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/25
Addresses2^103
/64 networks2^39
Network
fc7d:ec00::/25
First address
fc7d:ec00::
Last address
fc7d:ec7f:ffff:ffff:ffff:ffff:ffff:ffff
Addresses
10,141,204,801,825,835,211,973,625,643,008 (2^103)
/64 networks (LANs)
549,755,813,888 (2^39)
Full form
fc7d:ec00:0000:0000:0000:0000:0000:0000
Type
Unique local (ULA) fc00::/7
Private IPv6, like RFC 1918; usually fd00::/8
Reverse DNS zones
0.c.e.d.7.c.f.ip6.arpa
1.c.e.d.7.c.f.ip6.arpa
2.c.e.d.7.c.f.ip6.arpa
3.c.e.d.7.c.f.ip6.arpa
4.c.e.d.7.c.f.ip6.arpa
5.c.e.d.7.c.f.ip6.arpa
6.c.e.d.7.c.f.ip6.arpa
7.c.e.d.7.c.f.ip6.arpa
/25 is not on a 4-bit boundary, so it takes 8 /28 zones.
Split into smaller subnets/32
/26 (2)/27 (4)/28 (8)/29 (16)/32 (128)/36 (2,048)/40 (32,768)

fc7d:ec00::/25 makes 128 subnets of /32.

Subnets
#SubnetLast address
1fc7d:ec00::/32fc7d:ec00:ffff:ffff:ffff:ffff:ffff:ffff
2fc7d:ec01::/32fc7d:ec01:ffff:ffff:ffff:ffff:ffff:ffff
3fc7d:ec02::/32fc7d:ec02:ffff:ffff:ffff:ffff:ffff:ffff
4fc7d:ec03::/32fc7d:ec03:ffff:ffff:ffff:ffff:ffff:ffff
5fc7d:ec04::/32fc7d:ec04:ffff:ffff:ffff:ffff:ffff:ffff
6fc7d:ec05::/32fc7d:ec05:ffff:ffff:ffff:ffff:ffff:ffff
7fc7d:ec06::/32fc7d:ec06:ffff:ffff:ffff:ffff:ffff:ffff
8fc7d:ec07::/32fc7d:ec07:ffff:ffff:ffff:ffff:ffff:ffff
9fc7d:ec08::/32fc7d:ec08:ffff:ffff:ffff:ffff:ffff:ffff
10fc7d:ec09::/32fc7d:ec09:ffff:ffff:ffff:ffff:ffff:ffff
11fc7d:ec0a::/32fc7d:ec0a:ffff:ffff:ffff:ffff:ffff:ffff
12fc7d:ec0b::/32fc7d:ec0b:ffff:ffff:ffff:ffff:ffff:ffff
13fc7d:ec0c::/32fc7d:ec0c:ffff:ffff:ffff:ffff:ffff:ffff
14fc7d:ec0d::/32fc7d:ec0d:ffff:ffff:ffff:ffff:ffff:ffff
15fc7d:ec0e::/32fc7d:ec0e:ffff:ffff:ffff:ffff:ffff:ffff
16fc7d:ec0f::/32fc7d:ec0f:ffff:ffff:ffff:ffff:ffff:ffff
17fc7d:ec10::/32fc7d:ec10:ffff:ffff:ffff:ffff:ffff:ffff
18fc7d:ec11::/32fc7d:ec11:ffff:ffff:ffff:ffff:ffff:ffff
19fc7d:ec12::/32fc7d:ec12:ffff:ffff:ffff:ffff:ffff:ffff
20fc7d:ec13::/32fc7d:ec13:ffff:ffff:ffff:ffff:ffff:ffff
21fc7d:ec14::/32fc7d:ec14:ffff:ffff:ffff:ffff:ffff:ffff
