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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.

Network81.0.0.0/9
Usable hosts8,388,606
Subnet mask255.128.0.0
Addresses8,388,608
Network address
81.0.0.0
Broadcast address
81.127.255.255
First usable
81.0.0.1
Last usable
81.127.255.254
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 51000000 · Integer 1358954496 to 1367343103
Reverse DNS zones
0.81.in-addr.arpa
1.81.in-addr.arpa
2.81.in-addr.arpa
3.81.in-addr.arpa
4.81.in-addr.arpa
5.81.in-addr.arpa
6.81.in-addr.arpa
7.81.in-addr.arpa
8.81.in-addr.arpa
9.81.in-addr.arpa
10.81.in-addr.arpa
11.81.in-addr.arpa
12.81.in-addr.arpa
13.81.in-addr.arpa
14.81.in-addr.arpa
15.81.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
Address01010001.00000000.00000000.0000000081.0.0.0
Subnet mask11111111.10000000.00000000.00000000255.128.0.0
Network01010001.00000000.00000000.0000000081.0.0.0
Broadcast01010001.01111111.11111111.1111111181.127.255.255
Split into smaller subnets/21
/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)

81.0.0.0/9 makes 4,096 subnets of /21; the first 256 are listed.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
181.0.0.0/2181.0.0.1 to 81.0.7.25481.0.7.2552,046
281.0.8.0/2181.0.8.1 to 81.0.15.25481.0.15.2552,046
381.0.16.0/2181.0.16.1 to 81.0.23.25481.0.23.2552,046
481.0.24.0/2181.0.24.1 to 81.0.31.25481.0.31.2552,046
581.0.32.0/2181.0.32.1 to 81.0.39.25481.0.39.2552,046
681.0.40.0/2181.0.40.1 to 81.0.47.25481.0.47.2552,046
781.0.48.0/2181.0.48.1 to 81.0.55.25481.0.55.2552,046
881.0.56.0/2181.0.56.1 to 81.0.63.25481.0.63.2552,046
981.0.64.0/2181.0.64.1 to 81.0.71.25481.0.71.2552,046
1081.0.72.0/2181.0.72.1 to 81.0.79.25481.0.79.2552,046
1181.0.80.0/2181.0.80.1 to 81.0.87.25481.0.87.2552,046
1281.0.88.0/2181.0.88.1 to 81.0.95.25481.0.95.2552,046
1381.0.96.0/2181.0.96.1 to 81.0.103.25481.0.103.2552,046
1481.0.104.0/2181.0.104.1 to 81.0.111.25481.0.111.2552,046
1581.0.112.0/2181.0.112.1 to 81.0.119.25481.0.119.2552,046
1681.0.120.0/2181.0.120.1 to 81.0.127.25481.0.127.2552,046
1781.0.128.0/2181.0.128.1 to 81.0.135.25481.0.135.2552,046
1881.0.136.0/2181.0.136.1 to 81.0.143.25481.0.143.2552,046
1981.0.144.0/2181.0.144.1 to 81.0.151.25481.0.151.2552,046
2081.0.152.0/2181.0.152.1 to 81.0.159.25481.0.159.2552,046
2181.0.160.0/2181.0.160.1 to 81.0.167.25481.0.167.2552,046
2281.0.168.0/2181.0.168.1 to 81.0.175.25481.0.175.2552,046
2381.0.176.0/2181.0.176.1 to 81.0.183.25481.0.183.2552,046
2481.0.184.0/2181.0.184.1 to 81.0.191.25481.0.191.2552,046
2581.0.192.0/2181.0.192.1 to 81.0.199.25481.0.199.2552,046
2681.0.200.0/2181.0.200.1 to 81.0.207.25481.0.207.2552,046
2781.0.208.0/2181.0.208.1 to 81.0.215.25481.0.215.2552,046
