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.

Network201.2.96.0/20
Usable hosts4,094
Subnet mask255.255.240.0
Addresses4,096
Network address
201.2.96.0
Broadcast address
201.2.111.255
First usable
201.2.96.1
Last usable
201.2.111.254
Usable hosts
4,094 (4,096 less the network and broadcast addresses)
Subnet mask
255.255.240.0
Wildcard mask
0.0.15.255 (Cisco ACLs, OSPF)
Prefix length
/20
Type
Public public
Old class
C (default /24)
As numbers
Hex C9026000 · Integer 3372376064 to 3372380159
Reverse DNS zones
96.2.201.in-addr.arpa
97.2.201.in-addr.arpa
98.2.201.in-addr.arpa
99.2.201.in-addr.arpa
100.2.201.in-addr.arpa
101.2.201.in-addr.arpa
102.2.201.in-addr.arpa
103.2.201.in-addr.arpa
104.2.201.in-addr.arpa
105.2.201.in-addr.arpa
106.2.201.in-addr.arpa
107.2.201.in-addr.arpa
108.2.201.in-addr.arpa
109.2.201.in-addr.arpa
110.2.201.in-addr.arpa
111.2.201.in-addr.arpa
/20 is not on a 8-bit boundary, so it takes 16 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11001001.00000010.01100000.00000000201.2.96.0
Subnet mask11111111.11111111.11110000.00000000255.255.240.0
Network11001001.00000010.01100000.00000000201.2.96.0
Broadcast11001001.00000010.01101111.11111111201.2.111.255
Split into smaller subnets/27
/21 (2)/22 (4)/23 (8)/24 (16)/25 (32)/26 (64)/27 (128)/28 (256)/29 (512)/30 (1,024)/31 (2,048)/32 (4,096)

201.2.96.0/20 makes 128 subnets of /27.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1201.2.96.0/27201.2.96.1 to 201.2.96.30201.2.96.3130
2201.2.96.32/27201.2.96.33 to 201.2.96.62201.2.96.6330
3201.2.96.64/27201.2.96.65 to 201.2.96.94201.2.96.9530
4201.2.96.96/27201.2.96.97 to 201.2.96.126201.2.96.12730
5201.2.96.128/27201.2.96.129 to 201.2.96.158201.2.96.15930
6201.2.96.160/27201.2.96.161 to 201.2.96.190201.2.96.19130
7201.2.96.192/27201.2.96.193 to 201.2.96.222201.2.96.22330
8201.2.96.224/27201.2.96.225 to 201.2.96.254201.2.96.25530
9201.2.97.0/27201.2.97.1 to 201.2.97.30201.2.97.3130
10201.2.97.32/27201.2.97.33 to 201.2.97.62201.2.97.6330
11201.2.97.64/27201.2.97.65 to 201.2.97.94201.2.97.9530
12201.2.97.96/27201.2.97.97 to 201.2.97.126201.2.97.12730
13201.2.97.128/27201.2.97.129 to 201.2.97.158201.2.97.15930
14201.2.97.160/27201.2.97.161 to 201.2.97.190201.2.97.19130
15201.2.97.192/27201.2.97.193 to 201.2.97.222201.2.97.22330
16201.2.97.224/27201.2.97.225 to 201.2.97.254201.2.97.25530
17201.2.98.0/27201.2.98.1 to 201.2.98.30201.2.98.3130
18201.2.98.32/27201.2.98.33 to 201.2.98.62201.2.98.6330
19201.2.98.64/27201.2.98.65 to 201.2.98.94201.2.98.9530
20201.2.98.96/27201.2.98.97 to 201.2.98.126201.2.98.12730
21201.2.98.128/27201.2.98.129 to 201.2.98.158201.2.98.15930
22201.2.98.160/27201.2.98.161 to 201.2.98.190201.2.98.19130
23201.2.98.192/27201.2.98.193 to 201.2.98.222201.2.98.22330
24201.2.98.224/27201.2.98.225 to 201.2.98.254201.2.98.25530
25201.2.99.0/27201.2.99.1 to 201.2.99.30201.2.99.3130
26201.2.99.32/27201.2.99.33 to 201.2.99.62201.2.99.6330
27201.2.99.64/27201.2.99.65 to 201.2.99.94201.2.99.9530
28201.2.99.96/27201.2.99.97 to 201.2.99.126201.2.99.12730
29201.2.99.128/27201.2.99.129 to 201.2.99.158201.2.99.15930
