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.

Network143.16.64.0/18
Usable hosts16,382
Subnet mask255.255.192.0
Addresses16,384
Network address
143.16.64.0
Broadcast address
143.16.127.255
First usable
143.16.64.1
Last usable
143.16.127.254
Usable hosts
16,382 (16,384 less the network and broadcast addresses)
Subnet mask
255.255.192.0
Wildcard mask
0.0.63.255 (Cisco ACLs, OSPF)
Prefix length
/18
Type
Public public
Old class
B (default /16)
As numbers
Hex 8F104000 · Integer 2400206848 to 2400223231
Reverse DNS zones
64.16.143.in-addr.arpa
65.16.143.in-addr.arpa
66.16.143.in-addr.arpa
67.16.143.in-addr.arpa
68.16.143.in-addr.arpa
69.16.143.in-addr.arpa
70.16.143.in-addr.arpa
71.16.143.in-addr.arpa
72.16.143.in-addr.arpa
73.16.143.in-addr.arpa
74.16.143.in-addr.arpa
75.16.143.in-addr.arpa
76.16.143.in-addr.arpa
77.16.143.in-addr.arpa
78.16.143.in-addr.arpa
79.16.143.in-addr.arpa
and 48 more
/18 is not on a 8-bit boundary, so it takes 64 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address10001111.00010000.01000000.00000000143.16.64.0
Subnet mask11111111.11111111.11000000.00000000255.255.192.0
Network10001111.00010000.01000000.00000000143.16.64.0
Broadcast10001111.00010000.01111111.11111111143.16.127.255
Split into smaller subnets/25
/19 (2)/20 (4)/21 (8)/22 (16)/23 (32)/24 (64)/25 (128)/26 (256)/27 (512)/28 (1,024)/29 (2,048)/30 (4,096)

143.16.64.0/18 makes 128 subnets of /25.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1143.16.64.0/25143.16.64.1 to 143.16.64.126143.16.64.127126
2143.16.64.128/25143.16.64.129 to 143.16.64.254143.16.64.255126
3143.16.65.0/25143.16.65.1 to 143.16.65.126143.16.65.127126
4143.16.65.128/25143.16.65.129 to 143.16.65.254143.16.65.255126
5143.16.66.0/25143.16.66.1 to 143.16.66.126143.16.66.127126
6143.16.66.128/25143.16.66.129 to 143.16.66.254143.16.66.255126
7143.16.67.0/25143.16.67.1 to 143.16.67.126143.16.67.127126
8143.16.67.128/25143.16.67.129 to 143.16.67.254143.16.67.255126
9143.16.68.0/25143.16.68.1 to 143.16.68.126143.16.68.127126
10143.16.68.128/25143.16.68.129 to 143.16.68.254143.16.68.255126
11143.16.69.0/25143.16.69.1 to 143.16.69.126143.16.69.127126
12143.16.69.128/25143.16.69.129 to 143.16.69.254143.16.69.255126
13143.16.70.0/25143.16.70.1 to 143.16.70.126143.16.70.127126
14143.16.70.128/25143.16.70.129 to 143.16.70.254143.16.70.255126
15143.16.71.0/25143.16.71.1 to 143.16.71.126143.16.71.127126
16143.16.71.128/25143.16.71.129 to 143.16.71.254143.16.71.255126
17143.16.72.0/25143.16.72.1 to 143.16.72.126143.16.72.127126
18143.16.72.128/25143.16.72.129 to 143.16.72.254143.16.72.255126
19143.16.73.0/25143.16.73.1 to 143.16.73.126143.16.73.127126
20143.16.73.128/25143.16.73.129 to 143.16.73.254143.16.73.255126
21143.16.74.0/25143.16.74.1 to 143.16.74.126143.16.74.127126
22143.16.74.128/25143.16.74.129 to 143.16.74.254143.16.74.255126
23143.16.75.0/25143.16.75.1 to 143.16.75.126143.16.75.127126
24143.16.75.128/25143.16.75.129 to 143.16.75.254143.16.75.255126
25143.16.76.0/25143.16.76.1 to 143.16.76.126143.16.76.127126
26143.16.76.128/25143.16.76.129 to 143.16.76.254143.16.76.255126
27143.16.77.0/25143.16.77.1 to 143.16.77.126143.16.77.127126
28143.16.77.128/25143.16.77.129 to 143.16.77.254143.16.77.255126
29143.16.78.0/25143.16.78.1 to 143.16.78.126143.16.78.127126
