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.

Network125.76.0.0/17
Usable hosts32,766
Subnet mask255.255.128.0
Addresses32,768
Network address
125.76.0.0
Broadcast address
125.76.127.255
First usable
125.76.0.1
Last usable
125.76.127.254
Usable hosts
32,766 (32,768 less the network and broadcast addresses)
Subnet mask
255.255.128.0
Wildcard mask
0.0.127.255 (Cisco ACLs, OSPF)
Prefix length
/17
Type
Public public
Old class
A (default /8)
As numbers
Hex 7D4C0000 · Integer 2102132736 to 2102165503
Reverse DNS zones
0.76.125.in-addr.arpa
1.76.125.in-addr.arpa
2.76.125.in-addr.arpa
3.76.125.in-addr.arpa
4.76.125.in-addr.arpa
5.76.125.in-addr.arpa
6.76.125.in-addr.arpa
7.76.125.in-addr.arpa
8.76.125.in-addr.arpa
9.76.125.in-addr.arpa
10.76.125.in-addr.arpa
11.76.125.in-addr.arpa
12.76.125.in-addr.arpa
13.76.125.in-addr.arpa
14.76.125.in-addr.arpa
15.76.125.in-addr.arpa
and 112 more
/17 is not on a 8-bit boundary, so it takes 128 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address01111101.01001100.00000000.00000000125.76.0.0
Subnet mask11111111.11111111.10000000.00000000255.255.128.0
Network01111101.01001100.00000000.00000000125.76.0.0
Broadcast01111101.01001100.01111111.11111111125.76.127.255
Split into smaller subnets/24
/18 (2)/19 (4)/20 (8)/21 (16)/22 (32)/23 (64)/24 (128)/25 (256)/26 (512)/27 (1,024)/28 (2,048)/29 (4,096)

125.76.0.0/17 makes 128 subnets of /24.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1125.76.0.0/24125.76.0.1 to 125.76.0.254125.76.0.255254
2125.76.1.0/24125.76.1.1 to 125.76.1.254125.76.1.255254
3125.76.2.0/24125.76.2.1 to 125.76.2.254125.76.2.255254
4125.76.3.0/24125.76.3.1 to 125.76.3.254125.76.3.255254
5125.76.4.0/24125.76.4.1 to 125.76.4.254125.76.4.255254
6125.76.5.0/24125.76.5.1 to 125.76.5.254125.76.5.255254
7125.76.6.0/24125.76.6.1 to 125.76.6.254125.76.6.255254
8125.76.7.0/24125.76.7.1 to 125.76.7.254125.76.7.255254
9125.76.8.0/24125.76.8.1 to 125.76.8.254125.76.8.255254
10125.76.9.0/24125.76.9.1 to 125.76.9.254125.76.9.255254
11125.76.10.0/24125.76.10.1 to 125.76.10.254125.76.10.255254
12125.76.11.0/24125.76.11.1 to 125.76.11.254125.76.11.255254
13125.76.12.0/24125.76.12.1 to 125.76.12.254125.76.12.255254
14125.76.13.0/24125.76.13.1 to 125.76.13.254125.76.13.255254
15125.76.14.0/24125.76.14.1 to 125.76.14.254125.76.14.255254
16125.76.15.0/24125.76.15.1 to 125.76.15.254125.76.15.255254
17125.76.16.0/24125.76.16.1 to 125.76.16.254125.76.16.255254
18125.76.17.0/24125.76.17.1 to 125.76.17.254125.76.17.255254
19125.76.18.0/24125.76.18.1 to 125.76.18.254125.76.18.255254
20125.76.19.0/24125.76.19.1 to 125.76.19.254125.76.19.255254
21125.76.20.0/24125.76.20.1 to 125.76.20.254125.76.20.255254
22125.76.21.0/24125.76.21.1 to 125.76.21.254125.76.21.255254
23125.76.22.0/24125.76.22.1 to 125.76.22.254125.76.22.255254
24125.76.23.0/24125.76.23.1 to 125.76.23.254125.76.23.255254
25125.76.24.0/24125.76.24.1 to 125.76.24.254125.76.24.255254
26125.76.25.0/24125.76.25.1 to 125.76.25.254125.76.25.255254
27125.76.26.0/24125.76.26.1 to 125.76.26.254125.76.26.255254
28125.76.27.0/24125.76.27.1 to 125.76.27.254125.76.27.255254
