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.

Prefix/120
Addresses256
/64 networksPart of one
Network
2c19:dd:ec00:c25:c25e:dd:dd4e:cd00/120
First address
2c19:dd:ec00:c25:c25e:dd:dd4e:cd00
Last address
2c19:dd:ec00:c25:c25e:dd:dd4e:cdff
Addresses
256
/64 networks (LANs)
None: smaller than one /64 LAN
Full form
2c19:00dd:ec00:0c25:c25e:00dd:dd4e:cd00
Type
Global unicast 2000::/3
Public internet addresses
Reverse DNS zone
d.c.e.4.d.d.d.d.0.0.e.5.2.c.5.2.c.0.0.0.c.e.d.d.0.0.9.1.c.2.ip6.arpa
Split into smaller subnets/128
/121 (2)/122 (4)/123 (8)/124 (16)/127 (128)/128 (256)

2c19:dd:ec00:c25:c25e:dd:dd4e:cd00/120 makes 256 subnets of /128.

Subnets
#SubnetLast address
12c19:dd:ec00:c25:c25e:dd:dd4e:cd00/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd00
22c19:dd:ec00:c25:c25e:dd:dd4e:cd01/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd01
32c19:dd:ec00:c25:c25e:dd:dd4e:cd02/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd02
42c19:dd:ec00:c25:c25e:dd:dd4e:cd03/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd03
52c19:dd:ec00:c25:c25e:dd:dd4e:cd04/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd04
62c19:dd:ec00:c25:c25e:dd:dd4e:cd05/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd05
72c19:dd:ec00:c25:c25e:dd:dd4e:cd06/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd06
82c19:dd:ec00:c25:c25e:dd:dd4e:cd07/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd07
92c19:dd:ec00:c25:c25e:dd:dd4e:cd08/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd08
102c19:dd:ec00:c25:c25e:dd:dd4e:cd09/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd09
112c19:dd:ec00:c25:c25e:dd:dd4e:cd0a/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd0a
122c19:dd:ec00:c25:c25e:dd:dd4e:cd0b/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd0b
132c19:dd:ec00:c25:c25e:dd:dd4e:cd0c/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd0c
142c19:dd:ec00:c25:c25e:dd:dd4e:cd0d/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd0d
152c19:dd:ec00:c25:c25e:dd:dd4e:cd0e/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd0e
162c19:dd:ec00:c25:c25e:dd:dd4e:cd0f/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd0f
172c19:dd:ec00:c25:c25e:dd:dd4e:cd10/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd10
182c19:dd:ec00:c25:c25e:dd:dd4e:cd11/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd11
192c19:dd:ec00:c25:c25e:dd:dd4e:cd12/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd12
202c19:dd:ec00:c25:c25e:dd:dd4e:cd13/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd13
212c19:dd:ec00:c25:c25e:dd:dd4e:cd14/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd14
222c19:dd:ec00:c25:c25e:dd:dd4e:cd15/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd15
232c19:dd:ec00:c25:c25e:dd:dd4e:cd16/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd16
242c19:dd:ec00:c25:c25e:dd:dd4e:cd17/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd17
252c19:dd:ec00:c25:c25e:dd:dd4e:cd18/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd18
262c19:dd:ec00:c25:c25e:dd:dd4e:cd19/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd19
272c19:dd:ec00:c25:c25e:dd:dd4e:cd1a/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd1a
282c19:dd:ec00:c25:c25e:dd:dd4e:cd1b/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd1b
292c19:dd:ec00:c25:c25e:dd:dd4e:cd1c/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd1c
302c19:dd:ec00:c25:c25e:dd:dd4e:cd1d/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd1d
312c19:dd:ec00:c25:c25e:dd:dd4e:cd1e/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd1e
322c19:dd:ec00:c25:c25e:dd:dd4e:cd1f/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd1f
332c19:dd:ec00:c25:c25e:dd:dd4e:cd20/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd20
342c19:dd:ec00:c25:c25e:dd:dd4e:cd21/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd21
352c19:dd:ec00:c25:c25e:dd:dd4e:cd22/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd22
362c19:dd:ec00:c25:c25e:dd:dd4e:cd23/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd23
