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.

Network246.0.0.0/11
Usable hosts2,097,150
Subnet mask255.224.0.0
Addresses2,097,152
Network address
246.0.0.0
Broadcast address
246.31.255.255
First usable
246.0.0.1
Last usable
246.31.255.254
Usable hosts
2,097,150 (2,097,152 less the network and broadcast addresses)
Subnet mask
255.224.0.0
Wildcard mask
0.31.255.255 (Cisco ACLs, OSPF)
Prefix length
/11
Type
Reserved 240.0.0.0/4
Future use; not usable on most systems
Old class
E (reserved)
As numbers
Hex F6000000 · Integer 4127195136 to 4129292287
Reverse DNS zones
0.246.in-addr.arpa
1.246.in-addr.arpa
2.246.in-addr.arpa
3.246.in-addr.arpa
4.246.in-addr.arpa
5.246.in-addr.arpa
6.246.in-addr.arpa
7.246.in-addr.arpa
8.246.in-addr.arpa
9.246.in-addr.arpa
10.246.in-addr.arpa
11.246.in-addr.arpa
12.246.in-addr.arpa
13.246.in-addr.arpa
14.246.in-addr.arpa
15.246.in-addr.arpa
and 16 more
/11 is not on a 8-bit boundary, so it takes 32 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address11110110.00000000.00000000.00000000246.0.0.0
Subnet mask11111111.11100000.00000000.00000000255.224.0.0
Network11110110.00000000.00000000.00000000246.0.0.0
Broadcast11110110.00011111.11111111.11111111246.31.255.255
Split into smaller subnets/18
/12 (2)/13 (4)/14 (8)/15 (16)/16 (32)/17 (64)/18 (128)/19 (256)/20 (512)/21 (1,024)/22 (2,048)/23 (4,096)

246.0.0.0/11 makes 128 subnets of /18.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1246.0.0.0/18246.0.0.1 to 246.0.63.254246.0.63.25516,382
2246.0.64.0/18246.0.64.1 to 246.0.127.254246.0.127.25516,382
3246.0.128.0/18246.0.128.1 to 246.0.191.254246.0.191.25516,382
4246.0.192.0/18246.0.192.1 to 246.0.255.254246.0.255.25516,382
5246.1.0.0/18246.1.0.1 to 246.1.63.254246.1.63.25516,382
6246.1.64.0/18246.1.64.1 to 246.1.127.254246.1.127.25516,382
7246.1.128.0/18246.1.128.1 to 246.1.191.254246.1.191.25516,382
8246.1.192.0/18246.1.192.1 to 246.1.255.254246.1.255.25516,382
9246.2.0.0/18246.2.0.1 to 246.2.63.254246.2.63.25516,382
10246.2.64.0/18246.2.64.1 to 246.2.127.254246.2.127.25516,382
11246.2.128.0/18246.2.128.1 to 246.2.191.254246.2.191.25516,382
12246.2.192.0/18246.2.192.1 to 246.2.255.254246.2.255.25516,382
13246.3.0.0/18246.3.0.1 to 246.3.63.254246.3.63.25516,382
14246.3.64.0/18246.3.64.1 to 246.3.127.254246.3.127.25516,382
15246.3.128.0/18246.3.128.1 to 246.3.191.254246.3.191.25516,382
16246.3.192.0/18246.3.192.1 to 246.3.255.254246.3.255.25516,382
17246.4.0.0/18246.4.0.1 to 246.4.63.254246.4.63.25516,382
18246.4.64.0/18246.4.64.1 to 246.4.127.254246.4.127.25516,382
19246.4.128.0/18246.4.128.1 to 246.4.191.254246.4.191.25516,382
20246.4.192.0/18246.4.192.1 to 246.4.255.254246.4.255.25516,382
21246.5.0.0/18246.5.0.1 to 246.5.63.254246.5.63.25516,382
22246.5.64.0/18246.5.64.1 to 246.5.127.254246.5.127.25516,382
23246.5.128.0/18246.5.128.1 to 246.5.191.254246.5.191.25516,382
24246.5.192.0/18246.5.192.1 to 246.5.255.254246.5.255.25516,382
25246.6.0.0/18246.6.0.1 to 246.6.63.254246.6.63.25516,382
26246.6.64.0/18246.6.64.1 to 246.6.127.254246.6.127.25516,382
27246.6.128.0/18246.6.128.1 to 246.6.191.254246.6.191.25516,382
28246.6.192.0/18246.6.192.1 to 246.6.255.254246.6.255.25516,382
29246.7.0.0/18246.7.0.1 to 246.7.63.254246.7.63.25516,382
30246.7.64.0/18246.7.64.1 to 246.7.127.254246.7.127.25516,382
