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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.

Network21.128.0.0/9
Usable hosts8,388,606
Subnet mask255.128.0.0
Addresses8,388,608
Network address
21.128.0.0
Broadcast address
21.255.255.255
First usable
21.128.0.1
Last usable
21.255.255.254
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
Public public
Old class
A (default /8)
As numbers
Hex 15800000 · Integer 360710144 to 369098751
Reverse DNS zones
128.21.in-addr.arpa
129.21.in-addr.arpa
130.21.in-addr.arpa
131.21.in-addr.arpa
132.21.in-addr.arpa
133.21.in-addr.arpa
134.21.in-addr.arpa
135.21.in-addr.arpa
136.21.in-addr.arpa
137.21.in-addr.arpa
138.21.in-addr.arpa
139.21.in-addr.arpa
140.21.in-addr.arpa
141.21.in-addr.arpa
142.21.in-addr.arpa
143.21.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
Address00010101.10000000.00000000.0000000021.128.0.0
Subnet mask11111111.10000000.00000000.00000000255.128.0.0
Network00010101.10000000.00000000.0000000021.128.0.0
Broadcast00010101.11111111.11111111.1111111121.255.255.255
Split into smaller subnets/17
/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)

21.128.0.0/9 makes 256 subnets of /17.

Subnets
#SubnetUsable hosts rangeBroadcastHosts
121.128.0.0/1721.128.0.1 to 21.128.127.25421.128.127.25532,766
221.128.128.0/1721.128.128.1 to 21.128.255.25421.128.255.25532,766
321.129.0.0/1721.129.0.1 to 21.129.127.25421.129.127.25532,766
421.129.128.0/1721.129.128.1 to 21.129.255.25421.129.255.25532,766
521.130.0.0/1721.130.0.1 to 21.130.127.25421.130.127.25532,766
621.130.128.0/1721.130.128.1 to 21.130.255.25421.130.255.25532,766
721.131.0.0/1721.131.0.1 to 21.131.127.25421.131.127.25532,766
821.131.128.0/1721.131.128.1 to 21.131.255.25421.131.255.25532,766
921.132.0.0/1721.132.0.1 to 21.132.127.25421.132.127.25532,766
1021.132.128.0/1721.132.128.1 to 21.132.255.25421.132.255.25532,766
1121.133.0.0/1721.133.0.1 to 21.133.127.25421.133.127.25532,766
1221.133.128.0/1721.133.128.1 to 21.133.255.25421.133.255.25532,766
1321.134.0.0/1721.134.0.1 to 21.134.127.25421.134.127.25532,766
1421.134.128.0/1721.134.128.1 to 21.134.255.25421.134.255.25532,766
1521.135.0.0/1721.135.0.1 to 21.135.127.25421.135.127.25532,766
1621.135.128.0/1721.135.128.1 to 21.135.255.25421.135.255.25532,766
1721.136.0.0/1721.136.0.1 to 21.136.127.25421.136.127.25532,766
1821.136.128.0/1721.136.128.1 to 21.136.255.25421.136.255.25532,766
1921.137.0.0/1721.137.0.1 to 21.137.127.25421.137.127.25532,766
2021.137.128.0/1721.137.128.1 to 21.137.255.25421.137.255.25532,766
2121.138.0.0/1721.138.0.1 to 21.138.127.25421.138.127.25532,766
2221.138.128.0/1721.138.128.1 to 21.138.255.25421.138.255.25532,766
2321.139.0.0/1721.139.0.1 to 21.139.127.25421.139.127.25532,766
2421.139.128.0/1721.139.128.1 to 21.139.255.25421.139.255.25532,766
2521.140.0.0/1721.140.0.1 to 21.140.127.25421.140.127.25532,766
2621.140.128.0/1721.140.128.1 to 21.140.255.25421.140.255.25532,766
2721.141.0.0/1721.141.0.1 to 21.141.127.25421.141.127.25532,766
2821.141.128.0/1721.141.128.1 to 21.141.255.25421.141.255.25532,766
