128.0/1816.42.128.1 to 16.42.191.25416.42.191.25516,382
4416.42.192.0/1816.42.192.1 to 16.42.255.25416.42.255.25516,382
4516.43.0.0/1816.43.0.1 to 16.43.63.25416.43.63.25516,382
4616.43.64.0/1816.43.64.1 to 16.43.127.25416.43.127.25516,382
4716.43.128.0/1816.43.128.1 to 16.43.191.25416.43.191.25516,382
4816.43.192.0/1816.43.192.1 to 16.43.255.25416.43.255.25516,382
4916.44.0.0/1816.44.0.1 to 16.44.63.25416.44.63.25516,382
5016.44.64.0/1816.44.64.1 to 16.44.127.25416.44.127.25516,382
5116.44.128.0/1816.44.128.1 to 16.44.191.25416.44.191.25516,382
5216.44.192.0/1816.44.192.1 to 16.44.255.25416.44.255.25516,382
5316.45.0.0/1816.45.0.1 to 16.45.63.25416.45.63.25516,382
5416.45.64.0/1816.45.64.1 to 16.45.127.25416.45.127.25516,382
5516.45.128.0/1816.45.128.1 to 16.45.191.25416.45.191.25516,382
5616.45.192.0/1816.45.192.1 to 16.45.255.25416.45.255.25516,382
5716.46.0.0/1816.46.0.1 to 16.46.63.25416.46.63.25516,382
5816.46.64.0/1816.46.64.1 to 16.46.127.25416.46.127.25516,382
5916.46.128.0/1816.46.128.1 to 16.46.191.25416.46.191.25516,382
6016.46.192.0/1816.46.192.1 to 16.46.255.25416.46.255.25516,382
6116.47.0.0/1816.47.0.1 to 16.47.63.25416.47.63.25516,382
6216.47.64.0/1816.47.64.1 to 16.47.127.25416.47.127.25516,382
6316.47.128.0/1816.47.128.1 to 16.47.191.25416.47.191.25516,382
6416.47.192.0/1816.47.192.1 to 16.47.255.25416.47.255.25516,382
6516.48.0.0/1816.48.0.1 to 16.48.63.25416.48.63.25516,382
6616.48.64.0/1816.48.64.1 to 16.48.127.25416.48.127.25516,382
6716.48.128.0/1816.48.128.1 to 16.48.191.25416.48.191.25516,382
6816.48.192.0/1816.48.192.1 to 16.48.255.25416.48.255.25516,382
6916.49.0.0/1816.49.0.1 to 16.49.63.25416.49.63.25516,382
7016.49.64.0/1816.49.64.1 to 16.49.127.25416.49.127.25516,382
7116.49.128.0/1816.49.128.1 to 16.49.191.25416.49.191.25516,382
7216.49.192.0/1816.49.192.1 to 16.49.255.25416.49.255.25516,382
7316.50.0.0/1816.50.0.1 to 16.50.63.25416.50.63.25516,382
7416.50.64.0/1816.50.64.1 to 16.50.127.25416.50.127.25516,382
7516.50.128.0/1816.50.128.1 to 16.50.191.25416.50.191.25516,382
7616.50.192.0/1816.50.192.1 to 16.50.255.25416.50.255.25516,382
7716.51.0.0/1816.51.0.1 to 16.51.63.25416.51.63.25516,382
7816.51.64.0/1816.51.64.1 to 16.51.127.25416.51.127.25516,382
7916.51.128.0/1816.51.128.1 to 16.51.191.25416.51.191.25516,382
8016.51.192.0/1816.51.192.1 to 16.51.255.25416.51.255.25516,382
8116.52.0.0/1816.52.0.1 to 16.52.63.25416.52.63.25516,382
8216.52.64.0/1816.52.64.1 to 16.52.127.25416.52.127.25516,382
8316.52.128.0/1816.52.128.1 to 16.52.191.25416.52.191.25516,382
8416.52.192.0/1816.52.192.1 to 16.52.255.25416.52.255.25516,382
8516.53.0.0/1816.53.0.1 to 16.53.63.25416.53.63.25516,382
8616.53.64.0/1816.53.64.1 to 16.53.127.25416.53.127.25516,382
