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/103
Addresses33,554,432
/64 networksPart of one
Network
2c19:dd:ddc:c00a:f00a:c00a:dc00:0/103
First address
2c19:dd:ddc:c00a:f00a:c00a:dc00:0
Last address
2c19:dd:ddc:c00a:f00a:c00a:ddff:ffff
Addresses
33,554,432
/64 networks (LANs)
None: smaller than one /64 LAN
Full form
2c19:00dd:0ddc:c00a:f00a:c00a:dc00:0000
Type
Global unicast 2000::/3
Public internet addresses
Reverse DNS zones
c.d.a.0.0.c.a.0.0.f.a.0.0.c.c.d.d.0.d.d.0.0.9.1.c.2.ip6.arpa
d.d.a.0.0.c.a.0.0.f.a.0.0.c.c.d.d.0.d.d.0.0.9.1.c.2.ip6.arpa
/103 is not on a 4-bit boundary, so it takes 2 /104 zones.
Split into smaller subnets/112
/104 (2)/105 (4)/106 (8)/107 (16)/108 (32)/112 (512)/116 (8,192)

2c19:dd:ddc:c00a:f00a:c00a:dc00:0/103 makes 512 subnets of /112; the first 256 are listed.

Subnets
#SubnetLast address
12c19:dd:ddc:c00a:f00a:c00a:dc00:0/1122c19:dd:ddc:c00a:f00a:c00a:dc00:ffff
22c19:dd:ddc:c00a:f00a:c00a:dc01:0/1122c19:dd:ddc:c00a:f00a:c00a:dc01:ffff
32c19:dd:ddc:c00a:f00a:c00a:dc02:0/1122c19:dd:ddc:c00a:f00a:c00a:dc02:ffff
42c19:dd:ddc:c00a:f00a:c00a:dc03:0/1122c19:dd:ddc:c00a:f00a:c00a:dc03:ffff
52c19:dd:ddc:c00a:f00a:c00a:dc04:0/1122c19:dd:ddc:c00a:f00a:c00a:dc04:ffff
62c19:dd:ddc:c00a:f00a:c00a:dc05:0/1122c19:dd:ddc:c00a:f00a:c00a:dc05:ffff
72c19:dd:ddc:c00a:f00a:c00a:dc06:0/1122c19:dd:ddc:c00a:f00a:c00a:dc06:ffff
82c19:dd:ddc:c00a:f00a:c00a:dc07:0/1122c19:dd:ddc:c00a:f00a:c00a:dc07:ffff
92c19:dd:ddc:c00a:f00a:c00a:dc08:0/1122c19:dd:ddc:c00a:f00a:c00a:dc08:ffff
102c19:dd:ddc:c00a:f00a:c00a:dc09:0/1122c19:dd:ddc:c00a:f00a:c00a:dc09:ffff
112c19:dd:ddc:c00a:f00a:c00a:dc0a:0/1122c19:dd:ddc:c00a:f00a:c00a:dc0a:ffff
122c19:dd:ddc:c00a:f00a:c00a:dc0b:0/1122c19:dd:ddc:c00a:f00a:c00a:dc0b:ffff
132c19:dd:ddc:c00a:f00a:c00a:dc0c:0/1122c19:dd:ddc:c00a:f00a:c00a:dc0c:ffff
142c19:dd:ddc:c00a:f00a:c00a:dc0d:0/1122c19:dd:ddc:c00a:f00a:c00a:dc0d:ffff
152c19:dd:ddc:c00a:f00a:c00a:dc0e:0/1122c19:dd:ddc:c00a:f00a:c00a:dc0e:ffff
162c19:dd:ddc:c00a:f00a:c00a:dc0f:0/1122c19:dd:ddc:c00a:f00a:c00a:dc0f:ffff
172c19:dd:ddc:c00a:f00a:c00a:dc10:0/1122c19:dd:ddc:c00a:f00a:c00a:dc10:ffff
182c19:dd:ddc:c00a:f00a:c00a:dc11:0/1122c19:dd:ddc:c00a:f00a:c00a:dc11:ffff
192c19:dd:ddc:c00a:f00a:c00a:dc12:0/1122c19:dd:ddc:c00a:f00a:c00a:dc12:ffff
202c19:dd:ddc:c00a:f00a:c00a:dc13:0/1122c19:dd:ddc:c00a:f00a:c00a:dc13:ffff
212c19:dd:ddc:c00a:f00a:c00a:dc14:0/1122c19:dd:ddc:c00a:f00a:c00a:dc14:ffff
222c19:dd:ddc:c00a:f00a:c00a:dc15:0/1122c19:dd:ddc:c00a:f00a:c00a:dc15:ffff
232c19:dd:ddc:c00a:f00a:c00a:dc16:0/1122c19:dd:ddc:c00a:f00a:c00a:dc16:ffff
