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.

Network161.2.0.0/18
Usable hosts16,382
Subnet mask255.255.192.0
Addresses16,384
Network address
161.2.0.0
Broadcast address
161.2.63.255
First usable
161.2.0.1
Last usable
161.2.63.254
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 A1020000 · Integer 2701262848 to 2701279231
Reverse DNS zones
0.2.161.in-addr.arpa
1.2.161.in-addr.arpa
2.2.161.in-addr.arpa
3.2.161.in-addr.arpa
4.2.161.in-addr.arpa
5.2.161.in-addr.arpa
6.2.161.in-addr.arpa
7.2.161.in-addr.arpa
8.2.161.in-addr.arpa
9.2.161.in-addr.arpa
10.2.161.in-addr.arpa
11.2.161.in-addr.arpa
12.2.161.in-addr.arpa
13.2.161.in-addr.arpa
14.2.161.in-addr.arpa
15.2.161.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
Address10100001.00000010.00000000.00000000161.2.0.0
Subnet mask11111111.11111111.11000000.00000000255.255.192.0
Network10100001.00000010.00000000.00000000161.2.0.0
Broadcast10100001.00000010.00111111.11111111161.2.63.255
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)

161.2.0.0/18 makes 128 subnets of /25.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1161.2.0.0/25161.2.0.1 to 161.2.0.126161.2.0.127126
2161.2.0.128/25161.2.0.129 to 161.2.0.254161.2.0.255126
3161.2.1.0/25161.2.1.1 to 161.2.1.126161.2.1.127126
4161.2.1.128/25161.2.1.129 to 161.2.1.254161.2.1.255126
5161.2.2.0/25161.2.2.1 to 161.2.2.126161.2.2.127126
6161.2.2.128/25161.2.2.129 to 161.2.2.254161.2.2.255126
7161.2.3.0/25161.2.3.1 to 161.2.3.126161.2.3.127126
8161.2.3.128/25161.2.3.129 to 161.2.3.254161.2.3.255126
9161.2.4.0/25161.2.4.1 to 161.2.4.126161.2.4.127126
10161.2.4.128/25161.2.4.129 to 161.2.4.254161.2.4.255126
11161.2.5.0/25161.2.5.1 to 161.2.5.126161.2.5.127126
12161.2.5.128/25161.2.5.129 to 161.2.5.254161.2.5.255126
13161.2.6.0/25161.2.6.1 to 161.2.6.126161.2.6.127126
14161.2.6.128/25161.2.6.129 to 161.2.6.254161.2.6.255126
15161.2.7.0/25161.2.7.1 to 161.2.7.126161.2.7.127126
16161.2.7.128/25161.2.7.129 to 161.2.7.254161.2.7.255126
17161.2.8.0/25161.2.8.1 to 161.2.8.126161.2.8.127126
18161.2.8.128/25161.2.8.129 to 161.2.8.254161.2.8.255126
19161.2.9.0/25161.2.9.1 to 161.2.9.126161.2.9.127126
20161.2.9.128/25161.2.9.129 to 161.2.9.254161.2.9.255126
21161.2.10.0/25161.2.10.1 to 161.2.10.126161.2.10.127126
22161.2.10.128/25161.2.10.129 to 161.2.10.254161.2.10.255126
23161.2.11.0/25161.2.11.1 to 161.2.11.126161.2.11.127126
24161.2.11.128/25161.2.11.129 to 161.2.11.254161.2.11.255126
25161.2.12.0/25161.2.12.1 to 161.2.12.126161.2.12.127126
26161.2.12.128/25161.2.12.129 to 161.2.12.254161.2.12.255126
27161.2.13.0/25161.2.13.1 to 161.2.13.126161.2.13.127126
28161.2.13.128/25161.2.13.129 to 161.2.13.254161.2.13.255126
29161.2.14.0/25161.2.14.1 to 161.2.14.126161.2.14.127126
30161.2.14.128/25161.2.14.129 to 161.2.14.254161.2.14.255126
31161.2.15.0/25161.2.15.1 to 161.2.15.126161.2.15.127126
32161.2.15.128/25161.2.15.129 to 161.2.15.254161.2.15.255126