30201.2.99.160/27201.2.99.161 to 201.2.99.190201.2.99.19130
31201.2.99.192/27201.2.99.193 to 201.2.99.222201.2.99.22330
32201.2.99.224/27201.2.99.225 to 201.2.99.254201.2.99.25530
33201.2.100.0/27201.2.100.1 to 201.2.100.30201.2.100.3130
34201.2.100.32/27201.2.100.33 to 201.2.100.62201.2.100.6330
35201.2.100.64/27201.2.100.65 to 201.2.100.94201.2.100.9530
36201.2.100.96/27201.2.100.97 to 201.2.100.126201.2.100.12730
37201.2.100.128/27201.2.100.129 to 201.2.100.158201.2.100.15930
38201.2.100.160/27201.2.100.161 to 201.2.100.190201.2.100.19130
39201.2.100.192/27201.2.100.193 to 201.2.100.222201.2.100.22330
40201.2.100.224/27201.2.100.225 to 201.2.100.254201.2.100.25530
41201.2.101.0/27201.2.101.1 to 201.2.101.30201.2.101.3130
42201.2.101.32/27201.2.101.33 to 201.2.101.62201.2.101.6330
43201.2.101.64/27201.2.101.65 to 201.2.101.94201.2.101.9530
44201.2.101.96/27201.2.101.97 to 201.2.101.126201.2.101.12730
45201.2.101.128/27201.2.101.129 to 201.2.101.158201.2.101.15930
46201.2.101.160/27201.2.101.161 to 201.2.101.190201.2.101.19130
47201.2.101.192/27201.2.101.193 to 201.2.101.222201.2.101.22330
48201.2.101.224/27201.2.101.225 to 201.2.101.254201.2.101.25530
49201.2.102.0/27201.2.102.1 to 201.2.102.30201.2.102.3130
50201.2.102.32/27201.2.102.33 to 201.2.102.62201.2.102.6330
51201.2.102.64/27201.2.102.65 to 201.2.102.94201.2.102.9530
52201.2.102.96/27201.2.102.97 to 201.2.102.126201.2.102.12730
53201.2.102.128/27201.2.102.129 to 201.2.102.158201.2.102.15930
54201.2.102.160/27201.2.102.161 to 201.2.102.190201.2.102.19130
55201.2.102.192/27201.2.102.193 to 201.2.102.222201.2.102.22330
56201.2.102.224/27201.2.102.225 to 201.2.102.254201.2.102.25530
57201.2.103.0/27201.2.103.1 to 201.2.103.30201.2.103.3130
58201.2.103.32/27201.2.103.33 to 201.2.103.62201.2.103.6330
59201.2.103.64/27201.2.103.65 to 201.2.103.94201.2.103.9530
60201.2.103.96/27201.2.103.97 to 201.2.103.126201.2.103.12730
61201.2.103.128/27201.2.103.129 to 201.2.103.158201.2.103.15930
62201.2.103.160/27201.2.103.161 to 201.2.103.190201.2.103.19130
63201.2.103.192/27201.2.103.193 to 201.2.103.222201.2.103.22330
64201.2.103.224/27201.2.103.225 to 201.2.103.254201.2.103.25530
65201.2.104.0/27201.2.104.1 to 201.2.104.30201.2.104.3130
66201.2.104.32/27201.2.104.33 to 201.2.104.62201.2.104.6330
67201.2.104.64/27201.2.104.65 to 201.2.104.94201.2.104.9530
68201.2.104.96/27201.2.104.97 to 201.2.104.126201.2.104.12730
69201.2.104.128/27201.2.104.129 to 201.2.104.158201.2.104.15930
70201.2.104.160/27201.2.104.161 to 201.2.104.190201.2.104.19130
71201.2.104.192/27201.2.104.193 to 201.2.104.222201.2.104.22330
72201.2.104.224/27201.2.104.225 to 201.2.104.254201.2.104.25530
73201.2.105.0/27201.2.105.1 to 201.2.105.30201.2.105.3130
74201.2.105.32/27201.2.105.33 to 201.2.105.62201.2.105.6330
75201.2.105.64/27201.2.105.65 to 201.2.105.94201.2.105.9530
76201.2.105.96/27201.2.105.97 to 201.2.105.126201.2.105.12730
77201.2.105.128/27201.2.105.129 to 201.2.105.158201.2.105.15930
78201.2.105.160/27201.2.105.161 to 201.2.105.190201.2.105.19130
79201.2.105.192/27201.2.105.193 to 201.2.105.222201.2.105.22330