2921.142.0.0/1721.142.0.1 to 21.142.127.25421.142.127.25532,766
3021.142.128.0/1721.142.128.1 to 21.142.255.25421.142.255.25532,766
3121.143.0.0/1721.143.0.1 to 21.143.127.25421.143.127.25532,766
3221.143.128.0/1721.143.128.1 to 21.143.255.25421.143.255.25532,766
3321.144.0.0/1721.144.0.1 to 21.144.127.25421.144.127.25532,766
3421.144.128.0/1721.144.128.1 to 21.144.255.25421.144.255.25532,766
3521.145.0.0/1721.145.0.1 to 21.145.127.25421.145.127.25532,766
3621.145.128.0/1721.145.128.1 to 21.145.255.25421.145.255.25532,766
3721.146.0.0/1721.146.0.1 to 21.146.127.25421.146.127.25532,766
3821.146.128.0/1721.146.128.1 to 21.146.255.25421.146.255.25532,766
3921.147.0.0/1721.147.0.1 to 21.147.127.25421.147.127.25532,766
4021.147.128.0/1721.147.128.1 to 21.147.255.25421.147.255.25532,766
4121.148.0.0/1721.148.0.1 to 21.148.127.25421.148.127.25532,766
4221.148.128.0/1721.148.128.1 to 21.148.255.25421.148.255.25532,766
4321.149.0.0/1721.149.0.1 to 21.149.127.25421.149.127.25532,766
4421.149.128.0/1721.149.128.1 to 21.149.255.25421.149.255.25532,766
4521.150.0.0/1721.150.0.1 to 21.150.127.25421.150.127.25532,766
4621.150.128.0/1721.150.128.1 to 21.150.255.25421.150.255.25532,766
4721.151.0.0/1721.151.0.1 to 21.151.127.25421.151.127.25532,766
4821.151.128.0/1721.151.128.1 to 21.151.255.25421.151.255.25532,766
4921.152.0.0/1721.152.0.1 to 21.152.127.25421.152.127.25532,766
5021.152.128.0/1721.152.128.1 to 21.152.255.25421.152.255.25532,766
5121.153.0.0/1721.153.0.1 to 21.153.127.25421.153.127.25532,766
5221.153.128.0/1721.153.128.1 to 21.153.255.25421.153.255.25532,766
5321.154.0.0/1721.154.0.1 to 21.154.127.25421.154.127.25532,766
5421.154.128.0/1721.154.128.1 to 21.154.255.25421.154.255.25532,766
5521.155.0.0/1721.155.0.1 to 21.155.127.25421.155.127.25532,766
5621.155.128.0/1721.155.128.1 to 21.155.255.25421.155.255.25532,766
5721.156.0.0/1721.156.0.1 to 21.156.127.25421.156.127.25532,766
5821.156.128.0/1721.156.128.1 to 21.156.255.25421.156.255.25532,766
5921.157.0.0/1721.157.0.1 to 21.157.127.25421.157.127.25532,766
6021.157.128.0/1721.157.128.1 to 21.157.255.25421.157.255.25532,766
6121.158.0.0/1721.158.0.1 to 21.158.127.25421.158.127.25532,766
6221.158.128.0/1721.158.128.1 to 21.158.255.25421.158.255.25532,766
6321.159.0.0/1721.159.0.1 to 21.159.127.25421.159.127.25532,766
6421.159.128.0/1721.159.128.1 to 21.159.255.25421.159.255.25532,766
6521.160.0.0/1721.160.0.1 to 21.160.127.25421.160.127.25532,766
6621.160.128.0/1721.160.128.1 to 21.160.255.25421.160.255.25532,766
6721.161.0.0/1721.161.0.1 to 21.161.127.25421.161.127.25532,766
6821.161.128.0/1721.161.128.1 to 21.161.255.25421.161.255.25532,766
6921.162.0.0/1721.162.0.1 to 21.162.127.25421.162.127.25532,766
7021.162.128.0/1721.162.128.1 to 21.162.255.25421.162.255.25532,766
7121.163.0.0/1721.163.0.1 to 21.163.127.25421.163.127.25532,766
7221.163.128.0/1721.163.128.1 to 21.163.255.25421.163.255.25532,766
7321.164.0.0/1721.164.0.1 to 21.164.127.25421.164.127.25532,766
7421.164.128.0/1721.164.128.1 to 21.164.255.25421.164.255.25532,766