22fc7d:ec15::/32fc7d:ec15:ffff:ffff:ffff:ffff:ffff:ffff
23fc7d:ec16::/32fc7d:ec16:ffff:ffff:ffff:ffff:ffff:ffff
24fc7d:ec17::/32fc7d:ec17:ffff:ffff:ffff:ffff:ffff:ffff
25fc7d:ec18::/32fc7d:ec18:ffff:ffff:ffff:ffff:ffff:ffff
26fc7d:ec19::/32fc7d:ec19:ffff:ffff:ffff:ffff:ffff:ffff
27fc7d:ec1a::/32fc7d:ec1a:ffff:ffff:ffff:ffff:ffff:ffff
28fc7d:ec1b::/32fc7d:ec1b:ffff:ffff:ffff:ffff:ffff:ffff
29fc7d:ec1c::/32fc7d:ec1c:ffff:ffff:ffff:ffff:ffff:ffff
30fc7d:ec1d::/32fc7d:ec1d:ffff:ffff:ffff:ffff:ffff:ffff
31fc7d:ec1e::/32fc7d:ec1e:ffff:ffff:ffff:ffff:ffff:ffff
32fc7d:ec1f::/32fc7d:ec1f:ffff:ffff:ffff:ffff:ffff:ffff
33fc7d:ec20::/32fc7d:ec20:ffff:ffff:ffff:ffff:ffff:ffff
34fc7d:ec21::/32fc7d:ec21:ffff:ffff:ffff:ffff:ffff:ffff
35fc7d:ec22::/32fc7d:ec22:ffff:ffff:ffff:ffff:ffff:ffff
36fc7d:ec23::/32fc7d:ec23:ffff:ffff:ffff:ffff:ffff:ffff
37fc7d:ec24::/32fc7d:ec24:ffff:ffff:ffff:ffff:ffff:ffff
38fc7d:ec25::/32fc7d:ec25:ffff:ffff:ffff:ffff:ffff:ffff
39fc7d:ec26::/32fc7d:ec26:ffff:ffff:ffff:ffff:ffff:ffff
40fc7d:ec27::/32fc7d:ec27:ffff:ffff:ffff:ffff:ffff:ffff
41fc7d:ec28::/32fc7d:ec28:ffff:ffff:ffff:ffff:ffff:ffff
42fc7d:ec29::/32fc7d:ec29:ffff:ffff:ffff:ffff:ffff:ffff
43fc7d:ec2a::/32fc7d:ec2a:ffff:ffff:ffff:ffff:ffff:ffff
44fc7d:ec2b::/32fc7d:ec2b:ffff:ffff:ffff:ffff:ffff:ffff
45fc7d:ec2c::/32fc7d:ec2c:ffff:ffff:ffff:ffff:ffff:ffff
46fc7d:ec2d::/32fc7d:ec2d:ffff:ffff:ffff:ffff:ffff:ffff
47fc7d:ec2e::/32fc7d:ec2e:ffff:ffff:ffff:ffff:ffff:ffff
48fc7d:ec2f::/32fc7d:ec2f:ffff:ffff:ffff:ffff:ffff:ffff
49fc7d:ec30::/32fc7d:ec30:ffff:ffff:ffff:ffff:ffff:ffff
50fc7d:ec31::/32fc7d:ec31:ffff:ffff:ffff:ffff:ffff:ffff
51fc7d:ec32::/32fc7d:ec32:ffff:ffff:ffff:ffff:ffff:ffff
52fc7d:ec33::/32fc7d:ec33:ffff:ffff:ffff:ffff:ffff:ffff
53fc7d:ec34::/32fc7d:ec34:ffff:ffff:ffff:ffff:ffff:ffff
54fc7d:ec35::/32fc7d:ec35:ffff:ffff:ffff:ffff:ffff:ffff
55fc7d:ec36::/32fc7d:ec36:ffff:ffff:ffff:ffff:ffff:ffff
56fc7d:ec37::/32fc7d:ec37:ffff:ffff:ffff:ffff:ffff:ffff
57fc7d:ec38::/32fc7d:ec38:ffff:ffff:ffff:ffff:ffff:ffff
