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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.

Network71.240.0.0/12
Usable hosts1,048,574
Subnet mask255.240.0.0
Addresses1,048,576
Network address
71.240.0.0
Broadcast address
71.255.255.255
First usable
71.240.0.1
Last usable
71.255.255.254
Usable hosts
1,048,574 (1,048,576 less the network and broadcast addresses)
Subnet mask
255.240.0.0
Wildcard mask
0.15.255.255 (Cisco ACLs, OSPF)
Prefix length
/12
Type
Public public
Old class
A (default /8)
As numbers
Hex 47F00000 · Integer 1206910976 to 1207959551
Reverse DNS zones
240.71.in-addr.arpa
241.71.in-addr.arpa
242.71.in-addr.arpa
243.71.in-addr.arpa
244.71.in-addr.arpa
245.71.in-addr.arpa
246.71.in-addr.arpa
247.71.in-addr.arpa
248.71.in-addr.arpa
249.71.in-addr.arpa
250.71.in-addr.arpa
251.71.in-addr.arpa
252.71.in-addr.arpa
253.71.in-addr.arpa
254.71.in-addr.arpa
255.71.in-addr.arpa
/12 is not on a 8-bit boundary, so it takes 16 /16 zones.
Binary
Binary view
Binary (network bits bold, host bits grey)Dotted
Address01000111.11110000.00000000.0000000071.240.0.0
Subnet mask11111111.11110000.00000000.00000000255.240.0.0
Network01000111.11110000.00000000.0000000071.240.0.0
Broadcast01000111.11111111.11111111.1111111171.255.255.255
Split into smaller subnets/19
/13 (2)/14 (4)/15 (8)/16 (16)/17 (32)/18 (64)/19 (128)/20 (256)/21 (512)/22 (1,024)/23 (2,048)/24 (4,096)

71.240.0.0/12 makes 128 subnets of /19.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
171.240.0.0/1971.240.0.1 to 71.240.31.25471.240.31.2558,190
271.240.32.0/1971.240.32.1 to 71.240.63.25471.240.63.2558,190
371.240.64.0/1971.240.64.1 to 71.240.95.25471.240.95.2558,190
471.240.96.0/1971.240.96.1 to 71.240.127.25471.240.127.2558,190
571.240.128.0/1971.240.128.1 to 71.240.159.25471.240.159.2558,190
671.240.160.0/1971.240.160.1 to 71.240.191.25471.240.191.2558,190
771.240.192.0/1971.240.192.1 to 71.240.223.25471.240.223.2558,190
871.240.224.0/1971.240.224.1 to 71.240.255.25471.240.255.2558,190
971.241.0.0/1971.241.0.1 to 71.241.31.25471.241.31.2558,190
1071.241.32.0/1971.241.32.1 to 71.241.63.25471.241.63.2558,190
1171.241.64.0/1971.241.64.1 to 71.241.95.25471.241.95.2558,190
1271.241.96.0/1971.241.96.1 to 71.241.127.25471.241.127.2558,190
1371.241.128.0/1971.241.128.1 to 71.241.159.25471.241.159.2558,190
1471.241.160.0/1971.241.160.1 to 71.241.191.25471.241.191.2558,190
1571.241.192.0/1971.241.192.1 to 71.241.223.25471.241.223.2558,190
1671.241.224.0/1971.241.224.1 to 71.241.255.25471.241.255.2558,190
1771.242.0.0/1971.242.0.1 to 71.242.31.25471.242.31.2558,190
1871.242.32.0/1971.242.32.1 to 71.242.63.25471.242.63.2558,190
1971.242.64.0/1971.242.64.1 to 71.242.95.25471.242.95.2558,190
2071.242.96.0/1971.242.96.1 to 71.242.127.25471.242.127.2558,190
2171.242.128.0/1971.242.128.1 to 71.242.159.25471.242.159.2558,190
2271.242.160.0/1971.242.160.1 to 71.242.191.25471.242.191.2558,190
2371.242.192.0/1971.242.192.1 to 71.242.223.25471.242.223.2558,190
2471.242.224.0/1971.242.224.1 to 71.242.255.25471.242.255.2558,190
2571.243.0.0/1971.243.0.1 to 71.243.31.25471.243.31.2558,190
2671.243.32.0/1971.243.32.1 to 71.243.63.25471.243.63.2558,190
2771.243.64.0/1971.243.64.1 to 71.243.95.25471.243.95.2558,190
2871.243.96.0/1971.243.96.1 to 71.243.127.25471.243.127.2558,190
