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.

Network207.0.0.0/8
Usable hosts16,777,214
Subnet mask255.0.0.0
Addresses16,777,216
Network address
207.0.0.0
Broadcast address
207.255.255.255
First usable
207.0.0.1
Last usable
207.255.255.254
Usable hosts
16,777,214 (16,777,216 less the network and broadcast addresses)
Subnet mask
255.0.0.0
Wildcard mask
0.255.255.255 (Cisco ACLs, OSPF)
Prefix length
/8
Type
Public public
Old class
C (default /24)
As numbers
Hex CF000000 · Integer 3472883712 to 3489660927
Reverse DNS zone
207.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11001111..00000000.00000000.00000000207.0.0.0
Subnet mask11111111..00000000.00000000.00000000255.0.0.0
Network11001111..00000000.00000000.00000000207.0.0.0
Broadcast11001111..11111111.11111111.11111111207.255.255.255
Split into smaller subnets/15
/9 (2)/10 (4)/11 (8)/12 (16)/13 (32)/14 (64)/15 (128)/16 (256)/17 (512)/18 (1,024)/19 (2,048)/20 (4,096)

207.0.0.0/8 makes 128 subnets of /15.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1207.0.0.0/15207.0.0.1 to 207.1.255.254207.1.255.255131,070
2207.2.0.0/15207.2.0.1 to 207.3.255.254207.3.255.255131,070
3207.4.0.0/15207.4.0.1 to 207.5.255.254207.5.255.255131,070
4207.6.0.0/15207.6.0.1 to 207.7.255.254207.7.255.255131,070
5207.8.0.0/15207.8.0.1 to 207.9.255.254207.9.255.255131,070
6207.10.0.0/15207.10.0.1 to 207.11.255.254207.11.255.255131,070
7207.12.0.0/15207.12.0.1 to 207.13.255.254207.13.255.255131,070
8207.14.0.0/15207.14.0.1 to 207.15.255.254207.15.255.255131,070
9207.16.0.0/15207.16.0.1 to 207.17.255.254207.17.255.255131,070
10207.18.0.0/15207.18.0.1 to 207.19.255.254207.19.255.255131,070
11207.20.0.0/15207.20.0.1 to 207.21.255.254207.21.255.255131,070
12207.22.0.0/15207.22.0.1 to 207.23.255.254207.23.255.255131,070
13207.24.0.0/15207.24.0.1 to 207.25.255.254207.25.255.255131,070
14207.26.0.0/15207.26.0.1 to 207.27.255.254207.27.255.255131,070
15207.28.0.0/15207.28.0.1 to 207.29.255.254207.29.255.255131,070
16207.30.0.0/15207.30.0.1 to 207.31.255.254207.31.255.255131,070
17207.32.0.0/15207.32.0.1 to 207.33.255.254207.33.255.255131,070
18207.34.0.0/15207.34.0.1 to 207.35.255.254207.35.255.255131,070
19207.36.0.0/15207.36.0.1 to 207.37.255.254207.37.255.255131,070
20207.38.0.0/15207.38.0.1 to 207.39.255.254207.39.255.255131,070
21207.40.0.0/15207.40.0.1 to 207.41.255.254207.41.255.255131,070
22207.42.0.0/15207.42.0.1 to 207.43.255.254207.43.255.255131,070
23207.44.0.0/15207.44.0.1 to 207.45.255.254207.45.255.255131,070
24207.46.0.0/15207.46.0.1 to 207.47.255.254207.47.255.255131,070
25207.48.0.0/15207.48.0.1 to 207.49.255.254207.49.255.255131,070
26207.50.0.0/15207.50.0.1 to 207.51.255.254207.51.255.255131,070
27207.52.0.0/15207.52.0.1 to 207.53.255.254207.53.255.255131,070
28207.54.0.0/15207.54.0.1 to 207.55.255.254207.55.255.255131,070
29207.56.0.0/15207.56.0.1 to 207.57.255.254207.57.255.255131,070
30207.58.0.0/15207.58.0.1 to 207.59.255.254207.59.255.255131,070
31207.60.0.0/15207.60.0.1 to 207.61.255.254207.61.255.255131,070
32207.62.0.0/15207.62.0.1 to 207.63.255.254207.63.255.255131,070
33207.64.0.0/15207.64.0.1 to 207.65.255.254207.65.255.255131,070
34207.66.0.0/15207.66.0.1 to 207.67.255.254207.67.255.255131,070