2881.0.216.0/2181.0.216.1 to 81.0.223.25481.0.223.2552,046
2981.0.224.0/2181.0.224.1 to 81.0.231.25481.0.231.2552,046
3081.0.232.0/2181.0.232.1 to 81.0.239.25481.0.239.2552,046
3181.0.240.0/2181.0.240.1 to 81.0.247.25481.0.247.2552,046
3281.0.248.0/2181.0.248.1 to 81.0.255.25481.0.255.2552,046
3381.1.0.0/2181.1.0.1 to 81.1.7.25481.1.7.2552,046
3481.1.8.0/2181.1.8.1 to 81.1.15.25481.1.15.2552,046
3581.1.16.0/2181.1.16.1 to 81.1.23.25481.1.23.2552,046
3681.1.24.0/2181.1.24.1 to 81.1.31.25481.1.31.2552,046
3781.1.32.0/2181.1.32.1 to 81.1.39.25481.1.39.2552,046
3881.1.40.0/2181.1.40.1 to 81.1.47.25481.1.47.2552,046
3981.1.48.0/2181.1.48.1 to 81.1.55.25481.1.55.2552,046
4081.1.56.0/2181.1.56.1 to 81.1.63.25481.1.63.2552,046
4181.1.64.0/2181.1.64.1 to 81.1.71.25481.1.71.2552,046
4281.1.72.0/2181.1.72.1 to 81.1.79.25481.1.79.2552,046
4381.1.80.0/2181.1.80.1 to 81.1.87.25481.1.87.2552,046
4481.1.88.0/2181.1.88.1 to 81.1.95.25481.1.95.2552,046
4581.1.96.0/2181.1.96.1 to 81.1.103.25481.1.103.2552,046
4681.1.104.0/2181.1.104.1 to 81.1.111.25481.1.111.2552,046
4781.1.112.0/2181.1.112.1 to 81.1.119.25481.1.119.2552,046
4881.1.120.0/2181.1.120.1 to 81.1.127.25481.1.127.2552,046
4981.1.128.0/2181.1.128.1 to 81.1.135.25481.1.135.2552,046
5081.1.136.0/2181.1.136.1 to 81.1.143.25481.1.143.2552,046
5181.1.144.0/2181.1.144.1 to 81.1.151.25481.1.151.2552,046
5281.1.152.0/2181.1.152.1 to 81.1.159.25481.1.159.2552,046
5381.1.160.0/2181.1.160.1 to 81.1.167.25481.1.167.2552,046
5481.1.168.0/2181.1.168.1 to 81.1.175.25481.1.175.2552,046
5581.1.176.0/2181.1.176.1 to 81.1.183.25481.1.183.2552,046
5681.1.184.0/2181.1.184.1 to 81.1.191.25481.1.191.2552,046
5781.1.192.0/2181.1.192.1 to 81.1.199.25481.1.199.2552,046
5881.1.200.0/2181.1.200.1 to 81.1.207.25481.1.207.2552,046
5981.1.208.0/2181.1.208.1 to 81.1.215.25481.1.215.2552,046
6081.1.216.0/2181.1.216.1 to 81.1.223.25481.1.223.2552,046
6181.1.224.0/2181.1.224.1 to 81.1.231.25481.1.231.2552,046
6281.1.232.0/2181.1.232.1 to 81.1.239.25481.1.239.2552,046
6381.1.240.0/2181.1.240.1 to 81.1.247.25481.1.247.2552,046
6481.1.248.0/2181.1.248.1 to 81.1.255.25481.1.255.2552,046
6581.2.0.0/2181.2.0.1 to 81.2.7.25481.2.7.2552,046
6681.2.8.0/2181.2.8.1 to 81.2.15.25481.2.15.2552,046
6781.2.16.0/2181.2.16.1 to 81.2.23.25481.2.23.2552,046
6881.2.24.0/2181.2.24.1 to 81.2.31.25481.2.31.2552,046
6981.2.32.0/2181.2.32.1 to 81.2.39.25481.2.39.2552,046
7081.2.40.0/2181.2.40.1 to 81.2.47.25481.2.47.2552,046
7181.2.48.0/2181.2.48.1 to 81.2.55.25481.2.55.2552,046
7281.2.56.0/2181.2.56.1 to 81.2.63.25481.2.63.2552,046
7381.2.64.0/2181.2.64.1 to 81.2.71.25481.2.71.2552,046
