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.

Network238.3.64.0/19
Usable hosts8,190
Subnet mask255.255.224.0
Addresses8,192
Network address
238.3.64.0
Broadcast address
238.3.95.255
First usable
238.3.64.1
Last usable
238.3.95.254
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
Multicast 224.0.0.0/4
One-to-many traffic, such as IPTV and routing protocols
Old class
D (multicast)
As numbers
Hex EE034000 · Integer 3993190400 to 3993198591
Reverse DNS zones
64.3.238.in-addr.arpa
65.3.238.in-addr.arpa
66.3.238.in-addr.arpa
67.3.238.in-addr.arpa
68.3.238.in-addr.arpa
69.3.238.in-addr.arpa
70.3.238.in-addr.arpa
71.3.238.in-addr.arpa
72.3.238.in-addr.arpa
73.3.238.in-addr.arpa
74.3.238.in-addr.arpa
75.3.238.in-addr.arpa
76.3.238.in-addr.arpa
77.3.238.in-addr.arpa
78.3.238.in-addr.arpa
79.3.238.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
Address11101110.00000011.01000000.00000000238.3.64.0
Subnet mask11111111.11111111.11100000.00000000255.255.224.0
Network11101110.00000011.01000000.00000000238.3.64.0
Broadcast11101110.00000011.01011111.11111111238.3.95.255
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)

238.3.64.0/19 makes 128 subnets of /26.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1238.3.64.0/26238.3.64.1 to 238.3.64.62238.3.64.6362
2238.3.64.64/26238.3.64.65 to 238.3.64.126238.3.64.12762
3238.3.64.128/26238.3.64.129 to 238.3.64.190238.3.64.19162
4238.3.64.192/26238.3.64.193 to 238.3.64.254238.3.64.25562
5238.3.65.0/26238.3.65.1 to 238.3.65.62238.3.65.6362
6238.3.65.64/26238.3.65.65 to 238.3.65.126238.3.65.12762
7238.3.65.128/26238.3.65.129 to 238.3.65.190238.3.65.19162
8238.3.65.192/26238.3.65.193 to 238.3.65.254238.3.65.25562
9238.3.66.0/26238.3.66.1 to 238.3.66.62238.3.66.6362
10238.3.66.64/26238.3.66.65 to 238.3.66.126238.3.66.12762
11238.3.66.128/26238.3.66.129 to 238.3.66.190238.3.66.19162
12238.3.66.192/26238.3.66.193 to 238.3.66.254238.3.66.25562
13238.3.67.0/26238.3.67.1 to 238.3.67.62238.3.67.6362
14238.3.67.64/26238.3.67.65 to 238.3.67.126238.3.67.12762
15238.3.67.128/26238.3.67.129 to 238.3.67.190238.3.67.19162
16238.3.67.192/26238.3.67.193 to 238.3.67.254238.3.67.25562
17238.3.68.0/26238.3.68.1 to 238.3.68.62238.3.68.6362
18238.3.68.64/26238.3.68.65 to 238.3.68.126238.3.68.12762
19238.3.68.128/26238.3.68.129 to 238.3.68.190238.3.68.19162
20238.3.68.192/26238.3.68.193 to 238.3.68.254238.3.68.25562
21238.3.69.0/26238.3.69.1 to 238.3.69.62238.3.69.6362
22238.3.69.64/26238.3.69.65 to 238.3.69.126238.3.69.12762
23238.3.69.128/26238.3.69.129 to 238.3.69.190238.3.69.19162
24238.3.69.192/26238.3.69.193 to 238.3.69.254238.3.69.25562
25238.3.70.0/26238.3.70.1 to 238.3.70.62238.3.70.6362
26238.3.70.64/26238.3.70.65 to 238.3.70.126238.3.70.12762
27238.3.70.128/26238.3.70.129 to 238.3.70.190238.3.70.19162
28238.3.70.192/26238.3.70.193 to 238.3.70.254238.3.70.25562
29238.3.71.0/26238.3.71.1 to 238.3.71.62238.3.71.6362