242c19:dd:ddc:c00a:f00a:c00a:dc17:0/1122c19:dd:ddc:c00a:f00a:c00a:dc17:ffff
252c19:dd:ddc:c00a:f00a:c00a:dc18:0/1122c19:dd:ddc:c00a:f00a:c00a:dc18:ffff
262c19:dd:ddc:c00a:f00a:c00a:dc19:0/1122c19:dd:ddc:c00a:f00a:c00a:dc19:ffff
272c19:dd:ddc:c00a:f00a:c00a:dc1a:0/1122c19:dd:ddc:c00a:f00a:c00a:dc1a:ffff
282c19:dd:ddc:c00a:f00a:c00a:dc1b:0/1122c19:dd:ddc:c00a:f00a:c00a:dc1b:ffff
292c19:dd:ddc:c00a:f00a:c00a:dc1c:0/1122c19:dd:ddc:c00a:f00a:c00a:dc1c:ffff
302c19:dd:ddc:c00a:f00a:c00a:dc1d:0/1122c19:dd:ddc:c00a:f00a:c00a:dc1d:ffff
312c19:dd:ddc:c00a:f00a:c00a:dc1e:0/1122c19:dd:ddc:c00a:f00a:c00a:dc1e:ffff
322c19:dd:ddc:c00a:f00a:c00a:dc1f:0/1122c19:dd:ddc:c00a:f00a:c00a:dc1f:ffff
332c19:dd:ddc:c00a:f00a:c00a:dc20:0/1122c19:dd:ddc:c00a:f00a:c00a:dc20:ffff
342c19:dd:ddc:c00a:f00a:c00a:dc21:0/1122c19:dd:ddc:c00a:f00a:c00a:dc21:ffff
352c19:dd:ddc:c00a:f00a:c00a:dc22:0/1122c19:dd:ddc:c00a:f00a:c00a:dc22:ffff
362c19:dd:ddc:c00a:f00a:c00a:dc23:0/1122c19:dd:ddc:c00a:f00a:c00a:dc23:ffff
372c19:dd:ddc:c00a:f00a:c00a:dc24:0/1122c19:dd:ddc:c00a:f00a:c00a:dc24:ffff
382c19:dd:ddc:c00a:f00a:c00a:dc25:0/1122c19:dd:ddc:c00a:f00a:c00a:dc25:ffff
392c19:dd:ddc:c00a:f00a:c00a:dc26:0/1122c19:dd:ddc:c00a:f00a:c00a:dc26:ffff
402c19:dd:ddc:c00a:f00a:c00a:dc27:0/1122c19:dd:ddc:c00a:f00a:c00a:dc27:ffff
412c19:dd:ddc:c00a:f00a:c00a:dc28:0/1122c19:dd:ddc:c00a:f00a:c00a:dc28:ffff
422c19:dd:ddc:c00a:f00a:c00a:dc29:0/1122c19:dd:ddc:c00a:f00a:c00a:dc29:ffff
432c19:dd:ddc:c00a:f00a:c00a:dc2a:0/1122c19:dd:ddc:c00a:f00a:c00a:dc2a:ffff
442c19:dd:ddc:c00a:f00a:c00a:dc2b:0/1122c19:dd:ddc:c00a:f00a:c00a:dc2b:ffff
452c19:dd:ddc:c00a:f00a:c00a:dc2c:0/1122c19:dd:ddc:c00a:f00a:c00a:dc2c:ffff
462c19:dd:ddc:c00a:f00a:c00a:dc2d:0/1122c19:dd:ddc:c00a:f00a:c00a:dc2d:ffff
472c19:dd:ddc:c00a:f00a:c00a:dc2e:0/1122c19:dd:ddc:c00a:f00a:c00a:dc2e:ffff
482c19:dd:ddc:c00a:f00a:c00a:dc2f:0/1122c19:dd:ddc:c00a:f00a:c00a:dc2f:ffff
492c19:dd:ddc:c00a:f00a:c00a:dc30:0/1122c19:dd:ddc:c00a:f00a:c00a:dc30:ffff
502c19:dd:ddc:c00a:f00a:c00a:dc31:0/1122c19:dd:ddc:c00a:f00a:c00a:dc31:ffff
512c19:dd:ddc:c00a:f00a:c00a:dc32:0/1122c19:dd:ddc:c00a:f00a:c00a:dc32:ffff
522c19:dd:ddc:c00a:f00a:c00a:dc33:0/1122c19:dd:ddc:c00a:f00a:c00a:dc33:ffff
532c19:dd:ddc:c00a:f00a:c00a:dc34:0/1122c19:dd:ddc:c00a:f00a:c00a:dc34:ffff
542c19:dd:ddc:c00a:f00a:c00a:dc35:0/1122c19:dd:ddc:c00a:f00a:c00a:dc35:ffff
552c19:dd:ddc:c00a:f00a:c00a:dc36:0/1122c19:dd:ddc:c00a:f00a:c00a:dc36:ffff
562c19:dd:ddc:c00a:f00a:c00a:dc37:0/1122c19:dd:ddc:c00a:f00a:c00a:dc37:ffff
