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.

Network143.3.128.0/19
Usable hosts8,190
Subnet mask255.255.224.0
Addresses8,192
Network address
143.3.128.0
Broadcast address
143.3.159.255
First usable
143.3.128.1
Last usable
143.3.159.254
Usable hosts
8,190 (8,192 less the network and broadcast addresses)
Subnet mask
255.255.224.0
Wildcard mask
0.0.31.255 (Cisco ACLs, OSPF)
Prefix length
/19
Type
Public public
Old class
B (default /16)
As numbers
Hex 8F038000 · Integer 2399371264 to 2399379455
Reverse DNS zones
128.3.143.in-addr.arpa
129.3.143.in-addr.arpa
130.3.143.in-addr.arpa
131.3.143.in-addr.arpa
132.3.143.in-addr.arpa
133.3.143.in-addr.arpa
134.3.143.in-addr.arpa
135.3.143.in-addr.arpa
136.3.143.in-addr.arpa
137.3.143.in-addr.arpa
138.3.143.in-addr.arpa
139.3.143.in-addr.arpa
140.3.143.in-addr.arpa
141.3.143.in-addr.arpa
142.3.143.in-addr.arpa
143.3.143.in-addr.arpa
and 16 more
/19 is not on a 8-bit boundary, so it takes 32 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address10001111.00000011.10000000.00000000143.3.128.0
Subnet mask11111111.11111111.11100000.00000000255.255.224.0
Network10001111.00000011.10000000.00000000143.3.128.0
Broadcast10001111.00000011.10011111.11111111143.3.159.255
Split into smaller subnets/26
/20 (2)/21 (4)/22 (8)/23 (16)/24 (32)/25 (64)/26 (128)/27 (256)/28 (512)/29 (1,024)/30 (2,048)/31 (4,096)

143.3.128.0/19 makes 128 subnets of /26.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1143.3.128.0/26143.3.128.1 to 143.3.128.62143.3.128.6362
2143.3.128.64/26143.3.128.65 to 143.3.128.126143.3.128.12762
3143.3.128.128/26143.3.128.129 to 143.3.128.190143.3.128.19162
4143.3.128.192/26143.3.128.193 to 143.3.128.254143.3.128.25562
5143.3.129.0/26143.3.129.1 to 143.3.129.62143.3.129.6362
6143.3.129.64/26143.3.129.65 to 143.3.129.126143.3.129.12762
7143.3.129.128/26143.3.129.129 to 143.3.129.190143.3.129.19162
8143.3.129.192/26143.3.129.193 to 143.3.129.254143.3.129.25562
9143.3.130.0/26143.3.130.1 to 143.3.130.62143.3.130.6362
10143.3.130.64/26143.3.130.65 to 143.3.130.126143.3.130.12762
11143.3.130.128/26143.3.130.129 to 143.3.130.190143.3.130.19162
12143.3.130.192/26143.3.130.193 to 143.3.130.254143.3.130.25562
13143.3.131.0/26143.3.131.1 to 143.3.131.62143.3.131.6362
14143.3.131.64/26143.3.131.65 to 143.3.131.126143.3.131.12762
15143.3.131.128/26143.3.131.129 to 143.3.131.190143.3.131.19162
16143.3.131.192/26143.3.131.193 to 143.3.131.254143.3.131.25562
17143.3.132.0/26143.3.132.1 to 143.3.132.62143.3.132.6362
18143.3.132.64/26143.3.132.65 to 143.3.132.126143.3.132.12762
19143.3.132.128/26143.3.132.129 to 143.3.132.190143.3.132.19162
20143.3.132.192/26143.3.132.193 to 143.3.132.254143.3.132.25562
21143.3.133.0/26143.3.133.1 to 143.3.133.62143.3.133.6362
22143.3.133.64/26143.3.133.65 to 143.3.133.126143.3.133.12762
23143.3.133.128/26143.3.133.129 to 143.3.133.190143.3.133.19162
24143.3.133.192/26143.3.133.193 to 143.3.133.254143.3.133.25562
25143.3.134.0/26143.3.134.1 to 143.3.134.62143.3.134.6362
26143.3.134.64/26143.3.134.65 to 143.3.134.126143.3.134.12762
27143.3.134.128/26143.3.134.129 to 143.3.134.190143.3.134.19162
28143.3.134.192/26143.3.134.193 to 143.3.134.254143.3.134.25562
