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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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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
fc4e:dd80::/25
First address
fc4e:dd80::
Last address
fc4e:ddff: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
fc4e:dd80:0000:0000:0000:0000:0000:0000
Type
Unique local (ULA) fc00::/7
Private IPv6, like RFC 1918; usually fd00::/8
Reverse DNS zones
8.d.d.e.4.c.f.ip6.arpa
9.d.d.e.4.c.f.ip6.arpa
a.d.d.e.4.c.f.ip6.arpa
b.d.d.e.4.c.f.ip6.arpa
c.d.d.e.4.c.f.ip6.arpa
d.d.d.e.4.c.f.ip6.arpa
e.d.d.e.4.c.f.ip6.arpa
f.d.d.e.4.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)

fc4e:dd80::/25 makes 128 subnets of /32.

Subnets
#SubnetLast address
1fc4e:dd80::/32fc4e:dd80:ffff:ffff:ffff:ffff:ffff:ffff
2fc4e:dd81::/32fc4e:dd81:ffff:ffff:ffff:ffff:ffff:ffff
3fc4e:dd82::/32fc4e:dd82:ffff:ffff:ffff:ffff:ffff:ffff
4fc4e:dd83::/32fc4e:dd83:ffff:ffff:ffff:ffff:ffff:ffff
5fc4e:dd84::/32fc4e:dd84:ffff:ffff:ffff:ffff:ffff:ffff
6fc4e:dd85::/32fc4e:dd85:ffff:ffff:ffff:ffff:ffff:ffff
7fc4e:dd86::/32fc4e:dd86:ffff:ffff:ffff:ffff:ffff:ffff
8fc4e:dd87::/32fc4e:dd87:ffff:ffff:ffff:ffff:ffff:ffff
9fc4e:dd88::/32fc4e:dd88:ffff:ffff:ffff:ffff:ffff:ffff
10fc4e:dd89::/32fc4e:dd89:ffff:ffff:ffff:ffff:ffff:ffff
11fc4e:dd8a::/32fc4e:dd8a:ffff:ffff:ffff:ffff:ffff:ffff
12fc4e:dd8b::/32fc4e:dd8b:ffff:ffff:ffff:ffff:ffff:ffff
13fc4e:dd8c::/32fc4e:dd8c:ffff:ffff:ffff:ffff:ffff:ffff
14fc4e:dd8d::/32fc4e:dd8d:ffff:ffff:ffff:ffff:ffff:ffff
15fc4e:dd8e::/32fc4e:dd8e:ffff:ffff:ffff:ffff:ffff:ffff
16fc4e:dd8f::/32fc4e:dd8f:ffff:ffff:ffff:ffff:ffff:ffff
17fc4e:dd90::/32fc4e:dd90:ffff:ffff:ffff:ffff:ffff:ffff
18fc4e:dd91::/32fc4e:dd91:ffff:ffff:ffff:ffff:ffff:ffff
19fc4e:dd92::/32fc4e:dd92:ffff:ffff:ffff:ffff:ffff:ffff
20fc4e:dd93::/32fc4e:dd93:ffff:ffff:ffff:ffff:ffff:ffff
21fc4e:dd94::/32fc4e:dd94:ffff:ffff:ffff:ffff:ffff:ffff
22fc4e:dd95::/32fc4e:dd95:ffff:ffff:ffff:ffff:ffff:ffff