31246.7.128.0/18246.7.128.1 to 246.7.191.254246.7.191.25516,382
32246.7.192.0/18246.7.192.1 to 246.7.255.254246.7.255.25516,382
33246.8.0.0/18246.8.0.1 to 246.8.63.254246.8.63.25516,382
34246.8.64.0/18246.8.64.1 to 246.8.127.254246.8.127.25516,382
35246.8.128.0/18246.8.128.1 to 246.8.191.254246.8.191.25516,382
36246.8.192.0/18246.8.192.1 to 246.8.255.254246.8.255.25516,382
37246.9.0.0/18246.9.0.1 to 246.9.63.254246.9.63.25516,382
38246.9.64.0/18246.9.64.1 to 246.9.127.254246.9.127.25516,382
39246.9.128.0/18246.9.128.1 to 246.9.191.254246.9.191.25516,382
40246.9.192.0/18246.9.192.1 to 246.9.255.254246.9.255.25516,382
41246.10.0.0/18246.10.0.1 to 246.10.63.254246.10.63.25516,382
42246.10.64.0/18246.10.64.1 to 246.10.127.254246.10.127.25516,382
43246.10.128.0/18246.10.128.1 to 246.10.191.254246.10.191.25516,382
44246.10.192.0/18246.10.192.1 to 246.10.255.254246.10.255.25516,382
45246.11.0.0/18246.11.0.1 to 246.11.63.254246.11.63.25516,382
46246.11.64.0/18246.11.64.1 to 246.11.127.254246.11.127.25516,382
47246.11.128.0/18246.11.128.1 to 246.11.191.254246.11.191.25516,382
48246.11.192.0/18246.11.192.1 to 246.11.255.254246.11.255.25516,382
49246.12.0.0/18246.12.0.1 to 246.12.63.254246.12.63.25516,382
50246.12.64.0/18246.12.64.1 to 246.12.127.254246.12.127.25516,382
51246.12.128.0/18246.12.128.1 to 246.12.191.254246.12.191.25516,382
52246.12.192.0/18246.12.192.1 to 246.12.255.254246.12.255.25516,382
53246.13.0.0/18246.13.0.1 to 246.13.63.254246.13.63.25516,382
54246.13.64.0/18246.13.64.1 to 246.13.127.254246.13.127.25516,382
55246.13.128.0/18246.13.128.1 to 246.13.191.254246.13.191.25516,382
56246.13.192.0/18246.13.192.1 to 246.13.255.254246.13.255.25516,382
57246.14.0.0/18246.14.0.1 to 246.14.63.254246.14.63.25516,382
58246.14.64.0/18246.14.64.1 to 246.14.127.254246.14.127.25516,382
59246.14.128.0/18246.14.128.1 to 246.14.191.254246.14.191.25516,382
60246.14.192.0/18246.14.192.1 to 246.14.255.254246.14.255.25516,382
61246.15.0.0/18246.15.0.1 to 246.15.63.254246.15.63.25516,382
62246.15.64.0/18246.15.64.1 to 246.15.127.254246.15.127.25516,382
63246.15.128.0/18246.15.128.1 to 246.15.191.254246.15.191.25516,382
64246.15.192.0/18246.15.192.1 to 246.15.255.254246.15.255.25516,382
65246.16.0.0/18246.16.0.1 to 246.16.63.254246.16.63.25516,382
66246.16.64.0/18246.16.64.1 to 246.16.127.254246.16.127.25516,382
67246.16.128.0/18246.16.128.1 to 246.16.191.254246.16.191.25516,382
68246.16.192.0/18246.16.192.1 to 246.16.255.254246.16.255.25516,382
69246.17.0.0/18246.17.0.1 to 246.17.63.254246.17.63.25516,382
70246.17.64.0/18246.17.64.1 to 246.17.127.254246.17.127.25516,382
71246.17.128.0/18246.17.128.1 to 246.17.191.254246.17.191.25516,382
72246.17.192.0/18246.17.192.1 to 246.17.255.254246.17.255.25516,382
73246.18.0.0/18246.18.0.1 to 246.18.63.254246.18.63.25516,382
74246.18.64.0/18246.18.64.1 to 246.18.127.254246.18.127.25516,382
75246.18.128.0/18246.18.128.1 to 246.18.191.254246.18.191.25516,382
76246.18.192.0/18246.18.192.1 to 246.18.255.254246.18.255.25516,382
77246.19.0.0/18246.19.0.1 to 246.19.63.254246.19.63.25516,382
78246.19.64.0/18246.19.64.1 to 246.19.127.254246.19.127.25516,382
79246.19.128.0/18246.19.128.1 to 246.19.191.254246.19.191.25516,382
80246.19.192.0/18246.19.192.1 to 246.19.255.254246.19.255.25516,382
