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.

Network135.2.0.0/19
Usable hosts8,190
Subnet mask255.255.224.0
Addresses8,192
Network address
135.2.0.0
Broadcast address
135.2.31.255
First usable
135.2.0.1
Last usable
135.2.31.254
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
Public public
Old class
B (default /16)
As numbers
Hex 87020000 · Integer 2265055232 to 2265063423
Reverse DNS zones
0.2.135.in-addr.arpa
1.2.135.in-addr.arpa
2.2.135.in-addr.arpa
3.2.135.in-addr.arpa
4.2.135.in-addr.arpa
5.2.135.in-addr.arpa
6.2.135.in-addr.arpa
7.2.135.in-addr.arpa
8.2.135.in-addr.arpa
9.2.135.in-addr.arpa
10.2.135.in-addr.arpa
11.2.135.in-addr.arpa
12.2.135.in-addr.arpa
13.2.135.in-addr.arpa
14.2.135.in-addr.arpa
15.2.135.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
Address10000111.00000010.00000000.00000000135.2.0.0
Subnet mask11111111.11111111.11100000.00000000255.255.224.0
Network10000111.00000010.00000000.00000000135.2.0.0
Broadcast10000111.00000010.00011111.11111111135.2.31.255
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)

135.2.0.0/19 makes 128 subnets of /26.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1135.2.0.0/26135.2.0.1 to 135.2.0.62135.2.0.6362
2135.2.0.64/26135.2.0.65 to 135.2.0.126135.2.0.12762
3135.2.0.128/26135.2.0.129 to 135.2.0.190135.2.0.19162
4135.2.0.192/26135.2.0.193 to 135.2.0.254135.2.0.25562
5135.2.1.0/26135.2.1.1 to 135.2.1.62135.2.1.6362
6135.2.1.64/26135.2.1.65 to 135.2.1.126135.2.1.12762
7135.2.1.128/26135.2.1.129 to 135.2.1.190135.2.1.19162
8135.2.1.192/26135.2.1.193 to 135.2.1.254135.2.1.25562
9135.2.2.0/26135.2.2.1 to 135.2.2.62135.2.2.6362
10135.2.2.64/26135.2.2.65 to 135.2.2.126135.2.2.12762
11135.2.2.128/26135.2.2.129 to 135.2.2.190135.2.2.19162
12135.2.2.192/26135.2.2.193 to 135.2.2.254135.2.2.25562
13135.2.3.0/26135.2.3.1 to 135.2.3.62135.2.3.6362
14135.2.3.64/26135.2.3.65 to 135.2.3.126135.2.3.12762
15135.2.3.128/26135.2.3.129 to 135.2.3.190135.2.3.19162
16135.2.3.192/26135.2.3.193 to 135.2.3.254135.2.3.25562
17135.2.4.0/26135.2.4.1 to 135.2.4.62135.2.4.6362
18135.2.4.64/26135.2.4.65 to 135.2.4.126135.2.4.12762
19135.2.4.128/26135.2.4.129 to 135.2.4.190135.2.4.19162
20135.2.4.192/26135.2.4.193 to 135.2.4.254135.2.4.25562
21135.2.5.0/26135.2.5.1 to 135.2.5.62135.2.5.6362
22135.2.5.64/26135.2.5.65 to 135.2.5.126135.2.5.12762
23135.2.5.128/26135.2.5.129 to 135.2.5.190135.2.5.19162
24135.2.5.192/26135.2.5.193 to 135.2.5.254135.2.5.25562
25135.2.6.0/26135.2.6.1 to 135.2.6.62135.2.6.6362
26135.2.6.64/26135.2.6.65 to 135.2.6.126135.2.6.12762
27135.2.6.128/26135.2.6.129 to 135.2.6.190135.2.6.19162
28135.2.6.192/26135.2.6.193 to 135.2.6.254135.2.6.25562
29135.2.7.0/26135.2.7.1 to 135.2.7.62135.2.7.6362
30135.2.7.64/26135.2.7.65 to 135.2.7.126135.2.7.12762
31135.2.7.128/26135.2.7.129 to 135.2.7.190135.2.7.19162