23fc4e:dd96::/32fc4e:dd96:ffff:ffff:ffff:ffff:ffff:ffff
24fc4e:dd97::/32fc4e:dd97:ffff:ffff:ffff:ffff:ffff:ffff
25fc4e:dd98::/32fc4e:dd98:ffff:ffff:ffff:ffff:ffff:ffff
26fc4e:dd99::/32fc4e:dd99:ffff:ffff:ffff:ffff:ffff:ffff
27fc4e:dd9a::/32fc4e:dd9a:ffff:ffff:ffff:ffff:ffff:ffff
28fc4e:dd9b::/32fc4e:dd9b:ffff:ffff:ffff:ffff:ffff:ffff
29fc4e:dd9c::/32fc4e:dd9c:ffff:ffff:ffff:ffff:ffff:ffff
30fc4e:dd9d::/32fc4e:dd9d:ffff:ffff:ffff:ffff:ffff:ffff
31fc4e:dd9e::/32fc4e:dd9e:ffff:ffff:ffff:ffff:ffff:ffff
32fc4e:dd9f::/32fc4e:dd9f:ffff:ffff:ffff:ffff:ffff:ffff
33fc4e:dda0::/32fc4e:dda0:ffff:ffff:ffff:ffff:ffff:ffff
34fc4e:dda1::/32fc4e:dda1:ffff:ffff:ffff:ffff:ffff:ffff
35fc4e:dda2::/32fc4e:dda2:ffff:ffff:ffff:ffff:ffff:ffff
36fc4e:dda3::/32fc4e:dda3:ffff:ffff:ffff:ffff:ffff:ffff
37fc4e:dda4::/32fc4e:dda4:ffff:ffff:ffff:ffff:ffff:ffff
38fc4e:dda5::/32fc4e:dda5:ffff:ffff:ffff:ffff:ffff:ffff
39fc4e:dda6::/32fc4e:dda6:ffff:ffff:ffff:ffff:ffff:ffff
40fc4e:dda7::/32fc4e:dda7:ffff:ffff:ffff:ffff:ffff:ffff
41fc4e:dda8::/32fc4e:dda8:ffff:ffff:ffff:ffff:ffff:ffff
42fc4e:dda9::/32fc4e:dda9:ffff:ffff:ffff:ffff:ffff:ffff
43fc4e:ddaa::/32fc4e:ddaa:ffff:ffff:ffff:ffff:ffff:ffff
44fc4e:ddab::/32fc4e:ddab:ffff:ffff:ffff:ffff:ffff:ffff
45fc4e:ddac::/32fc4e:ddac:ffff:ffff:ffff:ffff:ffff:ffff
46fc4e:ddad::/32fc4e:ddad:ffff:ffff:ffff:ffff:ffff:ffff
47fc4e:ddae::/32fc4e:ddae:ffff:ffff:ffff:ffff:ffff:ffff
48fc4e:ddaf::/32fc4e:ddaf:ffff:ffff:ffff:ffff:ffff:ffff
49fc4e:ddb0::/32fc4e:ddb0:ffff:ffff:ffff:ffff:ffff:ffff
50fc4e:ddb1::/32fc4e:ddb1:ffff:ffff:ffff:ffff:ffff:ffff
51fc4e:ddb2::/32fc4e:ddb2:ffff:ffff:ffff:ffff:ffff:ffff
52fc4e:ddb3::/32fc4e:ddb3:ffff:ffff:ffff:ffff:ffff:ffff
53fc4e:ddb4::/32fc4e:ddb4:ffff:ffff:ffff:ffff:ffff:ffff
54fc4e:ddb5::/32fc4e:ddb5:ffff:ffff:ffff:ffff:ffff:ffff
55fc4e:ddb6::/32fc4e:ddb6:ffff:ffff:ffff:ffff:ffff:ffff
56fc4e:ddb7::/32fc4e:ddb7:ffff:ffff:ffff:ffff:ffff:ffff
57fc4e:ddb8::/32fc4e:ddb8:ffff:ffff:ffff:ffff:ffff:ffff
58fc4e:ddb9::/32fc4e:ddb9:ffff:ffff:ffff:ffff:ffff:ffff