33161.2.16.0/25161.2.16.1 to 161.2.16.126161.2.16.127126
34161.2.16.128/25161.2.16.129 to 161.2.16.254161.2.16.255126
35161.2.17.0/25161.2.17.1 to 161.2.17.126161.2.17.127126
36161.2.17.128/25161.2.17.129 to 161.2.17.254161.2.17.255126
37161.2.18.0/25161.2.18.1 to 161.2.18.126161.2.18.127126
38161.2.18.128/25161.2.18.129 to 161.2.18.254161.2.18.255126
39161.2.19.0/25161.2.19.1 to 161.2.19.126161.2.19.127126
40161.2.19.128/25161.2.19.129 to 161.2.19.254161.2.19.255126
41161.2.20.0/25161.2.20.1 to 161.2.20.126161.2.20.127126
42161.2.20.128/25161.2.20.129 to 161.2.20.254161.2.20.255126
43161.2.21.0/25161.2.21.1 to 161.2.21.126161.2.21.127126
44161.2.21.128/25161.2.21.129 to 161.2.21.254161.2.21.255126
45161.2.22.0/25161.2.22.1 to 161.2.22.126161.2.22.127126
46161.2.22.128/25161.2.22.129 to 161.2.22.254161.2.22.255126
47161.2.23.0/25161.2.23.1 to 161.2.23.126161.2.23.127126
48161.2.23.128/25161.2.23.129 to 161.2.23.254161.2.23.255126
49161.2.24.0/25161.2.24.1 to 161.2.24.126161.2.24.127126
50161.2.24.128/25161.2.24.129 to 161.2.24.254161.2.24.255126
51161.2.25.0/25161.2.25.1 to 161.2.25.126161.2.25.127126
52161.2.25.128/25161.2.25.129 to 161.2.25.254161.2.25.255126
53161.2.26.0/25161.2.26.1 to 161.2.26.126161.2.26.127126
54161.2.26.128/25161.2.26.129 to 161.2.26.254161.2.26.255126
55161.2.27.0/25161.2.27.1 to 161.2.27.126161.2.27.127126
56161.2.27.128/25161.2.27.129 to 161.2.27.254161.2.27.255126
57161.2.28.0/25161.2.28.1 to 161.2.28.126161.2.28.127126
58161.2.28.128/25161.2.28.129 to 161.2.28.254161.2.28.255126
59161.2.29.0/25161.2.29.1 to 161.2.29.126161.2.29.127126
60161.2.29.128/25161.2.29.129 to 161.2.29.254161.2.29.255126
61161.2.30.0/25161.2.30.1 to 161.2.30.126161.2.30.127126
62161.2.30.128/25161.2.30.129 to 161.2.30.254161.2.30.255126
63161.2.31.0/25161.2.31.1 to 161.2.31.126161.2.31.127126
64161.2.31.128/25161.2.31.129 to 161.2.31.254161.2.31.255126
65161.2.32.0/25161.2.32.1 to 161.2.32.126161.2.32.127126
66161.2.32.128/25161.2.32.129 to 161.2.32.254161.2.32.255126
67161.2.33.0/25161.2.33.1 to 161.2.33.126161.2.33.127126
68161.2.33.128/25161.2.33.129 to 161.2.33.254161.2.33.255126
69161.2.34.0/25161.2.34.1 to 161.2.34.126161.2.34.127126
70161.2.34.128/25161.2.34.129 to 161.2.34.254161.2.34.255126
71161.2.35.0/25161.2.35.1 to 161.2.35.126161.2.35.127126
72161.2.35.128/25161.2.35.129 to 161.2.35.254161.2.35.255126
73161.2.36.0/25161.2.36.1 to 161.2.36.126161.2.36.127126
74161.2.36.128/25161.2.36.129 to 161.2.36.254161.2.36.255126
75161.2.37.0/25161.2.37.1 to 161.2.37.126161.2.37.127126
76161.2.37.128/25161.2.37.129 to 161.2.37.254161.2.37.255126
77161.2.38.0/25161.2.38.1 to 161.2.38.126161.2.38.127126
78161.2.38.128/25161.2.38.129 to 161.2.38.254161.2.38.255126
79161.2.39.0/25161.2.39.1 to 161.2.39.126161.2.39.127126
80161.2.39.128/25161.2.39.129 to 161.2.39.254161.2.39.255126
81161.2.40.0/25161.2.40.1 to 161.2.40.126161.2.40.127126