29143.3.135.0/26143.3.135.1 to 143.3.135.62143.3.135.6362
30143.3.135.64/26143.3.135.65 to 143.3.135.126143.3.135.12762
31143.3.135.128/26143.3.135.129 to 143.3.135.190143.3.135.19162
32143.3.135.192/26143.3.135.193 to 143.3.135.254143.3.135.25562
33143.3.136.0/26143.3.136.1 to 143.3.136.62143.3.136.6362
34143.3.136.64/26143.3.136.65 to 143.3.136.126143.3.136.12762
35143.3.136.128/26143.3.136.129 to 143.3.136.190143.3.136.19162
36143.3.136.192/26143.3.136.193 to 143.3.136.254143.3.136.25562
37143.3.137.0/26143.3.137.1 to 143.3.137.62143.3.137.6362
38143.3.137.64/26143.3.137.65 to 143.3.137.126143.3.137.12762
39143.3.137.128/26143.3.137.129 to 143.3.137.190143.3.137.19162
40143.3.137.192/26143.3.137.193 to 143.3.137.254143.3.137.25562
41143.3.138.0/26143.3.138.1 to 143.3.138.62143.3.138.6362
42143.3.138.64/26143.3.138.65 to 143.3.138.126143.3.138.12762
43143.3.138.128/26143.3.138.129 to 143.3.138.190143.3.138.19162
44143.3.138.192/26143.3.138.193 to 143.3.138.254143.3.138.25562
45143.3.139.0/26143.3.139.1 to 143.3.139.62143.3.139.6362
46143.3.139.64/26143.3.139.65 to 143.3.139.126143.3.139.12762
47143.3.139.128/26143.3.139.129 to 143.3.139.190143.3.139.19162
48143.3.139.192/26143.3.139.193 to 143.3.139.254143.3.139.25562
49143.3.140.0/26143.3.140.1 to 143.3.140.62143.3.140.6362
50143.3.140.64/26143.3.140.65 to 143.3.140.126143.3.140.12762
51143.3.140.128/26143.3.140.129 to 143.3.140.190143.3.140.19162
52143.3.140.192/26143.3.140.193 to 143.3.140.254143.3.140.25562
53143.3.141.0/26143.3.141.1 to 143.3.141.62143.3.141.6362
54143.3.141.64/26143.3.141.65 to 143.3.141.126143.3.141.12762
55143.3.141.128/26143.3.141.129 to 143.3.141.190143.3.141.19162
56143.3.141.192/26143.3.141.193 to 143.3.141.254143.3.141.25562
57143.3.142.0/26143.3.142.1 to 143.3.142.62143.3.142.6362
58143.3.142.64/26143.3.142.65 to 143.3.142.126143.3.142.12762
59143.3.142.128/26143.3.142.129 to 143.3.142.190143.3.142.19162
60143.3.142.192/26143.3.142.193 to 143.3.142.254143.3.142.25562
61143.3.143.0/26143.3.143.1 to 143.3.143.62143.3.143.6362
62143.3.143.64/26143.3.143.65 to 143.3.143.126143.3.143.12762
63143.3.143.128/26143.3.143.129 to 143.3.143.190143.3.143.19162
64143.3.143.192/26143.3.143.193 to 143.3.143.254143.3.143.25562
65143.3.144.0/26143.3.144.1 to 143.3.144.62143.3.144.6362
66143.3.144.64/26143.3.144.65 to 143.3.144.126143.3.144.12762
67143.3.144.128/26143.3.144.129 to 143.3.144.190143.3.144.19162
68143.3.144.192/26143.3.144.193 to 143.3.144.254143.3.144.25562
69143.3.145.0/26143.3.145.1 to 143.3.145.62143.3.145.6362
70143.3.145.64/26143.3.145.65 to 143.3.145.126143.3.145.12762
71143.3.145.128/26143.3.145.129 to 143.3.145.190143.3.145.19162
72143.3.145.192/26143.3.145.193 to 143.3.145.254143.3.145.25562
73143.3.146.0/26143.3.146.1 to 143.3.146.62143.3.146.6362
74143.3.146.64/26143.3.146.65 to 143.3.146.126143.3.146.12762
75143.3.146.128/26143.3.146.129 to 143.3.146.190143.3.146.19162
76143.3.146.192/26143.3.146.193 to 143.3.146.254143.3.146.25562
77143.3.147.0/26143.3.147.1 to 143.3.147.62143.3.147.6362
78143.3.147.64/26143.3.147.65 to 143.3.147.126143.3.147.12762