572c19:dd:ddc:c00a:f00a:c00a:dc38:0/1122c19:dd:ddc:c00a:f00a:c00a:dc38:ffff
582c19:dd:ddc:c00a:f00a:c00a:dc39:0/1122c19:dd:ddc:c00a:f00a:c00a:dc39:ffff
592c19:dd:ddc:c00a:f00a:c00a:dc3a:0/1122c19:dd:ddc:c00a:f00a:c00a:dc3a:ffff
602c19:dd:ddc:c00a:f00a:c00a:dc3b:0/1122c19:dd:ddc:c00a:f00a:c00a:dc3b:ffff
612c19:dd:ddc:c00a:f00a:c00a:dc3c:0/1122c19:dd:ddc:c00a:f00a:c00a:dc3c:ffff
622c19:dd:ddc:c00a:f00a:c00a:dc3d:0/1122c19:dd:ddc:c00a:f00a:c00a:dc3d:ffff
632c19:dd:ddc:c00a:f00a:c00a:dc3e:0/1122c19:dd:ddc:c00a:f00a:c00a:dc3e:ffff
642c19:dd:ddc:c00a:f00a:c00a:dc3f:0/1122c19:dd:ddc:c00a:f00a:c00a:dc3f:ffff
652c19:dd:ddc:c00a:f00a:c00a:dc40:0/1122c19:dd:ddc:c00a:f00a:c00a:dc40:ffff
662c19:dd:ddc:c00a:f00a:c00a:dc41:0/1122c19:dd:ddc:c00a:f00a:c00a:dc41:ffff
672c19:dd:ddc:c00a:f00a:c00a:dc42:0/1122c19:dd:ddc:c00a:f00a:c00a:dc42:ffff
682c19:dd:ddc:c00a:f00a:c00a:dc43:0/1122c19:dd:ddc:c00a:f00a:c00a:dc43:ffff
692c19:dd:ddc:c00a:f00a:c00a:dc44:0/1122c19:dd:ddc:c00a:f00a:c00a:dc44:ffff
702c19:dd:ddc:c00a:f00a:c00a:dc45:0/1122c19:dd:ddc:c00a:f00a:c00a:dc45:ffff
712c19:dd:ddc:c00a:f00a:c00a:dc46:0/1122c19:dd:ddc:c00a:f00a:c00a:dc46:ffff
722c19:dd:ddc:c00a:f00a:c00a:dc47:0/1122c19:dd:ddc:c00a:f00a:c00a:dc47:ffff
732c19:dd:ddc:c00a:f00a:c00a:dc48:0/1122c19:dd:ddc:c00a:f00a:c00a:dc48:ffff
742c19:dd:ddc:c00a:f00a:c00a:dc49:0/1122c19:dd:ddc:c00a:f00a:c00a:dc49:ffff
752c19:dd:ddc:c00a:f00a:c00a:dc4a:0/1122c19:dd:ddc:c00a:f00a:c00a:dc4a:ffff
762c19:dd:ddc:c00a:f00a:c00a:dc4b:0/1122c19:dd:ddc:c00a:f00a:c00a:dc4b:ffff
772c19:dd:ddc:c00a:f00a:c00a:dc4c:0/1122c19:dd:ddc:c00a:f00a:c00a:dc4c:ffff
782c19:dd:ddc:c00a:f00a:c00a:dc4d:0/1122c19:dd:ddc:c00a:f00a:c00a:dc4d:ffff
792c19:dd:ddc:c00a:f00a:c00a:dc4e:0/1122c19:dd:ddc:c00a:f00a:c00a:dc4e:ffff
802c19:dd:ddc:c00a:f00a:c00a:dc4f:0/1122c19:dd:ddc:c00a:f00a:c00a:dc4f:ffff
812c19:dd:ddc:c00a:f00a:c00a:dc50:0/1122c19:dd:ddc:c00a:f00a:c00a:dc50:ffff
822c19:dd:ddc:c00a:f00a:c00a:dc51:0/1122c19:dd:ddc:c00a:f00a:c00a:dc51:ffff
832c19:dd:ddc:c00a:f00a:c00a:dc52:0/1122c19:dd:ddc:c00a:f00a:c00a:dc52:ffff
842c19:dd:ddc:c00a:f00a:c00a:dc53:0/1122c19:dd:ddc:c00a:f00a:c00a:dc53:ffff
852c19:dd:ddc:c00a:f00a:c00a:dc54:0/1122c19:dd:ddc:c00a:f00a:c00a:dc54:ffff
862c19:dd:ddc:c00a:f00a:c00a:dc55:0/1122c19:dd:ddc:c00a:f00a:c00a:dc55:ffff
872c19:dd:ddc:c00a:f00a:c00a:dc56:0/1122c19:dd:ddc:c00a:f00a:c00a:dc56:ffff
882c19:dd:ddc:c00a:f00a:c00a:dc57:0/1122c19:dd:ddc:c00a:f00a:c00a:dc57:ffff
892c19:dd:ddc:c00a:f00a:c00a:dc58:0/1122c19:dd:ddc:c00a:f00a:c00a:dc58:ffff
902c19:dd:ddc:c00a:f00a:c00a:dc59:0/1122c19:dd:ddc:c00a:f00a:c00a:dc59:ffff