58fc7d:ec39::/32fc7d:ec39:ffff:ffff:ffff:ffff:ffff:ffff
59fc7d:ec3a::/32fc7d:ec3a:ffff:ffff:ffff:ffff:ffff:ffff
60fc7d:ec3b::/32fc7d:ec3b:ffff:ffff:ffff:ffff:ffff:ffff
61fc7d:ec3c::/32fc7d:ec3c:ffff:ffff:ffff:ffff:ffff:ffff
62fc7d:ec3d::/32fc7d:ec3d:ffff:ffff:ffff:ffff:ffff:ffff
63fc7d:ec3e::/32fc7d:ec3e:ffff:ffff:ffff:ffff:ffff:ffff
64fc7d:ec3f::/32fc7d:ec3f:ffff:ffff:ffff:ffff:ffff:ffff
65fc7d:ec40::/32fc7d:ec40:ffff:ffff:ffff:ffff:ffff:ffff
66fc7d:ec41::/32fc7d:ec41:ffff:ffff:ffff:ffff:ffff:ffff
67fc7d:ec42::/32fc7d:ec42:ffff:ffff:ffff:ffff:ffff:ffff
68fc7d:ec43::/32fc7d:ec43:ffff:ffff:ffff:ffff:ffff:ffff
69fc7d:ec44::/32fc7d:ec44:ffff:ffff:ffff:ffff:ffff:ffff
70fc7d:ec45::/32fc7d:ec45:ffff:ffff:ffff:ffff:ffff:ffff
71fc7d:ec46::/32fc7d:ec46:ffff:ffff:ffff:ffff:ffff:ffff
72fc7d:ec47::/32fc7d:ec47:ffff:ffff:ffff:ffff:ffff:ffff
73fc7d:ec48::/32fc7d:ec48:ffff:ffff:ffff:ffff:ffff:ffff
74fc7d:ec49::/32fc7d:ec49:ffff:ffff:ffff:ffff:ffff:ffff
75fc7d:ec4a::/32fc7d:ec4a:ffff:ffff:ffff:ffff:ffff:ffff
76fc7d:ec4b::/32fc7d:ec4b:ffff:ffff:ffff:ffff:ffff:ffff
77fc7d:ec4c::/32fc7d:ec4c:ffff:ffff:ffff:ffff:ffff:ffff
78fc7d:ec4d::/32fc7d:ec4d:ffff:ffff:ffff:ffff:ffff:ffff
79fc7d:ec4e::/32fc7d:ec4e:ffff:ffff:ffff:ffff:ffff:ffff
80fc7d:ec4f::/32fc7d:ec4f:ffff:ffff:ffff:ffff:ffff:ffff
81fc7d:ec50::/32fc7d:ec50:ffff:ffff:ffff:ffff:ffff:ffff
82fc7d:ec51::/32fc7d:ec51:ffff:ffff:ffff:ffff:ffff:ffff
83fc7d:ec52::/32fc7d:ec52:ffff:ffff:ffff:ffff:ffff:ffff
84fc7d:ec53::/32fc7d:ec53:ffff:ffff:ffff:ffff:ffff:ffff
85fc7d:ec54::/32fc7d:ec54:ffff:ffff:ffff:ffff:ffff:ffff
86fc7d:ec55::/32fc7d:ec55:ffff:ffff:ffff:ffff:ffff:ffff
87fc7d:ec56::/32fc7d:ec56:ffff:ffff:ffff:ffff:ffff:ffff
88fc7d:ec57::/32fc7d:ec57:ffff:ffff:ffff:ffff:ffff:ffff
89fc7d:ec58::/32fc7d:ec58:ffff:ffff:ffff:ffff:ffff:ffff
90fc7d:ec59::/32fc7d:ec59:ffff:ffff:ffff:ffff:ffff:ffff
91fc7d:ec5a::/32fc7d:ec5a:ffff:ffff:ffff:ffff:ffff:ffff
92fc7d:ec5b::/32fc7d:ec5b:ffff:ffff:ffff:ffff:ffff:ffff
93fc7d:ec5c::/32fc7d:ec5c:ffff:ffff:ffff:ffff:ffff:ffff