30238.3.71.64/26238.3.71.65 to 238.3.71.126238.3.71.12762
31238.3.71.128/26238.3.71.129 to 238.3.71.190238.3.71.19162
32238.3.71.192/26238.3.71.193 to 238.3.71.254238.3.71.25562
33238.3.72.0/26238.3.72.1 to 238.3.72.62238.3.72.6362
34238.3.72.64/26238.3.72.65 to 238.3.72.126238.3.72.12762
35238.3.72.128/26238.3.72.129 to 238.3.72.190238.3.72.19162
36238.3.72.192/26238.3.72.193 to 238.3.72.254238.3.72.25562
37238.3.73.0/26238.3.73.1 to 238.3.73.62238.3.73.6362
38238.3.73.64/26238.3.73.65 to 238.3.73.126238.3.73.12762
39238.3.73.128/26238.3.73.129 to 238.3.73.190238.3.73.19162
40238.3.73.192/26238.3.73.193 to 238.3.73.254238.3.73.25562
41238.3.74.0/26238.3.74.1 to 238.3.74.62238.3.74.6362
42238.3.74.64/26238.3.74.65 to 238.3.74.126238.3.74.12762
43238.3.74.128/26238.3.74.129 to 238.3.74.190238.3.74.19162
44238.3.74.192/26238.3.74.193 to 238.3.74.254238.3.74.25562
45238.3.75.0/26238.3.75.1 to 238.3.75.62238.3.75.6362
46238.3.75.64/26238.3.75.65 to 238.3.75.126238.3.75.12762
47238.3.75.128/26238.3.75.129 to 238.3.75.190238.3.75.19162
48238.3.75.192/26238.3.75.193 to 238.3.75.254238.3.75.25562
49238.3.76.0/26238.3.76.1 to 238.3.76.62238.3.76.6362
50238.3.76.64/26238.3.76.65 to 238.3.76.126238.3.76.12762
51238.3.76.128/26238.3.76.129 to 238.3.76.190238.3.76.19162
52238.3.76.192/26238.3.76.193 to 238.3.76.254238.3.76.25562
53238.3.77.0/26238.3.77.1 to 238.3.77.62238.3.77.6362
54238.3.77.64/26238.3.77.65 to 238.3.77.126238.3.77.12762
55238.3.77.128/26238.3.77.129 to 238.3.77.190238.3.77.19162
56238.3.77.192/26238.3.77.193 to 238.3.77.254238.3.77.25562
57238.3.78.0/26238.3.78.1 to 238.3.78.62238.3.78.6362
58238.3.78.64/26238.3.78.65 to 238.3.78.126238.3.78.12762
59238.3.78.128/26238.3.78.129 to 238.3.78.190238.3.78.19162
60238.3.78.192/26238.3.78.193 to 238.3.78.254238.3.78.25562
61238.3.79.0/26238.3.79.1 to 238.3.79.62238.3.79.6362
62238.3.79.64/26238.3.79.65 to 238.3.79.126238.3.79.12762
63238.3.79.128/26238.3.79.129 to 238.3.79.190238.3.79.19162
64238.3.79.192/26238.3.79.193 to 238.3.79.254238.3.79.25562
65238.3.80.0/26238.3.80.1 to 238.3.80.62238.3.80.6362
66238.3.80.64/26238.3.80.65 to 238.3.80.126238.3.80.12762
67238.3.80.128/26238.3.80.129 to 238.3.80.190238.3.80.19162
68238.3.80.192/26238.3.80.193 to 238.3.80.254238.3.80.25562
69238.3.81.0/26238.3.81.1 to 238.3.81.62238.3.81.6362
70238.3.81.64/26238.3.81.65 to 238.3.81.126238.3.81.12762
71238.3.81.128/26238.3.81.129 to 238.3.81.190238.3.81.19162
72238.3.81.192/26238.3.81.193 to 238.3.81.254238.3.81.25562
73238.3.82.0/26238.3.82.1 to 238.3.82.62238.3.82.6362
74238.3.82.64/26238.3.82.65 to 238.3.82.126238.3.82.12762
75238.3.82.128/26238.3.82.129 to 238.3.82.190238.3.82.19162
76238.3.82.192/26238.3.82.193 to 238.3.82.254238.3.82.25562
77238.3.83.0/26238.3.83.1 to 238.3.83.62238.3.83.6362
78238.3.83.64/26238.3.83.65 to 238.3.83.126238.3.83.12762
79238.3.83.128/26238.3.83.129 to 238.3.83.190238.3.83.19162
