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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
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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.

Prefix/9
Addresses2^119
/64 networks2^55
Network
2500::/9
First address
2500::
Last address
257f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
Addresses
664,613,997,892,457,936,451,903,530,140,172,288 (2^119)
/64 networks (LANs)
36,028,797,018,963,968 (2^55)
Full form
2500:0000:0000:0000:0000:0000:0000:0000
Type
Global unicast 2000::/3
Public internet addresses
Reverse DNS zones
0.5.2.ip6.arpa
1.5.2.ip6.arpa
2.5.2.ip6.arpa
3.5.2.ip6.arpa
4.5.2.ip6.arpa
5.5.2.ip6.arpa
6.5.2.ip6.arpa
7.5.2.ip6.arpa
/9 is not on a 4-bit boundary, so it takes 8 /12 zones.
Split into smaller subnets/16
/10 (2)/11 (4)/12 (8)/13 (16)/16 (128)/20 (2,048)/24 (32,768)

2500::/9 makes 128 subnets of /16.

Subnets
#SubnetLast address
12500::/162500:ffff:ffff:ffff:ffff:ffff:ffff:ffff
22501::/162501:ffff:ffff:ffff:ffff:ffff:ffff:ffff
32502::/162502:ffff:ffff:ffff:ffff:ffff:ffff:ffff
42503::/162503:ffff:ffff:ffff:ffff:ffff:ffff:ffff
52504::/162504:ffff:ffff:ffff:ffff:ffff:ffff:ffff
62505::/162505:ffff:ffff:ffff:ffff:ffff:ffff:ffff
72506::/162506:ffff:ffff:ffff:ffff:ffff:ffff:ffff
82507::/162507:ffff:ffff:ffff:ffff:ffff:ffff:ffff
92508::/162508:ffff:ffff:ffff:ffff:ffff:ffff:ffff
102509::/162509:ffff:ffff:ffff:ffff:ffff:ffff:ffff
11250a::/16250a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
12250b::/16250b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
13250c::/16250c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
14250d::/16250d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
15250e::/16250e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
16250f::/16250f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
172510::/162510:ffff:ffff:ffff:ffff:ffff:ffff:ffff
182511::/162511:ffff:ffff:ffff:ffff:ffff:ffff:ffff
192512::/162512:ffff:ffff:ffff:ffff:ffff:ffff:ffff
202513::/162513:ffff:ffff:ffff:ffff:ffff:ffff:ffff
212514::/162514:ffff:ffff:ffff:ffff:ffff:ffff:ffff
222515::/162515:ffff:ffff:ffff:ffff:ffff:ffff:ffff
232516::/162516:ffff:ffff:ffff:ffff:ffff:ffff:ffff
242517::/162517:ffff:ffff:ffff:ffff:ffff:ffff:ffff
252518::/162518:ffff:ffff:ffff:ffff:ffff:ffff:ffff
262519::/162519:ffff:ffff:ffff:ffff:ffff:ffff:ffff
27251a::/16251a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
28251b::/16251b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
29251c::/16251c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
30251d::/16251d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
31251e::/16251e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
32251f::/16251f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
332520::/162520:ffff:ffff:ffff:ffff:ffff:ffff:ffff
342521::/162521:ffff:ffff:ffff:ffff:ffff:ffff:ffff
352522::/162522:ffff:ffff:ffff:ffff:ffff:ffff:ffff
362523::/162523:ffff:ffff:ffff:ffff:ffff:ffff:ffff
372524::/162524:ffff:ffff:ffff:ffff:ffff:ffff:ffff
382525::/162525:ffff:ffff:ffff:ffff:ffff:ffff:ffff
392526::/162526:ffff:ffff:ffff:ffff:ffff:ffff:ffff
402527::/162527:ffff:ffff:ffff:ffff:ffff:ffff:ffff
412528::/162528:ffff:ffff:ffff:ffff:ffff:ffff:ffff
422529::/162529:ffff:ffff:ffff:ffff:ffff:ffff:ffff
43252a::/16252a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
44252b::/16252b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
45252c::/16252c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
46252d::/16252d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
47252e::/16252e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
48252f::/16252f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
492530::/162530:ffff:ffff:ffff:ffff:ffff:ffff:ffff
502531::/162531:ffff:ffff:ffff:ffff:ffff:ffff:ffff
512532::/162532:ffff:ffff:ffff:ffff:ffff:ffff:ffff
522533::/162533:ffff:ffff:ffff:ffff:ffff:ffff:ffff
532534::/162534:ffff:ffff:ffff:ffff:ffff:ffff:ffff
542535::/162535:ffff:ffff:ffff:ffff:ffff:ffff:ffff
552536::/162536:ffff:ffff:ffff:ffff:ffff:ffff:ffff
562537::/162537:ffff:ffff:ffff:ffff:ffff:ffff:ffff
572538::/162538:ffff:ffff:ffff:ffff:ffff:ffff:ffff
582539::/162539:ffff:ffff:ffff:ffff:ffff:ffff:ffff
59253a::/16253a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
