What is IPv4 Subnetting?
IPv4 Subnetting is the logical division of a single physical IP network into multiple smaller sub-networks (subnets). Subnetting mitigates broadcast traffic overhead, optimizes IP address space allocation, and establishes security boundaries between organizational departments.
Key Subnetting Fundamentals
- Classless Inter-Domain Routing (CIDR): Replaced rigid Class A, B, and C networks with prefix notation (e.g.,
/24), specifying the exact number of network bits.
- Subnet Mask: A 32-bit number separating the IP address into Network and Host portions using consecutive 1s (network) and 0s (host).
- Network Address: The first address in a subnet, used to identify the network itself (Host bits are all
0).
- Broadcast Address: The final address in a subnet, used to send data to all hosts on that network (Host bits are all
1).
- Usable Host Addresses: The range of IP addresses between the Network and Broadcast addresses, calculated as
2^(32 - Prefix) - 2.
Special IPv4 Address Ranges
- RFC 1918 Private IP Ranges:
10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16.
- Loopback Address:
127.0.0.0/8 (Reserved for internal host testing).
- APIPA (Link-Local):
169.254.0.0/16 (Auto-assigned when DHCP server is unreachable).