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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.

Network243.128.0.0/9
Usable hosts8,388,606
Subnet mask255.128.0.0
Addresses8,388,608
Network address
243.128.0.0
Broadcast address
243.255.255.255
First usable
243.128.0.1
Last usable
243.255.255.254
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
Reserved 240.0.0.0/4
Future use; not usable on most systems
Old class
E (reserved)
As numbers
Hex F3800000 · Integer 4085252096 to 4093640703
Reverse DNS zones
128.243.in-addr.arpa
129.243.in-addr.arpa
130.243.in-addr.arpa
131.243.in-addr.arpa
132.243.in-addr.arpa
133.243.in-addr.arpa
134.243.in-addr.arpa
135.243.in-addr.arpa
136.243.in-addr.arpa
137.243.in-addr.arpa
138.243.in-addr.arpa
139.243.in-addr.arpa
140.243.in-addr.arpa
141.243.in-addr.arpa
142.243.in-addr.arpa
143.243.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
Address11110011.10000000.00000000.00000000243.128.0.0
Subnet mask11111111.10000000.00000000.00000000255.128.0.0
Network11110011.10000000.00000000.00000000243.128.0.0
Broadcast11110011.11111111.11111111.11111111243.255.255.255
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)

243.128.0.0/9 makes 128 subnets of /16.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
1243.128.0.0/16243.128.0.1 to 243.128.255.254243.128.255.25565,534
2243.129.0.0/16243.129.0.1 to 243.129.255.254243.129.255.25565,534
3243.130.0.0/16243.130.0.1 to 243.130.255.254243.130.255.25565,534
4243.131.0.0/16243.131.0.1 to 243.131.255.254243.131.255.25565,534
5243.132.0.0/16243.132.0.1 to 243.132.255.254243.132.255.25565,534
6243.133.0.0/16243.133.0.1 to 243.133.255.254243.133.255.25565,534
7243.134.0.0/16243.134.0.1 to 243.134.255.254243.134.255.25565,534
8243.135.0.0/16243.135.0.1 to 243.135.255.254243.135.255.25565,534
9243.136.0.0/16243.136.0.1 to 243.136.255.254243.136.255.25565,534
10243.137.0.0/16243.137.0.1 to 243.137.255.254243.137.255.25565,534
11243.138.0.0/16243.138.0.1 to 243.138.255.254243.138.255.25565,534
12243.139.0.0/16243.139.0.1 to 243.139.255.254243.139.255.25565,534
13243.140.0.0/16243.140.0.1 to 243.140.255.254243.140.255.25565,534
14243.141.0.0/16243.141.0.1 to 243.141.255.254243.141.255.25565,534
15243.142.0.0/16243.142.0.1 to 243.142.255.254243.142.255.25565,534
16243.143.0.0/16243.143.0.1 to 243.143.255.254243.143.255.25565,534
17243.144.0.0/16243.144.0.1 to 243.144.255.254243.144.255.25565,534
18243.145.0.0/16243.145.0.1 to 243.145.255.254243.145.255.25565,534
19243.146.0.0/16243.146.0.1 to 243.146.255.254243.146.255.25565,534
20243.147.0.0/16243.147.0.1 to 243.147.255.254243.147.255.25565,534
21243.148.0.0/16243.148.0.1 to 243.148.255.254243.148.255.25565,534
22243.149.0.0/16243.149.0.1 to 243.149.255.254243.149.255.25565,534
23243.150.0.0/16243.150.0.1 to 243.150.255.254243.150.255.25565,534
24243.151.0.0/16243.151.0.1 to 243.151.255.254243.151.255.25565,534
25243.152.0.0/16243.152.0.1 to 243.152.255.254243.152.255.25565,534
26243.153.0.0/16243.153.0.1 to 243.153.255.254243.153.255.25565,534
27243.154.0.0/16243.154.0.1 to 243.154.255.254243.154.255.25565,534
28243.155.0.0/16243.155.0.1 to 243.155.255.254243.155.255.25565,534
29243.156.0.0/16243.156.0.1 to 243.156.255.254243.156.255.25565,534
30243.157.0.0/16243.157.0.1 to 243.157.255.254243.157.255.25565,534
31243.158.0.0/16243.158.0.1 to 243.158.255.254243.158.255.25565,534
