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.

Network204.0.0.0/7
Usable hosts33,554,430
Subnet mask254.0.0.0
Addresses33,554,432
Network address
204.0.0.0
Broadcast address
205.255.255.255
First usable
204.0.0.1
Last usable
205.255.255.254
Usable hosts
33,554,430 (33,554,432 less the network and broadcast addresses)
Subnet mask
254.0.0.0
Wildcard mask
1.255.255.255 (Cisco ACLs, OSPF)
Prefix length
/7
Type
Public public
Old class
C (default /24)
As numbers
Hex CC000000 · Integer 3422552064 to 3456106495
Reverse DNS zones
204.in-addr.arpa
205.in-addr.arpa
/7 is not on a 8-bit boundary, so it takes 2 /8 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11001100.00000000.00000000.00000000204.0.0.0
Subnet mask11111110.00000000.00000000.00000000254.0.0.0
Network11001100.00000000.00000000.00000000204.0.0.0
Broadcast11001101.11111111.11111111.11111111205.255.255.255
Split into smaller subnets/14
/8 (2)/9 (4)/10 (8)/11 (16)/12 (32)/13 (64)/14 (128)/15 (256)/16 (512)/17 (1,024)/18 (2,048)/19 (4,096)

204.0.0.0/7 makes 128 subnets of /14.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1204.0.0.0/14204.0.0.1 to 204.3.255.254204.3.255.255262,142
2204.4.0.0/14204.4.0.1 to 204.7.255.254204.7.255.255262,142
3204.8.0.0/14204.8.0.1 to 204.11.255.254204.11.255.255262,142
4204.12.0.0/14204.12.0.1 to 204.15.255.254204.15.255.255262,142
5204.16.0.0/14204.16.0.1 to 204.19.255.254204.19.255.255262,142
6204.20.0.0/14204.20.0.1 to 204.23.255.254204.23.255.255262,142
7204.24.0.0/14204.24.0.1 to 204.27.255.254204.27.255.255262,142
8204.28.0.0/14204.28.0.1 to 204.31.255.254204.31.255.255262,142
9204.32.0.0/14204.32.0.1 to 204.35.255.254204.35.255.255262,142
10204.36.0.0/14204.36.0.1 to 204.39.255.254204.39.255.255262,142
11204.40.0.0/14204.40.0.1 to 204.43.255.254204.43.255.255262,142
12204.44.0.0/14204.44.0.1 to 204.47.255.254204.47.255.255262,142
13204.48.0.0/14204.48.0.1 to 204.51.255.254204.51.255.255262,142
14204.52.0.0/14204.52.0.1 to 204.55.255.254204.55.255.255262,142
15204.56.0.0/14204.56.0.1 to 204.59.255.254204.59.255.255262,142
16204.60.0.0/14204.60.0.1 to 204.63.255.254204.63.255.255262,142
17204.64.0.0/14204.64.0.1 to 204.67.255.254204.67.255.255262,142
18204.68.0.0/14204.68.0.1 to 204.71.255.254204.71.255.255262,142
19204.72.0.0/14204.72.0.1 to 204.75.255.254204.75.255.255262,142
20204.76.0.0/14204.76.0.1 to 204.79.255.254204.79.255.255262,142
21204.80.0.0/14204.80.0.1 to 204.83.255.254204.83.255.255262,142
22204.84.0.0/14204.84.0.1 to 204.87.255.254204.87.255.255262,142
23204.88.0.0/14204.88.0.1 to 204.91.255.254204.91.255.255262,142
24204.92.0.0/14204.92.0.1 to 204.95.255.254204.95.255.255262,142
25204.96.0.0/14204.96.0.1 to 204.99.255.254204.99.255.255262,142
26204.100.0.0/14204.100.0.1 to 204.103.255.254204.103.255.255262,142
27204.104.0.0/14204.104.0.1 to 204.107.255.254204.107.255.255262,142
28204.108.0.0/14204.108.0.1 to 204.111.255.254204.111.255.255262,142
29204.112.0.0/14204.112.0.1 to 204.115.255.254204.115.255.255262,142
30204.116.0.0/14204.116.0.1 to 204.119.255.254204.119.255.255262,142
31204.120.0.0/14204.120.0.1 to 204.123.255.254204.123.255.255262,142
32204.124.0.0/14204.124.0.1 to 204.127.255.254204.127.255.255262,142
33204.128.0.0/14204.128.0.1 to 204.131.255.254204.131.255.255262,142