7521.165.0.0/1721.165.0.1 to 21.165.127.25421.165.127.25532,766
7621.165.128.0/1721.165.128.1 to 21.165.255.25421.165.255.25532,766
7721.166.0.0/1721.166.0.1 to 21.166.127.25421.166.127.25532,766
7821.166.128.0/1721.166.128.1 to 21.166.255.25421.166.255.25532,766
7921.167.0.0/1721.167.0.1 to 21.167.127.25421.167.127.25532,766
8021.167.128.0/1721.167.128.1 to 21.167.255.25421.167.255.25532,766
8121.168.0.0/1721.168.0.1 to 21.168.127.25421.168.127.25532,766
8221.168.128.0/1721.168.128.1 to 21.168.255.25421.168.255.25532,766
8321.169.0.0/1721.169.0.1 to 21.169.127.25421.169.127.25532,766
8421.169.128.0/1721.169.128.1 to 21.169.255.25421.169.255.25532,766
8521.170.0.0/1721.170.0.1 to 21.170.127.25421.170.127.25532,766
8621.170.128.0/1721.170.128.1 to 21.170.255.25421.170.255.25532,766
8721.171.0.0/1721.171.0.1 to 21.171.127.25421.171.127.25532,766
8821.171.128.0/1721.171.128.1 to 21.171.255.25421.171.255.25532,766
8921.172.0.0/1721.172.0.1 to 21.172.127.25421.172.127.25532,766
9021.172.128.0/1721.172.128.1 to 21.172.255.25421.172.255.25532,766
9121.173.0.0/1721.173.0.1 to 21.173.127.25421.173.127.25532,766
9221.173.128.0/1721.173.128.1 to 21.173.255.25421.173.255.25532,766
9321.174.0.0/1721.174.0.1 to 21.174.127.25421.174.127.25532,766
9421.174.128.0/1721.174.128.1 to 21.174.255.25421.174.255.25532,766
9521.175.0.0/1721.175.0.1 to 21.175.127.25421.175.127.25532,766
9621.175.128.0/1721.175.128.1 to 21.175.255.25421.175.255.25532,766
9721.176.0.0/1721.176.0.1 to 21.176.127.25421.176.127.25532,766
9821.176.128.0/1721.176.128.1 to 21.176.255.25421.176.255.25532,766
9921.177.0.0/1721.177.0.1 to 21.177.127.25421.177.127.25532,766
10021.177.128.0/1721.177.128.1 to 21.177.255.25421.177.255.25532,766
10121.178.0.0/1721.178.0.1 to 21.178.127.25421.178.127.25532,766
10221.178.128.0/1721.178.128.1 to 21.178.255.25421.178.255.25532,766
10321.179.0.0/1721.179.0.1 to 21.179.127.25421.179.127.25532,766
10421.179.128.0/1721.179.128.1 to 21.179.255.25421.179.255.25532,766
10521.180.0.0/1721.180.0.1 to 21.180.127.25421.180.127.25532,766
10621.180.128.0/1721.180.128.1 to 21.180.255.25421.180.255.25532,766
10721.181.0.0/1721.181.0.1 to 21.181.127.25421.181.127.25532,766
10821.181.128.0/1721.181.128.1 to 21.181.255.25421.181.255.25532,766
10921.182.0.0/1721.182.0.1 to 21.182.127.25421.182.127.25532,766
11021.182.128.0/1721.182.128.1 to 21.182.255.25421.182.255.25532,766
11121.183.0.0/1721.183.0.1 to 21.183.127.25421.183.127.25532,766
11221.183.128.0/1721.183.128.1 to 21.183.255.25421.183.255.25532,766
11321.184.0.0/1721.184.0.1 to 21.184.127.25421.184.127.25532,766
11421.184.128.0/1721.184.128.1 to 21.184.255.25421.184.255.25532,766
11521.185.0.0/1721.185.0.1 to 21.185.127.25421.185.127.25532,766
11621.185.128.0/1721.185.128.1 to 21.185.255.25421.185.255.25532,766
11721.186.0.0/1721.186.0.1 to 21.186.127.25421.186.127.25532,766
11821.186.128.0/1721.186.128.1 to 21.186.255.25421.186.255.25532,766
11921.187.0.0/1721.187.0.1 to 21.187.127.25421.187.127.25532,766
12021.187.128.0/1721.187.128.1 to 21.187.255.25421.187.255.25532,766
