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.

Network231.128.0.0/10
Usable hosts4,194,302
Subnet mask255.192.0.0
Addresses4,194,304
Network address
231.128.0.0
Broadcast address
231.191.255.255
First usable
231.128.0.1
Last usable
231.191.255.254
Usable hosts
4,194,302 (4,194,304 less the network and broadcast addresses)
Subnet mask
255.192.0.0
Wildcard mask
0.63.255.255 (Cisco ACLs, OSPF)
Prefix length
/10
Type
Multicast 224.0.0.0/4
One-to-many traffic, such as IPTV and routing protocols
Old class
D (multicast)
As numbers
Hex E7800000 · Integer 3883925504 to 3888119807
Reverse DNS zones
128.231.in-addr.arpa
129.231.in-addr.arpa
130.231.in-addr.arpa
131.231.in-addr.arpa
132.231.in-addr.arpa
133.231.in-addr.arpa
134.231.in-addr.arpa
135.231.in-addr.arpa
136.231.in-addr.arpa
137.231.in-addr.arpa
138.231.in-addr.arpa
139.231.in-addr.arpa
140.231.in-addr.arpa
141.231.in-addr.arpa
142.231.in-addr.arpa
143.231.in-addr.arpa
and 48 more
/10 is not on a 8-bit boundary, so it takes 64 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11100111.10000000.00000000.00000000231.128.0.0
Subnet mask11111111.11000000.00000000.00000000255.192.0.0
Network11100111.10000000.00000000.00000000231.128.0.0
Broadcast11100111.10111111.11111111.11111111231.191.255.255
Split into smaller subnets/17
/11 (2)/12 (4)/13 (8)/14 (16)/15 (32)/16 (64)/17 (128)/18 (256)/19 (512)/20 (1,024)/21 (2,048)/22 (4,096)

231.128.0.0/10 makes 128 subnets of /17.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1231.128.0.0/17231.128.0.1 to 231.128.127.254231.128.127.25532,766
2231.128.128.0/17231.128.128.1 to 231.128.255.254231.128.255.25532,766
3231.129.0.0/17231.129.0.1 to 231.129.127.254231.129.127.25532,766
4231.129.128.0/17231.129.128.1 to 231.129.255.254231.129.255.25532,766
5231.130.0.0/17231.130.0.1 to 231.130.127.254231.130.127.25532,766
6231.130.128.0/17231.130.128.1 to 231.130.255.254231.130.255.25532,766
7231.131.0.0/17231.131.0.1 to 231.131.127.254231.131.127.25532,766
8231.131.128.0/17231.131.128.1 to 231.131.255.254231.131.255.25532,766
9231.132.0.0/17231.132.0.1 to 231.132.127.254231.132.127.25532,766
10231.132.128.0/17231.132.128.1 to 231.132.255.254231.132.255.25532,766
11231.133.0.0/17231.133.0.1 to 231.133.127.254231.133.127.25532,766
12231.133.128.0/17231.133.128.1 to 231.133.255.254231.133.255.25532,766
13231.134.0.0/17231.134.0.1 to 231.134.127.254231.134.127.25532,766
14231.134.128.0/17231.134.128.1 to 231.134.255.254231.134.255.25532,766
15231.135.0.0/17231.135.0.1 to 231.135.127.254231.135.127.25532,766
16231.135.128.0/17231.135.128.1 to 231.135.255.254231.135.255.25532,766
17231.136.0.0/17231.136.0.1 to 231.136.127.254231.136.127.25532,766
18231.136.128.0/17231.136.128.1 to 231.136.255.254231.136.255.25532,766
19231.137.0.0/17231.137.0.1 to 231.137.127.254231.137.127.25532,766
20231.137.128.0/17231.137.128.1 to 231.137.255.254231.137.255.25532,766
21231.138.0.0/17231.138.0.1 to 231.138.127.254231.138.127.25532,766
22231.138.128.0/17231.138.128.1 to 231.138.255.254231.138.255.25532,766
23231.139.0.0/17231.139.0.1 to 231.139.127.254231.139.127.25532,766
24231.139.128.0/17231.139.128.1 to 231.139.255.254231.139.255.25532,766
25231.140.0.0/17231.140.0.1 to 231.140.127.254231.140.127.25532,766
26231.140.128.0/17231.140.128.1 to 231.140.255.254231.140.255.25532,766
27231.141.0.0/17231.141.0.1 to 231.141.127.254231.141.127.25532,766
28231.141.128.0/17231.141.128.1 to 231.141.255.254231.141.255.25532,766
29231.142.0.0/17231.142.0.1 to 231.142.127.254231.142.127.25532,766
