Chapter 19
Chapter 19 of Data Communications and Networking by Behrouz A. Forouzan focuses on Logical Addressing within the Network Layer. Below are detailed notes on the chapter:
19.1 IPv4 Addresses
IPv4 addresses are 32-bit identifiers that uniquely and universally define a connection of a device to the Internet. Every device connected to the Internet must have a unique IP address.
IPv4 addresses are represented in two notations:
Binary Notation: Represents the address as a 32-bit binary number.
Dotted-Decimal Notation: Easier to read, this format divides the 32-bit address into four 8-bit blocks, each represented as a decimal number separated by dots (e.g., 192.168.1.1).
Address Space
IPv4's address space is (2^{32}), which means there are over 4.29 billion possible unique addresses.
Classful Addressing
IPv4 addresses are traditionally divided into classes (A, B, C, D, E) based on the leading bits of the address, which determine the division of the address into network and host identifiers.
Class A: Starts with 0; supports a few large networks.
Class B: Starts with 10; supports medium-sized networks.
Class C: Starts with 110; supports many small networks.
Class D: Used for multicast.
Class E: Reserved for experimental purposes.
Classless Addressing
The limitations of classful addressing, particularly the inefficient allocation of IP addresses, led to Classless Inter-Domain Routing (CIDR). CIDR uses a prefix length (e.g., /24) to indicate the division between network and host portions of the address, providing more efficient allocation.
Network Address Translation (NAT)
NAT allows multiple devices on a local network to share a single public IP address by mapping private addresses to public addresses dynamically. This conserves IP addresses and helps alleviate IPv4 address exhaustion.
19.2 IPv6 Addresses
IPv6 is designed to replace IPv4, offering a vastly expanded address space due to its 128-bit addresses.
Hexadecimal Colon Notation is used in IPv6, dividing the 128-bit address into eight 16-bit blocks, each represented by four hexadecimal digits separated by colons (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334).
IPv6 allows address abbreviation to remove leading zeros and compress consecutive zeros.
Types of IPv6 Addresses:
Unicast: Identifies a single device.
Anycast: Identifies multiple devices; the packet is delivered to the closest device.
Multicast: Delivers packets to multiple devices simultaneously.
Summary
The chapter covers the transition from IPv4 to IPv6, including both protocols' structures and addressing methods. While IPv4 is still widely used, IPv6 addresses the issue of address depletion and provides features suited for the modern Internet, such as improved routing, scalability, and support for security features like encryption.
These key concepts provide the foundation for understanding how devices are addressed within the Internet and how the network layer manages the global delivery of packets.
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