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.

Network236.0.0.0/8
Usable hosts16,777,214
Subnet mask255.0.0.0
Addresses16,777,216
Network address
236.0.0.0
Broadcast address
236.255.255.255
First usable
236.0.0.1
Last usable
236.255.255.254
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
Multicast 224.0.0.0/4
One-to-many traffic, such as IPTV and routing protocols
Old class
D (multicast)
As numbers
Hex EC000000 · Integer 3959422976 to 3976200191
Reverse DNS zone
236.in-addr.arpa
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11101100..00000000.00000000.00000000236.0.0.0
Subnet mask11111111..00000000.00000000.00000000255.0.0.0
Network11101100..00000000.00000000.00000000236.0.0.0
Broadcast11101100..11111111.11111111.11111111236.255.255.255
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)

236.0.0.0/8 makes 128 subnets of /15.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1236.0.0.0/15236.0.0.1 to 236.1.255.254236.1.255.255131,070
2236.2.0.0/15236.2.0.1 to 236.3.255.254236.3.255.255131,070
3236.4.0.0/15236.4.0.1 to 236.5.255.254236.5.255.255131,070
4236.6.0.0/15236.6.0.1 to 236.7.255.254236.7.255.255131,070
5236.8.0.0/15236.8.0.1 to 236.9.255.254236.9.255.255131,070
6236.10.0.0/15236.10.0.1 to 236.11.255.254236.11.255.255131,070
7236.12.0.0/15236.12.0.1 to 236.13.255.254236.13.255.255131,070
8236.14.0.0/15236.14.0.1 to 236.15.255.254236.15.255.255131,070
9236.16.0.0/15236.16.0.1 to 236.17.255.254236.17.255.255131,070
10236.18.0.0/15236.18.0.1 to 236.19.255.254236.19.255.255131,070
11236.20.0.0/15236.20.0.1 to 236.21.255.254236.21.255.255131,070
12236.22.0.0/15236.22.0.1 to 236.23.255.254236.23.255.255131,070
13236.24.0.0/15236.24.0.1 to 236.25.255.254236.25.255.255131,070
14236.26.0.0/15236.26.0.1 to 236.27.255.254236.27.255.255131,070
15236.28.0.0/15236.28.0.1 to 236.29.255.254236.29.255.255131,070
16236.30.0.0/15236.30.0.1 to 236.31.255.254236.31.255.255131,070
17236.32.0.0/15236.32.0.1 to 236.33.255.254236.33.255.255131,070
18236.34.0.0/15236.34.0.1 to 236.35.255.254236.35.255.255131,070
19236.36.0.0/15236.36.0.1 to 236.37.255.254236.37.255.255131,070
20236.38.0.0/15236.38.0.1 to 236.39.255.254236.39.255.255131,070
21236.40.0.0/15236.40.0.1 to 236.41.255.254236.41.255.255131,070
22236.42.0.0/15236.42.0.1 to 236.43.255.254236.43.255.255131,070
23236.44.0.0/15236.44.0.1 to 236.45.255.254236.45.255.255131,070
24236.46.0.0/15236.46.0.1 to 236.47.255.254236.47.255.255131,070
25236.48.0.0/15236.48.0.1 to 236.49.255.254236.49.255.255131,070
26236.50.0.0/15236.50.0.1 to 236.51.255.254236.51.255.255131,070
27236.52.0.0/15236.52.0.1 to 236.53.255.254236.53.255.255131,070
28236.54.0.0/15236.54.0.1 to 236.55.255.254236.55.255.255131,070
29236.56.0.0/15236.56.0.1 to 236.57.255.254236.57.255.255131,070
30236.58.0.0/15236.58.0.1 to 236.59.255.254236.59.255.255131,070
31236.60.0.0/15236.60.0.1 to 236.61.255.254236.61.255.255131,070
32236.62.0.0/15236.62.0.1 to 236.63.255.254236.63.255.255131,070
33236.64.0.0/15236.64.0.1 to 236.65.255.254236.65.255.255131,070
34236.66.0.0/15236.66.0.1 to 236.67.255.254236.67.255.255131,070
35236.68.0.0/15236.68.0.1 to 236.69.255.254236.69.255.255131,070
36236.70.0.0/15236.70.0.1 to 236.71.255.254236.71.255.255131,070