372c19:dd:ec00:c25:c25e:dd:dd4e:cd24/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd24
382c19:dd:ec00:c25:c25e:dd:dd4e:cd25/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd25
392c19:dd:ec00:c25:c25e:dd:dd4e:cd26/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd26
402c19:dd:ec00:c25:c25e:dd:dd4e:cd27/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd27
412c19:dd:ec00:c25:c25e:dd:dd4e:cd28/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd28
422c19:dd:ec00:c25:c25e:dd:dd4e:cd29/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd29
432c19:dd:ec00:c25:c25e:dd:dd4e:cd2a/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd2a
442c19:dd:ec00:c25:c25e:dd:dd4e:cd2b/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd2b
452c19:dd:ec00:c25:c25e:dd:dd4e:cd2c/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd2c
462c19:dd:ec00:c25:c25e:dd:dd4e:cd2d/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd2d
472c19:dd:ec00:c25:c25e:dd:dd4e:cd2e/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd2e
482c19:dd:ec00:c25:c25e:dd:dd4e:cd2f/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd2f
492c19:dd:ec00:c25:c25e:dd:dd4e:cd30/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd30
502c19:dd:ec00:c25:c25e:dd:dd4e:cd31/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd31
512c19:dd:ec00:c25:c25e:dd:dd4e:cd32/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd32
522c19:dd:ec00:c25:c25e:dd:dd4e:cd33/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd33
532c19:dd:ec00:c25:c25e:dd:dd4e:cd34/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd34
542c19:dd:ec00:c25:c25e:dd:dd4e:cd35/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd35
552c19:dd:ec00:c25:c25e:dd:dd4e:cd36/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd36
562c19:dd:ec00:c25:c25e:dd:dd4e:cd37/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd37
572c19:dd:ec00:c25:c25e:dd:dd4e:cd38/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd38
582c19:dd:ec00:c25:c25e:dd:dd4e:cd39/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd39
592c19:dd:ec00:c25:c25e:dd:dd4e:cd3a/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd3a
602c19:dd:ec00:c25:c25e:dd:dd4e:cd3b/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd3b
612c19:dd:ec00:c25:c25e:dd:dd4e:cd3c/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd3c
622c19:dd:ec00:c25:c25e:dd:dd4e:cd3d/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd3d
632c19:dd:ec00:c25:c25e:dd:dd4e:cd3e/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd3e
642c19:dd:ec00:c25:c25e:dd:dd4e:cd3f/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd3f
652c19:dd:ec00:c25:c25e:dd:dd4e:cd40/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd40
662c19:dd:ec00:c25:c25e:dd:dd4e:cd41/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd41
672c19:dd:ec00:c25:c25e:dd:dd4e:cd42/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd42
682c19:dd:ec00:c25:c25e:dd:dd4e:cd43/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd43
692c19:dd:ec00:c25:c25e:dd:dd4e:cd44/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd44
702c19:dd:ec00:c25:c25e:dd:dd4e:cd45/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd45
712c19:dd:ec00:c25:c25e:dd:dd4e:cd46/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd46
722c19:dd:ec00:c25:c25e:dd:dd4e:cd47/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd47
732c19:dd:ec00:c25:c25e:dd:dd4e:cd48/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd48
742c19:dd:ec00:c25:c25e:dd:dd4e:cd49/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd49
752c19:dd:ec00:c25:c25e:dd:dd4e:cd4a/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd4a
762c19:dd:ec00:c25:c25e:dd:dd4e:cd4b/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd4b
772c19:dd:ec00:c25:c25e:dd:dd4e:cd4c/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd4c
782c19:dd:ec00:c25:c25e:dd:dd4e:cd4d/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd4d
792c19:dd:ec00:c25:c25e:dd:dd4e:cd4e/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd4e