32135.2.7.192/26135.2.7.193 to 135.2.7.254135.2.7.25562
33135.2.8.0/26135.2.8.1 to 135.2.8.62135.2.8.6362
34135.2.8.64/26135.2.8.65 to 135.2.8.126135.2.8.12762
35135.2.8.128/26135.2.8.129 to 135.2.8.190135.2.8.19162
36135.2.8.192/26135.2.8.193 to 135.2.8.254135.2.8.25562
37135.2.9.0/26135.2.9.1 to 135.2.9.62135.2.9.6362
38135.2.9.64/26135.2.9.65 to 135.2.9.126135.2.9.12762
39135.2.9.128/26135.2.9.129 to 135.2.9.190135.2.9.19162
40135.2.9.192/26135.2.9.193 to 135.2.9.254135.2.9.25562
41135.2.10.0/26135.2.10.1 to 135.2.10.62135.2.10.6362
42135.2.10.64/26135.2.10.65 to 135.2.10.126135.2.10.12762
43135.2.10.128/26135.2.10.129 to 135.2.10.190135.2.10.19162
44135.2.10.192/26135.2.10.193 to 135.2.10.254135.2.10.25562
45135.2.11.0/26135.2.11.1 to 135.2.11.62135.2.11.6362
46135.2.11.64/26135.2.11.65 to 135.2.11.126135.2.11.12762
47135.2.11.128/26135.2.11.129 to 135.2.11.190135.2.11.19162
48135.2.11.192/26135.2.11.193 to 135.2.11.254135.2.11.25562
49135.2.12.0/26135.2.12.1 to 135.2.12.62135.2.12.6362
50135.2.12.64/26135.2.12.65 to 135.2.12.126135.2.12.12762
51135.2.12.128/26135.2.12.129 to 135.2.12.190135.2.12.19162
52135.2.12.192/26135.2.12.193 to 135.2.12.254135.2.12.25562
53135.2.13.0/26135.2.13.1 to 135.2.13.62135.2.13.6362
54135.2.13.64/26135.2.13.65 to 135.2.13.126135.2.13.12762
55135.2.13.128/26135.2.13.129 to 135.2.13.190135.2.13.19162
56135.2.13.192/26135.2.13.193 to 135.2.13.254135.2.13.25562
57135.2.14.0/26135.2.14.1 to 135.2.14.62135.2.14.6362
58135.2.14.64/26135.2.14.65 to 135.2.14.126135.2.14.12762
59135.2.14.128/26135.2.14.129 to 135.2.14.190135.2.14.19162
60135.2.14.192/26135.2.14.193 to 135.2.14.254135.2.14.25562
61135.2.15.0/26135.2.15.1 to 135.2.15.62135.2.15.6362
62135.2.15.64/26135.2.15.65 to 135.2.15.126135.2.15.12762
63135.2.15.128/26135.2.15.129 to 135.2.15.190135.2.15.19162
64135.2.15.192/26135.2.15.193 to 135.2.15.254135.2.15.25562
65135.2.16.0/26135.2.16.1 to 135.2.16.62135.2.16.6362
66135.2.16.64/26135.2.16.65 to 135.2.16.126135.2.16.12762
67135.2.16.128/26135.2.16.129 to 135.2.16.190135.2.16.19162
68135.2.16.192/26135.2.16.193 to 135.2.16.254135.2.16.25562
69135.2.17.0/26135.2.17.1 to 135.2.17.62135.2.17.6362
70135.2.17.64/26135.2.17.65 to 135.2.17.126135.2.17.12762
71135.2.17.128/26135.2.17.129 to 135.2.17.190135.2.17.19162
72135.2.17.192/26135.2.17.193 to 135.2.17.254135.2.17.25562
73135.2.18.0/26135.2.18.1 to 135.2.18.62135.2.18.6362
74135.2.18.64/26135.2.18.65 to 135.2.18.126135.2.18.12762
75135.2.18.128/26135.2.18.129 to 135.2.18.190135.2.18.19162
76135.2.18.192/26135.2.18.193 to 135.2.18.254135.2.18.25562
77135.2.19.0/26135.2.19.1 to 135.2.19.62135.2.19.6362
78135.2.19.64/26135.2.19.65 to 135.2.19.126135.2.19.12762
79135.2.19.128/26135.2.19.129 to 135.2.19.190135.2.19.19162
80135.2.19.192/26135.2.19.193 to 135.2.19.254135.2.19.25562
81135.2.20.0/26135.2.20.1 to 135.2.20.62135.2.20.6362
