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.

Network190.136.0.0/15
Usable hosts131,070
Subnet mask255.254.0.0
Addresses131,072
Network address
190.136.0.0
Broadcast address
190.137.255.255
First usable
190.136.0.1
Last usable
190.137.255.254
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
Public public
Old class
B (default /16)
As numbers
Hex BE880000 · Integer 3196583936 to 3196715007
Reverse DNS zones
136.190.in-addr.arpa
137.190.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
Address10111110.10001000.00000000.00000000190.136.0.0
Subnet mask11111111.11111110.00000000.00000000255.254.0.0
Network10111110.10001000.00000000.00000000190.136.0.0
Broadcast10111110.10001001.11111111.11111111190.137.255.255
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)

190.136.0.0/15 makes 128 subnets of /22.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1190.136.0.0/22190.136.0.1 to 190.136.3.254190.136.3.2551,022
2190.136.4.0/22190.136.4.1 to 190.136.7.254190.136.7.2551,022
3190.136.8.0/22190.136.8.1 to 190.136.11.254190.136.11.2551,022
4190.136.12.0/22190.136.12.1 to 190.136.15.254190.136.15.2551,022
5190.136.16.0/22190.136.16.1 to 190.136.19.254190.136.19.2551,022
6190.136.20.0/22190.136.20.1 to 190.136.23.254190.136.23.2551,022
7190.136.24.0/22190.136.24.1 to 190.136.27.254190.136.27.2551,022
8190.136.28.0/22190.136.28.1 to 190.136.31.254190.136.31.2551,022
9190.136.32.0/22190.136.32.1 to 190.136.35.254190.136.35.2551,022
10190.136.36.0/22190.136.36.1 to 190.136.39.254190.136.39.2551,022
11190.136.40.0/22190.136.40.1 to 190.136.43.254190.136.43.2551,022
12190.136.44.0/22190.136.44.1 to 190.136.47.254190.136.47.2551,022
13190.136.48.0/22190.136.48.1 to 190.136.51.254190.136.51.2551,022
14190.136.52.0/22190.136.52.1 to 190.136.55.254190.136.55.2551,022
15190.136.56.0/22190.136.56.1 to 190.136.59.254190.136.59.2551,022
16190.136.60.0/22190.136.60.1 to 190.136.63.254190.136.63.2551,022
17190.136.64.0/22190.136.64.1 to 190.136.67.254190.136.67.2551,022
18190.136.68.0/22190.136.68.1 to 190.136.71.254190.136.71.2551,022
19190.136.72.0/22190.136.72.1 to 190.136.75.254190.136.75.2551,022
20190.136.76.0/22190.136.76.1 to 190.136.79.254190.136.79.2551,022
21190.136.80.0/22190.136.80.1 to 190.136.83.254190.136.83.2551,022
22190.136.84.0/22190.136.84.1 to 190.136.87.254190.136.87.2551,022
23190.136.88.0/22190.136.88.1 to 190.136.91.254190.136.91.2551,022
24190.136.92.0/22190.136.92.1 to 190.136.95.254190.136.95.2551,022
25190.136.96.0/22190.136.96.1 to 190.136.99.254190.136.99.2551,022
26190.136.100.0/22190.136.100.1 to 190.136.103.254190.136.103.2551,022
27190.136.104.0/22190.136.104.1 to 190.136.107.254190.136.107.2551,022
28190.136.108.0/22190.136.108.1 to 190.136.111.254190.136.111.2551,022
29190.136.112.0/22190.136.112.1 to 190.136.115.254190.136.115.2551,022
30190.136.116.0/22190.136.116.1 to 190.136.119.254190.136.119.2551,022
31190.136.120.0/22190.136.120.1 to 190.136.123.254190.136.123.2551,022
32190.136.124.0/22190.136.124.1 to 190.136.127.254190.136.127.2551,022
33190.136.128.0/22190.136.128.1 to 190.136.131.254190.136.131.2551,022
34190.136.132.0/22190.136.132.1 to 190.136.135.254190.136.135.2551,022
35190.136.136.0/22190.136.136.1 to 190.136.139.254190.136.139.2551,022