60253b::/16253b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
61253c::/16253c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
62253d::/16253d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
63253e::/16253e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
64253f::/16253f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
652540::/162540:ffff:ffff:ffff:ffff:ffff:ffff:ffff
662541::/162541:ffff:ffff:ffff:ffff:ffff:ffff:ffff
672542::/162542:ffff:ffff:ffff:ffff:ffff:ffff:ffff
682543::/162543:ffff:ffff:ffff:ffff:ffff:ffff:ffff
692544::/162544:ffff:ffff:ffff:ffff:ffff:ffff:ffff
702545::/162545:ffff:ffff:ffff:ffff:ffff:ffff:ffff
712546::/162546:ffff:ffff:ffff:ffff:ffff:ffff:ffff
722547::/162547:ffff:ffff:ffff:ffff:ffff:ffff:ffff
732548::/162548:ffff:ffff:ffff:ffff:ffff:ffff:ffff
742549::/162549:ffff:ffff:ffff:ffff:ffff:ffff:ffff
75254a::/16254a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
76254b::/16254b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
77254c::/16254c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
78254d::/16254d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
79254e::/16254e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
80254f::/16254f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
812550::/162550:ffff:ffff:ffff:ffff:ffff:ffff:ffff
822551::/162551:ffff:ffff:ffff:ffff:ffff:ffff:ffff
832552::/162552:ffff:ffff:ffff:ffff:ffff:ffff:ffff
842553::/162553:ffff:ffff:ffff:ffff:ffff:ffff:ffff
852554::/162554:ffff:ffff:ffff:ffff:ffff:ffff:ffff
862555::/162555:ffff:ffff:ffff:ffff:ffff:ffff:ffff
872556::/162556:ffff:ffff:ffff:ffff:ffff:ffff:ffff
882557::/162557:ffff:ffff:ffff:ffff:ffff:ffff:ffff
892558::/162558:ffff:ffff:ffff:ffff:ffff:ffff:ffff
902559::/162559:ffff:ffff:ffff:ffff:ffff:ffff:ffff
91255a::/16255a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
92255b::/16255b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
93255c::/16255c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
94255d::/16255d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
95255e::/16255e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
96255f::/16255f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
972560::/162560:ffff:ffff:ffff:ffff:ffff:ffff:ffff
982561::/162561:ffff:ffff:ffff:ffff:ffff:ffff:ffff
992562::/162562:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1002563::/162563:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1012564::/162564:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1022565::/162565:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1032566::/162566:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1042567::/162567:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1052568::/162568:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1062569::/162569:ffff:ffff:ffff:ffff:ffff:ffff:ffff
107256a::/16256a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
108256b::/16256b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
109256c::/16256c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
110256d::/16256d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
111256e::/16256e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
112256f::/16256f:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1132570::/162570:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1142571::/162571:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1152572::/162572:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1162573::/162573:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1172574::/162574:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1182575::/162575:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1192576::/162576:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1202577::/162577:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1212578::/162578:ffff:ffff:ffff:ffff:ffff:ffff:ffff
1222579::/162579:ffff:ffff:ffff:ffff:ffff:ffff:ffff
123257a::/16257a:ffff:ffff:ffff:ffff:ffff:ffff:ffff
124257b::/16257b:ffff:ffff:ffff:ffff:ffff:ffff:ffff
125257c::/16257c:ffff:ffff:ffff:ffff:ffff:ffff:ffff
126257d::/16257d:ffff:ffff:ffff:ffff:ffff:ffff:ffff
127257e::/16257e:ffff:ffff:ffff:ffff:ffff:ffff:ffff
128257f::/16257f:ffff:ffff:ffff:ffff:ffff:ffff:ffff

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.