912c19:dd:ddc:c00a:f00a:c00a:dc5a:0/1122c19:dd:ddc:c00a:f00a:c00a:dc5a:ffff
922c19:dd:ddc:c00a:f00a:c00a:dc5b:0/1122c19:dd:ddc:c00a:f00a:c00a:dc5b:ffff
932c19:dd:ddc:c00a:f00a:c00a:dc5c:0/1122c19:dd:ddc:c00a:f00a:c00a:dc5c:ffff
942c19:dd:ddc:c00a:f00a:c00a:dc5d:0/1122c19:dd:ddc:c00a:f00a:c00a:dc5d:ffff
952c19:dd:ddc:c00a:f00a:c00a:dc5e:0/1122c19:dd:ddc:c00a:f00a:c00a:dc5e:ffff
962c19:dd:ddc:c00a:f00a:c00a:dc5f:0/1122c19:dd:ddc:c00a:f00a:c00a:dc5f:ffff
972c19:dd:ddc:c00a:f00a:c00a:dc60:0/1122c19:dd:ddc:c00a:f00a:c00a:dc60:ffff
982c19:dd:ddc:c00a:f00a:c00a:dc61:0/1122c19:dd:ddc:c00a:f00a:c00a:dc61:ffff
992c19:dd:ddc:c00a:f00a:c00a:dc62:0/1122c19:dd:ddc:c00a:f00a:c00a:dc62:ffff
1002c19:dd:ddc:c00a:f00a:c00a:dc63:0/1122c19:dd:ddc:c00a:f00a:c00a:dc63:ffff
1012c19:dd:ddc:c00a:f00a:c00a:dc64:0/1122c19:dd:ddc:c00a:f00a:c00a:dc64:ffff
1022c19:dd:ddc:c00a:f00a:c00a:dc65:0/1122c19:dd:ddc:c00a:f00a:c00a:dc65:ffff
1032c19:dd:ddc:c00a:f00a:c00a:dc66:0/1122c19:dd:ddc:c00a:f00a:c00a:dc66:ffff
1042c19:dd:ddc:c00a:f00a:c00a:dc67:0/1122c19:dd:ddc:c00a:f00a:c00a:dc67:ffff
1052c19:dd:ddc:c00a:f00a:c00a:dc68:0/1122c19:dd:ddc:c00a:f00a:c00a:dc68:ffff
1062c19:dd:ddc:c00a:f00a:c00a:dc69:0/1122c19:dd:ddc:c00a:f00a:c00a:dc69:ffff
1072c19:dd:ddc:c00a:f00a:c00a:dc6a:0/1122c19:dd:ddc:c00a:f00a:c00a:dc6a:ffff
1082c19:dd:ddc:c00a:f00a:c00a:dc6b:0/1122c19:dd:ddc:c00a:f00a:c00a:dc6b:ffff
1092c19:dd:ddc:c00a:f00a:c00a:dc6c:0/1122c19:dd:ddc:c00a:f00a:c00a:dc6c:ffff
1102c19:dd:ddc:c00a:f00a:c00a:dc6d:0/1122c19:dd:ddc:c00a:f00a:c00a:dc6d:ffff
1112c19:dd:ddc:c00a:f00a:c00a:dc6e:0/1122c19:dd:ddc:c00a:f00a:c00a:dc6e:ffff
1122c19:dd:ddc:c00a:f00a:c00a:dc6f:0/1122c19:dd:ddc:c00a:f00a:c00a:dc6f:ffff
1132c19:dd:ddc:c00a:f00a:c00a:dc70:0/1122c19:dd:ddc:c00a:f00a:c00a:dc70:ffff
1142c19:dd:ddc:c00a:f00a:c00a:dc71:0/1122c19:dd:ddc:c00a:f00a:c00a:dc71:ffff
1152c19:dd:ddc:c00a:f00a:c00a:dc72:0/1122c19:dd:ddc:c00a:f00a:c00a:dc72:ffff
1162c19:dd:ddc:c00a:f00a:c00a:dc73:0/1122c19:dd:ddc:c00a:f00a:c00a:dc73:ffff
1172c19:dd:ddc:c00a:f00a:c00a:dc74:0/1122c19:dd:ddc:c00a:f00a:c00a:dc74:ffff
1182c19:dd:ddc:c00a:f00a:c00a:dc75:0/1122c19:dd:ddc:c00a:f00a:c00a:dc75:ffff
1192c19:dd:ddc:c00a:f00a:c00a:dc76:0/1122c19:dd:ddc:c00a:f00a:c00a:dc76:ffff
1202c19:dd:ddc:c00a:f00a:c00a:dc77:0/1122c19:dd:ddc:c00a:f00a:c00a:dc77:ffff
1212c19:dd:ddc:c00a:f00a:c00a:dc78:0/1122c19:dd:ddc:c00a:f00a:c00a:dc78:ffff
1222c19:dd:ddc:c00a:f00a:c00a:dc79:0/1122c19:dd:ddc:c00a:f00a:c00a:dc79:ffff
1232c19:dd:ddc:c00a:f00a:c00a:dc7a:0/1122c19:dd:ddc:c00a:f00a:c00a:dc7a:ffff
1242c19:dd:ddc:c00a:f00a:c00a:dc7b:0/1122c19:dd:ddc:c00a:f00a:c00a:dc7b:ffff