29125.76.28.0/24125.76.28.1 to 125.76.28.254125.76.28.255254
30125.76.29.0/24125.76.29.1 to 125.76.29.254125.76.29.255254
31125.76.30.0/24125.76.30.1 to 125.76.30.254125.76.30.255254
32125.76.31.0/24125.76.31.1 to 125.76.31.254125.76.31.255254
33125.76.32.0/24125.76.32.1 to 125.76.32.254125.76.32.255254
34125.76.33.0/24125.76.33.1 to 125.76.33.254125.76.33.255254
35125.76.34.0/24125.76.34.1 to 125.76.34.254125.76.34.255254
36125.76.35.0/24125.76.35.1 to 125.76.35.254125.76.35.255254
37125.76.36.0/24125.76.36.1 to 125.76.36.254125.76.36.255254
38125.76.37.0/24125.76.37.1 to 125.76.37.254125.76.37.255254
39125.76.38.0/24125.76.38.1 to 125.76.38.254125.76.38.255254
40125.76.39.0/24125.76.39.1 to 125.76.39.254125.76.39.255254
41125.76.40.0/24125.76.40.1 to 125.76.40.254125.76.40.255254
42125.76.41.0/24125.76.41.1 to 125.76.41.254125.76.41.255254
43125.76.42.0/24125.76.42.1 to 125.76.42.254125.76.42.255254
44125.76.43.0/24125.76.43.1 to 125.76.43.254125.76.43.255254
45125.76.44.0/24125.76.44.1 to 125.76.44.254125.76.44.255254
46125.76.45.0/24125.76.45.1 to 125.76.45.254125.76.45.255254
47125.76.46.0/24125.76.46.1 to 125.76.46.254125.76.46.255254
48125.76.47.0/24125.76.47.1 to 125.76.47.254125.76.47.255254
49125.76.48.0/24125.76.48.1 to 125.76.48.254125.76.48.255254
50125.76.49.0/24125.76.49.1 to 125.76.49.254125.76.49.255254
51125.76.50.0/24125.76.50.1 to 125.76.50.254125.76.50.255254
52125.76.51.0/24125.76.51.1 to 125.76.51.254125.76.51.255254
53125.76.52.0/24125.76.52.1 to 125.76.52.254125.76.52.255254
54125.76.53.0/24125.76.53.1 to 125.76.53.254125.76.53.255254
55125.76.54.0/24125.76.54.1 to 125.76.54.254125.76.54.255254
56125.76.55.0/24125.76.55.1 to 125.76.55.254125.76.55.255254
57125.76.56.0/24125.76.56.1 to 125.76.56.254125.76.56.255254
58125.76.57.0/24125.76.57.1 to 125.76.57.254125.76.57.255254
59125.76.58.0/24125.76.58.1 to 125.76.58.254125.76.58.255254
60125.76.59.0/24125.76.59.1 to 125.76.59.254125.76.59.255254
61125.76.60.0/24125.76.60.1 to 125.76.60.254125.76.60.255254
62125.76.61.0/24125.76.61.1 to 125.76.61.254125.76.61.255254
63125.76.62.0/24125.76.62.1 to 125.76.62.254125.76.62.255254
64125.76.63.0/24125.76.63.1 to 125.76.63.254125.76.63.255254
65125.76.64.0/24125.76.64.1 to 125.76.64.254125.76.64.255254
66125.76.65.0/24125.76.65.1 to 125.76.65.254125.76.65.255254
67125.76.66.0/24125.76.66.1 to 125.76.66.254125.76.66.255254
68125.76.67.0/24125.76.67.1 to 125.76.67.254125.76.67.255254
69125.76.68.0/24125.76.68.1 to 125.76.68.254125.76.68.255254
70125.76.69.0/24125.76.69.1 to 125.76.69.254125.76.69.255254
71125.76.70.0/24125.76.70.1 to 125.76.70.254125.76.70.255254
72125.76.71.0/24125.76.71.1 to 125.76.71.254125.76.71.255254
73125.76.72.0/24125.76.72.1 to 125.76.72.254125.76.72.255254
74125.76.73.0/24125.76.73.1 to 125.76.73.254125.76.73.255254
75125.76.74.0/24125.76.74.1 to 125.76.74.254125.76.74.255254
76125.76.75.0/24125.76.75.1 to 125.76.75.254125.76.75.255254
77125.76.76.0/24125.76.76.1 to 125.76.76.254125.76.76.255254
78125.76.77.0/24125.76.77.1 to 125.76.77.254125.76.77.255254
79125.76.78.0/24125.76.78.1 to 125.76.78.254125.76.78.255254
80125.76.79.0/24125.76.79.1 to 125.76.79.254125.76.79.255254
