Summary
Highlights
The video introduces the topic of IPv4 addressing, building upon previous discussions on binary and decimal conversions. It covers classful and classless IPv4 addresses, the five classes, and the subnet mask. The Internet Assigned Numbers Authority (IANA) is introduced as the global manager of IP addresses, dividing the world into five regional internet registries (Africa, Asia, Americas, Latin America/Caribbean, Europe/Middle East) which in turn allocate IP addresses to internet service providers (ISPs).
The concept of classful IP addresses is explained, detailing how routers use the destination IP address to determine the network portion. Routers, similar to post offices, look up the destination IP in a routing table to find the correct path. In classful addressing, the IP address is divided into network and host portions. Routers are only concerned with the network portion. The video highlights that in the past, routers determined the network portion by the IP address's class, being A, B, or C.
The five classes of IPv4 addresses (A, B, C, D, and E) are detailed based on the first byte range. Class A (1-127) has the first byte as the network and the last three as the host. Class B (128-191) uses the first two bytes for the network and the last two for the host. Class C (192-223) designates the first three bytes for the network and the last for the host. Class D (224-239) is for multicasting, and Class E (240-255) is reserved for internet experimentation. Routers determine the class by examining the most significant bits (MSB) of the first byte.
An example demonstrates how a router identifies an IP address, such as 178.16.156.154, as Class B, meaning the first two bytes (178.16) are the network address. The video then transitions to the limitations of classful addressing, especially with the internet's growth. To overcome these limitations, 'classless' addressing was introduced, which uses a subnet mask to dynamically define the network and host portions, providing more flexibility than fixed 8, 16, or 24-bit network portions.
The subnet mask is introduced as a way to mask the host portion of an IP address, thereby revealing the network portion without relying on predefined classes. This flexibility allows for variable-length network addresses. The video explains CIDR (Classless Inter-Domain Routing) notation, where a slash followed by a number (e.g., /16) indicates the number of bits in the network portion. A /16 mask, for instance, translates to 255.255.0.0 in decimal, signifying that the first 16 bits define the network. The next video will further explain how routers use this mask.