7481.2.72.0/2181.2.72.1 to 81.2.79.25481.2.79.2552,046
7581.2.80.0/2181.2.80.1 to 81.2.87.25481.2.87.2552,046
7681.2.88.0/2181.2.88.1 to 81.2.95.25481.2.95.2552,046
7781.2.96.0/2181.2.96.1 to 81.2.103.25481.2.103.2552,046
7881.2.104.0/2181.2.104.1 to 81.2.111.25481.2.111.2552,046
7981.2.112.0/2181.2.112.1 to 81.2.119.25481.2.119.2552,046
8081.2.120.0/2181.2.120.1 to 81.2.127.25481.2.127.2552,046
8181.2.128.0/2181.2.128.1 to 81.2.135.25481.2.135.2552,046
8281.2.136.0/2181.2.136.1 to 81.2.143.25481.2.143.2552,046
8381.2.144.0/2181.2.144.1 to 81.2.151.25481.2.151.2552,046
8481.2.152.0/2181.2.152.1 to 81.2.159.25481.2.159.2552,046
8581.2.160.0/2181.2.160.1 to 81.2.167.25481.2.167.2552,046
8681.2.168.0/2181.2.168.1 to 81.2.175.25481.2.175.2552,046
8781.2.176.0/2181.2.176.1 to 81.2.183.25481.2.183.2552,046
8881.2.184.0/2181.2.184.1 to 81.2.191.25481.2.191.2552,046
8981.2.192.0/2181.2.192.1 to 81.2.199.25481.2.199.2552,046
9081.2.200.0/2181.2.200.1 to 81.2.207.25481.2.207.2552,046
9181.2.208.0/2181.2.208.1 to 81.2.215.25481.2.215.2552,046
9281.2.216.0/2181.2.216.1 to 81.2.223.25481.2.223.2552,046
9381.2.224.0/2181.2.224.1 to 81.2.231.25481.2.231.2552,046
9481.2.232.0/2181.2.232.1 to 81.2.239.25481.2.239.2552,046
9581.2.240.0/2181.2.240.1 to 81.2.247.25481.2.247.2552,046
9681.2.248.0/2181.2.248.1 to 81.2.255.25481.2.255.2552,046
9781.3.0.0/2181.3.0.1 to 81.3.7.25481.3.7.2552,046
9881.3.8.0/2181.3.8.1 to 81.3.15.25481.3.15.2552,046
9981.3.16.0/2181.3.16.1 to 81.3.23.25481.3.23.2552,046
10081.3.24.0/2181.3.24.1 to 81.3.31.25481.3.31.2552,046
10181.3.32.0/2181.3.32.1 to 81.3.39.25481.3.39.2552,046
10281.3.40.0/2181.3.40.1 to 81.3.47.25481.3.47.2552,046
10381.3.48.0/2181.3.48.1 to 81.3.55.25481.3.55.2552,046
10481.3.56.0/2181.3.56.1 to 81.3.63.25481.3.63.2552,046
10581.3.64.0/2181.3.64.1 to 81.3.71.25481.3.71.2552,046
10681.3.72.0/2181.3.72.1 to 81.3.79.25481.3.79.2552,046
10781.3.80.0/2181.3.80.1 to 81.3.87.25481.3.87.2552,046
10881.3.88.0/2181.3.88.1 to 81.3.95.25481.3.95.2552,046
10981.3.96.0/2181.3.96.1 to 81.3.103.25481.3.103.2552,046
11081.3.104.0/2181.3.104.1 to 81.3.111.25481.3.111.2552,046
11181.3.112.0/2181.3.112.1 to 81.3.119.25481.3.119.2552,046
11281.3.120.0/2181.3.120.1 to 81.3.127.25481.3.127.2552,046
11381.3.128.0/2181.3.128.1 to 81.3.135.25481.3.135.2552,046
11481.3.136.0/2181.3.136.1 to 81.3.143.25481.3.143.2552,046
11581.3.144.0/2181.3.144.1 to 81.3.151.25481.3.151.2552,046
11681.3.152.0/2181.3.152.1 to 81.3.159.25481.3.159.2552,046
11781.3.160.0/2181.3.160.1 to 81.3.167.25481.3.167.2552,046
11881.3.168.0/2181.3.168.1 to 81.3.175.25481.3.175.2552,046
11981.3.176.0/2181.3.176.1 to 81.3.183.25481.3.183.2552,046
12081.3.184.0/2181.3.184.1 to 81.3.191.25481.3.191.2552,046
