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.

Network231.30.0.0/15
Usable hosts131,070
Subnet mask255.254.0.0
Addresses131,072
Network address
231.30.0.0
Broadcast address
231.31.255.255
First usable
231.30.0.1
Last usable
231.31.255.254
Usable hosts
131,070 (131,072 less the network and broadcast addresses)
Subnet mask
255.254.0.0
Wildcard mask
0.1.255.255 (Cisco ACLs, OSPF)
Prefix length
/15
Type
Multicast 224.0.0.0/4
One-to-many traffic, such as IPTV and routing protocols
Old class
D (multicast)
As numbers
Hex E71E0000 · Integer 3877502976 to 3877634047
Reverse DNS zones
30.231.in-addr.arpa
31.231.in-addr.arpa
/15 is not on a 8-bit boundary, so it takes 2 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11100111.00011110.00000000.00000000231.30.0.0
Subnet mask11111111.11111110.00000000.00000000255.254.0.0
Network11100111.00011110.00000000.00000000231.30.0.0
Broadcast11100111.00011111.11111111.11111111231.31.255.255
Split into smaller subnets/22
/16 (2)/17 (4)/18 (8)/19 (16)/20 (32)/21 (64)/22 (128)/23 (256)/24 (512)/25 (1,024)/26 (2,048)/27 (4,096)

231.30.0.0/15 makes 128 subnets of /22.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1231.30.0.0/22231.30.0.1 to 231.30.3.254231.30.3.2551,022
2231.30.4.0/22231.30.4.1 to 231.30.7.254231.30.7.2551,022
3231.30.8.0/22231.30.8.1 to 231.30.11.254231.30.11.2551,022
4231.30.12.0/22231.30.12.1 to 231.30.15.254231.30.15.2551,022
5231.30.16.0/22231.30.16.1 to 231.30.19.254231.30.19.2551,022
6231.30.20.0/22231.30.20.1 to 231.30.23.254231.30.23.2551,022
7231.30.24.0/22231.30.24.1 to 231.30.27.254231.30.27.2551,022
8231.30.28.0/22231.30.28.1 to 231.30.31.254231.30.31.2551,022
9231.30.32.0/22231.30.32.1 to 231.30.35.254231.30.35.2551,022
10231.30.36.0/22231.30.36.1 to 231.30.39.254231.30.39.2551,022
11231.30.40.0/22231.30.40.1 to 231.30.43.254231.30.43.2551,022
12231.30.44.0/22231.30.44.1 to 231.30.47.254231.30.47.2551,022
13231.30.48.0/22231.30.48.1 to 231.30.51.254231.30.51.2551,022
14231.30.52.0/22231.30.52.1 to 231.30.55.254231.30.55.2551,022
15231.30.56.0/22231.30.56.1 to 231.30.59.254231.30.59.2551,022
16231.30.60.0/22231.30.60.1 to 231.30.63.254231.30.63.2551,022
17231.30.64.0/22231.30.64.1 to 231.30.67.254231.30.67.2551,022
18231.30.68.0/22231.30.68.1 to 231.30.71.254231.30.71.2551,022
19231.30.72.0/22231.30.72.1 to 231.30.75.254231.30.75.2551,022
20231.30.76.0/22231.30.76.1 to 231.30.79.254231.30.79.2551,022
21231.30.80.0/22231.30.80.1 to 231.30.83.254231.30.83.2551,022
22231.30.84.0/22231.30.84.1 to 231.30.87.254231.30.87.2551,022
23231.30.88.0/22231.30.88.1 to 231.30.91.254231.30.91.2551,022
24231.30.92.0/22231.30.92.1 to 231.30.95.254231.30.95.2551,022
25231.30.96.0/22231.30.96.1 to 231.30.99.254231.30.99.2551,022
26231.30.100.0/22231.30.100.1 to 231.30.103.254231.30.103.2551,022
27231.30.104.0/22231.30.104.1 to 231.30.107.254231.30.107.2551,022
28231.30.108.0/22231.30.108.1 to 231.30.111.254231.30.111.2551,022
29231.30.112.0/22231.30.112.1 to 231.30.115.254231.30.115.2551,022
30231.30.116.0/22231.30.116.1 to 231.30.119.254231.30.119.2551,022
31231.30.120.0/22231.30.120.1 to 231.30.123.254231.30.123.2551,022
32231.30.124.0/22231.30.124.1 to 231.30.127.254231.30.127.2551,022