35207.68.0.0/15207.68.0.1 to 207.69.255.254207.69.255.255131,070
36207.70.0.0/15207.70.0.1 to 207.71.255.254207.71.255.255131,070
37207.72.0.0/15207.72.0.1 to 207.73.255.254207.73.255.255131,070
38207.74.0.0/15207.74.0.1 to 207.75.255.254207.75.255.255131,070
39207.76.0.0/15207.76.0.1 to 207.77.255.254207.77.255.255131,070
40207.78.0.0/15207.78.0.1 to 207.79.255.254207.79.255.255131,070
41207.80.0.0/15207.80.0.1 to 207.81.255.254207.81.255.255131,070
42207.82.0.0/15207.82.0.1 to 207.83.255.254207.83.255.255131,070
43207.84.0.0/15207.84.0.1 to 207.85.255.254207.85.255.255131,070
44207.86.0.0/15207.86.0.1 to 207.87.255.254207.87.255.255131,070
45207.88.0.0/15207.88.0.1 to 207.89.255.254207.89.255.255131,070
46207.90.0.0/15207.90.0.1 to 207.91.255.254207.91.255.255131,070
47207.92.0.0/15207.92.0.1 to 207.93.255.254207.93.255.255131,070
48207.94.0.0/15207.94.0.1 to 207.95.255.254207.95.255.255131,070
49207.96.0.0/15207.96.0.1 to 207.97.255.254207.97.255.255131,070
50207.98.0.0/15207.98.0.1 to 207.99.255.254207.99.255.255131,070
51207.100.0.0/15207.100.0.1 to 207.101.255.254207.101.255.255131,070
52207.102.0.0/15207.102.0.1 to 207.103.255.254207.103.255.255131,070
53207.104.0.0/15207.104.0.1 to 207.105.255.254207.105.255.255131,070
54207.106.0.0/15207.106.0.1 to 207.107.255.254207.107.255.255131,070
55207.108.0.0/15207.108.0.1 to 207.109.255.254207.109.255.255131,070
56207.110.0.0/15207.110.0.1 to 207.111.255.254207.111.255.255131,070
57207.112.0.0/15207.112.0.1 to 207.113.255.254207.113.255.255131,070
58207.114.0.0/15207.114.0.1 to 207.115.255.254207.115.255.255131,070
59207.116.0.0/15207.116.0.1 to 207.117.255.254207.117.255.255131,070
60207.118.0.0/15207.118.0.1 to 207.119.255.254207.119.255.255131,070
61207.120.0.0/15207.120.0.1 to 207.121.255.254207.121.255.255131,070
62207.122.0.0/15207.122.0.1 to 207.123.255.254207.123.255.255131,070
63207.124.0.0/15207.124.0.1 to 207.125.255.254207.125.255.255131,070
64207.126.0.0/15207.126.0.1 to 207.127.255.254207.127.255.255131,070
65207.128.0.0/15207.128.0.1 to 207.129.255.254207.129.255.255131,070
66207.130.0.0/15207.130.0.1 to 207.131.255.254207.131.255.255131,070
67207.132.0.0/15207.132.0.1 to 207.133.255.254207.133.255.255131,070
68207.134.0.0/15207.134.0.1 to 207.135.255.254207.135.255.255131,070
69207.136.0.0/15207.136.0.1 to 207.137.255.254207.137.255.255131,070
70207.138.0.0/15207.138.0.1 to 207.139.255.254207.139.255.255131,070
71207.140.0.0/15207.140.0.1 to 207.141.255.254207.141.255.255131,070
72207.142.0.0/15207.142.0.1 to 207.143.255.254207.143.255.255131,070
73207.144.0.0/15207.144.0.1 to 207.145.255.254207.145.255.255131,070
74207.146.0.0/15207.146.0.1 to 207.147.255.254207.147.255.255131,070
75207.148.0.0/15207.148.0.1 to 207.149.255.254207.149.255.255131,070
76207.150.0.0/15207.150.0.1 to 207.151.255.254207.151.255.255131,070
77207.152.0.0/15207.152.0.1 to 207.153.255.254207.153.255.255131,070
78207.154.0.0/15207.154.0.1 to 207.155.255.254207.155.255.255131,070
79207.156.0.0/15207.156.0.1 to 207.157.255.254207.157.255.255131,070
80207.158.0.0/15207.158.0.1 to 207.159.255.254207.159.255.255131,070
81207.160.0.0/15207.160.0.1 to 207.161.255.254207.161.255.255131,070
82207.162.0.0/15207.162.0.1 to 207.163.255.254207.163.255.255131,070