81246.20.0.0/18246.20.0.1 to 246.20.63.254246.20.63.25516,382
82246.20.64.0/18246.20.64.1 to 246.20.127.254246.20.127.25516,382
83246.20.128.0/18246.20.128.1 to 246.20.191.254246.20.191.25516,382
84246.20.192.0/18246.20.192.1 to 246.20.255.254246.20.255.25516,382
85246.21.0.0/18246.21.0.1 to 246.21.63.254246.21.63.25516,382
86246.21.64.0/18246.21.64.1 to 246.21.127.254246.21.127.25516,382
87246.21.128.0/18246.21.128.1 to 246.21.191.254246.21.191.25516,382
88246.21.192.0/18246.21.192.1 to 246.21.255.254246.21.255.25516,382
89246.22.0.0/18246.22.0.1 to 246.22.63.254246.22.63.25516,382
90246.22.64.0/18246.22.64.1 to 246.22.127.254246.22.127.25516,382
91246.22.128.0/18246.22.128.1 to 246.22.191.254246.22.191.25516,382
92246.22.192.0/18246.22.192.1 to 246.22.255.254246.22.255.25516,382
93246.23.0.0/18246.23.0.1 to 246.23.63.254246.23.63.25516,382
94246.23.64.0/18246.23.64.1 to 246.23.127.254246.23.127.25516,382
95246.23.128.0/18246.23.128.1 to 246.23.191.254246.23.191.25516,382
96246.23.192.0/18246.23.192.1 to 246.23.255.254246.23.255.25516,382
97246.24.0.0/18246.24.0.1 to 246.24.63.254246.24.63.25516,382
98246.24.64.0/18246.24.64.1 to 246.24.127.254246.24.127.25516,382
99246.24.128.0/18246.24.128.1 to 246.24.191.254246.24.191.25516,382
100246.24.192.0/18246.24.192.1 to 246.24.255.254246.24.255.25516,382
101246.25.0.0/18246.25.0.1 to 246.25.63.254246.25.63.25516,382
102246.25.64.0/18246.25.64.1 to 246.25.127.254246.25.127.25516,382
103246.25.128.0/18246.25.128.1 to 246.25.191.254246.25.191.25516,382
104246.25.192.0/18246.25.192.1 to 246.25.255.254246.25.255.25516,382
105246.26.0.0/18246.26.0.1 to 246.26.63.254246.26.63.25516,382
106246.26.64.0/18246.26.64.1 to 246.26.127.254246.26.127.25516,382
107246.26.128.0/18246.26.128.1 to 246.26.191.254246.26.191.25516,382
108246.26.192.0/18246.26.192.1 to 246.26.255.254246.26.255.25516,382
109246.27.0.0/18246.27.0.1 to 246.27.63.254246.27.63.25516,382
110246.27.64.0/18246.27.64.1 to 246.27.127.254246.27.127.25516,382
111246.27.128.0/18246.27.128.1 to 246.27.191.254246.27.191.25516,382
112246.27.192.0/18246.27.192.1 to 246.27.255.254246.27.255.25516,382
113246.28.0.0/18246.28.0.1 to 246.28.63.254246.28.63.25516,382
114246.28.64.0/18246.28.64.1 to 246.28.127.254246.28.127.25516,382
115246.28.128.0/18246.28.128.1 to 246.28.191.254246.28.191.25516,382
116246.28.192.0/18246.28.192.1 to 246.28.255.254246.28.255.25516,382
117246.29.0.0/18246.29.0.1 to 246.29.63.254246.29.63.25516,382
118246.29.64.0/18246.29.64.1 to 246.29.127.254246.29.127.25516,382
119246.29.128.0/18246.29.128.1 to 246.29.191.254246.29.191.25516,382
120246.29.192.0/18246.29.192.1 to 246.29.255.254246.29.255.25516,382
121246.30.0.0/18246.30.0.1 to 246.30.63.254246.30.63.25516,382
122246.30.64.0/18246.30.64.1 to 246.30.127.254246.30.127.25516,382
123246.30.128.0/18246.30.128.1 to 246.30.191.254246.30.191.25516,382
124246.30.192.0/18246.30.192.1 to 246.30.255.254246.30.255.25516,382
125246.31.0.0/18246.31.0.1 to 246.31.63.254246.31.63.25516,382
126246.31.64.0/18246.31.64.1 to 246.31.127.254246.31.127.25516,382
127246.31.128.0/18246.31.128.1 to 246.31.191.254246.31.191.25516,382
128246.31.192.0/18246.31.192.1 to 246.31.255.254246.31.255.25516,382

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.