36190.136.140.0/22190.136.140.1 to 190.136.143.254190.136.143.2551,022
37190.136.144.0/22190.136.144.1 to 190.136.147.254190.136.147.2551,022
38190.136.148.0/22190.136.148.1 to 190.136.151.254190.136.151.2551,022
39190.136.152.0/22190.136.152.1 to 190.136.155.254190.136.155.2551,022
40190.136.156.0/22190.136.156.1 to 190.136.159.254190.136.159.2551,022
41190.136.160.0/22190.136.160.1 to 190.136.163.254190.136.163.2551,022
42190.136.164.0/22190.136.164.1 to 190.136.167.254190.136.167.2551,022
43190.136.168.0/22190.136.168.1 to 190.136.171.254190.136.171.2551,022
44190.136.172.0/22190.136.172.1 to 190.136.175.254190.136.175.2551,022
45190.136.176.0/22190.136.176.1 to 190.136.179.254190.136.179.2551,022
46190.136.180.0/22190.136.180.1 to 190.136.183.254190.136.183.2551,022
47190.136.184.0/22190.136.184.1 to 190.136.187.254190.136.187.2551,022
48190.136.188.0/22190.136.188.1 to 190.136.191.254190.136.191.2551,022
49190.136.192.0/22190.136.192.1 to 190.136.195.254190.136.195.2551,022
50190.136.196.0/22190.136.196.1 to 190.136.199.254190.136.199.2551,022
51190.136.200.0/22190.136.200.1 to 190.136.203.254190.136.203.2551,022
52190.136.204.0/22190.136.204.1 to 190.136.207.254190.136.207.2551,022
53190.136.208.0/22190.136.208.1 to 190.136.211.254190.136.211.2551,022
54190.136.212.0/22190.136.212.1 to 190.136.215.254190.136.215.2551,022
55190.136.216.0/22190.136.216.1 to 190.136.219.254190.136.219.2551,022
56190.136.220.0/22190.136.220.1 to 190.136.223.254190.136.223.2551,022
57190.136.224.0/22190.136.224.1 to 190.136.227.254190.136.227.2551,022
58190.136.228.0/22190.136.228.1 to 190.136.231.254190.136.231.2551,022
59190.136.232.0/22190.136.232.1 to 190.136.235.254190.136.235.2551,022
60190.136.236.0/22190.136.236.1 to 190.136.239.254190.136.239.2551,022
61190.136.240.0/22190.136.240.1 to 190.136.243.254190.136.243.2551,022
62190.136.244.0/22190.136.244.1 to 190.136.247.254190.136.247.2551,022
63190.136.248.0/22190.136.248.1 to 190.136.251.254190.136.251.2551,022
64190.136.252.0/22190.136.252.1 to 190.136.255.254190.136.255.2551,022
65190.137.0.0/22190.137.0.1 to 190.137.3.254190.137.3.2551,022
66190.137.4.0/22190.137.4.1 to 190.137.7.254190.137.7.2551,022
67190.137.8.0/22190.137.8.1 to 190.137.11.254190.137.11.2551,022
68190.137.12.0/22190.137.12.1 to 190.137.15.254190.137.15.2551,022
69190.137.16.0/22190.137.16.1 to 190.137.19.254190.137.19.2551,022
70190.137.20.0/22190.137.20.1 to 190.137.23.254190.137.23.2551,022
71190.137.24.0/22190.137.24.1 to 190.137.27.254190.137.27.2551,022
72190.137.28.0/22190.137.28.1 to 190.137.31.254190.137.31.2551,022
73190.137.32.0/22190.137.32.1 to 190.137.35.254190.137.35.2551,022
74190.137.36.0/22190.137.36.1 to 190.137.39.254190.137.39.2551,022
75190.137.40.0/22190.137.40.1 to 190.137.43.254190.137.43.2551,022
76190.137.44.0/22190.137.44.1 to 190.137.47.254190.137.47.2551,022
77190.137.48.0/22190.137.48.1 to 190.137.51.254190.137.51.2551,022
78190.137.52.0/22190.137.52.1 to 190.137.55.254190.137.55.2551,022
79190.137.56.0/22190.137.56.1 to 190.137.59.254190.137.59.2551,022
80190.137.60.0/22190.137.60.1 to 190.137.63.254190.137.63.2551,022
81190.137.64.0/22190.137.64.1 to 190.137.67.254190.137.67.2551,022
82190.137.68.0/22190.137.68.1 to 190.137.71.254190.137.71.2551,022
83190.137.72.0/22190.137.72.1 to 190.137.75.254190.137.75.2551,022