1252c19:dd:ddc:c00a:f00a:c00a:dc7c:0/1122c19:dd:ddc:c00a:f00a:c00a:dc7c:ffff
1262c19:dd:ddc:c00a:f00a:c00a:dc7d:0/1122c19:dd:ddc:c00a:f00a:c00a:dc7d:ffff
1272c19:dd:ddc:c00a:f00a:c00a:dc7e:0/1122c19:dd:ddc:c00a:f00a:c00a:dc7e:ffff
1282c19:dd:ddc:c00a:f00a:c00a:dc7f:0/1122c19:dd:ddc:c00a:f00a:c00a:dc7f:ffff
1292c19:dd:ddc:c00a:f00a:c00a:dc80:0/1122c19:dd:ddc:c00a:f00a:c00a:dc80:ffff
1302c19:dd:ddc:c00a:f00a:c00a:dc81:0/1122c19:dd:ddc:c00a:f00a:c00a:dc81:ffff
1312c19:dd:ddc:c00a:f00a:c00a:dc82:0/1122c19:dd:ddc:c00a:f00a:c00a:dc82:ffff
1322c19:dd:ddc:c00a:f00a:c00a:dc83:0/1122c19:dd:ddc:c00a:f00a:c00a:dc83:ffff
1332c19:dd:ddc:c00a:f00a:c00a:dc84:0/1122c19:dd:ddc:c00a:f00a:c00a:dc84:ffff
1342c19:dd:ddc:c00a:f00a:c00a:dc85:0/1122c19:dd:ddc:c00a:f00a:c00a:dc85:ffff
1352c19:dd:ddc:c00a:f00a:c00a:dc86:0/1122c19:dd:ddc:c00a:f00a:c00a:dc86:ffff
1362c19:dd:ddc:c00a:f00a:c00a:dc87:0/1122c19:dd:ddc:c00a:f00a:c00a:dc87:ffff
1372c19:dd:ddc:c00a:f00a:c00a:dc88:0/1122c19:dd:ddc:c00a:f00a:c00a:dc88:ffff
1382c19:dd:ddc:c00a:f00a:c00a:dc89:0/1122c19:dd:ddc:c00a:f00a:c00a:dc89:ffff
1392c19:dd:ddc:c00a:f00a:c00a:dc8a:0/1122c19:dd:ddc:c00a:f00a:c00a:dc8a:ffff
1402c19:dd:ddc:c00a:f00a:c00a:dc8b:0/1122c19:dd:ddc:c00a:f00a:c00a:dc8b:ffff
1412c19:dd:ddc:c00a:f00a:c00a:dc8c:0/1122c19:dd:ddc:c00a:f00a:c00a:dc8c:ffff
1422c19:dd:ddc:c00a:f00a:c00a:dc8d:0/1122c19:dd:ddc:c00a:f00a:c00a:dc8d:ffff
1432c19:dd:ddc:c00a:f00a:c00a:dc8e:0/1122c19:dd:ddc:c00a:f00a:c00a:dc8e:ffff
1442c19:dd:ddc:c00a:f00a:c00a:dc8f:0/1122c19:dd:ddc:c00a:f00a:c00a:dc8f:ffff
1452c19:dd:ddc:c00a:f00a:c00a:dc90:0/1122c19:dd:ddc:c00a:f00a:c00a:dc90:ffff
1462c19:dd:ddc:c00a:f00a:c00a:dc91:0/1122c19:dd:ddc:c00a:f00a:c00a:dc91:ffff
1472c19:dd:ddc:c00a:f00a:c00a:dc92:0/1122c19:dd:ddc:c00a:f00a:c00a:dc92:ffff
1482c19:dd:ddc:c00a:f00a:c00a:dc93:0/1122c19:dd:ddc:c00a:f00a:c00a:dc93:ffff
1492c19:dd:ddc:c00a:f00a:c00a:dc94:0/1122c19:dd:ddc:c00a:f00a:c00a:dc94:ffff
1502c19:dd:ddc:c00a:f00a:c00a:dc95:0/1122c19:dd:ddc:c00a:f00a:c00a:dc95:ffff
1512c19:dd:ddc:c00a:f00a:c00a:dc96:0/1122c19:dd:ddc:c00a:f00a:c00a:dc96:ffff
1522c19:dd:ddc:c00a:f00a:c00a:dc97:0/1122c19:dd:ddc:c00a:f00a:c00a:dc97:ffff
1532c19:dd:ddc:c00a:f00a:c00a:dc98:0/1122c19:dd:ddc:c00a:f00a:c00a:dc98:ffff
1542c19:dd:ddc:c00a:f00a:c00a:dc99:0/1122c19:dd:ddc:c00a:f00a:c00a:dc99:ffff
1552c19:dd:ddc:c00a:f00a:c00a:dc9a:0/1122c19:dd:ddc:c00a:f00a:c00a:dc9a:ffff
1562c19:dd:ddc:c00a:f00a:c00a:dc9b:0/1122c19:dd:ddc:c00a:f00a:c00a:dc9b:ffff
1572c19:dd:ddc:c00a:f00a:c00a:dc9c:0/1122c19:dd:ddc:c00a:f00a:c00a:dc9c:ffff