34204.132.0.0/14204.132.0.1 to 204.135.255.254204.135.255.255262,142
35204.136.0.0/14204.136.0.1 to 204.139.255.254204.139.255.255262,142
36204.140.0.0/14204.140.0.1 to 204.143.255.254204.143.255.255262,142
37204.144.0.0/14204.144.0.1 to 204.147.255.254204.147.255.255262,142
38204.148.0.0/14204.148.0.1 to 204.151.255.254204.151.255.255262,142
39204.152.0.0/14204.152.0.1 to 204.155.255.254204.155.255.255262,142
40204.156.0.0/14204.156.0.1 to 204.159.255.254204.159.255.255262,142
41204.160.0.0/14204.160.0.1 to 204.163.255.254204.163.255.255262,142
42204.164.0.0/14204.164.0.1 to 204.167.255.254204.167.255.255262,142
43204.168.0.0/14204.168.0.1 to 204.171.255.254204.171.255.255262,142
44204.172.0.0/14204.172.0.1 to 204.175.255.254204.175.255.255262,142
45204.176.0.0/14204.176.0.1 to 204.179.255.254204.179.255.255262,142
46204.180.0.0/14204.180.0.1 to 204.183.255.254204.183.255.255262,142
47204.184.0.0/14204.184.0.1 to 204.187.255.254204.187.255.255262,142
48204.188.0.0/14204.188.0.1 to 204.191.255.254204.191.255.255262,142
49204.192.0.0/14204.192.0.1 to 204.195.255.254204.195.255.255262,142
50204.196.0.0/14204.196.0.1 to 204.199.255.254204.199.255.255262,142
51204.200.0.0/14204.200.0.1 to 204.203.255.254204.203.255.255262,142
52204.204.0.0/14204.204.0.1 to 204.207.255.254204.207.255.255262,142
53204.208.0.0/14204.208.0.1 to 204.211.255.254204.211.255.255262,142
54204.212.0.0/14204.212.0.1 to 204.215.255.254204.215.255.255262,142
55204.216.0.0/14204.216.0.1 to 204.219.255.254204.219.255.255262,142
56204.220.0.0/14204.220.0.1 to 204.223.255.254204.223.255.255262,142
57204.224.0.0/14204.224.0.1 to 204.227.255.254204.227.255.255262,142
58204.228.0.0/14204.228.0.1 to 204.231.255.254204.231.255.255262,142
59204.232.0.0/14204.232.0.1 to 204.235.255.254204.235.255.255262,142
60204.236.0.0/14204.236.0.1 to 204.239.255.254204.239.255.255262,142
61204.240.0.0/14204.240.0.1 to 204.243.255.254204.243.255.255262,142
62204.244.0.0/14204.244.0.1 to 204.247.255.254204.247.255.255262,142
63204.248.0.0/14204.248.0.1 to 204.251.255.254204.251.255.255262,142
64204.252.0.0/14204.252.0.1 to 204.255.255.254204.255.255.255262,142
65205.0.0.0/14205.0.0.1 to 205.3.255.254205.3.255.255262,142
66205.4.0.0/14205.4.0.1 to 205.7.255.254205.7.255.255262,142
67205.8.0.0/14205.8.0.1 to 205.11.255.254205.11.255.255262,142
68205.12.0.0/14205.12.0.1 to 205.15.255.254205.15.255.255262,142
69205.16.0.0/14205.16.0.1 to 205.19.255.254205.19.255.255262,142
70205.20.0.0/14205.20.0.1 to 205.23.255.254205.23.255.255262,142
71205.24.0.0/14205.24.0.1 to 205.27.255.254205.27.255.255262,142
72205.28.0.0/14205.28.0.1 to 205.31.255.254205.31.255.255262,142
73205.32.0.0/14205.32.0.1 to 205.35.255.254205.35.255.255262,142
74205.36.0.0/14205.36.0.1 to 205.39.255.254205.39.255.255262,142
75205.40.0.0/14205.40.0.1 to 205.43.255.254205.43.255.255262,142
76205.44.0.0/14205.44.0.1 to 205.47.255.254205.47.255.255262,142
77205.48.0.0/14205.48.0.1 to 205.51.255.254205.51.255.255262,142
78205.52.0.0/14205.52.0.1 to 205.55.255.254205.55.255.255262,142
79205.56.0.0/14205.56.0.1 to 205.59.255.254205.59.255.255262,142
80205.60.0.0/14205.60.0.1 to 205.63.255.254205.63.255.255262,142
81205.64.0.0/14205.64.0.1 to 205.67.255.254205.67.255.255262,142
