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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.

Network23.0.0.0/9
Usable hosts8,388,606
Subnet mask255.128.0.0
Addresses8,388,608
Network address
23.0.0.0
Broadcast address
23.127.255.255
First usable
23.0.0.1
Last usable
23.127.255.254
Usable hosts
8,388,606 (8,388,608 less the network and broadcast addresses)
Subnet mask
255.128.0.0
Wildcard mask
0.127.255.255 (Cisco ACLs, OSPF)
Prefix length
/9
Type
Public public
Old class
A (default /8)
As numbers
Hex 17000000 · Integer 385875968 to 394264575
Reverse DNS zones
0.23.in-addr.arpa
1.23.in-addr.arpa
2.23.in-addr.arpa
3.23.in-addr.arpa
4.23.in-addr.arpa
5.23.in-addr.arpa
6.23.in-addr.arpa
7.23.in-addr.arpa
8.23.in-addr.arpa
9.23.in-addr.arpa
10.23.in-addr.arpa
11.23.in-addr.arpa
12.23.in-addr.arpa
13.23.in-addr.arpa
14.23.in-addr.arpa
15.23.in-addr.arpa
and 112 more
/9 is not on a 8-bit boundary, so it takes 128 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00010111.00000000.00000000.0000000023.0.0.0
Subnet mask11111111.10000000.00000000.00000000255.128.0.0
Network00010111.00000000.00000000.0000000023.0.0.0
Broadcast00010111.01111111.11111111.1111111123.127.255.255
Split into smaller subnets/15
/10 (2)/11 (4)/12 (8)/13 (16)/14 (32)/15 (64)/16 (128)/17 (256)/18 (512)/19 (1,024)/20 (2,048)/21 (4,096)

