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.

Network125.0.0.0/8
Usable hosts16,777,214
Subnet mask255.0.0.0
Addresses16,777,216
Network address
125.0.0.0
Broadcast address
125.255.255.255
First usable
125.0.0.1
Last usable
125.255.255.254
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
A (default /8)
As numbers
Hex 7D000000 · Integer 2097152000 to 2113929215
Reverse DNS zone
125.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address01111101..00000000.00000000.00000000125.0.0.0
Subnet mask11111111..00000000.00000000.00000000255.0.0.0
Network01111101..00000000.00000000.00000000125.0.0.0
Broadcast01111101..11111111.11111111.11111111125.255.255.255
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)

125.0.0.0/8 makes 128 subnets of /15.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1125.0.0.0/15125.0.0.1 to 125.1.255.254125.1.255.255131,070
2125.2.0.0/15125.2.0.1 to 125.3.255.254125.3.255.255131,070
3125.4.0.0/15125.4.0.1 to 125.5.255.254125.5.255.255131,070
4125.6.0.0/15125.6.0.1 to 125.7.255.254125.7.255.255131,070
5125.8.0.0/15125.8.0.1 to 125.9.255.254125.9.255.255131,070
6125.10.0.0/15125.10.0.1 to 125.11.255.254125.11.255.255131,070
7125.12.0.0/15125.12.0.1 to 125.13.255.254125.13.255.255131,070
8125.14.0.0/15125.14.0.1 to 125.15.255.254125.15.255.255131,070
9125.16.0.0/15125.16.0.1 to 125.17.255.254125.17.255.255131,070
10125.18.0.0/15125.18.0.1 to 125.19.255.254125.19.255.255131,070
11125.20.0.0/15125.20.0.1 to 125.21.255.254125.21.255.255131,070
12125.22.0.0/15125.22.0.1 to 125.23.255.254125.23.255.255131,070
13125.24.0.0/15125.24.0.1 to 125.25.255.254125.25.255.255131,070
14125.26.0.0/15125.26.0.1 to 125.27.255.254125.27.255.255131,070
15125.28.0.0/15125.28.0.1 to 125.29.255.254125.29.255.255131,070
16125.30.0.0/15125.30.0.1 to 125.31.255.254125.31.255.255131,070
17125.32.0.0/15125.32.0.1 to 125.33.255.254125.33.255.255131,070
18125.34.0.0/15125.34.0.1 to 125.35.255.254125.35.255.255131,070
19125.36.0.0/15125.36.0.1 to 125.37.255.254125.37.255.255131,070
20125.38.0.0/15125.38.0.1 to 125.39.255.254125.39.255.255131,070
21125.40.0.0/15125.40.0.1 to 125.41.255.254125.41.255.255131,070
22125.42.0.0/15125.42.0.1 to 125.43.255.254125.43.255.255131,070
23125.44.0.0/15125.44.0.1 to 125.45.255.254125.45.255.255131,070
24125.46.0.0/15125.46.0.1 to 125.47.255.254125.47.255.255131,070
25125.48.0.0/15125.48.0.1 to 125.49.255.254125.49.255.255131,070
26125.50.0.0/15125.50.0.1 to 125.51.255.254125.51.255.255131,070
27125.52.0.0/15125.52.0.1 to 125.53.255.254125.53.255.255131,070
28125.54.0.0/15125.54.0.1 to 125.55.255.254125.55.255.255131,070
29125.56.0.0/15125.56.0.1 to 125.57.255.254125.57.255.255131,070
30125.58.0.0/15125.58.0.1 to 125.59.255.254125.59.255.255131,070
31125.60.0.0/15125.60.0.1 to 125.61.255.254125.61.255.255131,070
32125.62.0.0/15125.62.0.1 to 125.63.255.254125.63.255.255131,070
33125.64.0.0/15125.64.0.1 to 125.65.255.254125.65.255.255131,070
34125.66.0.0/15125.66.0.1 to 125.67.255.254125.67.255.255131,070
35125.68.0.0/15125.68.0.1 to 125.69.255.254125.69.255.255131,070
36125.70.0.0/15125.70.0.1 to 125.71.255.254125.71.255.255131,070
37125.72.0.0/15125.72.0.1 to 125.73.255.254125.73.255.255131,070