81125.76.80.0/24125.76.80.1 to 125.76.80.254125.76.80.255254
82125.76.81.0/24125.76.81.1 to 125.76.81.254125.76.81.255254
83125.76.82.0/24125.76.82.1 to 125.76.82.254125.76.82.255254
84125.76.83.0/24125.76.83.1 to 125.76.83.254125.76.83.255254
85125.76.84.0/24125.76.84.1 to 125.76.84.254125.76.84.255254
86125.76.85.0/24125.76.85.1 to 125.76.85.254125.76.85.255254
87125.76.86.0/24125.76.86.1 to 125.76.86.254125.76.86.255254
88125.76.87.0/24125.76.87.1 to 125.76.87.254125.76.87.255254
89125.76.88.0/24125.76.88.1 to 125.76.88.254125.76.88.255254
90125.76.89.0/24125.76.89.1 to 125.76.89.254125.76.89.255254
91125.76.90.0/24125.76.90.1 to 125.76.90.254125.76.90.255254
92125.76.91.0/24125.76.91.1 to 125.76.91.254125.76.91.255254
93125.76.92.0/24125.76.92.1 to 125.76.92.254125.76.92.255254
94125.76.93.0/24125.76.93.1 to 125.76.93.254125.76.93.255254
95125.76.94.0/24125.76.94.1 to 125.76.94.254125.76.94.255254
96125.76.95.0/24125.76.95.1 to 125.76.95.254125.76.95.255254
97125.76.96.0/24125.76.96.1 to 125.76.96.254125.76.96.255254
98125.76.97.0/24125.76.97.1 to 125.76.97.254125.76.97.255254
99125.76.98.0/24125.76.98.1 to 125.76.98.254125.76.98.255254
100125.76.99.0/24125.76.99.1 to 125.76.99.254125.76.99.255254
101125.76.100.0/24125.76.100.1 to 125.76.100.254125.76.100.255254
102125.76.101.0/24125.76.101.1 to 125.76.101.254125.76.101.255254
103125.76.102.0/24125.76.102.1 to 125.76.102.254125.76.102.255254
104125.76.103.0/24125.76.103.1 to 125.76.103.254125.76.103.255254
105125.76.104.0/24125.76.104.1 to 125.76.104.254125.76.104.255254
106125.76.105.0/24125.76.105.1 to 125.76.105.254125.76.105.255254
107125.76.106.0/24125.76.106.1 to 125.76.106.254125.76.106.255254
108125.76.107.0/24125.76.107.1 to 125.76.107.254125.76.107.255254
109125.76.108.0/24125.76.108.1 to 125.76.108.254125.76.108.255254
110125.76.109.0/24125.76.109.1 to 125.76.109.254125.76.109.255254
111125.76.110.0/24125.76.110.1 to 125.76.110.254125.76.110.255254
112125.76.111.0/24125.76.111.1 to 125.76.111.254125.76.111.255254
113125.76.112.0/24125.76.112.1 to 125.76.112.254125.76.112.255254
114125.76.113.0/24125.76.113.1 to 125.76.113.254125.76.113.255254
115125.76.114.0/24125.76.114.1 to 125.76.114.254125.76.114.255254
116125.76.115.0/24125.76.115.1 to 125.76.115.254125.76.115.255254
117125.76.116.0/24125.76.116.1 to 125.76.116.254125.76.116.255254
118125.76.117.0/24125.76.117.1 to 125.76.117.254125.76.117.255254
119125.76.118.0/24125.76.118.1 to 125.76.118.254125.76.118.255254
120125.76.119.0/24125.76.119.1 to 125.76.119.254125.76.119.255254
121125.76.120.0/24125.76.120.1 to 125.76.120.254125.76.120.255254
122125.76.121.0/24125.76.121.1 to 125.76.121.254125.76.121.255254
123125.76.122.0/24125.76.122.1 to 125.76.122.254125.76.122.255254
124125.76.123.0/24125.76.123.1 to 125.76.123.254125.76.123.255254
125125.76.124.0/24125.76.124.1 to 125.76.124.254125.76.124.255254
126125.76.125.0/24125.76.125.1 to 125.76.125.254125.76.125.255254
127125.76.126.0/24125.76.126.1 to 125.76.126.254125.76.126.255254
128125.76.127.0/24125.76.127.1 to 125.76.127.254125.76.127.255254

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.