12181.3.192.0/2181.3.192.1 to 81.3.199.25481.3.199.2552,046
12281.3.200.0/2181.3.200.1 to 81.3.207.25481.3.207.2552,046
12381.3.208.0/2181.3.208.1 to 81.3.215.25481.3.215.2552,046
12481.3.216.0/2181.3.216.1 to 81.3.223.25481.3.223.2552,046
12581.3.224.0/2181.3.224.1 to 81.3.231.25481.3.231.2552,046
12681.3.232.0/2181.3.232.1 to 81.3.239.25481.3.239.2552,046
12781.3.240.0/2181.3.240.1 to 81.3.247.25481.3.247.2552,046
12881.3.248.0/2181.3.248.1 to 81.3.255.25481.3.255.2552,046
12981.4.0.0/2181.4.0.1 to 81.4.7.25481.4.7.2552,046
13081.4.8.0/2181.4.8.1 to 81.4.15.25481.4.15.2552,046
13181.4.16.0/2181.4.16.1 to 81.4.23.25481.4.23.2552,046
13281.4.24.0/2181.4.24.1 to 81.4.31.25481.4.31.2552,046
13381.4.32.0/2181.4.32.1 to 81.4.39.25481.4.39.2552,046
13481.4.40.0/2181.4.40.1 to 81.4.47.25481.4.47.2552,046
13581.4.48.0/2181.4.48.1 to 81.4.55.25481.4.55.2552,046
13681.4.56.0/2181.4.56.1 to 81.4.63.25481.4.63.2552,046
13781.4.64.0/2181.4.64.1 to 81.4.71.25481.4.71.2552,046
13881.4.72.0/2181.4.72.1 to 81.4.79.25481.4.79.2552,046
13981.4.80.0/2181.4.80.1 to 81.4.87.25481.4.87.2552,046
14081.4.88.0/2181.4.88.1 to 81.4.95.25481.4.95.2552,046
14181.4.96.0/2181.4.96.1 to 81.4.103.25481.4.103.2552,046
14281.4.104.0/2181.4.104.1 to 81.4.111.25481.4.111.2552,046
14381.4.112.0/2181.4.112.1 to 81.4.119.25481.4.119.2552,046
14481.4.120.0/2181.4.120.1 to 81.4.127.25481.4.127.2552,046
14581.4.128.0/2181.4.128.1 to 81.4.135.25481.4.135.2552,046
14681.4.136.0/2181.4.136.1 to 81.4.143.25481.4.143.2552,046
14781.4.144.0/2181.4.144.1 to 81.4.151.25481.4.151.2552,046
14881.4.152.0/2181.4.152.1 to 81.4.159.25481.4.159.2552,046
14981.4.160.0/2181.4.160.1 to 81.4.167.25481.4.167.2552,046
15081.4.168.0/2181.4.168.1 to 81.4.175.25481.4.175.2552,046
15181.4.176.0/2181.4.176.1 to 81.4.183.25481.4.183.2552,046
15281.4.184.0/2181.4.184.1 to 81.4.191.25481.4.191.2552,046
15381.4.192.0/2181.4.192.1 to 81.4.199.25481.4.199.2552,046
15481.4.200.0/2181.4.200.1 to 81.4.207.25481.4.207.2552,046
15581.4.208.0/2181.4.208.1 to 81.4.215.25481.4.215.2552,046
15681.4.216.0/2181.4.216.1 to 81.4.223.25481.4.223.2552,046
15781.4.224.0/2181.4.224.1 to 81.4.231.25481.4.231.2552,046
15881.4.232.0/2181.4.232.1 to 81.4.239.25481.4.239.2552,046
15981.4.240.0/2181.4.240.1 to 81.4.247.25481.4.247.2552,046
16081.4.248.0/2181.4.248.1 to 81.4.255.25481.4.255.2552,046
16181.5.0.0/2181.5.0.1 to 81.5.7.25481.5.7.2552,046
16281.5.8.0/2181.5.8.1 to 81.5.15.25481.5.15.2552,046
16381.5.16.0/2181.5.16.1 to 81.5.23.25481.5.23.2552,046
16481.5.24.0/2181.5.24.1 to 81.5.31.25481.5.31.2552,046
16581.5.32.0/2181.5.32.1 to 81.5.39.25481.5.39.2552,046
16681.5.40.0/2181.5.40.1 to 81.5.47.25481.5.47.2552,046
