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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.

Network18.97.12.0/23
Usable hosts510
Subnet mask255.255.254.0
Addresses512
Network address
18.97.12.0
Broadcast address
18.97.13.255
First usable
18.97.12.1
Last usable
18.97.13.254
Usable hosts
510 (512 less the network and broadcast addresses)
Subnet mask
255.255.254.0
Wildcard mask
0.0.1.255 (Cisco ACLs, OSPF)
Prefix length
/23
Type
Public public
Old class
A (default /8)
As numbers
Hex 12610C00 · Integer 308349952 to 308350463
Reverse DNS zones
12.97.18.in-addr.arpa
13.97.18.in-addr.arpa
/23 is not on a 8-bit boundary, so it takes 2 /24 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address00010010.01100001.00001100.0000000018.97.12.0
Subnet mask11111111.11111111.11111110.00000000255.255.254.0
Network00010010.01100001.00001100.0000000018.97.12.0
Broadcast00010010.01100001.00001101.1111111118.97.13.255
Split into smaller subnets/29
/24 (2)/25 (4)/26 (8)/27 (16)/28 (32)/29 (64)/30 (128)/31 (256)/32 (512)

18.97.12.0/23 makes 64 subnets of /29.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
118.97.12.0/2918.97.12.1 to 18.97.12.618.97.12.76
218.97.12.8/2918.97.12.9 to 18.97.12.1418.97.12.156
318.97.12.16/2918.97.12.17 to 18.97.12.2218.97.12.236
418.97.12.24/2918.97.12.25 to 18.97.12.3018.97.12.316
518.97.12.32/2918.97.12.33 to 18.97.12.3818.97.12.396
618.97.12.40/2918.97.12.41 to 18.97.12.4618.97.12.476
718.97.12.48/2918.97.12.49 to 18.97.12.5418.97.12.556
818.97.12.56/2918.97.12.57 to 18.97.12.6218.97.12.636
918.97.12.64/2918.97.12.65 to 18.97.12.7018.97.12.716
1018.97.12.72/2918.97.12.73 to 18.97.12.7818.97.12.796
1118.97.12.80/2918.97.12.81 to 18.97.12.8618.97.12.876
1218.97.12.88/2918.97.12.89 to 18.97.12.9418.97.12.956
1318.97.12.96/2918.97.12.97 to 18.97.12.10218.97.12.1036
1418.97.12.104/2918.97.12.105 to 18.97.12.11018.97.12.1116
1518.97.12.112/2918.97.12.113 to 18.97.12.11818.97.12.1196
1618.97.12.120/2918.97.12.121 to 18.97.12.12618.97.12.1276
1718.97.12.128/2918.97.12.129 to 18.97.12.13418.97.12.1356
1818.97.12.136/2918.97.12.137 to 18.97.12.14218.97.12.1436
1918.97.12.144/2918.97.12.145 to 18.97.12.15018.97.12.1516
2018.97.12.152/2918.97.12.153 to 18.97.12.15818.97.12.1596
2118.97.12.160/2918.97.12.161 to 18.97.12.16618.97.12.1676
2218.97.12.168/2918.97.12.169 to 18.97.12.17418.97.12.1756
2318.97.12.176/2918.97.12.177 to 18.97.12.18218.97.12.1836
2418.97.12.184/2918.97.12.185 to 18.97.12.19018.97.12.1916
2518.97.12.192/2918.97.12.193 to 18.97.12.19818.97.12.1996
2618.97.12.200/2918.97.12.201 to 18.97.12.20618.97.12.2076
2718.97.12.208/2918.97.12.209 to 18.97.12.21418.97.12.2156
2818.97.12.216/2918.97.12.217 to 18.97.12.22218.97.12.2236
2918.97.12.224/2918.97.12.225 to 18.97.12.23018.97.12.2316
3018.97.12.232/2918.97.12.233 to 18.97.12.23818.97.12.2396
3118.97.12.240/2918.97.12.241 to 18.97.12.24618.97.12.2476
3218.97.12.248/2918.97.12.249 to 18.97.12.25418.97.12.2556
3318.97.13.0/2918.97.13.1 to 18.97.13.618.97.13.76
3418.97.13.8/2918.97.13.9 to 18.97.13.1418.97.13.156
3518.97.13.16/2918.97.13.17 to 18.97.13.2218.97.13.236
3618.97.13.24/2918.97.13.25 to 18.97.13.3018.97.13.316
3718.97.13.32/2918.97.13.33 to 18.97.13.3818.97.13.396
3818.97.13.40/2918.97.13.41 to 18.97.13.4618.97.13.476
3918.97.13.48/2918.97.13.49 to 18.97.13.5418.97.13.556
4018.97.13.56/2918.97.13.57 to 18.97.13.6218.97.13.636
4118.97.13.64/2918.97.13.65 to 18.97.13.7018.97.13.716
4218.97.13.72/2918.97.13.73 to 18.97.13.7818.97.13.796
4318.97.13.80/2918.97.13.81 to 18.97.13.8618.97.13.876
4418.97.13.88/2918.97.13.89 to 18.97.13.9418.97.13.956
4518.97.13.96/2918.97.13.97 to 18.97.13.10218.97.13.1036
4618.97.13.104/2918.97.13.105 to 18.97.13.11018.97.13.1116
4718.97.13.112/2918.97.13.113 to 18.97.13.11818.97.13.1196
4818.97.13.120/2918.97.13.121 to 18.97.13.12618.97.13.1276
4918.97.13.128/2918.97.13.129 to 18.97.13.13418.97.13.1356
5018.97.13.136/2918.97.13.137 to 18.97.13.14218.97.13.1436
5118.97.13.144/2918.97.13.145 to 18.97.13.15018.97.13.1516
5218.97.13.152/2918.97.13.153 to 18.97.13.15818.97.13.1596
5318.97.13.160/2918.97.13.161 to 18.97.13.16618.97.13.1676
5418.97.13.168/2918.97.13.169 to 18.97.13.17418.97.13.1756
5518.97.13.176/2918.97.13.177 to 18.97.13.18218.97.13.1836
5618.97.13.184/2918.97.13.185 to 18.97.13.19018.97.13.1916
5718.97.13.192/2918.97.13.193 to 18.97.13.19818.97.13.1996
5818.97.13.200/2918.97.13.201 to 18.97.13.20618.97.13.2076
5918.97.13.208/2918.97.13.209 to 18.97.13.21418.97.13.2156
6018.97.13.216/2918.97.13.217 to 18.97.13.22218.97.13.2236
6118.97.13.224/2918.97.13.225 to 18.97.13.23018.97.13.2316
6218.97.13.232/2918.97.13.233 to 18.97.13.23818.97.13.2396
6318.97.13.240/2918.97.13.241 to 18.97.13.24618.97.13.2476
6418.97.13.248/2918.97.13.249 to 18.97.13.25418.97.13.2556

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.