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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/16
/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 128 subnets of /16.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
123.0.0.0/1623.0.0.1 to 23.0.255.25423.0.255.25565,534
223.1.0.0/1623.1.0.1 to 23.1.255.25423.1.255.25565,534
323.2.0.0/1623.2.0.1 to 23.2.255.25423.2.255.25565,534
423.3.0.0/1623.3.0.1 to 23.3.255.25423.3.255.25565,534
523.4.0.0/1623.4.0.1 to 23.4.255.25423.4.255.25565,534
623.5.0.0/1623.5.0.1 to 23.5.255.25423.5.255.25565,534
723.6.0.0/1623.6.0.1 to 23.6.255.25423.6.255.25565,534
823.7.0.0/1623.7.0.1 to 23.7.255.25423.7.255.25565,534
923.8.0.0/1623.8.0.1 to 23.8.255.25423.8.255.25565,534
1023.9.0.0/1623.9.0.1 to 23.9.255.25423.9.255.25565,534
1123.10.0.0/1623.10.0.1 to 23.10.255.25423.10.255.25565,534
1223.11.0.0/1623.11.0.1 to 23.11.255.25423.11.255.25565,534
1323.12.0.0/1623.12.0.1 to 23.12.255.25423.12.255.25565,534
1423.13.0.0/1623.13.0.1 to 23.13.255.25423.13.255.25565,534
1523.14.0.0/1623.14.0.1 to 23.14.255.25423.14.255.25565,534
1623.15.0.0/1623.15.0.1 to 23.15.255.25423.15.255.25565,534
1723.16.0.0/1623.16.0.1 to 23.16.255.25423.16.255.25565,534
1823.17.0.0/1623.17.0.1 to 23.17.255.25423.17.255.25565,534
1923.18.0.0/1623.18.0.1 to 23.18.255.25423.18.255.25565,534
2023.19.0.0/1623.19.0.1 to 23.19.255.25423.19.255.25565,534
2123.20.0.0/1623.20.0.1 to 23.20.255.25423.20.255.25565,534
2223.21.0.0/1623.21.0.1 to 23.21.255.25423.21.255.25565,534
2323.22.0.0/1623.22.0.1 to 23.22.255.25423.22.255.25565,534
2423.23.0.0/1623.23.0.1 to 23.23.255.25423.23.255.25565,534
2523.24.0.0/1623.24.0.1 to 23.24.255.25423.24.255.25565,534
2623.25.0.0/1623.25.0.1 to 23.25.255.25423.25.255.25565,534
2723.26.0.0/1623.26.0.1 to 23.26.255.25423.26.255.25565,534
2823.27.0.0/1623.27.0.1 to 23.27.255.25423.27.255.25565,534
2923.28.0.0/1623.28.0.1 to 23.28.255.25423.28.255.25565,534
3023.29.0.0/1623.29.0.1 to 23.29.255.25423.29.255.25565,534
3123.30.0.0/1623.30.0.1 to 23.30.255.25423.30.255.25565,534
3223.31.0.0/1623.31.0.1 to 23.31.255.25423.31.255.25565,534
3323.32.0.0/1623.32.0.1 to 23.32.255.25423.32.255.25565,534
3423.33.0.0/1623.33.0.1 to 23.33.255.25423.33.255.25565,534
3523.34.0.0/1623.34.0.1 to 23.34.255.25423.34.255.25565,534
3623.35.0.0/1623.35.0.1 to 23.35.255.25423.35.255.25565,534
3723.36.0.0/1623.36.0.1 to 23.36.255.25423.36.255.25565,534
3823.37.0.0/1623.37.0.1 to 23.37.255.25423.37.255.25565,534
3923.38.0.0/1623.38.0.1 to 23.38.255.25423.38.255.25565,534
4023.39.0.0/1623.39.0.1 to 23.39.255.25423.39.255.25565,534
4123.40.0.0/1623.40.0.1 to 23.40.255.25423.40.255.25565,534
4223.41.0.0/1623.41.0.1 to 23.41.255.25423.41.255.25565,534