38125.74.0.0/15125.74.0.1 to 125.75.255.254125.75.255.255131,070
39125.76.0.0/15125.76.0.1 to 125.77.255.254125.77.255.255131,070
40125.78.0.0/15125.78.0.1 to 125.79.255.254125.79.255.255131,070
41125.80.0.0/15125.80.0.1 to 125.81.255.254125.81.255.255131,070
42125.82.0.0/15125.82.0.1 to 125.83.255.254125.83.255.255131,070
43125.84.0.0/15125.84.0.1 to 125.85.255.254125.85.255.255131,070
44125.86.0.0/15125.86.0.1 to 125.87.255.254125.87.255.255131,070
45125.88.0.0/15125.88.0.1 to 125.89.255.254125.89.255.255131,070
46125.90.0.0/15125.90.0.1 to 125.91.255.254125.91.255.255131,070
47125.92.0.0/15125.92.0.1 to 125.93.255.254125.93.255.255131,070
48125.94.0.0/15125.94.0.1 to 125.95.255.254125.95.255.255131,070
49125.96.0.0/15125.96.0.1 to 125.97.255.254125.97.255.255131,070
50125.98.0.0/15125.98.0.1 to 125.99.255.254125.99.255.255131,070
51125.100.0.0/15125.100.0.1 to 125.101.255.254125.101.255.255131,070
52125.102.0.0/15125.102.0.1 to 125.103.255.254125.103.255.255131,070
53125.104.0.0/15125.104.0.1 to 125.105.255.254125.105.255.255131,070
54125.106.0.0/15125.106.0.1 to 125.107.255.254125.107.255.255131,070
55125.108.0.0/15125.108.0.1 to 125.109.255.254125.109.255.255131,070
56125.110.0.0/15125.110.0.1 to 125.111.255.254125.111.255.255131,070
57125.112.0.0/15125.112.0.1 to 125.113.255.254125.113.255.255131,070
58125.114.0.0/15125.114.0.1 to 125.115.255.254125.115.255.255131,070
59125.116.0.0/15125.116.0.1 to 125.117.255.254125.117.255.255131,070
60125.118.0.0/15125.118.0.1 to 125.119.255.254125.119.255.255131,070
61125.120.0.0/15125.120.0.1 to 125.121.255.254125.121.255.255131,070
62125.122.0.0/15125.122.0.1 to 125.123.255.254125.123.255.255131,070
63125.124.0.0/15125.124.0.1 to 125.125.255.254125.125.255.255131,070
64125.126.0.0/15125.126.0.1 to 125.127.255.254125.127.255.255131,070
65125.128.0.0/15125.128.0.1 to 125.129.255.254125.129.255.255131,070
66125.130.0.0/15125.130.0.1 to 125.131.255.254125.131.255.255131,070
67125.132.0.0/15125.132.0.1 to 125.133.255.254125.133.255.255131,070
68125.134.0.0/15125.134.0.1 to 125.135.255.254125.135.255.255131,070
69125.136.0.0/15125.136.0.1 to 125.137.255.254125.137.255.255131,070
70125.138.0.0/15125.138.0.1 to 125.139.255.254125.139.255.255131,070
71125.140.0.0/15125.140.0.1 to 125.141.255.254125.141.255.255131,070
72125.142.0.0/15125.142.0.1 to 125.143.255.254125.143.255.255131,070
73125.144.0.0/15125.144.0.1 to 125.145.255.254125.145.255.255131,070
74125.146.0.0/15125.146.0.1 to 125.147.255.254125.147.255.255131,070
75125.148.0.0/15125.148.0.1 to 125.149.255.254125.149.255.255131,070
76125.150.0.0/15125.150.0.1 to 125.151.255.254125.151.255.255131,070
77125.152.0.0/15125.152.0.1 to 125.153.255.254125.153.255.255131,070
78125.154.0.0/15125.154.0.1 to 125.155.255.254125.155.255.255131,070
79125.156.0.0/15125.156.0.1 to 125.157.255.254125.157.255.255131,070
80125.158.0.0/15125.158.0.1 to 125.159.255.254125.159.255.255131,070
81125.160.0.0/15125.160.0.1 to 125.161.255.254125.161.255.255131,070
82125.162.0.0/15125.162.0.1 to 125.163.255.254125.163.255.255131,070
83125.164.0.0/15125.164.0.1 to 125.165.255.254125.165.255.255131,070