12121.188.0.0/1721.188.0.1 to 21.188.127.25421.188.127.25532,766
12221.188.128.0/1721.188.128.1 to 21.188.255.25421.188.255.25532,766
12321.189.0.0/1721.189.0.1 to 21.189.127.25421.189.127.25532,766
12421.189.128.0/1721.189.128.1 to 21.189.255.25421.189.255.25532,766
12521.190.0.0/1721.190.0.1 to 21.190.127.25421.190.127.25532,766
12621.190.128.0/1721.190.128.1 to 21.190.255.25421.190.255.25532,766
12721.191.0.0/1721.191.0.1 to 21.191.127.25421.191.127.25532,766
12821.191.128.0/1721.191.128.1 to 21.191.255.25421.191.255.25532,766
12921.192.0.0/1721.192.0.1 to 21.192.127.25421.192.127.25532,766
13021.192.128.0/1721.192.128.1 to 21.192.255.25421.192.255.25532,766
13121.193.0.0/1721.193.0.1 to 21.193.127.25421.193.127.25532,766
13221.193.128.0/1721.193.128.1 to 21.193.255.25421.193.255.25532,766
13321.194.0.0/1721.194.0.1 to 21.194.127.25421.194.127.25532,766
13421.194.128.0/1721.194.128.1 to 21.194.255.25421.194.255.25532,766
13521.195.0.0/1721.195.0.1 to 21.195.127.25421.195.127.25532,766
13621.195.128.0/1721.195.128.1 to 21.195.255.25421.195.255.25532,766
13721.196.0.0/1721.196.0.1 to 21.196.127.25421.196.127.25532,766
13821.196.128.0/1721.196.128.1 to 21.196.255.25421.196.255.25532,766
13921.197.0.0/1721.197.0.1 to 21.197.127.25421.197.127.25532,766
14021.197.128.0/1721.197.128.1 to 21.197.255.25421.197.255.25532,766
14121.198.0.0/1721.198.0.1 to 21.198.127.25421.198.127.25532,766
14221.198.128.0/1721.198.128.1 to 21.198.255.25421.198.255.25532,766
14321.199.0.0/1721.199.0.1 to 21.199.127.25421.199.127.25532,766
14421.199.128.0/1721.199.128.1 to 21.199.255.25421.199.255.25532,766
14521.200.0.0/1721.200.0.1 to 21.200.127.25421.200.127.25532,766
14621.200.128.0/1721.200.128.1 to 21.200.255.25421.200.255.25532,766
14721.201.0.0/1721.201.0.1 to 21.201.127.25421.201.127.25532,766
14821.201.128.0/1721.201.128.1 to 21.201.255.25421.201.255.25532,766
14921.202.0.0/1721.202.0.1 to 21.202.127.25421.202.127.25532,766
15021.202.128.0/1721.202.128.1 to 21.202.255.25421.202.255.25532,766
15121.203.0.0/1721.203.0.1 to 21.203.127.25421.203.127.25532,766
15221.203.128.0/1721.203.128.1 to 21.203.255.25421.203.255.25532,766
15321.204.0.0/1721.204.0.1 to 21.204.127.25421.204.127.25532,766
15421.204.128.0/1721.204.128.1 to 21.204.255.25421.204.255.25532,766
15521.205.0.0/1721.205.0.1 to 21.205.127.25421.205.127.25532,766
15621.205.128.0/1721.205.128.1 to 21.205.255.25421.205.255.25532,766
15721.206.0.0/1721.206.0.1 to 21.206.127.25421.206.127.25532,766
15821.206.128.0/1721.206.128.1 to 21.206.255.25421.206.255.25532,766
15921.207.0.0/1721.207.0.1 to 21.207.127.25421.207.127.25532,766
16021.207.128.0/1721.207.128.1 to 21.207.255.25421.207.255.25532,766
16121.208.0.0/1721.208.0.1 to 21.208.127.25421.208.127.25532,766
16221.208.128.0/1721.208.128.1 to 21.208.255.25421.208.255.25532,766
16321.209.0.0/1721.209.0.1 to 21.209.127.25421.209.127.25532,766
16421.209.128.0/1721.209.128.1 to 21.209.255.25421.209.255.25532,766
16521.210.0.0/1721.210.0.1 to 21.210.127.25421.210.127.25532,766
16621.210.128.0/1721.210.128.1 to 21.210.255.25421.210.255.25532,766