2971.243.128.0/1971.243.128.1 to 71.243.159.25471.243.159.2558,190
3071.243.160.0/1971.243.160.1 to 71.243.191.25471.243.191.2558,190
3171.243.192.0/1971.243.192.1 to 71.243.223.25471.243.223.2558,190
3271.243.224.0/1971.243.224.1 to 71.243.255.25471.243.255.2558,190
3371.244.0.0/1971.244.0.1 to 71.244.31.25471.244.31.2558,190
3471.244.32.0/1971.244.32.1 to 71.244.63.25471.244.63.2558,190
3571.244.64.0/1971.244.64.1 to 71.244.95.25471.244.95.2558,190
3671.244.96.0/1971.244.96.1 to 71.244.127.25471.244.127.2558,190
3771.244.128.0/1971.244.128.1 to 71.244.159.25471.244.159.2558,190
3871.244.160.0/1971.244.160.1 to 71.244.191.25471.244.191.2558,190
3971.244.192.0/1971.244.192.1 to 71.244.223.25471.244.223.2558,190
4071.244.224.0/1971.244.224.1 to 71.244.255.25471.244.255.2558,190
4171.245.0.0/1971.245.0.1 to 71.245.31.25471.245.31.2558,190
4271.245.32.0/1971.245.32.1 to 71.245.63.25471.245.63.2558,190
4371.245.64.0/1971.245.64.1 to 71.245.95.25471.245.95.2558,190
4471.245.96.0/1971.245.96.1 to 71.245.127.25471.245.127.2558,190
4571.245.128.0/1971.245.128.1 to 71.245.159.25471.245.159.2558,190
4671.245.160.0/1971.245.160.1 to 71.245.191.25471.245.191.2558,190
4771.245.192.0/1971.245.192.1 to 71.245.223.25471.245.223.2558,190
4871.245.224.0/1971.245.224.1 to 71.245.255.25471.245.255.2558,190
4971.246.0.0/1971.246.0.1 to 71.246.31.25471.246.31.2558,190
5071.246.32.0/1971.246.32.1 to 71.246.63.25471.246.63.2558,190
5171.246.64.0/1971.246.64.1 to 71.246.95.25471.246.95.2558,190
5271.246.96.0/1971.246.96.1 to 71.246.127.25471.246.127.2558,190
5371.246.128.0/1971.246.128.1 to 71.246.159.25471.246.159.2558,190
5471.246.160.0/1971.246.160.1 to 71.246.191.25471.246.191.2558,190
5571.246.192.0/1971.246.192.1 to 71.246.223.25471.246.223.2558,190
5671.246.224.0/1971.246.224.1 to 71.246.255.25471.246.255.2558,190
5771.247.0.0/1971.247.0.1 to 71.247.31.25471.247.31.2558,190
5871.247.32.0/1971.247.32.1 to 71.247.63.25471.247.63.2558,190
5971.247.64.0/1971.247.64.1 to 71.247.95.25471.247.95.2558,190
6071.247.96.0/1971.247.96.1 to 71.247.127.25471.247.127.2558,190
6171.247.128.0/1971.247.128.1 to 71.247.159.25471.247.159.2558,190
6271.247.160.0/1971.247.160.1 to 71.247.191.25471.247.191.2558,190
6371.247.192.0/1971.247.192.1 to 71.247.223.25471.247.223.2558,190
6471.247.224.0/1971.247.224.1 to 71.247.255.25471.247.255.2558,190
6571.248.0.0/1971.248.0.1 to 71.248.31.25471.248.31.2558,190
6671.248.32.0/1971.248.32.1 to 71.248.63.25471.248.63.2558,190
6771.248.64.0/1971.248.64.1 to 71.248.95.25471.248.95.2558,190
6871.248.96.0/1971.248.96.1 to 71.248.127.25471.248.127.2558,190
6971.248.128.0/1971.248.128.1 to 71.248.159.25471.248.159.2558,190
7071.248.160.0/1971.248.160.1 to 71.248.191.25471.248.191.2558,190
7171.248.192.0/1971.248.192.1 to 71.248.223.25471.248.223.2558,190
7271.248.224.0/1971.248.224.1 to 71.248.255.25471.248.255.2558,190
7371.249.0.0/1971.249.0.1 to 71.249.31.25471.249.31.2558,190
7471.249.32.0/1971.249.32.1 to 71.249.63.25471.249.63.2558,190
7571.249.64.0/1971.249.64.1 to 71.249.95.25471.249.95.2558,190
7671.249.96.0/1971.249.96.1 to 71.249.127.25471.249.127.2558,190
7771.249.128.0/1971.249.128.1 to 71.249.159.25471.249.159.2558,190
7871.249.160.0/1971.249.160.1 to 71.249.191.25471.249.191.2558,190
7971.249.192.0/1971.249.192.1 to 71.249.223.25471.249.223.2558,190
