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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.

Network129.232.0.0/15
Usable hosts131,070
Subnet mask255.254.0.0
Addresses131,072
Network address
129.232.0.0
Broadcast address
129.233.255.255
First usable
129.232.0.1
Last usable
129.233.255.254
Usable hosts
131,070 (131,072 less the network and broadcast addresses)
Subnet mask
255.254.0.0
Wildcard mask
0.1.255.255 (Cisco ACLs, OSPF)
Prefix length
/15
Type
Public public
Old class
B (default /16)
As numbers
Hex 81E80000 · Integer 2179465216 to 2179596287
Reverse DNS zones
232.129.in-addr.arpa
233.129.in-addr.arpa
/15 is not on a 8-bit boundary, so it takes 2 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address10000001.11101000.00000000.00000000129.232.0.0
Subnet mask11111111.11111110.00000000.00000000255.254.0.0
Network10000001.11101000.00000000.00000000129.232.0.0
Broadcast10000001.11101001.11111111.11111111129.233.255.255
Split into smaller subnets/21
/16 (2)/17 (4)/18 (8)/19 (16)/20 (32)/21 (64)/22 (128)/23 (256)/24 (512)/25 (1,024)/26 (2,048)/27 (4,096)

129.232.0.0/15 makes 64 subnets of /21.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1129.232.0.0/21129.232.0.1 to 129.232.7.254129.232.7.2552,046
2129.232.8.0/21129.232.8.1 to 129.232.15.254129.232.15.2552,046
3129.232.16.0/21129.232.16.1 to 129.232.23.254129.232.23.2552,046
4129.232.24.0/21129.232.24.1 to 129.232.31.254129.232.31.2552,046
5129.232.32.0/21129.232.32.1 to 129.232.39.254129.232.39.2552,046
6129.232.40.0/21129.232.40.1 to 129.232.47.254129.232.47.2552,046
7129.232.48.0/21129.232.48.1 to 129.232.55.254129.232.55.2552,046
8129.232.56.0/21129.232.56.1 to 129.232.63.254129.232.63.2552,046
9129.232.64.0/21129.232.64.1 to 129.232.71.254129.232.71.2552,046
10129.232.72.0/21129.232.72.1 to 129.232.79.254129.232.79.2552,046
11129.232.80.0/21129.232.80.1 to 129.232.87.254129.232.87.2552,046
12129.232.88.0/21129.232.88.1 to 129.232.95.254129.232.95.2552,046
13129.232.96.0/21129.232.96.1 to 129.232.103.254129.232.103.2552,046
14129.232.104.0/21129.232.104.1 to 129.232.111.254129.232.111.2552,046
15129.232.112.0/21129.232.112.1 to 129.232.119.254129.232.119.2552,046
16129.232.120.0/21129.232.120.1 to 129.232.127.254129.232.127.2552,046
17129.232.128.0/21129.232.128.1 to 129.232.135.254129.232.135.2552,046
18129.232.136.0/21129.232.136.1 to 129.232.143.254129.232.143.2552,046
19129.232.144.0/21129.232.144.1 to 129.232.151.254129.232.151.2552,046
20129.232.152.0/21129.232.152.1 to 129.232.159.254129.232.159.2552,046
21129.232.160.0/21129.232.160.1 to 129.232.167.254129.232.167.2552,046
22129.232.168.0/21129.232.168.1 to 129.232.175.254129.232.175.2552,046
23129.232.176.0/21129.232.176.1 to 129.232.183.254129.232.183.2552,046
24129.232.184.0/21129.232.184.1 to 129.232.191.254129.232.191.2552,046
25129.232.192.0/21129.232.192.1 to 129.232.199.254129.232.199.2552,046
26129.232.200.0/21129.232.200.1 to 129.232.207.254129.232.207.2552,046
27129.232.208.0/21129.232.208.1 to 129.232.215.254129.232.215.2552,046
28129.232.216.0/21129.232.216.1 to 129.232.223.254129.232.223.2552,046
29129.232.224.0/21129.232.224.1 to 129.232.231.254129.232.231.2552,046
30129.232.232.0/21129.232.232.1 to 129.232.239.254129.232.239.2552,046
31129.232.240.0/21129.232.240.1 to 129.232.247.254129.232.247.2552,046
32129.232.248.0/21129.232.248.1 to 129.232.255.254129.232.255.2552,046
33129.233.0.0/21129.233.0.1 to 129.233.7.254129.233.7.2552,046
34129.233.8.0/21129.233.8.1 to 129.233.15.254129.233.15.2552,046
35129.233.16.0/21129.233.16.1 to 129.233.23.254129.233.23.2552,046
36129.233.24.0/21129.233.24.1 to 129.233.31.254129.233.31.2552,046
37129.233.32.0/21129.233.32.1 to 129.233.39.254129.233.39.2552,046
38129.233.40.0/21129.233.40.1 to 129.233.47.254129.233.47.2552,046
39129.233.48.0/21129.233.48.1 to 129.233.55.254129.233.55.2552,046
40129.233.56.0/21129.233.56.1 to 129.233.63.254129.233.63.2552,046
41129.233.64.0/21129.233.64.1 to 129.233.71.254129.233.71.2552,046
42129.233.72.0/21129.233.72.1 to 129.233.79.254129.233.79.2552,046
43129.233.80.0/21129.233.80.1 to 129.233.87.254129.233.87.2552,046
44129.233.88.0/21129.233.88.1 to 129.233.95.254129.233.95.2552,046
45129.233.96.0/21129.233.96.1 to 129.233.103.254129.233.103.2552,046
46129.233.104.0/21129.233.104.1 to 129.233.111.254129.233.111.2552,046
47129.233.112.0/21129.233.112.1 to 129.233.119.254129.233.119.2552,046
48129.233.120.0/21129.233.120.1 to 129.233.127.254129.233.127.2552,046
49129.233.128.0/21129.233.128.1 to 129.233.135.254129.233.135.2552,046
50129.233.136.0/21129.233.136.1 to 129.233.143.254129.233.143.2552,046
51129.233.144.0/21129.233.144.1 to 129.233.151.254129.233.151.2552,046
52129.233.152.0/21129.233.152.1 to 129.233.159.254129.233.159.2552,046
53129.233.160.0/21129.233.160.1 to 129.233.167.254129.233.167.2552,046
54129.233.168.0/21129.233.168.1 to 129.233.175.254129.233.175.2552,046
55129.233.176.0/21129.233.176.1 to 129.233.183.254129.233.183.2552,046
56129.233.184.0/21129.233.184.1 to 129.233.191.254129.233.191.2552,046
57129.233.192.0/21129.233.192.1 to 129.233.199.254129.233.199.2552,046
58129.233.200.0/21129.233.200.1 to 129.233.207.254129.233.207.2552,046
59129.233.208.0/21129.233.208.1 to 129.233.215.254129.233.215.2552,046
60129.233.216.0/21129.233.216.1 to 129.233.223.254129.233.223.2552,046
61129.233.224.0/21129.233.224.1 to 129.233.231.254129.233.231.2552,046
62129.233.232.0/21129.233.232.1 to 129.233.239.254129.233.239.2552,046
63129.233.240.0/21129.233.240.1 to 129.233.247.254129.233.247.2552,046
64129.233.248.0/21129.233.248.1 to 129.233.255.254129.233.255.2552,046

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.