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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/18
Addresses2^110
/64 networks2^46
Network
fc17::/18
First address
fc17::
Last address
fc17:3fff:ffff:ffff:ffff:ffff:ffff:ffff
Addresses
1,298,074,214,633,706,907,132,624,082,305,024 (2^110)
/64 networks (LANs)
70,368,744,177,664 (2^46)
Full form
fc17:0000:0000:0000:0000:0000:0000:0000
Type
Unique local (ULA) fc00::/7
Private IPv6, like RFC 1918; usually fd00::/8
Reverse DNS zones
0.7.1.c.f.ip6.arpa
1.7.1.c.f.ip6.arpa
2.7.1.c.f.ip6.arpa
3.7.1.c.f.ip6.arpa
/18 is not on a 4-bit boundary, so it takes 4 /20 zones.
Split into smaller subnets/24
/19 (2)/20 (4)/21 (8)/22 (16)/24 (64)/28 (1,024)/32 (16,384)

fc17::/18 makes 64 subnets of /24.

Subnets
#SubnetLast address
1fc17::/24fc17:ff:ffff:ffff:ffff:ffff:ffff:ffff
2fc17:100::/24fc17:1ff:ffff:ffff:ffff:ffff:ffff:ffff
3fc17:200::/24fc17:2ff:ffff:ffff:ffff:ffff:ffff:ffff
4fc17:300::/24fc17:3ff:ffff:ffff:ffff:ffff:ffff:ffff
5fc17:400::/24fc17:4ff:ffff:ffff:ffff:ffff:ffff:ffff
6fc17:500::/24fc17:5ff:ffff:ffff:ffff:ffff:ffff:ffff
7fc17:600::/24fc17:6ff:ffff:ffff:ffff:ffff:ffff:ffff
8fc17:700::/24fc17:7ff:ffff:ffff:ffff:ffff:ffff:ffff
9fc17:800::/24fc17:8ff:ffff:ffff:ffff:ffff:ffff:ffff
10fc17:900::/24fc17:9ff:ffff:ffff:ffff:ffff:ffff:ffff
11fc17:a00::/24fc17:aff:ffff:ffff:ffff:ffff:ffff:ffff
12fc17:b00::/24fc17:bff:ffff:ffff:ffff:ffff:ffff:ffff
13fc17:c00::/24fc17:cff:ffff:ffff:ffff:ffff:ffff:ffff
14fc17:d00::/24fc17:dff:ffff:ffff:ffff:ffff:ffff:ffff
15fc17:e00::/24fc17:eff:ffff:ffff:ffff:ffff:ffff:ffff
16fc17:f00::/24fc17:fff:ffff:ffff:ffff:ffff:ffff:ffff
17fc17:1000::/24fc17:10ff:ffff:ffff:ffff:ffff:ffff:ffff
18fc17:1100::/24fc17:11ff:ffff:ffff:ffff:ffff:ffff:ffff
19fc17:1200::/24fc17:12ff:ffff:ffff:ffff:ffff:ffff:ffff
20fc17:1300::/24fc17:13ff:ffff:ffff:ffff:ffff:ffff:ffff
21fc17:1400::/24fc17:14ff:ffff:ffff:ffff:ffff:ffff:ffff
22fc17:1500::/24fc17:15ff:ffff:ffff:ffff:ffff:ffff:ffff
23fc17:1600::/24fc17:16ff:ffff:ffff:ffff:ffff:ffff:ffff
24fc17:1700::/24fc17:17ff:ffff:ffff:ffff:ffff:ffff:ffff
25fc17:1800::/24fc17:18ff:ffff:ffff:ffff:ffff:ffff:ffff
26fc17:1900::/24fc17:19ff:ffff:ffff:ffff:ffff:ffff:ffff
