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The following table provides a quick reference guide for subnet masks and their corresponding CIDR notation from /30 up to /8. It helps determine the number of available IP addresses, total network size, and broadcast addresses within a subnet.
IPv4
| CIDR | Netmask | Total addresses | Usable |
| /30 | 255.255.255.252 | 4 | 1 |
| /29 | 255.255.255.248 | 8 | 5 |
| /28 | 255.255.255.240 | 16 | 13 |
| /27 | 255.255.255.224 | 32 | 29 |
| /26 | 255.255.255.192 | 64 | 61 |
| /25 | 255.255.255.128 | 128 | 125 |
| /24 | 255.255.255.0 | 256 | 253 |
| /23 | 255.255.254.0 | 512 | 509 |
| /22 | 255.255.252.0 | 1,024 | 1,021 |
| /21 | 255.255.248.0 | 2,048 | 2,045 |
| /20 | 255.255.240.0 | 4,096 | 4,093 |
| /19 | 255.255.224.0 | 8,192 | 8,189 |
| /18 | 255.255.192.0 | 16,384 | 16,381 |
| /17 | 255.255.128.0 | 32,768 | 32,765 |
| /16 | 255.255.0.0 | 65,536 | 65,533 |
| /12 | 255.240.0.0 | 1,048,544 | 1,048,541 |
| /8 | 255.0.0.0 | 16,777,214 | 16,777,211 |
Example:
The subnet: 192.168.5.0/30 has 4 addresses
192.168.5.0 - Network Address
192.168.5.1 - Gateway
192.168.5.2 - Usable IP
192.168.5.3 - Broadcast
More information:
- Network Address: The network address represents the starting address of a subnet. It is used to identify the network itself and cannot be assigned to a host.
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CIDR Notation: CIDR (Classless Inter-Domain Routing) notation represents the subnet mask using a combination of an IP address and a slash ("/") followed by the prefix length. For example, the CIDR notation "192.168.10.0/30" signifies a subnet with a prefix length of 30.
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Usable IP Addresses: The usable IP addresses are the range of IP addresses that can be assigned to devices within a subnet. These IP addresses exclude the network and broadcast addresses.
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Broadcast Address: The broadcast address represents the last address in a subnet and is used to send a message to all devices within that subnet. It cannot be assigned to a host.
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Total IP Addresses: The total IP addresses in a subnet refer to the sum of usable IP addresses, network address, and broadcast address. It provides an overview of the size of the subnet.