84190.137.76.0/22190.137.76.1 to 190.137.79.254190.137.79.2551,022
85190.137.80.0/22190.137.80.1 to 190.137.83.254190.137.83.2551,022
86190.137.84.0/22190.137.84.1 to 190.137.87.254190.137.87.2551,022
87190.137.88.0/22190.137.88.1 to 190.137.91.254190.137.91.2551,022
88190.137.92.0/22190.137.92.1 to 190.137.95.254190.137.95.2551,022
89190.137.96.0/22190.137.96.1 to 190.137.99.254190.137.99.2551,022
90190.137.100.0/22190.137.100.1 to 190.137.103.254190.137.103.2551,022
91190.137.104.0/22190.137.104.1 to 190.137.107.254190.137.107.2551,022
92190.137.108.0/22190.137.108.1 to 190.137.111.254190.137.111.2551,022
93190.137.112.0/22190.137.112.1 to 190.137.115.254190.137.115.2551,022
94190.137.116.0/22190.137.116.1 to 190.137.119.254190.137.119.2551,022
95190.137.120.0/22190.137.120.1 to 190.137.123.254190.137.123.2551,022
96190.137.124.0/22190.137.124.1 to 190.137.127.254190.137.127.2551,022
97190.137.128.0/22190.137.128.1 to 190.137.131.254190.137.131.2551,022
98190.137.132.0/22190.137.132.1 to 190.137.135.254190.137.135.2551,022
99190.137.136.0/22190.137.136.1 to 190.137.139.254190.137.139.2551,022
100190.137.140.0/22190.137.140.1 to 190.137.143.254190.137.143.2551,022
101190.137.144.0/22190.137.144.1 to 190.137.147.254190.137.147.2551,022
102190.137.148.0/22190.137.148.1 to 190.137.151.254190.137.151.2551,022
103190.137.152.0/22190.137.152.1 to 190.137.155.254190.137.155.2551,022
104190.137.156.0/22190.137.156.1 to 190.137.159.254190.137.159.2551,022
105190.137.160.0/22190.137.160.1 to 190.137.163.254190.137.163.2551,022
106190.137.164.0/22190.137.164.1 to 190.137.167.254190.137.167.2551,022
107190.137.168.0/22190.137.168.1 to 190.137.171.254190.137.171.2551,022
108190.137.172.0/22190.137.172.1 to 190.137.175.254190.137.175.2551,022
109190.137.176.0/22190.137.176.1 to 190.137.179.254190.137.179.2551,022
110190.137.180.0/22190.137.180.1 to 190.137.183.254190.137.183.2551,022
111190.137.184.0/22190.137.184.1 to 190.137.187.254190.137.187.2551,022
112190.137.188.0/22190.137.188.1 to 190.137.191.254190.137.191.2551,022
113190.137.192.0/22190.137.192.1 to 190.137.195.254190.137.195.2551,022
114190.137.196.0/22190.137.196.1 to 190.137.199.254190.137.199.2551,022
115190.137.200.0/22190.137.200.1 to 190.137.203.254190.137.203.2551,022
116190.137.204.0/22190.137.204.1 to 190.137.207.254190.137.207.2551,022
117190.137.208.0/22190.137.208.1 to 190.137.211.254190.137.211.2551,022
118190.137.212.0/22190.137.212.1 to 190.137.215.254190.137.215.2551,022
119190.137.216.0/22190.137.216.1 to 190.137.219.254190.137.219.2551,022
120190.137.220.0/22190.137.220.1 to 190.137.223.254190.137.223.2551,022
121190.137.224.0/22190.137.224.1 to 190.137.227.254190.137.227.2551,022
122190.137.228.0/22190.137.228.1 to 190.137.231.254190.137.231.2551,022
123190.137.232.0/22190.137.232.1 to 190.137.235.254190.137.235.2551,022
124190.137.236.0/22190.137.236.1 to 190.137.239.254190.137.239.2551,022
125190.137.240.0/22190.137.240.1 to 190.137.243.254190.137.243.2551,022
126190.137.244.0/22190.137.244.1 to 190.137.247.254190.137.247.2551,022
127190.137.248.0/22190.137.248.1 to 190.137.251.254190.137.251.2551,022
128190.137.252.0/22190.137.252.1 to 190.137.255.254190.137.255.2551,022

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.