1582c19:dd:ddc:c00a:f00a:c00a:dc9d:0/1122c19:dd:ddc:c00a:f00a:c00a:dc9d:ffff
1592c19:dd:ddc:c00a:f00a:c00a:dc9e:0/1122c19:dd:ddc:c00a:f00a:c00a:dc9e:ffff
1602c19:dd:ddc:c00a:f00a:c00a:dc9f:0/1122c19:dd:ddc:c00a:f00a:c00a:dc9f:ffff
1612c19:dd:ddc:c00a:f00a:c00a:dca0:0/1122c19:dd:ddc:c00a:f00a:c00a:dca0:ffff
1622c19:dd:ddc:c00a:f00a:c00a:dca1:0/1122c19:dd:ddc:c00a:f00a:c00a:dca1:ffff
1632c19:dd:ddc:c00a:f00a:c00a:dca2:0/1122c19:dd:ddc:c00a:f00a:c00a:dca2:ffff
1642c19:dd:ddc:c00a:f00a:c00a:dca3:0/1122c19:dd:ddc:c00a:f00a:c00a:dca3:ffff
1652c19:dd:ddc:c00a:f00a:c00a:dca4:0/1122c19:dd:ddc:c00a:f00a:c00a:dca4:ffff
1662c19:dd:ddc:c00a:f00a:c00a:dca5:0/1122c19:dd:ddc:c00a:f00a:c00a:dca5:ffff
1672c19:dd:ddc:c00a:f00a:c00a:dca6:0/1122c19:dd:ddc:c00a:f00a:c00a:dca6:ffff
1682c19:dd:ddc:c00a:f00a:c00a:dca7:0/1122c19:dd:ddc:c00a:f00a:c00a:dca7:ffff
1692c19:dd:ddc:c00a:f00a:c00a:dca8:0/1122c19:dd:ddc:c00a:f00a:c00a:dca8:ffff
1702c19:dd:ddc:c00a:f00a:c00a:dca9:0/1122c19:dd:ddc:c00a:f00a:c00a:dca9:ffff
1712c19:dd:ddc:c00a:f00a:c00a:dcaa:0/1122c19:dd:ddc:c00a:f00a:c00a:dcaa:ffff
1722c19:dd:ddc:c00a:f00a:c00a:dcab:0/1122c19:dd:ddc:c00a:f00a:c00a:dcab:ffff
1732c19:dd:ddc:c00a:f00a:c00a:dcac:0/1122c19:dd:ddc:c00a:f00a:c00a:dcac:ffff
1742c19:dd:ddc:c00a:f00a:c00a:dcad:0/1122c19:dd:ddc:c00a:f00a:c00a:dcad:ffff
1752c19:dd:ddc:c00a:f00a:c00a:dcae:0/1122c19:dd:ddc:c00a:f00a:c00a:dcae:ffff
1762c19:dd:ddc:c00a:f00a:c00a:dcaf:0/1122c19:dd:ddc:c00a:f00a:c00a:dcaf:ffff
1772c19:dd:ddc:c00a:f00a:c00a:dcb0:0/1122c19:dd:ddc:c00a:f00a:c00a:dcb0:ffff
1782c19:dd:ddc:c00a:f00a:c00a:dcb1:0/1122c19:dd:ddc:c00a:f00a:c00a:dcb1:ffff
1792c19:dd:ddc:c00a:f00a:c00a:dcb2:0/1122c19:dd:ddc:c00a:f00a:c00a:dcb2:ffff
1802c19:dd:ddc:c00a:f00a:c00a:dcb3:0/1122c19:dd:ddc:c00a:f00a:c00a:dcb3:ffff
1812c19:dd:ddc:c00a:f00a:c00a:dcb4:0/1122c19:dd:ddc:c00a:f00a:c00a:dcb4:ffff
1822c19:dd:ddc:c00a:f00a:c00a:dcb5:0/1122c19:dd:ddc:c00a:f00a:c00a:dcb5:ffff
1832c19:dd:ddc:c00a:f00a:c00a:dcb6:0/1122c19:dd:ddc:c00a:f00a:c00a:dcb6:ffff
1842c19:dd:ddc:c00a:f00a:c00a:dcb7:0/1122c19:dd:ddc:c00a:f00a:c00a:dcb7:ffff
1852c19:dd:ddc:c00a:f00a:c00a:dcb8:0/1122c19:dd:ddc:c00a:f00a:c00a:dcb8:ffff
1862c19:dd:ddc:c00a:f00a:c00a:dcb9:0/1122c19:dd:ddc:c00a:f00a:c00a:dcb9:ffff
1872c19:dd:ddc:c00a:f00a:c00a:dcba:0/1122c19:dd:ddc:c00a:f00a:c00a:dcba:ffff
1882c19:dd:ddc:c00a:f00a:c00a:dcbb:0/1122c19:dd:ddc:c00a:f00a:c00a:dcbb:ffff
1892c19:dd:ddc:c00a:f00a:c00a:dcbc:0/1122c19:dd:ddc:c00a:f00a:c00a:dcbc:ffff
1902c19:dd:ddc:c00a:f00a:c00a:dcbd:0/1122c19:dd:ddc:c00a:f00a:c00a:dcbd:ffff