59fc4e:ddba::/32fc4e:ddba:ffff:ffff:ffff:ffff:ffff:ffff
60fc4e:ddbb::/32fc4e:ddbb:ffff:ffff:ffff:ffff:ffff:ffff
61fc4e:ddbc::/32fc4e:ddbc:ffff:ffff:ffff:ffff:ffff:ffff
62fc4e:ddbd::/32fc4e:ddbd:ffff:ffff:ffff:ffff:ffff:ffff
63fc4e:ddbe::/32fc4e:ddbe:ffff:ffff:ffff:ffff:ffff:ffff
64fc4e:ddbf::/32fc4e:ddbf:ffff:ffff:ffff:ffff:ffff:ffff
65fc4e:ddc0::/32fc4e:ddc0:ffff:ffff:ffff:ffff:ffff:ffff
66fc4e:ddc1::/32fc4e:ddc1:ffff:ffff:ffff:ffff:ffff:ffff
67fc4e:ddc2::/32fc4e:ddc2:ffff:ffff:ffff:ffff:ffff:ffff
68fc4e:ddc3::/32fc4e:ddc3:ffff:ffff:ffff:ffff:ffff:ffff
69fc4e:ddc4::/32fc4e:ddc4:ffff:ffff:ffff:ffff:ffff:ffff
70fc4e:ddc5::/32fc4e:ddc5:ffff:ffff:ffff:ffff:ffff:ffff
71fc4e:ddc6::/32fc4e:ddc6:ffff:ffff:ffff:ffff:ffff:ffff
72fc4e:ddc7::/32fc4e:ddc7:ffff:ffff:ffff:ffff:ffff:ffff
73fc4e:ddc8::/32fc4e:ddc8:ffff:ffff:ffff:ffff:ffff:ffff
74fc4e:ddc9::/32fc4e:ddc9:ffff:ffff:ffff:ffff:ffff:ffff
75fc4e:ddca::/32fc4e:ddca:ffff:ffff:ffff:ffff:ffff:ffff
76fc4e:ddcb::/32fc4e:ddcb:ffff:ffff:ffff:ffff:ffff:ffff
77fc4e:ddcc::/32fc4e:ddcc:ffff:ffff:ffff:ffff:ffff:ffff
78fc4e:ddcd::/32fc4e:ddcd:ffff:ffff:ffff:ffff:ffff:ffff
79fc4e:ddce::/32fc4e:ddce:ffff:ffff:ffff:ffff:ffff:ffff
80fc4e:ddcf::/32fc4e:ddcf:ffff:ffff:ffff:ffff:ffff:ffff
81fc4e:ddd0::/32fc4e:ddd0:ffff:ffff:ffff:ffff:ffff:ffff
82fc4e:ddd1::/32fc4e:ddd1:ffff:ffff:ffff:ffff:ffff:ffff
83fc4e:ddd2::/32fc4e:ddd2:ffff:ffff:ffff:ffff:ffff:ffff
84fc4e:ddd3::/32fc4e:ddd3:ffff:ffff:ffff:ffff:ffff:ffff
85fc4e:ddd4::/32fc4e:ddd4:ffff:ffff:ffff:ffff:ffff:ffff
86fc4e:ddd5::/32fc4e:ddd5:ffff:ffff:ffff:ffff:ffff:ffff
87fc4e:ddd6::/32fc4e:ddd6:ffff:ffff:ffff:ffff:ffff:ffff
88fc4e:ddd7::/32fc4e:ddd7:ffff:ffff:ffff:ffff:ffff:ffff
89fc4e:ddd8::/32fc4e:ddd8:ffff:ffff:ffff:ffff:ffff:ffff
90fc4e:ddd9::/32fc4e:ddd9:ffff:ffff:ffff:ffff:ffff:ffff
91fc4e:ddda::/32fc4e:ddda:ffff:ffff:ffff:ffff:ffff:ffff
92fc4e:dddb::/32fc4e:dddb:ffff:ffff:ffff:ffff:ffff:ffff
93fc4e:dddc::/32fc4e:dddc:ffff:ffff:ffff:ffff:ffff:ffff