802c19:dd:ec00:c25:c25e:dd:dd4e:cd4f/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd4f
812c19:dd:ec00:c25:c25e:dd:dd4e:cd50/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd50
822c19:dd:ec00:c25:c25e:dd:dd4e:cd51/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd51
832c19:dd:ec00:c25:c25e:dd:dd4e:cd52/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd52
842c19:dd:ec00:c25:c25e:dd:dd4e:cd53/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd53
852c19:dd:ec00:c25:c25e:dd:dd4e:cd54/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd54
862c19:dd:ec00:c25:c25e:dd:dd4e:cd55/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd55
872c19:dd:ec00:c25:c25e:dd:dd4e:cd56/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd56
882c19:dd:ec00:c25:c25e:dd:dd4e:cd57/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd57
892c19:dd:ec00:c25:c25e:dd:dd4e:cd58/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd58
902c19:dd:ec00:c25:c25e:dd:dd4e:cd59/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd59
912c19:dd:ec00:c25:c25e:dd:dd4e:cd5a/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd5a
922c19:dd:ec00:c25:c25e:dd:dd4e:cd5b/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd5b
932c19:dd:ec00:c25:c25e:dd:dd4e:cd5c/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd5c
942c19:dd:ec00:c25:c25e:dd:dd4e:cd5d/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd5d
952c19:dd:ec00:c25:c25e:dd:dd4e:cd5e/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd5e
962c19:dd:ec00:c25:c25e:dd:dd4e:cd5f/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd5f
972c19:dd:ec00:c25:c25e:dd:dd4e:cd60/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd60
982c19:dd:ec00:c25:c25e:dd:dd4e:cd61/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd61
992c19:dd:ec00:c25:c25e:dd:dd4e:cd62/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd62
1002c19:dd:ec00:c25:c25e:dd:dd4e:cd63/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd63
1012c19:dd:ec00:c25:c25e:dd:dd4e:cd64/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd64
1022c19:dd:ec00:c25:c25e:dd:dd4e:cd65/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd65
1032c19:dd:ec00:c25:c25e:dd:dd4e:cd66/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd66
1042c19:dd:ec00:c25:c25e:dd:dd4e:cd67/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd67
1052c19:dd:ec00:c25:c25e:dd:dd4e:cd68/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd68
1062c19:dd:ec00:c25:c25e:dd:dd4e:cd69/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd69
1072c19:dd:ec00:c25:c25e:dd:dd4e:cd6a/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd6a
1082c19:dd:ec00:c25:c25e:dd:dd4e:cd6b/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd6b
1092c19:dd:ec00:c25:c25e:dd:dd4e:cd6c/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd6c
1102c19:dd:ec00:c25:c25e:dd:dd4e:cd6d/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd6d
1112c19:dd:ec00:c25:c25e:dd:dd4e:cd6e/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd6e
1122c19:dd:ec00:c25:c25e:dd:dd4e:cd6f/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd6f
1132c19:dd:ec00:c25:c25e:dd:dd4e:cd70/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd70
1142c19:dd:ec00:c25:c25e:dd:dd4e:cd71/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd71
1152c19:dd:ec00:c25:c25e:dd:dd4e:cd72/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd72
1162c19:dd:ec00:c25:c25e:dd:dd4e:cd73/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd73
1172c19:dd:ec00:c25:c25e:dd:dd4e:cd74/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd74
1182c19:dd:ec00:c25:c25e:dd:dd4e:cd75/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd75
1192c19:dd:ec00:c25:c25e:dd:dd4e:cd76/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd76
1202c19:dd:ec00:c25:c25e:dd:dd4e:cd77/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd77
1212c19:dd:ec00:c25:c25e:dd:dd4e:cd78/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd78
1222c19:dd:ec00:c25:c25e:dd:dd4e:cd79/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd79
1232c19:dd:ec00:c25:c25e:dd:dd4e:cd7a/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd7a