80238.3.83.192/26238.3.83.193 to 238.3.83.254238.3.83.25562
81238.3.84.0/26238.3.84.1 to 238.3.84.62238.3.84.6362
82238.3.84.64/26238.3.84.65 to 238.3.84.126238.3.84.12762
83238.3.84.128/26238.3.84.129 to 238.3.84.190238.3.84.19162
84238.3.84.192/26238.3.84.193 to 238.3.84.254238.3.84.25562
85238.3.85.0/26238.3.85.1 to 238.3.85.62238.3.85.6362
86238.3.85.64/26238.3.85.65 to 238.3.85.126238.3.85.12762
87238.3.85.128/26238.3.85.129 to 238.3.85.190238.3.85.19162
88238.3.85.192/26238.3.85.193 to 238.3.85.254238.3.85.25562
89238.3.86.0/26238.3.86.1 to 238.3.86.62238.3.86.6362
90238.3.86.64/26238.3.86.65 to 238.3.86.126238.3.86.12762
91238.3.86.128/26238.3.86.129 to 238.3.86.190238.3.86.19162
92238.3.86.192/26238.3.86.193 to 238.3.86.254238.3.86.25562
93238.3.87.0/26238.3.87.1 to 238.3.87.62238.3.87.6362
94238.3.87.64/26238.3.87.65 to 238.3.87.126238.3.87.12762
95238.3.87.128/26238.3.87.129 to 238.3.87.190238.3.87.19162
96238.3.87.192/26238.3.87.193 to 238.3.87.254238.3.87.25562
97238.3.88.0/26238.3.88.1 to 238.3.88.62238.3.88.6362
98238.3.88.64/26238.3.88.65 to 238.3.88.126238.3.88.12762
99238.3.88.128/26238.3.88.129 to 238.3.88.190238.3.88.19162
100238.3.88.192/26238.3.88.193 to 238.3.88.254238.3.88.25562
101238.3.89.0/26238.3.89.1 to 238.3.89.62238.3.89.6362
102238.3.89.64/26238.3.89.65 to 238.3.89.126238.3.89.12762
103238.3.89.128/26238.3.89.129 to 238.3.89.190238.3.89.19162
104238.3.89.192/26238.3.89.193 to 238.3.89.254238.3.89.25562
105238.3.90.0/26238.3.90.1 to 238.3.90.62238.3.90.6362
106238.3.90.64/26238.3.90.65 to 238.3.90.126238.3.90.12762
107238.3.90.128/26238.3.90.129 to 238.3.90.190238.3.90.19162
108238.3.90.192/26238.3.90.193 to 238.3.90.254238.3.90.25562
109238.3.91.0/26238.3.91.1 to 238.3.91.62238.3.91.6362
110238.3.91.64/26238.3.91.65 to 238.3.91.126238.3.91.12762
111238.3.91.128/26238.3.91.129 to 238.3.91.190238.3.91.19162
112238.3.91.192/26238.3.91.193 to 238.3.91.254238.3.91.25562
113238.3.92.0/26238.3.92.1 to 238.3.92.62238.3.92.6362
114238.3.92.64/26238.3.92.65 to 238.3.92.126238.3.92.12762
115238.3.92.128/26238.3.92.129 to 238.3.92.190238.3.92.19162
116238.3.92.192/26238.3.92.193 to 238.3.92.254238.3.92.25562
117238.3.93.0/26238.3.93.1 to 238.3.93.62238.3.93.6362
118238.3.93.64/26238.3.93.65 to 238.3.93.126238.3.93.12762
119238.3.93.128/26238.3.93.129 to 238.3.93.190238.3.93.19162
120238.3.93.192/26238.3.93.193 to 238.3.93.254238.3.93.25562
121238.3.94.0/26238.3.94.1 to 238.3.94.62238.3.94.6362
122238.3.94.64/26238.3.94.65 to 238.3.94.126238.3.94.12762
123238.3.94.128/26238.3.94.129 to 238.3.94.190238.3.94.19162
124238.3.94.192/26238.3.94.193 to 238.3.94.254238.3.94.25562
125238.3.95.0/26238.3.95.1 to 238.3.95.62238.3.95.6362
126238.3.95.64/26238.3.95.65 to 238.3.95.126238.3.95.12762
127238.3.95.128/26238.3.95.129 to 238.3.95.190238.3.95.19162
128238.3.95.192/26238.3.95.193 to 238.3.95.254238.3.95.25562

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.