1912c19:dd:ddc:c00a:f00a:c00a:dcbe:0/1122c19:dd:ddc:c00a:f00a:c00a:dcbe:ffff
1922c19:dd:ddc:c00a:f00a:c00a:dcbf:0/1122c19:dd:ddc:c00a:f00a:c00a:dcbf:ffff
1932c19:dd:ddc:c00a:f00a:c00a:dcc0:0/1122c19:dd:ddc:c00a:f00a:c00a:dcc0:ffff
1942c19:dd:ddc:c00a:f00a:c00a:dcc1:0/1122c19:dd:ddc:c00a:f00a:c00a:dcc1:ffff
1952c19:dd:ddc:c00a:f00a:c00a:dcc2:0/1122c19:dd:ddc:c00a:f00a:c00a:dcc2:ffff
1962c19:dd:ddc:c00a:f00a:c00a:dcc3:0/1122c19:dd:ddc:c00a:f00a:c00a:dcc3:ffff
1972c19:dd:ddc:c00a:f00a:c00a:dcc4:0/1122c19:dd:ddc:c00a:f00a:c00a:dcc4:ffff
1982c19:dd:ddc:c00a:f00a:c00a:dcc5:0/1122c19:dd:ddc:c00a:f00a:c00a:dcc5:ffff
1992c19:dd:ddc:c00a:f00a:c00a:dcc6:0/1122c19:dd:ddc:c00a:f00a:c00a:dcc6:ffff
2002c19:dd:ddc:c00a:f00a:c00a:dcc7:0/1122c19:dd:ddc:c00a:f00a:c00a:dcc7:ffff
2012c19:dd:ddc:c00a:f00a:c00a:dcc8:0/1122c19:dd:ddc:c00a:f00a:c00a:dcc8:ffff
2022c19:dd:ddc:c00a:f00a:c00a:dcc9:0/1122c19:dd:ddc:c00a:f00a:c00a:dcc9:ffff
2032c19:dd:ddc:c00a:f00a:c00a:dcca:0/1122c19:dd:ddc:c00a:f00a:c00a:dcca:ffff
2042c19:dd:ddc:c00a:f00a:c00a:dccb:0/1122c19:dd:ddc:c00a:f00a:c00a:dccb:ffff
2052c19:dd:ddc:c00a:f00a:c00a:dccc:0/1122c19:dd:ddc:c00a:f00a:c00a:dccc:ffff
2062c19:dd:ddc:c00a:f00a:c00a:dccd:0/1122c19:dd:ddc:c00a:f00a:c00a:dccd:ffff
2072c19:dd:ddc:c00a:f00a:c00a:dcce:0/1122c19:dd:ddc:c00a:f00a:c00a:dcce:ffff
2082c19:dd:ddc:c00a:f00a:c00a:dccf:0/1122c19:dd:ddc:c00a:f00a:c00a:dccf:ffff
2092c19:dd:ddc:c00a:f00a:c00a:dcd0:0/1122c19:dd:ddc:c00a:f00a:c00a:dcd0:ffff
2102c19:dd:ddc:c00a:f00a:c00a:dcd1:0/1122c19:dd:ddc:c00a:f00a:c00a:dcd1:ffff
2112c19:dd:ddc:c00a:f00a:c00a:dcd2:0/1122c19:dd:ddc:c00a:f00a:c00a:dcd2:ffff
2122c19:dd:ddc:c00a:f00a:c00a:dcd3:0/1122c19:dd:ddc:c00a:f00a:c00a:dcd3:ffff
2132c19:dd:ddc:c00a:f00a:c00a:dcd4:0/1122c19:dd:ddc:c00a:f00a:c00a:dcd4:ffff
2142c19:dd:ddc:c00a:f00a:c00a:dcd5:0/1122c19:dd:ddc:c00a:f00a:c00a:dcd5:ffff
2152c19:dd:ddc:c00a:f00a:c00a:dcd6:0/1122c19:dd:ddc:c00a:f00a:c00a:dcd6:ffff
2162c19:dd:ddc:c00a:f00a:c00a:dcd7:0/1122c19:dd:ddc:c00a:f00a:c00a:dcd7:ffff
2172c19:dd:ddc:c00a:f00a:c00a:dcd8:0/1122c19:dd:ddc:c00a:f00a:c00a:dcd8:ffff
2182c19:dd:ddc:c00a:f00a:c00a:dcd9:0/1122c19:dd:ddc:c00a:f00a:c00a:dcd9:ffff
2192c19:dd:ddc:c00a:f00a:c00a:dcda:0/1122c19:dd:ddc:c00a:f00a:c00a:dcda:ffff
2202c19:dd:ddc:c00a:f00a:c00a:dcdb:0/1122c19:dd:ddc:c00a:f00a:c00a:dcdb:ffff
2212c19:dd:ddc:c00a:f00a:c00a:dcdc:0/1122c19:dd:ddc:c00a:f00a:c00a:dcdc:ffff
2222c19:dd:ddc:c00a:f00a:c00a:dcdd:0/1122c19:dd:ddc:c00a:f00a:c00a:dcdd:ffff
2232c19:dd:ddc:c00a:f00a:c00a:dcde:0/1122c19:dd:ddc:c00a:f00a:c00a:dcde:ffff