1242c19:dd:ec00:c25:c25e:dd:dd4e:cd7b/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd7b
1252c19:dd:ec00:c25:c25e:dd:dd4e:cd7c/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd7c
1262c19:dd:ec00:c25:c25e:dd:dd4e:cd7d/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd7d
1272c19:dd:ec00:c25:c25e:dd:dd4e:cd7e/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd7e
1282c19:dd:ec00:c25:c25e:dd:dd4e:cd7f/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd7f
1292c19:dd:ec00:c25:c25e:dd:dd4e:cd80/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd80
1302c19:dd:ec00:c25:c25e:dd:dd4e:cd81/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd81
1312c19:dd:ec00:c25:c25e:dd:dd4e:cd82/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd82
1322c19:dd:ec00:c25:c25e:dd:dd4e:cd83/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd83
1332c19:dd:ec00:c25:c25e:dd:dd4e:cd84/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd84
1342c19:dd:ec00:c25:c25e:dd:dd4e:cd85/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd85
1352c19:dd:ec00:c25:c25e:dd:dd4e:cd86/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd86
1362c19:dd:ec00:c25:c25e:dd:dd4e:cd87/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd87
1372c19:dd:ec00:c25:c25e:dd:dd4e:cd88/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd88
1382c19:dd:ec00:c25:c25e:dd:dd4e:cd89/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd89
1392c19:dd:ec00:c25:c25e:dd:dd4e:cd8a/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd8a
1402c19:dd:ec00:c25:c25e:dd:dd4e:cd8b/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd8b
1412c19:dd:ec00:c25:c25e:dd:dd4e:cd8c/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd8c
1422c19:dd:ec00:c25:c25e:dd:dd4e:cd8d/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd8d
1432c19:dd:ec00:c25:c25e:dd:dd4e:cd8e/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd8e
1442c19:dd:ec00:c25:c25e:dd:dd4e:cd8f/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd8f
1452c19:dd:ec00:c25:c25e:dd:dd4e:cd90/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd90
1462c19:dd:ec00:c25:c25e:dd:dd4e:cd91/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd91
1472c19:dd:ec00:c25:c25e:dd:dd4e:cd92/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd92
1482c19:dd:ec00:c25:c25e:dd:dd4e:cd93/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd93
1492c19:dd:ec00:c25:c25e:dd:dd4e:cd94/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd94
1502c19:dd:ec00:c25:c25e:dd:dd4e:cd95/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd95
1512c19:dd:ec00:c25:c25e:dd:dd4e:cd96/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd96
1522c19:dd:ec00:c25:c25e:dd:dd4e:cd97/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd97
1532c19:dd:ec00:c25:c25e:dd:dd4e:cd98/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd98
1542c19:dd:ec00:c25:c25e:dd:dd4e:cd99/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd99
1552c19:dd:ec00:c25:c25e:dd:dd4e:cd9a/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd9a
1562c19:dd:ec00:c25:c25e:dd:dd4e:cd9b/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd9b
1572c19:dd:ec00:c25:c25e:dd:dd4e:cd9c/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd9c
1582c19:dd:ec00:c25:c25e:dd:dd4e:cd9d/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd9d
1592c19:dd:ec00:c25:c25e:dd:dd4e:cd9e/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd9e
1602c19:dd:ec00:c25:c25e:dd:dd4e:cd9f/1282c19:dd:ec00:c25:c25e:dd:dd4e:cd9f
1612c19:dd:ec00:c25:c25e:dd:dd4e:cda0/1282c19:dd:ec00:c25:c25e:dd:dd4e:cda0
1622c19:dd:ec00:c25:c25e:dd:dd4e:cda1/1282c19:dd:ec00:c25:c25e:dd:dd4e:cda1
1632c19:dd:ec00:c25:c25e:dd:dd4e:cda2/1282c19:dd:ec00:c25:c25e:dd:dd4e:cda2
1642c19:dd:ec00:c25:c25e:dd:dd4e:cda3/1282c19:dd:ec00:c25:c25e:dd:dd4e:cda3
1652c19:dd:ec00:c25:c25e:dd:dd4e:cda4/1282c19:dd:ec00:c25:c25e:dd:dd4e:cda4
1662c19:dd:ec00:c25:c25e:dd:dd4e:cda5/1282c19:dd:ec00:c25:c25e:dd:dd4e:cda5
1672c19:dd:ec00:c25:c25e:dd:dd4e:cda6/1282c19:dd:ec00:c25:c25e:dd:dd4e:cda6