8716.53.128.0/1816.53.128.1 to 16.53.191.25416.53.191.25516,382
8816.53.192.0/1816.53.192.1 to 16.53.255.25416.53.255.25516,382
8916.54.0.0/1816.54.0.1 to 16.54.63.25416.54.63.25516,382
9016.54.64.0/1816.54.64.1 to 16.54.127.25416.54.127.25516,382
9116.54.128.0/1816.54.128.1 to 16.54.191.25416.54.191.25516,382
9216.54.192.0/1816.54.192.1 to 16.54.255.25416.54.255.25516,382
9316.55.0.0/1816.55.0.1 to 16.55.63.25416.55.63.25516,382
9416.55.64.0/1816.55.64.1 to 16.55.127.25416.55.127.25516,382
9516.55.128.0/1816.55.128.1 to 16.55.191.25416.55.191.25516,382
9616.55.192.0/1816.55.192.1 to 16.55.255.25416.55.255.25516,382
9716.56.0.0/1816.56.0.1 to 16.56.63.25416.56.63.25516,382
9816.56.64.0/1816.56.64.1 to 16.56.127.25416.56.127.25516,382
9916.56.128.0/1816.56.128.1 to 16.56.191.25416.56.191.25516,382
10016.56.192.0/1816.56.192.1 to 16.56.255.25416.56.255.25516,382
10116.57.0.0/1816.57.0.1 to 16.57.63.25416.57.63.25516,382
10216.57.64.0/1816.57.64.1 to 16.57.127.25416.57.127.25516,382
10316.57.128.0/1816.57.128.1 to 16.57.191.25416.57.191.25516,382
10416.57.192.0/1816.57.192.1 to 16.57.255.25416.57.255.25516,382
10516.58.0.0/1816.58.0.1 to 16.58.63.25416.58.63.25516,382
10616.58.64.0/1816.58.64.1 to 16.58.127.25416.58.127.25516,382
10716.58.128.0/1816.58.128.1 to 16.58.191.25416.58.191.25516,382
10816.58.192.0/1816.58.192.1 to 16.58.255.25416.58.255.25516,382
10916.59.0.0/1816.59.0.1 to 16.59.63.25416.59.63.25516,382
11016.59.64.0/1816.59.64.1 to 16.59.127.25416.59.127.25516,382
11116.59.128.0/1816.59.128.1 to 16.59.191.25416.59.191.25516,382
11216.59.192.0/1816.59.192.1 to 16.59.255.25416.59.255.25516,382
11316.60.0.0/1816.60.0.1 to 16.60.63.25416.60.63.25516,382
11416.60.64.0/1816.60.64.1 to 16.60.127.25416.60.127.25516,382
11516.60.128.0/1816.60.128.1 to 16.60.191.25416.60.191.25516,382
11616.60.192.0/1816.60.192.1 to 16.60.255.25416.60.255.25516,382
11716.61.0.0/1816.61.0.1 to 16.61.63.25416.61.63.25516,382
11816.61.64.0/1816.61.64.1 to 16.61.127.25416.61.127.25516,382
11916.61.128.0/1816.61.128.1 to 16.61.191.25416.61.191.25516,382
12016.61.192.0/1816.61.192.1 to 16.61.255.25416.61.255.25516,382
12116.62.0.0/1816.62.0.1 to 16.62.63.25416.62.63.25516,382
12216.62.64.0/1816.62.64.1 to 16.62.127.25416.62.127.25516,382
12316.62.128.0/1816.62.128.1 to 16.62.191.25416.62.191.25516,382
12416.62.192.0/1816.62.192.1 to 16.62.255.25416.62.255.25516,382
12516.63.0.0/1816.63.0.1 to 16.63.63.25416.63.63.25516,382
12616.63.64.0/1816.63.64.1 to 16.63.127.25416.63.127.25516,382
12716.63.128.0/1816.63.128.1 to 16.63.191.25416.63.191.25516,382
12816.63.192.0/1816.63.192.1 to 16.63.255.25416.63.255.25516,382

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.