33231.30.128.0/22231.30.128.1 to 231.30.131.254231.30.131.2551,022
34231.30.132.0/22231.30.132.1 to 231.30.135.254231.30.135.2551,022
35231.30.136.0/22231.30.136.1 to 231.30.139.254231.30.139.2551,022
36231.30.140.0/22231.30.140.1 to 231.30.143.254231.30.143.2551,022
37231.30.144.0/22231.30.144.1 to 231.30.147.254231.30.147.2551,022
38231.30.148.0/22231.30.148.1 to 231.30.151.254231.30.151.2551,022
39231.30.152.0/22231.30.152.1 to 231.30.155.254231.30.155.2551,022
40231.30.156.0/22231.30.156.1 to 231.30.159.254231.30.159.2551,022
41231.30.160.0/22231.30.160.1 to 231.30.163.254231.30.163.2551,022
42231.30.164.0/22231.30.164.1 to 231.30.167.254231.30.167.2551,022
43231.30.168.0/22231.30.168.1 to 231.30.171.254231.30.171.2551,022
44231.30.172.0/22231.30.172.1 to 231.30.175.254231.30.175.2551,022
45231.30.176.0/22231.30.176.1 to 231.30.179.254231.30.179.2551,022
46231.30.180.0/22231.30.180.1 to 231.30.183.254231.30.183.2551,022
47231.30.184.0/22231.30.184.1 to 231.30.187.254231.30.187.2551,022
48231.30.188.0/22231.30.188.1 to 231.30.191.254231.30.191.2551,022
49231.30.192.0/22231.30.192.1 to 231.30.195.254231.30.195.2551,022
50231.30.196.0/22231.30.196.1 to 231.30.199.254231.30.199.2551,022
51231.30.200.0/22231.30.200.1 to 231.30.203.254231.30.203.2551,022
52231.30.204.0/22231.30.204.1 to 231.30.207.254231.30.207.2551,022
53231.30.208.0/22231.30.208.1 to 231.30.211.254231.30.211.2551,022
54231.30.212.0/22231.30.212.1 to 231.30.215.254231.30.215.2551,022
55231.30.216.0/22231.30.216.1 to 231.30.219.254231.30.219.2551,022
56231.30.220.0/22231.30.220.1 to 231.30.223.254231.30.223.2551,022
57231.30.224.0/22231.30.224.1 to 231.30.227.254231.30.227.2551,022
58231.30.228.0/22231.30.228.1 to 231.30.231.254231.30.231.2551,022
59231.30.232.0/22231.30.232.1 to 231.30.235.254231.30.235.2551,022
60231.30.236.0/22231.30.236.1 to 231.30.239.254231.30.239.2551,022
61231.30.240.0/22231.30.240.1 to 231.30.243.254231.30.243.2551,022
62231.30.244.0/22231.30.244.1 to 231.30.247.254231.30.247.2551,022
63231.30.248.0/22231.30.248.1 to 231.30.251.254231.30.251.2551,022
64231.30.252.0/22231.30.252.1 to 231.30.255.254231.30.255.2551,022
65231.31.0.0/22231.31.0.1 to 231.31.3.254231.31.3.2551,022
66231.31.4.0/22231.31.4.1 to 231.31.7.254231.31.7.2551,022
67231.31.8.0/22231.31.8.1 to 231.31.11.254231.31.11.2551,022
68231.31.12.0/22231.31.12.1 to 231.31.15.254231.31.15.2551,022
69231.31.16.0/22231.31.16.1 to 231.31.19.254231.31.19.2551,022
70231.31.20.0/22231.31.20.1 to 231.31.23.254231.31.23.2551,022
71231.31.24.0/22231.31.24.1 to 231.31.27.254231.31.27.2551,022
72231.31.28.0/22231.31.28.1 to 231.31.31.254231.31.31.2551,022
73231.31.32.0/22231.31.32.1 to 231.31.35.254231.31.35.2551,022
74231.31.36.0/22231.31.36.1 to 231.31.39.254231.31.39.2551,022
75231.31.40.0/22231.31.40.1 to 231.31.43.254231.31.43.2551,022
76231.31.44.0/22231.31.44.1 to 231.31.47.254231.31.47.2551,022
77231.31.48.0/22231.31.48.1 to 231.31.51.254231.31.51.2551,022
78231.31.52.0/22231.31.52.1 to 231.31.55.254231.31.55.2551,022
79231.31.56.0/22231.31.56.1 to 231.31.59.254231.31.59.2551,022
80231.31.60.0/22231.31.60.1 to 231.31.63.254231.31.63.2551,022
81231.31.64.0/22231.31.64.1 to 231.31.67.254231.31.67.2551,022