23.0.0.0/9 makes 64 subnets of /15.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
123.0.0.0/1523.0.0.1 to 23.1.255.25423.1.255.255131,070
223.2.0.0/1523.2.0.1 to 23.3.255.25423.3.255.255131,070
323.4.0.0/1523.4.0.1 to 23.5.255.25423.5.255.255131,070
423.6.0.0/1523.6.0.1 to 23.7.255.25423.7.255.255131,070
523.8.0.0/1523.8.0.1 to 23.9.255.25423.9.255.255131,070
623.10.0.0/1523.10.0.1 to 23.11.255.25423.11.255.255131,070
723.12.0.0/1523.12.0.1 to 23.13.255.25423.13.255.255131,070
823.14.0.0/1523.14.0.1 to 23.15.255.25423.15.255.255131,070
923.16.0.0/1523.16.0.1 to 23.17.255.25423.17.255.255131,070
1023.18.0.0/1523.18.0.1 to 23.19.255.25423.19.255.255131,070
1123.20.0.0/1523.20.0.1 to 23.21.255.25423.21.255.255131,070
1223.22.0.0/1523.22.0.1 to 23.23.255.25423.23.255.255131,070
1323.24.0.0/1523.24.0.1 to 23.25.255.25423.25.255.255131,070
1423.26.0.0/1523.26.0.1 to 23.27.255.25423.27.255.255131,070
1523.28.0.0/1523.28.0.1 to 23.29.255.25423.29.255.255131,070
1623.30.0.0/1523.30.0.1 to 23.31.255.25423.31.255.255131,070
1723.32.0.0/1523.32.0.1 to 23.33.255.25423.33.255.255131,070
1823.34.0.0/1523.34.0.1 to 23.35.255.25423.35.255.255131,070
1923.36.0.0/1523.36.0.1 to 23.37.255.25423.37.255.255131,070
2023.38.0.0/1523.38.0.1 to 23.39.255.25423.39.255.255131,070
2123.40.0.0/1523.40.0.1 to 23.41.255.25423.41.255.255131,070
2223.42.0.0/1523.42.0.1 to 23.43.255.25423.43.255.255131,070
2323.44.0.0/1523.44.0.1 to 23.45.255.25423.45.255.255131,070
2423.46.0.0/1523.46.0.1 to 23.47.255.25423.47.255.255131,070
2523.48.0.0/1523.48.0.1 to 23.49.255.25423.49.255.255131,070
2623.50.0.0/1523.50.0.1 to 23.51.255.25423.51.255.255131,070
2723.52.0.0/1523.52.0.1 to 23.53.255.25423.53.255.255131,070
2823.54.0.0/1523.54.0.1 to 23.55.255.25423.55.255.255131,070
2923.56.0.0/1523.56.0.1 to 23.57.255.25423.57.255.255131,070
3023.58.0.0/1523.58.0.1 to 23.59.255.25423.59.255.255131,070
3123.60.0.0/1523.60.0.1 to 23.61.255.25423.61.255.255131,070
3223.62.0.0/1523.62.0.1 to 23.63.255.25423.63.255.255131,070
3323.64.0.0/1523.64.0.1 to 23.65.255.25423.65.255.255131,070
3423.66.0.0/1523.66.0.1 to 23.67.255.25423.67.255.255131,070
3523.68.0.0/1523.68.0.1 to 23.69.255.25423.69.255.255131,070
3623.70.0.0/1523.70.0.1 to 23.71.255.25423.71.255.255131,070
3723.72.0.0/1523.72.0.1 to 23.73.255.25423.73.255.255131,070
3823.74.0.0/1523.74.0.1 to 23.75.255.25423.75.255.255131,070
3923.76.0.0/1523.76.0.1 to 23.77.255.25423.77.255.255131,070
4023.78.0.0/1523.78.0.1 to 23.79.255.25423.79.255.255131,070
4123.80.0.0/1523.80.0.1 to 23.81.255.25423.81.255.255131,070
4223.82.0.0/1523.82.0.1 to 23.83.255.25423.83.255.255131,070
4323.84.0.0/1523.84.0.1 to 23.85.255.25423.85.255.255131,070
4423.86.0.0/1523.86.0.1 to 23.87.255.25423.87.255.255131,070
4523.88.0.0/1523.88.0.1 to 23.89.255.25423.89.255.255131,070
4623.90.0.0/1523.90.0.1 to 23.91.255.25423.91.255.255131,070
4723.92.0.0/1523.92.0.1 to 23.93.255.25423.93.255.255131,070
4823.94.0.0/1523.94.0.1 to 23.95.255.25423.95.255.255131,070
4923.96.0.0/1523.96.0.1 to 23.97.255.25423.97.255.255131,070
5023.98.0.0/1523.98.0.1 to 23.99.255.25423.99.255.255131,070
5123.100.0.0/1523.100.0.1 to 23.101.255.25423.101.255.255131,070
5223.102.0.0/1523.102.0.1 to 23.103.255.25423.103.255.255131,070
5323.104.0.0/1523.104.0.1 to 23.105.255.25423.105.255.255131,070
5423.106.0.0/1523.106.0.1 to 23.107.255.25423.107.255.255131,070
5523.108.0.0/1523.108.0.1 to 23.109.255.25423.109.255.255131,070
5623.110.0.0/1523.110.0.1 to 23.111.255.25423.111.255.255131,070
5723.112.0.0/1523.112.0.1 to 23.113.255.25423.113.255.255131,070
5823.114.0.0/1523.114.0.1 to 23.115.255.25423.115.255.255131,070
5923.116.0.0/1523.116.0.1 to 23.117.255.25423.117.255.255131,070
6023.118.0.0/1523.118.0.1 to 23.119.255.25423.119.255.255131,070
6123.120.0.0/1523.120.0.1 to 23.121.255.25423.121.255.255131,070
6223.122.0.0/1523.122.0.1 to 23.123.255.25423.123.255.255131,070
6323.124.0.0/1523.124.0.1 to 23.125.255.25423.125.255.255131,070
6423.126.0.0/1523.126.0.1 to 23.127.255.25423.127.255.255131,070

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.