Ipv4 Addressing

# IPv4 Addressing and Subnetting IPv4 addressing is one of the highest-leverage topics on the CCNA 200-301 v1.1 exam (120 minutes, 6 domains) — it appears directly in Network Fundamentals (20%) and bleeds into every other domain, from OSPF configuration to ACLs to NAT. Master this once and every other topic gets easier. --- ## Why IPv4 Addressing Matters The exam curriculum explicitly states: *"Master subnetting before moving forward — it appears in every domain."* You will encounter subnetting in multiple-choice questions, drag-and-drop questions, and embedded within simulation tasks. It is not optional to be fast and accurate here. --- ## Core Concepts ### The IPv4 Address Structure An IPv4 address is a 32-bit number written in dotted-decimal notation — four groups of 8 bits (called octets), each ranging from 0 to 255. Example: 192.168.10.50 Every IPv4 address has two logical parts: - Network portion — identifies the network segment - Host portion — identifies the specific device on that network The dividing line between them is set by the subnet mask. --- ### Subnet Masks and CIDR Notation A subnet mask is also 32 bits. Ones (1s) mark the network portion; zeros (0s) mark the host portion. | Dotted-Decimal Mask | CIDR Prefix | Network Bits | Host Bits | Usable Hosts | |---------------------|-------------|--------------|-----------|--------------| | 255.0.0.0 | /8 | 8 | 24 | 16,777,214 | | 255.255.0.0 | /16 | 16 | 16 | 65,534 | | 255.255.255.0 | /24 | 24 | 8 | 254 | | 255.255.255.128 | /25 | 25 | 7 | 126 |…