82205.68.0.0/14205.68.0.1 to 205.71.255.254205.71.255.255262,142
83205.72.0.0/14205.72.0.1 to 205.75.255.254205.75.255.255262,142
84205.76.0.0/14205.76.0.1 to 205.79.255.254205.79.255.255262,142
85205.80.0.0/14205.80.0.1 to 205.83.255.254205.83.255.255262,142
86205.84.0.0/14205.84.0.1 to 205.87.255.254205.87.255.255262,142
87205.88.0.0/14205.88.0.1 to 205.91.255.254205.91.255.255262,142
88205.92.0.0/14205.92.0.1 to 205.95.255.254205.95.255.255262,142
89205.96.0.0/14205.96.0.1 to 205.99.255.254205.99.255.255262,142
90205.100.0.0/14205.100.0.1 to 205.103.255.254205.103.255.255262,142
91205.104.0.0/14205.104.0.1 to 205.107.255.254205.107.255.255262,142
92205.108.0.0/14205.108.0.1 to 205.111.255.254205.111.255.255262,142
93205.112.0.0/14205.112.0.1 to 205.115.255.254205.115.255.255262,142
94205.116.0.0/14205.116.0.1 to 205.119.255.254205.119.255.255262,142
95205.120.0.0/14205.120.0.1 to 205.123.255.254205.123.255.255262,142
96205.124.0.0/14205.124.0.1 to 205.127.255.254205.127.255.255262,142
97205.128.0.0/14205.128.0.1 to 205.131.255.254205.131.255.255262,142
98205.132.0.0/14205.132.0.1 to 205.135.255.254205.135.255.255262,142
99205.136.0.0/14205.136.0.1 to 205.139.255.254205.139.255.255262,142
100205.140.0.0/14205.140.0.1 to 205.143.255.254205.143.255.255262,142
101205.144.0.0/14205.144.0.1 to 205.147.255.254205.147.255.255262,142
102205.148.0.0/14205.148.0.1 to 205.151.255.254205.151.255.255262,142
103205.152.0.0/14205.152.0.1 to 205.155.255.254205.155.255.255262,142
104205.156.0.0/14205.156.0.1 to 205.159.255.254205.159.255.255262,142
105205.160.0.0/14205.160.0.1 to 205.163.255.254205.163.255.255262,142
106205.164.0.0/14205.164.0.1 to 205.167.255.254205.167.255.255262,142
107205.168.0.0/14205.168.0.1 to 205.171.255.254205.171.255.255262,142
108205.172.0.0/14205.172.0.1 to 205.175.255.254205.175.255.255262,142
109205.176.0.0/14205.176.0.1 to 205.179.255.254205.179.255.255262,142
110205.180.0.0/14205.180.0.1 to 205.183.255.254205.183.255.255262,142
111205.184.0.0/14205.184.0.1 to 205.187.255.254205.187.255.255262,142
112205.188.0.0/14205.188.0.1 to 205.191.255.254205.191.255.255262,142
113205.192.0.0/14205.192.0.1 to 205.195.255.254205.195.255.255262,142
114205.196.0.0/14205.196.0.1 to 205.199.255.254205.199.255.255262,142
115205.200.0.0/14205.200.0.1 to 205.203.255.254205.203.255.255262,142
116205.204.0.0/14205.204.0.1 to 205.207.255.254205.207.255.255262,142
117205.208.0.0/14205.208.0.1 to 205.211.255.254205.211.255.255262,142
118205.212.0.0/14205.212.0.1 to 205.215.255.254205.215.255.255262,142
119205.216.0.0/14205.216.0.1 to 205.219.255.254205.219.255.255262,142
120205.220.0.0/14205.220.0.1 to 205.223.255.254205.223.255.255262,142
121205.224.0.0/14205.224.0.1 to 205.227.255.254205.227.255.255262,142
122205.228.0.0/14205.228.0.1 to 205.231.255.254205.231.255.255262,142
123205.232.0.0/14205.232.0.1 to 205.235.255.254205.235.255.255262,142
124205.236.0.0/14205.236.0.1 to 205.239.255.254205.239.255.255262,142
125205.240.0.0/14205.240.0.1 to 205.243.255.254205.243.255.255262,142
126205.244.0.0/14205.244.0.1 to 205.247.255.254205.247.255.255262,142
127205.248.0.0/14205.248.0.1 to 205.251.255.254205.251.255.255262,142
128205.252.0.0/14205.252.0.1 to 205.255.255.254205.255.255.255262,142

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.