🧠 Understanding Subnet Masks

* Understanding Subnet Masks A subnet mask divides an IP address into: • Network bits (1s) — identify the network • Host bits (0s) — identify the devices (hosts) within that network Each octet (group of 8 bits) in an IP address has a total of 8 bits, and the decimal value of all 8 bits set to 1 is 255. Binary to Decimal Reference Table Binary Bit Value 2^n 2⁰ 1 1 2¹ 2 2 2² 4 4 2³ 8 8 2⁴ 16 16 2⁵ 32 32 2⁶ 64 64 2⁷ 128 128 When you sum all these up: 1 + 2 + 4 + 8 + 16 + 32 + 64 + 128 = 255 That’s why a full octet of 1s (11111111) equals 255 in decimal. ________________________________________ 🌐 Example: 192.168.1.0 /24 • /24 means 24 bits are used for the network. • This leaves 8 bits (since there are 32 total bits in IPv4) for hosts. Subnet Mask Binary: 11111111.11111111.11111111.00000000 Decimal: 255.255.255.0 Network and Host Bits • Network bits: 24 (the first three octets) • Host bits: 8 (the last octet) ________________________________________ 🧮 Calculating the Number of IP Addresses Number of host addresses = 2number of host bits2^ {\text {number of host bits}}2number of host bits 👉 28=2562^8 = 25628=256 total addresses But two are reserved: • Network address: 192.168.1.0 • Broadcast address: 192.168.1.255 ✅ Usable IP addresses: 256−2=254256 - 2 = 254256−2=254 ________________________________________ 📋 Summary Property Value Network ID 192.168.1.0 Broadcast ID 192.168.1.255 Subnet Mask 255.255.255.0 CIDR Notation /24 Total Addresses 256 Usable Host Addresses 254 Host Range 192.168.1.1 → 192.168.1.254 ________________________________________ Would you like me to include an example of subletting this /24 network further (like splitting it into /26 or /28 subnets)? That’s often the next step in learning subnet masks.