4323.42.0.0/1623.42.0.1 to 23.42.255.25423.42.255.25565,534
4423.43.0.0/1623.43.0.1 to 23.43.255.25423.43.255.25565,534
4523.44.0.0/1623.44.0.1 to 23.44.255.25423.44.255.25565,534
4623.45.0.0/1623.45.0.1 to 23.45.255.25423.45.255.25565,534
4723.46.0.0/1623.46.0.1 to 23.46.255.25423.46.255.25565,534
4823.47.0.0/1623.47.0.1 to 23.47.255.25423.47.255.25565,534
4923.48.0.0/1623.48.0.1 to 23.48.255.25423.48.255.25565,534
5023.49.0.0/1623.49.0.1 to 23.49.255.25423.49.255.25565,534
5123.50.0.0/1623.50.0.1 to 23.50.255.25423.50.255.25565,534
5223.51.0.0/1623.51.0.1 to 23.51.255.25423.51.255.25565,534
5323.52.0.0/1623.52.0.1 to 23.52.255.25423.52.255.25565,534
5423.53.0.0/1623.53.0.1 to 23.53.255.25423.53.255.25565,534
5523.54.0.0/1623.54.0.1 to 23.54.255.25423.54.255.25565,534
5623.55.0.0/1623.55.0.1 to 23.55.255.25423.55.255.25565,534
5723.56.0.0/1623.56.0.1 to 23.56.255.25423.56.255.25565,534
5823.57.0.0/1623.57.0.1 to 23.57.255.25423.57.255.25565,534
5923.58.0.0/1623.58.0.1 to 23.58.255.25423.58.255.25565,534
6023.59.0.0/1623.59.0.1 to 23.59.255.25423.59.255.25565,534
6123.60.0.0/1623.60.0.1 to 23.60.255.25423.60.255.25565,534
6223.61.0.0/1623.61.0.1 to 23.61.255.25423.61.255.25565,534
6323.62.0.0/1623.62.0.1 to 23.62.255.25423.62.255.25565,534
6423.63.0.0/1623.63.0.1 to 23.63.255.25423.63.255.25565,534
6523.64.0.0/1623.64.0.1 to 23.64.255.25423.64.255.25565,534
6623.65.0.0/1623.65.0.1 to 23.65.255.25423.65.255.25565,534
6723.66.0.0/1623.66.0.1 to 23.66.255.25423.66.255.25565,534
6823.67.0.0/1623.67.0.1 to 23.67.255.25423.67.255.25565,534
6923.68.0.0/1623.68.0.1 to 23.68.255.25423.68.255.25565,534
7023.69.0.0/1623.69.0.1 to 23.69.255.25423.69.255.25565,534
7123.70.0.0/1623.70.0.1 to 23.70.255.25423.70.255.25565,534
7223.71.0.0/1623.71.0.1 to 23.71.255.25423.71.255.25565,534
7323.72.0.0/1623.72.0.1 to 23.72.255.25423.72.255.25565,534
7423.73.0.0/1623.73.0.1 to 23.73.255.25423.73.255.25565,534
7523.74.0.0/1623.74.0.1 to 23.74.255.25423.74.255.25565,534
7623.75.0.0/1623.75.0.1 to 23.75.255.25423.75.255.25565,534
7723.76.0.0/1623.76.0.1 to 23.76.255.25423.76.255.25565,534
7823.77.0.0/1623.77.0.1 to 23.77.255.25423.77.255.25565,534
7923.78.0.0/1623.78.0.1 to 23.78.255.25423.78.255.25565,534
8023.79.0.0/1623.79.0.1 to 23.79.255.25423.79.255.25565,534
8123.80.0.0/1623.80.0.1 to 23.80.255.25423.80.255.25565,534
8223.81.0.0/1623.81.0.1 to 23.81.255.25423.81.255.25565,534
8323.82.0.0/1623.82.0.1 to 23.82.255.25423.82.255.25565,534
8423.83.0.0/1623.83.0.1 to 23.83.255.25423.83.255.25565,534
8523.84.0.0/1623.84.0.1 to 23.84.255.25423.84.255.25565,534
8623.85.0.0/1623.85.0.1 to 23.85.255.25423.85.255.25565,534