16721.211.0.0/1721.211.0.1 to 21.211.127.25421.211.127.25532,766
16821.211.128.0/1721.211.128.1 to 21.211.255.25421.211.255.25532,766
16921.212.0.0/1721.212.0.1 to 21.212.127.25421.212.127.25532,766
17021.212.128.0/1721.212.128.1 to 21.212.255.25421.212.255.25532,766
17121.213.0.0/1721.213.0.1 to 21.213.127.25421.213.127.25532,766
17221.213.128.0/1721.213.128.1 to 21.213.255.25421.213.255.25532,766
17321.214.0.0/1721.214.0.1 to 21.214.127.25421.214.127.25532,766
17421.214.128.0/1721.214.128.1 to 21.214.255.25421.214.255.25532,766
17521.215.0.0/1721.215.0.1 to 21.215.127.25421.215.127.25532,766
17621.215.128.0/1721.215.128.1 to 21.215.255.25421.215.255.25532,766
17721.216.0.0/1721.216.0.1 to 21.216.127.25421.216.127.25532,766
17821.216.128.0/1721.216.128.1 to 21.216.255.25421.216.255.25532,766
17921.217.0.0/1721.217.0.1 to 21.217.127.25421.217.127.25532,766
18021.217.128.0/1721.217.128.1 to 21.217.255.25421.217.255.25532,766
18121.218.0.0/1721.218.0.1 to 21.218.127.25421.218.127.25532,766
18221.218.128.0/1721.218.128.1 to 21.218.255.25421.218.255.25532,766
18321.219.0.0/1721.219.0.1 to 21.219.127.25421.219.127.25532,766
18421.219.128.0/1721.219.128.1 to 21.219.255.25421.219.255.25532,766
18521.220.0.0/1721.220.0.1 to 21.220.127.25421.220.127.25532,766
18621.220.128.0/1721.220.128.1 to 21.220.255.25421.220.255.25532,766
18721.221.0.0/1721.221.0.1 to 21.221.127.25421.221.127.25532,766
18821.221.128.0/1721.221.128.1 to 21.221.255.25421.221.255.25532,766
18921.222.0.0/1721.222.0.1 to 21.222.127.25421.222.127.25532,766
19021.222.128.0/1721.222.128.1 to 21.222.255.25421.222.255.25532,766
19121.223.0.0/1721.223.0.1 to 21.223.127.25421.223.127.25532,766
19221.223.128.0/1721.223.128.1 to 21.223.255.25421.223.255.25532,766
19321.224.0.0/1721.224.0.1 to 21.224.127.25421.224.127.25532,766
19421.224.128.0/1721.224.128.1 to 21.224.255.25421.224.255.25532,766
19521.225.0.0/1721.225.0.1 to 21.225.127.25421.225.127.25532,766
19621.225.128.0/1721.225.128.1 to 21.225.255.25421.225.255.25532,766
19721.226.0.0/1721.226.0.1 to 21.226.127.25421.226.127.25532,766
19821.226.128.0/1721.226.128.1 to 21.226.255.25421.226.255.25532,766
19921.227.0.0/1721.227.0.1 to 21.227.127.25421.227.127.25532,766
20021.227.128.0/1721.227.128.1 to 21.227.255.25421.227.255.25532,766
20121.228.0.0/1721.228.0.1 to 21.228.127.25421.228.127.25532,766
20221.228.128.0/1721.228.128.1 to 21.228.255.25421.228.255.25532,766
20321.229.0.0/1721.229.0.1 to 21.229.127.25421.229.127.25532,766
20421.229.128.0/1721.229.128.1 to 21.229.255.25421.229.255.25532,766
20521.230.0.0/1721.230.0.1 to 21.230.127.25421.230.127.25532,766
20621.230.128.0/1721.230.128.1 to 21.230.255.25421.230.255.25532,766
20721.231.0.0/1721.231.0.1 to 21.231.127.25421.231.127.25532,766
20821.231.128.0/1721.231.128.1 to 21.231.255.25421.231.255.25532,766
20921.232.0.0/1721.232.0.1 to 21.232.127.25421.232.127.25532,766
21021.232.128.0/1721.232.128.1 to 21.232.255.25421.232.255.25532,766
21121.233.0.0/1721.233.0.1 to 21.233.127.25421.233.127.25532,766