8071.249.224.0/1971.249.224.1 to 71.249.255.25471.249.255.2558,190
8171.250.0.0/1971.250.0.1 to 71.250.31.25471.250.31.2558,190
8271.250.32.0/1971.250.32.1 to 71.250.63.25471.250.63.2558,190
8371.250.64.0/1971.250.64.1 to 71.250.95.25471.250.95.2558,190
8471.250.96.0/1971.250.96.1 to 71.250.127.25471.250.127.2558,190
8571.250.128.0/1971.250.128.1 to 71.250.159.25471.250.159.2558,190
8671.250.160.0/1971.250.160.1 to 71.250.191.25471.250.191.2558,190
8771.250.192.0/1971.250.192.1 to 71.250.223.25471.250.223.2558,190
8871.250.224.0/1971.250.224.1 to 71.250.255.25471.250.255.2558,190
8971.251.0.0/1971.251.0.1 to 71.251.31.25471.251.31.2558,190
9071.251.32.0/1971.251.32.1 to 71.251.63.25471.251.63.2558,190
9171.251.64.0/1971.251.64.1 to 71.251.95.25471.251.95.2558,190
9271.251.96.0/1971.251.96.1 to 71.251.127.25471.251.127.2558,190
9371.251.128.0/1971.251.128.1 to 71.251.159.25471.251.159.2558,190
9471.251.160.0/1971.251.160.1 to 71.251.191.25471.251.191.2558,190
9571.251.192.0/1971.251.192.1 to 71.251.223.25471.251.223.2558,190
9671.251.224.0/1971.251.224.1 to 71.251.255.25471.251.255.2558,190
9771.252.0.0/1971.252.0.1 to 71.252.31.25471.252.31.2558,190
9871.252.32.0/1971.252.32.1 to 71.252.63.25471.252.63.2558,190
9971.252.64.0/1971.252.64.1 to 71.252.95.25471.252.95.2558,190
10071.252.96.0/1971.252.96.1 to 71.252.127.25471.252.127.2558,190
10171.252.128.0/1971.252.128.1 to 71.252.159.25471.252.159.2558,190
10271.252.160.0/1971.252.160.1 to 71.252.191.25471.252.191.2558,190
10371.252.192.0/1971.252.192.1 to 71.252.223.25471.252.223.2558,190
10471.252.224.0/1971.252.224.1 to 71.252.255.25471.252.255.2558,190
10571.253.0.0/1971.253.0.1 to 71.253.31.25471.253.31.2558,190
10671.253.32.0/1971.253.32.1 to 71.253.63.25471.253.63.2558,190
10771.253.64.0/1971.253.64.1 to 71.253.95.25471.253.95.2558,190
10871.253.96.0/1971.253.96.1 to 71.253.127.25471.253.127.2558,190
10971.253.128.0/1971.253.128.1 to 71.253.159.25471.253.159.2558,190
11071.253.160.0/1971.253.160.1 to 71.253.191.25471.253.191.2558,190
11171.253.192.0/1971.253.192.1 to 71.253.223.25471.253.223.2558,190
11271.253.224.0/1971.253.224.1 to 71.253.255.25471.253.255.2558,190
11371.254.0.0/1971.254.0.1 to 71.254.31.25471.254.31.2558,190
11471.254.32.0/1971.254.32.1 to 71.254.63.25471.254.63.2558,190
11571.254.64.0/1971.254.64.1 to 71.254.95.25471.254.95.2558,190
11671.254.96.0/1971.254.96.1 to 71.254.127.25471.254.127.2558,190
11771.254.128.0/1971.254.128.1 to 71.254.159.25471.254.159.2558,190
11871.254.160.0/1971.254.160.1 to 71.254.191.25471.254.191.2558,190
11971.254.192.0/1971.254.192.1 to 71.254.223.25471.254.223.2558,190
12071.254.224.0/1971.254.224.1 to 71.254.255.25471.254.255.2558,190
12171.255.0.0/1971.255.0.1 to 71.255.31.25471.255.31.2558,190
12271.255.32.0/1971.255.32.1 to 71.255.63.25471.255.63.2558,190
12371.255.64.0/1971.255.64.1 to 71.255.95.25471.255.95.2558,190
12471.255.96.0/1971.255.96.1 to 71.255.127.25471.255.127.2558,190
12571.255.128.0/1971.255.128.1 to 71.255.159.25471.255.159.2558,190
12671.255.160.0/1971.255.160.1 to 71.255.191.25471.255.191.2558,190
12771.255.192.0/1971.255.192.1 to 71.255.223.25471.255.223.2558,190
12871.255.224.0/1971.255.224.1 to 71.255.255.25471.255.255.2558,190

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.