27fc17:1a00::/24fc17:1aff:ffff:ffff:ffff:ffff:ffff:ffff
28fc17:1b00::/24fc17:1bff:ffff:ffff:ffff:ffff:ffff:ffff
29fc17:1c00::/24fc17:1cff:ffff:ffff:ffff:ffff:ffff:ffff
30fc17:1d00::/24fc17:1dff:ffff:ffff:ffff:ffff:ffff:ffff
31fc17:1e00::/24fc17:1eff:ffff:ffff:ffff:ffff:ffff:ffff
32fc17:1f00::/24fc17:1fff:ffff:ffff:ffff:ffff:ffff:ffff
33fc17:2000::/24fc17:20ff:ffff:ffff:ffff:ffff:ffff:ffff
34fc17:2100::/24fc17:21ff:ffff:ffff:ffff:ffff:ffff:ffff
35fc17:2200::/24fc17:22ff:ffff:ffff:ffff:ffff:ffff:ffff
36fc17:2300::/24fc17:23ff:ffff:ffff:ffff:ffff:ffff:ffff
37fc17:2400::/24fc17:24ff:ffff:ffff:ffff:ffff:ffff:ffff
38fc17:2500::/24fc17:25ff:ffff:ffff:ffff:ffff:ffff:ffff
39fc17:2600::/24fc17:26ff:ffff:ffff:ffff:ffff:ffff:ffff
40fc17:2700::/24fc17:27ff:ffff:ffff:ffff:ffff:ffff:ffff
41fc17:2800::/24fc17:28ff:ffff:ffff:ffff:ffff:ffff:ffff
42fc17:2900::/24fc17:29ff:ffff:ffff:ffff:ffff:ffff:ffff
43fc17:2a00::/24fc17:2aff:ffff:ffff:ffff:ffff:ffff:ffff
44fc17:2b00::/24fc17:2bff:ffff:ffff:ffff:ffff:ffff:ffff
45fc17:2c00::/24fc17:2cff:ffff:ffff:ffff:ffff:ffff:ffff
46fc17:2d00::/24fc17:2dff:ffff:ffff:ffff:ffff:ffff:ffff
47fc17:2e00::/24fc17:2eff:ffff:ffff:ffff:ffff:ffff:ffff
48fc17:2f00::/24fc17:2fff:ffff:ffff:ffff:ffff:ffff:ffff
49fc17:3000::/24fc17:30ff:ffff:ffff:ffff:ffff:ffff:ffff
50fc17:3100::/24fc17:31ff:ffff:ffff:ffff:ffff:ffff:ffff
51fc17:3200::/24fc17:32ff:ffff:ffff:ffff:ffff:ffff:ffff
52fc17:3300::/24fc17:33ff:ffff:ffff:ffff:ffff:ffff:ffff
53fc17:3400::/24fc17:34ff:ffff:ffff:ffff:ffff:ffff:ffff
54fc17:3500::/24fc17:35ff:ffff:ffff:ffff:ffff:ffff:ffff
55fc17:3600::/24fc17:36ff:ffff:ffff:ffff:ffff:ffff:ffff
56fc17:3700::/24fc17:37ff:ffff:ffff:ffff:ffff:ffff:ffff
57fc17:3800::/24fc17:38ff:ffff:ffff:ffff:ffff:ffff:ffff
58fc17:3900::/24fc17:39ff:ffff:ffff:ffff:ffff:ffff:ffff
59fc17:3a00::/24fc17:3aff:ffff:ffff:ffff:ffff:ffff:ffff
60fc17:3b00::/24fc17:3bff:ffff:ffff:ffff:ffff:ffff:ffff
61fc17:3c00::/24fc17:3cff:ffff:ffff:ffff:ffff:ffff:ffff
62fc17:3d00::/24fc17:3dff:ffff:ffff:ffff:ffff:ffff:ffff
63fc17:3e00::/24fc17:3eff:ffff:ffff:ffff:ffff:ffff:ffff
64fc17:3f00::/24fc17:3fff: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.