37236.72.0.0/15236.72.0.1 to 236.73.255.254236.73.255.255131,070
38236.74.0.0/15236.74.0.1 to 236.75.255.254236.75.255.255131,070
39236.76.0.0/15236.76.0.1 to 236.77.255.254236.77.255.255131,070
40236.78.0.0/15236.78.0.1 to 236.79.255.254236.79.255.255131,070
41236.80.0.0/15236.80.0.1 to 236.81.255.254236.81.255.255131,070
42236.82.0.0/15236.82.0.1 to 236.83.255.254236.83.255.255131,070
43236.84.0.0/15236.84.0.1 to 236.85.255.254236.85.255.255131,070
44236.86.0.0/15236.86.0.1 to 236.87.255.254236.87.255.255131,070
45236.88.0.0/15236.88.0.1 to 236.89.255.254236.89.255.255131,070
46236.90.0.0/15236.90.0.1 to 236.91.255.254236.91.255.255131,070
47236.92.0.0/15236.92.0.1 to 236.93.255.254236.93.255.255131,070
48236.94.0.0/15236.94.0.1 to 236.95.255.254236.95.255.255131,070
49236.96.0.0/15236.96.0.1 to 236.97.255.254236.97.255.255131,070
50236.98.0.0/15236.98.0.1 to 236.99.255.254236.99.255.255131,070
51236.100.0.0/15236.100.0.1 to 236.101.255.254236.101.255.255131,070
52236.102.0.0/15236.102.0.1 to 236.103.255.254236.103.255.255131,070
53236.104.0.0/15236.104.0.1 to 236.105.255.254236.105.255.255131,070
54236.106.0.0/15236.106.0.1 to 236.107.255.254236.107.255.255131,070
55236.108.0.0/15236.108.0.1 to 236.109.255.254236.109.255.255131,070
56236.110.0.0/15236.110.0.1 to 236.111.255.254236.111.255.255131,070
57236.112.0.0/15236.112.0.1 to 236.113.255.254236.113.255.255131,070
58236.114.0.0/15236.114.0.1 to 236.115.255.254236.115.255.255131,070
59236.116.0.0/15236.116.0.1 to 236.117.255.254236.117.255.255131,070
60236.118.0.0/15236.118.0.1 to 236.119.255.254236.119.255.255131,070
61236.120.0.0/15236.120.0.1 to 236.121.255.254236.121.255.255131,070
62236.122.0.0/15236.122.0.1 to 236.123.255.254236.123.255.255131,070
63236.124.0.0/15236.124.0.1 to 236.125.255.254236.125.255.255131,070
64236.126.0.0/15236.126.0.1 to 236.127.255.254236.127.255.255131,070
65236.128.0.0/15236.128.0.1 to 236.129.255.254236.129.255.255131,070
66236.130.0.0/15236.130.0.1 to 236.131.255.254236.131.255.255131,070
67236.132.0.0/15236.132.0.1 to 236.133.255.254236.133.255.255131,070
68236.134.0.0/15236.134.0.1 to 236.135.255.254236.135.255.255131,070
69236.136.0.0/15236.136.0.1 to 236.137.255.254236.137.255.255131,070
70236.138.0.0/15236.138.0.1 to 236.139.255.254236.139.255.255131,070
71236.140.0.0/15236.140.0.1 to 236.141.255.254236.141.255.255131,070
72236.142.0.0/15236.142.0.1 to 236.143.255.254236.143.255.255131,070
73236.144.0.0/15236.144.0.1 to 236.145.255.254236.145.255.255131,070
74236.146.0.0/15236.146.0.1 to 236.147.255.254236.147.255.255131,070
75236.148.0.0/15236.148.0.1 to 236.149.255.254236.149.255.255131,070
76236.150.0.0/15236.150.0.1 to 236.151.255.254236.151.255.255131,070
77236.152.0.0/15236.152.0.1 to 236.153.255.254236.153.255.255131,070
78236.154.0.0/15236.154.0.1 to 236.155.255.254236.155.255.255131,070
79236.156.0.0/15236.156.0.1 to 236.157.255.254236.157.255.255131,070
80236.158.0.0/15236.158.0.1 to 236.159.255.254236.159.255.255131,070
81236.160.0.0/15236.160.0.1 to 236.161.255.254236.161.255.255131,070
82236.162.0.0/15236.162.0.1 to 236.163.255.254236.163.255.255131,070
83236.164.0.0/15236.164.0.1 to 236.165.255.254236.165.255.255131,070