79143.3.147.128/26143.3.147.129 to 143.3.147.190143.3.147.19162
80143.3.147.192/26143.3.147.193 to 143.3.147.254143.3.147.25562
81143.3.148.0/26143.3.148.1 to 143.3.148.62143.3.148.6362
82143.3.148.64/26143.3.148.65 to 143.3.148.126143.3.148.12762
83143.3.148.128/26143.3.148.129 to 143.3.148.190143.3.148.19162
84143.3.148.192/26143.3.148.193 to 143.3.148.254143.3.148.25562
85143.3.149.0/26143.3.149.1 to 143.3.149.62143.3.149.6362
86143.3.149.64/26143.3.149.65 to 143.3.149.126143.3.149.12762
87143.3.149.128/26143.3.149.129 to 143.3.149.190143.3.149.19162
88143.3.149.192/26143.3.149.193 to 143.3.149.254143.3.149.25562
89143.3.150.0/26143.3.150.1 to 143.3.150.62143.3.150.6362
90143.3.150.64/26143.3.150.65 to 143.3.150.126143.3.150.12762
91143.3.150.128/26143.3.150.129 to 143.3.150.190143.3.150.19162
92143.3.150.192/26143.3.150.193 to 143.3.150.254143.3.150.25562
93143.3.151.0/26143.3.151.1 to 143.3.151.62143.3.151.6362
94143.3.151.64/26143.3.151.65 to 143.3.151.126143.3.151.12762
95143.3.151.128/26143.3.151.129 to 143.3.151.190143.3.151.19162
96143.3.151.192/26143.3.151.193 to 143.3.151.254143.3.151.25562
97143.3.152.0/26143.3.152.1 to 143.3.152.62143.3.152.6362
98143.3.152.64/26143.3.152.65 to 143.3.152.126143.3.152.12762
99143.3.152.128/26143.3.152.129 to 143.3.152.190143.3.152.19162
100143.3.152.192/26143.3.152.193 to 143.3.152.254143.3.152.25562
101143.3.153.0/26143.3.153.1 to 143.3.153.62143.3.153.6362
102143.3.153.64/26143.3.153.65 to 143.3.153.126143.3.153.12762
103143.3.153.128/26143.3.153.129 to 143.3.153.190143.3.153.19162
104143.3.153.192/26143.3.153.193 to 143.3.153.254143.3.153.25562
105143.3.154.0/26143.3.154.1 to 143.3.154.62143.3.154.6362
106143.3.154.64/26143.3.154.65 to 143.3.154.126143.3.154.12762
107143.3.154.128/26143.3.154.129 to 143.3.154.190143.3.154.19162
108143.3.154.192/26143.3.154.193 to 143.3.154.254143.3.154.25562
109143.3.155.0/26143.3.155.1 to 143.3.155.62143.3.155.6362
110143.3.155.64/26143.3.155.65 to 143.3.155.126143.3.155.12762
111143.3.155.128/26143.3.155.129 to 143.3.155.190143.3.155.19162
112143.3.155.192/26143.3.155.193 to 143.3.155.254143.3.155.25562
113143.3.156.0/26143.3.156.1 to 143.3.156.62143.3.156.6362
114143.3.156.64/26143.3.156.65 to 143.3.156.126143.3.156.12762
115143.3.156.128/26143.3.156.129 to 143.3.156.190143.3.156.19162
116143.3.156.192/26143.3.156.193 to 143.3.156.254143.3.156.25562
117143.3.157.0/26143.3.157.1 to 143.3.157.62143.3.157.6362
118143.3.157.64/26143.3.157.65 to 143.3.157.126143.3.157.12762
119143.3.157.128/26143.3.157.129 to 143.3.157.190143.3.157.19162
120143.3.157.192/26143.3.157.193 to 143.3.157.254143.3.157.25562
121143.3.158.0/26143.3.158.1 to 143.3.158.62143.3.158.6362
122143.3.158.64/26143.3.158.65 to 143.3.158.126143.3.158.12762
123143.3.158.128/26143.3.158.129 to 143.3.158.190143.3.158.19162
124143.3.158.192/26143.3.158.193 to 143.3.158.254143.3.158.25562
125143.3.159.0/26143.3.159.1 to 143.3.159.62143.3.159.6362
126143.3.159.64/26143.3.159.65 to 143.3.159.126143.3.159.12762
127143.3.159.128/26143.3.159.129 to 143.3.159.190143.3.159.19162
128143.3.159.192/26143.3.159.193 to 143.3.159.254143.3.159.25562

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.