84125.166.0.0/15125.166.0.1 to 125.167.255.254125.167.255.255131,070
85125.168.0.0/15125.168.0.1 to 125.169.255.254125.169.255.255131,070
86125.170.0.0/15125.170.0.1 to 125.171.255.254125.171.255.255131,070
87125.172.0.0/15125.172.0.1 to 125.173.255.254125.173.255.255131,070
88125.174.0.0/15125.174.0.1 to 125.175.255.254125.175.255.255131,070
89125.176.0.0/15125.176.0.1 to 125.177.255.254125.177.255.255131,070
90125.178.0.0/15125.178.0.1 to 125.179.255.254125.179.255.255131,070
91125.180.0.0/15125.180.0.1 to 125.181.255.254125.181.255.255131,070
92125.182.0.0/15125.182.0.1 to 125.183.255.254125.183.255.255131,070
93125.184.0.0/15125.184.0.1 to 125.185.255.254125.185.255.255131,070
94125.186.0.0/15125.186.0.1 to 125.187.255.254125.187.255.255131,070
95125.188.0.0/15125.188.0.1 to 125.189.255.254125.189.255.255131,070
96125.190.0.0/15125.190.0.1 to 125.191.255.254125.191.255.255131,070
97125.192.0.0/15125.192.0.1 to 125.193.255.254125.193.255.255131,070
98125.194.0.0/15125.194.0.1 to 125.195.255.254125.195.255.255131,070
99125.196.0.0/15125.196.0.1 to 125.197.255.254125.197.255.255131,070
100125.198.0.0/15125.198.0.1 to 125.199.255.254125.199.255.255131,070
101125.200.0.0/15125.200.0.1 to 125.201.255.254125.201.255.255131,070
102125.202.0.0/15125.202.0.1 to 125.203.255.254125.203.255.255131,070
103125.204.0.0/15125.204.0.1 to 125.205.255.254125.205.255.255131,070
104125.206.0.0/15125.206.0.1 to 125.207.255.254125.207.255.255131,070
105125.208.0.0/15125.208.0.1 to 125.209.255.254125.209.255.255131,070
106125.210.0.0/15125.210.0.1 to 125.211.255.254125.211.255.255131,070
107125.212.0.0/15125.212.0.1 to 125.213.255.254125.213.255.255131,070
108125.214.0.0/15125.214.0.1 to 125.215.255.254125.215.255.255131,070
109125.216.0.0/15125.216.0.1 to 125.217.255.254125.217.255.255131,070
110125.218.0.0/15125.218.0.1 to 125.219.255.254125.219.255.255131,070
111125.220.0.0/15125.220.0.1 to 125.221.255.254125.221.255.255131,070
112125.222.0.0/15125.222.0.1 to 125.223.255.254125.223.255.255131,070
113125.224.0.0/15125.224.0.1 to 125.225.255.254125.225.255.255131,070
114125.226.0.0/15125.226.0.1 to 125.227.255.254125.227.255.255131,070
115125.228.0.0/15125.228.0.1 to 125.229.255.254125.229.255.255131,070
116125.230.0.0/15125.230.0.1 to 125.231.255.254125.231.255.255131,070
117125.232.0.0/15125.232.0.1 to 125.233.255.254125.233.255.255131,070
118125.234.0.0/15125.234.0.1 to 125.235.255.254125.235.255.255131,070
119125.236.0.0/15125.236.0.1 to 125.237.255.254125.237.255.255131,070
120125.238.0.0/15125.238.0.1 to 125.239.255.254125.239.255.255131,070
121125.240.0.0/15125.240.0.1 to 125.241.255.254125.241.255.255131,070
122125.242.0.0/15125.242.0.1 to 125.243.255.254125.243.255.255131,070
123125.244.0.0/15125.244.0.1 to 125.245.255.254125.245.255.255131,070
124125.246.0.0/15125.246.0.1 to 125.247.255.254125.247.255.255131,070
125125.248.0.0/15125.248.0.1 to 125.249.255.254125.249.255.255131,070
126125.250.0.0/15125.250.0.1 to 125.251.255.254125.251.255.255131,070
127125.252.0.0/15125.252.0.1 to 125.253.255.254125.253.255.255131,070
128125.254.0.0/15125.254.0.1 to 125.255.255.254125.255.255.255131,070

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.