30143.16.78.128/25143.16.78.129 to 143.16.78.254143.16.78.255126
31143.16.79.0/25143.16.79.1 to 143.16.79.126143.16.79.127126
32143.16.79.128/25143.16.79.129 to 143.16.79.254143.16.79.255126
33143.16.80.0/25143.16.80.1 to 143.16.80.126143.16.80.127126
34143.16.80.128/25143.16.80.129 to 143.16.80.254143.16.80.255126
35143.16.81.0/25143.16.81.1 to 143.16.81.126143.16.81.127126
36143.16.81.128/25143.16.81.129 to 143.16.81.254143.16.81.255126
37143.16.82.0/25143.16.82.1 to 143.16.82.126143.16.82.127126
38143.16.82.128/25143.16.82.129 to 143.16.82.254143.16.82.255126
39143.16.83.0/25143.16.83.1 to 143.16.83.126143.16.83.127126
40143.16.83.128/25143.16.83.129 to 143.16.83.254143.16.83.255126
41143.16.84.0/25143.16.84.1 to 143.16.84.126143.16.84.127126
42143.16.84.128/25143.16.84.129 to 143.16.84.254143.16.84.255126
43143.16.85.0/25143.16.85.1 to 143.16.85.126143.16.85.127126
44143.16.85.128/25143.16.85.129 to 143.16.85.254143.16.85.255126
45143.16.86.0/25143.16.86.1 to 143.16.86.126143.16.86.127126
46143.16.86.128/25143.16.86.129 to 143.16.86.254143.16.86.255126
47143.16.87.0/25143.16.87.1 to 143.16.87.126143.16.87.127126
48143.16.87.128/25143.16.87.129 to 143.16.87.254143.16.87.255126
49143.16.88.0/25143.16.88.1 to 143.16.88.126143.16.88.127126
50143.16.88.128/25143.16.88.129 to 143.16.88.254143.16.88.255126
51143.16.89.0/25143.16.89.1 to 143.16.89.126143.16.89.127126
52143.16.89.128/25143.16.89.129 to 143.16.89.254143.16.89.255126
53143.16.90.0/25143.16.90.1 to 143.16.90.126143.16.90.127126
54143.16.90.128/25143.16.90.129 to 143.16.90.254143.16.90.255126
55143.16.91.0/25143.16.91.1 to 143.16.91.126143.16.91.127126
56143.16.91.128/25143.16.91.129 to 143.16.91.254143.16.91.255126
57143.16.92.0/25143.16.92.1 to 143.16.92.126143.16.92.127126
58143.16.92.128/25143.16.92.129 to 143.16.92.254143.16.92.255126
59143.16.93.0/25143.16.93.1 to 143.16.93.126143.16.93.127126
60143.16.93.128/25143.16.93.129 to 143.16.93.254143.16.93.255126
61143.16.94.0/25143.16.94.1 to 143.16.94.126143.16.94.127126
62143.16.94.128/25143.16.94.129 to 143.16.94.254143.16.94.255126
63143.16.95.0/25143.16.95.1 to 143.16.95.126143.16.95.127126
64143.16.95.128/25143.16.95.129 to 143.16.95.254143.16.95.255126
65143.16.96.0/25143.16.96.1 to 143.16.96.126143.16.96.127126
66143.16.96.128/25143.16.96.129 to 143.16.96.254143.16.96.255126
67143.16.97.0/25143.16.97.1 to 143.16.97.126143.16.97.127126
68143.16.97.128/25143.16.97.129 to 143.16.97.254143.16.97.255126
69143.16.98.0/25143.16.98.1 to 143.16.98.126143.16.98.127126
70143.16.98.128/25143.16.98.129 to 143.16.98.254143.16.98.255126
71143.16.99.0/25143.16.99.1 to 143.16.99.126143.16.99.127126
72143.16.99.128/25143.16.99.129 to 143.16.99.254143.16.99.255126
73143.16.100.0/25143.16.100.1 to 143.16.100.126143.16.100.127126
74143.16.100.128/25143.16.100.129 to 143.16.100.254143.16.100.255126
75143.16.101.0/25143.16.101.1 to 143.16.101.126143.16.101.127126
76143.16.101.128/25143.16.101.129 to 143.16.101.254143.16.101.255126
77143.16.102.0/25143.16.102.1 to 143.16.102.126143.16.102.127126
78143.16.102.128/25143.16.102.129 to 143.16.102.254143.16.102.255126
79143.16.103.0/25143.16.103.1 to 143.16.103.126143.16.103.127126
80143.16.103.128/25143.16.103.129 to 143.16.103.254143.16.103.255126