1682c19:dd:ec00:c25:c25e:dd:dd4e:cda7/1282c19:dd:ec00:c25:c25e:dd:dd4e:cda7
1692c19:dd:ec00:c25:c25e:dd:dd4e:cda8/1282c19:dd:ec00:c25:c25e:dd:dd4e:cda8
1702c19:dd:ec00:c25:c25e:dd:dd4e:cda9/1282c19:dd:ec00:c25:c25e:dd:dd4e:cda9
1712c19:dd:ec00:c25:c25e:dd:dd4e:cdaa/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdaa
1722c19:dd:ec00:c25:c25e:dd:dd4e:cdab/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdab
1732c19:dd:ec00:c25:c25e:dd:dd4e:cdac/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdac
1742c19:dd:ec00:c25:c25e:dd:dd4e:cdad/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdad
1752c19:dd:ec00:c25:c25e:dd:dd4e:cdae/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdae
1762c19:dd:ec00:c25:c25e:dd:dd4e:cdaf/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdaf
1772c19:dd:ec00:c25:c25e:dd:dd4e:cdb0/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdb0
1782c19:dd:ec00:c25:c25e:dd:dd4e:cdb1/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdb1
1792c19:dd:ec00:c25:c25e:dd:dd4e:cdb2/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdb2
1802c19:dd:ec00:c25:c25e:dd:dd4e:cdb3/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdb3
1812c19:dd:ec00:c25:c25e:dd:dd4e:cdb4/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdb4
1822c19:dd:ec00:c25:c25e:dd:dd4e:cdb5/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdb5
1832c19:dd:ec00:c25:c25e:dd:dd4e:cdb6/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdb6
1842c19:dd:ec00:c25:c25e:dd:dd4e:cdb7/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdb7
1852c19:dd:ec00:c25:c25e:dd:dd4e:cdb8/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdb8
1862c19:dd:ec00:c25:c25e:dd:dd4e:cdb9/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdb9
1872c19:dd:ec00:c25:c25e:dd:dd4e:cdba/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdba
1882c19:dd:ec00:c25:c25e:dd:dd4e:cdbb/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdbb
1892c19:dd:ec00:c25:c25e:dd:dd4e:cdbc/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdbc
1902c19:dd:ec00:c25:c25e:dd:dd4e:cdbd/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdbd
1912c19:dd:ec00:c25:c25e:dd:dd4e:cdbe/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdbe
1922c19:dd:ec00:c25:c25e:dd:dd4e:cdbf/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdbf
1932c19:dd:ec00:c25:c25e:dd:dd4e:cdc0/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdc0
1942c19:dd:ec00:c25:c25e:dd:dd4e:cdc1/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdc1
1952c19:dd:ec00:c25:c25e:dd:dd4e:cdc2/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdc2
1962c19:dd:ec00:c25:c25e:dd:dd4e:cdc3/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdc3
1972c19:dd:ec00:c25:c25e:dd:dd4e:cdc4/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdc4
1982c19:dd:ec00:c25:c25e:dd:dd4e:cdc5/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdc5
1992c19:dd:ec00:c25:c25e:dd:dd4e:cdc6/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdc6
2002c19:dd:ec00:c25:c25e:dd:dd4e:cdc7/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdc7
2012c19:dd:ec00:c25:c25e:dd:dd4e:cdc8/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdc8
2022c19:dd:ec00:c25:c25e:dd:dd4e:cdc9/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdc9
2032c19:dd:ec00:c25:c25e:dd:dd4e:cdca/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdca
2042c19:dd:ec00:c25:c25e:dd:dd4e:cdcb/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdcb
2052c19:dd:ec00:c25:c25e:dd:dd4e:cdcc/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdcc
2062c19:dd:ec00:c25:c25e:dd:dd4e:cdcd/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdcd
2072c19:dd:ec00:c25:c25e:dd:dd4e:cdce/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdce
2082c19:dd:ec00:c25:c25e:dd:dd4e:cdcf/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdcf
2092c19:dd:ec00:c25:c25e:dd:dd4e:cdd0/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdd0
2102c19:dd:ec00:c25:c25e:dd:dd4e:cdd1/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdd1
2112c19:dd:ec00:c25:c25e:dd:dd4e:cdd2/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdd2