82231.31.68.0/22231.31.68.1 to 231.31.71.254231.31.71.2551,022
83231.31.72.0/22231.31.72.1 to 231.31.75.254231.31.75.2551,022
84231.31.76.0/22231.31.76.1 to 231.31.79.254231.31.79.2551,022
85231.31.80.0/22231.31.80.1 to 231.31.83.254231.31.83.2551,022
86231.31.84.0/22231.31.84.1 to 231.31.87.254231.31.87.2551,022
87231.31.88.0/22231.31.88.1 to 231.31.91.254231.31.91.2551,022
88231.31.92.0/22231.31.92.1 to 231.31.95.254231.31.95.2551,022
89231.31.96.0/22231.31.96.1 to 231.31.99.254231.31.99.2551,022
90231.31.100.0/22231.31.100.1 to 231.31.103.254231.31.103.2551,022
91231.31.104.0/22231.31.104.1 to 231.31.107.254231.31.107.2551,022
92231.31.108.0/22231.31.108.1 to 231.31.111.254231.31.111.2551,022
93231.31.112.0/22231.31.112.1 to 231.31.115.254231.31.115.2551,022
94231.31.116.0/22231.31.116.1 to 231.31.119.254231.31.119.2551,022
95231.31.120.0/22231.31.120.1 to 231.31.123.254231.31.123.2551,022
96231.31.124.0/22231.31.124.1 to 231.31.127.254231.31.127.2551,022
97231.31.128.0/22231.31.128.1 to 231.31.131.254231.31.131.2551,022
98231.31.132.0/22231.31.132.1 to 231.31.135.254231.31.135.2551,022
99231.31.136.0/22231.31.136.1 to 231.31.139.254231.31.139.2551,022
100231.31.140.0/22231.31.140.1 to 231.31.143.254231.31.143.2551,022
101231.31.144.0/22231.31.144.1 to 231.31.147.254231.31.147.2551,022
102231.31.148.0/22231.31.148.1 to 231.31.151.254231.31.151.2551,022
103231.31.152.0/22231.31.152.1 to 231.31.155.254231.31.155.2551,022
104231.31.156.0/22231.31.156.1 to 231.31.159.254231.31.159.2551,022
105231.31.160.0/22231.31.160.1 to 231.31.163.254231.31.163.2551,022
106231.31.164.0/22231.31.164.1 to 231.31.167.254231.31.167.2551,022
107231.31.168.0/22231.31.168.1 to 231.31.171.254231.31.171.2551,022
108231.31.172.0/22231.31.172.1 to 231.31.175.254231.31.175.2551,022
109231.31.176.0/22231.31.176.1 to 231.31.179.254231.31.179.2551,022
110231.31.180.0/22231.31.180.1 to 231.31.183.254231.31.183.2551,022
111231.31.184.0/22231.31.184.1 to 231.31.187.254231.31.187.2551,022
112231.31.188.0/22231.31.188.1 to 231.31.191.254231.31.191.2551,022
113231.31.192.0/22231.31.192.1 to 231.31.195.254231.31.195.2551,022
114231.31.196.0/22231.31.196.1 to 231.31.199.254231.31.199.2551,022
115231.31.200.0/22231.31.200.1 to 231.31.203.254231.31.203.2551,022
116231.31.204.0/22231.31.204.1 to 231.31.207.254231.31.207.2551,022
117231.31.208.0/22231.31.208.1 to 231.31.211.254231.31.211.2551,022
118231.31.212.0/22231.31.212.1 to 231.31.215.254231.31.215.2551,022
119231.31.216.0/22231.31.216.1 to 231.31.219.254231.31.219.2551,022
120231.31.220.0/22231.31.220.1 to 231.31.223.254231.31.223.2551,022
121231.31.224.0/22231.31.224.1 to 231.31.227.254231.31.227.2551,022
122231.31.228.0/22231.31.228.1 to 231.31.231.254231.31.231.2551,022
123231.31.232.0/22231.31.232.1 to 231.31.235.254231.31.235.2551,022
124231.31.236.0/22231.31.236.1 to 231.31.239.254231.31.239.2551,022
125231.31.240.0/22231.31.240.1 to 231.31.243.254231.31.243.2551,022
126231.31.244.0/22231.31.244.1 to 231.31.247.254231.31.247.2551,022
127231.31.248.0/22231.31.248.1 to 231.31.251.254231.31.251.2551,022
128231.31.252.0/22231.31.252.1 to 231.31.255.254231.31.255.2551,022

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.