2242c19:dd:ddc:c00a:f00a:c00a:dcdf:0/1122c19:dd:ddc:c00a:f00a:c00a:dcdf:ffff
2252c19:dd:ddc:c00a:f00a:c00a:dce0:0/1122c19:dd:ddc:c00a:f00a:c00a:dce0:ffff
2262c19:dd:ddc:c00a:f00a:c00a:dce1:0/1122c19:dd:ddc:c00a:f00a:c00a:dce1:ffff
2272c19:dd:ddc:c00a:f00a:c00a:dce2:0/1122c19:dd:ddc:c00a:f00a:c00a:dce2:ffff
2282c19:dd:ddc:c00a:f00a:c00a:dce3:0/1122c19:dd:ddc:c00a:f00a:c00a:dce3:ffff
2292c19:dd:ddc:c00a:f00a:c00a:dce4:0/1122c19:dd:ddc:c00a:f00a:c00a:dce4:ffff
2302c19:dd:ddc:c00a:f00a:c00a:dce5:0/1122c19:dd:ddc:c00a:f00a:c00a:dce5:ffff
2312c19:dd:ddc:c00a:f00a:c00a:dce6:0/1122c19:dd:ddc:c00a:f00a:c00a:dce6:ffff
2322c19:dd:ddc:c00a:f00a:c00a:dce7:0/1122c19:dd:ddc:c00a:f00a:c00a:dce7:ffff
2332c19:dd:ddc:c00a:f00a:c00a:dce8:0/1122c19:dd:ddc:c00a:f00a:c00a:dce8:ffff
2342c19:dd:ddc:c00a:f00a:c00a:dce9:0/1122c19:dd:ddc:c00a:f00a:c00a:dce9:ffff
2352c19:dd:ddc:c00a:f00a:c00a:dcea:0/1122c19:dd:ddc:c00a:f00a:c00a:dcea:ffff
2362c19:dd:ddc:c00a:f00a:c00a:dceb:0/1122c19:dd:ddc:c00a:f00a:c00a:dceb:ffff
2372c19:dd:ddc:c00a:f00a:c00a:dcec:0/1122c19:dd:ddc:c00a:f00a:c00a:dcec:ffff
2382c19:dd:ddc:c00a:f00a:c00a:dced:0/1122c19:dd:ddc:c00a:f00a:c00a:dced:ffff
2392c19:dd:ddc:c00a:f00a:c00a:dcee:0/1122c19:dd:ddc:c00a:f00a:c00a:dcee:ffff
2402c19:dd:ddc:c00a:f00a:c00a:dcef:0/1122c19:dd:ddc:c00a:f00a:c00a:dcef:ffff
2412c19:dd:ddc:c00a:f00a:c00a:dcf0:0/1122c19:dd:ddc:c00a:f00a:c00a:dcf0:ffff
2422c19:dd:ddc:c00a:f00a:c00a:dcf1:0/1122c19:dd:ddc:c00a:f00a:c00a:dcf1:ffff
2432c19:dd:ddc:c00a:f00a:c00a:dcf2:0/1122c19:dd:ddc:c00a:f00a:c00a:dcf2:ffff
2442c19:dd:ddc:c00a:f00a:c00a:dcf3:0/1122c19:dd:ddc:c00a:f00a:c00a:dcf3:ffff
2452c19:dd:ddc:c00a:f00a:c00a:dcf4:0/1122c19:dd:ddc:c00a:f00a:c00a:dcf4:ffff
2462c19:dd:ddc:c00a:f00a:c00a:dcf5:0/1122c19:dd:ddc:c00a:f00a:c00a:dcf5:ffff
2472c19:dd:ddc:c00a:f00a:c00a:dcf6:0/1122c19:dd:ddc:c00a:f00a:c00a:dcf6:ffff
2482c19:dd:ddc:c00a:f00a:c00a:dcf7:0/1122c19:dd:ddc:c00a:f00a:c00a:dcf7:ffff
2492c19:dd:ddc:c00a:f00a:c00a:dcf8:0/1122c19:dd:ddc:c00a:f00a:c00a:dcf8:ffff
2502c19:dd:ddc:c00a:f00a:c00a:dcf9:0/1122c19:dd:ddc:c00a:f00a:c00a:dcf9:ffff
2512c19:dd:ddc:c00a:f00a:c00a:dcfa:0/1122c19:dd:ddc:c00a:f00a:c00a:dcfa:ffff
2522c19:dd:ddc:c00a:f00a:c00a:dcfb:0/1122c19:dd:ddc:c00a:f00a:c00a:dcfb:ffff
2532c19:dd:ddc:c00a:f00a:c00a:dcfc:0/1122c19:dd:ddc:c00a:f00a:c00a:dcfc:ffff
2542c19:dd:ddc:c00a:f00a:c00a:dcfd:0/1122c19:dd:ddc:c00a:f00a:c00a:dcfd:ffff
2552c19:dd:ddc:c00a:f00a:c00a:dcfe:0/1122c19:dd:ddc:c00a:f00a:c00a:dcfe:ffff
2562c19:dd:ddc:c00a:f00a:c00a:dcff:0/1122c19:dd:ddc:c00a:f00a:c00a:dcff: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.