30231.142.128.0/17231.142.128.1 to 231.142.255.254231.142.255.25532,766
31231.143.0.0/17231.143.0.1 to 231.143.127.254231.143.127.25532,766
32231.143.128.0/17231.143.128.1 to 231.143.255.254231.143.255.25532,766
33231.144.0.0/17231.144.0.1 to 231.144.127.254231.144.127.25532,766
34231.144.128.0/17231.144.128.1 to 231.144.255.254231.144.255.25532,766
35231.145.0.0/17231.145.0.1 to 231.145.127.254231.145.127.25532,766
36231.145.128.0/17231.145.128.1 to 231.145.255.254231.145.255.25532,766
37231.146.0.0/17231.146.0.1 to 231.146.127.254231.146.127.25532,766
38231.146.128.0/17231.146.128.1 to 231.146.255.254231.146.255.25532,766
39231.147.0.0/17231.147.0.1 to 231.147.127.254231.147.127.25532,766
40231.147.128.0/17231.147.128.1 to 231.147.255.254231.147.255.25532,766
41231.148.0.0/17231.148.0.1 to 231.148.127.254231.148.127.25532,766
42231.148.128.0/17231.148.128.1 to 231.148.255.254231.148.255.25532,766
43231.149.0.0/17231.149.0.1 to 231.149.127.254231.149.127.25532,766
44231.149.128.0/17231.149.128.1 to 231.149.255.254231.149.255.25532,766
45231.150.0.0/17231.150.0.1 to 231.150.127.254231.150.127.25532,766
46231.150.128.0/17231.150.128.1 to 231.150.255.254231.150.255.25532,766
47231.151.0.0/17231.151.0.1 to 231.151.127.254231.151.127.25532,766
48231.151.128.0/17231.151.128.1 to 231.151.255.254231.151.255.25532,766
49231.152.0.0/17231.152.0.1 to 231.152.127.254231.152.127.25532,766
50231.152.128.0/17231.152.128.1 to 231.152.255.254231.152.255.25532,766
51231.153.0.0/17231.153.0.1 to 231.153.127.254231.153.127.25532,766
52231.153.128.0/17231.153.128.1 to 231.153.255.254231.153.255.25532,766
53231.154.0.0/17231.154.0.1 to 231.154.127.254231.154.127.25532,766
54231.154.128.0/17231.154.128.1 to 231.154.255.254231.154.255.25532,766
55231.155.0.0/17231.155.0.1 to 231.155.127.254231.155.127.25532,766
56231.155.128.0/17231.155.128.1 to 231.155.255.254231.155.255.25532,766
57231.156.0.0/17231.156.0.1 to 231.156.127.254231.156.127.25532,766
58231.156.128.0/17231.156.128.1 to 231.156.255.254231.156.255.25532,766
59231.157.0.0/17231.157.0.1 to 231.157.127.254231.157.127.25532,766
60231.157.128.0/17231.157.128.1 to 231.157.255.254231.157.255.25532,766
61231.158.0.0/17231.158.0.1 to 231.158.127.254231.158.127.25532,766
62231.158.128.0/17231.158.128.1 to 231.158.255.254231.158.255.25532,766
63231.159.0.0/17231.159.0.1 to 231.159.127.254231.159.127.25532,766
64231.159.128.0/17231.159.128.1 to 231.159.255.254231.159.255.25532,766
65231.160.0.0/17231.160.0.1 to 231.160.127.254231.160.127.25532,766
66231.160.128.0/17231.160.128.1 to 231.160.255.254231.160.255.25532,766
67231.161.0.0/17231.161.0.1 to 231.161.127.254231.161.127.25532,766
68231.161.128.0/17231.161.128.1 to 231.161.255.254231.161.255.25532,766
69231.162.0.0/17231.162.0.1 to 231.162.127.254231.162.127.25532,766
70231.162.128.0/17231.162.128.1 to 231.162.255.254231.162.255.25532,766
71231.163.0.0/17231.163.0.1 to 231.163.127.254231.163.127.25532,766
72231.163.128.0/17231.163.128.1 to 231.163.255.254231.163.255.25532,766
73231.164.0.0/17231.164.0.1 to 231.164.127.254231.164.127.25532,766
74231.164.128.0/17231.164.128.1 to 231.164.255.254231.164.255.25532,766
75231.165.0.0/17231.165.0.1 to 231.165.127.254231.165.127.25532,766
76231.165.128.0/17231.165.128.1 to 231.165.255.254231.165.255.25532,766
77231.166.0.0/17231.166.0.1 to 231.166.127.254231.166.127.25532,766
78231.166.128.0/17231.166.128.1 to 231.166.255.254231.166.255.25532,766
79231.167.0.0/17231.167.0.1 to 231.167.127.254231.167.127.25532,766