2122c19:dd:ec00:c25:c25e:dd:dd4e:cdd3/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdd3
2132c19:dd:ec00:c25:c25e:dd:dd4e:cdd4/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdd4
2142c19:dd:ec00:c25:c25e:dd:dd4e:cdd5/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdd5
2152c19:dd:ec00:c25:c25e:dd:dd4e:cdd6/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdd6
2162c19:dd:ec00:c25:c25e:dd:dd4e:cdd7/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdd7
2172c19:dd:ec00:c25:c25e:dd:dd4e:cdd8/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdd8
2182c19:dd:ec00:c25:c25e:dd:dd4e:cdd9/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdd9
2192c19:dd:ec00:c25:c25e:dd:dd4e:cdda/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdda
2202c19:dd:ec00:c25:c25e:dd:dd4e:cddb/1282c19:dd:ec00:c25:c25e:dd:dd4e:cddb
2212c19:dd:ec00:c25:c25e:dd:dd4e:cddc/1282c19:dd:ec00:c25:c25e:dd:dd4e:cddc
2222c19:dd:ec00:c25:c25e:dd:dd4e:cddd/1282c19:dd:ec00:c25:c25e:dd:dd4e:cddd
2232c19:dd:ec00:c25:c25e:dd:dd4e:cdde/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdde
2242c19:dd:ec00:c25:c25e:dd:dd4e:cddf/1282c19:dd:ec00:c25:c25e:dd:dd4e:cddf
2252c19:dd:ec00:c25:c25e:dd:dd4e:cde0/1282c19:dd:ec00:c25:c25e:dd:dd4e:cde0
2262c19:dd:ec00:c25:c25e:dd:dd4e:cde1/1282c19:dd:ec00:c25:c25e:dd:dd4e:cde1
2272c19:dd:ec00:c25:c25e:dd:dd4e:cde2/1282c19:dd:ec00:c25:c25e:dd:dd4e:cde2
2282c19:dd:ec00:c25:c25e:dd:dd4e:cde3/1282c19:dd:ec00:c25:c25e:dd:dd4e:cde3
2292c19:dd:ec00:c25:c25e:dd:dd4e:cde4/1282c19:dd:ec00:c25:c25e:dd:dd4e:cde4
2302c19:dd:ec00:c25:c25e:dd:dd4e:cde5/1282c19:dd:ec00:c25:c25e:dd:dd4e:cde5
2312c19:dd:ec00:c25:c25e:dd:dd4e:cde6/1282c19:dd:ec00:c25:c25e:dd:dd4e:cde6
2322c19:dd:ec00:c25:c25e:dd:dd4e:cde7/1282c19:dd:ec00:c25:c25e:dd:dd4e:cde7
2332c19:dd:ec00:c25:c25e:dd:dd4e:cde8/1282c19:dd:ec00:c25:c25e:dd:dd4e:cde8
2342c19:dd:ec00:c25:c25e:dd:dd4e:cde9/1282c19:dd:ec00:c25:c25e:dd:dd4e:cde9
2352c19:dd:ec00:c25:c25e:dd:dd4e:cdea/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdea
2362c19:dd:ec00:c25:c25e:dd:dd4e:cdeb/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdeb
2372c19:dd:ec00:c25:c25e:dd:dd4e:cdec/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdec
2382c19:dd:ec00:c25:c25e:dd:dd4e:cded/1282c19:dd:ec00:c25:c25e:dd:dd4e:cded
2392c19:dd:ec00:c25:c25e:dd:dd4e:cdee/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdee
2402c19:dd:ec00:c25:c25e:dd:dd4e:cdef/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdef
2412c19:dd:ec00:c25:c25e:dd:dd4e:cdf0/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdf0
2422c19:dd:ec00:c25:c25e:dd:dd4e:cdf1/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdf1
2432c19:dd:ec00:c25:c25e:dd:dd4e:cdf2/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdf2
2442c19:dd:ec00:c25:c25e:dd:dd4e:cdf3/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdf3
2452c19:dd:ec00:c25:c25e:dd:dd4e:cdf4/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdf4
2462c19:dd:ec00:c25:c25e:dd:dd4e:cdf5/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdf5
2472c19:dd:ec00:c25:c25e:dd:dd4e:cdf6/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdf6
2482c19:dd:ec00:c25:c25e:dd:dd4e:cdf7/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdf7
2492c19:dd:ec00:c25:c25e:dd:dd4e:cdf8/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdf8
2502c19:dd:ec00:c25:c25e:dd:dd4e:cdf9/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdf9
2512c19:dd:ec00:c25:c25e:dd:dd4e:cdfa/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdfa
2522c19:dd:ec00:c25:c25e:dd:dd4e:cdfb/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdfb
2532c19:dd:ec00:c25:c25e:dd:dd4e:cdfc/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdfc
2542c19:dd:ec00:c25:c25e:dd:dd4e:cdfd/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdfd
2552c19:dd:ec00:c25:c25e:dd:dd4e:cdfe/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdfe
2562c19:dd:ec00:c25:c25e:dd:dd4e:cdff/1282c19:dd:ec00:c25:c25e:dd:dd4e:cdff

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.