8723.86.0.0/1623.86.0.1 to 23.86.255.25423.86.255.25565,534
8823.87.0.0/1623.87.0.1 to 23.87.255.25423.87.255.25565,534
8923.88.0.0/1623.88.0.1 to 23.88.255.25423.88.255.25565,534
9023.89.0.0/1623.89.0.1 to 23.89.255.25423.89.255.25565,534
9123.90.0.0/1623.90.0.1 to 23.90.255.25423.90.255.25565,534
9223.91.0.0/1623.91.0.1 to 23.91.255.25423.91.255.25565,534
9323.92.0.0/1623.92.0.1 to 23.92.255.25423.92.255.25565,534
9423.93.0.0/1623.93.0.1 to 23.93.255.25423.93.255.25565,534
9523.94.0.0/1623.94.0.1 to 23.94.255.25423.94.255.25565,534
9623.95.0.0/1623.95.0.1 to 23.95.255.25423.95.255.25565,534
9723.96.0.0/1623.96.0.1 to 23.96.255.25423.96.255.25565,534
9823.97.0.0/1623.97.0.1 to 23.97.255.25423.97.255.25565,534
9923.98.0.0/1623.98.0.1 to 23.98.255.25423.98.255.25565,534
10023.99.0.0/1623.99.0.1 to 23.99.255.25423.99.255.25565,534
10123.100.0.0/1623.100.0.1 to 23.100.255.25423.100.255.25565,534
10223.101.0.0/1623.101.0.1 to 23.101.255.25423.101.255.25565,534
10323.102.0.0/1623.102.0.1 to 23.102.255.25423.102.255.25565,534
10423.103.0.0/1623.103.0.1 to 23.103.255.25423.103.255.25565,534
10523.104.0.0/1623.104.0.1 to 23.104.255.25423.104.255.25565,534
10623.105.0.0/1623.105.0.1 to 23.105.255.25423.105.255.25565,534
10723.106.0.0/1623.106.0.1 to 23.106.255.25423.106.255.25565,534
10823.107.0.0/1623.107.0.1 to 23.107.255.25423.107.255.25565,534
10923.108.0.0/1623.108.0.1 to 23.108.255.25423.108.255.25565,534
11023.109.0.0/1623.109.0.1 to 23.109.255.25423.109.255.25565,534
11123.110.0.0/1623.110.0.1 to 23.110.255.25423.110.255.25565,534
11223.111.0.0/1623.111.0.1 to 23.111.255.25423.111.255.25565,534
11323.112.0.0/1623.112.0.1 to 23.112.255.25423.112.255.25565,534
11423.113.0.0/1623.113.0.1 to 23.113.255.25423.113.255.25565,534
11523.114.0.0/1623.114.0.1 to 23.114.255.25423.114.255.25565,534
11623.115.0.0/1623.115.0.1 to 23.115.255.25423.115.255.25565,534
11723.116.0.0/1623.116.0.1 to 23.116.255.25423.116.255.25565,534
11823.117.0.0/1623.117.0.1 to 23.117.255.25423.117.255.25565,534
11923.118.0.0/1623.118.0.1 to 23.118.255.25423.118.255.25565,534
12023.119.0.0/1623.119.0.1 to 23.119.255.25423.119.255.25565,534
12123.120.0.0/1623.120.0.1 to 23.120.255.25423.120.255.25565,534
12223.121.0.0/1623.121.0.1 to 23.121.255.25423.121.255.25565,534
12323.122.0.0/1623.122.0.1 to 23.122.255.25423.122.255.25565,534
12423.123.0.0/1623.123.0.1 to 23.123.255.25423.123.255.25565,534
12523.124.0.0/1623.124.0.1 to 23.124.255.25423.124.255.25565,534
12623.125.0.0/1623.125.0.1 to 23.125.255.25423.125.255.25565,534
12723.126.0.0/1623.126.0.1 to 23.126.255.25423.126.255.25565,534
12823.127.0.0/1623.127.0.1 to 23.127.255.25423.127.255.25565,534

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.