82161.2.40.128/25161.2.40.129 to 161.2.40.254161.2.40.255126
83161.2.41.0/25161.2.41.1 to 161.2.41.126161.2.41.127126
84161.2.41.128/25161.2.41.129 to 161.2.41.254161.2.41.255126
85161.2.42.0/25161.2.42.1 to 161.2.42.126161.2.42.127126
86161.2.42.128/25161.2.42.129 to 161.2.42.254161.2.42.255126
87161.2.43.0/25161.2.43.1 to 161.2.43.126161.2.43.127126
88161.2.43.128/25161.2.43.129 to 161.2.43.254161.2.43.255126
89161.2.44.0/25161.2.44.1 to 161.2.44.126161.2.44.127126
90161.2.44.128/25161.2.44.129 to 161.2.44.254161.2.44.255126
91161.2.45.0/25161.2.45.1 to 161.2.45.126161.2.45.127126
92161.2.45.128/25161.2.45.129 to 161.2.45.254161.2.45.255126
93161.2.46.0/25161.2.46.1 to 161.2.46.126161.2.46.127126
94161.2.46.128/25161.2.46.129 to 161.2.46.254161.2.46.255126
95161.2.47.0/25161.2.47.1 to 161.2.47.126161.2.47.127126
96161.2.47.128/25161.2.47.129 to 161.2.47.254161.2.47.255126
97161.2.48.0/25161.2.48.1 to 161.2.48.126161.2.48.127126
98161.2.48.128/25161.2.48.129 to 161.2.48.254161.2.48.255126
99161.2.49.0/25161.2.49.1 to 161.2.49.126161.2.49.127126
100161.2.49.128/25161.2.49.129 to 161.2.49.254161.2.49.255126
101161.2.50.0/25161.2.50.1 to 161.2.50.126161.2.50.127126
102161.2.50.128/25161.2.50.129 to 161.2.50.254161.2.50.255126
103161.2.51.0/25161.2.51.1 to 161.2.51.126161.2.51.127126
104161.2.51.128/25161.2.51.129 to 161.2.51.254161.2.51.255126
105161.2.52.0/25161.2.52.1 to 161.2.52.126161.2.52.127126
106161.2.52.128/25161.2.52.129 to 161.2.52.254161.2.52.255126
107161.2.53.0/25161.2.53.1 to 161.2.53.126161.2.53.127126
108161.2.53.128/25161.2.53.129 to 161.2.53.254161.2.53.255126
109161.2.54.0/25161.2.54.1 to 161.2.54.126161.2.54.127126
110161.2.54.128/25161.2.54.129 to 161.2.54.254161.2.54.255126
111161.2.55.0/25161.2.55.1 to 161.2.55.126161.2.55.127126
112161.2.55.128/25161.2.55.129 to 161.2.55.254161.2.55.255126
113161.2.56.0/25161.2.56.1 to 161.2.56.126161.2.56.127126
114161.2.56.128/25161.2.56.129 to 161.2.56.254161.2.56.255126
115161.2.57.0/25161.2.57.1 to 161.2.57.126161.2.57.127126
116161.2.57.128/25161.2.57.129 to 161.2.57.254161.2.57.255126
117161.2.58.0/25161.2.58.1 to 161.2.58.126161.2.58.127126
118161.2.58.128/25161.2.58.129 to 161.2.58.254161.2.58.255126
119161.2.59.0/25161.2.59.1 to 161.2.59.126161.2.59.127126
120161.2.59.128/25161.2.59.129 to 161.2.59.254161.2.59.255126
121161.2.60.0/25161.2.60.1 to 161.2.60.126161.2.60.127126
122161.2.60.128/25161.2.60.129 to 161.2.60.254161.2.60.255126
123161.2.61.0/25161.2.61.1 to 161.2.61.126161.2.61.127126
124161.2.61.128/25161.2.61.129 to 161.2.61.254161.2.61.255126
125161.2.62.0/25161.2.62.1 to 161.2.62.126161.2.62.127126
126161.2.62.128/25161.2.62.129 to 161.2.62.254161.2.62.255126
127161.2.63.0/25161.2.63.1 to 161.2.63.126161.2.63.127126
128161.2.63.128/25161.2.63.129 to 161.2.63.254161.2.63.255126

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.