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In networking, a subnet mask is used to divide an IP address into its network and host components. To determine the appropriate subnet mask for a given IP address, you need to know the intended network prefix length, which specifies how many bits of the IP address are designated for the network portion.
Steps to Calculate a Subnet Mask:
Determine the Network Prefix Length:
The prefix length, often denoted in CIDR notation (e.g., /24), indicates the number of bits used for the network portion of the address.
Common prefix lengths include:
/8: Class A network
/16: Class B network
/24: Class C network
Construct the Subnet Mask:
Start with a 32-bit binary number.
Set the first n bits to 1, where n is the prefix length.
Set the remaining (32 – n) bits to 0.
Convert to Dotted-Decimal Notation:
Divide the 32-bit binary number into four 8-bit octets.
Convert each octet to its decimal equivalent.
Separate the octets with periods.
Example:
Let’s calculate the subnet mask for an IP address with a /24 prefix length:
Prefix Length: /24
Binary Subnet Mask:
First 24 bits set to 1: 11111111.11111111.11111111
Remaining 8 bits set to 0: 00000000
Combined: 11111111.11111111.11111111.00000000
Dotted-Decimal Notation:
Convert each octet:
11111111 → 255
11111111 → 255
11111111 → 255
00000000 → 0
Resulting subnet mask: 255.255.255.0
Therefore, an IP address with a /24 prefix length corresponds to a subnet mask of 255.255.255.0.
Additional Resources:
For more detailed information on subnetting and subnet masks, you can refer to the Subnet article on Wikipedia.
If you need assistance with subnet calculations, online tools like the IP Subnet Calculator can be helpful.
Understanding subnet masks is crucial for network configuration and management, as they define how IP addresses are allocated within subnets.
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