94fc7d:ec5d::/32fc7d:ec5d:ffff:ffff:ffff:ffff:ffff:ffff
95fc7d:ec5e::/32fc7d:ec5e:ffff:ffff:ffff:ffff:ffff:ffff
96fc7d:ec5f::/32fc7d:ec5f:ffff:ffff:ffff:ffff:ffff:ffff
97fc7d:ec60::/32fc7d:ec60:ffff:ffff:ffff:ffff:ffff:ffff
98fc7d:ec61::/32fc7d:ec61:ffff:ffff:ffff:ffff:ffff:ffff
99fc7d:ec62::/32fc7d:ec62:ffff:ffff:ffff:ffff:ffff:ffff
100fc7d:ec63::/32fc7d:ec63:ffff:ffff:ffff:ffff:ffff:ffff
101fc7d:ec64::/32fc7d:ec64:ffff:ffff:ffff:ffff:ffff:ffff
102fc7d:ec65::/32fc7d:ec65:ffff:ffff:ffff:ffff:ffff:ffff
103fc7d:ec66::/32fc7d:ec66:ffff:ffff:ffff:ffff:ffff:ffff
104fc7d:ec67::/32fc7d:ec67:ffff:ffff:ffff:ffff:ffff:ffff
105fc7d:ec68::/32fc7d:ec68:ffff:ffff:ffff:ffff:ffff:ffff
106fc7d:ec69::/32fc7d:ec69:ffff:ffff:ffff:ffff:ffff:ffff
107fc7d:ec6a::/32fc7d:ec6a:ffff:ffff:ffff:ffff:ffff:ffff
108fc7d:ec6b::/32fc7d:ec6b:ffff:ffff:ffff:ffff:ffff:ffff
109fc7d:ec6c::/32fc7d:ec6c:ffff:ffff:ffff:ffff:ffff:ffff
110fc7d:ec6d::/32fc7d:ec6d:ffff:ffff:ffff:ffff:ffff:ffff
111fc7d:ec6e::/32fc7d:ec6e:ffff:ffff:ffff:ffff:ffff:ffff
112fc7d:ec6f::/32fc7d:ec6f:ffff:ffff:ffff:ffff:ffff:ffff
113fc7d:ec70::/32fc7d:ec70:ffff:ffff:ffff:ffff:ffff:ffff
114fc7d:ec71::/32fc7d:ec71:ffff:ffff:ffff:ffff:ffff:ffff
115fc7d:ec72::/32fc7d:ec72:ffff:ffff:ffff:ffff:ffff:ffff
116fc7d:ec73::/32fc7d:ec73:ffff:ffff:ffff:ffff:ffff:ffff
117fc7d:ec74::/32fc7d:ec74:ffff:ffff:ffff:ffff:ffff:ffff
118fc7d:ec75::/32fc7d:ec75:ffff:ffff:ffff:ffff:ffff:ffff
119fc7d:ec76::/32fc7d:ec76:ffff:ffff:ffff:ffff:ffff:ffff
120fc7d:ec77::/32fc7d:ec77:ffff:ffff:ffff:ffff:ffff:ffff
121fc7d:ec78::/32fc7d:ec78:ffff:ffff:ffff:ffff:ffff:ffff
122fc7d:ec79::/32fc7d:ec79:ffff:ffff:ffff:ffff:ffff:ffff
123fc7d:ec7a::/32fc7d:ec7a:ffff:ffff:ffff:ffff:ffff:ffff
124fc7d:ec7b::/32fc7d:ec7b:ffff:ffff:ffff:ffff:ffff:ffff
125fc7d:ec7c::/32fc7d:ec7c:ffff:ffff:ffff:ffff:ffff:ffff
126fc7d:ec7d::/32fc7d:ec7d:ffff:ffff:ffff:ffff:ffff:ffff
127fc7d:ec7e::/32fc7d:ec7e:ffff:ffff:ffff:ffff:ffff:ffff
128fc7d:ec7f::/32fc7d:ec7f: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.