84236.166.0.0/15236.166.0.1 to 236.167.255.254236.167.255.255131,070
85236.168.0.0/15236.168.0.1 to 236.169.255.254236.169.255.255131,070
86236.170.0.0/15236.170.0.1 to 236.171.255.254236.171.255.255131,070
87236.172.0.0/15236.172.0.1 to 236.173.255.254236.173.255.255131,070
88236.174.0.0/15236.174.0.1 to 236.175.255.254236.175.255.255131,070
89236.176.0.0/15236.176.0.1 to 236.177.255.254236.177.255.255131,070
90236.178.0.0/15236.178.0.1 to 236.179.255.254236.179.255.255131,070
91236.180.0.0/15236.180.0.1 to 236.181.255.254236.181.255.255131,070
92236.182.0.0/15236.182.0.1 to 236.183.255.254236.183.255.255131,070
93236.184.0.0/15236.184.0.1 to 236.185.255.254236.185.255.255131,070
94236.186.0.0/15236.186.0.1 to 236.187.255.254236.187.255.255131,070
95236.188.0.0/15236.188.0.1 to 236.189.255.254236.189.255.255131,070
96236.190.0.0/15236.190.0.1 to 236.191.255.254236.191.255.255131,070
97236.192.0.0/15236.192.0.1 to 236.193.255.254236.193.255.255131,070
98236.194.0.0/15236.194.0.1 to 236.195.255.254236.195.255.255131,070
99236.196.0.0/15236.196.0.1 to 236.197.255.254236.197.255.255131,070
100236.198.0.0/15236.198.0.1 to 236.199.255.254236.199.255.255131,070
101236.200.0.0/15236.200.0.1 to 236.201.255.254236.201.255.255131,070
102236.202.0.0/15236.202.0.1 to 236.203.255.254236.203.255.255131,070
103236.204.0.0/15236.204.0.1 to 236.205.255.254236.205.255.255131,070
104236.206.0.0/15236.206.0.1 to 236.207.255.254236.207.255.255131,070
105236.208.0.0/15236.208.0.1 to 236.209.255.254236.209.255.255131,070
106236.210.0.0/15236.210.0.1 to 236.211.255.254236.211.255.255131,070
107236.212.0.0/15236.212.0.1 to 236.213.255.254236.213.255.255131,070
108236.214.0.0/15236.214.0.1 to 236.215.255.254236.215.255.255131,070
109236.216.0.0/15236.216.0.1 to 236.217.255.254236.217.255.255131,070
110236.218.0.0/15236.218.0.1 to 236.219.255.254236.219.255.255131,070
111236.220.0.0/15236.220.0.1 to 236.221.255.254236.221.255.255131,070
112236.222.0.0/15236.222.0.1 to 236.223.255.254236.223.255.255131,070
113236.224.0.0/15236.224.0.1 to 236.225.255.254236.225.255.255131,070
114236.226.0.0/15236.226.0.1 to 236.227.255.254236.227.255.255131,070
115236.228.0.0/15236.228.0.1 to 236.229.255.254236.229.255.255131,070
116236.230.0.0/15236.230.0.1 to 236.231.255.254236.231.255.255131,070
117236.232.0.0/15236.232.0.1 to 236.233.255.254236.233.255.255131,070
118236.234.0.0/15236.234.0.1 to 236.235.255.254236.235.255.255131,070
119236.236.0.0/15236.236.0.1 to 236.237.255.254236.237.255.255131,070
120236.238.0.0/15236.238.0.1 to 236.239.255.254236.239.255.255131,070
121236.240.0.0/15236.240.0.1 to 236.241.255.254236.241.255.255131,070
122236.242.0.0/15236.242.0.1 to 236.243.255.254236.243.255.255131,070
123236.244.0.0/15236.244.0.1 to 236.245.255.254236.245.255.255131,070
124236.246.0.0/15236.246.0.1 to 236.247.255.254236.247.255.255131,070
125236.248.0.0/15236.248.0.1 to 236.249.255.254236.249.255.255131,070
126236.250.0.0/15236.250.0.1 to 236.251.255.254236.251.255.255131,070
127236.252.0.0/15236.252.0.1 to 236.253.255.254236.253.255.255131,070
128236.254.0.0/15236.254.0.1 to 236.255.255.254236.255.255.255131,070

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.