16781.5.48.0/2181.5.48.1 to 81.5.55.25481.5.55.2552,046
16881.5.56.0/2181.5.56.1 to 81.5.63.25481.5.63.2552,046
16981.5.64.0/2181.5.64.1 to 81.5.71.25481.5.71.2552,046
17081.5.72.0/2181.5.72.1 to 81.5.79.25481.5.79.2552,046
17181.5.80.0/2181.5.80.1 to 81.5.87.25481.5.87.2552,046
17281.5.88.0/2181.5.88.1 to 81.5.95.25481.5.95.2552,046
17381.5.96.0/2181.5.96.1 to 81.5.103.25481.5.103.2552,046
17481.5.104.0/2181.5.104.1 to 81.5.111.25481.5.111.2552,046
17581.5.112.0/2181.5.112.1 to 81.5.119.25481.5.119.2552,046
17681.5.120.0/2181.5.120.1 to 81.5.127.25481.5.127.2552,046
17781.5.128.0/2181.5.128.1 to 81.5.135.25481.5.135.2552,046
17881.5.136.0/2181.5.136.1 to 81.5.143.25481.5.143.2552,046
17981.5.144.0/2181.5.144.1 to 81.5.151.25481.5.151.2552,046
18081.5.152.0/2181.5.152.1 to 81.5.159.25481.5.159.2552,046
18181.5.160.0/2181.5.160.1 to 81.5.167.25481.5.167.2552,046
18281.5.168.0/2181.5.168.1 to 81.5.175.25481.5.175.2552,046
18381.5.176.0/2181.5.176.1 to 81.5.183.25481.5.183.2552,046
18481.5.184.0/2181.5.184.1 to 81.5.191.25481.5.191.2552,046
18581.5.192.0/2181.5.192.1 to 81.5.199.25481.5.199.2552,046
18681.5.200.0/2181.5.200.1 to 81.5.207.25481.5.207.2552,046
18781.5.208.0/2181.5.208.1 to 81.5.215.25481.5.215.2552,046
18881.5.216.0/2181.5.216.1 to 81.5.223.25481.5.223.2552,046
18981.5.224.0/2181.5.224.1 to 81.5.231.25481.5.231.2552,046
19081.5.232.0/2181.5.232.1 to 81.5.239.25481.5.239.2552,046
19181.5.240.0/2181.5.240.1 to 81.5.247.25481.5.247.2552,046
19281.5.248.0/2181.5.248.1 to 81.5.255.25481.5.255.2552,046
19381.6.0.0/2181.6.0.1 to 81.6.7.25481.6.7.2552,046
19481.6.8.0/2181.6.8.1 to 81.6.15.25481.6.15.2552,046
19581.6.16.0/2181.6.16.1 to 81.6.23.25481.6.23.2552,046
19681.6.24.0/2181.6.24.1 to 81.6.31.25481.6.31.2552,046
19781.6.32.0/2181.6.32.1 to 81.6.39.25481.6.39.2552,046
19881.6.40.0/2181.6.40.1 to 81.6.47.25481.6.47.2552,046
19981.6.48.0/2181.6.48.1 to 81.6.55.25481.6.55.2552,046
20081.6.56.0/2181.6.56.1 to 81.6.63.25481.6.63.2552,046
20181.6.64.0/2181.6.64.1 to 81.6.71.25481.6.71.2552,046
20281.6.72.0/2181.6.72.1 to 81.6.79.25481.6.79.2552,046
20381.6.80.0/2181.6.80.1 to 81.6.87.25481.6.87.2552,046
20481.6.88.0/2181.6.88.1 to 81.6.95.25481.6.95.2552,046
20581.6.96.0/2181.6.96.1 to 81.6.103.25481.6.103.2552,046
20681.6.104.0/2181.6.104.1 to 81.6.111.25481.6.111.2552,046
20781.6.112.0/2181.6.112.1 to 81.6.119.25481.6.119.2552,046
20881.6.120.0/2181.6.120.1 to 81.6.127.25481.6.127.2552,046
20981.6.128.0/2181.6.128.1 to 81.6.135.25481.6.135.2552,046
21081.6.136.0/2181.6.136.1 to 81.6.143.25481.6.143.2552,046
21181.6.144.0/2181.6.144.1 to 81.6.151.25481.6.151.2552,046
