Lecture 5: IPv4 Addressing and Subnetting

IPv4 Address Structure

• A 32-bit address is split into a Network Portion and a Host Portion.
• The Subnet Mask isolates these portions using a logical ANDing process (where bitwise 1 AND 1 = 1, otherwise 0).
• Prefix Length (e.g., /24) indicates the number of bits set to 1 in the subnet mask.

Types of Addresses and Transmission

• Unicast: Sent from one host to one specific destination.
• Broadcast: Sent from one host to all hosts in a network (routers do not forward broadcasts).
• Multicast: Sent from one host to a selected group of hosts.
• Public vs. Private Addresses: RFC 1918 defines private addresses (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) which are used internally and translated to globally routable public addresses by NAT.
• Special Use Addresses: Loopback (127.0.0.1 for testing) and Link-Local/APIPA (169.254.0.0/16 for self-assigned IPs).

Subnetting and VLSM

• Large broadcast domains cause excessive traffic. Subnetting divides large networks into smaller ones, reducing broadcast traffic and improving security and performance.
• Traditional subnetting wastes addresses (e.g., point-to-point WAN links only need 2 IPs, but a /24 subnet assigns 254).
• VLSM (Variable Length Subnet Masking): Solves address waste by "subnetting a subnet," allowing different subnet mask lengths within the same overall network topology.