81143.16.104.0/25143.16.104.1 to 143.16.104.126143.16.104.127126
82143.16.104.128/25143.16.104.129 to 143.16.104.254143.16.104.255126
83143.16.105.0/25143.16.105.1 to 143.16.105.126143.16.105.127126
84143.16.105.128/25143.16.105.129 to 143.16.105.254143.16.105.255126
85143.16.106.0/25143.16.106.1 to 143.16.106.126143.16.106.127126
86143.16.106.128/25143.16.106.129 to 143.16.106.254143.16.106.255126
87143.16.107.0/25143.16.107.1 to 143.16.107.126143.16.107.127126
88143.16.107.128/25143.16.107.129 to 143.16.107.254143.16.107.255126
89143.16.108.0/25143.16.108.1 to 143.16.108.126143.16.108.127126
90143.16.108.128/25143.16.108.129 to 143.16.108.254143.16.108.255126
91143.16.109.0/25143.16.109.1 to 143.16.109.126143.16.109.127126
92143.16.109.128/25143.16.109.129 to 143.16.109.254143.16.109.255126
93143.16.110.0/25143.16.110.1 to 143.16.110.126143.16.110.127126
94143.16.110.128/25143.16.110.129 to 143.16.110.254143.16.110.255126
95143.16.111.0/25143.16.111.1 to 143.16.111.126143.16.111.127126
96143.16.111.128/25143.16.111.129 to 143.16.111.254143.16.111.255126
97143.16.112.0/25143.16.112.1 to 143.16.112.126143.16.112.127126
98143.16.112.128/25143.16.112.129 to 143.16.112.254143.16.112.255126
99143.16.113.0/25143.16.113.1 to 143.16.113.126143.16.113.127126
100143.16.113.128/25143.16.113.129 to 143.16.113.254143.16.113.255126
101143.16.114.0/25143.16.114.1 to 143.16.114.126143.16.114.127126
102143.16.114.128/25143.16.114.129 to 143.16.114.254143.16.114.255126
103143.16.115.0/25143.16.115.1 to 143.16.115.126143.16.115.127126
104143.16.115.128/25143.16.115.129 to 143.16.115.254143.16.115.255126
105143.16.116.0/25143.16.116.1 to 143.16.116.126143.16.116.127126
106143.16.116.128/25143.16.116.129 to 143.16.116.254143.16.116.255126
107143.16.117.0/25143.16.117.1 to 143.16.117.126143.16.117.127126
108143.16.117.128/25143.16.117.129 to 143.16.117.254143.16.117.255126
109143.16.118.0/25143.16.118.1 to 143.16.118.126143.16.118.127126
110143.16.118.128/25143.16.118.129 to 143.16.118.254143.16.118.255126
111143.16.119.0/25143.16.119.1 to 143.16.119.126143.16.119.127126
112143.16.119.128/25143.16.119.129 to 143.16.119.254143.16.119.255126
113143.16.120.0/25143.16.120.1 to 143.16.120.126143.16.120.127126
114143.16.120.128/25143.16.120.129 to 143.16.120.254143.16.120.255126
115143.16.121.0/25143.16.121.1 to 143.16.121.126143.16.121.127126
116143.16.121.128/25143.16.121.129 to 143.16.121.254143.16.121.255126
117143.16.122.0/25143.16.122.1 to 143.16.122.126143.16.122.127126
118143.16.122.128/25143.16.122.129 to 143.16.122.254143.16.122.255126
119143.16.123.0/25143.16.123.1 to 143.16.123.126143.16.123.127126
120143.16.123.128/25143.16.123.129 to 143.16.123.254143.16.123.255126
121143.16.124.0/25143.16.124.1 to 143.16.124.126143.16.124.127126
122143.16.124.128/25143.16.124.129 to 143.16.124.254143.16.124.255126
123143.16.125.0/25143.16.125.1 to 143.16.125.126143.16.125.127126
124143.16.125.128/25143.16.125.129 to 143.16.125.254143.16.125.255126
125143.16.126.0/25143.16.126.1 to 143.16.126.126143.16.126.127126
126143.16.126.128/25143.16.126.129 to 143.16.126.254143.16.126.255126
127143.16.127.0/25143.16.127.1 to 143.16.127.126143.16.127.127126
128143.16.127.128/25143.16.127.129 to 143.16.127.254143.16.127.255126

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.