94fc4e:dddd::/32fc4e:dddd:ffff:ffff:ffff:ffff:ffff:ffff
95fc4e:ddde::/32fc4e:ddde:ffff:ffff:ffff:ffff:ffff:ffff
96fc4e:dddf::/32fc4e:dddf:ffff:ffff:ffff:ffff:ffff:ffff
97fc4e:dde0::/32fc4e:dde0:ffff:ffff:ffff:ffff:ffff:ffff
98fc4e:dde1::/32fc4e:dde1:ffff:ffff:ffff:ffff:ffff:ffff
99fc4e:dde2::/32fc4e:dde2:ffff:ffff:ffff:ffff:ffff:ffff
100fc4e:dde3::/32fc4e:dde3:ffff:ffff:ffff:ffff:ffff:ffff
101fc4e:dde4::/32fc4e:dde4:ffff:ffff:ffff:ffff:ffff:ffff
102fc4e:dde5::/32fc4e:dde5:ffff:ffff:ffff:ffff:ffff:ffff
103fc4e:dde6::/32fc4e:dde6:ffff:ffff:ffff:ffff:ffff:ffff
104fc4e:dde7::/32fc4e:dde7:ffff:ffff:ffff:ffff:ffff:ffff
105fc4e:dde8::/32fc4e:dde8:ffff:ffff:ffff:ffff:ffff:ffff
106fc4e:dde9::/32fc4e:dde9:ffff:ffff:ffff:ffff:ffff:ffff
107fc4e:ddea::/32fc4e:ddea:ffff:ffff:ffff:ffff:ffff:ffff
108fc4e:ddeb::/32fc4e:ddeb:ffff:ffff:ffff:ffff:ffff:ffff
109fc4e:ddec::/32fc4e:ddec:ffff:ffff:ffff:ffff:ffff:ffff
110fc4e:dded::/32fc4e:dded:ffff:ffff:ffff:ffff:ffff:ffff
111fc4e:ddee::/32fc4e:ddee:ffff:ffff:ffff:ffff:ffff:ffff
112fc4e:ddef::/32fc4e:ddef:ffff:ffff:ffff:ffff:ffff:ffff
113fc4e:ddf0::/32fc4e:ddf0:ffff:ffff:ffff:ffff:ffff:ffff
114fc4e:ddf1::/32fc4e:ddf1:ffff:ffff:ffff:ffff:ffff:ffff
115fc4e:ddf2::/32fc4e:ddf2:ffff:ffff:ffff:ffff:ffff:ffff
116fc4e:ddf3::/32fc4e:ddf3:ffff:ffff:ffff:ffff:ffff:ffff
117fc4e:ddf4::/32fc4e:ddf4:ffff:ffff:ffff:ffff:ffff:ffff
118fc4e:ddf5::/32fc4e:ddf5:ffff:ffff:ffff:ffff:ffff:ffff
119fc4e:ddf6::/32fc4e:ddf6:ffff:ffff:ffff:ffff:ffff:ffff
120fc4e:ddf7::/32fc4e:ddf7:ffff:ffff:ffff:ffff:ffff:ffff
121fc4e:ddf8::/32fc4e:ddf8:ffff:ffff:ffff:ffff:ffff:ffff
122fc4e:ddf9::/32fc4e:ddf9:ffff:ffff:ffff:ffff:ffff:ffff
123fc4e:ddfa::/32fc4e:ddfa:ffff:ffff:ffff:ffff:ffff:ffff
124fc4e:ddfb::/32fc4e:ddfb:ffff:ffff:ffff:ffff:ffff:ffff
125fc4e:ddfc::/32fc4e:ddfc:ffff:ffff:ffff:ffff:ffff:ffff
126fc4e:ddfd::/32fc4e:ddfd:ffff:ffff:ffff:ffff:ffff:ffff
127fc4e:ddfe::/32fc4e:ddfe:ffff:ffff:ffff:ffff:ffff:ffff
128fc4e:ddff::/32fc4e:ddff: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.