21221.233.128.0/1721.233.128.1 to 21.233.255.25421.233.255.25532,766
21321.234.0.0/1721.234.0.1 to 21.234.127.25421.234.127.25532,766
21421.234.128.0/1721.234.128.1 to 21.234.255.25421.234.255.25532,766
21521.235.0.0/1721.235.0.1 to 21.235.127.25421.235.127.25532,766
21621.235.128.0/1721.235.128.1 to 21.235.255.25421.235.255.25532,766
21721.236.0.0/1721.236.0.1 to 21.236.127.25421.236.127.25532,766
21821.236.128.0/1721.236.128.1 to 21.236.255.25421.236.255.25532,766
21921.237.0.0/1721.237.0.1 to 21.237.127.25421.237.127.25532,766
22021.237.128.0/1721.237.128.1 to 21.237.255.25421.237.255.25532,766
22121.238.0.0/1721.238.0.1 to 21.238.127.25421.238.127.25532,766
22221.238.128.0/1721.238.128.1 to 21.238.255.25421.238.255.25532,766
22321.239.0.0/1721.239.0.1 to 21.239.127.25421.239.127.25532,766
22421.239.128.0/1721.239.128.1 to 21.239.255.25421.239.255.25532,766
22521.240.0.0/1721.240.0.1 to 21.240.127.25421.240.127.25532,766
22621.240.128.0/1721.240.128.1 to 21.240.255.25421.240.255.25532,766
22721.241.0.0/1721.241.0.1 to 21.241.127.25421.241.127.25532,766
22821.241.128.0/1721.241.128.1 to 21.241.255.25421.241.255.25532,766
22921.242.0.0/1721.242.0.1 to 21.242.127.25421.242.127.25532,766
23021.242.128.0/1721.242.128.1 to 21.242.255.25421.242.255.25532,766
23121.243.0.0/1721.243.0.1 to 21.243.127.25421.243.127.25532,766
23221.243.128.0/1721.243.128.1 to 21.243.255.25421.243.255.25532,766
23321.244.0.0/1721.244.0.1 to 21.244.127.25421.244.127.25532,766
23421.244.128.0/1721.244.128.1 to 21.244.255.25421.244.255.25532,766
23521.245.0.0/1721.245.0.1 to 21.245.127.25421.245.127.25532,766
23621.245.128.0/1721.245.128.1 to 21.245.255.25421.245.255.25532,766
23721.246.0.0/1721.246.0.1 to 21.246.127.25421.246.127.25532,766
23821.246.128.0/1721.246.128.1 to 21.246.255.25421.246.255.25532,766
23921.247.0.0/1721.247.0.1 to 21.247.127.25421.247.127.25532,766
24021.247.128.0/1721.247.128.1 to 21.247.255.25421.247.255.25532,766
24121.248.0.0/1721.248.0.1 to 21.248.127.25421.248.127.25532,766
24221.248.128.0/1721.248.128.1 to 21.248.255.25421.248.255.25532,766
24321.249.0.0/1721.249.0.1 to 21.249.127.25421.249.127.25532,766
24421.249.128.0/1721.249.128.1 to 21.249.255.25421.249.255.25532,766
24521.250.0.0/1721.250.0.1 to 21.250.127.25421.250.127.25532,766
24621.250.128.0/1721.250.128.1 to 21.250.255.25421.250.255.25532,766
24721.251.0.0/1721.251.0.1 to 21.251.127.25421.251.127.25532,766
24821.251.128.0/1721.251.128.1 to 21.251.255.25421.251.255.25532,766
24921.252.0.0/1721.252.0.1 to 21.252.127.25421.252.127.25532,766
25021.252.128.0/1721.252.128.1 to 21.252.255.25421.252.255.25532,766
25121.253.0.0/1721.253.0.1 to 21.253.127.25421.253.127.25532,766
25221.253.128.0/1721.253.128.1 to 21.253.255.25421.253.255.25532,766
25321.254.0.0/1721.254.0.1 to 21.254.127.25421.254.127.25532,766
25421.254.128.0/1721.254.128.1 to 21.254.255.25421.254.255.25532,766
25521.255.0.0/1721.255.0.1 to 21.255.127.25421.255.127.25532,766
25621.255.128.0/1721.255.128.1 to 21.255.255.25421.255.255.25532,766

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.