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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.

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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.

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Remote supportLet a Surftec engineer connect to your computer to help you.All workingA full-screen confirmation that everything is up and running.

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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/25
Addresses2^103
/64 networks2^39
Network
ffcf:ec00::/25
First address
ffcf:ec00::
Last address
ffcf: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
ffcf:ec00:0000:0000:0000:0000:0000:0000
Type
Multicast ff00::/8
One-to-many traffic; replaces broadcast
Reverse DNS zones
0.c.e.f.c.f.f.ip6.arpa
1.c.e.f.c.f.f.ip6.arpa
2.c.e.f.c.f.f.ip6.arpa
3.c.e.f.c.f.f.ip6.arpa
4.c.e.f.c.f.f.ip6.arpa
5.c.e.f.c.f.f.ip6.arpa
6.c.e.f.c.f.f.ip6.arpa
7.c.e.f.c.f.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)

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

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