80201.2.105.224/27201.2.105.225 to 201.2.105.254201.2.105.25530
81201.2.106.0/27201.2.106.1 to 201.2.106.30201.2.106.3130
82201.2.106.32/27201.2.106.33 to 201.2.106.62201.2.106.6330
83201.2.106.64/27201.2.106.65 to 201.2.106.94201.2.106.9530
84201.2.106.96/27201.2.106.97 to 201.2.106.126201.2.106.12730
85201.2.106.128/27201.2.106.129 to 201.2.106.158201.2.106.15930
86201.2.106.160/27201.2.106.161 to 201.2.106.190201.2.106.19130
87201.2.106.192/27201.2.106.193 to 201.2.106.222201.2.106.22330
88201.2.106.224/27201.2.106.225 to 201.2.106.254201.2.106.25530
89201.2.107.0/27201.2.107.1 to 201.2.107.30201.2.107.3130
90201.2.107.32/27201.2.107.33 to 201.2.107.62201.2.107.6330
91201.2.107.64/27201.2.107.65 to 201.2.107.94201.2.107.9530
92201.2.107.96/27201.2.107.97 to 201.2.107.126201.2.107.12730
93201.2.107.128/27201.2.107.129 to 201.2.107.158201.2.107.15930
94201.2.107.160/27201.2.107.161 to 201.2.107.190201.2.107.19130
95201.2.107.192/27201.2.107.193 to 201.2.107.222201.2.107.22330
96201.2.107.224/27201.2.107.225 to 201.2.107.254201.2.107.25530
97201.2.108.0/27201.2.108.1 to 201.2.108.30201.2.108.3130
98201.2.108.32/27201.2.108.33 to 201.2.108.62201.2.108.6330
99201.2.108.64/27201.2.108.65 to 201.2.108.94201.2.108.9530
100201.2.108.96/27201.2.108.97 to 201.2.108.126201.2.108.12730
101201.2.108.128/27201.2.108.129 to 201.2.108.158201.2.108.15930
102201.2.108.160/27201.2.108.161 to 201.2.108.190201.2.108.19130
103201.2.108.192/27201.2.108.193 to 201.2.108.222201.2.108.22330
104201.2.108.224/27201.2.108.225 to 201.2.108.254201.2.108.25530
105201.2.109.0/27201.2.109.1 to 201.2.109.30201.2.109.3130
106201.2.109.32/27201.2.109.33 to 201.2.109.62201.2.109.6330
107201.2.109.64/27201.2.109.65 to 201.2.109.94201.2.109.9530
108201.2.109.96/27201.2.109.97 to 201.2.109.126201.2.109.12730
109201.2.109.128/27201.2.109.129 to 201.2.109.158201.2.109.15930
110201.2.109.160/27201.2.109.161 to 201.2.109.190201.2.109.19130
111201.2.109.192/27201.2.109.193 to 201.2.109.222201.2.109.22330
112201.2.109.224/27201.2.109.225 to 201.2.109.254201.2.109.25530
113201.2.110.0/27201.2.110.1 to 201.2.110.30201.2.110.3130
114201.2.110.32/27201.2.110.33 to 201.2.110.62201.2.110.6330
115201.2.110.64/27201.2.110.65 to 201.2.110.94201.2.110.9530
116201.2.110.96/27201.2.110.97 to 201.2.110.126201.2.110.12730
117201.2.110.128/27201.2.110.129 to 201.2.110.158201.2.110.15930
118201.2.110.160/27201.2.110.161 to 201.2.110.190201.2.110.19130
119201.2.110.192/27201.2.110.193 to 201.2.110.222201.2.110.22330
120201.2.110.224/27201.2.110.225 to 201.2.110.254201.2.110.25530
121201.2.111.0/27201.2.111.1 to 201.2.111.30201.2.111.3130
122201.2.111.32/27201.2.111.33 to 201.2.111.62201.2.111.6330
123201.2.111.64/27201.2.111.65 to 201.2.111.94201.2.111.9530
124201.2.111.96/27201.2.111.97 to 201.2.111.126201.2.111.12730
125201.2.111.128/27201.2.111.129 to 201.2.111.158201.2.111.15930
126201.2.111.160/27201.2.111.161 to 201.2.111.190201.2.111.19130
127201.2.111.192/27201.2.111.193 to 201.2.111.222201.2.111.22330
128201.2.111.224/27201.2.111.225 to 201.2.111.254201.2.111.25530

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.