21281.6.152.0/2181.6.152.1 to 81.6.159.25481.6.159.2552,046
21381.6.160.0/2181.6.160.1 to 81.6.167.25481.6.167.2552,046
21481.6.168.0/2181.6.168.1 to 81.6.175.25481.6.175.2552,046
21581.6.176.0/2181.6.176.1 to 81.6.183.25481.6.183.2552,046
21681.6.184.0/2181.6.184.1 to 81.6.191.25481.6.191.2552,046
21781.6.192.0/2181.6.192.1 to 81.6.199.25481.6.199.2552,046
21881.6.200.0/2181.6.200.1 to 81.6.207.25481.6.207.2552,046
21981.6.208.0/2181.6.208.1 to 81.6.215.25481.6.215.2552,046
22081.6.216.0/2181.6.216.1 to 81.6.223.25481.6.223.2552,046
22181.6.224.0/2181.6.224.1 to 81.6.231.25481.6.231.2552,046
22281.6.232.0/2181.6.232.1 to 81.6.239.25481.6.239.2552,046
22381.6.240.0/2181.6.240.1 to 81.6.247.25481.6.247.2552,046
22481.6.248.0/2181.6.248.1 to 81.6.255.25481.6.255.2552,046
22581.7.0.0/2181.7.0.1 to 81.7.7.25481.7.7.2552,046
22681.7.8.0/2181.7.8.1 to 81.7.15.25481.7.15.2552,046
22781.7.16.0/2181.7.16.1 to 81.7.23.25481.7.23.2552,046
22881.7.24.0/2181.7.24.1 to 81.7.31.25481.7.31.2552,046
22981.7.32.0/2181.7.32.1 to 81.7.39.25481.7.39.2552,046
23081.7.40.0/2181.7.40.1 to 81.7.47.25481.7.47.2552,046
23181.7.48.0/2181.7.48.1 to 81.7.55.25481.7.55.2552,046
23281.7.56.0/2181.7.56.1 to 81.7.63.25481.7.63.2552,046
23381.7.64.0/2181.7.64.1 to 81.7.71.25481.7.71.2552,046
23481.7.72.0/2181.7.72.1 to 81.7.79.25481.7.79.2552,046
23581.7.80.0/2181.7.80.1 to 81.7.87.25481.7.87.2552,046
23681.7.88.0/2181.7.88.1 to 81.7.95.25481.7.95.2552,046
23781.7.96.0/2181.7.96.1 to 81.7.103.25481.7.103.2552,046
23881.7.104.0/2181.7.104.1 to 81.7.111.25481.7.111.2552,046
23981.7.112.0/2181.7.112.1 to 81.7.119.25481.7.119.2552,046
24081.7.120.0/2181.7.120.1 to 81.7.127.25481.7.127.2552,046
24181.7.128.0/2181.7.128.1 to 81.7.135.25481.7.135.2552,046
24281.7.136.0/2181.7.136.1 to 81.7.143.25481.7.143.2552,046
24381.7.144.0/2181.7.144.1 to 81.7.151.25481.7.151.2552,046
24481.7.152.0/2181.7.152.1 to 81.7.159.25481.7.159.2552,046
24581.7.160.0/2181.7.160.1 to 81.7.167.25481.7.167.2552,046
24681.7.168.0/2181.7.168.1 to 81.7.175.25481.7.175.2552,046
24781.7.176.0/2181.7.176.1 to 81.7.183.25481.7.183.2552,046
24881.7.184.0/2181.7.184.1 to 81.7.191.25481.7.191.2552,046
24981.7.192.0/2181.7.192.1 to 81.7.199.25481.7.199.2552,046
25081.7.200.0/2181.7.200.1 to 81.7.207.25481.7.207.2552,046
25181.7.208.0/2181.7.208.1 to 81.7.215.25481.7.215.2552,046
25281.7.216.0/2181.7.216.1 to 81.7.223.25481.7.223.2552,046
25381.7.224.0/2181.7.224.1 to 81.7.231.25481.7.231.2552,046
25481.7.232.0/2181.7.232.1 to 81.7.239.25481.7.239.2552,046
25581.7.240.0/2181.7.240.1 to 81.7.247.25481.7.247.2552,046
25681.7.248.0/2181.7.248.1 to 81.7.255.25481.7.255.2552,046

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.