32243.159.0.0/16243.159.0.1 to 243.159.255.254243.159.255.25565,534
33243.160.0.0/16243.160.0.1 to 243.160.255.254243.160.255.25565,534
34243.161.0.0/16243.161.0.1 to 243.161.255.254243.161.255.25565,534
35243.162.0.0/16243.162.0.1 to 243.162.255.254243.162.255.25565,534
36243.163.0.0/16243.163.0.1 to 243.163.255.254243.163.255.25565,534
37243.164.0.0/16243.164.0.1 to 243.164.255.254243.164.255.25565,534
38243.165.0.0/16243.165.0.1 to 243.165.255.254243.165.255.25565,534
39243.166.0.0/16243.166.0.1 to 243.166.255.254243.166.255.25565,534
40243.167.0.0/16243.167.0.1 to 243.167.255.254243.167.255.25565,534
41243.168.0.0/16243.168.0.1 to 243.168.255.254243.168.255.25565,534
42243.169.0.0/16243.169.0.1 to 243.169.255.254243.169.255.25565,534
43243.170.0.0/16243.170.0.1 to 243.170.255.254243.170.255.25565,534
44243.171.0.0/16243.171.0.1 to 243.171.255.254243.171.255.25565,534
45243.172.0.0/16243.172.0.1 to 243.172.255.254243.172.255.25565,534
46243.173.0.0/16243.173.0.1 to 243.173.255.254243.173.255.25565,534
47243.174.0.0/16243.174.0.1 to 243.174.255.254243.174.255.25565,534
48243.175.0.0/16243.175.0.1 to 243.175.255.254243.175.255.25565,534
49243.176.0.0/16243.176.0.1 to 243.176.255.254243.176.255.25565,534
50243.177.0.0/16243.177.0.1 to 243.177.255.254243.177.255.25565,534
51243.178.0.0/16243.178.0.1 to 243.178.255.254243.178.255.25565,534
52243.179.0.0/16243.179.0.1 to 243.179.255.254243.179.255.25565,534
53243.180.0.0/16243.180.0.1 to 243.180.255.254243.180.255.25565,534
54243.181.0.0/16243.181.0.1 to 243.181.255.254243.181.255.25565,534
55243.182.0.0/16243.182.0.1 to 243.182.255.254243.182.255.25565,534
56243.183.0.0/16243.183.0.1 to 243.183.255.254243.183.255.25565,534
57243.184.0.0/16243.184.0.1 to 243.184.255.254243.184.255.25565,534
58243.185.0.0/16243.185.0.1 to 243.185.255.254243.185.255.25565,534
59243.186.0.0/16243.186.0.1 to 243.186.255.254243.186.255.25565,534
60243.187.0.0/16243.187.0.1 to 243.187.255.254243.187.255.25565,534
61243.188.0.0/16243.188.0.1 to 243.188.255.254243.188.255.25565,534
62243.189.0.0/16243.189.0.1 to 243.189.255.254243.189.255.25565,534
63243.190.0.0/16243.190.0.1 to 243.190.255.254243.190.255.25565,534
64243.191.0.0/16243.191.0.1 to 243.191.255.254243.191.255.25565,534
65243.192.0.0/16243.192.0.1 to 243.192.255.254243.192.255.25565,534
66243.193.0.0/16243.193.0.1 to 243.193.255.254243.193.255.25565,534
67243.194.0.0/16243.194.0.1 to 243.194.255.254243.194.255.25565,534
68243.195.0.0/16243.195.0.1 to 243.195.255.254243.195.255.25565,534
69243.196.0.0/16243.196.0.1 to 243.196.255.254243.196.255.25565,534
70243.197.0.0/16243.197.0.1 to 243.197.255.254243.197.255.25565,534
71243.198.0.0/16243.198.0.1 to 243.198.255.254243.198.255.25565,534
72243.199.0.0/16243.199.0.1 to 243.199.255.254243.199.255.25565,534
73243.200.0.0/16243.200.0.1 to 243.200.255.254243.200.255.25565,534
74243.201.0.0/16243.201.0.1 to 243.201.255.254243.201.255.25565,534
75243.202.0.0/16243.202.0.1 to 243.202.255.254243.202.255.25565,534
76243.203.0.0/16243.203.0.1 to 243.203.255.254243.203.255.25565,534
77243.204.0.0/16243.204.0.1 to 243.204.255.254243.204.255.25565,534
78243.205.0.0/16243.205.0.1 to 243.205.255.254243.205.255.25565,534
79243.206.0.0/16243.206.0.1 to 243.206.255.254243.206.255.25565,534
80243.207.0.0/16243.207.0.1 to 243.207.255.254243.207.255.25565,534
