IP Addressing & Subnetting

An IPv4 address is 32 bits, written as four octets (e.g. 192.168.1.10). A subnet mask splits the address into a network portion and a host portion.

CIDR notation: /24 means the first 24 bits identify the network, leaving 8 bits (256 addresses, 254 usable) for hosts. /16 gives 65,534 hosts; /30 gives just 2 — perfect for point-to-point links.

Private ranges you must recognise: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. Seeing these tells you a host is internal and likely behind NAT.

Practice: given 192.168.10.0/26, the block size is 64. Valid subnets are .0, .64, .128, .192. A host at .100 lives in the .64 subnet with broadcast .127. Subnetting fluency is the most useful foundational skill in networking.