80231.167.128.0/17231.167.128.1 to 231.167.255.254231.167.255.25532,766
81231.168.0.0/17231.168.0.1 to 231.168.127.254231.168.127.25532,766
82231.168.128.0/17231.168.128.1 to 231.168.255.254231.168.255.25532,766
83231.169.0.0/17231.169.0.1 to 231.169.127.254231.169.127.25532,766
84231.169.128.0/17231.169.128.1 to 231.169.255.254231.169.255.25532,766
85231.170.0.0/17231.170.0.1 to 231.170.127.254231.170.127.25532,766
86231.170.128.0/17231.170.128.1 to 231.170.255.254231.170.255.25532,766
87231.171.0.0/17231.171.0.1 to 231.171.127.254231.171.127.25532,766
88231.171.128.0/17231.171.128.1 to 231.171.255.254231.171.255.25532,766
89231.172.0.0/17231.172.0.1 to 231.172.127.254231.172.127.25532,766
90231.172.128.0/17231.172.128.1 to 231.172.255.254231.172.255.25532,766
91231.173.0.0/17231.173.0.1 to 231.173.127.254231.173.127.25532,766
92231.173.128.0/17231.173.128.1 to 231.173.255.254231.173.255.25532,766
93231.174.0.0/17231.174.0.1 to 231.174.127.254231.174.127.25532,766
94231.174.128.0/17231.174.128.1 to 231.174.255.254231.174.255.25532,766
95231.175.0.0/17231.175.0.1 to 231.175.127.254231.175.127.25532,766
96231.175.128.0/17231.175.128.1 to 231.175.255.254231.175.255.25532,766
97231.176.0.0/17231.176.0.1 to 231.176.127.254231.176.127.25532,766
98231.176.128.0/17231.176.128.1 to 231.176.255.254231.176.255.25532,766
99231.177.0.0/17231.177.0.1 to 231.177.127.254231.177.127.25532,766
100231.177.128.0/17231.177.128.1 to 231.177.255.254231.177.255.25532,766
101231.178.0.0/17231.178.0.1 to 231.178.127.254231.178.127.25532,766
102231.178.128.0/17231.178.128.1 to 231.178.255.254231.178.255.25532,766
103231.179.0.0/17231.179.0.1 to 231.179.127.254231.179.127.25532,766
104231.179.128.0/17231.179.128.1 to 231.179.255.254231.179.255.25532,766
105231.180.0.0/17231.180.0.1 to 231.180.127.254231.180.127.25532,766
106231.180.128.0/17231.180.128.1 to 231.180.255.254231.180.255.25532,766
107231.181.0.0/17231.181.0.1 to 231.181.127.254231.181.127.25532,766
108231.181.128.0/17231.181.128.1 to 231.181.255.254231.181.255.25532,766
109231.182.0.0/17231.182.0.1 to 231.182.127.254231.182.127.25532,766
110231.182.128.0/17231.182.128.1 to 231.182.255.254231.182.255.25532,766
111231.183.0.0/17231.183.0.1 to 231.183.127.254231.183.127.25532,766
112231.183.128.0/17231.183.128.1 to 231.183.255.254231.183.255.25532,766
113231.184.0.0/17231.184.0.1 to 231.184.127.254231.184.127.25532,766
114231.184.128.0/17231.184.128.1 to 231.184.255.254231.184.255.25532,766
115231.185.0.0/17231.185.0.1 to 231.185.127.254231.185.127.25532,766
116231.185.128.0/17231.185.128.1 to 231.185.255.254231.185.255.25532,766
117231.186.0.0/17231.186.0.1 to 231.186.127.254231.186.127.25532,766
118231.186.128.0/17231.186.128.1 to 231.186.255.254231.186.255.25532,766
119231.187.0.0/17231.187.0.1 to 231.187.127.254231.187.127.25532,766
120231.187.128.0/17231.187.128.1 to 231.187.255.254231.187.255.25532,766
121231.188.0.0/17231.188.0.1 to 231.188.127.254231.188.127.25532,766
122231.188.128.0/17231.188.128.1 to 231.188.255.254231.188.255.25532,766
123231.189.0.0/17231.189.0.1 to 231.189.127.254231.189.127.25532,766
124231.189.128.0/17231.189.128.1 to 231.189.255.254231.189.255.25532,766
125231.190.0.0/17231.190.0.1 to 231.190.127.254231.190.127.25532,766
126231.190.128.0/17231.190.128.1 to 231.190.255.254231.190.255.25532,766
127231.191.0.0/17231.191.0.1 to 231.191.127.254231.191.127.25532,766
128231.191.128.0/17231.191.128.1 to 231.191.255.254231.191.255.25532,766

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.