81243.208.0.0/16243.208.0.1 to 243.208.255.254243.208.255.25565,534
82243.209.0.0/16243.209.0.1 to 243.209.255.254243.209.255.25565,534
83243.210.0.0/16243.210.0.1 to 243.210.255.254243.210.255.25565,534
84243.211.0.0/16243.211.0.1 to 243.211.255.254243.211.255.25565,534
85243.212.0.0/16243.212.0.1 to 243.212.255.254243.212.255.25565,534
86243.213.0.0/16243.213.0.1 to 243.213.255.254243.213.255.25565,534
87243.214.0.0/16243.214.0.1 to 243.214.255.254243.214.255.25565,534
88243.215.0.0/16243.215.0.1 to 243.215.255.254243.215.255.25565,534
89243.216.0.0/16243.216.0.1 to 243.216.255.254243.216.255.25565,534
90243.217.0.0/16243.217.0.1 to 243.217.255.254243.217.255.25565,534
91243.218.0.0/16243.218.0.1 to 243.218.255.254243.218.255.25565,534
92243.219.0.0/16243.219.0.1 to 243.219.255.254243.219.255.25565,534
93243.220.0.0/16243.220.0.1 to 243.220.255.254243.220.255.25565,534
94243.221.0.0/16243.221.0.1 to 243.221.255.254243.221.255.25565,534
95243.222.0.0/16243.222.0.1 to 243.222.255.254243.222.255.25565,534
96243.223.0.0/16243.223.0.1 to 243.223.255.254243.223.255.25565,534
97243.224.0.0/16243.224.0.1 to 243.224.255.254243.224.255.25565,534
98243.225.0.0/16243.225.0.1 to 243.225.255.254243.225.255.25565,534
99243.226.0.0/16243.226.0.1 to 243.226.255.254243.226.255.25565,534
100243.227.0.0/16243.227.0.1 to 243.227.255.254243.227.255.25565,534
101243.228.0.0/16243.228.0.1 to 243.228.255.254243.228.255.25565,534
102243.229.0.0/16243.229.0.1 to 243.229.255.254243.229.255.25565,534
103243.230.0.0/16243.230.0.1 to 243.230.255.254243.230.255.25565,534
104243.231.0.0/16243.231.0.1 to 243.231.255.254243.231.255.25565,534
105243.232.0.0/16243.232.0.1 to 243.232.255.254243.232.255.25565,534
106243.233.0.0/16243.233.0.1 to 243.233.255.254243.233.255.25565,534
107243.234.0.0/16243.234.0.1 to 243.234.255.254243.234.255.25565,534
108243.235.0.0/16243.235.0.1 to 243.235.255.254243.235.255.25565,534
109243.236.0.0/16243.236.0.1 to 243.236.255.254243.236.255.25565,534
110243.237.0.0/16243.237.0.1 to 243.237.255.254243.237.255.25565,534
111243.238.0.0/16243.238.0.1 to 243.238.255.254243.238.255.25565,534
112243.239.0.0/16243.239.0.1 to 243.239.255.254243.239.255.25565,534
113243.240.0.0/16243.240.0.1 to 243.240.255.254243.240.255.25565,534
114243.241.0.0/16243.241.0.1 to 243.241.255.254243.241.255.25565,534
115243.242.0.0/16243.242.0.1 to 243.242.255.254243.242.255.25565,534
116243.243.0.0/16243.243.0.1 to 243.243.255.254243.243.255.25565,534
117243.244.0.0/16243.244.0.1 to 243.244.255.254243.244.255.25565,534
118243.245.0.0/16243.245.0.1 to 243.245.255.254243.245.255.25565,534
119243.246.0.0/16243.246.0.1 to 243.246.255.254243.246.255.25565,534
120243.247.0.0/16243.247.0.1 to 243.247.255.254243.247.255.25565,534
121243.248.0.0/16243.248.0.1 to 243.248.255.254243.248.255.25565,534
122243.249.0.0/16243.249.0.1 to 243.249.255.254243.249.255.25565,534
123243.250.0.0/16243.250.0.1 to 243.250.255.254243.250.255.25565,534
124243.251.0.0/16243.251.0.1 to 243.251.255.254243.251.255.25565,534
125243.252.0.0/16243.252.0.1 to 243.252.255.254243.252.255.25565,534
126243.253.0.0/16243.253.0.1 to 243.253.255.254243.253.255.25565,534
127243.254.0.0/16243.254.0.1 to 243.254.255.254243.254.255.25565,534
128243.255.0.0/16243.255.0.1 to 243.255.255.254243.255.255.25565,534

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.