82135.2.20.64/26135.2.20.65 to 135.2.20.126135.2.20.12762
83135.2.20.128/26135.2.20.129 to 135.2.20.190135.2.20.19162
84135.2.20.192/26135.2.20.193 to 135.2.20.254135.2.20.25562
85135.2.21.0/26135.2.21.1 to 135.2.21.62135.2.21.6362
86135.2.21.64/26135.2.21.65 to 135.2.21.126135.2.21.12762
87135.2.21.128/26135.2.21.129 to 135.2.21.190135.2.21.19162
88135.2.21.192/26135.2.21.193 to 135.2.21.254135.2.21.25562
89135.2.22.0/26135.2.22.1 to 135.2.22.62135.2.22.6362
90135.2.22.64/26135.2.22.65 to 135.2.22.126135.2.22.12762
91135.2.22.128/26135.2.22.129 to 135.2.22.190135.2.22.19162
92135.2.22.192/26135.2.22.193 to 135.2.22.254135.2.22.25562
93135.2.23.0/26135.2.23.1 to 135.2.23.62135.2.23.6362
94135.2.23.64/26135.2.23.65 to 135.2.23.126135.2.23.12762
95135.2.23.128/26135.2.23.129 to 135.2.23.190135.2.23.19162
96135.2.23.192/26135.2.23.193 to 135.2.23.254135.2.23.25562
97135.2.24.0/26135.2.24.1 to 135.2.24.62135.2.24.6362
98135.2.24.64/26135.2.24.65 to 135.2.24.126135.2.24.12762
99135.2.24.128/26135.2.24.129 to 135.2.24.190135.2.24.19162
100135.2.24.192/26135.2.24.193 to 135.2.24.254135.2.24.25562
101135.2.25.0/26135.2.25.1 to 135.2.25.62135.2.25.6362
102135.2.25.64/26135.2.25.65 to 135.2.25.126135.2.25.12762
103135.2.25.128/26135.2.25.129 to 135.2.25.190135.2.25.19162
104135.2.25.192/26135.2.25.193 to 135.2.25.254135.2.25.25562
105135.2.26.0/26135.2.26.1 to 135.2.26.62135.2.26.6362
106135.2.26.64/26135.2.26.65 to 135.2.26.126135.2.26.12762
107135.2.26.128/26135.2.26.129 to 135.2.26.190135.2.26.19162
108135.2.26.192/26135.2.26.193 to 135.2.26.254135.2.26.25562
109135.2.27.0/26135.2.27.1 to 135.2.27.62135.2.27.6362
110135.2.27.64/26135.2.27.65 to 135.2.27.126135.2.27.12762
111135.2.27.128/26135.2.27.129 to 135.2.27.190135.2.27.19162
112135.2.27.192/26135.2.27.193 to 135.2.27.254135.2.27.25562
113135.2.28.0/26135.2.28.1 to 135.2.28.62135.2.28.6362
114135.2.28.64/26135.2.28.65 to 135.2.28.126135.2.28.12762
115135.2.28.128/26135.2.28.129 to 135.2.28.190135.2.28.19162
116135.2.28.192/26135.2.28.193 to 135.2.28.254135.2.28.25562
117135.2.29.0/26135.2.29.1 to 135.2.29.62135.2.29.6362
118135.2.29.64/26135.2.29.65 to 135.2.29.126135.2.29.12762
119135.2.29.128/26135.2.29.129 to 135.2.29.190135.2.29.19162
120135.2.29.192/26135.2.29.193 to 135.2.29.254135.2.29.25562
121135.2.30.0/26135.2.30.1 to 135.2.30.62135.2.30.6362
122135.2.30.64/26135.2.30.65 to 135.2.30.126135.2.30.12762
123135.2.30.128/26135.2.30.129 to 135.2.30.190135.2.30.19162
124135.2.30.192/26135.2.30.193 to 135.2.30.254135.2.30.25562
125135.2.31.0/26135.2.31.1 to 135.2.31.62135.2.31.6362
126135.2.31.64/26135.2.31.65 to 135.2.31.126135.2.31.12762
127135.2.31.128/26135.2.31.129 to 135.2.31.190135.2.31.19162
128135.2.31.192/26135.2.31.193 to 135.2.31.254135.2.31.25562

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.