83207.164.0.0/15207.164.0.1 to 207.165.255.254207.165.255.255131,070
84207.166.0.0/15207.166.0.1 to 207.167.255.254207.167.255.255131,070
85207.168.0.0/15207.168.0.1 to 207.169.255.254207.169.255.255131,070
86207.170.0.0/15207.170.0.1 to 207.171.255.254207.171.255.255131,070
87207.172.0.0/15207.172.0.1 to 207.173.255.254207.173.255.255131,070
88207.174.0.0/15207.174.0.1 to 207.175.255.254207.175.255.255131,070
89207.176.0.0/15207.176.0.1 to 207.177.255.254207.177.255.255131,070
90207.178.0.0/15207.178.0.1 to 207.179.255.254207.179.255.255131,070
91207.180.0.0/15207.180.0.1 to 207.181.255.254207.181.255.255131,070
92207.182.0.0/15207.182.0.1 to 207.183.255.254207.183.255.255131,070
93207.184.0.0/15207.184.0.1 to 207.185.255.254207.185.255.255131,070
94207.186.0.0/15207.186.0.1 to 207.187.255.254207.187.255.255131,070
95207.188.0.0/15207.188.0.1 to 207.189.255.254207.189.255.255131,070
96207.190.0.0/15207.190.0.1 to 207.191.255.254207.191.255.255131,070
97207.192.0.0/15207.192.0.1 to 207.193.255.254207.193.255.255131,070
98207.194.0.0/15207.194.0.1 to 207.195.255.254207.195.255.255131,070
99207.196.0.0/15207.196.0.1 to 207.197.255.254207.197.255.255131,070
100207.198.0.0/15207.198.0.1 to 207.199.255.254207.199.255.255131,070
101207.200.0.0/15207.200.0.1 to 207.201.255.254207.201.255.255131,070
102207.202.0.0/15207.202.0.1 to 207.203.255.254207.203.255.255131,070
103207.204.0.0/15207.204.0.1 to 207.205.255.254207.205.255.255131,070
104207.206.0.0/15207.206.0.1 to 207.207.255.254207.207.255.255131,070
105207.208.0.0/15207.208.0.1 to 207.209.255.254207.209.255.255131,070
106207.210.0.0/15207.210.0.1 to 207.211.255.254207.211.255.255131,070
107207.212.0.0/15207.212.0.1 to 207.213.255.254207.213.255.255131,070
108207.214.0.0/15207.214.0.1 to 207.215.255.254207.215.255.255131,070
109207.216.0.0/15207.216.0.1 to 207.217.255.254207.217.255.255131,070
110207.218.0.0/15207.218.0.1 to 207.219.255.254207.219.255.255131,070
111207.220.0.0/15207.220.0.1 to 207.221.255.254207.221.255.255131,070
112207.222.0.0/15207.222.0.1 to 207.223.255.254207.223.255.255131,070
113207.224.0.0/15207.224.0.1 to 207.225.255.254207.225.255.255131,070
114207.226.0.0/15207.226.0.1 to 207.227.255.254207.227.255.255131,070
115207.228.0.0/15207.228.0.1 to 207.229.255.254207.229.255.255131,070
116207.230.0.0/15207.230.0.1 to 207.231.255.254207.231.255.255131,070
117207.232.0.0/15207.232.0.1 to 207.233.255.254207.233.255.255131,070
118207.234.0.0/15207.234.0.1 to 207.235.255.254207.235.255.255131,070
119207.236.0.0/15207.236.0.1 to 207.237.255.254207.237.255.255131,070
120207.238.0.0/15207.238.0.1 to 207.239.255.254207.239.255.255131,070
121207.240.0.0/15207.240.0.1 to 207.241.255.254207.241.255.255131,070
122207.242.0.0/15207.242.0.1 to 207.243.255.254207.243.255.255131,070
123207.244.0.0/15207.244.0.1 to 207.245.255.254207.245.255.255131,070
124207.246.0.0/15207.246.0.1 to 207.247.255.254207.247.255.255131,070
125207.248.0.0/15207.248.0.1 to 207.249.255.254207.249.255.255131,070
126207.250.0.0/15207.250.0.1 to 207.251.255.254207.251.255.255131,070
127207.252.0.0/15207.252.0.1 to 207.253.255.254207.253.255.255131,070
128207.254.0.0/15207.254.0.1 to 207.255.255.254207.255.255.255131,070

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.